Chelation (from Greek χηλή, chelè, meaning claw; pronounced [ˌki:ˈleɪʃən]) is the binding or complexation of a bi- or multidentate ligand. These ligands, which are often organic compounds, are called chelants, chelators, chelating agents, or sequestering agent. The ligand forms a chelate complex with the substrate. The term is reserved for complexes in which the metal ion is bound to two or more atoms of the chelating agent, although the bonds may be any combination of coordination or ionic bonds. Binding can mean: Binding (computer science) - a tie (for example) to certain names in programming languages Binding (knot) - A type of knot Binding (linguistics) - a property relating to anaphors (pronouns and R-expressions) and c-command Bookbinding - the protective cover of a book; and the art of constructing this Ski... Synthesis of copper(II)-tetraphenylporphine, a metal complex, from tetraphenylporphine and copper(II) acetate monohydrate. ... In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. ... Sequestration, the act of removing, separating or seizing anything from the possession of its owner, particularly in law, of the taking possession of property under process of law for the benefit of creditors or the state. ... A coordinate covalent bond (also known as dative bond) is a description of covalent bonding in many kinds of compounds. ... Sodium and chlorine bonding ionically to form sodium chloride. ...

Metal-EDTA chelate

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... EDTA is a widely-used acronym for the chemical compound ethylenediamine tetraacetic acid (and many other names, see table). ...

History

The term chelate was first applied in 1920 by Sir Gilbert T. Morgan and H. D. K. Drew, who stated: "The adjective chelate, derived from the great claw or chele (Greek) 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."^[1] Year 1920 (MCMXX) was a leap year starting on Thursday (link will display 1920) of the Gregorian calendar. ... Subfamilies and Genera Neophoberinae Acanthacaris Thymopinae Nephropsis Nephropides Thymops Thymopsis Nephropinae Homarus Nephrops Homarinus Metanephrops Eunephrops Thymopides Clawed lobsters comprise a family (Nephropidae, sometimes also Homaridae) of large marine crustaceans. ... Heterocyclic compounds are substances which contain a ring structure as found in benzene and the aromatic compounds, or aromatic hydrocarbons, but in which other atoms than carbon, such as sulfur, oxygen or nitrogen are found as part of the ring. ...

General

Relative to the aqua complexes, e.g. [M(H₂O)₆]²⁺, 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. Synthesis of copper(II)-tetraphenylporphine, a metal complex, from tetraphenylporphine and copper(II) acetate monohydrate. ... EDTA is a widely-used acronym for the chemical compound ethylenediamine tetraacetic acid (and many other names, see table). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... For other uses, see Ammonia (disambiguation). ... For other uses of the term entropy, see Entropy (disambiguation) The thermodynamic entropy S, often simply called the entropy in the context of thermodynamics, is a measure of the amount of energy in a physical system that cannot be used to do work. ...

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 siderophores secreted by microorganisms. Histidine, malate and phytochelatin are typical chelators used by plants to avoid having poisonous metal ions in a free form.^[2][3][4] Structure of porphine, the simplest porphyrin. ... Structure of hemoglobin. ... Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. ... For other uses, see Iron (disambiguation). ... A Siderophore (Greek for iron carrier) is an iron chelating compound secreted by microorganisms. ... A cluster of Escherichia coli bacteria magnified 10,000 times. ... Histidine is one of the 20 most common natural amino acids present in proteins. ... Malate (O−OC-CH2-CH(OH)-COO−) is the ionized form of malic acid. ... Chemical structure of phytochelatin. ...

In geology

In earth science, chemical weathering is attributed to organic chelating agents, e.g. peptides and sugars, that have the ability to solubilize the metal ions in minerals and rocks.^[5] Most metal complexes in the environment and in nature are bound in some form of chelate ring, e.g. with "humic acid" 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.^[6] Weathering is the decomposition of rocks, soils and their minerals through direct contact with the Earths atmosphere. ... Peptides (from the Greek πεπτος, digestible), are the family of short molecules formed from the linking, in a defined order, of various α-amino acids. ... This article is about sugar as food and as an important and widely traded commodity. ... Humic acid is one of the major components of humic substances which are dark brown and major constituents of soil organic matter humus that contributes to soil chemical and physical quality and are also precursors of some fossil fuels. ... For alternative meanings see metal (disambiguation). ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland For the American hard rock band, see SOiL. For the System of a Down song, see Soil (song). ... For alternative meanings see metal (disambiguation). ... u fuck in ua ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... For other uses, see Heavy metal (disambiguation). ... Bioremediation can be defined as any process that uses microorganisms, fungi, green plants or their enzymes to return the environment altered by contaminants to its original condition. ...

