Photosensitization of DNA bases by 4(5)-nitroimidazole: a steady state and flash photolysis study

Abstract

UV photolysis and laser flash photolysis of 4(5)-nitroimidazole in the presence of thymine and/or uracil generates the respective glycols under conditions where the bases do not absorb any light. The reaction is mediated through the triplet state of 4(5)-nitroimidazole which generates a highly oxidizing N-centred radical. The radical has an absorption maximum at ca. 350 nm and reacts efficiently with the DNA bases resulting in the formation of glycols. The rate constant of reaction of the radical with the DNA bases and nucleosides is of the order of ca. 10⁸ dm³ mol^–1 s^–1, the rate being slower with the nucleosides than with the free bases.