Pseudomonas fluorescens is able to grow on R‐benzoin as the sole carbon and energy source because it harbours the enzyme benzaldehyde lyase that cleaves the acyloin linkage using thiamine diphosphate (ThDP) as a cofactor. In the reverse reaction, this lyase catalyses the carboligation of two aldehydes with high substrate and stereospecificity. The enzyme structure was determined by X‐ray diffraction at 2.6 Å resolution. A structure‐based comparison with other proteins showed that benzaldehyde lyase belongs to a group of closely related ThDP‐dependent enzymes. The ThDP cofactors of these enzymes are fixed at their two ends in separate domains, suspending a comparatively mobile thiazolium ring between them. While the residues binding the two ends of ThDP are well conserved, the lining of the active centre pocket around the thiazolium moiety varies greatly within the group. Accounting for the known reaction chemistry, the natural substrate R‐benzoin was modelled unambiguously into the active centre of the reported benzaldehyde lyase. Due to its substrate spectrum and stereospecificity, the enzyme extends the synthetic potential for carboligations appreciably.

Resistive switching based on transition metal oxide memristive devices is suspected to be caused by the electric-field-driven motion and internal redistribution of oxygen vacancies. Deriving the detailed mechanistic picture of the switching process is complicated, however, by the frequently observed influence of the surrounding atmosphere. Specifically, the presence or absence of water vapor in the atmosphere has a strong impact on the switching properties, but the redox reactions between water and the active layer have yet to be clarified. To investigate the role of oxygen and water species during resistive switching in greater detail, isotope labeling experiments in a N /H O tracer gas atmosphere combined with time-of-flight secondary-ion mass spectrometry are used. It is explicitly demonstrated that during the RESET operation in resistive switching SrTiO -based memristive devices, oxygen is incorporated directly from water molecules or oxygen molecules into the active layer. In humid atmospheres, the reaction pathway via water molecules predominates. These findings clearly resolve the role of humidity as both oxidizing agent and source of protonic defects during the RESET operation.

The diffusion of oxygen in dense ceramics of monoclinic HfO2 was studied by means of (18O/16O) isotope exchange annealing and subsequent determination of isotope depth profiles by Secondary Ion Mass Spectrometry. Anneals were performed in the temperature range of 573 ≤T/K≤ 973 at an oxygen partial pressure of pO2=200 mbar. All measured isotope profiles exhibited two features: the first feature, closer to the surface, was attributed mainly to slow oxygen diffusion in an impurity silicate phase; the second feature, deeper in the sample, was attributed to oxygen diffusion in bulk monoclinic HfO2. The activation enthalpy of oxygen tracer diffusion in bulk HfO2 was found to be ΔHD∗≈0.5 eV.

Organic chemistry Organic chemistry Z 0200Thiamin-Diphosphate-Dependent Enzymes: New Aspects of Asymmetric C-C Bond Formation -[75 refs.]. -(POHL, M.; LINGEN, B.; MUELLER*, M.; Chem. Eur.

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