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In chemistry, an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3. Note that in fields that commonly deal with groundwater chemistry, arsenite is used generically to identify soluble As^III anions. IUPAC have recommended that arsenite compounds are to be named as arsenate(III), for example ortho-arsenatite is called trioxidoarsenate(III). Ortho-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]

A number of different arsenite anions are known:

AsO₃³⁻ ortho-arsenite, an ion of arsenous acid, with a pyramidal shape^[1]
[AsO₂⁻]_n meta-arsenite, a polymeric chain anion.^[2]
As₂O₅⁴⁻ pyro-arsenite, O₂As-O-AsO₂
As₃O₇⁵⁻ a polyarsenite, [O₂As-O-As(O)-O-AsO₂]^[3]
As₄O₉⁶⁻ a polyarsenite, [O₂As-O-As(O)-O-As(O)-O-AsO₂]^[3]
[As₆O₁₁⁴⁻]_n, a polymeric anion

In all of these the geometry around the As^III centers are approximately trigonal, the lone pair on the arsenic atom is stereochemically active.^[1] Well known examples of arsenites include sodium meta-arsenite which contains a polymeric linear anion, [AsO₂⁻]_n, and silver ortho-arsenite, Ag₃AsO₃, which contains the trigonal, AsO₃³⁻ anion.

Preparation of arsenites

Some arsenite salts can be prepared from an aqueous solution of As₂O₃. Examples of these are the meta-arsenite salts and at low temperature, hydrogen arsenite salts can be prepared, such as Na₂(H₂As₄O8), NaAsO₂·4H₂O, Na₂(HAsO₃)·5 H₂O and Na₅(HAsO₃)(AsO₃)·12H₂O ^[4]

Arsenite minerals

A number of minerals contain arsenite anions, Reinerite, Zn₃(AsO₃)₂,^[2] Finnemanite, Pb₅Cl(AsO₃)₃,^[2] Paulmooreite, Pb₂As₂O₅,^[2] Stenhuggarite, CaFeSbAs₂O₇, (contains complex polymeric anion),^[2] Schneiderhöhnite, Fe^IIFe^III₃(As₂O₅)₂ AsO₃,^[5] Magnussonite Mn₅(OH)(AsO₃)₃,^[2] Trippkeite, CuAs₂O₄,^[2] Trigonite, Pb₃Mn(AsO₃)₂(HAsO₃),^[2] Tooeleite, Fe₆(AsO₃)₄SO₄(OH)₄·4H₂O ^[6]

Arsenites in the environment

Arsenic can enter groundwater due to naturally occurring arsenic at deeper levels or from mine workings. Arsenic(III) can be removed from water by a number of methods, oxidation of As^III to As^V for example with chlorine followed by coagulation with for example iron(III) sulfate. Other methods include ion-exchange and filtration. Filtration is only effective if arsenic is present as particulates, if the arsenite is in solution it passes though the filtration membrane.^[7]

Uses

Sodium arsenite is used in the water gas shift reaction to remove carbon dioxide. Fowler's solution first introduced in the 18th century was made up from As₂O₃ ^[8] as a solution of potassium meta arsenite, KAsO2.^[9]

Bacteria using and generating arsenite

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.^[10]

