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Abstract: The main differences between electron and proton transfers that take place in biological systems are examined. The relation between the distance dependence of the rate constant and the mass of the transferred particle is analyzed in detail. Differences between the two processes have important consequences at the experimental level, which are discussed. The various mechanisms that ensure the coupling between electron and proton transfers are briefly described. [Copyright &y& Elsevier]

Abstract: This study deals with the secondary ion yield improvement induced by using C60 + primary ions instead of Ga+ to enhance the detection thresholds of the organic contaminations at the Si wafer surfaces by ToF-SIMS. For that purpose, a piece of Si wafer has been analysed with both ion sources. A large improvement is observed for the detection of hydrocarbon contaminants with C60 + primary ions as compared to Ga+ ions. A similar improvement for organic contaminations, such as phthalates and aliphatic amines, is observed in both secondary ion polarities. The Si atomic ion constitutes a minor peak with C60 + ions while it dominates the spectrum in the case of Ga+ ions. However, with the C60 + source, inorganic combination peaks with the elements Si and O, are observed in the positive spectra (i.e. Si2O2H+), while they are marginal with the Ga+ source. Furthermore, a series of negative silicon oxide clusters, Si n O(2n+1)H−, is observed up to n =16 (977m/z) in the case of C60 + ions. With Ga+ ions, the largest negative silicon oxide cluster corresponds to n =4 (257m/z). The detection of backscattered C60 fragments is evoked to explain the origin of some hydrocarbon peaks with low H content. On average, for a comparable number of primary ions per spectrum, the C60 + ion source gives intensities between two and four orders of magnitude higher than the Ga+ one. [Copyright &y& Elsevier]

Abstract: In Rhodobacter sphaeroides periplasmic nitrate reductase NapAB, the major Mo(V) form (the “high g” species) in air-purified samples is inactive and requires reduction to irreversibly convert into a catalytically competent form (Fourmond et al., J. Phys. Chem., 2008). In the present work, we study the kinetics of the activation process by combining EPR spectroscopy and direct electrochemistry. Upon reduction, the Mo (V) “high g” resting EPR signal slowly decays while the other redox centers of the protein are rapidly reduced, which we interpret as a slow and gated (or coupled) intramolecular electron transfer between the [4Fe–4S] center and the Mo cofactor in the inactive enzyme. Besides, we detect spin–spin interactions between the Mo(V) ion and the [4Fe–4S]1+ cluster which are modified upon activation of the enzyme, while the EPR signatures associated to the Mo cofactor remain almost unchanged. This shows that the activation process, which modifies the exchange coupling pathway between the Mo and the [4Fe–4S]1+ centers, occurs further away than in the first coordination sphere of the Mo ion. Relying on structural data and studies on Mo-pyranopterin and models, we propose a molecular mechanism of activation which involves the pyranopterin moiety of the molybdenum cofactor that is proximal to the [4Fe–4S] cluster. The mechanism implies both the cyclization of the pyran ring and the reduction of the oxidized pterin to give the competent tricyclic tetrahydropyranopterin form. [Copyright &y& Elsevier]

Abstract: Reproducing the naturally occurring O2-tolerant hydrogenases is a potential strategy to make the oxygen sensitive enzymes, produced by organisms of biotechnological interest, more resistant. The search for resistance “hotspots” that could be transposed into sensitive hydrogenases is underway. Here, we replaced two residues (Y77 and V78) of the oxygen sensitive [NiFe] hydrogenase from Desulfovibrio fructosovorans with Gly and with Cys, respectively, to copy the active site pocket of the resistant membrane-bound [NiFe] enzyme from Ralstonia eutropha and we examined how this affected oxygen sensitivity. The results are discussed in the light of a short review of the recent results dealing with the reactivity of hydrogenases towards oxygen. [ABSTRACT FROM AUTHOR]

