Fluorescence of hydrocarbon-deoxyribonucleoside adducts

In comparison with the fluorescence emission spectra of 7-methylbenz[a]-anthracene-nucleoside adducts, the fluorescence emission spectra of hydrocarbon-deoxyribonucleoside adducts containing a methyl substituent in the "bay region" lack spectral resolution at room temperature and appear at substantially longer wavelength. This spectral resolution is improved when spectra are measured at 77 K and an irreversible spectral shift to shorter wavelength, accompanied by improved resolution, results from mild acid hydrolysis. These spectral properties peculiar to the "bay region-substituted" adducts presumably result from an intramolecular interaction between the hydrocarbon fluorophore and the attached nucleoside brought about, in the examples studied here, by the presence of the 12-methyl group in 7,12-dimethylbenz[awanthracene (DMBA) and in 7-hydroxymethyl-12-methylbenz[a]anthracene. This interaction suggests that the site of nucleoside attachment is in close proximity to the 12-methyl group and that binding occurs, therefore, through the intermediacy of a 3,4-diol-1,2-oxide, i.e. a "bay region" diol-epoxide in each case.