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Primary Photophysical Properties of Ofloxacin ¶
Author(s) -
Navaratnam Suppiah,
Claridge Jennifer
Publication year - 2000
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 - 10.1562/0031-8655(2000)0720283pppoo2.0.co2
Subject(s) - chemistry , photochemistry , quantum yield , photoionization , radiolysis , excited state , molar absorptivity , singlet oxygen , triplet state , solvated electron , singlet state , radical , flash photolysis , aqueous solution , reaction rate constant , ion , fluorescence , oxygen , ionization , atomic physics , molecule , organic chemistry , kinetics , physics , quantum mechanics , optics
Steady‐state fluorescence has been used to study the excited singlet state of ofloxacin (OFLX) in aqueous solutions. Fluorescence emission was found to be pH dependent, with a maximum quantum yield of 0.17 at pH 7. Two pK a *s of around 2 and 8.5 were obtained for the excited singlet state. Laser flash photolysis and pulse radiolysis have been used to study the excited states and free radicals of OFLX in aqueous solutions. OFLX undergoes monophotonic photoionization from the excited singlet state with a quantum yield of 0.2. The cation radical so produced absorbs maximally at 770 nm with an extinction coefficient of 5000 ± 500 dm 3 mol −1 cm −1 . This is confirmed by one‐electron oxidation in the pulse radiolysis experiments. The hydrated electron produced in the photoionization process reacts with ground state OFLX with a rate constant of 2.0 ± 0.2 × 10 10 dm 3 mol −1 s −1 , and the anion thus produced has two absorption bands at 410 nm (extinction coefficient = 3000 ± 300 dm 3 mol −1 cm −1 ) and at 530 nm. Triplet–triplet absorption has a maximum at 610 nm with an extinction coefficient of 11 000 ± 1500 dm 3 mol −1 cm −1 . The quantum yield of triplet formation has been determined to be 0.33 ± 0.05. In the presence of oxygen, the triplet reacts to form both excited singlet oxygen and superoxide anion with quantum yields of 0.13 and ≤0.2, respectively. Moreover, superoxide anion is also formed by the reaction of oxygen with the hydrated electron from photoionization. Hence the photosensitivity due to OFLX could be initiated by the oxygen radicals and/or by OFLX radicals acting as haptens.