Liquid-Phase Cyclohexene Oxidation with O2 over Spray-Flame-Synthesized La1−xSrxCoO3 Perovskite Nanoparticles

La_1−xSr_xCoO₃ (x=0, 0.1, 0.2, 0.3, 0.4) nanoparticles were prepared by spray-flame synthesis and applied in the liquid-phase oxidation of cyclohexene with molecular O₂ as oxidant under mild conditions. The catalysts were systematically characterized by state-of-the-art techniques. With increasing Sr content, the concentration of surface oxygen vacancy defects increases, which is beneficial for cyclohexene oxidation, but the surface concentration of less active Co²⁺ was also increased. However, Co²⁺ cations have a superior activity towards peroxide decomposition, which also plays an important role in cyclohexene oxidation. A Sr doping of 20 at. % was found to be the optimum in terms of activity and product selectivity. The catalyst also showed excellent reusability over three catalytic runs; this can be attributed to its highly stable particle size and morphology. Kinetic investigations revealed first-order reaction kinetics for temperatures between 60 and 100 °C and an apparent activation energy of 68 kJ mol⁻¹ for cyclohexene oxidation. Moreover, the reaction was not affected by the applied O₂ pressure in the range from 10 to 20 bar. In situ attenuated total reflection infrared spectroscopy was used to monitor the conversion of cyclohexene and the formation of reaction products including the key intermediate cyclohex-2-ene-1-hydroperoxide; spin trap electron paramagnetic resonance spectroscopy provided strong evidence for a radical reaction pathway by identifying the cyclohexenyl alkoxyl radical.     

Traveling waves for chemotaxis–systems

In this paper we study the existence of traveling wave solutions to the Keller‐Segel model, a general model of chemotaxis, where the species do not reproduce. In the case of logarithmic sensitivity we show that various functionals modeling the reactive feedback on the chemo‐attractant do allow for traveling waves and a wide range of qualitatively different behavior is possible. We can find monotone fronts as well as pulse solutions in the densities of the population and the chemical. In particular, a new kind of solution exists, where both densities travel as pulses.     

Neues über Protein-Thiolgruppen und Disulfidbindungen

Eine der vom französischen Centre National de la Recherche Scientifique (CNRS) veranstalteten „Conferences Jacques Monod”︁ war dem Thema „Intracellular Redox Controls by Thioredoxin and Glutaredoxin Systems”︁ gewidmet. Zu der Konferenz kamen im Juli in der Biologischen Station Roscoff (Bretagne) etwa 100 Wissenschaftler aus 15 Ländern zusammen.     

Structural influences on the properties of aromatic polyamidines

Polyamidines with both nitrogens in the main chain (-X-NH-CR=N-) were obtained by polycondensation of diamines with different orthoesters. The thermal properties could be tailored by the choice of diamine and orthoester. Quantitative formation of a cyclic trimer could be observed when 2,6-diamino-pyridine was converted with triethyl orthoformate. ¹H, ¹³C and ¹⁵N NMR spectroscopic investigations in solution and in solid state showed that the configuration of the amidine group was strongly dependent on the residue R. In polyformamidines, strong interactions caused by hydrogen bonds could be evidenced.