Modifying Silica with Corannulene...

Modifying Silica with

Corannulene Derivatives

Preparing stationary phase using click reaction to separate fullerene mixtures

Thuy-Tran, Ho-Thi

Master thesis, 30 hp Examiner: Fredrik Almqvist

Passed: XX June 2020

I

Abstract

The immobilization of corannulene derivatives onto porous silica substrate was

performed by the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) “click”

reaction in order to prepare stationary phases for HPLC. The synthesis was

accomplished in four steps. In the first step, the silica surface was activated in order

to form hydroxyl groups for further modifications with (3-azido-propyl) trimethoxy-

silane. This latter material was formed through a substitution reaction between

sodium azide and (3-chloro-propyl)-trimethoxy-silane. In the final step, the azide

groups available on silica surface were allowed to react with terminal alkyne of

corannulene derivatives, forming triazole rings. Furthermore, a variety of solvents

were tested for C60-molecular imprinting simultaneously with the click reaction. C60

was used as a template molecule, which has π-π interactions with corannulene. After

removal of the template, the shape of the cavity resembles that of C60, which was

believed to increase the selectivity as well as efficiency of the material. The

characterization of the synthesized materials was carried out by several analytical

techniques such as FT-IR, 1H NMR,

13C solid state NMR spectroscopies and XPS.

Fullerenes and fullerane isomers were tested on chromatography columns filled with

two different corannulene-modified silica.

III

List of abbreviations

APPI Atmospheric photoionization

C4O2 Corannulene with oxygenated linker containing 4 carbons and 2

oxygens

C6O3 Corannulene with oxygenated linker containing 6 carbons and 3

oxygens

C6 Corannulene attached with a six carbons linker

CuAAC Copper (I)- Catalyzed Alkyne-Azide Cycloaddition

DMF Dimethylformamide

EDTA Ethylenediaminetetraacetic acid

FT-IR Fourier Transform Infrared Spectroscopy

FWHM Full Width at Half Maximum

HPLC High-Performance Liquid Chromatography

MS Mass Spectrometry

MI Molecular Imprinting

NI Non-Imprinting

NMR Nuclear Magnetic Resonance

XPS X-ray Photoelectron Spectroscopy

Author contribution

The corannulene derivatives were provided by a group, led by Prof. Jay S. Siegel

from School of Pharmaceutical Science & Technology at Tianjin University,

China[13]. Fullerenes and hydrogenated fullerenes were supported by Alexandr

Talyzin from the Department of Physics at Umeå University, Sweden. The synthetic

procedure is a continuation of the master thesis of Piotr Jablonski[10].

The 13

C solid-state NMR was operated by Tobias Sparrman, who is a first research

engineer at the Department of Chemistry at Umeå University, Sweden. XPS

measurement was managed by Andrey Shchukarev, who is a research fellow at

Department of Chemistry at Umeå University, Sweden.

All of the experiments and some characterizations have been done by myself,

involving FT-IR and 1H NMR.

V

Table of contents

Abstract .......................................................................................................................... I Author contribution ..................................................................................................... III 1. Introduction................................................................................................................ 1

2. Popular scientific summary including social and ethical aspects .............................. 2 2.1 Popular scientific summary ................................................................................. 2 2.2 Social and ethical aspects .................................................................................... 3

3. Experimental .............................................................................................................. 3 3.1 FTIR- Diffuse reflectance spectroscopy ............................................................. 3

3.2 1H NMR and solid state

13C NMR ....................................................................... 3

3.3 X-ray Photoelectron Spectroscopy ...................................................................... 3 3.4 Column preparation ............................................................................................. 4

3.5 HPLC-MS ............................................................................................................ 4 3.6 Activating silica ................................................................................................... 4 3.7 Substitution of (3-chloropropyl)-(trimethoxy)-silane with azide groups[11] ...... 4 3.8 Azide functionalization on activated silica[11,12] .............................................. 4

3.9 Click reaction on azide-functionalized silica ....................................................... 5 3.10 Solvent tests for C60-molecular imprinting ...................................................... 5

4. Results and discussion .......................................................................................... 6 4.1

1H NMR of substituted product ........................................................................... 6

4.2 FT-IR of azide silica and click reaction products ................................................ 7 4.3 Solid state

13C NMR of modified and imprinted silica ....................................... 8

4.4 XPS of azide silica and „click‟ products .............................................................. 8

4.5 HPLC-MS ............................................................................................................ 9

..................................................................................................................................... 12 ..................................................................................................................................... 12 5. Conclusions and Outlook ......................................................................................... 13

Acknowledgement ....................................................................................................... 13 References.................................................................................................................... 14

Appendix...................................................................................................................... 15

1

1. Introduction

The existence of fullerenes, which has been known as the third form of carbon was

for the first time published in 1970 by Eiji Osawa[15]. Until 1985, the group of

scientists leading by Harry Kroto noticed that there were two stable ions present for

C60 (m/z=720) and C70 (m/z=840) on the mass spectrum[15]. These results were

observed by vaporizing a graphite disc, using laser source[15]. Fullerenes are hollow,

ellipsoid spheres consisting only of carbon atoms. For instance, there are twenty

hexagons and twelve pentagons in the structure of C60, forming a closed spherical

cage and resembling like a soccer ball. The most abundant are C60 and C70,

therefore, their appearance has become an interesting area in scientific community[1].

