KINETICS AND MECHANISM OF VO and Cu IONS CATALYZED OXIDATION OF AMINO ACIDS … · 2017-02-06 ·...

KINETICS AND MECHANISM OF VO2+ and Cu2+ IONS

CATALYZED OXIDATION OF AMINO ACIDS BY

PEROXOMONOSULPHATE

A THESIS

Submitted by

KANNIAPPAN. L

Under the guidance of

Dr. D. EASWARAMOORTHY

in partial fulfillment for the award of the degree of

DOCTOR OF PHILOSOPHY

In

CHEMISTRY

October 2016

BONAFIDE CERTIFICATE

Certified that this thesis report “KINETICS AND MECHANISM OF VO2+ and

Cu2+ IONS CATALYZED OXIDATION OF AMINO ACIDS BY

PEROXOMONOSULPHATE” is the bonafide work of KANNIAPPAN L.

(RRN: 1391141) who carried out the thesis work under my supervision. Certified further,

that to the best of my knowledge the work reported herein does not form part of any

other thesis report or dissertation on the basis of which a degree or award was

conferred on an earlier occasion on this or any other candidate.

Dr. D. EASWARAMOORTHY

RESEARCH SUPERVISOR

Professor

Department of Chemistry

B.S. Abdur Rahman University

Vandalur, Chennai – 600 048

Dr. S.KUTTI RANI

HEAD OF THE DEPARTMENT

Professor & Head

Department of Chemistry

B.S. Abdur Rahman University

Vandalur, Chennai – 600 048

CERTIFICATE

This is to certified that the corrections and suggestions pointed out by the

External examiner and the subject experts have been incorporated in the thesis

Entitled“Kinetics and Mechanism of VO2+ and Cu2+ ions catalyzed oxidation of

Amino acids by peroxomonosulphate”, submitted by Mr. L. Kanniappan(RRN:

1391141).

Signature of the Supervisor Place:

Date:

ABSTRACT

Oxidation of amino acids is one of the most prevalent forms of chemical reactions

and is susceptible to modification by a wide array of oxidants. Uncharacteristic oxidation

reactions are of particular concern in biotechnology and medicine. Therefore, it is

important to understand the amino acid metabolism with a model system towards

oxidants. In textile industry and tanneries the waste sent out to nearby area contain

some simple amino acids which rise up the nutrients on that particular place. This may

not be suitable for living plants and affects their growth and population. Therefore,

before discharge, they may be treated completely and converted into ecofriendly

products.

Peroxomonosulphate (PMS) is a highly effective oxidant for various oxidation

reactions of both inorganic and organic substrates. It is a versatile oxidant and widely

used in waste water treatment as well. Metal ion-catalyzed oxidation of amino acids was

performed by researchers to mimic the oxidative decarboxylation of bioactive

molecules. With these objectives in mind, the model system of kinetics of metal ions

(VO2+ and Cu2+) catalyzed oxidation of amino acid was constructed to mimic the

enzymatic oxidative decarboxylation in to non enzymatic mode by using effective

oxidant such as PMS.

Kinetic studies were carried out at 308K in perchloric acid medium under pseudo

first order conditions with a large excess of [amino acids]» [PMS]. The reaction rate was

measured by monitoring the concentration of unreacted [PMS]t at various time intervals

by iodometry. The kinetics and mechanism of VO2+ catalyzed oxidation of five

structurally different amino acids such as glycine, alanine, valine, N-methyl glycine and

2-amino isobutyric acid by PMS in perchloric acid medium was studied. The reaction did

not proceed at all in the absence of VO2+ ions. The VO2+ ion was not oxidized by PMS

under this condition. The reaction rate increases with increase in [AA], [VO2+] and

decreases with [H+]. The reaction rate was also measured at different temperatures to

calculate the thermodynamic parameters like free energy of activation (∆G#), enthalpy of

activation (∆H#) and entropy of activation (∆S#). The activation enthalpies and entropies

of the various amino acids were linearly interrelated, revealing that all the amino acids

were oxidized by the same mechanism. The reaction proceeded by a non radical

pathway as confirmed by EPR studies. Cyclic voltammetric and UV-Vis spectral studies

confirmed the formation of VO2+ − amino acid −PMS complex. The proposed

mechanism involved the abstraction of hydrogen from amine group of amino acid by

HSO5- followed by the elimination of CO2 to give the vanadyl imine intermediate which

on hydrolysis gave the corresponding carbonyl compound as a product, which was

confirmed by Gas Chromatography (GC).

Kinetic of N-Phenyl Glycine (NPG) was very fast at 308K and unable to follow the

reaction rate by iodometric method. Hence the kinetic studies of this reaction were

carried out at 278K and the oxidation of NPG by PMS was studied both in the absence

and presence of Cu2+ and VO2+ions. The reaction rate increases with increase in [NPG],

[VO2+], [Cu2+] and decreases with [H+]. No significant effect of ionic strength and

dielectric constant on the reaction rate was observed. Kinetics of oxidation of alanine

and 2-amino isobutyric acid (2-AIBA) by PMS in the presence of Cu(II) ions at 308K was

investigated in perchloric acid medium under pseudo-first order conditions. An

autocatalytic effect was observed due to the formation copper peroxide intermediate.

The rate constant for the catalyzed (k2obs) and uncatalyzed (k1

obs) reactions were

calculated. The kinetic data showed that both the reactions were first order with respect

to [AA] and [Cu(II)] and inverse first order with respect to [H+]. Further, VO2+/Cu2+ -

amino acid complex were synthesized and characterized by FT-IR spectroscopy. The

VO2+/Cu2+ ion – amino acid complexes are screened for their antibacterial and

anticancer activity and showed good anticancer activities with high percentage of cell

inhibition.

ACKNOWLEDGEMENT

At this moment of accomplishment, first of all I pay respect to my guide,

Dr. D. Easwaramoorthy, Professor of chemistry Department, B.S.Abdhur Rhaman

University, Vandalur. This work would not have been possible without his guidance,

support and encouragement.

I am also extremely indebted to Dr. I.Mohammed Bilal, Controller of

Examinations, B.S.Abdhur Rhaman University, for his valuable suggestions and

corrections during the review of my thesis progress. I warmly thank Dr. S.Kutti Rani,

Head & Dean (SPCS), B.S.Abdhur Rhaman University, for her valuable advice,

constructive criticism and I wish to acknowledge all the faculty members of the

Department of Chemistry, B.S.Abdhur Rhaman University, who helped for the

completion of the research work.

I gratefully acknowledge Dr.S.Hemalatha, Dean (SLS), B.S.Abdhur Rhaman

University, for her valuable suggestions and also for the biological studies. My sincere

thanks to Dr. S. Rani and Dr. G. Natarajan for their encouragement and personal

attention during my Ph.D. tenure. I also thank my Doctoral committee members,

Dr.J.Santhanalkshmi and Dr.R. Rajendran for their helpful suggestions and

comments. I am indebted to my student colleagues Mr.R.Mohanraj,

Mr. Sathiyanarayanan, and Mr. M.Vadivelu for their timely helps.

Last but not least, I would like to pay high regards to my wife

Mrs. K. Kavitha and my daughters who have been a moral support and all of my

family members for their continuous encouragement and inspiration. I thank them all

whole heartedly.

Kanniappan. L

i

TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

ABSTRACT iii

ACKNOWLEDGMENT v

LIST OF TABLES xii

LIST OF FIGURES xv

LIST OF SCHEMES xxi

LIST OF SYMBOLS AND ABBREVIATIONS xxiii

I INTRODUCTION 1

1.1 Importance of amino acids 1

1.2 Oxidation of proteins and amino acids 1

1.3 LITERATURE OVERVIEWE 3

1.3.1 Decomposition of Peroxomonosulphate 3

1.3.2 Decomposition of PMS in the absence of

metal ions 3

1.3.3 Decomposition of PMS in the presence of

metal ions 5

1.4 OXIDATION OF AMINO ACID BY PEROXOMONO

SULPHATE 7

1.5 OXIDATION OF AMINO ACID BY OTHER PEROXO

OXIDANT 11

1.5.1 Oxidation of amino acid by Peroxydisulphate 11

1.5.2 Oxidation of amino acid by Hydrogen peroxide 12

1.6 METAL IONS CATALYZED OXIDATION OF AMINO

ACID 14

1.7 OXIDATION OF VARIOUS COMPOUNDS BY

PEROXOMONOSULPHATE 19

ii


1.8 SCOPE OF THE PRESENT INVESTIGATION 25

1.9 OBJECTIVES OF THE PRESENT INVESTIGATION 27

1.10 OUTLINE OF THE THESIS 28

II MATERIALS AND METHODS 30

2.1 MATERIALS 30

2.2 CHEMICALS 30

2.2.1 α-Amino acids 30

2.2.2 Peroxomonosulphate (HSO5-) 31

2.2.3 Vanadyl sulphate pentahydrate 31

2.2.4 Copper sulphate pentahydrate 31

2.2.5 Percholric acid 31

2.2.6 Other Reagents 32

2.3 EXPERIMENTAL METHODS 32

2.3.1 Measurement of Rate constants 32

2.3.2 Stoichiometry 33

2.3.3 Product analysis 34

2.3.4 Gas Chromatographic analysis 34

2.3.5 UV-Visible Spectral analysis 35

2.3.6 Electron Paramagnetic Resonance

Spectral analysis 36

2.3.7 Cyclic Voltammetry measurments 36

2.3.8 Preparation of Amino acid Metal ions

complex 37

2.3.9 FT-IR spectroscopy 37

2.3.10 Antibacterial activity assay 38

2.3.11 In Vitro anticancer activity by MTT assay 38

iii


III VANADIUM (IV) CATALYZED OXIDATION OF AMINO

ACIDS BY PEROXOMONOSULPHATE- KINETICS AND

MECHANISTIC STUDIES 39

3.1 Stoichiometry 41

3.2 Product analysis 41

3.3 EFFECT OF VARYING THE CONCENTRATION OF

THE REACTANT ON kobs 44

3.3.1 Effect of [amino acid] on kobs 44

3.3.2 Effect of [H+] on kobs 46

3.3.3 Effect of [metal ions] on kobs 47

3.3.4 Effect of [PMS] on kobs 49

3.3.5 Effect of ionic strength on kobs 50

3.3.6 Effect of dielectric constant 51

3.3.7 Test for free radicals 53

3.3.8 Effect of Temperature 53

3.4 SPECTRAL STUDIES FOR THE OXIDATION OF

AMINO ACIDS 57

3.4.1 UV-Visible spectral measurements 57

3.4.2 EPR spectral studies 66

3.4.3 FT-IR spectral studies 73

3.5 ELECTROCHEMICAL STUDIES FOR THE

OXIDATION OF AMINO ACIDS 77

3.5.1 Cyclic voltammetric studies 77

3.6 Reaction mechanism of the VO2+ ions catalyzed

oxidation of amino acids by peroxomonosulphate 84

IV OXIDATION OF N-PHENYL GLYCINE BY

PEROXOMONOSULPHATE- CATALYTIC EFFECT OF 89

VO2+ AND Cu2+ IONS


iv





4.3.1 Effect of [NPG] on kobs 93


4.3.3 Effect of [metal ions] on kobs 96






4.3.9 Catalytic activity 104

4.4 SPECTRAL STUDIES FOR THE OXIDATION OF

NPG 105

4.4.1 UV-Visible spectral studies 105

4.4.2 EPR Spectral studies 111



OXIDATION OF NPG 118

4.5.1 Cyclic Voltammetric studies 118

4.6 Reaction mechanism of the uncatalyzed and metal

ions catalyzed oxidation of NPG by

peroxomonosulphate 123

V COPPER (II) IONS CATALYZED OXIDATION OF

α-AMINO ACID BY PEROXOMONOSULPHATE-

AUTOCATALYTIC STUDIES 127



v




5.3.1 Effect of [amino acid] on kobs 132


5.3.3 Effect of [Cu2+] on kobs 136






5.4 SPECTRAL STUDIES FOR THE OXIDATION

OF AMINO ACID 146

5.4.1 UV-Visible spectral measurments 146

5.4.2 EPR Spectral studies 150



OXIDATION OF AMINO ACID 157

5.5.1 Cyclic voltammetric studies 157

5.6 Reaction mechanism of the autocatalyzed

oxidation of amino acids by peroxomonosulphate 159

VI BIOLOGICAL STUDY OF THE METAL IONS –

AMINO ACID COMPLEXES 162

6.1 Antibacterial activity 162

6.2 In Vitro anticancer activity 163

vi


VII SUMMARY AND CONCLUSION 165

VIII SCOPE FOR FUTURE WORK 170

IX REFERENCES 171

LIST OF PUBLICATIONS 185

TECHNICAL BIOGRAPHY 187

vii

LIST OF TABLES

TABLE NO. TITLE PAGE NO.

2.1 Stoichiometry of the oxidation of α-amino acids

by PMS 33

2.2 Gas Chromatographic result for the oxidation of

amino acids 35

3.1 Relationship of unreacted PMS (log[PMS]t) with

respect to time 40

3.2 Effect of [amino acid] on kobs 45

3.3 Effect of [H+] on kobs 46

3.4 Effect of [metal ions] on kobs 48

3.5 Effect of [PMS] on kobs 49

3.6 Effect of ionic strength on kobs 51

3.7 Effect of dielectric constant on kobs in the presence

of acetonitrile 52


of t-butylalcohol 52

3.9 Effect of Temperature on kobs 54

3.10 Thermodynamic parameters for the oxidation of

amino acids 56

3.11 Absorbance of VO2+ ions and its complexes 65

3.12 EPR parameters of VO2+ ions and its complexes 72

3.13 Selected FT-IR spectral bands of the amino acids and

its VO2+ ions complexes 76

3.14 Cyclic voltammetric data of VO2+ ions and its

complexes 83

3.15 Kinetic parameters for the oxidation of amino acids

at 308K 88

viii


4.1 Relationship of unreacted PMS (log[PMS]t) with

respect to time 90

4.2 Effect of [NPG] on kobs 93


4.4 Effect of [metal ions] on kobs 96


4.6 Effect of Ionic strength on kobs 99


of acetonitrile 100





NPG 102

4.11 Catalytic activity for the oxidation of NPG 105

4.12 Absorbance of metal ions and its complexes 111

4.13 EPR parameters of metal ions and its

complexes 115

4.14 Selected FT-IR spectral bands of the NPG and

its metal ions complexes 117

4.15 Cyclic voltammetric data of metal ions and its

complexes 122

4.16 Kinetic parameters for the oxidation of NPG

at 278K 126

ix


5.1 Relationship of unreacted PMS (log[PMS]t)

with respect to time 128

5.2 Effect of [amino acid] on kobs 133


5.4 Effect of [Cu2+] on kobs 137


5.6 Effect of ionic strength on kobs 140


of acetonitrile 141





amino acids 145

5.11 Absorbance of copper (II) metal ions and its

complexes 150

5.12 EPR parameters of copper (II) metal ions and its

complexes 154

5.13 Selected FT-IR spectral bands of the amino acids

and its metal ions complexes 156

5.14 Cyclic voltammetric data of copper(II) metal ions and

its complexes 158

x

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

3.1 Plot of log[PMS]t vs time for the reactions

at 308 K 39

3.2 Gas chromatogram of the product in the

VO2+ ions catalyzed oxidation of glycine 42


VO2+ ions catalyzed oxidation of alanine 42


VO2+ ions catalyzed oxidation of valine 43


VO2+ ions catalyzed oxidation of 2-AIBA 43


VO2+ ions catalyzed oxidation of NMG 44

3.7 Plot of kobs vs [AA] at 308 K 45

3.8 Plot of kobs vs [H+]-1at 308 K 47

3.9 Plot of kobs vs [VO2+] at 308 K 48

3.10 Plot of 1/kobs vs [PMS] at 308 K 50

3.11 Arrhenius plot of logkobs vs 1/T for the oxidation

of amino acids 54


of NMG 55

3.13 Eyring plot of log(kobs /T) vs 1/T for the oxidation

of amino acids 55

3.14 Eyring plot of log(kobs /T) vs 1/T for the oxidation

of NMG 56

3.15 UV-Visible spectrum of the reaction mixture at

various time intervals (glycine) 57

xi



various time intervals (alanine) 58


various time intervals (valine) 59


various time intervals (2-AIBA) 60


various time intervals (NMG) 61

3.20 UV-Visible spectra at high concentration of the

reaction mixture (glycine and alnine) 62

3.21 UV-Visible spectra at high concentration of

the reaction mixture (valine and 2-AIBA) 63

3.22 UV-Visible spectra at high concentration of

the reaction mixture (NMG) 64

3.23 Comparison of the EPR spectrum of the

reaction mixture (glycine) 67


reaction mixture (alanine) 68

3.25 Comparison of the EPR spectrum of the reaction

mixture (valine) 69


mixture (2-AIBA) 70


mixture (NMG) 71

3.28 Comparison of the FT-IR spectra of the

VO2+ ions and its glycine complex 74

3.29 Comparison of the FT-IR spectrum of the

VO2+ ions and its alanine complex 74

xii



VO2+ ions and its valine complex 75


VO2+ ions and its 2-AIBA complex 75


VO2+ ions and its NMG complex 76

3.33 Comparison of the cyclic voltammogram of the

reaction mixture (glycine) 78


reaction mixture (alanine) 79


reaction mixture (valine) 80


reaction mixture (2-AIBA) 81


reaction mixture (NMG) 82

3.38 Plot of ∆H# vs ∆S# for the oxidation of

amino acids 86

4.1 Plot of log[PMS]t vs time for the reactions

at 278 K 89

4.2 Gas chromatogram of the products in the

uncatalyzed oxidation of NPG 91


VO2+ ions catalyzed oxidation of NPG 92


Cu2+ ions catalyzed oxidation of NPG 92

4.5 Plot of kobs vs [NPG] at 278 K 94

4.6 Plot of kobs vs [H+]-1at 278 K 95

4.7 Plot of kobs vs [metal ions] at 278 K 97

xiii



of NPG 103

4.9 Eyring plot of log(kobs/T) vs 1/T for the oxidation

of NPG 103


various time intervals (without metal ions) 106


various time intervals (with VO2+ ions) 107


reaction mixture (NPG and VO2+ ions) 108


various time intervals (with Cu2+ ions) 109


reaction mixture (NPG and Cu2+ ions) 110


mixture (NPG and VO2+ ions) 112

4.16 EPR spectrum of copper(II) ions in

perchloric acid 113



4.18 Comparison of the FT-IR spectra of VO2+ ions and

its NPG complex 116

4.19 Comparison of the FT-IR spectra of Cu2+ ions and

its NPG complex 117


reaction mixture (NPG without metal ions) 119


reaction mixture (NPG and VO2+ ions) 120

xiv




5.1 Plot of log [PMS]t vs time for the oxidation of

alanine at 308 K 129

5.2 Plot of log[PMS]t vs time for the oxidation of

2-AIBA at 308 K 129

5.3 Plot of rate/[PMS]t vs [PMS]t for the oxidation

of alanine 130

5.4 Plot of rate/[PMS]t vs [PMS]t for the oxidation

of 2-AIBA 130


autocatalyzed oxidation of alanine 131


autocatalyzed oxidation of 2-AIBA 132

5.7 Plot of k1(obs) vs [AA] at 308 K 133

5.8 Plot of k2(obs) vs [AA] at 308 K 134

5.9 Plot of k1(obs) vs1/ [H+] at 308 K 135

5.10 Plot of k2(obs) vs1/ [H+] at 308 K 136

5.11 Plot of k1(obs) vs [Cu2+] at 308 K 137

5.12 Plot of k2(obs) vs [Cu2+] at 308 K 138

5.13 Arrhenius plot of logk1(obs) vs 1/T for the

uncatalyzed reaction 143

5.14 Arrhenius plot of logk2(obs) vs 1/T for the

autocatalyzed reaction 144

5.15 Eyring plot of log(k1(obs) /T) vs 1/T for the

uncatalyzed reaction 144

5.16 Eyring plot of log(k2(obs) /T) vs 1/T for the

autocatalyzed reaction 145

xv



various time intervals (Cu2+ ions and alanine) 146


various time intervals (Cu2+ ions and 2-AIBA) 147


reaction mixture (Cu2+ ions and alanine) 148


reaction mixture (Cu2+ ions and 2-AIBA) 149

5.21 EPR spectrum of copper(II) ions in perchloric acid 151


mixture (alanine and Cu2+ ions) 152


mixture (2-AIBA and Cu2+ ions) 153


its alanine complex 155


its 2-AIBA complex 156


reaction mixture (alanine and Cu2+ ions) 157


reaction mixture (2-AIBA and Cu2+ ions) 158

6.1 Efficacy of antibacterial and synthesized complexes

(VO2+ - amino acid complexes) on human pathogens 162

6.2 Anticancer activity of the (metal ions - amino

acid) complexes 164

xvi

LIST OF SCHEMES

SCHEME NO. TITLE PAGE NO.

1.1 Plausible mechanism for the Mn(II) catalyzed

decomposition of PMS 6

1.2 Plausible mechanism for the oxidation of

α-amino acids by PMS 8


amino acid by H2O2 in the presence of FeSO4 12

1.4 Plausible mechanism for the oxidation of amino

acid by H2O2 in the presence of Mn(II) and

Fe(II) ions 13


aldehydes by PMS 19

1.6 Plausible Mechanism for the oxidation of vanillin

by PMS 22

3.1 Mechanism for the VO2+ ions catalyzed oxidation of

amino acids by peroxomonosulphate 87

4.1 Mechanism for the oxidation of NPG by

Peroxomonosulphate 124

4.2 Mechanism for the metal ions catalyzed oxidation

of NPG by peroxomonosulphate 125

5.1 Mechanism for the autocatalytic oxidation of

amino acids by peroxomonosulphate 161

xvii

LIST OF SYMBOLS AND ABBREVATIONS

% - Percentage

∆G# - Free energy of activation

∆H# - Enthalpy of activation

∆S# - Entropy of activation

°C - Degree centigrade

α - Alpha

β - Beta

max - Wavelength for maximum absorption

- Ionic strength

ξmax - Molar absorptivity

1H NMR - Proton nuclear magnetic resonance spectroscopy

2-AIBA - 2-Amino isobutyric acid

a.u - atomic unit

AA - Amino acid

Abs - Absorbance

Ala - Alanine

aq - Aqeous

cm - Centi meter

CV - Cyclic voltammtery

D - Relative permittivity

dm - decimeter

DMF - Dimethyl formamide

DPA - Diperiodatoargentate

E - Potential

Ea - Energy of activation

EDTA - Ethyline diamine tetraacetic acid

EPR - Electron paramagnetic resonance spectroscopy

EtOH - Ethanol

xviii

FT-IR - Fourier transform-infrared spectroscopy

G - Gauss

GC - Gas chromatography

GCE - Glassy carbon electrode

GC-MS - Gas chromatograpy- Mass spectrometry

Gly - Glycine

I - Current

IR - Infrared spectroscopy

J - Joule

K - Kelvin

K1 - Equilibrium constant

kc - Catalytic constant

kJ - kilo joule

kobs - Observed rate constant

M - Molar

min - Minute

ml - Milliliter

mol - mole

nm - Nanometer

NMG - N-Methylglycine

NPG - N-Phenylglycine

OMH - Ornithine monohydrochloride

PDS - Peroxydisulphate

PMC - Peroxomonocarbonate

PMP - Peroxomonophosphate

PMS - Peroxomonosulphate

PTC - Phase transfer catalyst

R - Regression coefficient

RT - Retention Time

s - Second

xix

T - Temperature

TBAC - Tetrabutylammonium chloride

TBPC - Tetrabutylphosphonoum chloride

TLC - Thin layer chromatography

UV-Vis - Ultrviolet-visible spectroscopy

V - Volt

Val - Valine

vs - Versus

CHAPTER I

INTRODUCTION

1.1. Importance of amino acids

Proteins are polymers of amino acids that have diverse structural and functional

roles in the body of humans. Amino acids are important building blocks of proteins in the

body and used for the growth and repair of damaged cells / tissues, synthesis of

enzymes, plasma proteins, antibodies and some hormones. Besides their use in

constructing proteins in the various cells of the body, amino acids are used as chemical

precursors for the synthesis of various neurotransmitters.

1.2. Oxidation of proteins and amino acids

In animals and human beings, amino acids undergo oxidative degradation in

three different metabolic circumstances:

During the normal synthesis and degradation of cellular proteins, some amino

acids are released from protein breakdown and are not needed for new protein

synthesis. These discarded amino acids undergo oxidative degradation.

