Unveiling Toxic Heavy Elements with MultiNuclear NMR

1. National Seminar OnToxicity 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 Presentation file : Dr.S.Aravamudhan

2. 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. In a Scheme of an Atom Electrons circulate in Orbits 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 NUCLEUS is stationery at the center Presentation file : Dr.S.Aravamudhan 2

3. 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 Presentation file : Dr.S.Aravamudhan 3

4. When all the extra nuclearelectrons 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 Presentation file : Dr.S.Aravamudhan 4

5. 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. Presentation file : Dr.S.Aravamudhan 5

6. Magnetic moment Magnetic moment SPIN SPIN This unique value of ‘γ’for each element’s nucleus different from every other element is what makes multi nuclear NMR possible These tiny nuclear magnetic moments are similar to the bar magnets which are influenced by Externally applied magnetic fields SpinQuantum number value= 3/2 Illustration is a case of SPIN=3/2results in 4 equally spaced energy levels or The central nucleus of some of the elements posses intrinsic spin and hence also can be associated with a magnetic moment or The value of γdiffers fromone nucleus to the other. or Only Discrete orientations of the spin are possible due to the quantization criteria at atomic regimes 2πν= γH Similar 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. Applied magnetic field Electromagnetic radiation with frequency νcan cause transition between these levels and this is the resonance phenomenon Discrete orientations RESULTS in discrete energy levels Presentation file : Dr.S.Aravamudhan

7. 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. Presentation file : Dr.S.Aravamudhan 7

8. aluminium toxicity is associated with the development of bone disorders including fractures, osteopenia and osteomalacia 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 fromoverexposure to copper; Low exposure to chromiumcan 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; Long term exposure to cadmiumis 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; Manganeseis 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. Exposure to leadcan 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; 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; Inorganic mercurypoisoning 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; Presentation file : Dr.S.Aravamudhan 8

9. CRITERIA FOR THE DIRECT DETECTION OF HEAVY ELEMENTS 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 Presentation file : Dr.S.Aravamudhan 9