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In chemistry, an arsenite is a chemical compound containing an arsenic oxyanion where arsenic has oxidation state +3. Note that in fields that commonly deal with groundwater chemistry, arsenite is used generically to identify soluble AsIII anions. IUPAC have recommended that arsenite compounds are to be named as arsenate(III), for example ortho-arsenite is called trioxidoarsenate(III). Ortho-arsenite contrasts to the corresponding anions of the lighter members of group 15, phosphite which has the structure and nitrite, which is bent.
A number of different arsenite anions are known:
In all of these the geometry around the AsIII centers are approximately trigonal, the lone pair on the arsenic atom is stereochemically active. Well known examples of arsenites include sodium arsenite which contains a polymeric linear anion, , and silver ortho-arsenite, , which contains the trigonal anion.
Arsenic in its trioxide, As2O3, (brand name Trisenox, ATO) is used as a chemotherapy drug against acute promyelocytic leukaemia (APL), a type of myeloid leukemia. The detailed mechanism of action is unknown, but it is suspected to speed up apoptosis of cancer cells. Arsenic trioxide triggers morphological changes and DNA fragmentations in NB4 in vitro model for APL. It also degrades retinoic acid receptor alpha (RARA). RARA gene is important regulator of premyelocytic immune cell development, differentiation, and apoptosis.
In 2008, bacteria were discovered that employ a version of photosynthesis with arsenites as , 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. "Arsenic-loving bacteria rewrite photosynthesis rules", Chemistry World, 15 August 2008
In humans, arsenite inhibits pyruvate dehydrogenase (PDH complex) in the pyruvate-acetyl CoA reaction, by binding to the Thiol group of lipoamide, a participant coenzyme. It also inhibits the oxoglutarate dehydrogenase complex by the same mechanism. The inhibition of these enzymes disrupts energy production.
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