Silica-supported TEMPO catalysts: synthesis and application in the Anelli oxidation of alcohols.

The application of silica-supported TEMPO as a recyclable catalyst in the Anelli oxidation of alcohols is reported. The catalyst is easily obtained in a one-step reductive amination procedure starting from a commercially available aminopropyl-functionalized silica. Details of the synthesis of the supported catalyst and its analysis by MAS NMR are presented. Various alcohol oxidations according to the Anelli protocol have been carried out and the stability of the applied silica-supported TEMPO has been studied.     

New solid-state glass electrodes by using zinc oxide thin films as interface layer

Novel glass electrodes for the determination of cations with reversible internal solid contact are introduced. They are based on a semiconducting zinc oxide layer with a maximum thickness of 1 μm in contact with ion selective glasses on one side and with a metal layer on the other side. The metal oxide layer is thereby generated either by ultrasonic spray pyrolysis from zinc acetate solution, by electrochemical deposition from zinc nitrate solution or by spin coating from a dispersion of ZnO in an organic binder. A following activation in a palladium chloride solution allows the chemical reductive deposition of NiP as electronic conductor. Dipping-type and flow through electrodes as well as planar glass electrodes in thick film technology fabricated in the above-mentioned method are described. In this case gold electrodes are applied by screen printing on isolated steel substrates. The zinc oxide layers, created in different manners, are covered afterwards with cation selective glasses in thick film technology. They cause a stabilisation of the half-cell potentials of the all solid state indicator electrodes proved by suitable measurements.     

Structural tuning of ligand-based two-electron intervalence charge transfer

The lowest-energy optical transition of two-electron-oxidized porphyrinogens [L(Delta)M] is a ligand-based charge transfer. The color of the intermediary, two-electron mixed-valent oxidation state shifts from vermilion (lambdamax = 480 nm) to yellow (lambdamax = 270 nm) upon increasing the ionic radius of the central metal dication from Mg2+ to Zn2+ and Ca2+. Structural, spectroscopic, and computational studies establish that the relative energies of the highest occupied and lowest unoccupied orbitals, between which the intervalence charge-transfer optical transition occurs, are modulated by the molecular dipole moment, which in turn depends on the only structural variable among the [L(Delta)M] compounds, the position of M2+ relative to the dianionic dipyrrole unit.     

Characterization of polyalkylvinyl ether phases by solid-state and suspended-state nuclear magnetic resonance investigations

Pure organic polyalkylvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C₄VE) and n-octadecylvinyl ether (C₁₈VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and ¹H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of ¹H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the ¹H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin–lattice relaxation times (T₁) as well as accumulation of a 2D wide line separation NMR spectrum.     

Infrared laser specific reactions of boranes. Conversion of diborane to icosaborane(16), B20H16

Monochromatic low power radiation of a CO₂ laser (1.5 W) initiates in diborane B₂H₆ a chain reaction in the course of which icosaborane(16) B₂₀H₁₆ is formed as the main product. This reaction is accompanied by visible luminescence.     

Metrische Teilebenen hyperbolischer projektiv-metrischer Ebenen

Ohne Zusammenfassung     

Higher-Order Temporal and Spatial Plasma Wave Echoes

The collisionsless Boltzmann equation is solved in two ways by the method of characteristics. The solution is used for an exact treatment of higher-order temporal and spatial plasma wave echoes in the absence of steady external fields. The second-order spatial echo is treated separately and analyzed numerically.