Selenate and Arsenate

A facultative autotroph (lithotroph) strain MLHE-1 was able to oxidize arsenite under anaerobic conditions to arsenate using nitrate as electron acceptor (Oremland et al. 2002). 

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OxYANioNs Nitrate, Sulfate, Chlorate, Selenate, and Arsenate Nitrate and Related Compounds... 

Arsenite is also an intermediate in the fungal biomethylation of arsenic (Bentley and Chasteen 2002) and oxidation to the less toxic arsenate can be accomplished by heterotrophic bacteria including Alcaligenes faecalis. Exceptionally, arsenite can serve as electron donor for chemolithotrophic growth of an organism designated NT-26 (Santini et al. 2000), and both selenate and arsenate can be involved in dissimilation reactions as alternative electron acceptors. 

Waychunas, G.A. fuller, C.C. Davis, J.A. Big-ham, J.M. Schwertmann, U. (1995a) EX-AFS and simulation study of selenate and arsenate anion positions in coprecipitated schwertmannites. Abstract Amer. Geophys. Union... 

A much broader range of substrates is amenable to reduction by oxo-Mo(fV) complexes (equation 11). These include many biological substrates such as S- and A-oxides and nitrate, and species related to selenate and arsenate. These reactions are also first order in both the substrate and metal complex they are proposed to proceed by associative mechanisms involving coordination of substrate to Mo and concomitant OAT. A thermodynamic scale for OAT reactions has been described by Holm and Donahue. ... 

Oremland, R., and Stolz, J. (2000). Dissimilatory reduction of selenate and arsenate in nature. In Environmental Microbe-Metal Interactions,ed. Lovley, D. R., ASM Press, Washington, DC, 199-224. 

R. G. Gerritse and J, A. Adeney, Rapid determination in water of chloride, sulfate, sulfite, selenite, selenate, and arsenate among other inorganic and organic solutes by ion chromatography with UV detection below 195 nra,/ Chromatogr., 347,419,1985. 

Borates, molybdates, selenates, and arsenates occur in such trace quantities in soils that they probably exist only as impurities in major soil particles and on particle surfaces rather than as separate minerals. Soils in humid regions sometimes benefit from borate and, less often, molybdate additions. The range between deficient and excess is narrow, so spreading a few kg ha-1 (a few Ibs/acre) uniformly over the soil is difficult unless the borate and molybdate salts are mixed in with other fertilizers or inert materials. 

In comparative studies with C. humicola (90), Cox and Alexander reported that phosphate will inhibit (CH3)3As formation from arsenite, arsenate, or methylarsonate but not from cacodylate. Selenite, selenate, and... 

Cellulose is insol in w, ale, eth all known simple org solvs. The best solv for it is cuprammonium hydroxide, [Cu(NH3)4(OH)2], also called Schweitzer s Reagent. It is also sol in a coned soln of Ca thiocyanate alone or in combination with formaldehyde. Other solvs gelatinizers for cellulose include zinc chloride (in 40% soln on heating), basic beryllium perchlorate, 84% phosphoric acid, selenic acid, arsenic acid, sulfurous acid, 66% HBr, 70-75% HF, coned HI, chloral with pyridine, chloral hydrate in H2S04, and inorg salts(such as NaCl) in coned solns at high temps. Coned solns of NaOH at ca -10° only partially dissolve cellulose while the remainder is swelled "mercerized . 

Write formulas for (a) magnesium arsenate, (b) calcium selenate, and (c) acetic acid. 

Fe anchored amino-functionalized MCM-41 effectively adsorbs toxic oxyanions, arsenate, chromate, selenate and molybdate, in the aqueous solution. These adsorbents show ones of the largest adsorption capacities reported in the literature. The molar ratio, oxyanion / Fe, is 2.8, 1.8, 1.5 and 2.3, respectively. They are consistent with the coordination mmibers in the EXAFS structural analysis of adsorption complexes. Cr-Fe adsorption centre is uniform, where 2 1 complex is uniformly generated. On the contraiy, chloride ion remains in As- and Se-Fe complexes and two kinds of coordination with different bonding distances were found in As- and Mo-Fe complexes. 

Selenate and tellurate also are potent inhibitors of methane formation, and we postulate that these compounds are reduced and methylated in a manner similar to that of arsenate. 

It has been agreed for some time that several anions sorb along the double octahedral chains of goethite by bonding two singly coordinated A-type OH groups [41]. They therefore form binuclear, bidentate, inner-sphere complexes. There has been some controversy about some of the other oxy-anions but Manceau and Charlet [42] recently concluded that a similar structure occurs for selenate and sulfate in addition to phosphate, arsenate and selenite. 

The bio-availabilities of these elements through the gastrointestinal tract vary markedly. Molybdenum, iodine, fluorine, and arsenic are apparently highly bio-available, whereas medium uptake occurs with haem iron, cobalt, zinc, chromium in the presence of a glucose tolerance factor, selenium, either as selenate or as organo selenium compounds, whereas only low bio-availability is experienced with non-haem iron,... 

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