E.S.R. of Spin-trapped Radicals in Gamma-irradiated Polycrystalline Nucleic Acid Constituents and Their Halogenated Derivatives

Summary

Free radicals in γ-irradiated polycrystalline nucleic acid constituents and their 5-halogenated derivatives have been studied by e.s.r. and spin-trapping. After γ-irradiation at room temperature, the polycrystalline samples were dissolved in aqueous solutions of t-nitrosobutane (tNB) in the absence or presence of oxygen. For many of the nucleic acid constituents, two types of radicals, –C(5)RH–Ċ(6)H– and –Ċ(5)R–C(6)H₂–, formed by H-addition to the double bond [–C(5)R = C(6)H–] of the base, were observed, where R is –CH₃ or –H. In addition, radicals formed on the sugar moiety were found for some nucleosides. When oxygen was present in the tNB solution, the relative stability of trapped radicals was changed, and thus the presence of more than one radical species could be established. For halogenated bases, the radical produced by H-abstraction from N(1) was observed, and an additional radical species formed by H-addition to the C(6) position was found for 5-fluorouracil. For halogenated nucleosides, the same spectrum was observed in all compounds except the 5-fluoroderivatives, and was assigned to the radicals produced on the sugar moiety. For 5-fluorodeoxyuridine and 5-fluorouridine, the radical formed by H-addition to the C(6) position of the base was observed.

In general, the present results are in good agreement with those of previous single crystal studies, but in the case of halogenated compounds other than the 5-fluoroderivatives, it was not possible to spin-trap the α-halo radicals which were the most prominent radicals formed from γ-irradiation of single crystals at room temperature.