Marc Beley

Electrocatalytic reduction of carbon dioxide by nickel cyclam2+ in water: study of the factors affecting the efficiency and the selectivity of the process

The electrocatalytic properties of Ni cyclam/sup 2 +/ in CO/sub 2/ reduction have been studies. The influence of various experimental factors on the course of the reaction has been investigated. Under given conditions, Ni cyclam/sup 2 +/ is remarkably efficient and selective for electroreduction of CO/sub 2/ into CO, even in water. The stability of the system has been tested in long range electrolysis, showing that even after thousands of catalytic cycles no deactivation occurs. The mechanistic investigation presently described points to the importance of molecular species adsorbed on the cathode surface. The contribution of reduced species in the bulk is marginal. In addition, during the electrocatalytic process, a nickel(I) carbonyl complex is present: (Ni(cyclam)(CO))/sup +/. The latter complex may be involved in the catalytic reaction leading to CO evolution. Surprisingly, the behavior of Ni cyclam/sup 2 +/ as electrocatalyst is unique. Among the numerous complexes investigated, only Ni cyclam/sup 2 +/ shows such a large selectivity for the electroreduction of CO/sub 2/ over the electroreduction of water. The size of the cyclam ligand and the presence of secondary amine groups (NH) might account for the very special properties of the electrocatalyst.

A room temperature luminescent cyclometallated ruthenium(II) complex of 6-phenyl-2,2'-bipyridine

Abstract The cyclometallated complex Ru(tt)(phbp) + (tt=4′-tolyl-2,2′:6′2″-terpyridine, phbp=6-phenyl-2,2′-bipyridine) with a (N,N,N)(C,N,N) coordination, has been synthesized and characterized by 1 H NMR, UV, FAB-MS spectral techniques and by elemental analysis. We have compared its electrochemical and photophysical properties with those of the non-orthometallated analogues Ru(tt) 2 2+ and Ru(terpy) 2 2+ (terpy=2,2′:6′,2″-terpyridine). The most remarkable feature of Ru(tt)(phbp) + is its ability to luminesce at room temperature in alcoholic and nitrile solvents. The lifetime of its 3 MLCT excited state is 60 ns in CH 3 CN.

Electrochemical regeneration of nicotinamide cofactor using a polypyrrole rhodium bis-terpyridine modified electrode

Abstract A rhodium (III) bis-terpyridine complex covalently linked to two pyrrole groups has been electropolymerized on a reticulated vitreous carbon electrode. The resulting modified electrode has been used in the electrocatalytic reduction of nicotinamide adenine dinucleotide into 1,4-NADH. The efficiency of a system incorporating cyclohexanone as substrate and liver alcohol dehydrogenase as enzyme has demonstrated the feasibility of bioreactors with electrochemical regeneration of NADH cofactor.

Molecular catalysts in photoelectrochemical cells: Study of an efficient system for the selective photoelectroreduction of CO2: p-GaP or p-GaAs/Ni(cyclam)2+, aqueous medium

Abstract For about 15 years, the electroreduction of carbon dioxide has again attracted close attention. This work shows the interest in using photoelectrochemical cells which associate molecular catalysts with a semiconducting electrode, in order to increase the efficiency of CO2 reduction. Two systems are analysed more precisely: p-GaAs/0.1 M KClO4, H2O, Ni(cyclam)2+ (A) and p-GaP/0.1 M NaClO4, H2O, Ni(cyclam)2+ (B), which undergo the photo-assisted selective reduction of CO2 to CO as early as −0.2 V (vs. SHE). The working principle of these systems has been investigated, as well as the possible causes of their loss in efficiency in the course of experiment. The latter is attributed to the progressive formation of “carbon” islands on the irradiated semiconductor surface, this process being almost completely inhibited at sufficiently high catalyst concentrations.

Combination of Cobalt and Iron Polypyridine Complexes for Improving the Charge Separation and Collection in Ru(terpyridine)2‐Sensitised Solar Cells

Mixtures of polypyridine Fe(II) and Co(II) complexes are used as electron mediators in Ru-thienyltpy-sensitised solar cells (tpy=terpyridine). The use of the metalorganic redox couples allows for improved charge-collection efficiency with respect to the classical iodide/iodine couple which, when associated to Ru-tpy(2) dyes, usually produces poor performance. The improved charge collection is explained by a combination of effective dye regeneration and decreased recombination with the oxidised electrolyte on the basis of data obtained by transient spectroscopy and photoelectrochemical measurements. The efficiency of the regeneration cascade is also critically dependent upon the ability of the Co(II) complex to intercept Fe(III) centres, as clearly indicated by chronocoulometry experiments.

Theoretical study of new ruthenium-based dyes for dye-sensitized solar cells.

Two relevant, recently reported, ruthenium-based complexes to be used as sensitizers in Grätzel photovoltaic cells are theoretically studied. The UV/vis absorption spectra have been computed within the time-dependent density functional theory formalism. The obtained excitation energies are compared with the experimental results, and the nature of the transition is analyzed in terms of the electronic density. A preliminary study on the performance of different functionals against the equation of motion coupled cluster is performed on a smaller model system.

Photoassisted electro-reduction of CO2 on p-GaAs in the presence of Ni cyclam2+

Donnees sur la reduction photoelectrochimique de CO 2 sur GaAs-p, avec utilisation des proprietes electrocatalytiques de Ni cyclane 2+ avec cyclane=tetraaza-1,4,8,11 cyclotetradecane

Synthesis of bis-cyclometallating N-C-N hexadentate ligands via C-C aromatic couplings and their dinuclear ruthenium(II) complexes

Abstract By combining palladium catalyzed C-C coupling procedures either based on aromatic stannanes or utilizing boronic acids or esters (Suzukis reaction), various bis-cyclometallating N-C-N ligands could be prepared. Their di-ruthenium(II) complexes have also been synthesized.

Apoptosis/necrosis switch in two different cancer cell lines: Influence of benzoquinone- and hydrogen peroxide-induced oxidative stress intensity, and glutathione

Depending on the strength of oxidative stress, cells exhibit proliferative, apoptotic or necrotic responses. We have investigated whether the severity of glutathione (GSH) depletion could determine the type of cell death using 1,4-benzoquinone (BQ) and H(2)O(2) in two different tumor cell lines (human mammary gland carcinoma MCF-7 and rat hepatoma H5-6). BQ-treated surviving cells showed an increase in GSH, but no detectable oxidized glutathione (GSSG) nor reactive oxygen species (ROS) augmentation. Alternatively, H(2)O(2) depressed GSH. BQ induced mostly apoptosis, up to 90% cell elimination, while necrosis was prominent in H(2)O(2)-treated cultures. The resistance of BQ-treated cells to necrosis could be due to increased cellular GSH and formation of BQ-GSH conjugates which are less toxic than free BQ, minimal toxicity being provided by GS4-BHQ. This ability of certain cancer cells to tightly keep the apoptotic pathway may have therapeutic applications for oxidation-based drugs.

Photophysical and photochemical properties of ruthenium and osmium complexes with substituted terpyridines

Ruthenium(II) and osmium(II) complexes with 2,2′:6′,2″-terpyridine (terpy), 4′-(p-tolyl)-2,2′:6′,2″-terpyridine (tterpy) and 4,4′,4″-triphenyl-2,2′:6′,2″-terpyridine (tterpy) have been prepared and characterized. Their electrochemical, photophysical and photochemical properties (room temperature) have been studied. Metal-to-ligand charge-transfer excited-state quenching measurements using various redox active species clearly show that [Ru(tpterpy)2]2+ is a good electron-transfer agent under light irradiation.