When a diet is rich in proteins and the ingested amino acids exceed the body’s

needs for protein synthesis, the surplus amino acids are catabolized. When

protein rich diet is consumed, there is an increase in urea excretion.

During starvation or in uncontrolled diabetes mellitus, when carbohydrates are

either unavailable or not properly utilized, cellular proteins are used as fuel.

In addition, change in the pH of amino acid or availability of free radicals or

oxidizing agents or temperature of the human body may result in the oxidation of amino

acids.

Oxidative decarboxylation of α-amino acids is a well documented biochemical

reaction. Kinetics and mechanism of decarboxylation of α-amino acids by peroxo

oxidants is an area of intensive research by chemists. Hence in the literature survey,

the kinetics and mechanism of the reactions of amino acids by peroxomonosulphate are

discussed.

Peroxo oxidants such as peroxomonosulphate (PMS), Peroxomonophosphate

(PMP), Peroxydisulphate (PDS) and Peroxomonocarbonate (PMC) are being utilized for

the oxidation reaction. Peroxomonosulphate is a highly effective oxidant for various

oxidation reactions of both inorganic and organic substrates [1] - [3]. This thesis

emphasizes the influence of metal ion on the oxidation of amino acids by PMS in highly

acidic medium (pH<2). Literature survey pertaining to the following is reviewed.

Studies on the decomposition of peroxomonosulphate (PMS) and the

influence of metal ions.

Studies on the oxidation of amino acids by PMS.

Studies on the oxidation of amino acids by other peroxo oxidants.

Studies on the metal ions catalyzed oxidation of amino acids.

Studies on the oxidation of various compounds by PMS.

1.3 LITERATURE OVERVIEW

1.3.1 Decomposition of Peroxomonosulphate

The decomposition of PMS was studied both in the presence and absence of

metal ions catalyst. Peroxomonosulphuric acid is commonly known as Caro’s acid.

Stable salt of the acid was prepared as KHSO5 in admixture with K2SO4 and

KHSO4.The structure of H2SO5 is

H O S

O

O

O O H

Peroxomonosulphuric acid is a dibasic acid having two ionisable protons and the

first pKa value is -3.0 ± 0.1 and the second pKa value is 9.4 ± 0.2 [4]. IR studies

reavealed that the O - O stretching frequency is higher than that of H2O2 and the OH

groups are structurally different [5].

1.3.2 Decomposition of PMS in the absence of metal ions

The decomposition of PMS over a wide range of pH was investigated [6]. The

results confirmed the direct interaction between SO52- and OH- in highly alkaline

medium. From the results obtained, the following rate equation was derived.

The

mechanism proposed in acid medium involved the formation of H2O2 by the

hydrolysis of HSO5-.

The rate equation was given as,

Further studies confirmed that the above rate equation was invalid in the

presence of H2O2 and S2O82- and metal ions. Review on the self decomposition of PMS

and peroxides was reported in the literature [7].

Radiolytic decomposition of PMS has been studied extensively [8]. Energetic

radiation produces three reactive species in water (H˙, OH˙ and eaq–). It is inferred that

both eaq– and OH˙ are efficient in the decomposition of PMS.

Photolytic decomposition of potassium peroxomonosulphate [9] was first-order

dependent on [PMS] with respect to photolytic exposure. The primary radical products

viz., SO4–˙ and OH˙ are formed by homolytic splitting of PMS. These were identified by

spin-trapping agents such as fumaric and maleic acids.

The kinetics of induced decomposition of PMS by the phase transfer catalysts

(PTC) such as tetrabutylammonium chloride [TBAC] and tetrabutylphosphonium

chloride [TBPC] was investigated [10]. The effect of [PMS], [PTC], ionic strength of the

medium and temperature on the rate of decomposition of PMS was studied. The

reaction rate was monitored under pseudo-first-order condition and the observed rate of

the reaction was first order with respect to [TBAC] and half order in [TBPC].

The kinetics and mechanism of decomposition of peroxomonosulphate catalyzed

by β-cyclodextrin in aqueous sodium hydroxide medium was investigated [11]. The rate

of decomposition of PMS was considerably enhanced by the added β-cyclodextrin. The

experimental results suggested the formation of β-cyclodextrin peroxy anion by the

interaction between SO52−, and β-cyclodextrin anion (BCDO−). The β-Cyclodextrin

peroxy anion subsequently reacted with PMS to give O2, SO42− and β-cyclodextrin

anion.

1.3.3 Decomposition of PMS in the presence of metal ions

Metal ions had influence on the rate of decomposition of PMS to a greater

extent. Studies on the uncatalyzed decomposition of PMS in the pH range 6-12,

revealed that oxygen was evolved [12]. In strongly acidic medium the product formed

was hydrogen peroxide with both oxygen atoms originating from the peroxide moiety in

PMS. However, in the metal ion catalyzed decomposition a redox process was

observed. Metal ion catalyzed decomposition of PMS in acidic and weakly alkaline

medium were widely reported [13] and [14].

Continuous-flow EPR studies of the reaction between Ce(IV) and the

peroxymonosulphate anion (HOOSO3–) at low pH enable the isotropic EPR spectrum of

SO5˙– to be characterized [15]. Alkylperoxyl radicals (RO2˙) detected when the reaction

was carried out in the presence of alkenes (methyl methacrylate) were shown to arise

from reactions of SO4˙–(derived from self-reaction of SO5˙–) with the alkene, and

subsequent addition of oxygen (also formed from SO5˙–).

Kinectics and mechanism of Mn(II) catalyzed decomposition of

peroxomonosulphate in highly alkaline medium was reported [16]. In the mechanism

proposed, it was suggested that Mn – PMS complex formed which decomposed to form

manganese peroxide intermediate. The mechanism is depicted below:

Mn(OH)2 + OH-

k1Mn

OH

OH

OH2

OH

_

Mn

OH

OH

OH2

OH

_

+ SO4

2- Mn

OH

OH O

O

S

O

O-

O

+ OH-

Mn

OH

OH O

O

S

O

O-

OMn

O

O

SO4

2-+ + H2O

k1

k2

Mn

O

O

SO5

2-+ Mn

2+ + SO4

2- + O2 + 2e

-

SO5

2-

fast

SO4

2- + O2

k2

Scheme 1.1 Plausible mechanism for the Mn(II) catalyzed decomposition

of PMS

The kinetics of the one-electron versus two-electron oxidation reaction of the

peroxomonosulphate ion with iron(II), cerium(III), chloride, bromide, and iodide ions was

reported [17]. Cerium(III) and Iron(II) are most probably oxidized through one-electron

transfer producing sulphate ion radicals as intermediates. The halide ions are oxidized

in a two-electron process, which included oxygen-atom transfer.

Study of the oxygen production reaction between Co(II) and oxone at a pH of 4.5

revealed that the reaction was first order with respect to [Co(II)] and [oxone]. However,

the overall reaction was second order with Co(III) and sulphate radical as intermediates

[18].

1.4 OXIDATION OF AMINO ACID BY PEROXOMONOSULPHATE

Kinetics and mechanism of the oxidation of α-amino acids by PMS in acetic

acid/sodium acetate buffered medium (pH 3.6 - 5.2) were reported [19] - [21]. The

kinetics of oxidation of amino acids by PMS in presence of formaldehyde as well as in

its absence was studied [22]. From the kinetic results, it was reported that the

formaldehyde catalyzed reaction occurred approximately 105 times faster than the

uncatalyzed reaction and this was attributed to the formation of Schiff base.

The kinetics and mechanism of the oxidation of α-amino acids by PMS in acetic

acid/sodium acetate buffered medium (pH 3.6 – 5.2) was reported [23]. The SO52- ion

was more reactive than HSO5- ion and this higher reactivity was attributed to the

nucleophilic attack of peroxide at the amino group.

Scheme 1.2 Plausible mechanism for the oxidation of α-amino acids

by PMS

The kinetics of oxidation of amino acids by PMS in aqueous alkaline medium was

reported [24]. It was observed that the rate was first order with respect to both [PMS]

and [amino acid]. Based on the experimental results, a reaction scheme was proposed

in which the electrophilic attack of HSO5- occurred at the amino acid nitrogen. The

breakdown of the intermediate was influenced by the nature of the substituents at the

amino carbon atom. The intermediate disintegrated to give either imine or imino acids,

which hydrolysed to the corresponding aldehyde.

Study of the kinetics and mechanism of decarboxylation of α-amino acids viz.,

glycine and N-methyl glycine by PMS in acetic acid/sodium acetate buffered medium

[25]. The results revealed that the reaction was autocatalytic and was more pronounced

in N-methyl glycine, which indicated that the formation of Schiff base was not the reason

for the autocatalysis as reported earlier. Formation of hydroperoxide was cited as the

reason for autocatalysis.

The study of oxidation of β-alanine by PMS in the presence of Cu(II) ion at pH

4.2 (acetic acid/sodium acetate) [26] revealed that autocatalysis was observed only in

presence of Cu(II) ion which was attributed to the formation of hydroperoxide

intermediate.

From the investigation on the kinetics and mechanism of oxidation of lysine, by

oxone in an acetic acid/sodium acetate buffered medium [27], it was observed that there

was no sign of autocatalysis, which was found in the case of other neutral α-amino

acids under the same kinetic conditions. This behavior of lysine was attributed to the

formation of 6-amino-2-oxo hexanoic acid, a ketonic product, which did not initiate the

autocatalysis.

The formation of manganese peroxide (Mn(O2)) intermediate in the study of

kinetics and mechanism of Mn(II) catalyzed oxidative decarboxylation of five structurally

different amino acids such as alanine, valine, leucine, phenyl alanine and 2-methyl

alanine by PMS in alkaline medium [28]. The corresponding carbonyl compounds were

identified as products.

The report on the kinetics of Ag(I) catalyzed oxidation of amino acids by PMS in

aqueous perchloric acid medium showed that silver catalyzed reaction occurred

approximately 104 times faster than the uncatalyzed reaction, the reason for the rapid

reaction was attributed to the formation of (adduct) 2+ [29].

Copper(II) catalyzed oxidation of ornithine by PMS in acetic acid-sodium acetate

buffered medium (pH 3.6−5.2) was studied [30] and the catalyzed reaction was found to

be 2.6 times faster than the uncatalyzed reaction. EPR spectral data ruled out the

participation of free radical intermediate. Cyclic voltammetric and absorption studies

confirmed the formation of copper –ornithine – PMS complex.

The oxidation of free α-amino acids by PMS using copper nanoparticles as

catalyst in aqueous medium was investigated by cyclic voltammetry [31]. The products

were identified as N-hydroxylated aminoacids using TLC and FT-IR spectra and the

results showed the oxidation order was alanine > glycine > leucine > valine >

phenylalanine > serine.

The oxidation of alanine in the presence of perchloric acid in DMF-water medium

was studied [32] and the reaction was found to be fractional order with respect to [H+]

and [alanine]. The reaction rate increased with increasing volume percentage of DMF in

the reaction mixture, suggesting the involvement of an ion and neutral molecule in the

rate-determining step.

The oxidation of α-amino acids by PMS in micellar medium was investigated [33].

The reaction was first order with respect to [PMS] and [α-amino acids]. The rate of

electron transfer from α-amino acids to PMS increased with an increase in the

[micelles].

The kinetics of oxidation of alanine in perchloric acid and acetic acid medium was

inverse first order in [H+] [34]. The reaction rate increased with increase in [amino acid]

and followed the Michaelis-Mentene kinetics. The reaction rate decreased with increase

in [H+], suggesting that the protonated amino acid was the non reactive species.

Solvent and kinetic isotope effects in the reaction of oxidative deamination of L-

alanine in acetic acid medium and also in carbonate buffer medium at pH 10.2 was

reported [35].

1.5 OXIDATION OF AMINOACID BY OTHER PEROXO OXIDANT

1.5.1 Oxidation of amino acid by Peroxydisulphate

Anticatalytic effect of Mn(II) in the silver catalyzed oxidations by

peroxydisulphate (PDS) was reported [36]. The Mn(II) was found to be an anticatalyst

in the silver catalyzed oxidations of oxalate, citrate, tartrate, malonate and arsenious

ions.

The kinetics of the silver ion catalyzed oxidation of α-alanine by peroxidisulphate

was studied [37]. The reaction was first order with respect to [peroxidisulphate] and

[silver ion] and independent of [alanine] and also showed a negative salt effect.

The kinetics and mechanism of oxidative decarboxylation of amino acids by PDS

and also in the presence of various metal ions catalyst has been studied [38] - [41]. The

kinetics and mechanism of oxidation of alanine, asparagine, cysteine, glutamic acid,

lysine, phenylalanine and serine by peroxydisulphate were studied in aqueous acidic

medium [42] and [43]. The reaction rate showed first order dependence on

[peroxydisulphate], and zero order dependence on [amino acid]. They observed an

autocatalytic effect in this oxidation due to formation of Schiff base between the

aldehyde formed and parent amino acid. The rate of amino acid oxidation was greater in

presence of mixture of Ag+ and Cu2+ than in presence of either Ag+ or Cu2+ alone.

Kinetics of copper nanoparticle catalyzed oxidation of glycine by

peroxodisulphate in aqueous medium has been studied [44]. It was found that, the

catalytic activity depends on the size of nanoparticles and the kinetics of the reaction

was found to be first order with respect to [peroxodisulphate] and independent of

[glycine]. Addition of neutral salts showed a retarding effect.

1.5.2 Oxidation of amino acid by Hydrogen peroxide

Kinetics and mechanism of oxidation of some amino acids by hydrogen

peroxide in the presence of FeSO4 (Fentons reagent) was reported [45]. The

mechanism involving the formation of OH˙ radical is given below:

The hydroxyl radical reacts with the α-amino acids through the abstraction of α-

hydrogen as represented below:

Scheme 1.3 Plausible mechanism for the oxidation of amino acid by

H2O2 in the presence of FeSO4

The kinetics of Mn(II) and Fe(II) catalyzed oxidation of amino acids by hydrogen

peroxide in HCO3-/CO32- buffer was investigated [46]. The result showed that the amino

acids facilitated the dismutation of H2O2.

Scheme 1.4 Plausible mechanism for the oxidation of amino acid by

H2O2 in the presence of Mn(II) and Fe(II) ions

The oxidative decarboxylation of N-alkyl amino acids [47] with hydrogen peroxide

using tungstate catalyst under phase transfer conditions to get the corresponding

nitrones.The activation of hydrogen peroxide by different Cu(II) –amino acid complexes

and compared with quinaldine blue as an oxidation indicator [48]. Rate of the reaction

was first order in [Cu(II) – amino acid complexes] and variable order in [hydrogen

peroxide] by Michaelis-Menton kinetics. This indicated that the formation of ligand –

Cu(II) – peroxide complex was responsible for the activation of hydrogen peroxide. They

proposed a mechanistic pathway involving the formation of ligand – Cu(II) – peroxide

complex and hydroxy free radicals.

The catalytic decomposition of hydrogen peroxide by Cu(II) complexes with

polymers bearing L-alanine and glycylglycine in their side chain was studied in alkaline

media [49]. The reactions showed pseudo-first order with respect to [H2O2] and [L-

Cu(II)] (L stands for Ala or Glygly) and the reaction rate increased with increase in pH.

They proposed a mechanism involving the Cu(II)/Cu(I) redox pair, and was found to

have more catalytic efficiency due to differences in modes of complexation and in the

conformation of the macromolecular ligands.

1.6 METAL IONS CATALYZED OXIDATION OF AMINO ACID

The kinetics of the Cr(III) catalyzed oxidation of L-leucine and L-isoleucine by

alkaline permanganate was reported [50]. The rate of the reaction was first order with

respect to [oxidant] and [catalyst] with an apparently less than unit order in [substrate]

and zero order with respect to [alkali]. The results suggested the formation of a complex

between the amino acid and the hydroxylated species of Cr(III) complexes. The

complex reacts further with the permanganate in the rate-determining step, resulting in

the formation of a free radical, which again reacted with the permanganate in a

subsequent fast step to yield the products. The observed rate of oxidation of leucine

was faster than the isoleucine.

The kinetics of Cu(II) ions catalyzed oxidation of threonine by

diperiodatocuprate(III) in aqueous alkaline medium was studied spectrophotometrically

[51]. The reaction rate was first order with respect to [oxidant] and [threonine] and less

than unit order in [alkali]. They observed the autocatalysis and the periodate had

retarding effect on the reaction rate. The reactive species of the oxidant was the

monoperiodatocuprate(III) for both the uncatalyzed and the autocatalyzed reaction.

Kinetics and mechanism of oxidation of leucine and alanine by Ag(III) complex

was studied spectrophotometrically in alkaline medium [52]. The reaction was first order

with respect to [Ag(III) complex ] and [amino acids]. The second-order rate constant

decreased with increase in [OH-] and [IO4-].

The influence of substitution on the oxidation of glycine and sarcosine by

permanganate oxidation in sulphuric acid medium was reported [53]. The reaction

followed autocatalysis and the reaction showed first-order dependence on

[permanganate] and [sarcosine] in both catalytic and noncatalytic pathways, and

apparent first-order dependence on [Mn2+] in catalytic pathways.

The oxidation of glycine and alanine by bis(dihydrogen-tellurto) argentite(III) ion

was studied by stopped-flow spectrophotometery [54]. The reaction was first order in

[Ag(III) complex] and less than unit order with respect to [amino acid].

An investigation on the Ru(III) ions catalyzed oxidation of DL-ornithine

hydrochloride (OMH) by silver(III) periodate complex in aqueous alkaline medium [55]

revealed that the reaction proceeded via a Ru(III) – OMH complex. The catalytic

constant was also calculated for the reaction at different temperature to elucidate the

activation parameters.

In the Ag(I) catalyzed oxidation of valine by Ce(IV) [56] the reaction rate

decreased with increase in [Ce(IV)] and the reaction exhibited a fractional dependence

on [valine] due to the formation of an adduct with Ag(I).

Investigation on the kinetics of oxidation of glycine, alanine and valine by

manganese (III) acetate in aqueous sulphuric acid medium [57] revealed that the

reaction showed an inverse dependence on [H2SO4], second order dependence with

respect to [Mn(III)] and first order dependence with respect to [amino acid].

The kinetics and oxidation of L-methionine and N-acetyl L-methionine by Ce(IV)

in sulphuric acid–sulphate media and also the Ag(I)-catalyzed oxidation of L-alanine by

Ce (IV) in sulphuric acid medium was studied [58]. It was found that the Ce4+ was the

kinetically active species of cerium and the reaction system initiated the polymerization

of acrylonitrile, indicating the generation of free radicals during the course of the

reaction.

In the kinetics study of Os(VIII) and Ru(III) catalyzed oxidation of L-valine by

diperiodatoargentate(III) in aqueous alkaline medium [59] the reaction was found to be

first order with respect to [Os(VIII)], [Ru(III)], and [DPA], less than unit order in [L-valine]

and negative fractional order in [OH−]. The catalytic efficiency for the reaction was

observed in the order of Os(VIII) > Ru(III).

The kinetics of oxidation of L-amino acids such as glycine, alanine, valine,

isoleucine, leucine, proline and phenylalanine by Mn3+ ions in sulphuric acid medium

[60] was first-order with respect to [amino acid] and [Mn3+]. It was found that the

oxidation reaction proceeded through the amino acid-metal ion complex.

Oxidation of tryptophan by vanadium (V) in sulphuric acid medium [61] followed

first order kinetics in [oxidant], [tryptophan] and [H+]. The observed stoichiometry,

positive salt and solvent effect suggested a mechanism involving the interaction of

cationic oxidant with the neutral molecule of the amino acid in the rate determining step.

It was observed that the amino acid suffered electrophilic attack by the oxidant yielding

a free radical intermediate. In subsequent fast steps the free radical suffered attack by

the other equivalent of vanadium (V) and yielded the corresponding aldehyde by

decarboxylation, followed by deamination which was also supported by the negative test

of keto acid as intermediate.

The kinetics of oxidation and the effect of Mn(II) on the rate of oxidative

deamination and decarboxylation reaction of glycine , L-alanine, L-valine and L-luecine

in the presence of anionic surfactant (sodium lauryl sulphate) by acidic potassium

permanganate was investigated [62]. The kinetics of permanganate oxidation of L-valine

was also studied in neutral aqueous solutions as well [63].

The kinetics of Ir(III) catalyzed oxidation of arginine and lysine by

hexacyanoferrate (III) ions in aqueous alkaline medium was studied [64] and from the

results the authors proposed a mechanism involving the complex formation between

catalyst and the amino acids.

The Os(VIII) catalyzed oxidation of L-valine by hexacyanoferrate (III) in alkaline

medium was investigated [65]. The mechanism proposed for this reaction involving the

formation of a complex between L-valine and Os(VIII) and the main product for this

reaction was the corresponding aldehyde.

Results obtained from the study on the kinetics of Cu(II), Ni(II) and Zn(II)

catalyzed oxidation of L-lysine by potassium permanganate in alkaline medium [66].

Formation of a complex between the amino acid and the hydroxylated species of metal

ions was ascertained and the reactivity order of the catalyst was Cu(II) > Ni(II) > Zn(II).

In the kinetics of silver (I) catalyzed oxidation of hydroxy lysine by cerium (IV) in

perchloric acid medium [67], the mode of electron transfer was indicated through an

adduct between Ag(I) and hydroxyl lysine, via oxygen atom of the carboxyl group rather

than the amino group of the amino acid.

The kinetics of Ru(III) catalyzed and uncatalyzed oxidation of DL-alanine by N-

bromosuccinimide in aqueous acetic acid and in the presence of perchloric acid was

studied [68]. It was observed that the reaction rate decreased with the increase in

[perchloric acid] and addition of halide ions. The reactions were of fractional order with

respect to [Ru(III)]. By varying the solvent composition, it was found that the reaction

rate decreased with the decrease in dielectric constant of the solvent.

Kinetics and mechanism of oxidation of L-proline by PMS in neutral medium

(phosphate buffer, pH 6-8) in the presence of Cu(II) ions catalyst as was well as without

catalyst was reported recently [69]. The reaction proceeded through free a radical

pathway which was confirmed by the non oxidation of L-proline methyl ester by PMS at

this condition. Variation of ionic strength had negligible effect on the rate of the reaction

ruling out the interaction between carboxylate group of L-proline with SO52- of PMS. The

initial step was the removal of CO2 and formation of carbon free radical which on

hydrolysis led to the formation of the product 4-aminobutanal which was confirmed by

IR and mass spectral studies.

1.7 OXIDATION OF VARIOUS COMPOUNDS BY PEROXOMONO

SULPHATE

The kinetics of oxidation of ethyl methyl ketone, isobutyl methyl ketone, and

acetophenone by PMS was investigated in aqueous H2SO4 medium and also in

aqueous acetic acid medium [70]. The reactions obeyed total second-order kinetics, first

order each with respect to [ketone] and [PMS] for all the ketones. It exhibited acid

catalysis with the concurrent occurrence of acid-independent reaction paths conforming

to the rate law.

The oxidation of aldehydes by peroxomonosulphate in aqueous acetone with the

formation of dimethyl dioxirane as given below [71].

Scheme 1.5 Plausible mechanism for the oxidation of aldehydes by PMS

The kinetics of oxidation of some sulphoxides with oxone and the catalytic

activity of Ru(III) with several diaryl, dialkyl and alkyl aryl sulphoxides were explored.

They were found to undergo oxidation under homogeneous conditions [72]. A

mechanism involving electron transfer from electrophilic perhydroxyl oxygen of oxone to

the sulphoxides was suggested.

The kinetics of oxidation of hypophosphorous acid by PMS in aqueous medium

was investigated [73], which followed first order with respect to each reactant and the

rate was independent of ionic strength, hydrogen ion concentration. Any possibility of

involvement of free radicals was ruled out.

The oxidation of Indole -3- acetic acid by PMS in acetonitrile medium was

reported [74]. The reaction followed a second order, first order each with respect to

[substrate] and [PMS]. It was observed that the reaction proceeded through a non-

radical pathway.

The kinetics of oxidation of ascorbic acid by PMS in aqueous acidic (pH 4.4),

neutral (pH 7.0) and alkaline (pH 9.0) medium was investigated [75] and the reactions

were found to obey second order, first-order each with respect to [PMS] and [ascorbic

acid]. Dehydroascorbic acid was detected as the product of the reaction. The

stoichiometry of the reaction was 1:1, indicating the absence of self-decomposition of

PMS and a mechanism involving the formation of hydroxyl, sulphate and ascorbate free

radicals as intermediates was proposed.