Abstract: Vanadia-titania catalysts are highly regarded for the control of industrial and domestic gas effluents. They are particularly used for the abatement of volatile organic compounds and for the removal of aromatic, polyaromatic and polychlorinated air pollutants like furans and dioxins. Here, mixed oxide catalysts are formed by non-hydrolytic condensation of chloride precursors with diisopropyl ether in non-aqueous medium. Calcination was applied to provoke the migration of the vanadium oxide toward the surface of the anatase particles, leading to well-spread vanadia species. The materials are made of mesoporous spherical particles of a few microns, themselves constituted by the aggregation of 10–25nm sized particles. Their chemical composition is precisely controlled. The samples are characterized by ICP-AES, N2-physisorption, XRD, XPS, SEM and TOF-SIMS. Their performances as total oxidation catalyst are evaluated in the deep oxidation of benzene, chosen as a model atmospheric pollutant. The activity of the materials compares well with that of catalysts prepared by classical wet impregnation. Along with the V surface concentration, the environment in which V surface species are located is identified as a key parameter. The superior activity of polymeric species as compared to isolated ones is shown. [Copyright &y& Elsevier]

Abstract: In NiFe hydrogenases, electrons are transferred from the active site to the redox partner via a chain of three Iron–Sulfur clusters. Intriguingly, the surface-exposed [4Fe4S] cluster has three cysteines and one histidine as a ligand, which is quite unusual. When this Histidine (H184 in Desulfovibrio fructosovorans) was changed into a glycine, the distal cubane was still assembled but the oxidative activity of the mutants was 3% of that of the WT. As glycine is not a cubane ligand, a water molecule is likely to stabilize the fourth iron atom, making this coordination position labile. It was then possible to exchange the water ligand with an exogenous ligand. Depending on the molecule tested, the enzyme exhibited various activity levels, making possible a modulation of the enzyme activity. [Copyright &y& Elsevier]

Abstract: The influence of the presence of H2 on the physico-chemical properties of a Pd(10wt.%)/γ-Al2O3 catalyst was investigated. Catalysts were treated under methane combustion conditions with various amounts of H2 in the feed. Samples obtained were characterized by BET, CO-chemisorption, XRD, XPS and/or ToF-SIMS techniques. The effect of H2 is essentially to sinter the palladium phase and to help remove surface chlorine coming from the palladium precursor. In presence of low amounts of H2, O migration phenomena are suggested to occur to maintain the surface of the palladium particles in an oxidized state while, as the H2 concentration increases, metallic palladium progressively forms in the bulk. Above a threshold value, the H2 concentration becomes too high, metallic palladium is formed on the surface. [Copyright &y& Elsevier]

Reduced PTFE can be grafted by nitro and bromo-phenyl diazonium tetrafluoroborate salts in a manner similar to that used for carbon, except that no application of a reductive potential during grafting was required. Grafting was evidenced by cyclic voltammetry, X-ray fluorescence or ToF-SIMS. Nitro- and bromo-phenyl moieties were covalently linked to the PTFE material and could be eliminated only by abrasion. [Copyright &y& Elsevier]

The hndABCD operon from Desulfovibrio fructosovorans encodes an uncommon heterotetrameric NADP-reducing iron hydrogenase. The presence of a [2Fe–2S] cluster likely located in the C-terminal region of the HndA subunit has already been revealed. We have cloned and expressed the truncated hndA gene in Escherichia coli to isolate the structural [2Fe–2S] module. Optical and EPR spectra are found identical to that of the native HndA subunit and the midpoint redox potential (−385 mV) is similar to that of the native protein (−395 mV). These results clearly demonstrate that the C-terminal region of HndA is a structurally independent [2Fe2S] ferredoxin-like domain. In the same way, the N-terminal domain of the HndD subunit was overproduced in E. coli and characterized. The presence of a [2Fe–2S] cluster was evidenced by optical spectroscopy. The midpoint redox potential (−380 mV) of this domain was found very close to that of the truncated HndA subunit but the EPR properties were significantly different. The various EPR properties allowed us to observe an electron exchange between the two [2Fe–2S] ferredoxin-like domains of the HndA and HndD subunits. Moreover, domain–domain interactions, observed by far-western experiments, indicate that these subunits are direct partners in the native complex. [Copyright &y& Elsevier]