Radical combination processes under the direct effects of gamma radiation on thymidine

Abstract

The isolation and structural analysis of a variety of dimeric thymidine products produced by the direct effects of γ-radiation on thymidine in frozen aqueous solution are described. These products may, with the exception of the spore photoproducts, be accounted for by the simple combination of various primary and secondary radicals. As well as being thymidine lesions possibly formed in cellular DNA and therefore of biological interest, from a mechanistic point of view, the formation of these adducts provides good support for the formation of the respective free-radical precursors. In particular, evidence is provided for the formation of the N (3)-centred radical formed by deprotonation of the thymidine radical cation at this position. Other important radicals formed are centred at the C(5), C(6), C(5′), and the methyl-group positions.