Interaction of triplet-state nucleic acid bases with electroaffinic molecules in solution by laser flash photolysis

Abstract

Triplet-state thymine, thymidine, and uracil, generated by 249.1 nm laser flash photolysis, are quenched by a range of electroaffinic molecules, including the radiosensitising drugs metronidazole and misonidazole, at rates which accord satisfactorily with the predictions of the Rehm–Weller equation for photoelectron transfer. Such a mechanism is confirmed for two of the selected solutes, tetranitromethane and galvinoxyl, when the spectrum of C(NO₂)₃^– and of galvinoxyl anion are observed, indicating net electron transfer with yields of 0.69 ± 0.03 (thymine) and 0.40 ± 0.03 (uracil) for C(NO₂)₃^– and of 0.024 ± 0.002 (thymine) and 0.0135 ± 0.0005 (uracil) for galvinoxyl anion. The mechanistic implications of these results for photo- and radiation-damage to DNA and cellular systems are discussed.