Synthesis,Characterization and Application of New Rhodium Complexes for Indirect Electrochemical Cofactor Regeneration

Electroenzymatic synthesis often suffers from electrochemical reaction steps which proceed slower than the coupled enzyme reaction. For indirect electrochemical cofactor regeneration, we here report two new mediators with superior properties compared to the established rhodium complex (2,2′‐bipyridyl)(pentamethylcyclopentadienyl)rhodium [Cp*Rh(2,2′‐bipyridine)]. After constructing a robotic system for fast and reliable cyclic voltammetry measurements, we screened twelve rhodium complexes with substituted 2,2′‐bipyridine ligands for their reduction potentials and catalytic activity towards the reduction of NADP. Promising complexes were investigated in more detail by cyclic voltammetry and under batch electrolysis conditions. The new complexes Cp*Rh(5,5′‐methyl‐2,2′‐bipyridine) and Cp*Rh(4,4′‐methoxy‐2,2′‐bipyridine) reduced NADP to NADPH three times faster than the established mediator, resulting in volumetric productivities of up to 136 mmol L⁻¹ d⁻¹ and turnover frequencies of up to 113 h⁻¹. This increased reaction rate of these new mediators makes indirect electrochemical approach significantly more competitive to other methods of cofactor regeneration. Abbreviations: ADH=alcohol dehydrogenase; Ag|AgCl=silver|silver chloride reference electrode; bpy=2,2′‐bipyridine; ci=current increase; Cp*=pentamethylcyclopentadienyl; CV=cyclic voltammetry; Ep=peak potential; equiv=equivalent; NADP/NADPH=nicotinamide adenine dinucleotide phosphate oxidised/reduced form.     

Flame-ionization detector response to methyl, ethyl, propyl, and butyl esters of fatty acids

The concept of theoretical response factors is not directly applicable to methyl esters of short-chain fatty acids (FA), since their carbon deficiency is larger than expected from theory. Substituting the methyl group by an ethyl, propyl, or butyl group improved the flame-ionization efficiency of fatty acid esters gradually, up to the point where the empirical response factors of the butyl esters were identical within experimental error to the theoretical values. Butyl esters of FA have a uniform flame-ionization detection (FID) response irrespective of the number of carbon atoms contained in the FA. They exhibit a carbon deficiency of 1.0, i.e. the carbonyl carbon atom does not respond, as expected from theory. Compared to methyl esters, which have a carbon deficiency of 1.4–1.5 for short-chain FA, use of butyl esters has the advantage that a precalculation of the FID response enables the analyst to judge whether the analytical system employed works properly and the data produced are accurate and reliable. Both acid (BF₃ or H₂SO₄)-and alkali (butoxide)-catalyzed butyl ester preparation were equally effective, giving the analyst a choice of methods so that different analytical needs can be addressed efficiently. Computing response factors and comparing the theoretically expected values with those obtained experimentally gives the experimenter an indication whether the analytical system employed for FA profiling (transesterification plus the subsequent gasliquid chromatographic separation and quantitation by FID) works properly. This setup is particularly useful for an accurate analysis of the FA profile of milk fat.     

High-Temperature Oxidation Behavior of Refractory High-Entropy Alloys: Effect of Alloy Composition

The high-temperature oxidation behavior of a new family of refractory high-entropy alloys (HEAs) with compositions of W–Mo–Cr–Ti–Al, Nb–Mo–Cr–Ti–Al and Ta–Mo–Cr–Ti–Al was studied at 1000 and 1100 °C. Based on these equimolar starting compositions, the main incentive of this study was to select the most promising alloy system whose properties may then be successively improved. Despite the high amount of refractory elements, Ta–Mo–Cr–Ti–Al showed good oxidation resistance at 1000 and 1100 °C. Moderate values of mass gain and complex oxidation kinetics were observed for the W- and Nb-containing HEAs. These alloys formed inhomogeneous oxide scales possessing regions with thick and porous layers as well as areas revealing quite thin oxide scales due to the formation of discontinuous Cr- and Al-rich scales. The most promising behavior was shown by the alloy Ta–Mo–Cr–Ti–Al which followed the parabolic rate law for oxide growth due to the formation of a thin and compact Al-rich layer.     