In the normal state, fullerenes are black solids. Although many aromatic rings are

involved in fullerenes structure their chemical properties are more likely super-alkene

compounds rather than benzene[15]. Another interest is the cage-liked structure of

fullerenes that could harbor metal atoms like potassium to become a

superconductor[14]. As electron acceptor molecules, fullerenes are highly soluble in

п-donor solvents such as toluene[2]. In fact, the highest solubility of fullerenes was

reported in piperidine as 53.29 g/L[3]. Piperidine is a cyclic aliphatic amine with the

free electron pair on nitrogen atoms, which are able to form charge transfer

complexes with electron deficient fullerenes.

Under high temperature, fullerenes can be hydrogenated by reacting under extremely

high pressure of hydrogen gas, resulting in products known as fulleranes[4].

Numerous synthetic approaches have been carried out to produce fulleranes.

However, the simplest way to synthesize hydrogenated fullerenes is the reduction

reaction, using zinc and hydrochloric acid in toluene[5,6]. The formation of

hydrogenated fullerene is the addition of H2 at a C=C double bond to gain two C-H.

Therefore, there is only an even number of hydrogen atoms in the structure of

fulleranes such as C60H18 or C60H36. It was reported that the high level of

hydrogenation was unstable, thereby, fully saturation of fullerenes are hardly able to

observe[6]. The partial unconjugated structure of fulleranes have changed the

physical and chemical properties, compared to its ordinary[1], which opens many

opportunities in the modification of fullerenes.

Figure 1. (A)3D Buckyball-C60; (B) 3D-buckybowl-corannulene

Fullerenes and fulleranes have many possible applications in batteries, gas storage,

medicine, or optical sensors. Depending on the level of hydrogenation, buckyballs

could obtain a wide range of electrochemical capacities and become novel material in

battery technology. Moreover, if the process of hydrogenation and de-hydrogenation

of C60 is reversible, these materials could be ideal for hydrogen storage for fuel cells.

This application is environmental friendly and could greatly contribute to the

development of electric vehicles[1]. In addition, fullerenes own a unique optical

property that only allow low intensity light to pass through them and turns opaque

with intense light. Its optical limiting phenomenon has been widely used as a sensor

protection for eyes[1]. The limited solubility of fullerenes in aqueous phase could be

(A) (B)

2

solved by chemical modification with hydrophilic side chains that, in addition,

broadens the potential in pharmaceutical applications. In fact, C60 is able to work as

an anticancer drug delivery system to treat targeted tumors, resulting in reducing

doses for patients and thereby minimize side effects[15].

Corannulene (C20H10) is one of the simplest fragments of a fullerene cage that

contains one pentane ring fused with five benzenes, forming a bowl shape. This

compound has a high host potential for fullerenes recognition. The combination of its

concave structure and the conjugated system maximizes the π-π interaction between

buckybowls and fullerenes[7]. Therefore, a modified silica based-stationary phase

with corannulene derivatives turns out to be promising for separation of fullerene

derivatives by liquid chromatography.

The click chemistry is one of the possible ways to immobilize corannulene

derivatives onto silica support. Although three main types of click reactions are

efficient, the Copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) has been

reported as the most effective reaction in modifying materials[8]. In particular, the

CuAAC reaction occurs between a terminal alkyne and azide groups, forming stable

triazole rings. It was reported that the rate was improved significantly when using

Cu(I) as a catalyst compared to a catalyze free reaction[8]. In fact, a variety of copper

sources could be used with the appropriate oxidant/reductant species to obtain Cu(I).

In order to improve the retention and selectivity of fullerenes in chromatographic

separation, molecular imprinting technique is another possibility. In this approach,

C60 was used as a molecular template and added during the click reaction. The

formation of a template cavity was envisioned to be driven by π-π interactions

between C60 and corannulene-modified silica[9].

Firstly, a certain amount of corannulene-modified silica was synthesized as a

stationary phase. Secondly, chromatographic columns were packed with the prepared

materials. Finally, the separation ability was tested by liquid chromatography using a

MS detector. Numerous analytical techniques have been employed to characterize the

material throughout the synthetic processes, for instance, FT-IR spectroscopy, 1H and

13C solid state NMR spectroscopy and XPS.

