Biotransformation reactions sulfation

The concept of microbial models of mammalian metabolism was elaborated by Smith and Rosazza for just such a purpose (27-32). In principle, this concept recognizes the fact that microorganisms catalyze the same types of metabolic reactions as do mammals (32), and they accomplish these by using essentially the same type of enzymes (29). Useful biotransformation reactions common to microbial and mammalian systems include all of the known Phase I and Phase II metabolic reactions implied, including aromatic hydroxylation (accompanied by the NIH shift), N- and O-dealkylations, and glucuronide and sulfate conjugations of phenol to name but a few (27-34). All of these reactions have value in studies with the alkaloids. 

The sulfation of alcohols is a very eommon biotransformation reaction, particularly for phenols, such as phenols of physiological substrates (Coughtrie et al., 1998) ... 

Technical-grade endosulfan contains at least 94% a-endosulfan and (3-endosulfan. The a- and (3-isomers are present in the ratio of 7 3, respectively. The majority of the studies discussed below used technical-grade endosulfan. However, a few examined the effects of the pure a- and (3-isomers. Endosulfan sulfate is a reaction product found in technical-grade endosulfan as a result of oxidation, biotransformation, or photolysis. There is very little difference in toxicity between endosulfan and its metabolite, endosulfan sulfate. However, the a-isomer has been shown to be about three times as toxic as the P-isomer of endosulfan. 

Technical-grade endosulfan contains at least 94% of two pure isomers, a- and P-endosulfan (Maier-Bode 1968 NRCC 1975). The a- and p-isomers of endosulfan are present in the ratio of 7 3, respectively. Technical-grade endosulfan may also contain up to 2% endosulfan alcohol and 1% endosulfan ether. Endosulfan sulfate is a reaction product found in technical endosulfan it is also found in the environment due to photolysis and in organisms as a result of oxidation by biotransformation (EPA 1979 Coleman and Dolinger 1982). The chemical formula, structure, synonyms, and identification numbers for endosulfan, a-endosulfan, p-endosulfan, and endosulfan sulfate are listed in Tables 3-1, 3-2, 3-3, and 3-4, respectively. 

HCN is the most preferred cyanide source in cyanohydrin synthesis. Besides HCN, several different cyanide sources, like potassium cyanide, are being used in biotransformation. Alternative methods for the safe handling of cyanides on a laboratory scale are, for instance, to use cyanide salts in solution. These solutions can be acidified and used as the aqueous layer in two-phase systems or the HCN can be extracted into the organic layer with the desired solvent for reactions in an organic phase. After the reaction, excess cyanide can readily be destroyed with iron(II) sulfate, or iron(III) chloride or bleach. Cyanide can also be presented in the form of organic cyano, such as acetone cyanohydrin [46] or cyanoformates. However, as claimed by Effenberger, some results could not be reproduced [47]. 

As(V) and biotransformation 248 -9 bacterial 94, 111, 120, 324 low iron/sulfide-rich environment 114-15 microbial and sulfate 32, 305, 324 reactions 27-8... 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

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