基于有限元法的汽车变速器齿轮与轴承优化

采埃孚集团开发和生产了种类繁多的传动齿轮。对于齿轮的优化和可靠设计,有限元法是尤为适合的。而且,这种方法能容易集成于采埃孚的程序系统。本文展示了在开发过程中如何运用该方法进行齿轮优化。此外,文中多处演示了齿轮和轴承之间的相互作用。这也是采埃孚集团致力于开发轴承计算的原因。文中实例展现了如何优化滚动轴承以达到理想的齿轮接触印痕。当然,这些优化方法也适用于传动齿轮。     

Piezoelectric properties and phase transition temperatures of the solid solution of (1 − x)(Bi0.5Na0.5)TiO3–xSrTiO3

The phase diagram of (1 ? x)(Bi_0.5Na_0.5)TiO₃–xSrTiO₃ was completed and investigations on polarization and strain in this system were carried out. (1 ? x)(Bi_0.5Na_0.5)TiO₃–xSrTiO₃-ceramics were prepared by conventional mixed oxide processing. The depolarization temperature (T_d), the temperature of the rhombohedral–tetragonal phase transition (T_r–t) and the Curie temperature (T_m) were determined by measuring the temperature dependence of the relative permittivity. All solid solutions of (1 ? x)(Bi_0.5Na_0.5)TiO₃–xSrTiO₃ show relaxor behavior (A-site relaxor). From XRD-measurements a broad maximum of the lattice parameter can be observed around x = 0.5 but no structural evidence for a morphotropic phase boundary was found. SEM-analysis revealed a decrease of the grain size for increasing SrTiO₃-content. At room temperature a maximum of strain of about 0.29% was found at x = 0.25 which coincides with a transition from a ferroelectric to an antiferroelectric phase. The temperature dependence of the displacement indicates an additional contribution from a structural transition (rhombohedral–tetragonal), which would be of certain relevance for the existence of a morphotropic phase boundary.     

Probing the Conformation States of Neurotensin Receptor 1 Variants by NMR Site-Directed Methyl Labeling

G protein-coupled receptors (GPCRs) are key players in mediating signal transduction across the cell membrane. However, due to their intrinsic instability, many GPCRs are not suitable for structural investigations. Various approaches have been developed in recent years to remedy this situation, ranging from the use of more native membrane mimetics to protein-stabilization methods. The latter approach typically results in GPCRs that contain various numbers of mutations. However, probing the functionality of such variants by in vitro and in vivo assays is often time consuming. In addition, to validate the suitability of such GPCRs for structural investigations, an assessment of their conformation state is required. NMR spectroscopy has been proven to be suitable to probe the conformation state of GPCRs in solution. Here, by using chemical labeling with an isotope-labeled methyl probe, we show that the activity and the conformation state of stabilized neurotensin receptor 1 variants obtained from directed evolution can be efficiently assayed in 2D NMR experiments. This strategy enables the quantification of the active and inactive conformation states and the derivation of an estimation of the basal as well as agonist-induced activity of the receptor. Furthermore, this assay can be used as a readout when re-introducing agonist-dependent signaling into a highly stabilized, and thus rigidified, receptor by mutagenesis. This approach will be useful in cases where low production yields do not permit the addition of labeled compounds to the growth medium and where 1D NMR spectra of selectively ¹⁹F-labeled receptors are not sufficient to resolve signal overlap for a more detailed analysis.     

A New Research Infrastructure for Investigating Flow Hydraulics and Process Equipment at Critical Fluid Properties

An optimized equipment design for natural gas processing and liquefaction plants becomes increasingly difficult with changing process conditions: Particularly low values of surface tension create rising challenges on the design of phase separators and column internals. The TERESA test rig at HZDR was designed to allow the investigation of multiphase thermohydraulics and phase separator performance under critical fluid properties in industrial dimensions. A versatile pipe test section is available in DN200 and equipment internals may be tested in a sectional DN300/DN500 test separator. The applied test fluid shows a high vapor-liquid density difference between 1470 and 940 kg m⁻³, viscosity as low as 0.12 mm²s⁻¹, and surface tension down to 1.3 mN m⁻¹. Volumetric liquid and vapor flow rates may be varied up to 9 and 530 m³h⁻¹ in the test rig, respectively.     

