ESR and Spin-Trapping Study of Room-Temperature Radicals in γ-Irradiated Polycrystalline Pyrimidine Nucleotides

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Abstract
Free radicals produced in .gamma.-irradiated polycrystalline 5''-dCMP (free acid and 2Na), 3''-CMP (free acid and Li), and 5''-UMP (2Na) were studied by ESR and spin-trapping. The results were compared with those of previous single-crystal studies. Furthermore, attempts to identify free radicals in .gamma.-irradiated 5''-dUMP (2Na), 5''-CMP (free acid and 2Na), and 3''-UMP (Na), which have not been the subject of single-crystal studies to date, were made. After .gamma.-irradiation at room temperature to a dose of 100 kGy [gray], the polycrystalline samples were dissolved in aqueous solutions of t-nitrosobutane in the presence or absence of oxygen. The presence or absence of O was helpful in analyzing the presence of more than one radical species. Thus two types of radicals could be established for all samples. Radical -.ovrhdot.C5H-C6H2-, formed by H addition to the double bond of the base, was observed in the presence of oxygen, and radical -.ovrhdot.C5,H2, formed by the transformation of the radical due to loss of an H atom at the c5'', position of the sugar moiety, was observed in the absence of oxygen. In some cases, radicals located at the c1'', C4'', and C5'' of the sugar moiety were tentatively identified. For the ESR spectrum associated with radical at C1'', the possibility of another explanation was also discussed in relation to the spectrum due to radical at C5 of the base. Radical -C5H2-.ovrhdot.C6H-, formed by H addition to the double bond of the base, was not identified.