Control of Six Contiguous Stereocenters in an Asymmetric Organocatalytic One‐Pot Michael/Michael/Aldol Addition Sequence

The asymmetric organocatalytic one‐pot synthesis of polyfunctionalized cyclohexanes is described. Starting from β‐keto esters, nitroalkenes and α,β‐unstaturated aldehydes and employing a bifunctional norephedrine‐based thiourea catalyst, six contiguous stereocenters including one quarternary center are generated. The one‐pot protocol follows a Michael/Michael/aldol addition sequence and affords the highly substituted cyclohexanes in moderate to very good yields (22–70%), diastereomeric ratios of dr>95:5 and excellent enantioselectivities of 91–99% ee.     

Arrays and New Antenna Topologies for Increasing THz Power Generation Using Photomixers

Power limitations in CW THz generation imposed by conventional photomixers (“antenna emitters”, AEs) are the major drawbacks on THz generation. From the antenna point of view, two different strategies are proposed to increase the generated power: optimized arrays and lenses arrangements and the use of new dielectric horn antennas. Then, using multiple small lenses, one per each single element, instead of a large one, bigger than the array, makes the generated power much higher. In addition, horn antennas etched in the substrate are considered in order to reduce the energy distribution scattering. Finally, some manufacturing issues are discussed.     

Surface engineering in Cu(In,Ga)Se2 solar cells

Surface modifications of three‐stage co‐evaporated Cu(In,Ga)Se₂ (CIGS) thin films are investigated by finishing the evaporation with gallium‐free (CuInSe₂, CIS) stages of various lengths. Secondary‐ion mass spectrometry shows substantial interdiffusion of indium and gallium, smearing out the Ga/(Ga + In) profile so that the addition of a CIS layer merely lowers the gallium content at the surface. For the thinnest top layer, equivalent to 20 nm of pure CIS, X‐ray photoelectron spectroscopy does not detect any compositional difference compared with the reference device. The modifications are evaluated electrically both by temperature‐dependent characterisation of actual solar‐cell devices and by modelling, using the latest version of scaps‐1d (Electronics and Information Systems, Ghent University, Belgium). The best solar‐cell device from this series is obtained for the 20 nm top layer, with an efficiency of 16.6% after antireflective coating. However, we observe a trend of decreasing open‐circuit voltage for increasingly thick top layers, and we do not find direct evidence that the lowering of the gallium concentration at the CIGS surface should generally be expected to improve the device performance. A simulated device with reduced bulk and interface defect levels achieves nearly 20% efficiency, but the trends concerning the CIS top layer remain the same. Copyright © 2011 John Wiley & Sons, Ltd.     

Sex-related differences in clothing-microclimate and subjective perceptions while wearing two outdoor jackets during submaximal exercise in a cool environment

Abstract

This study aimed to identify sex-related differences in clothing-microclimate and subjective perceptions while wearing two outdoor jackets in a setting that is representative for outdoor sports at a leisure level. Ten male and 10 female subjects were testing a thin one-layer jacket and a wind- and waterproof three-layer membrane jacket in a climatic chamber (12?°C, 40% relative humidity) during rest, exercise and recovery. Relative humidity, temperature and sweat residues in the clothing system, perceptions of comfort and physiological parameters were measured. For females, relative humidity, sweat residues and loss of body mass were significantly lower without significantly influencing perceptions of comfort. It can be concluded that sex has a strong effect on clothing-microclimate in outdoor jackets with drier microclimate for females. Furthermore, our findings suggest that females are more sensitive to humidity within the clothing system and that they cool easier, especially in periods of rest.     

Hydration of Portland cement with high replacement by siliceous fly ash

The effects of two different low calcium fly ashes on the hydration of ordinary Portland cement (OPC) pastes containing 50 wt.% of fly ash were investigated over a hydration time of 550 days. The results were compared with a reference blend of OPC containing 50 wt.% of inert quartz powder allowing the distinction between "filler effect" and pozzolanic reaction.Until 2 days, no evidence of fly ash reaction was measured and its influence on the hydration is mainly related to the “filler effect”. From 7 days on, the effects of the pozzolanic reaction were observed by the consumption of portlandite, the change of the pore solution chemistry, the formation of a presumably water-rich inner hydration product and the change of the C–S–H composition towards higher Al/Si ratio compared to the C–S–H of neat OPC. Additional strength due to the pozzolanic reaction developed after 28 days of hydration.     

