Dimethylarsinous acid

Concerning anthropogenic sources, methyl arsenic compounds such as methyl arsonic acid and dimethylarsinic acid have been used as herbicides, and were once a significant source of environmental residues. Dimethyl-arsinic acid (Agent Blue) was used as a defoliant during the Vietnam War. 

The arsenic compounds most commonly found in environmental and biological materials, and in working places, are arsenite and arsenate ions [As(III) and As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsine, di- and tri-... 

Zinc complex formation with 1,3-diketones in aqueous solution has been investigated with pentane-2,4-dione, l,l,l-trifluoropentane-2,4-dione, and 4,4,4-trifluoro-l-(2-thienyl)butane-l, 3-dione. The buffer dimethylarsinic acid was shown to have a catalytic effect on complex formation with pentane-2,4-dione and the proton transfer reactions were affected.471,472 High-resolution solid state 13C NMR studies of bis(2,4-pentanedionato) zinc complexes have been carried out.473... 

In 1933 Challenger et al. discovered that trimethylarsine was synthesized from inorganic arsenic compounds by molds (93). Recently, McBride and Wolfe (94), have reported the synthesis of dimethylarsine from arsenate by cell extracts of the methanogenic bacterium M. O. H. Methylcobalamin is the alkylating coenzyme for this synthesis which requires reduction of arsenate to arsenite, methylation of arsenite to methylarsonic acid, reduction and methylation of methylarsonic acid to dimethylarsinic acid, and finally a four electron reduction of dimethylarsinic acid to dimethylarsine (Fig. 13). 

MMAA monomethylarsonic acid [(CH3)AsO(OH)2] DMAA dimethylarsinic acid [(CTbhAsOfOH)] MexSn MeSn3+, Me2Sn2+, Me3Sn+... 

Marine algae transform arsenate into nonvolatile methylated arsenic compounds such as methanearsonic and dimethylarsinic acids (Tamaki and Frankenberger 1992). Freshwater algae and macrophytes, like marine algae, synthesize lipid-soluble arsenic compounds and do not produce volatile methylarsines. Terrestrial plants preferentially accumulate arsenate over arsenite by a factor of about 4. Phosphate inhibits arsenate uptake by plants, but not the reverse. The mode of toxicity of arsenate in plants is to partially block protein synthesis and interfere with protein phosphorylation — a process that is prevented by phosphate (Tamaki and Frankenberger 1992). 

Dimethylarsinic acid is the major metabolite of orally administered arsenic trioxide, and is excreted rapidly in the urine (Yamauchi and Yamamura 1985). The methylation process is true detoxification, since methanearsonates and cacodylates are about 200 times less toxic than sodium arsenite (NAS 1977). The marmoset monkey (Callithrix jacchus), unlike all other animal species studied to date, was not able (for unknown reasons) to metabolize administered As+5 to demethylarsinic acid most was reduced to As+3. Only 20% of the total dose was excreted in urine as unchanged As+5, and another 20% as As+3. The rest was bound to tissues, giving distribution patterns similar to arsenite (Vahter and Marafante 1985). Accordingly, the marmoset, like the rat, may be unsuitable for research with arsenicals. 

Single oral dose Arsenous oxide Tetramethylarsonium iodide Dimethylarsinic acid Dimethylarsonic acid Arsenocholine Trimethylarsinoxide Arsenobetaine Sodium arsenate... 

Hughes, M.F. and E.M. Kenyon. 1998. Dose-dependent effects on the disposition of monomethylarsonic acid and dimethylarsinic acid in the mouse after intravenous administration. Jour. Toxicol. Environ. Health 53 A 95-112. 

Tezuka, M. et al., Gene damage induced in human alveolar type II (L-132) cells by exposure to dimethylarsinic acid, Biochem. Biophys. Res. Commun., 191, 1178, 1993. 

Dimethylarsinic acid (DMA), 3 274 present in water and food, 3 276t Dimethylbenzyl carbinol, aroma chemical derived from toluene, 3 234 N, AT-Dimethylbenzyl vinyl amine (DMBVA), 20 487 Dimethylbismuthine, 4 18, 26 Dimethylbromostibine, 3 68 Dimethylcadmium, 4 516-517 physical properties of, 4 517t Dimethyl carbonate, 6 313-314... 

Equilibration buffer contains potassium cacodylate (dimethylarsinic acid). Avoid contact with skin and eyes. Harmful if swallowed. Wear appropriate protective clothing. 

Some metals, arsenic and mercury for example, may be volatilized by methylation due to activity of anaerobic microorganisms. Arsenic can be methylated by methanogenic Archaea and fungi to volatile toxic dimethylarsine and trimethylarsine or can be converted to less toxic nonvolatile methanearsonic and dimethylarsinic acids by algae [42]. 

One factor has been overlooked in this reversion to seaweed use. Seaweed naturally contains high levels of arsenic, typically between 20 and 100 mg kg" dry weight (dw). Thus, sustained use of seaweed may lead to the buildup of arsenic in soils. The dominant species of arsenic in these seaweeds are in the form of arsenoribofuranosides (arsenosugars). These are assumed to be relatively nontoxic to humans and animals as compared to inorganic species. The arsenosugars are metabolized to different organo-arsenic species but mainly to DMA(V) (dimethylarsinic acid) when consumed as a food source. (Adapted from Castlehouse et ah, 2003)... 

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