The kinetics of oxidation of glyoxylic acid by PMS in perchlorate medium was

investigated to determine whether the peroxodiphosphate or peroxomonophosphate

oxidizes glycolic acid in the redox system [76].

The kinetics and mechanism of the oxidation of tris (1, 10-phenanthroline) iron(II)

by PMS was reported [77]. The oxidation reaction was first order with respect to both

the [substrate] and the [oxidant] and the rate was accelerated by the alkali metal ion.

The kinetics of the reaction between nickel(II)lactate and PMS in the presence of

formaldehyde was studied in the pH range 4.0–5.9 [78]. The result showed that when

the [HCHO] was greater than or equal to [Ni(II)], the self-decomposition of PMS was

observed, Nickel lactate reacted with formaldehyde to give a hemiacetal intermediate.

The kinetics of oxidation of glycolic acid, α-hydroxy acid [79], and tartaric acid

[80] by PMS in presence of Ni(II) and Cu(II) ions in acidic pH range 4.05–5.89 were

reported. The kinetics of ruthenium (III) chloride catalyzed oxidation of formic acid by

PMS in acid aqueous medium was studied [81].

The kinetics of oxidation of L-ascorbic acid by PMS in the presence and absence

of copper(II) catalyst in perchloric acid medium was studied [82] and the rate of the

reaction was first order with respect to [PMS]. The rate constant decreased with

increasing [perchloric acid] and increased with increasing ionic strength.

The oxidation of vanillin by PMS in acetic acid-sodium acetate buffer medium

followed first order with respect to [vanillin] and [PMS] and the rate increased with

increase in pH and the rate was too high at pH 5.2 [83]. The product of oxidation was

confirmed as vanillic acid by IR, 1H NMR and GC-MS spectral analysis and the following

reaction scheme was proposed.

Scheme 1.6 Plausible mechanism for the oxidation of vanillin by PMS

The kinetics of oxidation of nicotinic acid by PMS in acetate buffer medium [84]

was reported. Stoichiometry of the reaction corresponds to the reaction of one mole of

the oxidant with one mole of nicotinic acid. N-oxide product was confirmed both by UV

visible and IR spectroscopy.

The kinetics of oxidation of malic acid by PMS in the presence of Cu(II), Co(II)

and Ni(II) in the pH range 4.05–5.89 was studied [85]. The oxidation of Ni(II) malate

followed simple first-order kinetics with respect to both [PMS] and [Ni(II)], while the

oxidation of Cu(II) malate and Co(II) malate showed autocatalysis. There was an

appreciable induction period in the Cu(II) malate oxidation, while Co(II) malate oxidation

followed a simple curve.

In the kinetics study of the oxidation of aspartic acid by PMS catalyzed by

ruthenium (III) chloride in acidic medium [86], it was observed that the reaction rate

decreased with increasing [H+]. The experimental observations showed that the

cleavage of the bond between the α-carbon and the carboxylic carbon of amino acid

yielded the imine intermediate. Further, the hydrolysis of imine appeared to be the most

predominant path to yield a final product than oxidation with oxidizing species.

The mechanistic investigation of Mn(II) catalyzed oxidation of biotin by PMS in

alkaline medium was reported [87], in which the reaction showed polymerization in the

presence of acrylonitrile under the experimental conditions. The kinetic results indicated

that an intermediate complex of catalyst and PMS was formed which was confirmed by

UV-Vis spectra on the reaction mixture containing Mn(II), substrate in alkaline medium

with λmax at 348 nm. The Mn(II)-PMS complex oxidized biotin to biotin sulfoxide.

The kinetics of β-cyclodextrin catalyzed oxidation of glutamine by PMS in acetic

acid - sodium acetate buffered medium was investigated [88]. It was found that the

reaction was first order with respect to [glutamine] and [PMS]. Variation of the ionic

strength and the solvent polarity had negligible effect on the rate of the reaction. The

formation of inclusion complex between β-cyclodextrin and glutamine was analyzed by

UV-Vis spectrophotometry.

Kinetics of oxidation of isatin in an acidified solution of PMS was investigated

[89]. The result showed that the reaction was first order on [isatin], [H+] and independent

of [PMS]. The influence of ionic strength on the rate was found to be insignificant.

Kinetics of oxidation of indole by PMS in aqueous ethanol medium [90] and in

aqueous acetonitrile medium [91] were reported. The reaction followed a total second

order, first order each with respect to [Indole] and [PMS]. The rate of the reaction was

not affected by added [H+]. Variation of ionic strength had no influence on the reaction

rate. Increase of percentage of ethanol and acetonitrile decreased the reaction rate.

The Co(II) ion catalyzed decomposition of PMS and influence of organic

substrates such as ethanol, t-butyl alcohol, α-hydroxy acids and glycine have been

studied both in strong acidic and buffered medium [92]. The results showed that in

strong acidic medium, the reaction was inhibited by the organic substrates and the

redox process proceeded through formation of sulphate free radical intermediate.

However in buffered medium, the substrate other than t-butyl alcohol catalyzed the

reaction and gets oxidized. The authors suggested the molecular mechanism involving

a complex intermediate EtOH – Co(II) – SO52- and subsequent oxygen atom transfer

from SO52-.

The reactions between PMS and quinones were investigated [93]. It was

demonstrated that benzoquinone could efficiently activate PMS for the degradation of

sulfamethoxazole, a frequently detected antibiotic in the environments, and the

degradation rate increased with pH from 7 to 10. The quenching studies suggested that

neither hydroxyl radical nor sulphate radical was produced therein, the appearance of

O2 indicative products detected by electron paramagnetic resonance spectrometry,

liquid chromatography and mass spectrometry. A catalytic mechanism was proposed

involving the formation of a dioxirane intermediate between PMS and benzoquinone

and the subsequent decomposition of this intermediate into O2. The kinetics of the

oxidation of aromatic aldehydes by peroxomonosulphate was reported [94] and [95].

1.8 SCOPE OF THE PRESENT INVESTIGATION

It is important to understand the mechanism of oxidation of amino acids

proceeding through the formation of Schiff base intermediate with pyridoxal phosphate

in living systems. Biological reactions such as transamination, racemization and

decarboxylation in living systems are suggested to proceed via Schiff base

intermediate. As this Schiff base is a tridentate ligand with high coordinating capability

compared to either pyridoxal phosphate or amino acids which are bidentate, it readily

forms complex with any redox metal ions. In order to understand the mechanism of

oxidation, in the present study, pyridoxal is replaced by a metal ion, such as VO2+ and

Cu2+ ions and oxidant, PMS in perchloric acid medium.

Vanadium catalyzed oxygen-transfer reactions have attracted considerable

interest due to their relevance in biological processes. Due to their catalytic properties

[96] and [97], and biological activities, coordination chemistry of oxovanadium(IV) is an

interesting area of current research. Further, vanadium oxo anion and hydrogen

peroxide enhances the insulin mimetic effect over that of vanadate itself [98]. Oxidation

of amino acids has been carried out with peroxo oxidants such as H2O2, PDS, PMS and

PMP with an objective of designing model system to understand enzymatic oxidation of

amino acids.

Peroxomonosulphate is commercially available in the form of a triple salt, named

Oxone. It is a versatile oxidant and is widely used in environmental, industrial and

consumer applications such as decolorizing agent in denture cleansers, micro etchant in

electronics, shock-oxidizer for swimming pools, repulping agent in paper making or

oxidizer in wool treatment. The use of peroxomonosulphate ion is very common in

organic reactions. It was shown to be a convenient and efficient oxidant for a great

variety of synthetic purposes. Due to its stability, non toxicity, good solubility in water,

low cost and versatility of the reagent, it is being employed for the oxidation reaction.

It is reported that the oxidation of amino acids could be catalyzed by metal ions

such as Cr(III), Fe(II), Mn(II), V(V) and Ag(I). Although oxidation of amino acids by PMS

has been fully exploitated in alkaline and buffered medium, the same reaction has not

been studied in the presence of VO2+ and Cu2+ ions in highly acidic medium. This

particular study has been carried out to understand the influence of the metal ions

catalyst in the oxidation of amino acids. Hence in the present investigation, the role of

metal ions such as VO2+ and Cu2+ catalyzed oxidation of amino acids by PMS in

perchloric acid medium is undertaken.

The present investigation is based on the following facts (i) development of highly

efficient oxidation protocols and (ii) oxidation of amino acids by PMS catalyzed by VO2+

and Cu2+. The experimental results of the kinetics and mechanism of oxidation of amino

acids by PMS in presence of VO2+ and Cu2+ ions are discussed in the forthcoming

chapters.

The following amino acids are chosen for the present study and the structures

are given below.

1.9 OBJECTIVES OF THE PRESENT INVESTIGATION

The present investigations of kinetics of VO2+ and Cu2+ ions catalyzed oxidation

of amino acids by PMS in perchloric acid medium have the following objectives,

Determination of rate constant for both the catalyzed and uncatalyzed reactions

Influence of reactant concentration on the reaction rate

Influence of ionic strength and dielectric constant on the rate of the reaction

Influence of temperature on the rate of the reaction

Calculation of thermodynamic and kinetic parameters

Comparison of catalytic effect of metal ions and calculation of the catalytic

constant

Identification of intermediate product and sequence of the oxidation of amino

acids using spectral methods such as UV-Vis and EPR spectroscopy and

electrochemical method viz., cyclic voltammetry

Preparation of metal ions - amino acid complexes and characterization by FT-IR

spectroscopy

Analysis of the products of oxidation of amino acids by gas chromatography

Proposal of the plausible mechanism for the oxidation of amino acids by

peroxomonosulphate.

1.10 OUTLINE OF THE THESIS

The content of the current thesis has been divided into nine chapters.

Chapter One: This chapter throws light on the fundamental concepts and brief

introduction of the present work and the literature concerning peroxomonosulphate and

other oxidant used for the oxidation of metal ion catalyzed oxidation of amino acids and

other organic compounds.

Chapter Two: A detailed description of all the reagents and materials used,

procedures for kinetic measurements has been discussed in this chapter. Procedure for

the preparation of metal ions-amino acid complexes and the anticancer activity of the

synthesized compounds has been discussed.

Chapter Three: This chapter illustrates the kinetics and mechanism of the

vanadium (IV) catalyzed oxidation of amino acids such as glycine, alanine, valine, 2-

amino isobutyric acid (2-AIBA) and N-methyl glycine (NMG) by peroxomonosulphate in

perchloric acid medium at 308K.

Chapter Four: The kinetics and mechanism of the oxidation of N-Phenyl glycine

(NPG) by peroxomonosulphate in perchloric acid medium both in the presence and

absence of VO2+ and Cu2+ ions catalyst has been studied at 278K and the results are

discussed in this chapter.

Chapter Five: This chapter describes the kinetics of copper (II) ions catalyzed

oxidation of amino acid such as alanine and 2-AIBA by peroxomonosulpate in perchloric

acid medium at 308K and the results are discussed.

Chapter Six: This chapter describes the biological study such as antibacterial

and anticancer activities of the metal ions – amino acid complexes.

Chapter Seven: This is a concluding chapter which focuses on the summary and

conclusion of the present work.

Chapter Eight: The future prospect of the current investigation has been

presented in this chapter.

Chapter Nine: The list of references used throughout the thesis has been given

in this chapter.

CHAPTER II

MATERIALS AND METHODS

The kinetics of VO2+ and Cu2+ ions catalyzed oxidation of α-amino acids by

peroxomonosulphate (PMS) in perchloric acid medium was studied. The method of

purification of materials, experimental details, kinetic measurements, methods used for

analysis of the products, determination of stoichiometry, spectral and analytical

techniques employed for identification of intermediates and products, which include Gas

Chromatography, UV-visible spectroscopy, Electron paramagnetic resonance

spectroscopy, FT-IR spectroscopy and cyclic voltammetry have been discussed.

2.1 MATERIALS

Glass wares used for handling the reagents were cleaned with chromic acid,

rinsed thoroughly with doubly distilled water and then air dried at room temperature. All

the solutions used in this study were prepared by using double distilled water. The

reagents were prepared afresh every day before starting the experiments.

2.2 CHEMICALS

2.2.1 α-Amino acids

All the α-amino acids such as glycine, alanine, valine, N-methyl glycine

(NMG), 2-amino isobutyric acid (2-AIBA) and N-phenyl glycine (NPG) were from E-

Merck, India Ltd. and used as such. The purity of the compounds was checked by

measuring their melting point.

2.2.2 Peroxomonosulphate (HSO5-)

Peroxomonosulphate (PMS) was from Sigma Aldrich, USA by the trade name

“Oxone”. It is a triple salt with the composition 2KHSO5. KHSO4. K2SO4. The purity of

this reagent was estimated by iodometry and it was found to be > 98%. Tests with

permanganate showed the absence of free hydrogen peroxide and hence this reagent

was used without further purification. A fresh solution of PMS was prepared everyday

and stored in a black coloured flask to avoid photochemical decomposition and

standardized iodometrically.

2.2.3 Vanadyl sulphate pentahydrate

Vanadyl (VO2+) ions solution of 5.0 x 10-3 mol dm-3 was prepared by

dissolving 0.1265g of vanadyl sulphate pentahydrate (VOSO4.5H2O) from E- Merck in a

100 ml standard measuring flask by using double distilled water.

2.2.4 Copper sulphate pentahydrate

A stock solution of Cu2+ ions (5.0 x10-3 mol dm-3) was prepared by dissolving

an appropriate amount of CuSO4.5H2O (E-Merck) with the addition of known volume of

1M perchloric acid and made up to 100 ml in a standard measuring flask by using

double distilled water.

2.2.5 Perchloric acid

A stock solution of 2M perchloric acid (E-Merck) was prepared with distilled

water and standardized against sodium hydroxide (E-Merck, India Ltd.) using

phenolpthalein indicator. Solution with appropriate concentration was prepared from the

stock solution.

2.2.6 Other Reagents

All other chemicals such as sodium thiosulphate, potassium iodide, starch,

sodiumperchlorate, acetonitrile, t-butyl alcohol, acrylonitrile, sulphuric acid, hydrochloric

acid, oxalic acid, phenolphthalein, etc., were purchased from Loba Chemie, India and

purified by standard methods.

.

2.3 EXPERIMENTAL METHODS

The thermostat (Toshniwal & Co.) is a rectangular stainless steel tank with

glass windows. The tank was filled with distilled water and was stirred continuously and

heated electrically. The temperature of the water bath was maintained with an accuracy

of ± 0.1°C

2.3.1 Measurement of Rate constants

Kinetic studies were carried out at 308K in perchloric acid medium under

pseudo first order conditions with a large excess of [amino acids] over [PMS].The

reaction rate was measured by monitoring the unreacted [PMS]t at various time intervals

by iodometry. The reaction mixture containing the required amount of amino acids,

perchloric acid and metal ions was thermostated in a 250 ml blackened iodine flask and

kept in a thermostat at 308K. A known volume of PMS solution, thermostatted at the

same temperature separately, was pipetted out into the reaction mixture, and

simultaneously a timer was started. Aliquots were withdrawn at definite time intervals

and the rate of oxidation of amino acids was followed by monitoring the concentration of

unreacted [PMS] iodometrically using starch as an indicator [99]. First-order kinetics

was observed and the pseudo first order rate constant kobs were calculated from the

linear plot of log [PMS]t vs time according to the equation (2.1) which was linear up to

90% conversion of [PMS].

Linear square method was used to calculate the slope and intercept in all

studies. Statistical analysis was carried out with Microsoft Excel Version, Windows 98

operating system. The relative standard errors of the above mentioned rate constants

for a single run and the relative standard errors of the mean were about ± 2%.This

experiment was also carried out at different temperatures in the range 303-323K to

evaluate the thermodynamic parameters.

2.3.2 Stoichiometry

The stoichiometry of the reaction was determined by keeping the reaction

mixtures containing a large excess of [PMS] over [amino acids], (PMS: AA = 0.06:0.02

M) for 48h at room temperature for completion of reaction. The excess [PMS] present

was then estimated iodometrically. Corrections for the self-decomposition of PMS were

made from the values obtained from the blank solution under the identical experimental

conditions. The observed stoichiometry of the reaction was Amino acid:PMS = 1:2 for all

the amino acids, except 2-AIBA and NPG which showed a 1:1 stoichiometry (Table 2.1).

Table 2.1 Stoichiometry of the oxidation of α-amino acids by PMS

S. No. Amino acid : PMS Stoichiometry

(in ratio)

1. glycine : PMS 1:2

2. alanine : PMS 1:2

3. valine : PMS 1:2

4. NMG : PMS 1:2

5. 2-AIBA : PMS 1:1

6. NPG : PMS 1:1

2.3.3 Product analysis

The procedure followed for the analysis of the products formed in the

oxidation reaction is discussed below. The reaction mixture containing 0.2 mol dm-3 of

amino acid, 0.4 mol dm-3 of PMS in the presence of 4.0 x 10-3 mol dm-3 metal ions

(VO2+) in perchloric acid was kept for 48h for the completion of the reaction. After

completion of the reaction, the excess [PMS] was destroyed by adding sodium

bisulphite, and then the product was extracted with dichloromethane. The product

present in the organic layer was separated and dried and identified as the

corresponding carbonyl compounds by gas chromatography (GC).The chromatographic

results showed that the yield of the products obtained were greater than 80% .The

products were confirmed by spiking the authentic sample and noted the retention time.

The evolution of oxygen during the self-decomposition of PMS was confirmed by the

color change with alkaline sodium dithionite activated by indigo carmine [100]. The

same methodology was followed for the oxidation of amino acids in the presence of

Cu2+ ions as well.

2.3.4 Gas chromatographic analysis

The product for the metal ions catalyzed and uncatalyzed oxidation of amino

acids was analyzed by Gas chromatographic technique using Shimadzu Gas

chromatograph (GC-2014). The injection temperature was 553K and detection

temperature was 573K using nitrogen as the carrier gas with split ratio of 1:75. The

products of the oxidation of amino acids were identified as the corresponding carbonyl

compounds. The product was confirmed with the retention time (RT) of the authentic

samples and the results are shown in Table 2.2.

Table 2.2 Chromatographic result for the oxidation of amino acids

2.3.5 UV-Visible Spectral analysis

The UV- Visible (UV-vis.) spectrum of the reaction mixture was monitored

using Perkin Elmer (Lamba-25 UV-Vis- Spectrophotometer, USA) in the UV region of

200-400 nm to unravel the intermediate formed during the course of the reaction. The

reaction mixture used for UV-Vis studies was in the solution form and was placed in the

quartz cell. A reference cell containing water as a solvent was used. The reaction

mixture was prepared by adding PMS (3.6 × 10-3 mol dm-3) to a mixture containing

amino acid (0.05 mol dm-3), perchloric acid (0.10 mol dm-3) and VO2+ (5.0 x 10-4 mol

dm-3). The spectra were recorded at different time intervals. The complex formation

between metal ion and amino acids was confirmed by recording UV-Vis spectra in the

region of 400-1000nm separately using high concentration (0.2 mol dm-3) of VO2+/Cu2+

to the reaction mixture.

S.No Amino acids Product obtained Retention time (RT)

in (minutes)

1. glycine Formaldehyde 1.771

2. alanine Acetaldehyde 2.285

3. valine Iso valeraldehyde 2.996

4. NMG Formaldehyde

Methylamine

1.771

2.140

5. 2-AIBA Acetone 2.836

6. NPG Formaldehyde

Aniline

1.771

12.718

2.3.6 Electron Paramagnetic Resonance Spectral analysis

Electron Paramagnetic Resonance (EPR) spectrum gives the chemical

information regarding the structure of paramagnetic substances. The number of lines,

their spacing and their relative intensities unequivocally indicate a characteristic

structure of a species. This sensitive technique has proved useful in the study of the

electronic structures of many species, including organic free radicals, biradicals, and

most transition metals and rare-earth metals. In evaluation of an EPR spectrum, the

most important parameter is the g value, which is also known as spectroscopic splitting

factor. To ascertain the presence of free radical when amino acids was oxidized by

PMS in perchloric acid medium in the presence of metal ions (VO2+/Cu2+) catalyst, the

EPR spectrum for the reaction mixture was recorded using JEOL model JES FA 200,

USA, instruments. There was no EPR spectrum obtained for the oxidation in the

absence of metal ions, ruling out the formation of free radical intermediate.

2.3.7 Cyclic voltammetry measurements

Cyclic voltammetry (CV) is perhaps the most effective and versatile

electroanalytical technique available for the mechanistic study of redox systems. It

enables the electrode potential to be rapidly scanned in search of redox couples [101].

Once located, a couple can then be characterized from the potentials of peaks on the

cyclic voltammogram and from changes caused by variation of the scan rate. The

potential is measured between the reference electrode and the working electrode and

the current is measured between the working electrode and the counter electrode. This

datum is then plotted as current (i) vs potential (E). Electrochemical experiments were

recorded using a CHI 680 computer-controlled potentiostat (USA) with a standard three-

electrode single compartment cell system. A glassy carbon electrode (GCE) served as a

working electrode, a platinum wire was used as a counter-electrode with a saturated

Ag/AgCl as reference electrode. All potentials were reported with respect to standard

calomel electrode (SCE). The solutions were deoxygenated by passing dry nitrogen through

the solution for 30 minutes prior to the experiments, and during the experiments the flow was

maintained over the solution. Cyclic voltammogram was recorded for the following:

VO2+ ions in perchloric acid

Amino acid with VO2+ ions in perchloric acid

Amino acid with VO2+ ions and PMS in perchloric acid

Cu2+ ions in perchloric acid

Amino acid with Cu2+ ions in perchloric acid

Amino acid with Cu2+ ions and PMS in perchloric acid

2.3.8 Preparation of Amino acid Metal ions complex

The complex between VOSO4 5H2O and glycine was prepared in aqueous

alcoholic solution at room temperature [102] and [103]. 4.0 mmol of glycine in 10 ml

water was added to 25ml aqueous alcoholic solution of VOSO4 5H2O (2.0 mmol). The

aqueous alcoholic solution was stirred at room temperature for 6h. The dark green

colour precipitate was isolated and then filtered, washed repeatedly with ethyl alcohol

and dried in vacuum at room temperature to constant weight. The other complexes of

alanine, valine, 2-AIBA, NMG and NPG with VO2+ were also prepared by the same

method. The deep blue colour Cu2+ complex with amino acid was also prepared by the

same method. The prepared complex was characterized by FT-IR spectroscopy.

2.3.9 FT- IR spectroscopy

Fourier Transform Infrared spectroscopy (FT-IR) is a useful tool for the

structural investigation. When infrared light is passed through a sample, some

frequencies are absorbed while other frequencies are transmitted through the sample

without being absorbed. This can be plotted as percentage of transmittance vs

frequency. After evaporation of the solvent from the complex, the FT-IR spectrum was

recorded using JASCO analytical instruments (FT-IR 6300 spectrophotometer, JAPAN).

The spectrum was recorded in the range of 400 to 4000 cm-1.

2.3.10 Antibacterial activity assay

Bacterial strains were purchased from the American type culture collection,

E.coli (ATCC 25922), Klebsiella pneumoniae (ATCC 35657), Proteus mirabilis (ATCC

35659), Pseudomonas aeruginosa (ATCC 27853) and Salmonella typhimurium (ATCC

14028), MRSA (Methicillin resistance Staphylococcus aureus). Antimicrobial sensitivity

tests were performed on Mueller-Hinton agar (Hi media Mumbai) by Kirby-Bauer disk

diffusion method and interpreted according to CLSI (Clinical and Laboratory Standards

Institute) standard tables. The small molecule of VO2+ – amino acid complex such as

VO2+ – glycine, VO2+ – alanine, VO2+ – valine, VO2+ – 2-AIBA and VO2+ – NMG, 5mg

were dissolved in 500µl, 50% Dimethyl sulfoxide (DMSO) and 50µl was loaded in each

well and antibiotic Gentamycin was used as a control.

2.3.11 In Vitro anticancer activity by MTT assay

A549 cells (lung cancer cell line) were obtained from National facility for

Animal Tissue and Cell culture, Pune, India was used for the study. The cytotoxicity

assay was carried according to that described by Kiranmyai Gail (2011) [104]. The cells

were seeded in 96 well plate at a density of 1.5x103 cells per well. After the cells

reached 80% confluence they were treated with the compounds at different

concentrations (10µg/ml) for 24h. MTT assay was carried out and the intensity of purple

colour developed was measured at 570nm in Perkin Elmer Multimode plate reader. The

control was represented by untreated medium with cells.

