A rapid, spectrophotometric assay for the integrity of diol epoxides

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Abstract
One of the most widely studied ultimate carcinogens, 7r,8t-dihydroxy-9t, 10t-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE-I), is fairly stable in organic solvents but hydrolyses rapidly in the presence of water. Routine use of BPDE-I stock solutions involves multiple cycles of warming to room temperature and return to freezer temperature and results in some decomposition of the stock with time, presumably due to uptake of water from the atmosphere. We present a simple spectrophotometric assay which allows an investigator to quickly and safely estimate the extent of such decomposition to an accuracy of ±6%. The assay is based on the rapid reaction of BPDE-I with β-mercaptoethanol in alkaline solution resulting in an adduct which exhibits a significant red-shift in the absorption spectrum.