Explain the application of chelating agents especially in forensic science with suitable examples?
Solution: Chelating Agents: are the substances which act on absorbed metallic poisons. They have greater affinity for metals as compared to endogenous enzymes. The complex of agent and metal is more water soluble than metal itself, resulting in higher renal excretion of the complex. E.g.: British anti-lewisite (B.A.L., dimercaprol), E.D.T.A. (ethylene diamine-acetic acid), Penicillamine (Cuprimine), Desferroxamine etc. Dimercaprol, or British anti-lewisite (BAL), so called because it was developed as an antidote against the chemical warfare agent Lewisite, was found to be an antidote against poisons such as arsenic, gold, lead and mercury, which act on cellular sulphhydryle groups. The antidote is given by an intramuscular injection of the oily solution and acts by virtue of its sulphhydryle groups which competitively bind arsenic. Arsenic is deposited in skin, hair and nails because the keratin found there is rich in sulphhydryle groups. Since occipital head hair grows at an average rate of 1cm per month, analysis of hair cut into 1cm lengths gives an indication of the time-frame of the poisoning and is a technique which can be applied to the living, the freshly dead and exhumed bodies. EDTA is a polyprotic acid containing four carboxylic acid groups and two amine groups with lone-pair electrons that chelate calcium and several other metal ions. Calcium is necessary for a wide range of enzyme reactions of the coagulation cascade and its removal irreversibly prevents blood clotting within the collection tube. Historically, EDTA has been recommended as the anticoagulant of choice for hematological testing because it allows the best preservation of cellular components and morphology of blood cells. The remarkable expansion in laboratory test volume and complexity over recent decades has amplified the potential spectrum of applications for this anticoagulant, which can be used to stabilize blood for a variety of traditional and innovative tests. Specific data on the behavior of EDTA as an anticoagulant in hematology, including possible pitfalls, are presented. The use of EDTA for measuring cytokines, protein and peptides, and cardiac markers is described, with an outline of the protection of labile molecules provided by this anticoagulant.
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