CHAPTER III

VANADIUM (IV) CATALYZED OXIDATION OF AMINO ACIDS BY

PEROXOMONOSULPHATE- KINETICS AND MECHANISTIC STUDIES

The kinetics of VO2+ ions catalyzed oxidation of five structurally different amino

acids such as glycine, alanine, valine, 2-amino isobutyric acid (2-AIBA) and N-methyl

glycine (NMG) by peroxomonosulphate in perchloric acid medium was studied and the

results are discussed in this chapter. The reaction did not proceed at all in the absence

of VO2+ ions, the influence of VO2+ ions on the reaction rate was significant at minimum

concentration of 5.0 ×10-4 mol dm-3, and hence the [VO2+] was fixed at 5.0× 10-4 mol dm-

3. Kinetic studies were carried out at 308K in perchloric acid medium under pseudo first

order conditions with a large excess of [amino acids] over [PMS] and the results were

shown in Table 3.1. First-order kinetics was observed and the rate constant kobs was

calculated from the plot of log [PMS]t vs time which was linear up to 90% conversion of

[PMS] (Figure 3.1).

50 100 150 200 250

1.0

1.1

1.2

1.3

1.4

1.5

1.6

lo

g[P

MS

] t

Time (min)

A

B

CD E

Figure 3.1 Plot of log [PMS]t vs time for the reactions at 308 K

[AA] = 5.0×10−2 mol dm−3; [VO2+] = 5×10−4 mol dm−3;

[H+] = 0.1mol dm−3; [PMS] = 3.6×10−3 mol dm−3

(A). glycine; (B). alanine; (C). valine; (D). 2-AIBA; (E). NMG

Table 3.1 Relationship of unreacted PMS (log [PMS]t) with respect to time

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0 × 10-4 mol dm-3; [PMS] = 3.6 × 10-3 mol dm-3

time

(minutes)

log [PMS]t

glycine Alanine valine 2-AIBA NMG

1:00 1.4857 1.4885 1.4800 1.5465 1.5105

10:00 1.4517 1.4502 1.4149 1.5065 -

15:00 - - - - 1.4487

20:00 1.4166 1.4149 1.3883 1.4424 -

30:00 - - 1.3180 - 1.3979

35:00 1.3802 1.3765 - 1.3384 -

40:00 - - 1.2944 1.2852 -

45:00 - - - - 1.3710

50:00 1.3283 1.2966 - 1.2121 -

56:00 - - 1.2278 - -

61:00 - 1.2278 - - -

65:00 1.2718 - - 1.1242 1.3117

70:00 - 1.1846 1.1553 1.0492 -

78:00 - - - 1.0086 -

80:00 1.2095 - - - -

86:00 - - 1.0718 - -

95:00 - - 1.0334 - 1.2648

99:00 - 1.0569 - - -

102:00 1.0969 - - - -

109:00 - 1.0043 - - -

113:00 1.0293 - - - -

135:00 - - - - 1.1818

160:00 - - - - 1.1238

190:00 - - - - 1.0170

3.1 Stoichiometry

The stoichiometry of the reaction was determined by allowing the reaction

mixture containing a large excess of [PMS] over [amino acids] for 48h at room

temperature and the excess [PMS] was then estimated iodometrically. The calculated

stoichiometry of [amino acids]:[PMS] is 1:2. Similar results were obtained with all other

amino acids, except 2-AIBA, which showed a 1:1 stoichiometry. The reaction can be

written as in equation (3.1).

3.2 Product analysis

The reaction mixture containing 0.2 mol dm-3 amino acid and (0.4 mol dm-3)

PMS in presence of 4.0 ×10-3 mol dm-3 of VO2+ was kept for 48h for the completion of

the reaction. The excess PMS was destroyed by adding NaHSO3 and then the product

was extracted with dichloromethane. The products were confirmed as corresponding

carbonyl compounds by gas chromatograph (Figures 3.2 to 3.6) by comparing with the

authentic sample.

The evolution of oxygen during the self-decomposition of PMS was confirmed by

the colour change with alkaline sodium dithionite activated by indigo carmine [100].

Figure 3.2 Gas chromatogram of the product in the VO2+ ions catalyzed

oxidation of glycine


oxidation of alanine

1.7

71

/ F

orm

aldeh

yd

e

Dic

hlo

rom

eth

ane

2.2

85

/ A

ceta

ldeh

yde

Dic

hlo

rom

eth

ane


oxidation of valine


oxidation of 2-AIBA

Dic

hlo

rom

eth

ane

2.9

96

/ I

soval

eral

deh

yde

Dic

hlo

rom

eth

ane

2.8

36

/ A

ceto

ne


oxidation of NMG

3.3 EFFECT OF VARYING THE CONCENTRATION OF THE REACTANT

ON kobs

3.3.1 Effect of [amino acid] on kobs

The kinetics was carried out with various initial concentrations of amino acid

(AA), while keeping all other parameters at constant value. Perusal of the kinetic results

showed that the rate constant increased with increase in [AA] (Table 3.2). The reaction

obeyed first order with respect to [AA]. Further, the plot of kobs vs [AA] was linear with

positive intercepts for all the amino acid (Figure 3.7), which revealed that the reaction

proceeded by two steps one dependent on amino acids concentration and the other

independent of amino acids concentrations. The [amino acid] independent step was due

to self-decomposition of PMS under experimental conditions. This was confirmed by

conducting the reactions without amino acid in the reaction mixture at the same

conditions.

Dic

holo

rom

ethan

e

2.1

40

/ M

ethyla

min

e

1.7

71

/ F

orm

aldeh

yd

e

Table 3.2 Effect of [amino acid] on kobs

[H+] = 0.10 mol dm-3; [VO2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3

102 x [AA]

mol dm-3

104 x kobs (s-1) *


2.50 0.84 1.11 2.18 2.49 0.65

5.00 1.49 1.88 2.94 3.27 0.84

7.50 2.05 2.49 3.35 4.02 1.11

10.00 2.65 3.34 3.92 4.84 1.38

12.50 3.45 3.95 4.68 5.64 1.73

* Error bar for approximation was > 0.1 % < 0.6 %

0 2 4 6 8 10 12 14

0

1

2

3

4

5

6

104 ×

ko

bs (

s-1

)

102 × [AA] mol dm

-3

A

B

C

D

E

Figure 3.7 Plot of kobs vs [AA] at 308 K

[VO2+] = 5×10−4 mol dm−3, [H+] = 0.1 mol dm−3,

[PMS] = 3.6×10−3 mol dm−3


3.3.2 Effect of [H+] on kobs

The reaction rates were measured for various [H+] (6.0×10-2 - 15.0×10-2 mol dm-3)

by keeping all other parameters at predetermined values. The pseudo first order rate

constant decreased with the increase in [H+] (Table 3.3) which revealed that the

reaction was inhibited by acids. The retardation of rate by [H+] ions may be attributed to

the accumulation of the protonated form of amino acid which is less reactive. Further,

the plot of kobs vs [H+]-1 was linear (r = 0.9943) with a positive slope indicating that this

reaction was inverse first order with respect to [H+] (Figure 3.8). The results revealed

that the reaction proceeded by two steps one dependent of [H+] and the other

independent of [H+].

Table 3.3 Effect of [H+] on kobs

[AA] = 5.0 × 10-2 mol dm-3; [VO2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3

[H+]

mol dm-3

104 x kobs (s-1) *


0.06 2.85 3.26 3.76 4.61 1.46

0.08 2.22 2.65 3.03 3.75 1.23

0.10 1.73 2.03 2.37 2.89 0.99

0.13 1.46 1.61 1.96 2.27 0.84

0.15 1.12 1.30 1.61 1.80 0.73


0 2 4 6 8 10 12 14 16 18

0

1

2

3

4

5

104 ×

ko

bs (

s-1

)

[H+

]-1

mol dm-3

A

B

C

D

E

Figure 3. 8 Plot of kobs vs [H+]-1 at 308 K

[AA] = 5.0×10−2 mol dm−3; [VO2+] = 5×10−4 mol dm−3;

[PMS] = 3.6×10−3mol dm−3


3.3.3 Effect of [metal ions] on kobs

The reaction rates were measured with various concentrations of VO2+ (2.5×10-4 -

10.0×10-4 mol dm-3) while keeping all other parameters at predetermined values. The

observed reaction rate (kobs) increased with increase in [VO2+] (Table 3.4). The reaction

followed first order kinetics with respect to [VO2+], and the plot of kobs vs [VO2+] was a

straight line with high regression coefficient (r = 0.9986) with positive intercept (Figure

3.9). The positive intercept was due to the self decomposition of PMS.

Table 3.4 Effect of [metal ions] on kobs

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3

104 x [VO2+]

mol dm-3

104 x kobs (s-1) *


2.50 0.88 1.04 1.43 2.19 0.73

5.00 1.71 1.88 2.65 3.11 0.99

6.30 2.05 2.42 3.31 4.15 1.19

7.50 2.34 2.85 3.79 5.29 1.42

10.00 3.15 3.54 4.87 6.37 1.69


Figure 3.9 Plot of kobs vs [VO2+] at 308 K

[AA] = 5.0×10−2 mol dm−3; [H+] = 0.1 mol dm−3;

[PMS] = 3.6×10−3 mol dm−3


0 2 4 6 8 10

0

1

2

3

4

5

6

7

104 ×

ko

bs (

s-1

)

104 × [VO

2+] mol dm

-3

A

B

C

D

E

3.3.4 Effect of [PMS] on kobs

The effect of [PMS] was studied by increasing the concentration of PMS fivefold

(1.75×10-3 - 8.87×10-3 mol dm−3), keeping the other parameters at constant values. The

observed reaction rate kobs decreased with increase in [PMS] (Table 3.5). Further, the

plots of kobs-1

vs [PMS] were linear with a positive slope in all the amino acids (Figure

3.10). The decrease in the rate with increase in [PMS] was due to the dimerization of

the vanadyl imine intermediate to a less active form. The effect was well pronounced in

N-methyl glycine which might be due to the difficulty of the secondary imine to undergo

hydrolysis at a faster rate and hence the dimerization was predominantly observed.

Table 3.5 Effect of [PMS] on kobs

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0 × 10-4 mol dm-3

103x [PMS]

mol dm-3

104 x kobs (s-1) *


1.80 3.42 3.68 3.95 3.47 2.04

3.60 2.69 2.96 3.16 2.89 1.74

5.30 2.03 2.26 2.53 2.15 1.45

7.10 1.42 1.75 2.15 1.61 1.18

8.90 1.19 1.49 1.84 1.32 1.01


0 2 4 6 8 10

0.0

0.2

0.4

0.6

0.8

1.0

104 ×

1/k

ob

s (

s-1

)

103

× [PMS] mol dm-3

A

B

C

D

E

Figure 3.10 Plot of 1/kobs vs [PMS] at 308 K

[AA] =5.0×10−2 mol dm−3; [VO2+] = 5×10−4 mol dm−3;

[H+] = 0.1 mol dm−3


3.3.5 Effect of ionic strength on kobs

The reaction was studied with various concentration of sodiumperchlorate

(5.0×10-2 - 20.0×10-2 mol dm-3), by keeping the other parameters at constant values. No

significant effect of ionic strength ( ) on the reaction rate (Table 3.6) was observed

which ruled out the interaction between NH3+ group of amino acid with HSO5

- of the

oxidant. This result revealed further that HSO5- would not have interacted with

carboxylate anion of the amino acid in the rate determining step. Hence it was

categorically ascertained that the active form of the amino acid was free amino acid and

further the oxidant interacted with carboxylic acid group of amino acid only.

Table 3.6 Effect of ionic strength on kobs

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


102 x

[NaClO4]

mol dm-3

104 x kobs (s-1) *


0.00 1.49 1.88 2.94 3.27 0.84

0.05 1.50 1.90 2.90 3.27 0.85

0.10 1.49 1.92 2.93 3.30 0.88

0.15 1.48 1.86 2.94 3.29 0.90

0.20 1.51 1.88 3.01 3.26 0.85

0.25 1.48 1.90 2.95 3.32 8.87


3.3.6 Effect of dielectric constant

The effect of dielectric constant on the reaction rate was studied by varying the

acetonitrile-water and t-butyl alcohol-water (v/v) content in the reaction mixture with all

other parameters at constant values. It was found that dielectric constant of the medium

had no significant effect on the reaction rate (Tables 3.7 & 3.8), which ruled out the

formation of a more polar intermediate than the reactant.

Table 3.7 Effect of dielectric constant on kobs in the presence of acetonitrile

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


% of

acetonitrile

in water

104 x kobs (s-1) *


0.00 1.71 1.88 2.65 3.11 0.99

0.05 1.70 1.90 2.60 3.17 0.95

0.10 1.79 1.92 2.63 3.10 0.98

0.15 1.78 1.86 2.64 3.19 0.96

0.20 1.71 1.88 2.61 3.16 0.95

0.25 1.78 1.90 2.65 3.12 0.97


Table 3.8 Effect of dielectric constant on kobs in the presence of t-butylalcohol

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


% of

t-butyl alcohol

in water

104 x kobs (s-1) *


0.00 1.71 1.88 2.65 3.11 0.99

0.05 1.75 1.86 2.63 3.12 0.99

0.10 1.72 1.85 2.65 3.12 0.95

0.15 1.75 1.86 2.62 3.15 0.95

0.20 1.71 1.88 2.64 3.12 0.96

0.25 1.74 1.86 2.65 3.15 0.96


3.3.7 Test for free radicals

To ascertain the intervention/non intervention of free radicals in the reaction was

examined by adding a known volume of freshly distilled acrylonitrile monomer to the

reaction mixture and kept it for 2h under nitrogen atmosphere. On dilution with

methanol, no precipitate was observed, which ruled out the involvement of any free

radical intermediate. Further, the addition of t-butyl alcohol to the reaction mixture did

not alter the rate of the reaction, which clearly indicated the absence of sulphate free

radical, since t-butyl alcohol is an effective scavenger of sulphate free radical. The

formation of free radical intermediate in this oxidation reaction was ruled out by EPR

spectral studies as well.

3.3.8 Effect of Temperature

The rate of reaction was measured at different temperatures (303 to 323K). It

was observed that kobs value increased with increase in temperature (Table 3.9). The

plot of log kobs vs 1/T was a straight line (Figures 3.11 & 3.12). The activation energy Ea

was calculated from the slope of the above Arrhenius plot. From the Eyring plot of log

(kobs/T) vs 1/T (Figures 3.13 & 3.14), thermodynamic parameters like ΔH#, ΔS# and ΔG#

were calculated and shown in Table 3.10.

Table 3.9 Effect of Temperature on kobs

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


temperature

(K)

104 x kobs (s-1) *


303 1.46 1.49 1.81 1.97 0.59

308 2.07 2.15 2.34 2.68 0.84

313 3.26 3.21 3.57 3.89 1.14

318 4.57 4.17 4.72 4.95 1.56

323 5.72 5.45 5.98 6.28 2.13


0.00310 0.00315 0.00320 0.00325 0.00330

0.2

0.4

0.6

0.8

4 +

lo

g(k

ob

s)

1/T (K)

A

C

D

B

Figure 3.11 Arrhenius plot of logkobs vs 1/T for the oxidation of

amino acids

(A). glycine; (B). alanine; (C). valine; (D). 2-AIBA

0.00310 0.00315 0.00320 0.00325 0.00330

0.8

1.0

1.2

1.4

5 +

lo

g(k

ob

s)

1/T (K)

Figure 3.12 Arrhenius plot of logkobs vs 1/T for the oxidation of NMG

Figure 3.13 Eyring plot of log(kobs/T) vs 1/T for the oxidation of

amino acids

(A). glycine; (B). alanine; (C). valine; (D). 2-AIBA

0.00310 0.00315 0.00320 0.00325 0.00330

0.6

0.8

1.0

1.2

1.4

7 +

lo

g(k

ob

s/T

)

1/T (K)

A

B

C

D

0.00310 0.00315 0.00320 0.00325 0.00330

0.3

0.4

0.5

0.6

0.7

0.8

7 +

lo

g(k

ob

s/T

)

1/T (K)

Figure 3.14 Eyring plot of log(kobs/T) vs 1/T for the oxidation of NMG

Table 3.10 Thermodynamic parameters for the oxidation of amino acids

amino acid Ea

kJ mol-1

H#

kJ mol-1

S#

J K -1mol-1

G#

kJ mol-1

glycine 23.62 22.49 -155.10 76.73

alanine 21.89 23.02 -153.26 70.23

valine 20.87 21.92 -156.34 70.08

2-AIBA 19.55 20.67 -160.06 69.97

NMG 22.13 21.02 -158.98 77.69

The high positive values of free energy of activation (ΔG#) and enthalpy of

activation (ΔH#) in this study indicated that transition state was highly solvated [105].

The negative value of entropy of activation (ΔS#) suggested the formation of more

ordered transition state than the reactants with the reduction of degree of freedom of

molecules.

3.4 SPECTRAL STUDIES FOR THE OXIDATION OF AMINO ACIDS

3.4.1 UV-Visible spectral measurements

The UV-Visible spectrum of the reaction mixture containing amino acid, HClO4,

PMS and VO2+ ion (5.0×10-4 mol dm-3) showed an absorption maximum at 280.92 nm

which is attributed to the n→π* transition in the intra ligand charge transfer of amino

acids [106] and [107].

Time history of the peak revealed that the absorbance increased with increase in

time which might be due to the formation of VO2+ ion – amino acid complex (Figures

3.15 to 3.19). The complex formation involved the oxygen atom of –COOH group and

nitrogen atom of –NH2 group of the amino acid with VO2+ ions, which strengthened the

V-O and V-N bonds and involved in the charge transfer processes in the VO2+ ion –

amino acid complex.

250 275 300 325

0.2

0.4

0.6

0.8

1.0

Ab

so

rban

ce (

a.u

)

Wavelength (nm)

1min

70 min

Figure 3.15 UV-Visible spectrum of the reaction mixture at various time

intervals (glycine)

[glycine] = 0.05 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0×10-4 mol dm-3; [PMS] = 3.6×10-3 mol dm-3

250 275 300

0.3

0.4

0.5

A

bso

rban

ce (

a.u

)

Wavelength (nm)

1min

60 min

Figure 3.16 UV-Visible spectrum of the reaction mixture at various

time intervals (alanine)

[alanine] = 0.05 mol dm-3;

[H+] = 0.10 mol dm-3;

[VO2+] = 5.0×10-4 mol dm-3;

[PMS] = 3.6×10-3 mol dm-3

250 275 300 325

0.5

1.0

1.5

2.0

2.5

Ab

so

rban

ce (

a.u

)

Wavelength (nm)

1min

52 min


time intervals (valine)

[valine] = 0.05 mol dm-3;

[H+] = 0.10 mol dm-3;

[VO2+] = 5.0×10-4 mol dm-3;

[PMS] = 3.6×10-3 mol dm-3

250 275 300 325

0.4

0.8

1.2

1.6

2.0

Ab

so

rban

ce (

a.u

)

wavelength (nm)

1min

40 min


time intervals (2-AIBA)

[2-AIBA] = 0.05 mol dm-3;

[H+] = 0.10 mol dm-3;

[VO2+] = 5.0×10-4 mol dm-3;

[PMS] = 3.6×10-3 mol dm-3


time intervals (NMG)

[NMG] = 0.05 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0×10-4 mol dm-3; [PMS] = 3.6×10-3 mol dm-3

The spectrum in the visible domain at higher concentration of VO2+ ions (2.0x10-2

mol dm−3) in perchloric acid consist of a broad weak band with max at 770.23 nm

(Figures 3.20 to 3.22) which corresponds to d→d transition of vanadium metal ion. This

band was shifted towards lower wavelength when amino acid was added (Table 3.11).

This might be due to 2B2→2E transition [108]. This might be attributed to the formation of

non-centrosymmetric square pyramidal complex with C4V point group. The bond length

in the VO2+ ions is very short (1.69A˚), due to whicht the ligand field is highly

asymmetric. Hence the above transition was allowed in xy polarization and this reflected

the strong metal-ligand interaction in the VO2+ ion – amino acid complex.

255 270 285 300

1.0

1.2

1.4

1.6

Ab

so

rban

ce

(a

.u)

Wavelengthe (nm)

1min

90 min

500 600 700 800 900 1000

0.0

0.1

0.2

0.3

0.4

A

B

C

D

E

Ab

so

rban

ce (

a.u

)

Wavelength (nm)

Figure 3. 20 UV –Visible spectra at high concentration of the reaction

mixture (glycine and alanine)

(A). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2 mol dm-3

(B). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2 mol dm-3;

[Gly] = 0.1 mol dm-3

(C). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2 mol dm-3;

[Gly] = 0.1mol dm-3; [PMS] = 1.56 x10-3 mol dm-3

(D). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2 mol dm-3;

[Ala] = 0.1 mol dm-3

(E). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2 mol dm-3;

[Ala] = 0.1mol dm-3; [PMS] = 1.56 x 10-3 mol dm-3

500 600 700 800 900 1000

0.0

0.1

0.2

0.3

0.4

A

B

C

D

E

Ab

so

rban

ce (

a.u

)

Wavelength (nm)

Figure 3. 21 UV –Visible spectra at high concentration of the reaction

mixture (valine and 2-AIBA)


(B). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2 mol dm-3 ;

[Val] = 0.1 mol dm-3

(C). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2 mol dm-3;

[Val] = 0.1 mol dm-3; [PMS] = 1.56 x10-3 mol dm-3

(D). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2 mol dm-3;

[2-AIBA] = 0.1 mol dm-3

(E). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2mol dm-3;

[2-AIBA] = 0.1mol dm-3; [PMS] = 1.56 x10-3 mol dm-3

500 600 700 800 900 1000

0.0

0.1

0.2

0.3

0.4

Ab

so

rban

ce

(a

.u)

Wavelength (nm)

A

B

C

Figure 3.22 UV –Visible spectra at high concentration of the reaction

mixture (NMG)

(A). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2mol dm-3

(B). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2mol dm-3;

[NMG] = 0.1 mol dm-3

(C). [VO2+] = 0.02 mol dm-3 ; [HClO4] = 0.2mol dm-3;

[NMG] = 0.1 mol dm-3; [PMS] = 1.56 x10-3 mol dm-3

Further, the max value shifted to higher wavelength when 1.56 x10-3 mol dm-3 of

PMS was added to the above reaction mixture. This red shift in the max confirmed the

oxidation of amino acid through the formation of VO2+ – amino acid – PMS complex.

Table 3.11 Absorbance of VO2+ ions and its complexes

S.No. Description absorbance

(A) εmax

(M-1

cm-1

) wavelength

λmax (nm)

1.

VO2+ ions in HClO4

0.30

15.00

770.23

2.

VO2+ ions and glycine in HClO4

0.32

16.00

765.94

3.

VO2+ ions, glycine and PMS in HClO4

0.16

8.00

767.05

4.

VO2+ ions and alanine in HClO4

0.33

16.50

764.94

5.

VO2+ ions, alanine and PMS in HClO4

0.14

7.00

769.94

6.

VO2+ ions and valine in HClO4

0.35

17.50

763.83

7.

VO2+ ions, valine and PMS in HClO4

0.21

10.50

767.05

8.

VO2+ ions and 2-AIBA in HClO4

0.34

17.00

761.71

9.

VO2+ ions, 2-AIBA and PMS in HClO4

0.15

7.50

768.16

10.

VO2+ ions and NMG in HClO4

0.32

16.00

762.71

11.

VO2+ ions, NMG and PMS in HClO4

0.14

7.00

759.72

3.4.2 EPR spectral studies

Electron paramagnetic resonance (EPR) spectroscopy is defined as the form of

spectroscopy concerned with microwave-induced transitions between magnetic energy

levels of electrons having a net spin and orbital angular momentum. EPR spectroscopy

is a convenient and effective way to probe the electronic structure of paramagnetic

molecules and the oxidation state of the vanadium in the VO2+- amino acid complexes.

It is also a tool to ascertain the involvement of free radical intermediate and to decide

the donor atom of amino acid (O or N) is coordinated to the VO2+.

