Spectroscopic Properties of Fluoroquinolone Antibiotics in Water-methanol and Water-acetonitrile Mixed Solvents¶

Abstract

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 (π*) and hydrogen‐bond donor acidity (α). 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.

Fluoroquinolone Antibiotics Having the Potential to Interfere with Fluorescence‐Based Diagnosis†

“…It should be noted that the φ of norfloxacin and ofloxacin in water and various solvent mixtures has been previously reported (38). These reports detail the result of increasing hydrophobicity on the spectroscopic properties of fluoroquinolones.…”

Spectroscopic Properties of Various Quinolone Antibiotics in Aqueous—organic Solvent Mixtures¶

“…All compounds, both quinolones and naphthyridones, contain the keto oxygen at 4‐carbon atom and carboxylic acid side chain at 3‐carbon atom, both of which have now been found to be essential to activity. Quinolone antibiotics having different structures and substituents exhibit different antibacterial responses in various environments ( 4–8 ). Especially, the two groups of drugs, ofloxacin (OFL), norfloxacin (NOR), enoxacin (ENO) etc.…”

“…, which have the piperazinyl group at the 7‐carbon, and nalidixic acid (NAL), flumequine (FLU), oxolinic acid (OXO) etc. , which do not have this group, show completely different antibacterial responses and chemical properties as the physicochemical properties of environments are changed ( 5–8 ) (Scheme 1). Such observations suggest that there is a major difference between these two groups of drugs, with respect to either their mode of action or their mechanism of penetration into bacteria.…”

“…It is very important to study the physicochemical properties of these drugs in various environments, especially in vivo , because this investigation can provide essential knowledge in our understanding of the mechanism of antibacterial activity and cutaneous photosensitization. Because it is not easy to study the properties of quinolone antibiotics in vivo directly, several investigations have recently been done in biological mimic systems such as aerosol‐OT (AOT) reverse micelle or aqueous‐organic solvent mixture ( 5,7,10–14 ). The H 2 O‐CH 3 OH and H 2 O‐CH 3 CN solvent mixtures have been found suitable to emulate the biological conditions because they simultaneously show low polarity and a partially aqueous content, always present in biological systems ( 7,10,11 ).…”

“…Because it is not easy to study the properties of quinolone antibiotics in vivo directly, several investigations have recently been done in biological mimic systems such as aerosol‐OT (AOT) reverse micelle or aqueous‐organic solvent mixture ( 5,7,10–14 ). The H 2 O‐CH 3 OH and H 2 O‐CH 3 CN solvent mixtures have been found suitable to emulate the biological conditions because they simultaneously show low polarity and a partially aqueous content, always present in biological systems ( 7,10,11 ). In H 2 O‐CH 3 OH and H 2 O‐CH 3 CN mixed solvents, the change of π* scale, which is an index of solvent dipolarity–polarizability, is similar as the composition of binary mixtures is changed.…”