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.