The EPR spectra of the VO2+ ions and its amino acid complexes were recorded

at room temperature and at liquid nitrogen temperature. The EPR spectrum of vanadyl

ion in perchloric acid showed eight intense lines, separated by the hyperfine coupling

constant Aiso = 105.56G and hyperfine parameter giso = 2.0534, which are due to

hyperfine splitting arising from the interaction of the unpaired electron localized largely

in the dxy orbital of 51V nucleus having the nuclear spin number I=7/2. The anisotropy is

not noticed due to the rapid motion of molecules in solution at room temperature and

the average values of giso and Aiso were calculated and shown in the Table 3.12. The

giso and Aiso values were measured from the spectra which are in good agreement for a

square pyramidal structure [109] and [110].

Amino acid was added to VO2+ ions solution, which led to the formation of VO2+ –

amino acid complex and the new band appeared with the same values of giso and Aiso.

The giso values in the normal range indicated that the unpaired electron is mainly

confined to the vanadium atom. The giso and Aiso values of the complex did not vary to a

greater extent from that of free metal ions, indicating that the orbital angular momentum

of the unpaired electron of V(IV) has little influence on the hyperfine parameters and no

superfine interaction was observed because this unpaired electron does not overlap

with the atomic orbital of the N or O atom and the electron-nucleus interaction is very

weak. From this it was confirmed that the VO2+ ions was neither oxidized nor reduced

but acted only as a catalyst. Further, while PMS was added to the reaction mixture, the

EPR spectrum showed a shift in the band with same hyperfine parameters (Figures

3.23 to 3.27). This suggested that the PMS interacted with the complex to form VO2+–

amino acid – PMS complex which leads to the oxidation of amino acid.

3000 3200 3400 3600 3800 4000

-1000

-750

-500

-250

0

250

500

750

1000

Inte

nsit

y

Magnetic field (G)

A

B

C

Figure 3.23 Comparison of the EPR spectrum of the reaction mixture

(glycine)


(B). [VO2+] = 0.01 mol dm-3; [HClO4] = 0.2 mol dm-3;

[glycine] = 0.1 mol dm-3

(C). [VO2+] = 0.01 mol dm-3; [HClO4] = 0.2 mol dm-3;

[glycine] = 0.1 mol dm-3; [PMS] = 3.12 x10-3 mol dm-3

3000 3250 3500 3750 4000

-1000

-750

-500

-250

0

250

500

750

1000

In

ten

sit

y

Magnetic field (G)

A

B

C


(alanine)



[alanine] = 0.1 mol dm-3


[alanine] = 0.1 mol dm-3; [PMS] = 3.12 x10-3 mol dm-3

3000 3250 3500 3750 4000

-1000

-750

-500

-250

0

250

500

750

1000

Inte

nsit

y

Magnetic field (G)

A

B

C


(valine)

(A). [VO2+] = 0.01 mol dm-3; [HClO4] = 0.2 mol dm-3


[valine] = 0.1 mol dm-3


[valine] = 0.1 mol dm-3; [PMS] = 3.12 x10-3 mol dm-3

3000 3250 3500 3750 4000

-1000

-750

-500

-250

0

250

500

750

1000

In

ten

sit

y

Magnetic field (G)

A

B

C


(2-AIBA)


(B). [VO2+] = 0.01 mol dm-3; [HClO4] = 0.2 mol dm-3 ;

[2-AIBA]= 0.1 mol dm-3


[2-AIBA]= 0.1 mol dm-3; [PMS] = 3.12 x10-3 mol dm-3

3000 3250 3500 3750 4000

-1000

-750

-500

-250

0

250

500

750

1000

In

ten

sit

y

Magnetic field (G)

A

B

C

Figure 3.27 Comparison of the EPR spectrum for the reaction mixture

(NMG)

(A). [VO2+] = 0.01 mol dm-3 ; [HlO4] = 0.2 mol dm-3


[NMG] = 0.1 mol dm-3


[NMG] = 0.1 mol dm-3; [PMS] = 3.12 x10-3 mol dm-3

Table 3.12 EPR parameters of VO2+ ions and its complexes

S. No. Description giso Aiso

1.

VO2+ ions in HClO4

2.0534

105.56

2.


2.0538

105.57

3.


2.0536

105.56

4.


2.0560

105.58

5.


2.0566

105.57

6.


2.0565

105.58

7.


2.0561

105.58

8.


2.0583

105.78

9.


2.0576

105.57

10.


2.0556

105.58

11.


2.0560

105.57

3.4.3 FT-IR spectral studies

VO2+- amino acid complex was prepared in aqueous-alcoholic solution at room

temperature, as described in the experimental part and the complexes were

characterized by FT- IR. The spectra were recorded in the spectral domain of 4000 -

400 cm-1 shown in Figures 3.28 to 3.32.

The FT - IR spectra of the VO2+ ions and free amino acid were compared with the

spectra of the VO2+- amino acid complex. The VO2+ ions showed an intense strong

band at 950-1000 cm-1 [111], characteristic of the V=O group, which also appeared at

the same frequency for the VO2+- amino acid complex. It showed that the V=O group

was not affected by the complex formation. The ʋasy (COO-) and ʋsy(COO-) stretching

vibrations of –COOH group of free amino acid were observed at 1719 cm-1 and 1642

cm-1 respectively. In the oxovanadium (IV) complex, these bands were shifted to lower

frequency, which supported that the coordination of the amino acid to carboxyl group

[112]. The complex formation of VO2+ with oxygen donor atom was also confirmed by

the appearance of ʋ(V-O) band at 580-650 cm-1.

The band at 1577 cm-1, characteristic of ʋasy(NH3+). The ʋ(N-H) stretching

vibration appeared at 3118 cm-1 for free amino acid was shifted to lower frequency after

complexation with VO2+ ions. Further, the appearance of band around 430-510 cm-1

corresponds to ʋ(V-N) in the complex corroborate the evidence for the involvement of

coordination of –NH2 group of amino acid with VO2+ ion. The spectral results shown in

Table 3.13 suggest the possibility of formation of the chelate complex by the interaction

of non bonded electrons in the corboxylate oxygen and amine nitrogen of amino acid

with VO2+ ions. It reacts with HSO5- which gives imine intermediate which leads by the

oxidative decarboxylation of amino acids to form the end product.

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

% T

ranm

ittan

ce

Wave number (cm-1

)

A

B

Figure 3.28 Comparison of FT-IR spectra of the VO2+ ions and its

glycine complex

(A). VO2+ions; (B). VO2+ ions _ glycine complex

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

% T

ranm

ittan

ce

Wave number (cm-1)

A

B

Figure 3. 29 Comparison of FT-IR spectra of the VO2+ ions and its

alanine complex

(A). VO2+ions; (B). VO2+ ions _ alanine complex

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

120

% T

rans

mitt

ane

Wave number (cm-1

)

A

B


valine complex

(A). VO2+ions; (B). VO2+ ions _ valine complex

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

120

% T

rans

mitt

ance

Wave number (cm-1)

A

B


2-AIBA complex

(A). VO2+ions; (B). VO2+ ions _ 2-AIBA complex

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

% T

rans

mitt

ance

Wave number (cm-1

)

A

B

Figure 3.32 Comparison of FT-IR spectra of the VO2+ ions and its NMG

complex, (A). VO2+ions; (B). VO2+ ions _ NMG complex

Table 3.13 Selected FT-IR spectral bands of the amino acids and its

VO2+ ions complexes

FT- IR Band

VO2+ ions

free amino acid

VO2+-glycine

VO2+-alanine

VO2+-valine

VO2+- 2-AIBA

VO2+-NMG

ʋ(V=O)

cm-1

950-

1000 - 957 982 997 988 977

ʋasy(COO-)

cm-1 - 1719 1613 1683 1678 1606 1641

ʋsy(COO-)

cm-1 - 1642 1586 1606 1597 1568 1594

ʋasy(NH3+)

cm-1 - 1577 1403 1501 1505 1507 1493

ʋ(N-H)

cm-1 - 3118 2923 2910 3073 2924 2925

ʋ(V-O)

cm-1 - - 581 588 604 642 588

ʋ(V-N)

cm-1 - - 453 475 508 431 458

3.5 ELECTROCHEMICAL STUDIES FOR THE OXIDATION OF AMINO

ACIDS

3.5.1 Cyclic voltammetric studies

The interaction behavior of VO2+ with amino acid and PMS was studied by cyclic

voltammetric method as well. The cyclic voltammograms of the VO2+ion in perchloric

acid showed anodic peak at -0.489 V. In the presence of amino acid, the anodic peak

was shifted (Table 3.14). This suggested the formation of VO2+ – amino acid complex.

The intensities of the peaks were increased with the increase of metal as well as

amino acid concentration which might be due to the accumulation of VO2+ – amino acid

complex. When PMS was added to the reaction mixture further, the anodic peak was

shifted towards negative potential (Figures 3.33 to 3.37). This might be due to the

interaction of VO2+ – amino acid complex and PMS. Similar behaviour was observed in

all the other amino acids.

-1.0 -0.5 0.0 0.5 1.0 1.5

-0.00001

0.00000

0.00001

0.00002

0.00003

0.00004

C

urr

ean

t (A

)

Potential (V)

A

B

C

Figure 3.33 Comparison of the cyclic voltammogram of the reaction

mixture (glycine)

(A). [VO2+] = 5x10-4 mol dm-3; [HClO4] = 0.1mol dm-3

(B). [VO2+] = 5x10-4 mol dm-3; [HClO4] = 0.1mol dm-3;

[glycine] = 0.05 mol dm-3

(C). [VO2+] = 5x10-4 mol dm-3; [HClO4] = 0.1mol dm-3;

[glycine] = 0.05 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

-1.0 -0.5 0.0 0.5 1.0 1.5

-0.00001

0.00000

0.00001

0.00002

0.00003

Cu

rren

t (A

)

Potential (V)

C

B

A


mixture (alanine)





[alanine] = 0.05 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

-1.0 -0.5 0.0 0.5 1.0 1.5

-0.00001

0.00000

0.00001

0.00002

0.00003

C

urr

en

t (A

)

Potential (V)

A

C

B


mixture (valine)



[valine] = 0.05 mol dm-3


[valine] = 0.05 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

-1.0 -0.5 0.0 0.5 1.0 1.5

-0.00001

0.00000

0.00001

0.00002

0.00003

Cu

rre

nt

(A)

Potential (V)

A

C

B


mixture (2-AIBA)



[2-AIBA] = 0.05 mol dm-3


[2-AIBA] = 0.05 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

-1.0 -0.5 0.0 0.5 1.0 1.5

-0.00001

0.00000

0.00001

0.00002

0.00003

Cu

rre

nt

(A)

Potential (V)

A

B

C


mixture (NMG)



[NMG] = 0.05 mol dm-3


[NMG] = 0.05 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

Table 3.14 Cyclic voltammetric data of VO2+ ions and its complexes

S.No. Description anodic peak potential(V)

1.

VO2+ ions in HClO4

-0.489

2.


-0.527

3.


-0.565

4.


-0.507

5.


-0.520

6.


-0.514

7.


-0.469

8.


-0.501

9.


-0.526

10.


-0.495

11.


-0.539

3.6 Reaction mechanism of the VO2+ ions catalyzed oxidation of

amino acids by peroxomonosulphate

The pKa values of the amino acids suggested that they existed in the following

equilibrium in water. However, in the highly acidic medium they exist in the protonated

form.

The possible reactive species is either the protonated form or the neutral amino

acid. In the absence of the metal ions (VO2+) catalyst, the oxidation reaction did not

proceed at all even for 7h under the experimental conditions. In the presence of VO2+

ions (5.0×10-4 mol dm-3), the reaction proceeded at a measurable rate even at room

temperature. Further the reaction was inhibited by the added acid which led to the

accumulation of the protonated form which might be less reactive in this reaction. All

these results revealed that the free amino acid is the active form of amino acid.

Moreover the removal of a proton from the carboxylic acid of free amino acid is difficult

and hence the reaction did not proceed at all in the absence of VO2+ ions. However on

complex formation with VO2+ ions it is easy to remove the proton from the carboxylic

acid of amino acid in the complex since it is more acidic and hence the reaction proceed

at a measurable rate.

Peroxomonosulphate ion is a weak acid with pKa 9.4 at 25°C. In aqueous

solution, it exists as a mixture of HSO5- and SO5

2- due to the following equilibrium (3.3).

The redox potentials for HSO5-/SO4

2- and SO52-/SO4

2- are 1.75 and 1.22 V respectively.

This suggests that in highly acidic medium, PMS which exists predominantly as HSO5-

may be more reactive than SO52-. However, there is a possibility of nucleophilic

interaction of HSO5- with VO2+ – amino acid complex.

The effect of ionic strength on the rate and also the effect of [PMS] on the rate

was helpful in arriving at the plausible mechanism. The experimental observation

showed a negligible effect of ionic strength on the rate of reaction and this confirmed

that the interaction is only between the carboxylic group of amino acid with HSO5- of

PMS. Further, the active form of amino acid is neutral amino acid only and not the

protonated form.

Further, the reaction rate decreased with increase in [PMS]. Moreover the plots

of kobs-1 vs [PMS] were straight line with positive intercept in all the amino acids. This

might be due to the dimerization of the vanadyl imine intermediate. The dimerisation

effect was well pronounced in N-methyl glycine since the secondary imine did not

undergo hydrolysis at a faster rate compared to the primary imine in other amino acid

and hence the observed rate was slow in the case of N-methyl glycine.

The activation enthalpies and entropies obtained for the different amino acids

were linearly correlated (Figure 3.38), which implied that the oxidation of all the amino

acids followed the same mechanism.

Further, the oxidation was studied with the amino acids such as ornithine,

phenylalanine and proline in the absence of metal ions to confirm the significance of the

pKa values in this oxidation reaction. The observed first order rate constant for ornithine

was 11.5x10-5 s-1 and 3.83x10-5 s-1 for phenyl alanine. The pKa value of ornithine is

1.71, phenyl alanine is 1.83 and proline is 1.99. The oxidation reaction proceeded in the

case of ornithine and phenyl alanine but very sluggish in the case of proline. Hence, it is

observed that the pKa value of amino acid is playing a significant role in the oxidation

reaction. The results suggested that the oxidation of amino acids proceeded in the

absence of metal ions, if the pKa value of amino acids is 2.00. The reaction did not

proceed at all if the pKa value is 2.00. The results corroborates that highly acidic

amino acids (low pKa value) were oxidized easily. Further, the relatively low acidic

amino acids such as glycine, alanine, valine, 2-AIBA and NMG undergo oxidation only

in the presence of metal ions. When a metal ion is coordinated with the amino acids, the

pKa value of amino acids decreases and hence the oxidation takes place only in the

presence of metal ions.

However in the case of N-phenyl glycine (NPG), the pKa value is 1.81 which is

more acidic and also accelerated by the electron withdrawing phenyl group. (Refer

chapter IV)

20.5 21.0 21.5 22.0 22.5 23.0

-161

-160

-159

-158

-157

-156

-155

-154

-153

S

# J

K-1

mo

l-1

H#

kJ mol-1

2-AIBA

NMG

Valine

Alanine

Glycine

Figure 3.38 Plot of ΔH # vs ΔS # for the oxidation of amino acids

Based on the observed results and the discussion said above a detailed kinetic scheme

for the oxidation of amino acids was proposed.

Scheme 3.1 Mechanism for the VO2+ ions catalyzed oxidation of amino

acids by peroxomonosulphate

Kinetic parameters viz. k1K1K2, K3 and k2 were calculated from different plots and

the average values were tabulated in Table 3.15. The proposed mechanism is

consistent with all the experimental data obtained in the present study.

Table 3.15 Kinetic parameters for the oxidation of amino acids at 308 K

amino acid 103 x k1K1K2

s-1

10-3 x K3

mol-1dm3 s-1

103 x k2

s-1

glycine 0.61 707.96 0.81

alanine 0.68 689.32 0.41

valine 0.81 673.26 1.62

2-AIBA 0.86 793.47 1.69

NMG 0.33 209.20 0.33

CHAPTER IV

OXIDATION OF N-PHENYLGLYCINE BY PEROXOMONO SULPHATE –

CATALYTIC EFFECT OF VO2+ AND Cu2+ IONS

The kinetics and mechanism of the oxidation of N-Phenyl glycine (NPG) by

peroxomonosulphate (PMS) in perchloric acid medium both in the presence and

absence of metal ions such as VO2+ and Cu2+ ions was studied at 278K and the results

were discussed in this chapter.

The oxidation of NPG in perchloric acid medium was very fast at 308K and

unable to follow the reaction rate by iodometric method. Hence the kinetic studies were

carried out at 278K under pseudo first order conditions with a large excess of [NPG]

over [PMS]. The reaction rate was monitored by following the concentration of [PMS]t at

different time intervals by iodometry. The results are shown in Table 4.1. The

concentration of metal ions was fixed as 5.0 × 10-4 mol dm-3. The pseudo first order rate

constant kobs was calculated from the plot of log [PMS]t vs time (Figure 4.1).

0 5 10 15 20 25

0.8

1.0

1.2

1.4

1.6

C B A

log

[P

MS

] t

Time (minutes)

Figure 4.1 Plot of log [PMS]t vs time for the reactions at 278K

(A). without metal ions, (B). with Cu2+ions, (C). with VO2+ ions

Table 4.1 Relationship of unreacted PMS (log [PMS]t) with respect to time

[NPG] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0 × 10-4 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.5 × 10-3 mol dm-3

time (minutes)

log [PMS]t

without metal

ions

with Cu2+ions with VO2+ ions

0:00 1.5340 1.5340 1.5340

2:00 - 1.5024 1.4727

3:00 - - 1.3891

4:00 1.4668 1.4281 -

5:00 - - 1.3096

6:00 - 1.3710 -

7:00 1.4048 - -

8:00 - 1.3138 1.2270

10:00 1.3138 1.2671 1.1643

11:00 - - 1.1072

12:00 - 1.1846 -

13:00 1.2380 - 1.0211

14:00 - 1.1038 -

16:00 - 1.0211 -

17:00 1.1367 - -

19:00 1.0718 - -

21:00 0.9912 - -

4.1 Stoichiometry

The stoichiometry of the reaction was determined for both catalyzed and

uncatalyzed reactions by keeping the reaction mixture containing a large excess of

[PMS] over [NPG], i.e. [PMS] / [NPG] = 2.5 and kept for 48h at room temperature. After

completion of the reaction, the unreacted PMS was then estimated iodometrically which

showed that one mole of PMS was consumed for one mole of NPG. Thus, the

stoichiometric ratio for the reaction is given in equation 4.1


The reaction mixture containing 0.1 mol dm-3 of NPG and 0.2 mol dm-3 of PMS in

perchloric acid was kept for 48h for the completion of the reaction. The excess PMS

was removed by adding NaHSO3 and then the product was extracted with

dichloromethane. The same methodology was used for VO2+ ions and Cu2+ ions

catalyzed reactions as well. The products were confirmed as formaldehyde and aniline

by gas chromatograph (Figures 4.2, 4.3 & 4.4) and by comparing with the authentic

sample.

Figure 4.2 Gas chromatogram of the product in the uncatalyzed

oxidation of NPG

1.7

71

/ F

orm

aldeh

yd

e

Dic

holo

rom

ethan

e

12.7

18

/ A

nil

ine


oxidation of NPG.

Figure 4.4 Gas chromatogram of the product in the Cu2+ ions catalyzed

oxidation of NPG

1.7

71

/ F

orm

aldeh

yd

e

Dic

hlo

rom

eth

ane

12.7

18

/ A

nil

ine

1.7

71

/ F

orm

aldeh

yd

e

Dic

holo

rom

ethan

e

12.7

18

/ A

nil

ine

4.3 EFFECT OF VARYING THE CONCENTRATION OF THE

REACTANT ON kobs

4.3.1 Effect of [NPG] on kobs

The reactions were carried out with various concentrations of NPG (2.50×10-2

to 10.00×10-2 mol dm-3) by keeping other parameters at constant values. The pseudo

first order rate constants thus obtained increased with increase in [NPG] both in the

presence and in the absence of metal ions (Table 4.2). Moreover the plot of log kobs vs

log [NPG] revealed that the order of the reaction with respect to NPG is one. Further,

the plots of kobs vs [NPG] gave straight lines with positive intercepts (Figure 4.5) which

revealed that the reaction proceeded by two pathways, one dependent on [NPG] and

the other independent of [NPG]. The positive intercept was due to the self-

decomposition of PMS at this condition.

Table 4.2 Effect of [NPG] on kobs

[H+] = 0.10 mol dm-3; [VO2+] = 5.0 × 10-4 mol dm-3;

[Cu2+] = 5.0 × 10-4 mol dm-3; [PMS] = 3.5 × 10-3 mol dm-3

102 x [NPG]

mol dm-3

103 x kobs (s-1) *

in absence of

metal ions

in presence of

VO2+ ions

in presence of

Cu2+ ions

2.50 1.04 1.31 1.17

3.80 1.24 1.57 1.43

5.00 1.37 1.96 1.68

7.50 1.69 2.73 2.21

10.00 1.98 3.42 2.72


2 4 6 8 10 12

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

10

3 ×

ko

bs

(s

-1)

102 × [NPG] mol dm

-3

A

C

B

Figure 4.5 Plot of kobs vs [NPG] at 278 K

[H+] = 0.10 mol dm-3; [PMS] = 3.5 × 10-3 mol dm-3

(A). without metal ions; (B). [Cu2+] = 5.0 × 10-4 mol dm-3;

(C). [VO2+] = 5.0 × 10-4 mol dm-3


The reaction rates were measured with various concentrations of H+ ions

(5.0×10-2 - 15.0×10-2 mol dm-3) by keeping the concentration of other reactant at

constant values. The observed reaction rate decreased with the increase of [H+] for both

the uncatalyzed and catalyzed reactions (Table 4.3). The reaction rate was inverse first

order with respect to H+ ion concentration. High [H+] led to the protonation of amino acid

and it may be difficult to react with PMS. So the increase in [H+] retarded the reaction

rates. The plot of kobs vs [H+]-1 was linear (r =0.9970) with positive slope (Figure 4.6).


[NPG] = 5.0 × 10-2 mol dm-3; [VO2+] = 5.0 × 10-4 mol dm-3;


102 x [H+]

mol dm-3

103 x kobs (s-1) *

in absence of

metal ions

in presence of

VO2+ ions

in presence of

Cu2+ ions

5.00 1.58 3.45 2.72

7.50 1.18 2.46 2.04

10.00 0.99 2.01 1.66

12.50 0.81 1.73 1.46

15.00 0.72 1.43 1.23


0 5 10 15 20

0

1

2

3

4

103

× k

ob

s (

S-1

)

[H+]-1 mol dm

-3

A

C

B

Figure 4.6 Plot of kobs vs [H+]-1 at 278 K

[NPG] = 5.0 × 10-2 mol dm-3; [PMS] = 3.5 × 10-3 mol dm-3

(A). without metal ions; (B). [Cu2+] = 5.0 × 10-4 mol dm-3;

(C). [VO2+] = 5.0 × 10-4 mol dm-3

4.3.3 Effect of [metal ions] on kobs

The influence of [metal ions] on kobs was studied by keeping the other

parameters at constant values and varying the concentration of VO2+ ions (2.5 ×10-4 to

7.5 ×10-4 mol dm-3) and Cu2+ ions (2.5×10-4 to 7.5×10-4 mol dm-3). The kobs values

increased with increase in the concentration of both VO2+ and Cu2+ (Table 4.4). Further,

the plots of kobs vs [metal ions] were straight lines with positive intercepts (Figure 4.7).

The linear plot of log kobs vs log [metal ions] with a slope of nearly unity

showed first order dependence of the reaction rate on [metal ions]. Such dependence

can be ascribed to the formation of complex between metal ions and NPG. The

observed data revealed that the effect of metal ions was well pronounced in the case of

VO2+ ions compared to Cu2+ ions.

Table 4.4 Effect of [metal ions] on kobs

[NPG] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[PMS] = 3.5 × 10-3 mol dm-3

104 x [metal ions]

mol dm-3

103 x kobs (s-1) *

in presence of

VO2+ ions

in presence of

Cu2+ ions

2.50 1.42 1.37

3.80 1.74 1.68

5.00 2.15 1.98

6.30 2.49 2.31

7.50 2.76 2.53


0 1 2 3 4 5 6 7 8

0.5

1.0

1.5

2.0

2.5

3.0

103

×

ko

bs (

s-1

)

104

× [metal ions] mol dm-3

B

A

Figure 4.7 Plot of kobs vs [metal ions] at 278 K

[NPG] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[PMS] = 3.5 × 10-3 mol dm-3

(A). [VO2+] = 5.0 × 10-4 mol dm-3; (B). [Cu2+] = 5.0 × 10-4 mol dm-3


The concentration of PMS was varied from 1.8 × 10-3 to 8.9 × 10-3 mol dm−3 by

keeping other parameters at constant values. It was observed that the reaction rate was

fairly constant even for a fivefold increase in the concentration of PMS and the result is

shown in Table 4.5. The observed rate constant was independent of [PMS] for both

uncatalyzed and metal ions catalyzed reactions and hence the reaction rate was first

order with respect to [PMS]. This ruled out the dimerization of the oxidant or the reaction

intermediate.


