Oxidation of methanol at the network film of polyoxometallate-linked ruthenium-stabilized platinum nanoparticles

We explore here the ability of ruthenium hydroxo species to undergo spontaneous deposition on Pt nanoparticles and to form colloidal solutions of oxoruthenium-protected (-stabilized) nanoparticles of Pt. These particles can be spontaneously attracted to carbon substrates, and they form ultrathin self-assembled films. Fabrication of the multilayer network films on electrodes has been achieved by linking the positively charged oxoruthenium-covered Pt clusters with heteropolyanions of tungsten. By repeated alternate treatments in a solution of phosphododecatungstate (PW₁₂O₄₀^3–) and in a colloidal suspension of oxoruthenium-protected (-stabilized) Pt nanoparticles, the film thickness can be increased systematically (layer by layer) to form stable three-dimensional assemblies on carbon electrodes. It is apparent from cyclic voltammetric and chronoamperometric measurements (that were performed at 20 and 60 °C) that the resulting hybrid films show attractive properties towards the oxidation of methanol at fairly low potentials (0.25–0.4 V versus the saturated calomel electrode). With approximately the same loading of oxoruthenium-covered Pt nanoparticles and under analogous conditions, linking or derivatizing the nanoparticles with phosphotungstate leads to the systems higher electrocatalytic activity. It is possible that, in addition to ruthenium hydroxo species, PW₁₂O₄₀^3– exhibits an activating effect on dispersed Pt particles. An alternative explanation may involve the possibility of different morphologies of the catalytic films in the presence and absence of phosphotungstate anions.Dedicated to Zbigniew Galus on the occation of his 70th birthday     

Square-wave anodic stripping voltammetry with a mercury-plated reticulated vitreous carbon electrode

A rotating mercury-plated reticulated vitreous carbon (RVC) electrode is tested for square-wave anodic stripping voltammetry; RVC provides very large surface areas which are easily plated with mercury. Despite the ill-defined geometry of the electrode, the square-wave stripping peaks are very well defined; their behaviour conforms partly to known theory for square-wave stripping from mercury film electrodes. Fast analytical determinations of lead and cadmium in the μg l^?1 range are facilitated by the high efficiency of the preconcentration step and the high sensitivity given by the stripping waveform.     

Explicit finite-difference simulation of a dropping mercury electrode utilizing an exponentially expanded space grid

An exponentially expanded space grid has been applied in the explicit finite-difference computer simulation of a dropping mercury electrode (DME). The simulator has been proved to be considerably faster than previously described models using uniform grids (S.W. Feldberg, J. Electroanal. Chem., 109 (1980) 69) and easily adaptable to different electrode reaction stoichiometries and forms of excitation potential.     

Quark matter imprint on gravitational waves from oscillating stars

We discuss the possibility that the detection of gravitational waves emitted by compact stars may allow to constrain the MIT bag model of quark matter equation of state. Our results show that the combined knowledge of the frequency of the emitted gravitational wave and of the mass, or the radiation radius, of the source allows one to discriminate between strange stars and neutron stars and set stringent bounds on the bag constants.     

Solid-state NMR spectroscopy of a membrane protein in biphenyl phospholipid bicelles with the bilayer normal parallel to the magnetic field

Bicelles composed of the long-chain biphenyl phospholipid TBBPC (1-tetradecanoyl-2-(4-(4-biphenyl)butanoyl)-sn-glycero-3-PC) and the short-chain phospholipid DHPC align with their bilayer normals parallel to the direction of the magnetic field. In contrast, in typical bicelles the long-chain phospholipid is DMPC or DPPC, and the bilayers align with their normals perpendicular to the field. Samples of the membrane-bound form of the major coat protein of Pf1 bacteriophage in TBBPC bicelles are stable for several months, align magnetically over a wide range of temperatures, and yield well-resolved solid-state NMR spectra similar to those obtained from samples aligned mechanically on glass plates or in DMPC bicelle samples "flipped" with lanthanide ions so that their bilayer normals are parallel to the field. The order parameter of the TBBPC bicelle sample decreases from approximately 0.9 to 0.8 upon increasing the temperature from 20 degrees C to 60 degrees C. Since the frequency spans of the chemical shift and dipolar coupling interactions are twice as large as those obtained from proteins in DMPC bicelles without lanthanide ions, TBBPC bicelles provide an opportunity for structural studies with higher spectral resolution of the metal-binding membrane proteins without the risk of chemical or spectroscopic interference from the added lanthanide ions. In addition, the large temperature range of these samples is advantageous for the studies of membrane proteins that are unstable at elevated temperatures and for experiments requiring measurements as a function of temperature.