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AWWA standard for field welding of steel water pipe by American National Standards Institute.; American Water Works

By American National Standards Institute.; American Water Works Association

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Direct demonstration of the metabolic intervention of diol epoxides proved unfeasible due to the unusually high reactivity of these substrates in aqueous media. Each diol epoxide is hydrolyzed to a pair of tetraols (vide infra) and nonenzymatically reduced to pentahydro- BaP-triols (2£ and 27) by reduced nicotinamide-adenine dinucleotide (NADH), or reduced nicotinamide-adenine dinucleotide phosphate (NADPH) (Eqs. 9 and 10, respectively) (54,56). -32The optically pure levo- and dextrorotatory enantiomers of BaP 7,8-dihydrodiol {Y\_ and its enantiomer, respectively) were obtained by separation of the diastereomeric diesters with (-)α-methoxy-a-trifluoromethylphenylacetic acid and their metabolism to the optically pure forms of diol epoxides ]7_ and 18^ studied (57).

Microsomes from control and phenobarbitol pretreated rats are less stereospecific in the metabolic oxidation of enantiomers of BaP 7,8-dihydrodiol. , the dextrorotatory enantiomer affords mainly the s#n-diol epoxide 18_, whereas the levorotatory counterpart is converted primarily to the anti-άΛθλ epoxide 17_ (55,57). , BaP 4,5-, 7,8-, and 9,10-dihydrodiols (V3, 1J_, and ]2)9 tvansproduced metabolically from BaP by liver microsomes obtained from male rats pretreated with 3-methylcholanthrene were found to possess high optical purity (57,58,59).

12). Both acid-catalyzed (ku+) and spontaneous (k ) processes are thought to intervene. 2] is also formed in water under conditions of spontaneous hydrolysis (pH > 7 ) , presumably through a k mechanism in which a "NIH Shift" is operative. As the dioxane concentration is increased, the isomerization of ]S^ to ketone 37^ is enhanced; for example, in 25% and 50% aqueous dioxane solutions, the ketone 37^ is formed in 16% and 30%, respectively, which constitutes a fourto-eight-fold incremental increase when compared with that of water.

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