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In search for efficient electrocatalysts for the oxidation of L-cysteine on glassy carbon, multivanadium-substituted polyoxometalates (POMs, for short) were tested. (P 2 V 3 W 15 ). Electrochemistry shows that the sandwich-type POM contains 2 V IV centers and one V V center and must be formulated As 2 V 2 IV VW 18 , in agreement with titration, elemental analysis and magnetic measurements on this element. The two-electron composite wave that features the redox behaviour of the two V IV centers of As 2 V 2 IV VW 18 are very close to each other and remains practically merged whatever the potential scan rate. In addition of this sharp contrast with the behaviours of the two V V centers of P 2 V 2 W 16 or P 2 MoV 2 W 15 , the very slow electron transfer kinetics associated with the second wave of P 2 V 3 W 15 appears also at variance with the case of As 2 V 2 IV VW 18 . All the POMs of this work proved efficient for the oxidation of L-cysteine. Comparison of the present results with those of mono-Vanadium substituted POMs indicates that accumulation of vanadium atoms in the POM framework is beneficial in the electrocatalytic process. In addition, the present work highlights the important influence of the POM structure in the electrocatalytic oxidation of L-cysteine. The remarkable outcome of this work is that the potential for the oxidation of L-cysteine in the presence of the selected POMs has been substantially driven in the negative direction compared to the case of glassy carbon alone, a feature which is associated with faster kinetics.The stability of the systems must also be pointed out.

Cobalt I 7200Cobalt-Containing Silicotungstate Sandwich Dimer [{Co3(B-β-SiW9O33(OH))(B-β-SiW8O29(OH)2)}2] 22-. -Title compound (IV) is characterized by single crystal XRD, IR and UV/Vis spectroscopy, magnetic and electrochemical studies, and by gel filtration chromatography. (IV) crystallizes in the monoclinic space group P21/n with Z = 2. Its anion represents a novel class of asymmetric sandwich-type polyanions. It contains three cobalt ions, which are encapsulated between an unprecedented (B-β-SiW9O34) fragment and a (B-β-SiW8O31) unit. The two reversible redox couples observed by cyclic voltammetry in the positive potential domain are attributed to the redox processes of Co 2+ centers and indicate that the two types of Co 2+ centers in the structure are oxidized in separate waves. Such reversibility of Co 2+ centers within multi-Co-substituted polyoxometalates is uncommon. -(BASSIL, B. S.; KORTZ*, U.; TIGAN, A. S.; CLEMENTE-JUAN, J. M.; KEITA, B.; DE OLIVEIRA, P.; NADJO, L.; Inorg. Chem. 44 (2005) 25, 9360-9368; Sch. Eng. Sci., Intern. Univ. Bremen, D-28759 Bremen, Germany; Eng.) -Schramke 10-033

Large-bore natural gas engines may use pre-chamber ignition. Despite extensive research in engine environments, the exact nature of the jet, as it exits the pre-chamber orifice, is not thoroughly understood and this leads to uncertainty in the design of such systems. In this work, a specially-designed rig comprising a quartz pre-chamber fit with an orifice and a turbulent flowing mixture outside the pre-chamber was used to study the pre-chamber flame, the jet, and the subsequent premixed flame initiation mechanism by OH* and CH* chemiluminescence. Ethylene and methane were used. The experimental results are supplemented by LES and 0D modelling, providing insights into the mass flow rate evolution at the orifice and into the nature of the fluid there. Both LES and experiment suggest that for large orifice diameters, the flow that exits the orifice is composed of a column of hot products surrounded by an annulus of unburnt pre-chamber fluid. At the interface between these layers, a cylindrical reaction zone is formed that propagates in the main chamber in the axial direction assisted by convection in the jet, but with limited propagation in the cross-stream direction. For small orifice diameters, this cylinder is too thin, and the stretch rates are too high, for a vigorous reaction zone to escape the pre-chamber, making the subsequent ignition more difficult. The methane jet flame is much weaker than the one from ethylene, consistent with the lower flame speed of methane that suggests curvature-induced quenching at the nozzle and by turbulent stretch further downstream. The velocity of the jet is too high for the ambient turbulence to influence the jet, although the latter will affect the probability of initiating the main premixed flame. The experimental and modelling results are consistent with ongoing Direct Numerical Simulations at ETH Zurich.

Recent experimental results about the oxidation of methionine enkephalin by ·OH radicals indicated an intramolecular electron transfer between the C-terminal methionine radical cation and the tyrosine N-terminus too fast to be observed. We have investigated the thermodynamic possibility of this intramolecular electron transfer by calculating the one-electron redox potentials of both residues for several conformations of the peptide, extracted from the experimental data of the Protein Data Bank (1PLW). Using a QM/MM approach, we show that the redox potential of the Met(•+)/Met couple is higher than that of the TyrOH(•+)/TyrOH one (tyrosine is denoted as TyrOH) for all conformations. The intramolecular electron transfer between both residues (from TyrOH to Met(•+)) is thus always thermodynamically allowed. Previously, we had performed topological studies on the intramolecular electron transfer which predicted this charge transfer. A study by cyclic voltammetry pointed out that the wave belonging to methionine is not present when methionine enkephalin is oxidized and only the direct involvement of the tyrosine residue is observed.

We analyse the results of our experimental laboratory approximation of motorways networks with slime mould Physarum polycephalum. Motorway networks of fourteen geographical areas are considered: Australia, Africa, Belgium, Brazil, Canada, China, Germany, Iberia, Italy, Malaysia, Mexico, The Netherlands, UK, USA. For each geographical entity we represented major urban areas by oat flakes and inoculated the slime mould in a capital. After slime mould spanned all urban areas with a network of its protoplasmic tubes we extracted a generalised Physarum graph from the network and compared the graphs with an abstract motorway graph using most common measures. The measures employed are the number of independent cycles, cohesion, shortest paths lengths, diameter, the Harary index and the Randic index. We obtained a series of intriguing results, and found that the slime mould approximates best of all the motorway graphs of Belgium, Canada and China, and that for all entities studied the best match between Physarum and motorway graphs is detected by the Randic index (molecular branching index)

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