Primary photophysical properties of moxifloxacin - A fluoroquinolone antibiotic

Fernando Lorenzo, Suppiah Navaratnam, Ruth Edge, Norman S. Allen

    Research output: Contribution to journalArticlepeer-review


    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 (ɛ = 44 000 and 17 000 dm3 mol−1 cm−1, respectively). The absorption and emission properties of MOX are pH‐dependent, pKa 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 (ɛ470 = 3400 dm3 mol−1 cm−1). The photoionization process releases hydrated electron which rapidly reacts (k = 2.8 × 1010 dm3 mol−1 s−1) with ground state MOX, yielding a long‐lived anion radical with maximum absorption at 390 nm (ɛ390 = 2400 dm3 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 × 108 dm3 mol−1 s−1 and 1.3 × 108 dm3 mol−1 s−1, respectively. Singlet oxygen sensitized by the MOX triplet state was also detected only in oxygen‐saturated D2O solutions, with a quantum yield of 0.075.
    Original languageEnglish
    Pages (from-to)1118-1125
    JournalPhotochemistry and Photobiology
    Issue number5
    Publication statusPublished - 2008


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