Aim of the diploma work

The aim of the study was to extend the previous investigation[10] with other

derivatives (corannulene attached with oxygenated side chain linkers) to modify silica

surface by CuAAC-click chemistry. Buckybowl is a highly potential candidate to

separate fullerenes and their isomers by HPLC thanks to its strong π-π interaction

with guest molecules[7]. In addition, C60-molecular imprinting has been investigated

to increase the efficiency of the columns. Therefore, it is necessary to find a solvent

that works sufficiently for the CuAAC reaction as well as dissolving the template

molecules. The experiments were carried out with different organic solvents such as

toluene, pyridine, and piperidine. In this experiment, phenylacetylene was used as a

test substance for the click reaction.

2. Popular scientific summary including social and ethical

aspects

2.1 Popular scientific summary

Porous silica has been known as the most important stationary phase in liquid

chromatography. The chemical modification of silica surface makes it versatile,

especially in purification, qualitative or quantitative analysis. In this research, silica

was modified with corannulene derivatives that tend to separate fullerenes and

3

fulleranes. Fullerenes are new allotropes of carbon, which have many possible

applications in our life. One of the most interesting applications of fullerenes is the

capable of trapping atoms inside the cage. In cancer treatment, the radioactive gas

radon could be trapped in the C60 structure combined with antibodies attaching

outside fullerene that preferentially kills unhealthy tissue[15]. By controlling the

pathway of how radon gas reacts with tumor, it possibly prevents the tracer from

damaging healthy tissue rather than the targeted tumor cells. Therefore, the

purification after synthesis of fullerenes/fulleranes is indispensable for further

investigations. HPLC using corannulene-modified silica could be considered for this

purpose. HPLC is the abbreviation for High Performance Liquid Chromatography.

The sample has to be dissolved in a selected solvent before introducing into the

column. The mobile phase is flushed through the column filled with a properly

selected porous or gel bed. The mixtures/analytes are separated as the result of

intermolecular interactions with the stationary phase.

2.2 Social and ethical aspects

This thesis was reported with all the experimental data that was observed during lab

work. Additionally, there were no animal tests or other biological samples.

3. Experimental

3.1 FTIR- Diffuse reflectance spectroscopy

Bruker IFS 66v/S spectrometer (Bruker Optik GmbH, Ettlingen, Germany) was used.

KBr was purchased from Merck, Germany and used as a reference/matrix. The silica

was ground manually by mortar and pestle with KBr. FT-IR diffuse reflectance

technique was used for this analysis under high vacuum condition (~7 mbar) and the

spectrum was recorded within 256 scans in the region from 400-4000 cm-1

. The

baseline correction and normalization of spectra were controlled by OPUS software

(version 5.5).

3.2 1H NMR and solid state

13C NMR

Bruker Avance III 400 MHz spectrometer with a BBO-H/F SmartprodeTM

was used

to obtain proton NMR spectra. Deuterated chloroform (CDCl3) was used as solvent.

The sample was recorded within 16 scans and controlled by Topspin 3.6.2.

Bruker Avance III 500 MHz spectrometer with a 4 mm HX CP MAS probe that was

employed for 13C solid state NMR spectroscopy. The rotors were filled with azide-

silica and modified materials and spun at 10 kHz. The program used 90o excitation

pulse for 1H, followed by a 1.5 ms 13C spin lock at 60 kHz during which 1H was

ramped (45-90 kHz). The Spinal-64 1H decoupling condition was applied at 83 kHz.

The spectrum was recorded with a 2s relaxation delay and 6000 scans. The CH2

signal at 38.48 ppm of adamantine was used as an external reference.

3.3 X-ray Photoelectron Spectroscopy

Kratos Axis Ultra DLD electron spectrometer, equipped with monochromatic Al Kα

source, power supplied at 150 W was performed on the silica samples. The full wide

spectra were measured with analyzer pass energy at 160.0 eV, and 20.0 eV for each

photoelectron lines. The spectra were recorded by Kratos software. The binding

energy (BE) scale of all spectra was referenced to the Si-2p line set at 103.3 eV.

During measurement, the charge neutralizing is done by a built in system of the XPS

spectrometer.

4

3.4 Column preparation

A Knauer (Berlin, Germany) air-driven pneumatic pump was used at high pressure

350 bars to pack the column. Two metal HPLC columns (40 mm x 2.1 mm) from

Isolation Technologies (Middleboro, MA, USA) were packed with C4O2 and C6O3-

modified silica. These were dispersed in toluene (VWR, AnalR Normapur) and

flushed into the columns under high pressure.