Transition-metal-free oxidative coupling reactions for the formation of C-C and C-N bonds mediated by TEMPO and its derivatives

The application of nitroxides for the development of new synthetic methods and their implementation in polymer chemistry, material science and beyond is one of the major research topics in our laboratory in the institute of organic chemistry at the WWU Münster. This short review focuses on our recent progress towards nitroxide-based transition-metal-free oxidative coupling reactions. The demand for organic surrogates for transition metals in such transformations is in our eyes unquestionable, since environmental and economic issues have become progressively more important in recent years. For this purpose, the 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) is shown to be a highly efficient oxidant for the homo- and cross-coupling of Grignard reagents. This powerful C-C bond forming strategy allows the generation of conjugated polymers from bifunctional Grignard reagents. Moreover, cross-coupling of alkynyl Grignard compounds and nitrones can be accomplished under aerobic atmosphere with catalytic amounts of TEMPO. It is also shown that TEMPO-derived N-oxoammonium salts can act as suitable oxidants for formation of C-N bonds between non-preactivated benzoxazoles and secondary amines under metal-free conditions.     

C and N isotope fractionation during biodegradation of the pesticide metabolite 2,6-dichlorobenzamide (BAM): potential for environmental assessments

2,6-Dichlorobenzamide (BAM) is a metabolite of the herbicide 2,6-dichlorobenzonitrile (dichlobenil), and a prominent groundwater contaminant. Observable compound-specific isotope fractionation during BAM formation-through transformation of dichlobenil by Rhodococcus erythropolis DSM 9685-was small. In contrast, isotope fractionation during BAM degradation-with Aminobacter sp. MSH1 and ASI1, the only known bacterial strains capable of mineralizing BAM-was large, with pronounced carbon (ε(C) = -7.5‰ to -7.8‰) and nitrogen (ε(N) = -10.7‰ to -13.5‰) isotopic enrichment factors. BAM isotope values in natural samples are therefore expected to be dominated by the effects of its degradation rather than formation. Dual isotope slopes Δ (=Δδ(15)N/Δδ(13)C ≈ ε(N)/ε(C)) showed only small differences for MSH1 (1.75 ± 0.03) and ASI1 (1.45 ± 0.03) suggesting similar transformation mechanisms of BAM hydrolysis. Observations are in agreement with either a tetrahedral intermediate promoted by OH(-) or H(3)O(+) catalysis, or a concerted reaction mechanism. Therefore, owing to consistent carbon isotopic fractionation, isotope shifts of BAM can be linked to BAM biodegradation, and may even be used to quantify degradation of this persistent metabolite. In contrast, nitrogen isotope values may be rather indicative of different sources. Our results delineate a new approach to assessing the fate of BAM in the environment.     

Evidence-based medicine: quality and comparability of clinical trials investigating the efficacy of prostaglandin F(2α) for the treatment of bovine endometritis

The objective of this study was to evaluate the quality and comparability of published literature, and to summarize the effect of prostaglandin F(2α) (PGF(2α)) for the treatment of endometritis. It has been postulated that there is a dearth of high-level evidence-based research results in veterinary medicine. Also, there is a marked variation in the quality of studies in veterinary and animal science. Post-partum uterine infections occur commonly in dairy cattle and are reported to have a negative impact on reproductive performance. A comprehensive literature search was conducted utilizing online databases revealing a total of 2723 references. After applying specific exclusion criteria, a total of 68 trials were eligible for further analysis. These articles were evaluated utilizing specific parameters listed in an evaluation form such as randomization and the involvement of control groups. The analysis revealed that more than half of the trials (51·5%) were at least 20 years old. Furthermore, we found that about one third (36·8%) of all trials were controlled and randomized, while 3 of those (4·4%) were also blinded. Of those trials which calculated a calving-to-conception interval (n=30), 50% of the authors claimed an improvement, which was statistically significant in 23·3% of the cases. We conclude that there is a wide discrepancy between research results investigating the efficacy of PGF(2α).