[NPG] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0 × 10-4 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3

103 x [PMS]

mol dm-3

103 x kobs (s-1) *

in absence of

metal ions

in presence of

VO2+ ions

in presence of

Cu2+ ions

1.80 1.27 1.73 1.62

3.50 1.30 1.77 1.60

5.30 1.32 1.75 1.63

7.10 1.35 1.75 1.65

8.90 1.35 1.72 1.68



The effect of ionic strength on the reaction rate was studied by the addition of

various concentration of NaClO4 (5.0×10-2 - 20.0×10-2 mol dm-3) and keeping the other

parameters at predetermined values. The values of rate constants at different ionic

strengths are shown in Table 4.6.

The observed reaction rate for both uncatalyzed and metal ions catalyzed

reactions were unaffected by increasing the ionic strength. This indicated that there was

no interaction between amine group of amino acid and HSO5ˉ.


[NPG] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0 × 10-4 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.5 × 10-3 mol dm-3

102 x

[NaClO4]

mol dm-3

103 x kobs (s-1) *

in absence of

metal ions

in presence of

VO2+ ions

in presence of

Cu2+ ions

0.00 1.43 1.90 1.64

0.05 1.42 1.89 1.65

0.10 1.42 1.85 1.65

0.15 1.41 1.87 1.65

0.20 1.41 1.89 1.68

0.25 1.42 1.89 1.67



The effect of dielectric constant on the reaction rate was studied by varying the

composition of acetonitrile-water and t-butyl alcohol-water (v/v) content in the reaction

mixture by keeping all other parameters at constant values. It was found that dielectric

constant of the medium had no significant effect on the rate of both metal ions catalyzed

and uncatalyzed reactions (Tables 4.7 & 4.8).


[NPG] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0 × 10-4 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.5 × 10-3 mol dm-3

% of

acetonitrile

in water

103 x kobs (s-1) *

in absence of

metal ions

in presence of

VO2+ ions

in presence of

Cu2+ ions

0.00 1.37 1.96 1.68

5.00 1.35 2.02 1.65

10.00 1.40 2.08 1.70

15.00 1.42 1.98 1.82

20.00 1.46 1.98 1.82

25.00 1.48 2.10 1.96


Table 4.8 Effect of dielectric constant on kobs in the presence of t-butyl

alcohol

[NPG] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0 × 10-4 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.5 × 10-3 mol dm-3

% of t- butyl

alcohol

in water

103 x kobs (s-1) *

in absence of

metal ions

in presence of

VO2+ ions

in presence of

Cu2+ ions

0.00 1.40 2.05 1.72

5.00 1.45 2.08 1.70

10.00 1.51 2.15 1.78

15.00 1.56 2.10 1.82

20.00 1.48 2.12 1.86

25.00 1.50 2.06 1.92



The intervention of free radicals in the reaction was examined by adding a

known volume of freshly distilled acrylonitrile monomer into the reaction mixture and

kept for 2h under nitrogen atmosphere. On dilution with methanol, no precipitate was

observed, which ruled out the intervention of free radical intermediate.

Further, the variation of t-butyl alcohol did not lower the rate of the reaction,

ruling out the formation of sulphate free radical. Furthermore EPR study also confirmed

the non-involvement of free radical intermediate.


The rate of oxidation of NPG by PMS in perchloric acid medium was measured

at different temperatures (278 to 293K) for the determination of thermodynamic

parameters. The reaction rates were increased with increase in temperature as shown

in Table 4.9.

The energy of activation (Ea) was calculated from the slope of the linear

Arrhenius plot of log kobs vs 1/T as shown in Figure 4.8. Thermodynamic parameters like

ΔH#, ΔS# and ΔG# were calculated (Table 4.10), from the linear Eyring plot of log

(kobs/T) vs 1/T (Figure 4.9) for both uncatalyzed and catalyzed oxidation of NPG.

It was observed that the fairly high positive value of free energy activation (ΔG#)

and enthalpy of activation (ΔH#) of the reactions indicated that the transition state was

highly solvated while the negative value of entropy of activation (ΔS#) suggested the

formation of more ordered transition state than the reactant with the reduction of degree

of freedom of molecules.


[NPG] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[VO2+] = 5.0 × 10-4 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.5 × 10-3 mol dm-3

temperature

(K)

103 x kobs (s-1) *

in absence of

metal ions

in presence of

VO2+ ions

in presence of

Cu2+ ions

278 1.58 2.25 1.85

283 1.99 2.58 2.28

288 2.48 3.04 2.77

293 2.98 3.62 3.29


Table 4.10 Thermodynamic parameters for the oxidation of NPG

oxidation reaction Ea

kJ mol-1

H#

kJ mol-1

S#

J K -1mol-1

G#

kJ mol-1

in absence of

metal ions 12.43 11.40 -194.97 65.67

in presence of

Cu2+ ions 11.16 10.48 -192.22 63.92

in presence of

VO2+ ions 9.34 8.32 -185.11 59.78

0.00340 0.00345 0.00350 0.00355 0.00360

0.2

0.3

0.4

0.5

0.6

3+

log

(ko

bs)

1/T (K)

A

B

C

Figure 4.8 Arrhenius plot of log kobs vs 1/T for the oxidation of NPG

(A). absence of metal ions; (B). in presence of Cu2+ ions;

(C). in presence of VO2+ ions

0.00340 0.00345 0.00350 0.00355 0.00360

0.8

0.9

1.0

1.1

6+

log

(ko

bs

/T)

1/T (K)

A

B

C

Figure 4.9 Eyring plot of log (kobs/T) vs 1/T for the oxidation of NPG

(A). absence of metal ions; (B). in presence of of Cu2+ ions;

(C). in presence of of VO2+ ions

4.3.9 Catalytic activity

Moelwyn-Hughes [113] pointed out that, the uncatalyzed and metal ions

catalyzed reactions proceed simultaneously, so that

Here kT is the observed pseudo first-order rate constant in the presence of VO2+

or Cu2+ catalyst, kU is the pseudo first-order rate constant for the uncatalyzed reaction,

Kc is the catalytic constant and ‘x’ is the order of the reaction with respect to [VO2+] or

[Cu2+]. In the present investigations, ‘x’ values for the standard run were found to be

unity for both VO2+ and Cu2+ ions catalyst. Then the value of Kc was calculated using the

equation 4.3.

The values of KC were evaluated for both the catalysts at different temperatures

which was found to increase with increase in temperatures. These results are

summarized in Table 4.11. The value of KC for VO2+ ion catalyst is 1.33 mol-1 dm3 s-1

whereas for Cu2+ ion the value is 0.48 mol-1 dm3 s-1 at 278 K.

The value of KC inferred that the VO2+ ion is a more efficient catalyst compared to

Cu2+ ion. The catalytic activity of VO2+ ion is approximately three times greater

compared to Cu2+ ion catalyst.

Table 4.11 Catalytic activity for the oxidation of NPG

temperature

(K)

KC (mol-1 dm3 s-1)

with Cu2+ ions with VO2+ ions

278 0.48 1.33

283 0.61 1.19

288 0.59 1.14

293 0.62 1.27

4.4 SPECTRAL STUDIES FOR THE OXIDATION OF NPG

4.4.1 UV-Visible spectral studies

The progress of the reaction was monitored by the UV-Visible spectral method.

The absorption spectrum for the reaction mixture of the uncatalyzed reaction in the

absence of metal ions showed an absorption maximum (λmax) at 308.82 nm for π→π*

transitions and at 282.18 nm corresponds to n→π* transitions due to the intra ligand

charge transfer of amino acid (NPG) shown in Figure 4.10.

225 250 275 300 325 350 375 400

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Ab

so

rba

nc

e (

a.u

)

Wavelength(nm)

1 min

22min

Figure 4.10 UV –Visible spectrum of the reaction mixture at various time

intervals (without metal ions)

[NPG] = 1.0x10-3 mol dm-3; [HClO4] = 0.1mol dm-3;

[PMS] = 3.9x10-3 mol dm-3

VO2+ ions (1.0x10-4 mol dm-3) was added to the reaction mixture. A hypsochromic

shift (blue shift) was observed for both absorption peaks at 304.91nm and 280.52 nm

corresponding to π→π* and n→π* transitions of NPG respectively (Figure 4.11). These

shifts might be due to the overlapping of the π-orbitals of the carboxylate group and the

non bonding electron in the nitrogen atom of amino group of NPG with the dxy orbital of

the V(IV) ions. From this observation, it was concluded that the formation of chelate

complex between VO2+ ion with NPG through both the oxygen atom of carboxyl group

and the nitrogen atom of amine group of the NPG.

225 250 275 300 325 350 375 400

0.0

0.5

1.0

1.5

2.0

2.5

Ab

so

rba

nc

e (

a.u

)

Wavelength (nm)

1min

13min


intervals (with VO2+ ions)


[VO2+] = 1.0x10-4 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

The broad asymmetric peak towards longer wavelength λmax at 773.25 nm was

observed only at higher concentrations of VO2+ ion (0.02 mol dm-3) in perchloric acid.

When 0.1 mol dm-3 of NPG was added to the metal ion solution, the λmax shifted to

653.27 nm, this was attributed to the formation of square pyramidal complex of VO2+ –

NPG. The absorption maxima corresponds to 2B2→2E transition. This transition is

allowed in dxy polarization and this reflects the strong metal-ligand interaction in the

VO2+ ion. Further, the λmax value for the reaction mixture was shifted to 638.79 nm with

the addition of 1.56 x 10-3 mol dm-3 of PMS (Figure 4.12). This hypsochromic shift

corresponds to the interaction of VO2+ – NPG complex with HSO5- of PMS.

400 500 600 700 800 900

0.0

0.5

1.0

1.5

Ab

so

rban

ce (

a.u

)

Wavelength (nm)

A

B

C


mixture (NPG and VO2+ ions)



[NPG] = 0.1 mol dm-3


[NPG] = 0.1 mol dm-3; [PMS] = 1.56 x 10-3 mol dm-3

The Cu2+ ion catalyzed oxidation of NPG also showed a hypsochromic shift of

intra-ligand charge transfer bands with λmax of 305.42 nm and 279.83 nm corresponds

to π→π* and n→π* transitions respectively for the reaction mixture contains 1.0 x10-4

mol dm-3 of Cu2+ ions (Figure 4.13). These shifts might be correlated with involvement of

oxygen atom of carboxyl group and nitrogen of amino group of the NPG in the metal

coordination, which caused strengthening of Cu-O and Cu-N bonds involved in the

charge transfer complex between NPG and Cu2+ ions.

225 250 275 300 325 350 375 400

0.0

0.5

1.0

1.5

2.0

2.5

A

bs

orb

an

ce

(a

.u)

Wavelength(nm)

1min

18min


intervals (with Cu2+ ions)


[Cu2+] = 1.0x10-4 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

The broad peak with larger wavelength λmax at 810.80 nm corresponding to d→d

transition was observed only at higher concentration of Cu2+ ion (0.02 mol dm-3) in

perchloric acid. When NPG (0.1 mol dm-3) was added to the above Cu2+ ions solution,

the λmax was shifted to 802.31 nm corresponds to 2B1g→2A1g transition [114] and [115].

This transition is allowed in dx2- y2 polarization and this reflects the strong metal-ligand

interaction. It was attributed to the formation of square planar complex of Cu2+ – NPG.

Further, the λmax was shifted to 786.98 nm with the addition of PMS (1.56 x 10-3 mol dm-

3) (Figure 4.14). This hypsochromic shift was attributed to the interaction of Cu2+ – NPG

complex with HSO5- of PMS. From the absorption spectral studies, it was confirmed that

the oxidation of NPG proceeded through Cu2+ – NPG – PMS.

500 600 700 800 900 1000

0.00

0.25

0.50

0.75

1.00

Ab

so

rba

nc

e (

a.u

)

Wavelength (nm)

A

B

C


mixture (NPG and Cu2+ ions)

(A). [Cu2+] = 0.02 mol dm-3; [HClO4] = 0.2 mol dm-3

(B). [Cu2+] = 0.02 mol dm-3; [HClO4] = 0.2 mol dm-3;


(C). [Cu2+] = 0.02 mol dm-3; [HClO4] = 0.2 mol dm-3;

[NPG] = 0.1 mol dm-3; [PMS] = 1.56 x 10-3 mol dm-3

Table 4.12 Absorbance of metal ions and its complexes

S. No.

Description absorbance

(A) εmax

(M-1

cm-1

) wavelength λ

(nm)

1.

VO2+ ions in perchloric acid

0.31

15.50

773.25

2.

VO2+ ions and NPG in perchloric Acid

0.65

32.50

653.27

3.

VO2+ ions, NPG and PMS in perchloric acid

1.16

58.00

638.79

4.

Cu2+ ions in perchloric acid

0.67

33.50

810.80

5.

Cu2+ ions and NPG in perchloric Acid

0.77

38.50

802.31

6.

Cu2+ ions, NPG and PMS in perchloric acid

0.83

41.50

786.98

4.4.2 EPR spectral studies

EPR spectrum was taken for VO2+ ions catalyzed oxidation of amino acid, to

ascertain the involvement of free radical intermediate and to decide which donor atom

of amino acid (O or N) was coordinated to the VO2+. The EPR spectrum of vanadyl ion

in perchloric acid showed eight intense lines with the hyperfine parameters such as Aiso

= 105.56G and giso = 2.0534. It was attributed that the single unpaired electron localized

largely in the dxy orbital of vanadium (Figure 4.15).

When amino acid (NPG) was added to VO2+ ion solution, the VO2+– NPG

complex was formed and the spectrum showed a shift in the peaks with the same

values of giso and Aiso. It was indicated that the orbital angular momentum of the

unpaired electron of vanadium has little influence on the hyperfine parameters. Further,

no superfine interaction was observed because this unpaired electron does not overlap

with the atomic orbital of the nitrogen atom of the amine group or oxygen atom of the

carboxyl group of NPG, which involved only in the coordination bond with VO2+ ions.

From this it was confirmed that the VO2+ ions was neither oxidized nor reduced but

acted only as a catalyst. When PMS was added to the reaction mixture, the EPR

spectrum showed a shift in the peak with same values of hyperfine parameters,

indicating that the PMS interacted with the complex to form VO2+– NPG – PMS complex

and led the oxidation of NPG.

3000 3200 3400 3600 3800 4000

-1000

-750

-500

-250

0

250

500

750

1000

Inte

nsit

y

Magnetic field (G)

A

B

C


(NPG and VO2+ ions)





[NPG] = 0.1 mol dm-3 ; [PMS] = 3.12 x10-3 mol dm-3

The EPR spectrum of Cu2+ ions in perchloric acid showed a single peak with giso=

2.1936 due to formation of symmetric complex [116], shown in Figure 4.16. Further, with

NPG, it showed four well resolved unsymmetrical peaks with low intensities (Figure

4.17). This attributes the formation of Cu2+ – NPG, a square planar complex [117]. The

observed hyperfine parameters for this complex Aiso = 51.24G and giso = 2.1924

described the axial symmetry with the unpaired electron residing in the dx2- y2 orbital and

coordinated to Cu2+ ions through the N and O atom of NPG. When the PMS was added

to reaction mixture, a shift in the peak with the same values of giso and Aiso (Table 4.13)

was observed indicating that the orbital angular momentum of the uncoupled electron of

Cu2+ ions has little influence on the hyperfine parameters and no superfine interaction

due to the directly bonded atoms. From this it was confirmed that the Cu2+ ions were

neither oxidized nor reduced but acted only as a catalyst.

The EPR spectrum of NPG in perchloric acid and PMS in the absence of

Cu2+/VO2+ ions did not show any peak, this ruled out involvement of free radicals during

the oxidation reaction.

2600 2800 3000 3200 3400 3600

-1500

-1000

-500

0

500

1000

1500

Inte

nsi

ty

Mageneic fiel (G)

Figure 4.16 EPR spectrum for copper (II) ions in perchloric acid

2600 2800 3000 3200 3400 3600 3800

-1500

-1000

-500

0

500

1000

A

B

Inte

nsit

y

Magnetic field (G)


(NPG and Cu2+ ions)

(A). [Cu2+] = 0.01 mol dm-3; [HClO4] = 0.2 mol dm-3;



[NPG] = 0.1 mol dm-3; [PMS] = 3.12 x10-3 mol dm-3

Table 4.13 EPR parameters of metal ions and its complexes

S.No. Description giso Aiso

1. VO2+ ions in HClO4

2.0534

105.56

2. VO2+ ions and NPG in HClO4

2.0568

105.53

3. VO2+ ions,NPG and PMS in HClO4

2.0528

105.58

4. Cu2+ ions in HClO4

2.1936

-

5. Cu2+ ions and NPG in HClO4

2.1924

51.24

6. Cu2+ ions, NPG and PMS in HClO4

2.1930

51.45


The complexes of VO2+ and Cu2+ with NPG were prepared in aqueous-alcoholic

solution at room temperature which was described in the experimental part and

characterized by FT- IR. The VO2+ ions showed an intense strong band at 950 -1000

cm-1, characterstic of the V=O group [118]. Oxovanadium complex also showed a band

at the same frequency. It confirmed that the V=O group was not involved in the complex

formation.

The ʋasy(COO-) and ʋsy(COO-) stretching vibrations of –COOH group of free

amino acid were observed at 1763 cm-1 and 1657 cm-1 respectively. These bands were

shifted on complexation with VO2+ ion (Table 4.14), which supports the coordination of

VO2+ ion with the carboxyl group of NPG. The complexation of VO2+ ion with oxygen

donor atom was also confirmed by the appearance of ν(M-O) band [119]. The ʋ(N-H)

stretching vibration band of NPG appeared at 3146 cm-1. This band also shifted on

complex formation between NPG and VO2+ ion. Further, the appearance of ʋ(M-N) band

in the VO2+ ion – NPG complex supported the evidences for the involvement of

coordination of –NH2 group of NPG with metal ions (Figure 4.18). These spectral data

confirmed that the NPG forms a square pyramidal complex with VO2+ ion. The ʋasy(COO-

) and ʋsy(COO-) stretching vibrations of –COOH group of free amino acid were shifted

to 1652 cm-1 and 1534 cm-1 respectively after complex formation with Cu2+ ion (Table

4.14), which supported the coordination of Cu2+ ion with the carboxyl group of NPG. The

formation of complex with Cu2+ ion at oxygen donor atom was also confirmed by the

appearance of ʋ(M-O) band. The stretching vibration corresponds to ʋ(N-H) of free NPG

also shifted on complexation with Cu2+ ion. Further, the appearance of ʋ(M-N) band in

the Cu2+ ion – NPG complex supporting the evidences for the involvement of

coordination of –NH2 group of NPG with Cu2+ ion (Figure 4.19). These spectral data

confirmed that the NPG forms a square planar complex with Cu2+ ion.

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

120

% T

rans

mitt

ance

Wave number (cm-1

)

A

B

Figure 4.18 Comparison of the FT-IR spectra of VO2+ ions and its NPG

complex

(A). VO2+ions; (B). VO2+ ions _ NPG complex

4000 3500 3000 2500 2000 1500 1000 500

0

25

50

75

100

125

% T

rans

mitt

ance

Wave number (cm-1

)

Figure 4.19 Comparison of the FT-IR spectra of Cu2+ ions and its NPG

complex

(A). Cu2+ions; (B). Cu2+ ions _ NPG complex

Table 4.14 Selected FT-IR spectral bands of the NPG and its metal

ions complexes

Stretching

Band

free VO2+

ions

free

NPG

VO2+- NPG complex

Cu2+- NPG

complex

ʋ(V=O) cm-1 950 -1000 - 971 -

ʋasy(COO-) cm-1 - 1763 1615 1652

ʋsy(COO-) cm-1 - 1657 1513 1534

ʋ(N-H) cm-1 - 3146 3105 3014

ʋ(M-O) cm-1 - - 759 605

ʋ(M-N) cm-1 - - 596 435

4.5 ELECTROCHEMICAL STUDIES FOR THE OXIDATION OF NPG

4.5.1 Cyclic Voltammetric studies

Cyclic voltammetric studies were used to investigate the interaction behaviour

of VO2+ and Cu2+ ions with NPG. The cyclic voltammogram showed single redox peak

with single electron transfer and the result is shown in Table 4.15.

Cyclic voltammogram was recorded for NPG in perchloric acid and it showed an

anodic peak at 0.158 V and cathodic peak at 0.505 V. These peaks were shifted to

0.002 V and 0.598 V respectively in the presence of PMS (Figure 4.20). These shift in

the anodic and cathodic peaks suggested the reaction between NPG and PMS.

Cyclic voltammogram was recorded for VO2+ ions (5.0 x10-4 mol dm-3 ) in

perchloric acid and showed a redox couple with an anodic peak at 0.102 V and cathodic

peak at 0.583 V. When NPG was added to the above solution, the redox peaks shifted

to -0.022 V (anodic peak) and 0.568 V (cathodic peak). This indicated the formation of

complex between VO2+ ions and NPG. Further, the addition of PMS to the above

solution, the anodic and cathodic peaks were shifted to -0.074 V and 0.550 V

respectively (Figure 4.21). It suggested the interaction of PMS with VO2+ – NPG

complex.

Similarly cyclic voltammogram recorded for Cu2+ ions (5.0x10-4 mol dm-3 ) in

perchloric acid showed an anodic peak at 0.089 V and cathodic peak at 0.614 V

(Figure. 4.22). These peaks shifted to -0.033 V and 0.593 V with the addition of NPG.

The shift in the peak potential confirmed the formation of Cu2+ – NPG complex.

Further, the addition of PMS to the above solution, the anodic and cathodic

peaks were shifted to -0.142 V and 0.545 V respectively. It also suggested the oxidation

of NPG proceeded by the interaction of PMS with Cu2+ – NPG complex.

-0.5 0.0 0.5 1.0 1.5

-0.000024

-0.000016

-0.000008

0.000000

0.000008

0.000016

C

urr

en

t (A

)

Potential (V)

A

B


mixture (NPG without metal ions)

(A). [NPG] = 0.05 mol dm-3; [HClO4] = 0.1mol dm-3

(B). [NPG] = 0.05 mol dm-3; [HClO4] = 0.1mol dm-3;

[PMS] = 3.9x10-3 mol dm-3

-0.5 0.0 0.5 1.0 1.5

-0.000020

-0.000015

-0.000010

-0.000005

0.000000

0.000005

0.000010

0.000015

C

urr

en

t (A

)

Potential (V)

A

B

C


mixture (NPG and VO2+ ions)

(A). [VO2+] = 5.0x10-4 mol dm-3; [HClO4] = 0.1mol dm-3

(B). [VO2+] = 5.0x10-4 mol dm-3; [HClO4] = 0.1mol dm-3;

[NPG] = 0.05 mol dm-3

(C). [VO2+] = 5.0x10-4 mol dm-3; [HClO4] = 0.1mol dm-3;

[NPG] = 0.05 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

-1.0 -0.5 0.0 0.5 1.0 1.5

-0.000015

-0.000010

-0.000005

0.000000

0.000005

0.000010

0.000015

C

urr

en

t (A

)

Potential (V)

A

B

C


mixture (NPG and Cu2+ ions)

(A). [Cu2+] = 5.0x10-4 mol dm-3; [HClO4] = 0.1mol dm-3

(B). [Cu2+] = 5.0x10-4 mol dm-3; [HClO4] = 0.1mol dm-3;

[NPG] = 0.05 mol dm-3

(C). [Cu2+] = 5.0x10-4 mol dm-3; [HClO4] = 0.1mol dm-3;

[NPG] = 0.05 mol dm-3; [PMS] = 3.9x10-3 mol dm-3

Table 4.15 Cyclic voltammetric data of metal ions and its complexes

S.No. Description anodic peak potential (V)

cathodic peak potential (V)

1.

NPG in HClO4

0.158

0.505

2.

