The reactions of triplet-state difloxacin (DFX) with various amino acids and deoxyguanylic acid in aqueous media were studied using laser flash photolysis. Tryptophan, tyrosine, cysteine, and 2'-deoxyguanosine5'-monophosphate (dGMP) were found to completely quench the triplet state of DFX in aqueous solution, the corresponding second-order rate constants being 1.97 x 10(8), 1.48 x 10(8), 1.72 x 10(8), and 6.92 x 10(7) dm(3).mol(-l).s(-1) . The quenching mechanism involves electron transfer to the photoexcited triplet state of DFX from the tryptophan, tyrosine, cysteine, and dGMP moieties, followed by fast protonation of the resulting DFX anion radical.
