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chelate]] HISTORY The term ''chelate'' was first applied in ) of the Lobster or other crustaceans, is suggested for the caliperlike groups which function as two associating units and fasten to the central atom so as to produce Heterocyclic rings."''J. Chem. Soc.'', 1920, ''117'', 1456 GENERAL Relative to the aqua Complexes , e.g. the increased stability of a chelated complex, e.g. [M( EDTA 2- is called the chelate effect. Because chelating agents bind to metals through more than one coordination site, such ligands bind more tenaciously than unidentate ligands (like water). If a chelate were replaced by several monodentate ligands (such as Water or Ammonia ), the total number of molecules would decrease, whereas if several monodentate ligands were replaced by a chelate, the number of free molecules increases. The effect is therefore Entropic in that more sites are used by fewer ligands and this leaves more unbonded molecules: a total increase in the number of molecules in solution and a corresponding increase in entropy. CHELATION IN NATURE Virtually all biochemicals exhibit the ability to dissolve metal cations. Thus proteins, polysaccharides, and polynucleic acids are excellent polydentate ligands for many of the metal ions. In addition to these adventitious chelators, several are produced to specifically bind certain metals. Such chelating agents include the Porphyrin rings in Hemoglobin or Chlorophyll and the Fe3+ -chelating Siderophore s secreted by Microorganism s. In geology In earth science, chemical " or a protein. Thus, metal chelates are relevant to the mobilization of Metals in the Soil , the uptake and the accumulation of Metals into Plants and Micro-organisms . Selective chelation of Heavy Metals is relevant to Bioremediation , e.g. removal of 137Cs from radioactive waste.Prasad (ed). Metals in the Environment. University of Hyderabad. Dekker, New York, 2001 USES Chelators are used in Chemical Analysis , as Water Softener s, and are ingredients in many commercial products such as Shampoos and food Preservative s. A commonly used synthetic chelator is EDTA . The term is used in water treatment programs and specifically in Steam Engineering , to describe a Boiler Water Treatment System : ''Chelant Water Treatment system''. In medicine Antibiotic Drugs of the Tetracycline family are chelators of Ca2+ and Mg2+ ions. Chelation Therapy describes the use of chelating agents to detoxify Poison ous metal agents such as Mercury , Arsenic , and Lead by converting them to a chemically inert form that can be be excreted without further interaction with the body. Chelation is also used as a scientifically unverified Treatment for Autism or other conditions. This is a dangerous practice and has resulted in fatalities.AP story "US doctor sued in death of autistic boy from UK", http://news.lp.findlaw.com/ap/o/51/07-09-2007/8c28000a141344ea.htmlU.S. Centers for Disease Control, "Deaths Associated with Hypocalcemia from Chelation Therapy" (Mar. 3, 2006), http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5508a3.htm There is no scientific support for chelation therapy as a treatment for autism.1 EDTA is also used in root canal treatment as a way to irrigate the canal. EDTA is used as a chelating agent to either soften the dentin facilitating access to the entire canal length and to remove the smear layer formed during instrumentation. SEE ALSO REFERENCES CITED |
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