A Computer-controlled E.P.R. Analysis of Free Radical Formation in Dry Thymine and Derivatives after Electron Irradiation

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Abstract
Radical formation and transformation in electron irradiated dry thymine, thymidine, thymidine-5′-monophosphate, and DNA have been studied with 35 GHz electron paramagnetic resonance. Dry samples were irradiated at 77°K and the E.P.R. spectra taken at 77 and 300°K under anaerobic conditions. The spectra of the cation and the anion radical of thymine were identified. It was shown that the cation easily undergoes deprotonization. Conversely, the anion radical is transformed into the 5,6-dihydro-5-thymyl radical by proton capture. These processes were found to be significant for all the compounds investigated.