Optically detected magnetic resonance study of benzo[a]pyrene‐7,8‐dihydrodiol 9,10‐oxide covalently bound to DNA

Recent investigations of the potent carcinogenic activity of benzo [a] pyrene have indicated that the major metabolite of this molecule responsible for in vivo binding to nucleic acids is a specific 7,8-dihy-drodiol9,10-oxide derivative [l-7] denoted by BPDE and shown in fig. The in vitro adduct, prepared by the reaction of BPDE and DNA [8], exhibits an extent of binding -loo-times greater than the in vivo product, making it more convenient for physico-chemical studies of the binding process. Evidence was recently obtained by fluorescence quenching [8,9] and electric field induced linear dichroism techniques [lo] that in this in vitro adduct, the BPDE moiety, and in particular the pyrene-like chromophore, is not intercalated between the nucleic acid base pairs, but is instead located in a region external to the DNA helix. Other workers have asserted, however, that the pyrene-like chromophore is intercalated, based on the observations that BPDE I 60