Neutral aqueous solutions of deoxythymidine-5′-monophosphate (dTMP) were irradiated at 77 K and then annealed step by step until no detectable ESR signal remained. The highly complex spectra so produced are greatly modified after each annealing step, suggesting the presence of a composite, transforming radical population. The radical of H-addition at C-6 of the thymine ring and the thymine radical anion are not the main products involved in this process. Two other radicals are formed, one having been identified as the radical of OH-addition at C-6 of thymine. Despite the large amount of experimental data accumulated, no positive identification can yet be made of its low-temperature precursor. Such radical species are formed at absolute concentrations comparable with those of radicals ṪH and <tex-math>${\rm T}^{{}^{\underline{.}}}$</tex-math>. This work was performed by computer-assisted analysis of the temperature-dependent ESR spectra. To facilitate the isolation of the single-component patterns, selective radical scavengers and suitable radiomimetics were used. Computer reconstruction of the experimental spectra from the component patterns revealed the relative and absolute kinetics of each radical species.

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