Presentation file : Dr.S.Aravamudhan1 National Seminar On Toxicity Of Chemicals & their Hazards With...

Presentation file : Dr.S.Aravamudhan 1

National Seminar On

Toxicity Of Chemicals & their Hazards With SPECIAL REFERENCE To Heavy Metals”

23rd – 24th , October, 2008

St. Edmond’s College, SHILLONG

An article for the participation of Dr.S.Aravamudhan

Title: “MULTINUCLEAR NMR AND TOXIC HEAVY ELEMENTS”

An Introductory slide show

CONTAINS an Elementary Introduction to “NMR Phenomenon” for the familiarity with Multi Nuclear NMR in the context of TOXIC Heavy Elements

This slide show contains automatically timed animations at certain portions. When the slide is on display wait long enough for automatic animations to proceed and then CLICK. After every click wait for 6-10 Seconds before the next CLICK


In a Scheme of an Atom

Electrons circulate in Orbits

NUCLEUS is stationery at the center

Chemical Molecular structure depends on the electronic structural changes due to bonding between atoms. Nucleus plays no role in determining the optimum geometry except that they get an assigned place as they occupy in the molecule.

Molecular spectroscopic studies involve studies assuming an equilibrium structure, but the molecular phenomenon responsible for spectroscopic absorptions require changes in the electron dispositions around the equilibrium geometries


One of the aspect to be reckoned with is the fact that all the consequences of these transition metals is because of the electrons present in the elemental atom or ion because of which these metals can exhibit chemically binding characteristics.

It is known that the atoms and ions of such elements have their characteristic nucleus around which the electrons of the system revolve in orbits. For the chemical consequences there is not any significant role assigned to the nuclear characteristics unless it is a radio active element and the nuclear radiations can make it possible to be tracked by radio active tracer techniques.

The radio activity itself can be hazardous besides the toxic effects of such elements by chemical reactivities


When all the extra nuclear electrons are in such continuous motion and participate in the bonding, if there can be a stimulation of nucleus which does not in any way affect the electronic dispositions, then would that be in any way useful for such studies of molecular structure?

In magnetic resonance, the nuclei are stimulated in such a way that the electronic dispositions are not influenced by the perturbation of nuclei, but the resulting stimulated response is indicative of the specifics about prevailing electron dispositions


It is at this juncture it is worth trying to inquire the possibilities of using the Nuclear Magnetic Resonance [N.M.R] spectroscopy to follow the characteristics due to the presence of such nuclei invariably with the electron system to be identified as an element. An elementary description of Nuclear Magnetic Resonance [NMR] phenomena is given in the following paragraph.


The central nucleus of some of the elements posses intrinsic spin

and hence also can be associated with a magnetic moment

SPIN

Magnetic moment

These tiny nuclear magnetic moments are similar to the bar magnets which are influenced by Externally applied magnetic fields

Applied magnetic field

Only Discrete orientations of the spin are possible due to the quantization criteria at atomic regimes

or

or

or

Electromagnetic radiation with

frequency ν can cause transition between these levels and this is the resonance phenomenon

2π ν = γ HSimilar effects are possible with electrons also but only in PARAMGNETIC IONS or Molecules when there are unpaired electrons present. Here the reference is only to Diamagnetic Samples (compounds) to introduce NMR exclusive of any other effects.

The value of γ differs from one nucleus to the other.

This unique value of ‘γ’ for each element’s nucleus different from every other element is what makes multi nuclear NMR possible

SPIN

Magnetic moment

Discrete orientations RESULTS in discrete energy levels

Illustration is a case of SPIN=3/2 results in 4 equally spaced energy levels

Spin Quantum number value= 3/2


This NMR phenomenon is due to the fact that nuclei, placed in a strong external magnetic field, can resonate with externally applied electro magnetic radiations in the radio frequency range of the electro magnetic spectrum. Such of those nuclei which have nuclear magnetic moments are the candidates which can be detected by this resonance phenomenon. The frequency of the electro magnetic radiation at which the resonance can occur is governed by a specific equation which relates the frequency to the strength of the external magnetic field.


IsotopeSpin

NaturalAbundance (%)

