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Primary Photophysical Properties of Moxifloxacin— A Fluoroquinolone Antibiotic
Author(s) -
Lorenzo Fernando,
Navaratnam Suppiah,
Edge Ruth,
Allen Norman S.
Publication year - 2008
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2007.00269.x
Subject(s) - chemistry , quantum yield , photochemistry , triplet state , flash photolysis , aqueous solution , radiolysis , excited state , singlet oxygen , protonation , singlet state , photoionization , ultrafast laser spectroscopy , fluorescence , reaction rate constant , ion , oxygen , spectroscopy , organic chemistry , ionization , kinetics , atomic physics , molecule , physics , quantum mechanics
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 dm 3 mol −1 cm −1 , respectively). The absorption and emission properties of MOX are pH‐dependent, p K 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 (ɛ 470 = 3400 dm 3 mol −1 cm −1 ). The photoionization process releases hydrated electron which rapidly reacts ( k = 2.8 × 10 10 dm 3 mol −1 s −1 ) with ground state MOX, yielding a long‐lived anion radical with maximum absorption at 390 nm (ɛ 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 × 10 8 dm 3 mol −1 s −1 and 1.3 × 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.