3.5 HPLC-MS

The evaluation on LC-MS was performed by using a Shimadzu (Kyoto, Japan) LQ

LC-20AD and Agilent HP 1100 series G1310A pumps, they were connected by a

mixer before passing the column. As a detector LCQ Fleet (Thermo Scientific, USA)

ion trap mass spectrometer equipped with atmospheric photoionization accessory

(APPI), and a Rheodyne (Rohnert Park, CA, USA) 7010 injector with 20 µL metal

loop were used. The instrument was controlled by LCQ tune plus program. Toluene

(VWR, AnalR Normapur) and the mixture of toluene:methanol (Fisher Chemical,

HPLC grade) were used as mobile phases.

The MS detector was tuned by using low concentration of C60 in toluene (ca. 5.2

µg/ml) to optimize the operation condition and the positive mode was used. The

C60/C70 mixture, higher fullerenes as well as different levels of hydrogenated

fullerenes had concentrations of approximately 0.01-1.0 mg/ml in toluene.

3.6 Activating silica

2.0 gram of silica (Kromasil 200 Å, 5 µm) was added in a beaker, filled with 25 ml of

1M HCl. The reaction was allowed to run for one hour at 100 oC. The silica was then

filtered on a glass filter. After that the silica was washed with deionized water and

once with methanol to remove excess acid, following by drying in a vacuum oven

overnight at 40 oC. The silanol groups were formed in this step by protonating oxygen

atoms on silica surface.

3.7 Substitution of (3-chloropropyl)-(trimethoxy)-silane with azide groups[11]

10 ml of (3-chloropropyl)-(trimethoxy)-silane (≥ 97%; Sigma-Aldrich) was added to

250 ml in a dried round bottom flask, containing 125 ml of dry DMF. The water was

removed from DMF by a glass contour solvent system (SG, Water, USA) by flushing

the flask with argon gas for three times before collecting the solvent. 5.20 g of

sodium azide (> 99%; Merck) was added to the mixture, followed by KI (20 mg) as a

catalyst. The mixture was stirred under nitrogen gas, at 110 oC, overnight. The

reaction was quenched by diluting with diethyl ether and transferred into a separatory

funnel. The organic layer was washed thrice with 25 ml of deionized water and once

with 25 ml of brine to remove all the unreacted reagents. The combined aqueous

phases were extracted once with diethyl ether. The combined organic phase was dried

with anhydrous MgSO4 and filtered before evaporating in a rotary evaporator. The

product (3-azidopropyl)-(trimethoxy)-silane with high viscosity was collected and

confirmed by 1H NMR.

3.8 Azide functionalization on activated silica[11,12]

0.50 g of activated silica was added to a pressure resistant vial and 0.59 ml of (3-

azidopropyl)-(trimethoxy)-silane was pipetted in the presence of dry DMF (1ml) as a

solvent. The reaction was heated to 110 oC in a GC oven simultaneously with rotation

by a rotor, for 24 hours. The modified silica was filtrated and washed twice with

deionized water and once with methanol. The aizde-silica was then dried in a vacuum

5

oven overnight at 40 oC. The product was characterized by FT-IR spectroscopy and

13C solid state NMR.

3.9 Click reaction on azide-functionalized silica

0.50 g of azide silica was added to a vial containing 1.0 ml of dry DMF, followed by

80.0 mg of oxygenated corannulene with terminal alkyne (C4O2). CuSO4 and a

reductant (sodium L-ascorbate) were then added to this mixture. The solution was

allowed to react at 60 oC, for 24 hours. The reaction was quenched by adding 25.0 ml

of 0.1 M EDTA, following by filtering on a glass filter and washing with deionized

water and methanol[12]. The final product was dried in the vacuum oven at 40oC

overnight and characterized by FT-IR spectroscopy, solid state 13C-NMR.

Figure 2. The mechanism of ‘click’ reaction between azide group and terminal alkyne of corannulene

attached with C4O2 linker

3.10 Solvent tests for C60-molecular imprinting

0.25 g of azide silica was added to a vial containing 1.0 ml of dry DMF. 0.29 ml of

phenyl acetylene was added, followed by CuSO4 and a reductant (sodium L-

ascorbate). The solution was allowed to react at 60 oC, for 24 hours. The reaction was

quenched by adding 25 ml of 0.1 M EDTA, following by filtering on a glass filter and

washing with deionized water and methanol[12]. The final product was dried in the

vacuum oven at 40 oC overnight and characterized by FT-IR spectroscopy. The same

procedure was applied for piperidine, pyridine, and toluene.

0.50 g of azide silica was added to a vial containing 1.0 ml of a chosen solvent,

followed by 80 mg of corannulene attached with a six carbon side chain. 80 mg of

C60 (0.5 equiv.) was dissolved in 2 ml of the chosen solvent before adding to the vial,

followed by CuSO4 and a reductant (sodium L-ascorbate). The calculated amount of

C60 was based on the idea that one fullerene was surrounded by two corannulenes to

form a cavity (Figure 3). The solution was allowed to react at 60 oC, for 24 hours.

