chelating agent

Examples of chelating agent in the following topics:

• Chelating Agents

  • Usually these ligands are organic compounds and are called chelants, chelators, chelating agents, or sequestering agents; the resulting complexes are called chelate compounds.
  • Chelation therapy is 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.
  • Such chelating agents include the porphyrin rings in hemoglobin and chlorophyll.
  • Enterobactin, produced by E. coli, is the strongest chelating agent known.
  • Ethylenediamine serves as a chelating agent by binding via its two nitrogen atoms.

• Iron Overload and Tissue Damage

  • For those unable to tolerate routine blood draws, there is a chelating agent available for use.
  • Two newer iron chelating drugs that are licensed for use in patients receiving regular blood transfusions to treat thalassaemia (and, thus, who develop iron overload as a result) are deferasirox and deferiprone.

• Gram-Positive Cell Envelope

  • The functions of teichoic acid are not fully known but it is believed to serve as a chelating agent and means of adherence for the bacteria.

• Siderophores

  • Therefore, siderophores are chelating agents that bind the iron ions.

• Coordination Number, Ligands, and Geometries

  • Ligands that bind via more than one atom are often termed polydentate or chelating.
  • Chelating ligands are commonly formed by linking donor groups via organic linkers.
  • A classic example of a polydentate ligand is the hexadentate chelating agent EDTA, which is able to bond through six sites, completely surrounding some metals.

• Siderophores

  • Siderophores are classified by which ligands they use to chelate the ferric iron, including the catecholates, hydroxamates, and carboxylates.
  • Siderophores are small, high-affinity iron chelating compounds secreted by microorganisms such as bacteria, fungi, and grasses.
  • Siderophores are amongst the strongest soluble Fe3+ binding agents known.
  • Because of this property, they have attracted interest from medical science in metal chelation therapy, with the siderophore desferrioxamine B gaining widespread use in treatments for iron poisoning and thalassemia.
  • Siderophores are usually classified by the ligands used to chelate the ferric iron.

• Reactions of Coordination Compounds

  • In chemistry, a coordination or metal complex consists of an atom or ion (usually metallic) and a surrounding array of bound molecules or anions known as ligands or complexing agents.
  • These complexes are called chelate complexes, the formation of which is called chelation, complexation, and coordination.

• Purifying Proteins by Affinity Tag

  • Often these tags are removable by chemical agents or by enzymatic means, such as proteolysis or intein splicing.
  • Some affinity tags have a dual role as a solubilization agent, such as MBP and GST.
  • His-tag, 5-10 histidines bound by a nickel or cobalt chelate (HHHHHH)

• Models for Addition to Acyclic Substrates

  • The silyl ether derivative in example 9 is a case of steric hindrance to chelation.
  • The chelation model leads to a similar prediction.
  • A further test of this rationalization is provided by removing the chelating metal species.
  • The absence of a chelating metal combined with the bulk of the hydride donor results in a >95 %de, despite the replacement of chlorine by the much stronger chelating ligands (CH3)2N- and CH3CO2-.
  • An interesting example in which steric effects and chelation are eliminated is shown at the bottom of the preceding diagram.

• Enantioselective Aldol Reactions

  • Although the enolborinate by itself might be expected to exist in a chelated form, with two B–O bonds, the aldol reaction requires a reorganization of this chelation in order to activate the aldehyde carbonyl group for nucleophilic addition.
  • As shown by the formula in brackets, the free oxazolidinone ring has rotated 180º from its chelated position in order to minimize dipole repulsion.
  • If the auxiliary remains chelated to the enolate during the aldol reaction the stereochemical outcome is changed.
  • In the upper equation a chelated Z-titanium enolate is initially formed and then reacted with an aldehyde.
  • The change in selectivity relative to the siloxy substituent is due to its chelation effect in the lithium enolate and non-chelated polar effect in the boron enolate.