PHOTOSENSITIZATION OF DNA BASES BY 4(5)-NITROIMIDAZOLE - A STEADY-STATE AND FLASH-PHOTOLYSIS STUDY

UV photolysis and laser flash photolysis of 4(5)-nitroimidazole in the presence of thymine and/or uracil generates the respective glycols un der conditions where the bases do not absorb any light. The reaction i s mediated through the triplet state of 4(5)-nitroimidazole which gene rates a highly oxidizing N-centred radical. The radical has an absorpt ion maximum at ca. 350 nm and reacts efficiently with the DNA bases re sulting 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. 10(8) dm(3) mol(-1) s(-1), the rate being slower with the nucleosides than with the free bases.