Fluoride recognition by a chiral urea receptor linked to a phthalimide chromophore.

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.

Synthesis, primary photophysical and antibacterial properties of naphthyl ester cinoxacin and nalidixic acid derivatives.

We have synthesized two naphthyl ester quinolone derivates and determined their ability to generate reactive oxygen species (ROS) such as (1)O(2), ()OH, H(2)O(2) upon photolysis with UV-A light. The ability of cinoxacin (1) and nalidixic acid (2), and their naphthyl ester derivatives (3 and 4) to generate a dose-dependent amount of singlet oxygen and ROS (()(-)O(2), ()OH) in cell-free systems was detected by histidine assay and by luminol-enhanced chemiluminescence (LCL), respectively. Their electronic absorption and emission spectra were quantified and their photostability was determined. Their tendency to generate peroxidic derivative species showed the following order: 3>4; in contrast, their ability to generate singlet oxygen was 4>3 and these were better sensitizers than their parent quinolones 1 and 2. The antibacterial activity in darkness and under irradiation of compounds 3 and 4 was tested on Escherichia coli and compared with that of their parent compounds. An enhanced antibacterial activity by irradiation of the naphthyl esters of cinoxacin and nalidixic acid on E. coli was observed.

Photodegradation pathways and the in vitro phototoxicity of pyrazinamide, a phototoxic antitubercular drug.

The phototoxic antitubercular drug pyrazinamide (1) is photolabile under irradiation with UV-A light as well as with a N2 laser (at 337 nm) in aerobic conditions. Irradiation in methanolic and in aqueous solutions of 1 produces four and three photoproducts, respectively. Their formation involves primary alpha-cleavage between the excited carbonyl of the amido group and the aromatic ring followed by hydrogen abstraction and dimerization. Pyrazinamide was able to cause photohemolysis in human erythrocytes and peroxidation of linoleic acid. Inhibition of both processes on addition of reduced glutathione (GSH) or ascorbic acid suggests the involvement of radicals. The absence of inhibition of the photohemolysis and lipid peroxidation processes in the presence of sodium azide (NaN3), or irradiation under argon, and the absence of singlet oxygen during the photolysis confirmed with 2,5-dimethylfuran rules out the possibility of participation of 1O2 in this process. Glutathione depletion was also observed. A radical intermediate was evidenced by thiobarbituric acid that was used as a radical probe, as well as by the dimerization of cysteine. No photohemolysis was detected in presence of the isolated photoproduct. We have also determined the relative efficiencies for the formation of single strand breaks after the irradiation of pBR322 DNA and pyrazinamide, which was also reduced in the presence of GSH.

Estudios in vitro de los mecanismos fotooxidantes y antioxidantes de los principios activos del aloe vera / Study in vitro of the mechanim phototoxicity and antioxidant of the pricipios actives of the aloe-emodina

En este trabajo se determinó la fototoxicidad in vitro sobre eritrocitos humanos, de los principios activos del Aloe Vera, emodina aloe-emodina y rheina. Esto fue analizado por medio de espectrofotometría UV-Vis y fluorescencia en diferentes medios, bajo fuentes de irradiación Visible y UV-A. El estudio de la capacidad antioxidante de estos tres compuestos se determinó mediante estudios de quimioluminescencia y se comparó con la de las vitaminas E y C. La capacidad de desactivar radicales hidroxilo fue evidenciado para la Emodina y Rheina, siendo similar a las de la vitaminas E y C. Mientras que la capacidad antioxidante de la Aloe-emodina fue mucho menor que las anteriores

Photo-induced interaction of antibacterial quinolones with human serum albumin.

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.