Biocatalytic asymmetric hydroxylation of hydrocarbons with the topsoil-microorganism Bacillus megaterium

A Bacillus megaterium strain was isolated from topsoil by a selective screening procedure with allylbenzene as a xenobiotic substrate. This strain performed the hydroxylation chemoselectively (no arene oxidation and overoxidized products) and enantioselectively (up to 99% ee) in the benzylic and nonbenzylic positions of a variety of unfunctionalized arylalkanes. Salycilate and phenobarbital, which are potent inducers of cytochrome P-450 activity, changed the regioselectivity of the microbial CH insertion, without an effect on the enantioselectivity. The biotransformation conditions were optimized in regard to product yield and enantioselectivity by variation of the oxygen-gas supply and the time of the substrate addition. The different product distributions (alpha- versus beta-hydroxylated product) that are obtained on induction of cytochrome P-450 enzyme activity demonstrate the involvement of two or more hydroxylating enzymes with distinct regioselectivities in this biotransformation. An oxygen-rebound mechanism is assumed for the cytochrome P-450-type monooxygenase activity, in which steric interactions between the substrate and the enzyme determine the preferred face of the hydroxy-group transfer to the radical intermediate.     

Physical Properties and Erosion Behavior of Poly(trimethylene carbonate‐co‐ε‐caprolactone) Networks

Form‐stable resorbable networks are prepared by gamma irradiating trimethylene carbonate (TMC)‐ and ε‐caprolactone (CL)‐based (co)polymer films. To evaluate their suitability for biomedical applications, their physical properties and erosion behavior are investigated. Homopolymer and copolymer networks that are amorphous at room temperature are flexible and rubbery with elastic moduli ranging from 1.8 ± 0.3 to 5.2 ± 0.4 MPa and permanent set values as low as 0.9% strain. The elastic moduli of the semicrystalline networks are higher and range from 61 ± 3 to 484 ± 34 MPa. The erosion behavior of (co)polymer networks is investigated in vitro using macrophage cultures, and in vivo by subcutaneous implantation in rats. In macrophage cultures, as well as upon implantation, a surface erosion process is observed for the amorphous (co)polymer networks, while an abrupt decrease in the rate and a change in the nature of the erosion process are observed with increasing crystallinity. These resorbable and form‐stable networks with tuneable properties may find application in a broad range of biomedical applications.

     

A conformationally constrained fused tricyclic nisin AB-ring system mimic toward an improved pyrophosphate binder of lipid II

The bacteria-specific membrane component lipid II is essential for bacterial cell wall synthesis. A tricyclic nisin mimic was designed and synthesized in which both thioether moieties were mimicked by an alkane-bridge, as well as the introduction of a third conformational constraint consisting of a macrocyclic lactam-bridge between the N-terminus and the B-ring. The newly designed tricyclic AB-ring mimic was found to bind lipid II since it was able to inhibit nisin-induced membrane leakage in a dose-dependent manner. These results imply that the tricyclic AB-ring mimic may form a novel class of lead structures for the development of nisin-based peptide antibiotics.     

First Measurement of the Gerasimov-Drell-Hearn Sum Rule for 1H from 0.7 to 1.8 GeV at ELSA

To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68-1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4pi detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9+/-2.4(stat)+/-2.2(syst)] microb.     

Synthesis of α,β-epoxy diazomethyl ketones

The preparation of eighteen epoxy diazomethyl ketones 1 is described. Two general methods were developed. Firstly, treatment of the mixed anhydrides of glycidic acids and carbonic acid ester with diazomethane led to the title compounds in yields ranging from 17–74%. Secondly, glycidyl chlorides which were obtained from sodium glycidates and oxalyl chloride, gave the desired products upon treatment with diazomethane (yields 60–74%). The required α,β-epoxy carboxylic esters were prepared by Darzens condensation and epoxidation of α,β-unsaturated esters, but in some cases also by reaction of α-oxo carboxylic esters with diazomethane.     

Messung der longitudinalen Polarisation von Betastrahlen aus RaE (Bi210) und Sb124 mit Hilfe der Møller-Streuung

The electron-electron (Møller) scattering method is used for the determination of the helicity of beta rays from the 1.17 MeV transition of RaE and from the 2.31 MeV transition of Sb¹²⁴. The apparatus is described and the evaluation of the efficiency of polarization detection for this apparatus is given in detail. The depolarization corrections are discussed. The results of the helicity measurements areP = ? (0·77±0·09)v/cfor RaE at a mean energy of 640 keV andP = ? (0·90±0·14)v/c for Sb¹²⁴ at a mean energy of 1550 keV.     

Reducing power losses caused by ionic shortcut currents in reverse electrodialysis stacks by a validated model

Both in electrodialysis and in reverse electrodialysis ionic shortcut currents through feed and drain channels cause a considerable loss in efficiency. Model calculations based on an equivalent electric system of a reverse electrodialysis stack reveal that the effect of these salt bridges could be reduced via a proper stack design. The critical parameters which are to be optimized are ρ/r and R/r, where ρ is the lateral resistance along the spacers, R is the resistance of the feed and drain channels between two adjacent cells, and r is the internal resistance of a cell. Because these two parameters are dimensionless, different stacks can be easily compared. The model is validated with two experimental stacks differing in membrane type and spacer thickness, one with large ionic shortcut currents and one where this effect is less. The loss in efficiency decreased from 25 to 5% for a well-designed stack. The loss of efficiency in reverse electrodialysis and in electrodialysis can be reduced with the aid of the design parameters presented in this paper.