Arsenate

Arsenate

Names
IUPAC name arsorate
Identifiers
CAS Number	12523-21-6
3D model (Jmol)	Interactive image
ChemSpider	25498
PubChem	27401
InChI InChI=1S/AsH3O4/c2-1(3,4)5/h(H3,2,3,4,5)/p-3 Key: DJHGAFSJWGLOIV-UHFFFAOYSA-K InChI=1/AsH3O4/c2-1(3,4)5/h(H3,2,3,4,5)/p-3 Key: DJHGAFSJWGLOIV-DFZHHIFOAQ
SMILES [O-][As](=O)([O-])[O-]
Properties
Chemical formula	AsO3− 4
Molar mass	138.919
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

The arsenate ion is AsO3−
4. An arsenate (compound) is any compound that contains this ion. Arsenates are salts or esters of arsenic acid. The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As(V). Arsenate resembles phosphate in many respects, since arsenic and phosphorus occur in the same group (column) of the periodic table. Arsenates are moderate oxidizers, with an electrode potential of +0.56 V for reduction to arsenites.

Occurrence

Arsenates occur naturally in a variety of minerals. Those minerals may contain hydrated or anhydrous arsenates. Unlike phosphates, arsenates are not lost from a mineral during weathering. Examples of arsenate-containing minerals include adamite, alarsite, annabergite, erythrite and legrandite.^[1]

Ions

• In strongly acidic conditions it exists as arsenic acid, H₃AsO₄;
• in weakly acidic conditions it exists as dihydrogen arsenate ion, H
  2AsO−
  4;
• in weakly basic conditions it exists as hydrogen arsenate ion HAsO2−
  4;
• and finally, in strongly basic conditions, it exists as the arsenate ion AsO3−
  4.

Arsenate poisoning

Arsenate can replace inorganic phosphate in the step of glycolysis that produces 1,3-bisphosphoglycerate from glyceraldehyde 3-phosphate. This yields 1-arseno-3-phosphoglycerate instead, which is unstable and quickly hydrolyzes, forming the next intermediate in the pathway, 3-phosphoglycerate. Therefore glycolysis proceeds, but the ATP molecule that would be generated from 1,3-bisphosphoglycerate is lost – arsenate is an uncoupler of glycolysis, explaining its toxicity.^[2]

As with other arsenic compounds, arsenate can also inhibit the conversion of pyruvate into acetyl-CoA, blocking the Krebs cycle and therefore resulting in further loss of ATP.^[3]

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.^[4]

In 2010, a team at NASA's Astrobiology Institute cultured samples of arsenic-resistant GFAJ-1 bacteria from Mono Lake, using a medium high in arsenate and low in phosphate concentration. The findings suggest that the bacteria may partially incorporate arsenate in place of phosphate in some biomolecules, including DNA,^[5][6] However, these claims were immediately debated and critiqued in correspondence to the original journal of publication,^[7] and have since come to be widely disbelieved.^[8] Reports refuting the most significant aspects of the original results have been published in the journal of the original research in 2012, including by researchers from the University of British Columbia and Princeton University.^[9][10] Following the publication of the articles challenging the conclusions of the original Science article first describing GFAJ-1 it was argued that the original article should be retracted because of misrepesentation of critical data.^[11]

See also

• Category:Arsenates

References

1. Mineralienatlas - Mineralklasse Phosphate, Arsenate, Vanadate. (German)
2. Hughes, Michael F. (2002). "Arsenic toxicity and potential mechanisms of action" (PDF). Toxicology Letters (133): 4.
3. Kim Gehle; Selene Chou; William S. Beckett (2009-10-01), Arsenic Toxicity Case Study, Agency for Toxic Substances and Disease Registry
4. "Arsenic-loving bacteria rewrite photosynthesis rules", Chemistry World, 15 August 2008
5. "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus". Wolfe-Simon F., Blum J.S., Kulp T.R., Gordon G.W., Hoeft S.E., Pett-Ridge J., Stolz J.F., Webb S.M., Weber P.K., Davies P.C.W., Anbar A.D., Oremland R.S. Science Express. 2 December 2010.
6. "NASA Finds New Arsenic-Based Life Form in California", Wired Science, 2 December 2010
7. Wolfe-Simon, F., Blum, J.S., Kulp, T.R., Gordon, G.W., Hoeft, S.E., Pett-Ridge, J., Stolz, J.F., Webb, S.M., Weber, P.K., Davies, P.C.W., Anbar, A.D. & Oremland, R.S. Response to Comments on "A Bacterium That Can Grow Using Arsenic Instead of Phosphorus", Science, 27 May 2011, and references therein. Bibcode 2011Sci...332.1149W. doi:10.1126/science.1202098. Accessed 30 May 2011
8. Drahl, C. "The Arsenic-Based-Life Aftermath. Researchers challenge a sensational claim, while others revisit arsenic biochemistry", Chem. Eng. News 90(5), 42–47, 30 January 2012. http://cen.acs.org/articles/90/i5/Arsenic-Based-Life-Aftermath.html; accessed 13 October 2012
9. Science. 8 July 2012. "GFAJ-1 Is an Arsenate-Resistant, Phosphate-Dependent Organism." doi: 10.1126/science.1218455. Accessed 10 July 2012.
10. Science. 8 July 2012. "Absence of Detectable Arsenate in DNA from Arsenate-Grown GFAJ-1 Cells."
11. http://retractionwatch.wordpress.com/2012/07/09/despite-refutation-science-arsenic-life-paper-deserves-retraction-scientist-argues/#comments