Abstract
The photochemical properties of difloxacin (DFX) were investigated in neutral aqueous solution. DFX aqueous solution showed intense absorption with one peak at 273 nm (molar absorption coefficient epsilon=33000 dm(3).mol(-1).cm(-1)) and two other peaks at 323 and 335 nm (epsilon=15500 dm(3).mol(-l).cm(-1)) with the same molar absorption coefficient. Both the absorption and emission properties of DFX were pH-dependent. The acid dissociation constant (pK(a)) for the protonation equilibria of the ground state (5.9 and 9.8) were determined spectroscopically. DFX fluoresces weakly, and its maximum quantum yield for fluorescence emission was 0.06 at pH 3. Laser flash photolysis and pulse radiolysis studies were carried out to characterize the transient species of DFX aqueous solution. Triplet-triplet absorption reached a maximum at 620 nm with a molar absorption coefficient of 7900 dm(3).mol(-1).cm(-1). The energy transfer method was used to estimate the triplet energy of DFX, which was 263.5 kJ.mol(-1). The quantum yield of triplet formation was determined to be 0.21. Furthermore, DFX showed monophotonic photoionization with a quantum yield of 0.02. Pulse radiolysis indicated that DFX could react with e(aq)(-); and .OH, and the bimolecular rate constants for these reactions were 1.72x10(10) and 1.0x10(10) dm(3).mol(-1).s(-1), respectively. It is expected that this research may be helpful in determining the phototoxicity mechanism of DFX.
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