The sulphoxidation of thioanisole catalysed by lactoperoxidase and Coprinus cinereus peroxidase: evidence for an oxygen-rebound mechanism

Using both stopped-flow and conventional spectroscopy, the oxygenation of methyl phenyl sulphide by both lactoperoxidase (LPO) and Coprinus cinereus peroxidase (CiP) was monitored. Controlled continuous addition of H2O2 during turnover and monitoring the presence of native enzymes, compounds I, II and III, led to formation of the sulphoxide in high yield and enantioselectivity. Under those conditions, LPO catalysed the formation of (R) methyl phenyl sulphoxide with a yield of 85% and an enantiomeric excess (e.e.) of 80%. CiP catalysed the formation of (S) methyl phenyl sulphoxide with a yield of 84% and an e.e. of 73%. The enantioselective performance was markedly influenced by the purity of the enzymes used. Presence of compound III during turnover led to rapid inactivation of the peroxidases and, therefore, to both a lower yield of the sulphoxides and a lower enantioselectivity. Stopped-flow kinetic data show that, for both LPO and CiP, the transition of compound I to compound II depends on the concentration of the methyl phenyl sulphide, suggesting an oxygen-rebound mechanism. In line with this mechanism, a methyl phenyl sulphide radical cation was detected by EPR during turnover for LPO.     

Weitere Beiträge zur Kenntnis der Rekristallisation des kalt gewalzten Eisens

Quantitative Analyse der {200}-Polfiguren eines kalt gewalzten und angelassenen Weicheisens mit 0,016% C.     

Effect and control of impurities in the electrowinning of zinc

Most of the elements known can appear as impurities in zinc concentrates. This article presents a survey of those which are likely to cause trouble in electrolytic zinc plants.     

Problems of circadian periodicity and its disorders (author's transl)

The human circadian system controlling the variety of overt 24-h rhythms consists of some different oscillators which are separately self-sustained. Normally, all oscillators run synchronously to each other; under certain external and internal conditions (e.g. increasing score of neuroticism, or old age), however, they run in the steady state with different periods. The necessary synchronization of the endogenously driven oscillators to the environment is effected, in man, essentially by social timing mechanisms; their efficiency presupposes the possibility as well as the ability to establish social contacts. A timing mechanism may synchronize the circadian system only partially; as a result, only several oscillators are synchronized whereas others persist ot run autonomously. The different rhythm disorders, internal or external desynchronizations, when effective for a long time, may be sources of ill health.     

Chemische Diffusion in Eisen-Chrom- und Eisen-Chrom-Kohlenstoff-Legierungen im Bereich des Austenits

Probenherstellung, Diffusionsglühen und Analyse der Proben mit der Mikrosonde. Gemeinsamer Diffusionskoeffizient als Funktion der Kohlenstoffaktivität. Vergleich mit Selbstdiffusionsmessungen.     

Bücherschau

Ohne Zusammenfassung VDI     

A particularly strong organic acceptor for tuning the hole-injection barriers in modern organic devices

A better understanding of metal-organic interfaces combined with means to control their properties is crucial for the further improvement of organic (opto)electronic devices. In this context, the use of organic acceptors is an efficient tool to modify metal work functions and hole-injection barriers, which has the potential to considerably improve the performance of organic devices. Here, we use density functional theory based calculations to discuss a particularly potent acceptor suitable for that purpose, 3,5-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane (F2HCNQ), which clearly outperforms the frequently applied and in the meantime prototypical system 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Comparative calculations for a single monolayer of the two molecules adsorbed on an Ag(1 1 1) surface reveal that (i) the work-function increase induced by F2HCNQ is more than 20% higher than for F4TCNQ and that (ii) at the same time the adsorption energy basically is unaffected, while (iii) the electronic structure is slightly modified. In the end of the day, F2HCNQ is a highly promising candidate for applications in organic devices.     

Initial Stages in the Metal-dusting Process on Alloy 800

The initial stages of the metal-dusting process on Alloy 800 at 620 °C were investigated by light optical microscopy, RAMAN spectroscopy, atomic-force microscopy, Auger electron spectroscopy, transmission-electron microscopy and electron back-scatter diffraction. As it turned out the incubation period for metal-dusting is characterized by simultaneous formation of a heterogeneously growing oxide scale and deposition of carbon. The material surface shows different tarnish colors depending on the substrate-grain orientation with different susceptibility to the beginning of metal-dusting attack. “Low-index” grains were not attacked within the times investigated while the other grain orientations showed pitting. Carbon is evidently incorporated into the oxide scale from the very beginning of exposure with different intensities depending on the underlying substrate-grain orientation leading to differences in the tarnish colors. As a consequence carbides are formed even underneath “dense” oxide layers. Evidently metal-dusting attack starts at positions of the oxide scale where “higher carbon concentrations” are present.     

INTERACTION BETWEEN CREEP AND FATIGUE OF A NICKELBASED SUPERALLOY IN738LC AT ELEVATED TEMPERATURE—DECREASING OF CYCLIC LIFE WITH INCREASING CREEP DEFORMATION

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