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The loss of absorption of the chromophoric group of thymine on irradiation in aqueous solution with γ-rays has been studied under a variety of conditions. The effects of thymine and oxygen concentrations, of pH and of the presence of N2O have been investigated. In solutions containing oxygen, the loss of absorption is the result of initial OH radical attack on the pyrimidine molecule; radiation-induced electron attachment to thymine does not lead to destruction of the chromophoric group if oxygen is present in the system. Aerated thymine solutions (8 × 10–5-2 × 10–4 M) have been used to determine, spectrophotometrically, the relative reactivities of solutes towards OH radicals; because of an unusual pH effect observed in neutral solutions, the competition experiments were carried out below pH 6. The reactivities of a number of organic solutes have been obtained. Similar rate constant ratios were obtained in solutions containing N2O, indicating that N2O– was not an oxidizing species under the conditions of the experiments.
Scholes et al. (Sun,) studied this question.