Uses

Chelators are used in chemical analysis, as water softeners, and are ingredients in many commercial products such as shampoos and food preservatives. 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. Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. ... A water softener reduces calcium or magnesium concentration in hard water. ... A shampoo is a traditional Indian and Persian body massage given after pouring warm water over the body and rubbing it with extracts from herbs. ... This article does not cite any references or sources. ... EDTA is a widely-used acronym for the chemical compound ethylenediamine tetraacetic acid (and many other names, see table). ...

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 poisonous metal agents such as mercury, arsenic, and lead by converting them to a chemically inert form that can be excreted without further interaction with the body. Chelation is also used as a scientifically treatment for autism or other conditions. There are no published peer review publications regarding the efficacy of chelation agents for the treatment of autism.^[7] Staphylococcus aureus - Antibiotics test plate. ... This article does not cite any references or sources. ... Tetracycline (INN) (IPA: ) is a broad-spectrum antibiotic produced by the streptomyces bacterium, indicated for use against many bacterial infections. ... For other uses, see Calcium (disambiguation). ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... Chelation therapy is the administration of chelating agents to remove heavy metals from the body. ... For other uses, see Poison (disambiguation). ... It has been suggested that Acrodynia be merged into this article or section. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... This article is about the metal. ... It has been suggested that this article or section be merged with Biomedical intervention for autism. ... Autism is a brain development disorder characterized by impairments in social interaction and communication, and restricted and repetitive behavior, all exhibited before a child is three years old. ...

EDTA chelation can be a dangerous practice, especially when Na₂EDTA is prescribed rather than CaEDTA. The CDC reports that use of Na₂EDTA has resulted in fatalities due to hypocalcemia.^[8] In medicine, hypocalcaemia is the presence of less than a total calcium of 2. ...

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

• Bioremediation
• Chelation therapy
• Electron counting

Bioremediation can be defined as any process that uses microorganisms, fungi, green plants or their enzymes to return the environment altered by contaminants to its original condition. ... Chelation therapy is the administration of chelating agents to remove heavy metals from the body. ... Electron counting is a formalism used for classifying compounds and for explaining or predicting electronic structure and bonding. ...

References cited

1. ^ J. Chem. Soc., 1920, 117, 1456
2. ^ U Krämer, J D Cotter-Howells, J M Charnock, A H J M Baker, J A C Smith (1996). "Free histidine as a metal chelator in plants that accumulate nickel". Nature 379. 
3. ^ Jurandir Vieira Magalhaes (2006). "Aluminum tolerance genes are conserved between monocots and dicots". Proc Natl Acad Sci U S A 103 (26). 
4. ^ Suk-Bong Ha, Aaron P. Smith, Ross Howden, Wendy M. Dietrich, Sarah Bugg, Matthew J. O'Connell, Peter B. Goldsbrough, and Christopher S. Cobbett (1999). "Phytochelatin synthase genes from arabidopsis and the yeast Schizosaccharomyces pombe". Plant Cell 11. 
5. ^ Dr. Michael Pidwirny, University of British Columbia Okanagan, http://www.physicalgeography.net/fundamentals/10r.html
6. ^ Prasad (ed). Metals in the Environment. University of Hyderabad. Dekker, New York, 2001
7. ^ Doja A, Roberts W (2006). "Immunizations and autism: a review of the literature". Can J Neurol Sci 33 (4): 341–46. PMID 17168158. 
8. ^ U.S. Centers for Disease Control, "Deaths Associated with Hypocalcemia from Chelation Therapy" (March 3, 2006), http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5508a3.htm