Modèles de jonctions sucre-protéine marqués par Spin: synthèse, étude spectroscopique, premiers tests d'activité biologique

L'introduction d'un pont hydroxylimino entre un acide aminé et un sucre représente la caractéristique principale de ce travail. Nous décrivons la synthèse de ces composés modèles et leurs propriétés spectroscopiques

Electrochemical Reduction of Cyanides at Metallic Cathodes: A Comparison with Biological HCN Reduction

The electrochemical reduction of cyanides has been studied at a number of cathodes both in near-neutral and in alkaline solutions. Nickel appears as the most effective cathode material, promoting cyanide reduction with current efficiencies close to 70%, even in moderately alkaline solutions. In all cases, the eletroreduction of cyanides leads to a mixture of (methylamine) and products (methane and ammonia). The use of Nafion films loaded with Ni microparticles enabled us to markedly increase the effective current densities for cyanide reduction. The electrochemical reduction of is shown to present interesting similarities and differences with the biological cyanide reduction process. </p

Reductive Cleavage of the Carbon−Halogen Bond in Simple Methyl and Methylene Halides. Reactions of the Methyl Radical and Carbene at the Polarized Electrode/Aqueous Solution Interface

Reactivities of methyl radical and carbene species, electrogenerated on the surfaces of group IB metals via reductive cleavage of simple methyl and methylene halides (bromides and iodides) in aqueous solution, are investigated using cyclic voltammetry associated with the products' identification by gas chromatography/mass spectrometry. To appreciate specific changes in the electrochemical behavior of the above halides, related to the nature of the electrode material, similar measurements have also been carried out employing an inert glassy carbon electrode. The replacement of glassy carbon by the group IB metals Ag and Cu was found to lead to a sensible shift (several hundred mV) in their reduction potentials (Ep). Consequently, the reduction of CH2Br2, CH2I2, and CH3I starts at potentials positive with respect to the potentials of zero charge (pzc) of Ag and Cu, producing significant amounts of ethylene and ethane, respectively. Methane becomes the dominant reaction product only at the potentials more negative than Ep. The extent of interaction between the reaction intermediates and the electrode surface clearly depends not only on the potential but also on the electronic structure of the electrode. This was confirmed by the results of experiments conducted using the Au and glassy carbon electrodes, having pzc values much more positive than Ag and Cu, at which methane was the only detected product of the CH3X and CH2X2 reduction, over the entire range of potentials. The collected results demonstrate that the reactions undergone by the electrogenerated CH2 and •CH3 species can be oriented toward formation of either ethylene/ethane or methane by a suitable choice of the electrode material and of the range of applied potentials. The use in this study of Ag and Cu electrodes allows generation of the CH2 and •CH3 radicals above the onset potential for H2 evolution, so that their reactivity can be investigated virtually in the absence of competing reactions

Spin labeled hydroxyproline analogues

Abstract The synthesis and properties of both epimers of 4-(N-hydroxyamino)-N-tosyl-L-proline methyl ester and derivatives thereof are reported. In the presence of air, the compounds bearing a free N-hydroxyamino group oxidized in solution to give the corresponding aminoxyl free radicals, EPR spectra of which were recorded. None of these compounds showed any interesting biological activity as such, but they constitute potential synthetic building blocks towards spin labeled glycopeptide or oligopeptide analogues

Photoelectrolytic oxidation of organic species at mesoporous tungsten trioxide film electrodes under visible light illumination

Operation of a photoelectrolyser fitted with a semitransparent semiconducting WO3 film photoanode is described. Due to its band-gap energy of 2.5 eV, the photoresponse of the WO3 electrode extends into the blue part of the visible spectrum up to 500 nm. The WO3 photoanode exhibits particularly high incident photon-to-current efficiencies for the oxidation of several organic species with the maximum occurring at ca. 400 nm. Experiments conducted under simulated AM 1.5 solar illumination demonstrated efficient photodegradation of a variety of organic chemicals including small organic molecules as well as EDTA and anthraquinonic Acid Blue 80 dye. Although, due to the inherent mass transport limitations, the described device appears best suited to the treatment of industrial wastewater containing from 100 ppm to few g L−1 of impurities, almost complete removal of organic carbon was observed in several photoelectrolysis runs. This is apparently associated with the concomitant photooxidation of sulphate-based supporting electrolyte resulting in the formation of a powerful chemical oxidant-persulphate

Spin labeled hydroxyproline analogues

The synthesis and properties of both epimers of 4-(N-hydroxyamino)-N-tosyl-Image -proline methyl ester and derivatives thereof are reported. In the presence of air, the compounds bearing a free N-hydroxyamino group oxidized in solution to give the corresponding aminoxyl free radicals, EPR spectra of which were Recorded. None of these compounds showed any interesting biological activity as such, but they constitute potential synthetic building blocks towards spin labeled glycopeptide or oligopeptide analogues

Photoelectrochemical Oxidation of Water at Transparent Ferric Oxide Film Electrodes

The fabrication of thin-film Fe2O3 photoanodes from the spray pyrolysis of Fe(III)-containing solutions is reported along with their structural characterization and application to the photoelectrolysis of water. These films combine good performance, measured in terms of photocurrent density, with excellent mechanical stability. A full investigation into the effects that modifications of the spray-pyrolysis method, such as the addition of dopants or structure-directing agents and changes in precursor species or carrier solvent, have on the performance of the photoanodes has been realized. The largest photocurrents were obtained from photoanodes prepared from ferric chloride precursor solutions, simultaneously doped with Ti4+ (5%) and Al3+ (1%). Doping with Zn2+ also shows promise, cathodically shifting the onset potential by 0.22 V

Spin labeled nucleoside analogues : 4'-hydroxymorpholin-2'-ylpurines and pyrimidines

Upon borane-pyridine reduction, a series of nucleoside dialdehyde dioximes 2 underwent cyclization to the corresponding 4'-hydroxymorpholin-2'-ylpurines or pyrimidines 3 from which the peracetyl derivatives 4 were prepared. At room temperature, compounds 3 and 4 exist as a mixture of invertomers in which the 4'S (equatorial 4'-OH or 4'-OAc) predominates. A 14 kcal/mol, nitrogen inversion barrier was estimated from variable temperature experiments. N.O.E. and 3JCH measurements established the anti conformation of the base-"sugar" bond. Compounds 3 spontaneously oxidized to the corresponding aminoxyl free radicals, EPR spectra of which showed that they existed in a chair conformation