Arsenite

In chemistry an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3. Examples of arsenites include sodium arsenite which contains a polymeric linear anion, [AsO₂⁻]_n, and silver arsenite, Ag₃AsO₃, which contains the trigonal, As O₃³⁻ anion.
The different forms of the anion are the next ones:

ortho-arsenite^[1]
: AsO₃^3-
meta-arsenite: AsO₂^-

Arsenite contrasts to the corresponding anions of the lighter members of group 15, phosphite which has the structure HPO₃²⁻ and nitrite, NO₂⁻ which is bent.^[1] Sodium arsenite is used in the water gas shift reaction to remove carbon dioxide. Arsenites are salts of arsenious acid.

Note that in fields that commonly deal with groundwater chemistry, arsenite commonly refers to As₂O₃, the acid anhydride of arsenious acid. Its white odorless crystals are toxic and very soluble in water. It occurs in nature as arsenolite and claudetite, and is also a byproduct of metal smelting. Its main use is in producing chromated copper arsenate (CCA) to treat timber. It is also used for arsenic pesticides, glass production, pharmaceuticals and non-ferrous alloys.

Bacteria using and generating arsenate

Some species of bacteria obtain their energy by oxidizing various fuels while reducing arsenates to form arsenites. The enzymes involved are known as arsenate reductases.

In 2008, bacteria were discovered that employ a version of photosynthesis with arsenites as electron donors, producing arsenates (just like ordinary photosynthesis uses water as electron donor, producing molecular oxygen). The researchers conjectured that historically these photosynthesizing organisms produced the arsenates that allowed the arsenate-reducing bacteria to thrive.^[2]

In humans, arsenite inhibits pyruvate dehydrogenase (PDH complex) in the pyruvate acetyl CoA reaction, and binds to the SH group of lipoamide, a participant coenzyme. In this inhibition, arsenite poisoning affects energy production in the body.

References

^ ^a ^b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
^ Arsenic-loving bacteria rewrite photosynthesis rules, Chemistry World, 15 August 2008

External links

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[Greenwood-1] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[2] Arsenic-loving bacteria rewrite photosynthesis rules, Chemistry World, 15 August 2008

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