E.S.R. Study of the Post-radiolysis Growth of Spin-trapped Radicals in γ-irradiated Aqueous Solutions of Thymine

Summary

The post-irradiation growth of the spin-adduct nitroxide radical produced by the addition of the thymine-OD radical to t-nitrosobutane (tNB) in γ-irradiated, de-aerated D₂O solutions was investigated by e.s.r. The thymine-OD radical was formed by the addition of an OD radical to the C(5) position of thymine. Growth reached a greater maximum value and was more rapid with increasing dose. At a fixed dose, growth was also greater and more rapid if oxygen was present after γ-radiolysis. The addition of a second radical to the spin-adduct nitroxide during radiolysis to give a diamagnetic intermediate, which can regenerate the spin-adduct radical during storage in air-free and in air-saturated solutions at room temperature, was inferred to be responsible for post-irradiation growth. U.V. photolysis at 260–280 nm of a solution containing the diamagnetic intermediate rapidly regenerates the spin-adduct nitroxide. The longer lifetime of the diamagnetic intermediate in oxygen-free solutions may be relevant to an understanding of the anoxic sensitization by nitroxides in cellular systems.