The reaction was quenched by adding 25 ml of 0.1 M EDTA, following by filtering

on a glass filter and washing with deionized water and methanol[12] . The material

was packed in a metal column and the template was removed by flushing with toluene

at 0.3 ml/min, overnight. The imprinted material was dried in the vacuum oven at 40 oC overnight and characterized by FT-IR and

13C solid state NMR.

6

Figure 3. The suggestion structure of C6-modified silica and the imprinted process during click

reaction, using C60 as template molecules

4. Results and discussion

4.1 1H NMR of substituted product

(3-chloropropyl)(trimethoxy)silane was substituted with sodium azide (NaN3) to

obtain the terminal azide functional groups that allow click reaction in the following

steps. In order to examine whether the reaction occurred, 1H NMR was performed on

the starting material and the substituted product.

Figure 4. 1H spectra and structures of (3-chloropropyl)(trimethoxy)silane(A); and azide silane(B)

It can be seen from Figure 4a below that there were totally three groups of proton.

Two of them were at 0.78 ppm and 1.87 ppm corresponding to protons on the first

(A)

(B)

7

and the second carbon, respectively. The other at 3.55 ppm is overlapping signal of

trimethoxy groups and protons on the third carbon, where the substitution occurred.

After the reaction (Figure 4b), the proton at substituted position has shifted from 3.52

to 3.20 ppm. As the results, the reaction was successful and the substitution yield was

about 91.9%.

4.2 FT-IR of azide silica and click reaction products

After completing the substitution, (3-azidopropyl)-(trimethoxy)-silane was attached to

activated silica. The attachment occurred between azide silane reagents and surface

silanol groups. After that the azide groups reacted with ω-terminal alkyne

corannulene derivatives via click chemistry to immobilize corannulene on silica

support.

Figure 5 shows that the silica was successfully modified with (3-azidopropyl)-

(trimethoxy)-silane due to strong band of azide stretching (N=N=N) at 2150 cm-1

.

The immobilization of corannulene derivatives on silica support was successful as

shown by the significant decrease of the azide band and there is a small signal in the

region over 3000 cm-1

, arising from aromatic C-H stretching of corannulene.

However, there were some residual azide groups on silica surface or not all of them

were accessible for coupling.

The characterization of „click‟ products in different solvents such as DMF, piperidine,

pyridine and toluene were shown in Figure 6. In the previous studies[14], DMF was

used successfully as a solvent, thereby, it was also used as a reference, marked as red

color in Figure 6b in this experiment. After reaction, the azide signal completely

disappeared when using piperidine (Figure 6c), indicating that the modification of

silica was successful. The other evidences were the aromatic C-H stretching/C=C

bending bands at 3060 cm-1

, 1480 cm-1

, respectively. In addition, the spectrum was

similar to the one using DMF as solvent. Piperidine was chosen for imprinting

reaction (appendix 1).

In contrast, there was an incomplete reaction in pyridine, which can be seen from

Figure 6d. Additionally, there was a band at 1650 cm-1

, relating to C=N that possibly

came from pyridine residual in the product. The reaction was not able to be

performed in toluene. Since there was a strong signal of azide in the spectrum (Figure

6e) and no aromatic appearance.

(a)

(b)

(c)

(d)

(e)

Figure 6. FT-IR spectra of azide silica (a) and

click reaction products using DMF (b); piperidine

(c); pyridine (d); toluene (e) as solvent

Figure 5. FT-IR spectra of azide silica (a) and

C4O2-modified silica (b); C6O3-modified silica

(c)

(a)

(b)

(c)

A.U

A.U

8

4.3 Solid state 13

C NMR of modified and imprinted silica

Further confirmation was obtained from 13

C solid state NMR spectroscopy (Figure

7). After the reaction, aromatic carbon signals appeared (from 110-150 ppm) in both

materials, which means that silica was successfully modified with corannulene

derivatives. In addition, in Figure 7(b,c), there was a new signal at 70 ppm was the

carbon that bound directly to oxygen in the linker. The region from 10-55 ppm

belongs to aliphatic carbons, which can be seen easily in Figure 7a.

The 13C NMR solid-state spectrum of molecularly imprinted product was compared

to non-imprinted material, which is shown in Figure 8. There was a new peak at 136

ppm (Figure 8b), which is characteristic for C60. In the solid state, pure C60 has a

high speed of rotation and gives rise to a sharp peak at 143 ppm (296 K)[16]. The

main reason to the change in the chemical shift as well as a broadening of the peak is

probably due to the π-π interaction between corannulene and C60. Despite the hard

attempt to remove template molecules by flushing with toluene, the result proved that

C60 interacts strongly with corannulene and is very difficult to remove from the

material.

