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Information about Chelating Agent

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.

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]

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.

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.

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.[2] 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.[3]

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.

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 unverified treatment for autism or other conditions. There are no published peer review publications regarding the efficacy of chelation agents for the treatment of autism.[4]

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.[5]

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

1. ^ J. Chem. Soc., 1920, 117, 1456
2. ^ Dr. Michael Pidwirny, University of British Columbia Okanagan, [1]
3. ^ Prasad (ed). Metals in the Environment. University of Hyderabad. Dekker, New York, 2001
4. ^ Doja A, Roberts W (2006). "Immunizations and autism: a review of the literature". Can J Neurol Sci 33 (4): 341–46. PMID 17168158. 
5. ^ U.S. Centers for Disease Control, "Deaths Associated with Hypocalcemia from Chelation Therapy" (March 3, 2006), [2]
Greek}}} 
Writing system: Greek alphabet 
Official status
Official language of:  Greece
 Cyprus
 European Union
recognised as minority language in parts of:
 European Union
 Italy
 Turkey
Regulated by:
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Binding may refer to:
  • Ski binding, a device for connecting a foot to a ski
  • Snowboard binding, a device for connecting a foot to a snowboard
  • Bookbinding, the protective cover of a book and the art of constructing this

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complex in chemistry usually is used to describe molecules or ensembles formed by the combination of ligands and metal ions. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds.
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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
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organic compounds]] An organic compound is any member of a large class of chemical compounds whose molecules contain carbon; for historical reasons discussed below, a few types of compounds such as carbonates, carbon oxides and cyanides, as well as elemental carbon are
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The term sequestration can have different meanings according to the context.
  • Sequestration (law), the act of seizing property from the owner under process of law for the benefit of creditors or the state

Biochemistry


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coordinate covalent bond (also known as dative bond) is a description of covalent bonding between two atoms in which both electrons shared in the bond come from the same atom.
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ionic bond (or electrovalent bond) is a type of chemical bond based on electrostatic forces between two oppositely-charged ions. In ionic bond formation, a metal donates an electron, due to a low electronegativity, to form a positive ion or cation.
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19th century - 20th century - 21st century
1890s  1900s  1910s  - 1920s -  1930s  1940s  1950s
1917 1918 1919 - 1920 - 1921 1922 1923

Year 1920 (MCMXX
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Greek}}} 
Writing system: Greek alphabet 
Official status
Official language of:  Greece
 Cyprus
 European Union
recognised as minority language in parts of:
 European Union
 Italy
 Turkey
Regulated by:
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Nephropidae
Dana, 1852

Subfamilies and Genera
  • Neophoberinae
  • Acanthacaris
  • Thymopinae
  • Nephropsis

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Heterocyclic compounds are organic compounds that contain a ring structure containing atoms in addition to carbon, such as sulfur, oxygen or nitrogen, as part of the ring. They may be either simple aromatic rings or non-aromatic rings.
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complex in chemistry usually is used to describe molecules or ensembles formed by the combination of ligands and metal ions. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds.
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Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of the planet as a precursor to foodstuffs and fertilizers.
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Ice melting - a classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice.
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porphyrin is a heterocyclic macrocycle derived from four pyrrole-like subunits interconnected via their α carbon atoms via methine bridges (=CH-). The macrocycle, therefore, is a highly conjugated system, and is consequently deeply coloured—the name porphyrin
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Hemoglobin, also spelled haemoglobin and abbreviated Hb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of the blood in vertebrates and other animals.
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Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from ancient Greek: chloros = green and phyllon = leaf.
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3, 4, 6
(amphoteric oxide)
Electronegativity 1.83 (Pauling scale)
Ionization energies
(more) 1st: 762.5 kJmol−1
2nd: 1561.9 kJmol−1
3rd: 2957 kJmol−1

Atomic radius 140 pm
Atomic radius (calc.
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A Siderophore (Greek for iron carrier) is an iron chelating compound secreted by microorganisms. Iron Fe3+ ions have a very low solubility at neutral pH and therefore cannot be utilized by organisms.
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microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of microorganisms is called microbiology.
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Weathering is the decomposition of rocks, soils and their minerals through direct contact with the Earth's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not to be confused with erosion, which involves the movement and disintegration of rocks
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Peptides (from the Greek πεπτίδια, "small digestibles") are short polymers formed from the linking, in a defined order, of α-amino acids.
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Sugars, brown
Nutritional value per 100 g (3.5 oz)
Energy 0 kcal   0 kJ

Carbohydrates     97.33 g
- Sugars  96.21 g
- Dietary fiber  0 g  
Fat 0 g
Protein 0 g
Water 1.77 g
Thiamin (Vit. B1)  0.
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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.
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The Macro Expansion Template Attribute Language complements TAL, providing macros which allow the reuse of code across template files. Both were created for Zope but are used in other Python projects as well.
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SOiL is a five-piece Hard Rock band from Chicago, Illinois, United States. They formed in 1997 and are still active. They are signed to DRT Entertainment and have released four albums, their most recent being True Self which was released in March 27 2006.
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The Macro Expansion Template Attribute Language complements TAL, providing macros which allow the reuse of code across template files. Both were created for Zope but are used in other Python projects as well.
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Plantae
Haeckel, 1866[1]

Divisions

Green algae
  • Chlorophyta
  • Charophyta
Land plants (embryophytes)
  • Non-vascular land plants (bryophytes)

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