NPG and PMS in HClO4

0.002

0.598

3.

VO2+ ions in HClO4

0.102

0.583

4.

VO2+ ions and NPG in HClO4

-0.022

0.568

5.

VO2+ ions,NPG and PMS in HClO4

-0.074

0.550

6.

Cu2+ ions in HClO4

0.089

0.614

7.

Cu2+ ions and NPG in HClO4

-0.033

0.593

8.

Cu2+ ions,NPG and PMS in HClO4

-0.142

0.545

Based on the above results a suitable mechanism for the oxidation of NPG by

peroxomonosulphate was proposed.

4.6 Reaction mechanism of the uncatalyzed and metal ions

catalyzed oxidation of NPG by peroxomonosulphate

In aqueous solution PMS exists as a mixture of HSO5- and SO5

2- due to the

following equilibrium.

The Kd value was reported as 4.0 ×10−10 mol dm−3 at 25°C [4] and under the

experimental condition (in the perchloric acid medium) PMS exists as HSO5- which is

the most reactive species of PMS [82]. The higher reactivity of HSO5- is consistent with

the electrostatic effect and with a weakening of the peroxide bond.

In the present study, NPG reacts with HSO5- to form imine intermediate.

However, when the metal ions catalyzed the oxidation reaction, the chelate complex

was suggested to be formed by the interaction of non-bonded electrons through the

carboxylate oxygen and amine nitrogen atom of NPG with metal ions. The complex

interacted with PMS to give imine intermediate.

The formation of moderately stable intermediate is supported by the observed

thermodynamic parameters (Table 4.10). The complex formation is favoured by the

enthalpy and entropy values. The high negative value of entropy indicates a rigid

structure and the transition state becomes highly solvated and more ordered than the

reactants [120]. The negligible effect of ionic strength and dielectric constant of the

medium on the reaction rate suggested that the reaction between neutral and negatively

charged ions followed the scheme 4.1, given below:

Scheme 4.1 Mechanism for the oxidation of NPG by peroxomonosulphate

The rate equation explained the observed rate constant is first order with respect

to [NPG], as well as the increase in rate with [NPG] and decrease in rate with [H+]. From

the rate equation the kinetic constant such as k1K1 and k2 were calculated from the

different plots and the average values are shown in Table 4.16.

Scheme 4.2 Mechanism for the metal ions (VO2+, Cu2+) catalyzed oxidation of

NPG by peroxomonosulphate

The rate equation explained that the observed rate constant was first order with

respect to concentration of metal ions and NPG, as well as the increase in rate with

[metal ions] and [NPG] and decreased with [H+]. The kinetic constants such as k1K1K2

and k2 for the metal ions catalyzed reaction were calculated from the different plots and

the values are presented in Table 4.16.

Table 4.16 Kinetic parameters for the oxidation of NPG at 278 K

Reaction 103 x k1K1

s-1

10-3 x k1K1 K2

mol-1dm3 s-1

103 x k2

s-1

in absence of

metal ions 1.26 - 0.54

in presence of

Cu2+ ions - 3.51 0.66

in presence of

VO2+ ions - 4.57 0.58

The uncatalyzed reaction has been shown to proceed via a NPG – PMS complex

which decomposed slowly in a rate determining step to give the product. However in the

metal ions catalyzed reaction, it has been shown to proceed via NPG – metal ions

complex, which further reacted with one mole of PMS in the rate determining step to

give the products.

CHAPTER V

COPPER (II) IONS CATALYZED OXIDATION OF α-AMINO ACID BY

PEROXOMONOSULPHATE - AUTOCATALYTIC STUDIES

The kinetics of copper (II) ions catalyzed oxidation of α-amino acid by

peroxomonosulphate in perchloric acid medium was studied and the results are

discussed in this chapter.

The rate of oxidation of α-amino acids such as alanine (ala) and 2-amino

isobutyric acid (2-AIBA) by peroxomono sulphate (PMS) did not proceed even after five

hours in the absence of Cu2+ ions. However, the influence of Cu2+ ions on the rate was

significant at a concentration of 5.0 ×10-4 mol dm-3, and hence the concentration of Cu2+

was fixed at 5.0×10-4 mol dm-3. Therefore, all the reactions are studied only in the

presence of Cu2+ ions at 308K.

Kinetic studies were carried out under pseudo first order conditions with a large

excess of [amino acid] over [PMS]. The reaction rate was measured by monitoring the

concentration of unreacted [PMS] at various time intervals by iodometry, as discussed

in the experimental section and the results are shown in Table 5.1. The rate was found

to be slow initially and the reaction proceeded at a faster rate after sometime and the

first order plot log [PMS]t vs time deviated from the linearity and showed curvature

towards X–axis as shown in Figures 5.1 & 5.2. This may be due to the fact that the

product formed catalyzes the reaction. The plot of (rate/[PMS]t) vs [PMS]t is linear

(Figures 5.3 & 5.4), which confirmed that the reaction proceeded through autocatalysis.

From the slope and intercept of the above plot, the rate constants for uncatalyzed (k1obs)

and catalyzed (k2obs) reactions were calculated using the known value of [PMS]0. The

relative standard errors of the above mentioned rate constants for a single run were

about 2%.

Table 5.1 Relationship of unreacted PMS (log [PMS]t) with respect

to time

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


time

(minutes)

log [PMS]t

alanine 2-AIBA

0:00 1.5289 1.5327

9:00 - 1.5289

30:00 - 1.5118

35:00 1.5092 -

50:00 - 1.4871

61:00 - 1.4698

70:00 1.4842 -

83:00 - 1.4216

95:00 1.4517 -

108:00 - 1.3365

120:00 1.4099 -

130:00 - 1.2148

140:00 1.3483 -

145:00 - 1.0334

160:00 1.2552 -

175:00 1.1673 -

190:00 1.0211 -

Figure 5.1 Plot of log [PMS]t vs time for the oxidation of alanine at 308K

[alanine] = 0.05 mol dm-3; [H+] = 0.10 mol dm-3;

[Cu2+] = 5.0 × 10-4 mol dm3; [PMS] = 3.6 × 10-3 mol dm-3

0 20 40 60 80 100 120 140 160

1.0

1.1

1.2

1.3

1.4

1.5

1.6

log

[PM

S] t

Time (min)

Figure 5.2 Plot of log [PMS]t vs time for the oxidation of 2-AIBA at 308K

[2-AIBA] = 0.05 mol dm-3; [H+] = 0.10 mol dm-3;


0 25 50 75 100 125 150 175 200

1.0

1.1

1.2

1.3

1.4

1.5

1.6

log

[PM

S] t

Time (min)

10 15 20 25 30 35

0

5

10

15

20

25

30

105

× r

ate

/[P

MS

] t

103

× [PMS]t mol dm

-3

Figure 5.3 Plot of rate/[PMS]t vs [PMS]t for the oxidation of alanine

10 15 20 25 30 35

0

7

14

21

28

35

105

× r

ate

/[P

MS

] t

103

× [PMS]t mol dm

-3

Figure 5.4 Plot of rate/[PMS]t vs [PMS]t for the oxidation of 2-AIBA

5.1 Stoichiometry

The stoichiometry of the reaction was determined by keeping the reaction

mixture containing a large excess of [PMS] over [amino acid], i.e, [PMS]/[AA] = 2.5 with

Cu2+ (5.0×10-4 mol dm-3) in perchloric acid for 48h at room temperature and the excess

[PMS] was then estimated iodometrically. The determination showed that two moles of

PMS was consumed for one mole of amino acids. Thus, the stoichiometric ratio for the

reaction was given in equation 5.1


The reaction mixture containing amino acid, PMS and Cu2+ ions was kept for

48h for the completion of the reaction. Then the product was extracted with

dichloromethane and the product obtained was identified as the corresponding carbonyl

compounds by gas chromatograph (Figures 5.5 & 5.6).

Figure 5.5 Gas chromatogram of the product in the autocatalyzed

oxidation of alanine

2.2

85

/ A

ceta

ldeh

yde

Dic

holo

rom

ethan

e

Figure 5.6 Gas chromatogram of the product in the autocatalyzed

oxidation of 2-AIBA

5.3 EFFECT OF VARYING THE CONCENTRATION OF THE REACTANT

ON kobs

5.3.1 Effect of [amino acid] on kobs

The reaction was carried out with various initial concentrations of amino acid

(2.5×10-2 - 7.5×10-2 mol dm-3), while keeping all the other parameters at constant values.

The observed rate constants for the uncatalyzed reaction k1(obs) and autocatalyzed

reaction k2(obs) increased with the increase in [amino acid] (Table 5.2). The plots of k1

(obs)

vs [AA] for an uncatalyzed reaction and k2(obs) vs [AA] for an autocatayzed reaction gave

straight lines passing through origin (r = 0.9958) (Figures 5.7 & 5.8). These suggested

that the reaction was first order with respect to [amino acid] for both the uncatalytic and

autocatalytic pathways. This observation also ruled out the self-decomposition of PMS

under the experimental condition employed in this study.

2.8

36

/ A

ceto

ne

Dic

holo

rom

ethan

e

Table 5.2 Effect of [amino acid] on kobs

[H+] = 0.10 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3

102 x [AA]

mol dm-3

alanine 2-AIBA

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

2.50 1.30 3.23 2.25 6.42

3.80 1.62 4.89 3.74 10.38

5.00 1.84 6.58 4.96 14.38

6.30 2.13 8.25 5.86 17.25

7.50 2.48 9.52 7.12 19.86


1 2 3 4 5 6 7 8

1

2

3

4

5

6

7

8

10

5 x

k1

(ob

s)

(s

-1)

102

x [AA] mol dm-3

B

A

Figure 5.7 Plot of k1

(obs) vs [AA] at 308K

[H+] = 0.10 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3

(A). alanine; (B). 2-AIBA

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

102 x

k2(o

bs)

( M

-1s-1

)

102 x [AA] mol dm

-3

A

B

Figure 5.8 Plot of k2(obs) vs [AA] at 308K

[H+] = 0.10 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3



The effect of [H+] on the reaction rate was investigated by varying the

concentration of H+ ions (6.0×10-2 - 15.0×10-2 mol dm-3) and keeping all other

parameters at predetermined values. The observed rate constants k1(obs) and k2

(obs)

decreased with the increase in [H+] (Table 5.3). The retardation of the reaction rate by

increase in [H+] may be attributed to the accumulation of the protonated form which was

less reactive. Further, the plot of k1(obs) vs 1/[H+] (Figure 5.9) and k2

(obs) vs 1/[H+] (Figure

5.10) were linear with positive slopes indicating that this reaction was inverse first order

with respect to [H+].


[AA] = 5.0 × 10-2 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3

[H+]

mol dm-3

alanine 2-AIBA

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *s

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

0.06 2.53 10.53 8.23 23.25

0.08 2.06 8.15 6.53 17.86

0.10 1.62 6.25 4.96 14.38

0.13 1.36 5.02 3.98 10.96

0.15 1.13 3.86 3.02 8.46


2 4 6 8 10 12 14 16 18 20

0

2

4

6

8

10

10

5 x

k1

(ob

s)

(s

-1)

1/ [H+] mol dm

-3

A

B

Figure 5.9 Plot of k1(obs) vs 1/[H+] at 308K

[AA] = 0.05 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3; (A). alanine; (B). 2-AIBA

0 5 10 15 20

0

5

10

15

20

25

10

2 x

k2

(ob

s)

(M-1

s-1

)

1/ [H+] mol dm

-3

A

B

Figure 5.10 Plot of k2(obs) vs 1/[H+] at 308K

[AA] = 0.05 mol dm-3; [Cu2+] = 5.0 × 10-4 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3


5.3.3 Effect of [Cu2+] on kobs

The effect of Cu2+ on the reaction rate was studied by varying the initial

concentration of Cu2+ ions (2.5×10-4 - 7.5×10-4 mol dm-3) and keeping other parameters

at constant values. The observed rate constant k1(obs) and k2

(obs) increased linearly with

the increase in the [Cu2+] (Table 5.4). The plots of k1(obs) vs [Cu2+] and k2

(obs) vs [Cu2+]

were straight line with high correlation coefficient (r = 0.9915) and passing through

origin (Figures 5.11 & 5.12). The rate of autocatalyzed reaction was higher (103 times)

compared to the uncatalyzed reaction, which suggested that the Cu2+ ions interacted

with HSO5-. The intermediate product obtained was copper peroxide, which might be

responsible for the autocatalytic pathway.

Table 5.4 Effect of [Cu2+] on kobs

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3

104 x [Cu2+]

mol dm-3

alanine 2-AIBA

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

2.50 1.28 4.05 2.68 7.26

3.80 1.58 5.86 4.05 11.36

5.00 1.89 8.02 4.96 14.38

6.30 2.25 9.25 6.23 18.36

7.50 2.63 11.85 8.05 21.36


1 2 3 4 5 6 7 8

1

2

3

4

5

6

7

8

9

10

5 x

k1

(ob

s)

(s

-1)

104 x [Cu

2+] mol dm

-3

A

B

Figure 5.11 Plot of k1(obs) vs [Cu2+] at 308K

[AA] = 0.05 mol dm-3; [H+] = 0.10 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3; (A). alanine; (B). 2-AIBA

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

25

1

02

x k

2(o

bs

) (

M-1

s-1

)

104

x [Cu2+

] mol dm-3

A

B

Figure 5.12 Plot of k2(obs) vs [Cu2+] at 308K

[AA] = 0.05 mol dm-3; [H+] = 0.10 mol dm-3;

[PMS] = 3.6 × 10-3 mol dm-3



The reaction was studied at various concentrations of PMS (1.80 × 10-3 to 8.90

× 10-3 mol dm−3) by keeping other parameters at constant values. It has been observed

that the increase in [PMS] does not alter the reaction rate and found to be fairly

constant. It showed that the rate of oxidation was independent of [PMS] and order of

reaction with respect to [PMS] was one, which ruled out the dimerization of PMS

intermediate (Table 5.5).


[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;

[Cu2+] = 5.0 × 10-4 mol dm-3

103 x [PMS]

mol dm-3

alanine 2-AIBA

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

1.80 1.21 4.35 3.85 6.36

3.60 1.20 4.89 4.01 6.03

5.30 1.23 4.23 4.19 6.25

7.10 1.22 4.14 4.46 6.28

8.90 1.25 4.27 4.22 6.73



The effect of ionic strength on the reaction rate was studied by varying the

concentration of NaClO4 (5.0×10-2 - 20.0×10-2 mol dm-3) and keeping the other

parameters at constant values. The values of rate constants at different ionic strengths

are shown in Table 5.6.

The reaction rate for both uncatalyzed and catalyzed reactions were found to

be unaffected by increasing the ionic strength ( ). This ruled out any interaction

between amine group of amino acid and HSO5-.


[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


102 x [NaClO4]

mol dm-3

alanine 2-AIBA

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

0.00 1.62 4.06 3.40 6.25

0.05 1.65 4.08 3.25 6.05

0.10 1.62 4.05 3.34 6.25

0.15 1.84 4.10 3.58 6.98

0.20 1.75 4.12 3.05 6.58



The effect dielectric constant on the reaction rate was studied by varying the

composition of acetonitrile-water and t-butyl alcohol-water (v/v) content in the reaction

mixture with all other parameters at constant values.

It was found that dielectric constant of the medium has no significant effect on

the rate of both uncatalyzed and autocatalyzed reactions (Table 5.7 & 5.8), which ruled

out the formation of more polar intermediate.


[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


% of

acetonitrile

in water

alanine 2-AIBA

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

0.00 1.38 3.93 3.25 6.42

5.00 1.35 4.08 3.25 6.55

10.00 1.42 3.85 3.46 6.35

15.00 1.45 3.87 3.17 6.78

20.00 1.35 4.05 3.15 6.58


Table 5.8 Effect of dielectric constant on kobs in the presence of

t- butyl alcohol

[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


% of

t- butyl

alcohol

in water

alanine 2-AIBA

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

0.00 1.42 3.85 3.35 6.32

5.00 1.45 3.78 3.32 6.47

10.00 1.42 3.85 3.46 6.45

15.00 1.48 3.87 3.57 6.58

20.00 1.45 3.92 3.45 6.42



The intervention of free radicals in the reaction was examined by adding a

known volume of freshly distilled acrylonitrile to the reaction mixture and kept it for 2h

under nitrogen atmosphere. On dilution with methanol, there was no precipitate formed,

which ruled out the involvement of free radical intermediate. Further, the reaction had

been studied in the presence of t-butyl alcohol, scavenger of sulphate free radicals, by

keeping other parameters at constant values. No significant effect of reaction rate was

observed, confirming the absence of sulphate free radicals. Furthermore, EPR study

ruled out the formation of free radical intermediate.


The reaction rate was measured at different temperatures (303K to 323K). It

was observed that the rate constant for both uncatalyzed and autocatalyzed reactions

increased with increase in temperature (Table 5.9).The plot of log k1(obs) vs 1/T and log

k2(obs) vs 1/T gave straight lines as shown in Figures 5.13 & 5.14. The activation energy

Ea was calculated from the slope of the above Arrhenius plot.

From the Eyring plot of log (k1(obs)/T) vs 1/T and log (k2

(obs)/T) vs 1/T shown in

Figures 5.15 & 5.16, thermodynamic parameters like ΔH#, ΔS# and ΔG# were calculated

(Table 5.10).

The high positive values of free energy of activation (ΔG#) in this study

indicated that the transition state was highly solvated. The negative value of entropy of

activation (ΔS#) suggested the transition state was more orderly compared to the

reactants.


[AA] = 5.0 × 10-2 mol dm-3; [H+] = 0.10 mol dm-3;


temperature

(K)

alanine 2-AIBA

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

105 x k1obs

(s-1) *

102 x k2obs

(M-1s-1) *

303 1.62 7.50 2.15 10.47

308 1.89 8.79 2.85 12.59

313 2.28 10.45 3.35 14.79

318 2.64 12.35 3.85 17.78


0.00315 0.00320 0.00325 0.00330

0.2

0.3

0.4

0.5

0.6

5 +

lo

g k

1(o

bs)

1/T (K)

A

B

Figure 5.13 Arrhenius plot of log k1(obs) vs 1/T for uncatalyzed reaction


0.00315 0.00320 0.00325 0.00330

0.8

0.9

1.0

1.1

1.2

1.3

2 +

lo

g k

2(o

bs)

1/T (K)

A

B

Figure 5.14 Arrhenius plot of log k2(obs) vs 1/T for autocatalyzed reaction


0.00315 0.00320 0.00325 0.00330

0.7

0.8

0.9

1.0

1.1

8 +

lo

g(k

1(o

bs)/

T)

1/T (K)

A

B

Figure 5.15 Eyring plot of log (k1(obs)/T) vs 1/T for uncatalyzed reaction


0.00315 0.00320 0.00325 0.00330

0.3

0.4

0.5

0.6

0.7

0.8

4 +

lo

g (

k2(o

bs)/

T)

1/T (K)

A

B

Figure 5.16 Eyring plot of log (k2(obs)/T) vs 1/T for autocatalyzed reaction


Table 5.10 Thermodynamic parameters for the autocatalytic oxidation

of amino acids

parameters

alanine 2-AIBA

uncatalyzed reaction

autocatalyzed

reaction

uncatalyzed

reaction

Autocatalyzed

reaction

Ea kJ mol-1 12.76 10.93 11.67 10.47

H# kJ mol-1 9.85 11.67 9.39 10.59

S#J K -1 mol-1 -169.61 -189.22 -170.65 -191.35

G# kJ mol-1 62.09 69.95 61.95 69.52

5.4 SPECTRAL STUDIES FOR THE OXIDATION OF AMINO ACID

5.4.1 UV-Visible spectral measurements

The UV-Visible spectrum of the reaction mixture containing amino acid, HClO4,

PMS and Cu2+ ions (5.0×10-4 mol dm-3) exhibited an absorption maximum at 282.15 nm

which corresponds to the n→π* transition (intra-ligand charge transfer of amino acids)

as shown in Figures 5.17 & 5.18. Time history of the peak revealed that the absorbance

increased with increase in time which might be due to the charge transfer from ligand to

metal, resulting in the formation of complex between Cu2+ ion and amino acid [121]. The

complex formation involved the oxygen atom of –COOH group with Cu2+ ion and

nitrogen atom of –NH2 group of the amino acid with Cu2+ ion, resulting in the

strengthening of the Cu-O and Cu-N bonds which are responsible for the charge

transfer processes in the complex.

255 270 285 300

1.0

1.2

1.4

1.6

Ab

so

rban

ce (

a.u

)

Wavelength (nm)

1min

80min


intervals (Cu2+ ions and alanine)

[alanine] = 0.05 mol dm-3; [H+] = 0.10 mol dm-3;

[Cu2+] = 5.0 ×10-4 mol dm-3; [PMS] = 3.6 ×10-3 mol dm-3

255 270 285 300

1.0

1.2

1.4

1.6

Ab

so

rba

nc

e (

a.u

)

Wavelength (nm)

65min

1min


intervals (Cu2+ ions and 2-AIBA)

[2-AIBA] = 0.05 mol dm-3; [H+] = 0.10 mol dm-3;

[Cu2+] = 5.0 ×10-4 mol dm-3; [PMS] = 3.6 ×10-3 mol dm-3

The spectrum in the visible domain at higher concentrations of Cu2+ ions (5.0x10-

2 mol dm−3) consist of a broad weak band with max at 808.74 nm corresponds to d → d

transition of copper metal ion [122]. This band was shifted towards lower wavelength by

the addition of amino acid in perchloric acid (Table 5.11). The shifted max value

corresponds to 2B1g→2A1g transition [123].

Further, the max value shifted to higher wavelength by the addition of PMS to the

reaction mixture (Figures 5.19 & 5.20). This red shift in the max confirmed the oxidation

of amino acid in the complex by copper peroxide which was produced by the reaction

between Cu2+ and HSO5- ions.

700 800 900 1000

0.2

0.4

0.6

0.8

A

bso

rban

ce (

a.u

)

Wavelength (nm)

A

B

C


mixture (Cu2+ ions and alanine)





[alanine] = 0.1 mol dm-3; [PMS] = 1.56 x 10-3 mol dm-3

700 800 900 1000

0.2

0.4

0.6

0.8

Ab

so

rban

ce (

a.u

)

Wavelength (nm)

A

B

C


mixture (Cu2+ ions and 2-AIBA)



[2-AIBA] = 0.1 mol dm-3


[2-AIBA] = 0.1 mol dm-3; [PMS] = 1.56 x 10-3 mol dm-3

Table 5.11 Absorbance of copper(II) metal ions and its complexes

S.No. Description absorbance

(A) εmax

(M-1

cm-1

) wavelength

λmax (nm)

1. Cu2+ ions in HClO4 0.65 32.50

808.74

2. Cu2+ ions and alanine in HClO4

0.69 34.50

798.04

3. Cu2+ ions, alanine and PMS in HClO4

0.66 33.00

803.84

4. Cu2+ ions and 2-AIBA in HClO4

0.67 33.50

801.94

5. Cu2+ ions, 2-AIBA and PMS in HClO4

0.68 34.00

806.31

5.4.2 EPR Spectral studies

EPR spectrum was taken for the reaction mixture containing amino acids and

copper (II) ions in perchloric acid, to ascertain if any free radical formation/involvement

of free radical intermediate and to describe the nature of the complex. The EPR

spectrum of Cu2+ ions in perchloric acid showed a single peak with giso = 2.2040 (Figure

5.21). Further, addition of amino acid to the above solution showed four well resolved

unsymmetrical peaks with low intensities (Figures 5.22 & 5.23), similar to the results

reported earlier [124].

The observed hyperfine parameters for this complex Aiso and giso (Table 5.12)

describes the axial symmetry with the unpaired electron residing in the dx2-y2 orbital

which was coordinated to Cu2+ ions through the nitrogen atom of amine group and

oxygen atom of carboxyl group of amino acids. When PMS was added to reaction

mixture, a shift in the band was observed and the Aiso and giso values remained the

same. It showed that the orbital angular momentum of the uncoupled electron of Cu2+

ions has little influence on the hyperfine parameters and no superfine interaction. Thus

it was confirmed that the copper (II) ions were neither oxidized nor reduced but acted

only as a catalyst [125].

The EPR spectrum of amino acid in perchloric acid and PMS in the absence of

Cu2+ ions did not show any peak, this ruled out involvement of free radicals during the

oxidation reaction.