4.4 XPS of azide silica and ‘click’ products

X-ray photoelectron spectroscopy is an efficient way to examine the atomic

compositions and thus was used to analyze functionalized silica and „click‟ products.

Table 1 showed that the substituted reaction was complete with the presence of azide

but no chlorine.

The signal of sp2 carbon (about 288.0 eV) from triazole ring is present in both

modified material, indicating the attachment of corannulene derivatives were

complete for both. However, in the C4O2-material, there was a trace signal of copper

catalyst in spectrum (appendix 2). XPS is known as a surface characterization

technique, therefore, in order to examine the coverage of corannulene in the bulk of

porous silica elemental analysis is necessary.

Figure 7. 13

C solid-state NMR spectra of

azide silica (a); C4O2-modified (b); C6O3-

modified silica (c)

Figure 8. 13

C solid-state NMR spectra of

corannulene attached with six carbons linker

modified silica NI (a); C60-MI (b)

9

Table 1. XPS characterization of azide silica, presenting atoms in the material via binding

energy (BE), atom concentration (AC%), and assignments.

Line Azide silica

Assignment BE (eV) AC (%)

C 1s 284.7 7.4 C-C

286.4 6.8 C-O; C-N

O 1s 532.6 52.6 SiO2

533.7 2.8 H2O

N 1s

397.4 0.2 -

398.8 1.7 -N=N=N-

400.5 1.9 -N=N=N-

404.3 0.7 NO2?

Si 2p 103.3 25.9 SiO2

Table 2. XPS characterization of C4O2, C6O3-modified silica, presenting atoms in the

material via binding energy (BE), atom concentration (AC%), and assignments.

Line C4O2-modified silica


C 1s

284.3 33.4 C-C

285.9 11.4 C-N, C-O

288.1 0.8 C=C-N

290.8 1.6 π-π* excitation

O 1s 532.5 33.0 SiO2, C-O-C

N 1s 399.8 2.9 -N=N=N-

401.3 1.1 -N=N=N-

Si 2p 103.3 15.8 SiO2

Line C6O3-modified silica


C 1s

284.4 22.0 C-C

286.0 11.2 C-N, C-O

288.0 0.5 C=C-N

O 1s 532.5 42.6 SiO2, C-O-C

N 1s

398.7 0.3 -

399.9 2.1 -N=N=N-

401.0 1.6 -N=N=N-

404.1 0.3 NO2?

Si 2p 103.3 19.4 SiO2

4.5 HPLC-MS

The modified materials were characterized many analytical techniques before packing

into the metal columns (40 x 2.1 mm). The HPLC evaluation was performed with the

mixture of C60/C70 and fulleranes. The composition of mobile phase was adjusted to

see whether the separation could be improved, especially for the mixture of

hydrogenated fullerenes.

10

Table 3. The chromatographic parameters of both columns were calculated from the

extracted chromatogram (figure 9)

Column Retention time

(min)

FWHM

(min)

Efficiency

(effective

theoretical plates)

Resolution

C4O2 5.66 2.50 28.40

1.90 21.33 7.22 48.35

C6O3 2.15 0.63 64.50

2.54 6.92 1.58 106.27

The chromatographic parameters of both columns are shown in Table 3. The results

showed that using corannulene as an active site in chromatographic phase for

fullerenes purification was efficient. The fullerenes are well-separated on both

columns, which was proved by a resolution larger than 1.50 (baseline resolution

requirement[17]). For instance, the C60 eluted (5.83 min) earlier than C70 (21.50

min) on the C4O2 column. The chromatographic condition was 100% toluene, 1.5

ml/min flow rate.

Although the C4O2 has higher carbon content than the C6O3 (Table 2), the efficiency

of C6O3 column was greater than C4O2, resulting in sharper peaks and better

resolution. It could be possibly explained C4O2 column was filled incompletely or

unevenly during the packing process, resulting in a dead volume. As consequences,

the peaks were broadening, leading to the longer retention time.

Figure 9. The chromatogram (smoothed, normalized 1,0) of C60/C70 on C4O2 column (left);

C6O3 (right). The LC operation condition was 100% toluene at 1.5 ml/min flow rate

A.U

A.U A.U

A.U

11

In general, the order of elution was from high to low hydrogenation due to the

reduction in number of sp2 carbons that able to interact with the corannulene

stationary phase. From the results we can observe a pattern that (Figure 10, 11), the

higher level of hydrogenation, the lower retention on both columns. In fact, the

compound C60H36 was not able to interact efficiently with the stationary phase.

However, C60H18 was completely separated from C60H36 on both columns. In

addition, the solubilized high hydrogenated fullerenes are tending to degrade and

precipitate after one hour, which caused an increase in the back pressure.

