Free-Radical Formation in Deoxythymidine-5′-Monophosphate γ-Irradiated in Frozen Solution. A Computer-Assisted Analysis of Temperature-Dependent ESR Spectra

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Abstract
Neutral aqueous solutions of deoxythymidine-5''-monophosphate (dTMP) were irradiated at 77 K and then annealed until no detectable ESR signal remained. The spectra 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 identified as the radical of OH-addition at C-6 of thymine. 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 .ovrhdot.TH and T. 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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