SensitivityNMR Frequency (MHz) at Field (T) 7.0483

S.NoRelative Absolute

27 Al 5/2 100 0.21 0.21 78.172 1

35 Cl 3/2 75.53 4.70x10-3 3.55x10-3 29.395 2

37 Cl 3/2 24.47 2.71 x10-3 6.63 x10-4 24.467 3

50 V 6 0.24 5.55 x10-2 1.33 x10-4 29.911 4

51 V 7/2 99.76 0.38 0.38 78.864 5

53 Cr 3/2 9.55 9.03 x10-4 8.62 x10-3 16.956 6

55 Mn 5/2 100 0.18 0.18 73.993 7

57 Fe 1/2 2.19 3.37 x10-5 7.38 x10-7 9.693 8

59 Co 7/2 100 0.28 0.28 70.842 9

61 Ni 3/2 1.19 3.57 x10-3 4.25 x10-5 26.808 10

63 Cu 3/2 69.09 9.31 x10-2 6.43 x10-2 79.515 11

65 Cu 3/2 30.91 0.11 3.52 x10-2 85.183 12

75 As 3/2 100 2.51 x10-2 2.51 x10-2 51.380 13

95 Mo 5/2 15.72 3.23 x10-3 5.07 x10-4 19.544 14

97 Mo 5/2 9.46 3.43 x10-3 3.24 x10-4 19.957 15

107

Ag 1/2 51.82 6.62 x10-5 3.43 x10-5 12.139 16

109

Ag 1/2 48.18 1.01 x10-4 4.86 x10-5 13.956 17

111

Cd 1/2 12.75 9.54 x10-3 1.21 x10-3 63.616 18

113

Cd 1/2 12.26 1.09 x10-2 1.33 x10-3 66.548 19

169

Tm 1/2 100 5.66 x10-4 5.66 x10-4 24.814 20

199

Hg 1/2 16.84 5.67 x10-3 9.54 x10-4 53.481 21

201

Hg 3/2 13.22 1.44 x10-3 1.90 x10-4 19.799 22

203

Tl 1/2 29.5 0.18 5.51 x10-2 171.448 23

205

Tl 1/2 70.5 0.19 0.13 173.448 24

207

Pb 1/2 22.6 9.16 x10-2 2.07 x10-3 62.765 25

235

U 7/2 0.72 1.21 x10-4 8.71 x10-7 5.371 26

Long term exposure to cadmium is associated with renal dysfunction. Cadmium is bio-persistent and once absorbed remains resident for many years. High exposure can lead to obstructive lung diseases and has been linked to lung cancer. Cadmium may also cause bone defects in humans and animals. The average daily intake for humans is estimated as 0.15µg from air and 1µg from water;

High doses of copper can cause anemia, liver and kidney damage, and stomach and intestinal irritation. People with Wilson's disease are at greater risk for health effects from

overexposure to copper;

Exposure to lead can lead to a wide range of biological defects in human depending on duration and level of exposure. The developing foetus and infants are far more sensitive than adults. High exposure can cause problems in the synthesis of hemoglobin’s, damage to the kidneys, gastrointestinal tract, joints, reproductive system and the nervous system. Studies have suggested that exposure to lead can cause up to a loss of 2 IQ points;

Low exposure to chromium can irritate the skin and cause ulceration. Long term exposure can cause kidney and liver damage. It can also cause damage to circulatory and nerve tissues;

Inorganic mercury poisoning is associated with tremors, gingivitis and/or minor psychological changes together with spontaneous abortion and congenital malformation. Mono-methyl-mercury causes damage to the brain and the central nervous system while fetal and post-natal exposure have given rise to abortion, congenital malformation and development changes in young children;

Excessive amounts of nickel can be mildly toxic. Long term exposure can cause decreased body weight, heart and liver damage and skin irritation;

Exposure to high levels of arsenic can cause death. All types of arsenic exposure can cause kidney and liver damage and in the most severe exposure there is erythrocyte hemolytic;

Manganese is known to block calcium channels and with chronic exposure results in CNS dopamine depletion. This duplicates almost all of the symptom logy of Parkinson's Disease.

aluminium toxicity is associated with the development of bone disorders including fractures, osteopenia and osteomalacia


1cc of water contains proton spins of the order of 10 exponentiated to 22 spins and the actual sample of water in the detectable region of nmr-probe would contain about 10 exponentiated to 21 spins corresponding to 100 microliter of water solvent. A typical spectrometer of the 300MHz frequency can detect conveniently a spin count of 10 exponentaited to 18 which amounts to volumes in a few ‘microliter’ ranges. But the present generation of Spectrometers at as much high field as corresponding to 900MHz can be sensitive enough detect 10 exponentiated to 11 spins which in terms of sample volume in the ‘pico liter’ range.

Pico liter water would be corresponding to nano grams scale of sample.If the atomic weight is about 100gms (water is typically 18 gms mol.wt)Then 1023 spins would weigh 100 gms.

If the sensitivity for protons is 1011 spins, the heavy elements whose sensitivity is 10-4 times that of protons, would be requiring 1015 spins to be detectable.

If the trace elements are in ppm levels in the medium, then 1021 molecules containing solution would have this ppm level for 1015 spins in the medium. If molecular weights are on the average of the order of 300gms, 1021 molecules can be contained in 0.01 moles which means the sample concentration must be 0.01 moles per 100 micro liter or 0.0001 liter. This would mean the original solution must be a 10 Molar solution.

For sensitivity of the order of 10-2 , a 0.1 Molar solubility would be necessary.http://www.angelfire.com/art3/saravamudhan/seminar_usic.html

CRITERIA FOR THE DIRECT DETECTION OF HEAVY ELEMENTS

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