The sample contains fullerenes hydrogenated at low level was injected (Figure 11)

and confirmed by mass spectrum (appendix 4), which showed the m/z=729, relating

to C60H9+. Furthermore, the mixture of toluene:methanol (80:20, v:v%) was also

tested (Figure 12).

Figure 10. The extracted chromatogram (smoothed, normalized 1,0) of C60H18/C60H36 on

C4O2 column (left); C6O3 (right). The LC operation condition was 100% toluene at 0.5

ml/min flow rate

Figure 11. The extracted chromatogram (smoothed, normalized 1,0) of low hydrogenation on

C4O2 column (left); C6O3 (right). The LC operation condition was 100% toluene at 1 ml/min

flow rate

C4O2 C6O3 A.U A.U

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Figure 12 showed that by adding 20%MeOH, C60 was able to be separated

completely from C60H8 on C4O2. However, the separation efficiency has not been

improved significantly by adding 10%MeOH (appendix 5). The strength of the eluent

decreased when increasing MeOH, which caused an increase in retention time. The

mobile phase was thus adjusted to improve the resolution. However, more of the

polar solvent, caused more precipitation in sample.

Figure 13 showed that C70H38 was not able to be separated efficiently on either

column. In other words, there was no retention of high level of hydrogenation of C70

on these columns. The mass spectrum of C70H38 is presented in appendix 6.

Figure 12. The extracted chromatogram (smoothed, normalized 1,0) of low hydrogenation

on C4O2 column 100% toluene (left); toluene:MeOH (80:20) (right) at 1 ml/min flow rate

100%Toluene 80%Toluene:20%MeOH

Figure 13. The extracted chromatogram (smoothed, normalized 1,0) of C70H38 on both

columns, 100% toluene at 1 ml/min flow rate

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5. Conclusions and Outlook

Porous silica derivatized with corannulene having oxygenated linkers were successful

synthesized by CuAAC click chemistry. The materials were characterized by FT-IR, 13

C solid state NMR spectroscopies and XPS. The C6O3 column has better separation

ability maybe due to a high degree of flexibility in space, which gives more efficient

interactions with fullerenes than C4O2. The number of the effective theoretical plates

of C6O3 was almost double to C4O2. In addition, the high level hydrogenation of

C60H18/C60H36 were sufficiently separated on both column, whereas, C70H38 has no

retention. For further investigation, the same length of side chain with other

electronegative groups such as amine could be investigated.

In theoretical terms, corannulene has a bowl-shaped structure that fits the convex

surface of carbon cages. Therefore, it could maximize the π-π interaction between

stationary phase and fullerenes, compared to the planar aromatic molecules. The

elemental analysis is required to determine the coverage of the lab scale synthesized

material. It is then possibly compared to the large scale commercial one.

Additionally, in order to test reproducibility of the packing more columns should be

prepared.

Piperidine was chosen as solvent for both the click reaction and molecular imprinting

experiment. The molecularly imprinted silica was unsuccessfully synthesized, as the

π-π interaction between fullerene and corannulene was too strong for C60 to be

washed out. Other ways should be investigated to remove the template such as

sonication, flushing with higher conjugated π system organic solvent to reduce the

strength of this bonding.

Acknowledgement

I would like to say thank you to all of my supervisors, Dan Johnels, Knut Irgum and

graduate student Piotr Jablonski, who are well-support during my thesis working

time. I do appreciate many good advices from Chau Huynh, who is a graduate student

in the same research group.

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References

[1] J. C. Withers, R. O. Loutfy, and P. Timothy, Fullerene Commercial Vision,

May 2013.

[2] S. Talukdar, P. Pradhan, and A. Banerji, Electron donor-acceptor interactions

of C60 with n-and π-donors : A rational approach towards its solubility,

Fuller. Sci. Technol., vol. 5, no. 3, pp. 547–557, 1997.

[3] D. Mahdaoui, M. Abderrabba, C. Hirata, T. Wakahara, and K. Miyazawa, The

Influence of Water and Temperature on the Solubility of C60 in Pyridine

Solution, J. Solution Chem, vol. 45, no. 8, pp. 1158–1170, 2016.

[4] A. V. Talyzin, Yury O. Tsybin, Jeremiah M. Purcell, Tanner M. Schaub, Yury

M. Shulga, Dag Noréus, Toyoto Sato, Andrzej Dzwilewski, Bertil Sundqvist,

Alan G. Marshall, Reaction of hydrogen gas with C60 at elevated pressure and

temperature: Hydrogenation and cage fragmentation, J. Phys. Chem. A, vol.

110, no. 27, pp. 8528–8534, 2006.