Metabolic Glycoengineering in hMSC-TERT as a Model for Skeletal Precursors by Using Modified Azide/Alkyne Monosaccharides

Metabolic glycoengineering enables a directed modification of cell surfaces by introducing target molecules to surface proteins displaying new features. Biochemical pathways involving glycans differ in dependence on the cell type; therefore, this technique should be tailored for the best results. We characterized metabolic glycoengineering in telomerase-immortalized human mesenchymal stromal cells (hMSC-TERT) as a model for primary hMSC, to investigate its applicability in TERT-modified cell lines. The metabolic incorporation of N-azidoacetylmannosamine (Ac₄ManNAz) and N-alkyneacetylmannosamine (Ac₄ManNAl) into the glycocalyx as a first step in the glycoengineering process revealed no adverse effects on cell viability or gene expression, and the in vitro multipotency (osteogenic and adipogenic differentiation potential) was maintained under these adapted culture conditions. In the second step, glycoengineered cells were modified with fluorescent dyes using Cu-mediated click chemistry. In these analyses, the two mannose derivatives showed superior incorporation efficiencies compared to glucose and galactose isomers. In time-dependent experiments, the incorporation of Ac₄ManNAz was detectable for up to six days while Ac₄ManNAl-derived metabolites were absent after two days. Taken together, these findings demonstrate the successful metabolic glycoengineering of immortalized hMSC resulting in transient cell surface modifications, and thus present a useful model to address different scientific questions regarding glycosylation processes in skeletal precursors.     

Development of an HPLC method for measurements of the stability of Irganox-type polymer antioxidants in fatty food simulants

 A reversed-phase high-performance liquid chromatography (RP-HPLC) method has been developed to measure the stability of four Irganox-type polymer antioxidants (Irganox 245, Irganox 1035, Irganox 1098 and Irganox 3114) in an olive oil food simulant and isooctane, which has been proposed as an alternative fatty food simulant. The tests of stability in olive oil were carried out under three different conditions, i.e. 40°C for 10 days, 100°C for 1 h and 175°C for 1 h. The exposure conditions for isooctane were 60°C for 3 h. Results showed that for all additives tested no instability phenomena in olive oil or isooctane simulants were observed under the exposure conditions applied. The analytical methodology developed could eventually be used for stability testing and migration studies of other similarly structured antioxidants in fatty food simulants. Received: 11 September 1997     

Effects of roscovitine on maintenance of the germinal vesicle in horse oocytes,subsequent nuclear maturation,and cleavage rates after intracytoplasmic sperm injection

This study was conducted to evaluate the effects of roscovitine on suppression of meiosis, subsequent meiotic maturation, and cleavage rates after intracytoplasmic sperm injection of horse oocytes. Oocytes were classified as having compact or expanded cumuli (Com or Exp oocytes) and were divided into three culture groups: 30 h culture in maturation medium (30 h Mat); 54 h culture in maturation medium (54 h Mat), or 24 h culture in medium containing 66 micro mol roscovitine l(-1) and then 30 h culture in maturation medium (Ros+M). After maturation, oocytes were subjected to intracytoplasmic sperm injection and cultured in G1.2 medium for 96 h. Among oocytes fixed immediately after roscovitine culture, 26 of 31 (84%) Com oocytes and 16 of 28 (57%) Exp oocytes were at the germinal vesicle stage (P<0.05). After maturation culture, there were no differences in maturation rates or morphological cleavage rates among treatments. Among Com oocytes, significantly more embryos in the Ros+M treatment than in the 54 h Mat treatment had cleaved with > or = two normal nuclei (63 versus 36%; P<0.05); whereas among Exp oocytes, significantly more embryos in the 30 h Mat treatment than in the Ros+M treatment (63 versus 42%; P<0.05) had cleaved with > or = two normal nuclei. The average number of nuclei in embryos at 96 h was significantly higher (P<0.05) in Ros+M Com oocytes (13.5) than in any other Com or Exp group. These results demonstrate that roscovitine can reversibly maintain equine oocytes in the germinal vesicle stage for up to 24 h, and that such suppression may increase the developmental potential of Com, but not Exp, oocytes.