2600 2800 3000 3200 3400 3600

-1500

-1000

-500

0

500

1000

1500

Inte

nsit

y

Mageneic fiel (G)

Figure 5.21 EPR Spectrum of copper (II) ions in perchloric acid

[Cu2+] = 0.01 mol dm-3; [HClO4] = 0.2 mol dm-3

2800 3000 3200 3400 3600

-1000

-500

0

500

1000

Inte

nsit

y

Magnetic field (G)

A

B


(alanine and Cu2+ ions)




[alanine] = 0.1 mol dm-3; [PMS] = 3.12 x10-3 mol dm-3

2800 3000 3200 3400 3600

-1500

-1000

-500

0

500

1000

1500

In

ten

sit

y

Magnetic field (G)

A

B


(2-AIBA and Cu2+ ions)


[2-AIBA] = 0.1 mol dm-3


[2-AIBA] = 0.1 mol dm-3; [PMS] = 3.12 x10-3 mol dm-3

Table 5.12 EPR parameters of copper(II) metal ions and its complexes

S.No. Description giso Aiso

1.

Cu2+ ions in HClO4

2.1936

-

2.

Cu2+ ions and alanine in HClO4

2.1906

51.24

3.

Cu2+ ions, alanine and PMS in HClO4

2.1907

51.45

4.

Cu2+ ions and 2-AIBA in HClO4

2.1856

51.63

5.

Cu2+ ions, 2-AIBA and PMS in HClO4

2.1856

51.90


The complex between Cu(II) ions and amino acid was prepared in aqueous-

alcoholic solution at room temperature as described in the experimental part and the

complexes were characterized by FT - IR and shown in Figures 5.24 & 5.25.

The IR spectra of the free amino acid were compared with the spectra of the

complex. The stretching vibrations ʋasy(COO-) and ʋsy(COO-) of –COOH group of free

amino acid were observed at 1739 cm-1 and 1581 cm-1 respectively. These bands were

shifted to 1578 cm-1 and 1521 cm-1 respectively, which confirmed the complexation of

Cu(II) with amino acid through the oxygen atom of the carboxyl group of amino acid.

The ʋasy(N-H) and ʋsy(N-H) stretching vibrations of the amine group of free amino

acid appeared at 3014 cm-1 and 2971 cm-1 respectively. These bands were shifted to

lower frequency, suggesting the coordination of amino acid to Cu(II) ion through

nitrogen atom of amine group of amino acid.

Further, the appearance of the stretching vibrations of ʋ(Cu-O) and ʋ(Cu-N)

around 580-620 cm-1 and 430-480 cm-1 (Table 5.13) respectively supported the

evidences for the coordination of –COOH group and –NH2 group of amino acid with

copper.

4000 3500 3000 2500 2000 1500 1000 500

-20

0

20

40

60

80

100

120

140

% T

ran

smit

tan

ce

Wave number (cm-1

)

A

B

Figure 5.24 Comparison of FT-IR spectra of the Cu2+ ions and its

alanine complex

(A). Cu2+ions; (B). Cu2+ ions _ alanine complex

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

120

% T

ran

smit

tan

ce

Wave number (cm-1

)

A

B

Figure 5.25 Comparison of FT-IR spectra of the Cu2+ ions and its

2-AIBA complex

(A). Cu2+ions; (B). Cu2+ ions _ 2-AIBA complex

Table 5.13 Selected FT-IR spectral bands of the amino acids and

its metal ions complexes

stretching

bands

Free

amino acid

Cu2+- alanine complex

Cu2+- 2-AIBA

complex

ʋasy(COO-) cm-1 1739 1578 1645

ʋsy(COO-) cm-1 1581 1521 1478

ʋasy(N-H) cm-1 3014 2946 2938

ʋsy(N-H) cm-1 2971 2834 2768

ʋ(Cu-O) cm-1 - 585 605

ʋ(Cu-N) cm-1 - 435 450

5.5 ELECTROCHEMICAL STUDIES FOR THE OXIDATION OF

AMINO ACIDS

5.5.1 Cyclic voltammetric studies

Cyclic voltammetric studies were also used to investigate the interaction

behavior of Cu2+ ions with amino acid. The voltammograms of Cu2+ ions in perchloric

acid showed the anodic peak at 0.083 V and cathodic peak at 0.619 V. This peak was

shifted by the addition of amino acid (Table 5.14). It was attributed to the formation of

[Cu(II)-(AA)2] chelate complex [126]. The peak potential further shifted with the addition

of PMS as shown in the Figures 5.26 & 5.27. This suggested that the oxidation reaction

carried out between the complex and PMS at lower energy state. The voltammogram

for the metal ion showed single redox peak with single electron process.

-1.0 -0.5 0.0 0.5 1.0 1.5

-0.000014

-0.000007

0.000000

0.000007

0.000014

0.000021

Cu

rren

t (A

)

Potential (V)

A

B

C


mixture (alanine and Cu2+ ions)

(A). [Cu2+] = 5.0x10-4 mol dm-3; [H+] = 0.1mol dm-3

(B). [Cu2+] = 5.0x10-4 mol dm-3; [H+] = 0.1mol dm-3;


(C). [Cu2+] = 5.0x10-4 mol dm-3; [H+] = 0.1mol dm-3;

[alanine] = 0.05 mol dm-3; [PMS] = 3.6x10-3 mol dm-3

-1.0 -0.5 0.0 0.5 1.0 1.5

-0.000014

-0.000007

0.000000

0.000007

0.000014

0.000021

Cu

rre

nt

(A)

Potential (V)

A

B

C


mixture (2-AIBA and Cu2+ ions)

(A). [Cu2+] = 5.0x10-4 mol dm-3; [H+] = 0.1mol dm-3

(B). [Cu2+] = 5.0x10-4 mol dm-3; [H+] = 0.1mol dm-3;

[2-AIBA] = 0.05 mol dm-3

(C). [Cu2+] = 5.0x10-4 mol dm-3; [H+] = 0.1mol dm-3;

[2-AIBA] = 0.05 mol dm-3; [PMS] = 3.6x10-3 mol dm-3

Table 5.14 Cyclic voltammetric data of copper (II) metal ions and

its complexes

S.No. Description anodic peak potential (V)

cathodic peak potential (V)

1.

Cu2+ ions in HClO4

0.083

0.619

2.

Cu2+ ions and alanine in HClO4

-0.405

0.877

3.

Cu2+ ions, alanine and PMS in HClO4

-0.443

0.698

4.

Cu2+ ions and 2-AIBA in HClO4

-0.277

0.844

5.

Cu2+ ions, 2-AIBA and PMS in

-0.325

0.945

HClO4

5.6 Reaction mechanism of the autocatalyzed oxidation of amino


The [PMS]t - time profiles showed that the rate of the oxidation of amino acid by

PMS in the presence of Cu2+ ions, was slow at initial period. After some time the

reaction proceeded at a faster rate and the first order plot showed simple curves. This is

characteristic of autocatalysis and the rate equation can be expressed as,

A plot of (rate/[PMS]t) vs [PMS]t, according to equation 5.3 as expected, gives

straight line with a negative slope. From the slope and intercept of this plot, the values

of k1(obs) and k2

(obs) were calculated using the known value of [PMS]o. These values also

being calculated more easily and accurately by nonlinear regression analysis of the

[PMS]t - time profile using equation 5.4, the integrated form of equation 5.3.

Literature studies on the autocatalytic reactions in the oxidation of amino acids

by PMS at pH 4.0–5.2, suggested that amino acids undergo oxidative decarboxylation

to form an aldehyde. The product aldehyde interacted with the amino group of amino

acid to give a hemiaminal intermediate which was responsible for autocatalysis. In the

present investigation, the oxidation of amino acid by PMS in perchloric acid medium in

the presence of Cu(II) ions forms an intermediate of copper peroxide, which is

responsible for the high reactivity.

The redox potential for HSO5-/SO4

2- and SO52-/SO4

2- are 1.75 and 1.22 V

respectively, suggested that in acidic medium, PMS which exists predominantly as

HSO5-. The linear decrease in the rate with an increase in the [H+] presumably due to

the accumulation of protonated form of amino acid which is kinetically inactive.

The kinetics and spectral results suggested the formation of the chelate complex

by the interaction of non bonded electrons in the carboxylate oxygen and amine

nitrogen of amino acid with Cu(II) ions, followed by the reaction with HSO5- giving

copper peroxide as active intermediate which is responsible for the autocatalysis

process. The formation of moderately stable intermediate is supported by the observed

thermodynamic parameters.

The positive values of the enthalpy of reaction ΔH# and Gibbs energy of reaction

ΔG# supported the formation of highly solvated transition state while the negative values

of entropy of activation (ΔS#) suggested the formation of rigid trasition state with

reduction in the degree of freedom of molecules.

Further, the experimental observation showed no effect of ionic strength on the

rate of reaction, which also substantiated the suggested mechanism. Based on the

observed results, a detailed kinetic scheme for the oxidation of amino acids is proposed.

Schem 5.1 Mechanism for the autocatalytic oxidation of amino


CHAPTER VI

BIOLOGICAL STUDY OF THE METAL IONS – AMINO ACID

COMPLEXES

6.1 Antibacterial activity

The antibacterial activity assay was performed with the human pathogenic

strains of bacteria. All the complexes of (VO2+ ion – amino acid) did not exhibit any

antibacterial activity. In silico studies of these compounds also correlated with in vitro

studies. The molecular docking with the compounds and the ESBL genes including

TEM and SHV showed weaker interactions and the values are negligible. These results

suggest that these compounds are not interacting with ESBL genes and hence there is

no antibacterial activity with these compounds (Figure 6.1).

Figure 6.1 Efficacy of antibacterial and synthesized complexes of (VO2+ ion-

amino acid) on human pathogens

6.2 In Vitro anticancer activity

Biological study such as anticancer activities of the (VO2+ ion – amino acid)

complexes and (Cu2+ion - amino acid) complexes were studied using MTT assay which

is described in the experimental part.

The MTT(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) in vitro

cell proliferation assay is one of the most widely used assays for evaluating preliminary

anticancer activity of both synthetic derivatives, natural products and natural product

extracts. This assay gives an indication of whole cell cytotoxicity.

The sample Cells (1 × 105/well) were plated in 100µL of medium. After 48h of

incubation, the cell reached the confluence. Then cells were incubated in the presence

of various concentrations of the samples in 0.1% dimethyl sulfoxide (DMSO) for 48h at

37°C. Viable cells were determined by the absorbance at 570 nm with reference at 655

nm. Measurements were performed, and the concentration required for 50% inhibition

of viability (IC50) was determined graphically. The absorbance at 570 nm was measured

with a UV spectrophotometer using wells without sample containing cells as blanks.

The effect of the samples on the proliferation of Human Lung cancer cells was

expressed as the % cell viability (Figure 6.2). It was observed that the VO2+ ion-amino

acid complexes and Cu2+ ion-amino acid complexes were showed good anticancer

activity and the percentage viability were found ≥ 50%. The VO2+ ion-glycine and VO2+

ion-2-AIBA complexes showed 74% and 72% of the percentage viability respectively.

The VO2+-amino acid complexes showed more anticancerous activity than Cu2+-amino

acid complexes.

In silico molecular docking correlated with the in vitro studies where the complex

amino acids interacted with PI3 kinase which is the key enzyme involved in cancer. In

recent years the drugs are designed to target PI3 kinase and these complex

https://en.wikipedia.org/wiki/Di-

https://en.wikipedia.org/wiki/Di-

https://en.wikipedia.org/wiki/Thiazole

https://en.wikipedia.org/wiki/Phenyl

compounds can be the potential drugs for cancer since it interacted very well with PI3K

and also induced apoptosis. However, the toxicity assays are to be carried out to

confirm it further. It was evident from the data that this activity significantly increased

due to the coordination of metal ions with amino acids through nitrogen and oxygen

donor atoms.

Figure 6.2 Anticancer activity of the (metal ions – amino acid) complexes

0

25

50

75

100

C 1 2 3 4 5 6 7

VO2+-glyince

VO2+-alanine

VO2+-valine

VO2+-

2-AIBA

VO2+-NMG

Cu2+-

alanine

Cu2+-

2-AIBA

Metal ions-amino acid complexes

CHAPTER VII

SUMMARY AND CONCLUSION

A systematic kinetic study on the oxidation of structurally different α-

amino acids namely glycine, alanine, valine, 2-amino isobutyric acid, N-methyl glycine

and N-phenyl glycine by PMS in perchloric acid medium and the catalytic effect of VO2+

and Cu2+ ions on the reaction was investigated at 308K. The reaction was studied under

pseudo first order condition with a large excess of [amino acid] over [PMS]. The reaction

rate was measured by monitoring the concentration of unreacted [PMS]t at various time

intervals by iodometry. First-order kinetics was observed and the rate constant kobs were

calculated from the plot of log [PMS]t vs time which was linear up to 90% conversion of

[PMS]. Linear square method was used to calculate the slope and intercept.

The effect of [reactants] on kobs was studied. The reaction rate was also

measured at different temperatures for the calculation of thermodynamic parameters

like free energy of activation (∆G#), enthalpy of activation (∆H#) and entropy of activation

(∆S#). Spectral and electro analytical techniques such as FT-IR spectroscopy, UV-

Visible spectroscopy, EPR and cyclic voltammetry were used to propose the plausible

reaction mechanism. The stoichiometry of the reactions was determined. Product

analysis was carriedout using GC.

The results obtained from the kinetics and mechanistic study of VO2+ catalyzed

oxidation of five structurally different amino acids (AA) such as glycine, alanine, valine,

N-methyl glycine and 2-amino isobutyric acid (2-AIBA) by PMS in perchloric acid

medium at 308K revealed that the reaction did not proceed at all in the absence of

VO2+ and the influence of VO2+ ions on the rate was significant even at a low

concentration of 5 × 10-4 mol dm-3, and hence the catalyst concentration was fixed at 5

× 10-4 mol dm-3. Further, the reaction between VO2+ ions and PMS did not proceed at all

under the experimental conditions, revealing that VO2+ ion was not oxidized by PMS

under the experimental condition.

The values of kobs decreased with increase in [PMS] and the plots of 1/kobs vs

[PMS] were linear which was due to the dimerization of the intermediate vanadyl imine

to a less active form. The kinetic result showed that the observed rate constant kobs

increased with increase in [AA] in all the cases and the plots of kobs vs [AA] were linear

with positive intercept which revealed that the reaction proceeded by two pathways, one

dependent on [AA] and the other independent of [AA]. The pseudo first order rate

constants increased with increase in [VO2+] ions. On varying the [H+], kobs value

decreased with the increase in [H+] and the plot of kobs vs 1/[H+] was a straight line. This

was due to the accumulation of the protonated form of amino acids which was less

reactive under this experimental condition.

The high positive values of free energy of activation (∆G#) and enthalpy of

activation (∆H#) indicated that the transition state was highly solvated while the negative

values of entropy of activation (∆S#) suggested the formation of rigid transition state with

reduction in degrees of freedom of molecules, compared to the reactants.

The kobs remained unaffected with the increase in composition of the solvents,

which ruled out the formation of more polar intermediate than the reactants. No

significant effect of ionic strength (μ) on the reaction rate was observed ruling out the

interaction between NH3+

group of amino acids and HSO5- of PMS.

The activation enthalpies and entropies of the oxidation of the amino acids

studied were linearly interrelated, implying that all the amino acids were oxidized by the

same mechanism. Further, the rate of the reaction was very slow for N-methyl glycine

since the secondary amine donot undergo hydrolysis. The initial reaction was the

abstraction of hydrogen from carboxylate group of amino acid in the VO2+ – amino acid

complex and led to the formation of carboxylate anion complex which subsequently

eliminates CO2 to give the imine intermediate.

The results on the oxidative decarboxylation of N-phenylglycine by peroxomonosulphate

under the same condition revealed that the rate was very fast at room temperature and

it proceeded even in the absence of metal ions as well. Hence the kinetic studies of this

reaction were carried out at 278K and this oxidation was studied both in the presence

and absence of metal ion catalyst. The observed reaction rate (kobs) remained constant

with increase in [PMS] in both catalyzed and uncatalyzed reaction, revealing the first

order dependence of [PMS] on the rate.

The results showed that the kobs increased with increase in [NPG] and the plots

of kobs vs [NPG] were linear for both the reactions. The positive intercept obtained in the

above plots revealed that the reaction proceeded by two pathways, one dependent on

[NPG] and the other independent of [NPG]. The reaction rate decreased with the

increase in [H+], and the plot of kobs vs 1/[H+] was linear. Similar observation was noticed

for the reaction in the presence of metal ions as well.

The influence of [metal ions] on kobs showed that the rate increased with the

increase in [VO2+] and [Cu2+]. Further, the plots of kobs vs [metal ions] were straight lines

with positive intercepts. The values of catalytic constant (KC) were evaluated for both the

catalysts at different temperatures and it increased with increase in temperature. The

value of KC for VO2+ and Cu2+ ions were 1.33 and 0.48 at 278 K respectively, which

suggested that the reaction catalyzed by VO2+ ions was 2.77 times faster than by Cu2+

ions due to the difference in the stability of the complexes.

From the data obtained during the measurment of reaction rate at different

temperatures, the thermodynamic parameters were calculated. The EPR spectral data

ruled out the formation of free radical intermediates. From the kinetics and spectral

data, a detailed mechanism of the oxidative decarboxylation of NPG by PMS both in the

presence and absence of metal ion catalyst were discussed.

The kinetics and mechanism of copper (II) ions catalyzed oxidation of amino

acids such as alanine and 2-AIBA by PMS in perchloric acid medium were studied at

308K. The influence of Cu2+ ions on the rate was significant even at minimum

concentration of 5×10-4 mol dm-3, and hence the concentration of Cu2+ was fixed at

5×10-4 mol dm-3. The reaction rate was found to be slow at initially and the reaction

proceeded at a faster rate later and the plot showed curvature towards X–axis which

confirmed that the reaction proceeded through autocatalysis. From the slope and

intercept of the plot (rate/[PMS]t) vs [PMS]t, the rate constants for uncatalyzed k1(obs) and

catalyzed k2(obs) reactions were calculated using the known value of [PMS]0.

The rate constants k1(obs) and k2

(obs) for the oxidation reaction were unaffected

with increase in [PMS]. The kinetic results for the variation of [amino acid] showed that

the k1(obs) and k2

(obs) increased with increase in [amino acid]. Further, the plots of k1(obs)

vs [amino acid] and k2(obs) vs [amino acid] were linear with positive intercepts which

revealed that the reaction proceeded by two pathways, one dependent on [amino acid]

and the other independent of [amino acid].

The observed rate constants decreased with the increase of [H+]. Further, the

plots of k1(obs) and k2

(obs) vs 1/[H+] were linear. The kinetic results for the effect of [Cu2+]

on k1(obs) and k2

(obs) showed that the rate increased with the increase in [Cu2+]. Further,

the plot of rate constant vs [Cu2+] was linear with a positive intercept.

Further, the reaction between Cu2+ ions and PMS under the experimental

conditions led to the formation of copper peroxide intermediate which was responsible

for autocatalysis. The thermodynamic parameters were calculated by studying the

kinetics at different temperature. Change in ionic strength () of the medium did not

affect the values of rate constant. EPR studies confirmed that the Cu2+ ion was neither

oxidized nor reduced but acted only as a catalyst by forming copper peroxide

intermediate with PMS.

Cyclic voltammetric and UV absorption studies confirmed the formation of

copper – amino acid – PMS complex. The FT-IR spectral data confirmed that the

complexation of amino acid with Cu2+ ions through both –COOH and –NH2 groups of

amino acid. Based on the spectral and kinetics data, a detailed mechanism for the

oxidation of amino acids in the presence of Cu2+ ions was suggested.

The synthesized (metal ions-amino acid) complex such as (VO2+ -amino acid)

complexes and (Cu2+ - amino acid) complexes were screened for their antibacterial and

anticancer activity.The molecular docking with the compounds and the ESBL genes

including TEM and SHV showed no antibacterial activity.

Investigations on the proliferation of Human Lung cancer cells showed that

the synthesized metal ions-amino acid complexes exhibited good anticancer activity and

the percentage viability was found ≥ 50%. The VO2+- amino acid complexes showed

more anticancerous activity than Cu2+- amino acid complexes.

CHAPTER VIII

SCOPE FOR FUTURE WORK

The following objectives are planned for future studies:

The VO2+ ions catalyzed oxidation reaction may be extended to other amino

acids.

To investigate the insulin acitivity of oxovanadium (IV) complexes.

The catalytic effect of copper in the oxidation of peptides will be studied.

The catalytic effect of VO2+ ions will be extended to other peroxo oxidants.

The catalyst will be incorporated in meso-porous materials viz., zeolite, KIT-6,

etc. which will enable the recovery and reuse of the catalyst used for organic

transformations.

To explore the biological activities including antimicrobial and antioxidant

efficiency of the metal ions - amino acid complexes.

CHAPTER IX

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List of Publications

Papers published:

[1]. Kanniappan L., Kutti Rani S. and Easwaramoorthy D., “Oxidative decarboxylation of N-phenylglycine by peroxomonosulphate in perchloric acid

medium - Catalytic effect of Cu2+ and VO2+ ions”, J. Ind. & Eng. Chem.

Res.,Vol.53, pp.13302-13307, 2014.

[2]. Kanniappan L., Kutti Rani S. and Easwaramoorthy D., “Oxidation of α-alanine by

peroxomonosulphate - Autocatalytic effect of copper peroxide”, J. chem & pharm.

Sci., Vol.9, pp.259-264, 2015.

Papers communicated:

[1]. Kanniappan L., Kutti Rani S. and Easwaramoorthy D., “E1cB elimination in VO2+

catalyzed oxidation of amino acids by peroxomonosulphate - Kinetics and

mechanistic studies.

[2]. Kanniappan L., Kutti Rani S. and Easwaramoorthy D., “Copper (II) ions catalyzed oxidation of 2-amino isobutyric acid by peroxomonosulphate in

perchloric acid medium: Kinetics and mechanistic study”.

[3]. Kanniappan L., Kutti Rani S., Hemalatha S. and Easwaramoorthy D., “Synthesis

and characterization of amino acid-oxovanadium(IV) complexes-molecular

docking and study of anticancer activity”.

National Conference and International Conference

[1]. Kanniappan L., Kutti Rani S. and Easwaramoorthy D., “Kinetics and mechanism

of oxidation of N-phenyl glycine by peroxomonosulphate”, National conference

on recent advances in materials and methods of chemistry, SRM University,

Chennai on 20th Febraury 2012.

[2]. Kanniappan L., Kutti Rani S. and Easwaramoorthy D., “Complexation in VO2+-

amino acid - PMS system studied by UV – Visible, ESR and CV studies”. NCAC 2013, Easwari Engineering College, Chennai on 2nd March 2013.

[3]. Kanniappan L., Kutti Rani S. and Easwaramoorthy D., “Oxidation of 2-amino

isobutyric acid by peroxomonosulphate in perchloric acid medium: Kinetics and

mechanistic study”, International conference on recent advancement in mechanical Engg & Tech, AVIT, Chennai on 23rd and 24th April 2015.

TECHNICAL BIOGRAPHY

Mr. Kanniappan L. (RRN: 1391141) was born on May 5th, 1976 in

Chengalpattu, Tamilnadu, India. He did his schooling in Government Higher

Secondary School, Singaperumal koil. He was graduated with distinction in

Chemistry from S.I.V.E.T College (Affiliated to University of Madras),

Gouriwakkam, Chennai and got his Master degree in Chemistry from

Pachaiyappa’s College (Affiliated to University of Madras), Chennai. He

obtained his Master of Philosophy in Chemistry from University of Madras,

Chennai.

He is working as an Assistant Professor in the Department of Chemistry

in R.V.Government Arts College, Chengalpattu. He has got sixteen years of

teaching experience. He is currently pursuing his Ph.D programme in the

Department of Chemistry, B. S. Abdur Rahman University, Chennai, in January

2013. He carried out his research work in the thrust area of “Kinetics and

mechanism of VO2+ and Cu2+ ions catalyzed oxidation of amino acids by

peroxomonosulphate”. He has published two papers and communicated two

papers in international peer-reviewed journals. Also, he has presented a paper

in National conference.

The e-mail ID is: lkanniappan@rediff mail.com and the contact number is:

9698792168.

KINETICS AND MECHANISM OF VO and Cu IONS CATALYZED OXIDATION OF AMINO ACIDS … · 2017-02-06 ·...

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