Mechanisms for radiation damage in DNA constituents and DNA. Reactions of the N1-substituted thymine π-cation radicals

Abstract

Reactions of the N₁-substituted thymine π-cation radicals were investigated by e.s.r. in several aqueous glasses. In 8 mol dm^–3 NaOD (NaOH) spectra suggestive of OD^–(OH^–) addition to position 6 in the π-cations of 1-methylthymine, and thymidine were found immediately after u.v. photolysis at 77 K. Production of the same radicals by electron attachment to 1-methyl-5-bromo-6-hydroxythymine and 5-bromo-6-hydroxythymidine in 8 mol dm^–3 NaOD confirms the OD^– addition mechanism. Results found for these brominated compounds in 12 mol dm^–3 LiCl(D₂O) after electron attachment show that the a₆(H) splitting was sensitive to changes in substituents at position 1 as well as changes in environment. This variation in splitting is shown to be accounted for by small conformational changes in the radicals. In 8 mol dm^–3 NaClO₄π-cations of the substituted thymines gave evidence for both deprotonation and OD^– addition.