Transient species of several fluoroquinolones and their reactions with amino acids

The photochemistry of several fluoroquinolone antibiotics (FQs), including enoxacin (ENX), norfloxacin (NFX), and ciprofloxacin (CPX), have been investigated in neutral aqueous solution by laser flash photolysis and pulse radiolysis. Transient absorption spectra of FQs were observed and transient species were assigned. The absorption maxima (λmax) of triplet states of ENX, NFX and CPX were located at 520 nm, 620 nm and 610 nm, respectively. The radical anions of FQs were characterized by λmax = 370 nm. Reactions of the FQ triplet states with amino acids (tyrosine [TyrOH], tryptophan [TrpH], glycine [Gly] and cysteine [Cys]) were investigated in different conditions. All three FQ triplet states can oxidize TrpH and TyrOH. The FQ radical anions and oxidized radicals of TrpH (Trp) and TyrOH (TyrO) were directly observed. Under aerobic conditions, the photooxidation of TrpH and TyrOH involves both Type I and Type II mechanisms. There were no distinct quenching reactions of the FQ triplet states by Gly and Cys in N2-saturated aqueous solutions.