Pentavalent arsenate

Hua et al. [71] carried out automated determination of total arsenic in seawater by flow constant-current stripping with gold fibre electrodes in which the sample was acidified and pentavalent arsenic was reduced to the trivalent form with iodide. The arsenic was then deposited potentiostatically for 4 min on a 25 xm gold fibre electrode, and subsequently stripped with constant current in 5 M hydrochloric acid. Cleaning and regeneration of the gold electrode were fully automated. 

In REACT, we prepare the calculation by disenabling the redox couple between trivalent and pentavalent arsenic (arsenite and arsenate, respectively). As well, we disenable the couples for ferric iron and cupric copper, since we will not consider either ferrous or cupric species. We load dataset FeOH+.dat , which contains the reactions from the Dzombak and Morel (1990) surface complexation model, including those for which binding constants have only been estimated. The procedure is... 

Hood, R.D., G.C. Vedel-Macrander, M.J. Zaworotko, F.M. Tatum, and R.G. Meeks. 1987. Distribution, metabolism, and fetal uptake of pentavalent arsenic in pregnant mice following oral or intraperitoneal administration. Teratology 35 19-25. 

The antiproliferative effects of arsenic are well documented. In vitro both divalent and pentavalent arsenicals inhibit murine [28] and bovine [18] phytohemaglutinin (PHA)-stimulated lymphoproliferation at concentrations of > 3 pM. Lymph node cells from arsenic treated, FTTC-sensitized mice displayed reduced lymphoproliferation in response to Con A, suggesting that the mechanism of antigen processing/presentation may be altered by arsenic exposure, inhibiting T-cell responsiveness [29], However, in vivo... 

Generally, inorganic arsenic can occur in the environment in several forms but in natural waters and thus in drinking water, it is mostly found as trivalent arsenite or pentavalent arsenate. Organic arsenic species, abundant in seafood, are very much less harmful to health and are readily eliminated by the body5. 

Melarsoprol is a divalent arsenical. It reacts with sulfhydryl groups. Melarsoprol is used for the late stage of sleeping sickness. It has to be administered intravenously. Slow i.v. injection is recommended. It is widely distributed and enters the CNS. It has a very short elimination half-life as it is biotransformed to a pentavalent arsenical. Adverse effects include hypersensitivity reactions and gastrointestinal toxicity causing severe vomiting and abdominal pain. CNS reactions are most serious as the encephalopathy may be fatal. Hemolytic anemia may... 

Other types of reduction catalyzed by non-microsomal enzymes have also been described for xenobiotics. Thus, reduction of aldehydes and ketones may be carried out either by alcohol dehydrogenase or NADPH-dependent cytosolic reductases present in the liver. Sulfoxides and sulfides may be reduced by cytosolic enzymes, in the latter case involving glutathione and glutathione reductase. Double bonds in unsaturated compounds and epoxides may also be reduced. Metals, such as pentavalent arsenic, can also be reduced. 

Vega, L Styblo, M., Patterson, R. et al. (2001) Differential effects of trivalent and pentavalent arsenicals on cell proliferation and cytokine secretion in normal human epidermal keratinocytes. Toxicology and Applied Pharmacology, 172(3), 225-32. 

Dimethylarsinic acid An organic pentavalent arsenical with the composition of (CH3)2AsO(OH), abbreviated DMA(V), see Figure B.4 (compare with dimethylarsinous acid, monomethylarsonic acid, and monomethylarsonous acid). 

Methylthioarsenate A chemical species containing pentavalent arsenic, sulfide, and methyl groups, as examples (CH3)As02S2-, (CH3)AsOS22, (CEE AsOS-, and (CH3)2AsS2- (compare with thioarsenic, thioarsenate, and thioarsenite). 

Thioarsenate An aqueous species, such as fLAsChS and H2ASS2O2-, that contains pentavalent arsenic and sulfide (compare with arsenate, thioarsenic, thioarsenite, and methylthioarsenate). 

A number of functional groups, such as nitro, diazo, carbonyl, disulfide sulfoxide, alkene, and pentavalent arsenic, are susceptible to reduction, although in many cases it is difficult to tell whether the reaction proceeds enzymatically or nonenzymatically by the action of such biologic reducing agents as reduced flavins or reduced pyridine nucleotides. In some cases, such as the reduction of the double bound in cinnamic acid (C6H5CH=CHCOOH), the reaction has been attributed to the intestinal microflora. Examples of reduction reactions are shown in Figure 7.12. 

Separation of arsenic(III) and dimethylarsinic acid by elution with sodium hydrogen carbonate was satisfactory in the pH range 5.2-6.0. Elution of monomethylarsonic acid was accelerated and satisfactory separation from arsenic(V) achieved using saturated aqueous carbon dioxide (pH4.0-4.2) containing lOg L 1 of ammonium chloride. In order to avoid oxidation of trivalent to pentavalent arsenic on the column, it was necessary to pretreat the resin with 1M nitric acid and 0.1M EDTA before use. 

A wide variety of minerals was observed however, this discussion will emphasize the mode of occurrence of the As-bearing phases both trivalent and pentavalent arsenic minerals were observed. 

Pentavalent arsenic compounds such as tryparsamide appear to require reduction to the trivalent state for antiparasitic activity (Figure 10.9C). Various arsenicals containing pentavalent arsenic have only slight in vitro antiprotozoal activity, whereas compounds containing trivalent arsenic are highly active. 

Althongh lewisite is only slightly soluble in water, 0.5 g/L (Rosenblatt et al., 1975), hydrolysis, resulting in the formation of lewisite oxide and HCl is rapid. Qi-Lewisite mnst be heated to over 40°C to react with NaOH to yield vinyl chloride, sodium arsenite, and acetylene (Rosenblatt et al., 1975). In aqneons solution, the cis isomer nndergoes a photoconversion to the trans isomer (Rosenblatt et al., 1975). Upon standing in water, the toxic trivalent arsenic of lewisite oxide is converted to the less toxic pentavalent arsenic (Epstein, 1956). 

Pentavalent arsenic sulfides are not well defined. The only accepted compound is AS2S5 which is prepared from H2S and a solution of an As compound (equation 24) or acidification of a thioarsenate salt (equation 25). ... 

The pentavalent arsenic selenide species has not been yet structurally characterized and it is produced in similar maimer to AS2S5. 

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