Organic arsenicals chemical structure

Concentration and chemical forms of arsenic in freshwater environment have been reviewed in detail by the present author . When comparing freshwater and marine organisms in the natural environment, there seems to be a clear difference in the total arsenic concentration, which in freshwater organisms is lower than in marine organisms. Trimethyl-, dimethyl- and monomethylarsenic compounds were detected in freshwater organisms whose chemical structure in vivo have not been confirmed . 

Fig. 6.1 Chemical structures of commonly used organic arsenicals.

Arsenate Poisoning Arsenate is structurally and chemically similar to inorganic phosphate (P4), and many enzymes that require phosphate will also use arsenate. Organic compounds of arsenate are less stable than analogous phosphate compounds, however. For example, acyl arsenates decompose rapidly by hydrolysis ... 

Lewisite [dichloro(2-chlorovinyl)arsine] is an organic arsenical known for its vesicant properties (Rosenblatt et al., 1975). It has a molecular weight of 207.32, vapor pressure of 0.58 mm HG at 25°C, a liquid density of 1,89 g/cm at 25°C, freezing point of -18°C, boiling point of 190°C, and is negligibly soluble in water (DA, 1974). The chemical structure of lewisite is shown below. Lewisite may occur as a trans-isomer and as a cis-isomer. In aqueous solutions, the cis-isomer undergoes photoconversion to the trans-isomer (Clark, 1989). hi the presence of moisture, lewisite is rapidly converted to the more stable but highly toxic lewisite oxide (2-chlorovinylarsenous acid) (Cameron et al., 1946). 

A number of different factors can influence the toxicity of arsenicals, including chemical structure, physical properties, mode of administration and species of organism. 

Advances in analytical instrumentation and techniques are such that the amount of an impurity available in a single injection can be used to obtain a multitude of data, from chromatographic retention time to nuclear magnetic resonance (NMR) spectra. The introduction of hyphenated techniques to the arsenal available to pharmaceutical scientists has led to increased efficiency for elucidation of organic chemical structures of impurities and degradants. 

Chemical structures of the arsenic compounds in marine organisms have been confirmed in many cases, but very few chemical species of arsenic in freshwater organisms have been found. Arsenic transformation via the freshwater food chain has rarely been reported. This chapter focuses on the toxicity of arsenicals and the biotransformation of arsenic in the freshwater organisms. 

The marine environment is a vast resource for the discovery of structurally unique bioactive secondary metabolites, some belonging to totally novel chemical classes.8 Sessile benthic organisms including the Porifera, Cnidaria, Bryozoa, and Tunicata as well as marine algae have developed an arsenal of compounds which have been demonstrated to confer a competitive advantage in ecosystems characterized by extreme resource limitations. Interactions of these organisms at the genetic,... 

The sudden appearance of 59 on the chemical scene is likely to produce a truly dramatic effect on the further development of organic chemistry, comparable in its significance with the discovery of benzene in 1825 by Michael Faraday. The essential difference between these two discoveries is that it took nine years to establish the molecular formula of benzene (Mitcherlich, 1834), an additional 31 years to understand its structure (Kekule, 1865), and several decades more to develop the chemistry in this area. The arsenal of modern science, on the other hand, made it possible to cover such a distance for the case of 59 and related compounds in a matter of just a few years. 

Resonance (ESR). The effects of radiation on arsenic, antimony and bismuth compounds are, however, considerably less documented a compilation of the corresponding information has been published in Landolt-Bomstein and this subject is periodically reviewed in Specialist Reports of the Royal Chemical Society. The purpose of this chapter is not to present an exhaustive compilation of all the species produced by radiolysis of organic compounds which contain an As, Sb or Bi atom, but only to deal with the most important types of radiogenic radicals formed from these compounds and, when possible, to compare the structures of these radicals with those of the corresponding phosphorous species. 

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