[5] M. P. Anachkov, F. Cataldo, and S. K. Rakovsky, Fullerenes , Nanotubes and

Carbon Nanostructures Reaction Kinetics of C 60 Fullerene Ozonation,

February 2014, pp. 37–41, 2007.

[6] S. M. Luzan, Y. O. Tsybin, and A. V. Talyzin, Reaction of C60 with hydrogen

gas: In situ monitoring and pathways, J. Phys. Chem. C, vol. 115, no. 23, pp.

11484–11492, 2011.

[7] E. M. Pérez and N. Martín, π−π Interactions in Carbon Nanostructures, R.

Soc. Chem, 2013.

[8] A. Marechal, R. El-Debs, V. Dugas, and C. Demesmay, “Is click chemistry

attractive for separation sciences?,” J. Sep. Sci., vol. 36, no. 13, pp. 2049–

2062, 2013, doi: 10.1002/jssc.201300231.

[9] L. Ye and K. Mosbach, “The technique of molecular imprinting - Principle,

state of the art, and future aspects,” J. Incl. Phenom., vol. 41, no. 1–4, pp. 107–

113, 2001.

[10] P. Jablonski, Synthesis of Silica Modified with Corannulene Ligands Attempts

to create an HPLC column capable of, 2016.

[11] H. Qiu, X. Liang, M. Sun, and S. Jiang, “Development of silica-based

stationary phases for high-performance liquid chromatography,” Anal. Bioanal.

Chem, vol. 399, no. 10, pp. 3307–3322, 2011.

[12] K. Zhao, Q. Bai, C. Song, F. Wang, and F. Yang, Preparation of weak cation

exchange packings for chromatographic separation of proteins using ‘click

chemistry, J. Sep. Sci., vol. 35, no. 8, pp. 907–914, 2012.

[13] A. M. Butterfield, B. Gilomen, and J. S. Siegel, Kilogram-Scale Production of

Corannulene, 2012.

[14] T. Orre, Synthesis of modified silica using copper catalyzed click chemistry,,

2014.

[15] Royal Society of Chemistry, The Age of the Molecule, 1st edition, 1

st May

1999.

[16] R Tycko, R. C Haddon, G Dabbagh, S. H Glarum, D. C Douglass, A. M

Mujsce, Solid-state magnetic resonance spectroscopy of fullerenes, 1991.

[17] Colin F. Poole, „The essence of Chromatography‟, first edition, 2003.

15

Appendix

Appendix 1 : The FT-IR of imprinting material with corannulene attached with six

carbons side chain.

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Appendix 2: The XPS spectrum of C4O2-modified silica, showing the trace amount

of Cu 2p, which came from the use of CuSO4 as catalyst.

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Appendix 3 : The mass spectrum of fullerene C60/C70

Appendix 4: The mass spectrum of low hydrogenated fullerene C60H8

C60C70-P2-2704-1st_01 #478 RT: 2.36 AV: 1 NL: 5.60E2

T: ITMS + c APCI corona Full ms [200.00-1000.00]

690 700 710 720 730 740 750 760 770 780 790

m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lative

Ab

un

da

nce

720.17

721.12

722.10750.40

751.49

723.12 755.42742.53

693.51767.64737.62 743.45717.95 763.12695.01 791.60724.17 777.46710.93 730.45 796.56700.77 780.73

C60C70-P2-2704-1st_01 #1381 RT: 7.10 AV: 1 NL: 1.63E2


770 780 790 800 810 820 830 840 850 860 870 880 890

m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

125

130

135

140

145

150

155

160

Re

lative

Ab

un

da

nce

840.06

841.09

842.15

769.52

853.22857.29843.15784.70

892.77776.57 793.32 807.45 817.39 873.26829.69799.05 882.43845.98839.24820.59 859.41

878.53

C60

C70

p1_C60C70lowH 80T20M 1st_01 #813 RT: 5.76 AV: 1 NL: 1.30E2


690 700 710 720 730 740 750 760 770 780 790 800 810 820

m/z

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

220

230

Re

lative

Ab

un

da

nce

729.22

730.21

731.26

728.16

732.17

727.11 751.61733.40699.61 715.62792.45753.63 799.43710.88 743.31691.12 817.15781.49776.59769.74 801.73 807.82

C60H9+

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Appendix 5: The extracted chromatogram (smoothed, normalized 1,0) of C60H8 on

C4O2 column, toluene:MeOH (90:10) at 1 ml/min flow rate.

Appendix 6: The mass spectrum of hydrogenated fullerene C70H38

p1 7038 1ml 2_01 #74 RT: 0.31 AV: 1 NL: 4.16E3


800 820 840 860 880 900 920 940 960 980 1000 1020 1040 1060 1080

m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lative

Ab

un

da

nce

878.70

852.48

840.33

866.55825.50907.40887.61

986.85806.57 1031.09953.37 1069.63934.16

C70H39+

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