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 ^c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
^ ^a ^b ^c ^d ^e ^f ^g ^h Carmalt, C.J & Norman, N.C. (1998). "Chapter 1: Arsenic, antimony and bismuth". In Norman, N.C. Chemistry of Arsenic, Antimony and Bismuth. Blackie Academic and Professional. pp. 118–121. ISBN 07514-0389-X.
^ ^a ^b Hamida, M. Ben; Wickleder, M. S. (2006). "Die neuencatena-Polyarsenite [As3O7]5− und [As4O9]6—". Zeitschrift für anorganische und allgemeine Chemie 632 (12-13): 2109–2109. doi:10.1002/zaac.200670065. ISSN 0044-2313.
^ Sheldrick, W. S.; Häusler, H.-J. (1987). "Zur Kenntnis von Natriumarseniten im Dreistoffsystem Na₂O–As₂O₃–H₂O bei 6°C". Zeitschrift für anorganische und allgemeine Chemie 549 (6): 177–186. doi:10.1002/zaac.19875490618. ISSN 0044-2313.
^ Hawthorne, Frank C. "Schneiderhoehnite, Fe (super 2+) Fe 3 (super 3+) As 5 (super 3+) O 13, a densely packed arsenite structure." The Canadian Mineralogist 23.4 (1985): 675-679.
^ Morin, G.; Rousse, G.; Elkaim, E. (2007). "Crystal structure of tooeleite, Fe6(AsO3)4SO4(OH)4{middle dot}4H2O, a new iron arsenite oxyhydroxy-sulfate mineral relevant to acid mine drainage". American Mineralogist 92 (1): 193–197. doi:10.2138/am.2007.2361. ISSN 0003-004X.
^ EPA, United states Environmental Protection Agency, Report 815R00012, Technologies and Costs for the Removal of Arsenic From Drinking Water, December 2000 http://water.epa.gov/drink/info/arsenic/upload/2005_11_10_arsenic_treatments_and_costs.pdf
^ Managing Arsenic in the Environment: From Soil to Human Health, R. Naidu, Csiro Publishing, 2006, ISBN 9780643068681
^ Jolliffe, D. M. (1993). "A history of the use of arsenicals in man" (pdf). Journal of the Royal Society of Medicine 86 (5): 287–289. PMC 1294007. PMID 8505753.
^ Arsenic-loving bacteria rewrite photosynthesis rules, Chemistry World, 15 August 2008

External links

Case Studies in Environmental Medicine - Arsenic Toxicity
Page at chemicalland21.com

UpToDate Contents

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1. ヒ素曝露と中毒 arsenic exposure and poisoning

English Journal

Single strand DNA functionalized single wall carbon nanotubes as sensitive electrochemical labels for arsenite detection.

Wang Y1, Wang P2, Wang Y2, He X3, Wang K4.
Talanta.Talanta.2015 Aug 15;141:122-7. doi: 10.1016/j.talanta.2015.03.040. Epub 2015 Mar 28.
In this work, a simple and sensitive electrochemical strategy for arsenite detection based on the ability of arsenite bound to single-strand DNA (ssDNA) and the signal transduction of single wall carbon nanotubes (SWCNTs) is developed. To realize this purpose, the ssDNA/SWCNTs complexes were formed
PMID 25966391

Arsenic extraction and speciation in plants: Method comparison and development.

Zhao D1, Li HB1, Xu JY1, Luo J1, Ma LQ2.
The Science of the total environment.Sci Total Environ.2015 Aug 1;523:138-45. doi: 10.1016/j.scitotenv.2015.03.051. Epub 2015 Apr 8.
We compared four methods to extract arsenic (As) from three different plants containing different As levels for As speciation with the goal of developing a more efficient method, i.e., As-hyperaccumulator Pteris vittata at 459-7714mgkg(-1), rice seedling at 53.4-574mgkg(-1), and tobacco leaf at 0.32
PMID 25863504

Akaganeite decorated graphene oxide composite for arsenic adsorption/removal and its proconcentration at ultra-trace level.

Chen ML1, Sun Y1, Huo CB1, Liu C1, Wang JH2.
Chemosphere.Chemosphere.2015 Jul;130:52-8. doi: 10.1016/j.chemosphere.2015.02.046. Epub 2015 Mar 21.
Carboxylic graphene oxide (GO-COOH) is decorated with akaganeite (β-FeOOH) to produce a β-FeOOH@GO-COOH nanocomposite. The nanocomposite acts as an efficient adsorption medium for the uptake of arsenite and arsenate within a wide range of pH 3-10, providing high adsorption capacities of 77.5mgg(-1
PMID 25800270

Japanese Journal

Protective Effects of Phyllanthus Emblica Leaf Extract on Sodium Arsenite-mediated Adverse Effects in Mice

ANWARUL AZIM AKHAND,RASHID ABDUR,OHGAMI NOBUTAKA,KATO MASASHI,AHSAN NAZMUL,SAYED SADIA
Nagoya Journal of Medical Science 77(1-2), 145-153, 2015-02
NAID 120005549560