The anion chemosensor 1 based on a urea-activated phthalimide with a stereogenic centre was synthesized using an efficient procedure involving a Curtius rearrangement. Its photophysical properties were estimated in several solvents. Sensor 1 detected fluoride with absorption as well as fluorescence changes and was only observable for this case and not for other halides. The appearance of a new CT complex emission at a longer wavelength and no changes in the singlet lifetime of 1 in the presence of fluoride supported a fluorescence static quenching mechanism. 1H-NMR studies, together with theoretical calculations based on DFT methods at the B3lYP/6-31G* level of theory confirmed the formation of a [1-F]- complex through H-bonding interactions rather than receptor deprotonation in the recognition process. Reversibility of this process was observed upon addition of a protic solvent.
The absorption and fluorescence spectrums of four antibacterial quinolones, namely, ciprofloxacin, norfloxacin, enoxacin, and cinoxacin, were studied in the presence of human serum albumin (HSA). Of the three fluoroquinolones studied, ciprofloxacin and norfloxacin were found to bind efficiently to HSA when irradiated with visible light, whereas the third, enoxacin, bound only moderately. On the other hand, cinoxacin, a nonfluorinated quinolone of the first generation, did not show any interaction with HSA. The findings were inferred by monitoring the evolution of the fluorescence spectrums of the solutions as a function of time. A direct relationship between the capacity of the photo-induced defluorination to produce aryl cation intermediates, and the subsequent binding reaction with HSA, was observed and is discussed.
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