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The progress and photosensitivity of quinolone antibiotics are briefly described. By the photolysis of nalidixic acid, the loss of COOH group is observed. The photoreaction of fluoroquinolones involves heterolytic CF bond fragmentation. The protonation and divalent cation complexation equilibria are also examined. The spectroscopic properties of these drugs are intensively investigated in biological mimetic systems such as AOT reverse micelle, and H2O–CH3OH and H2O–CH3CN mixed solvents. For ofloxacin and norfloxacin, the excited-state intramolecular charge transfer (ICT) is observed. So, fluorescence spectra exhibit reverse solvatochromism in mixed solvents. The change of radiative and non-radiative rate constant can also be explained using this ICT. The influence of dielectric effects of solvent is more significant compared with the specific hydrogen bonding interaction. Theoretical treatments support all of these results.

Protoporphyrin IX is very slightly soluble in water whereas it is soluble in acidic as well as in basic aqueous solution. The UV-vis absorption spectrum of the protoporphyrin IX shows a very sharp and strong maximum absorption peak at 400 nm in acetonitrile-water mixture solution (1∶1v/v). The maximum absorption peaks reacted with divalent transition metal ions such as Cu2+, Zn2+, Fe2+ were shifted to a longer wavelength and the absorbance of the maximum peak decreased as the contents of metal ions increased. However, the absorbance of the maximum absorption peak combined with representative divalent metal ion, Mg2+ has nearly same value and the peak did not shifted. The formation constant (Kf) of the metal protoporphyrin IX complexes reacted with Cu2+, Zn2+, Fe2+ in acetonitrile-water mixture solution (1∶1v/v) were found to be 370, 418 and 24, respectively.

First, the following rate constants (in dm3 mol-1 s-1 ) were reported: k(eaq -+ C2H5OH) = (1.2 ± 0.3) x 103, k(H + C2H5OH) = (2.8 ± 0.2) x 107 and k(OH + C 2H5OH) = (1.85 + 0.1) x 109 The major radiolytic products resulting from aqueous 10-2, 1 and 10 mol dm-3 ethanol were studied in the absence and presence of CO as a function of dose at pH 2 and 7. Probable reaction mechanisms are presented

The characteristic fluorescence properties of quercetin-3-O-rhamnoside (QCRM) and quercetin-3-O-rutinoside (QCRT) were studied in CH3OH-H2O and CH3CN-H2O mixed solvents. Although QCRM and QCRT are known as nonfluorescent molecules, significant fluorescence emissions were discovered at 360 nm in CH3OH and CH3CN when they were promoted to the second excited state. The emission band is broad and structureless and the intensity decreases quickly as the H2O composition in the solvent increases. When the amount of H2O exceeds 60% in both mixed solvents, this emission disappears due to the formation of the distorted excited state. This state will be formed due to the strong intermolecular hydrogen bonding between the polar groups of solute and H2O. As the composition of CH3OH or CH3CN in solvent becomes large, the number of molecules having several intramolecular hydrogen bonding increases. Some of these molecules will be changed to a fluorescent species during the decay process, after excitation. The theoretical calculation further supports these results. The change of the lifetimes, quantum yields, and radiative and nonradiative rate constants of molecules was also examined as a function of solvatochromic parameters for CH3OH-H2O and CH3CN-H2O.

The progress and photosensitivity of quinolone antibiotics are briefly described. By the photolysis of nalidixic acid, the loss of COOH group is observed. The photoreaction of fluoroquinolones involves heterolytic CF bond fragmentation. The protonation and divalent cation complexation equilibria are also examined. The spectroscopic properties of these drugs are intensively investigated in biological mimetic systems such as AOT reverse micelle, and H2O–CH3OH and H2O–CH3CN mixed solvents. For ofloxacin and norfloxacin, the excited-state intramolecular charge transfer (ICT) is observed. So, fluorescence spectra exhibit reverse solvatochromism in mixed solvents. The change of radiative and non-radiative rate constant can also be explained using this ICT. The influence of dielectric effects of solvent is more significant compared with the specific hydrogen bonding interaction. Theoretical treatments support all of these results.

