title: Primary photophysical properties of moxifloxacin--a fluoroquinolone antibiotic.
abstract: The photophysical properties of the fluoroquinolone antibiotic moxifloxacin (MOX) were investigated in aqueous media. MOX in water, at pH 7.4, shows two intense absorption bands at 287 and 338 nm (epsilon = 44,000 and 17,000 dm(3) mol(-1) cm(-1), respectively). The absorption and emission properties of MOX are pH-dependent, pK(a) values for the protonation equilibria of both the ground (6.1 and 9.6) and excited singlet states (6.8 and 9.1) of MOX were determined spectroscopically. MOX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Phosphorescence from the excited triplet state in frozen ethanol solution has a quantum yield of 0.046. Laser flash photolysis and pulse radiolysis studies have been carried out to characterize the transient species of MOX in aqueous solution. On laser excitation, MOX undergoes monophotonic photoionization with a quantum yield of 0.14. This leads to the formation of a long-lived cation radical whose absorption is maximum at 470 nm (epsilon(470) = 3400 dm(3) mol(-1) cm(-1)). The photoionization process releases hydrated electron which rapidly reacts (k = 2.8 x 10(10) dm(3) mol(-1) s(-1)) with ground state MOX, yielding a long-lived anion radical with maximum absorption at 390 nm (epsilon(390) = 2400 dm(3) mol(-1) cm(-1)). The cation radical of MOX is able to oxidize protein components tryptophan and tyrosine. The bimolecular rate constants for these reactions are 2.3 x 10(8) dm(3) mol(-1) s(-1) and 1.3 x 10(8) dm(3) mol(-1) s(-1), respectively. Singlet oxygen sensitized by the MOX triplet state was also detected only in oxygen-saturated D(2)O solutions, with a quantum yield of 0.075.
authors.affiliation: Free Radical Research Facility, STFC Daresbury Laboratory, Warrington, UK.
authors.forename: Fernando
authors.initials: F
authors.lastname: Lorenzo
authors.forename: Suppiah
authors.initials: S
authors.lastname: Navaratnam
authors.forename: Ruth
authors.initials: R
authors.lastname: Edge
authors.forename: Norman S
authors.initials: NS
authors.lastname: Allen
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000528:radiation effects; D001372:Aza Compounds / Q000737:chemistry* / Q000528:radiation effects; D024841:Fluoroquinolones; D006863:Hydrogen-Ion Concentration; D007834:Lasers; D008968:Molecular Conformation; D000077266:Moxifloxacin; D010777:Photochemistry; D010782:Photolysis; D011789:Quantum Theory; D011804:Quinolines / Q000737:chemistry* / Q000528:radiation effects; D015203:Reproducibility of Results; D013056:Spectrophotometry, Ultraviolet; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D001372:Aza Compounds; D024841:Fluoroquinolones; D011804:Quinolines; D014867:Water; D000077266:Moxifloxacin