E.S.R. Studies of Halogenated Pyrimidines in Gamma-irradiated Alkaline Glasses

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Abstract
The reactions of mobile electrons (em−) and oxygen radical anions (O·−) with halogenated bases and nucleosides have been studied in γ-irradiated alkaline glasses by e.s.r. and specific halogen-ion electrode techniques. It is shown that electrons react with halogenated uracil bases (XUr where X = Cl Br I but not F) by dissociative electron attachment to form uracil-5-yl radicals (U·) and halogen anions. The relative rates of reaction of em− with XUr decrease in the sequence BrUr > ClUr > FUr > IUr. Thermal annealing studies carried out on U· in H2O and D2O matrices support the hypothesis that U· in H2O hydrates across the 5–6 double bond in the temperature region 135°–155°K, and deuterates to a much smaller extent in D2O at temperatures above 155°K. Studies on bromouridine and bromodeoxyuridine suggest that em− reacts with the base moieties to form U· type radicals which abstract H· from the sugar moieties of adjacent nucleosides.