Free radicals from purine nucleosides after hydroxyl radical attack

Free radicals from imidazole, caffeine, guanosine, deoxyguanosine, inosine, adenosine, deoxyadenosine, and adenine, as well as β-D-ribose and β-D-deoxyribose, were generated by reaction with OH from H2O2--Ti3+ at pH 1.5-2 and studied by ESR, using a computerized, Q-band, fast-flow system. Purine base radicals, plus sugar radicals in nucleosides, were always observed. Prior deuteration of C8 made possible the assignment of the observed 10--15 gauss doublet splitting to the C8 proton in guanine derivatives, and to the C2 proton in adenine derivatives and inosine. Hueckel calculations (and INDO in a few cases) on possible radical species suggest that hydroxyl addition on nitrogens in the purine ring or on C5 may be responsible for the species which are observed. In imidazole, the radical species is a hydroxyl adduct. An anomalous effect of deuteration of CS on the spectrum obtained with caffeine is also reported