The fluorescence properties of ofloxacin (OFL), norfloxacin (NOR) and flumequine (FLU) were studied in H2O-CH3OH and H2O-CH3CN mixed solvents because these solvents were thought to behave as a biological mimetic system. The emission spectra of OFL and NOR were very sensitive to the composition of the solvents. In the Lippert-Mataga analysis of the steady-state fluorescence data of OFL and NOR, clear reverse solvatochromism was exhibited in both mixed solvents. This observation can be explained by the twisted excited-state intramolecular charge transfer, which is accelerated by water. Theoretical treatments further support these results. The radiative and nonradiative rate constants were analyzed as a function of solvent dipolarity-polarizability (pi*) and hydrogen-bond donor acidity (alpha). These results were well consistent with the suggested mechanism of the excited-state chemical process of OFL and NOR, which depended upon the solvent-solute interactions such as bulk dielectric effects and specific hydrogen-bonding interactions. However, the influence of dielectric effects was more significant. The solvent structures of H2O-CH3CN and the preferential solvation by water were also examined. The emission spectra of FLU do not exhibit any characteristic responses to the properties of the environment.

The spectroscopic properties of enoxacin (ENO), oxolinic acid (OXO) and nalidixic acid (NAL) were studied in various H2O–CH3OH and H2O–CH3CN mixed solvents because these solvents were thought to behave as a biological mimetic system. ENO has piperazinyl group, but OXO and NAL do not have this substituent. The fluorescence emission spectra of ENO were very sensitive to the composition of the solvents. In the Lippert–Mataga analysis of the steady-state fluorescence data, clear reverse solvatochromism was exhibited for ENO in both mixed solvents. This observation can be explained using the excited state twisted intramolecular charge transfer (TICT) from the nitrogen of the piperazinyl group to the keto oxygen. Theoretical calculations further support this observation. The nonradiative and radiative rate constants of these molecules were analyzed as a function of dipolarity–polarizability (π*) and hydrogen bond donor acidity (α) of the mixed solvents. These results for ENO were consistent with the su...

The fluorescence properties of ofloxacin (OFL), norfloxacin (NOR) and flumequine (FLU) were studied in H2O-CH3OH and H2O-CH3CN mixed solvents because these solvents were thought to behave as a biological mimetic system. The emission spectra of OFL and NOR were very sensitive to the composition of the solvents. In the Lippert-Mataga analysis of the steady-state fluorescence data of OFL and NOR, clear reverse solvatochromism was exhibited in both mixed solvents. This observation can be explained by the twisted excited-state intramolecular charge transfer, which is accelerated by water. Theoretical treatments further support these results. The radiative and nonradiative rate constants were analyzed as a function of solvent dipolarity-polarizability (pi*) and hydrogen-bond donor acidity (alpha). These results were well consistent with the suggested mechanism of the excited-state chemical process of OFL and NOR, which depended upon the solvent-solute interactions such as bulk dielectric effects and specific hydrogen-bonding interactions. However, the influence of dielectric effects was more significant. The solvent structures of H2O-CH3CN and the preferential solvation by water were also examined. The emission spectra of FLU do not exhibit any characteristic responses to the properties of the environment.

The photoinduced conversion of CO in aqueous solution under the influence of vacuum-uv radiation at λ = 185 nm has been investigated at pH values ranging from 2 to 13. Formaldehyde, glyoxal, carboxylic acids and small amounts of glycol were determined as final products. Initial quantum yields for product formation have been determined. A probable reaction mechanism is presented.

The photoinduced decomposition of aqueous formaldehyde in air-free solutions, some saturated with CO, was investigated. The initial quantum yield of aldehyde decomposition, Q i (—HCHO), strongly depends on the substrate concentration. The presence of CO in the solution essentially diminishes the aldehyde decomposition because of back reactions. The quantum yields of the final products, glyoxal and carboxylic acids (formic and oxalic), are determined under various experimental conditions. A probable reaction mechanism is presented in accordance with the results.