Combined carbon and hydrogen isotope fractionation investigations for elucidating benzene biodegradation pathways

Recently, combined carbon and hydrogen isotope fractionation investigations have emerged as a powerful tool for the characterization of reaction mechanisms relevant for the removal of organic pollutants. Here, we applied this approach in order to differentiate benzene biodegradation pathways under oxic and anoxic conditions in laboratory experiments. Carbon and hydrogen isotope fractionation of benzene was studied with four different aerobic strains using a monooxygenase or a dioxygenase for the initial benzene attack, a facultative anaerobic chlorate-reducing strain as well as a sulfate-reducing mixed culture. Carbon and hydrogen enrichment factors (epsilon(C), epsilon(H)) varied for the specific pathways and degradation conditions, respectively, so that from the individual enrichment factors only limited information could be obtained for the identification of benzene biodegradation pathways. However, using the slope derived from hydrogen vs carbon isotope discriminations or the ratio of hydrogen to carbon enrichment factors (lambda = deltaH/ deltaC approximately epsilon(H)/epsilon(C)), benzene degradation mechanisms could be distinguished. Although experimentally determined lambda values partially overlapped, ranges could be determined for different benzene biodegradation pathways. Specific lambda values were < 2 for dihydroxylation, between 7 and 9 for monohydroxylation, and > 17 for anaerobic degradation. Moreover, variations in lambda values suggest that more than one reaction mechanism exists for monohydroxylation as well as for anaerobic benzene degradation under nitrate-reducing, sulfate-reducing, or methanogenic conditions. Our results show that the combined carbon and hydrogen isotope fractionation approach has potential to elucidate biodegradation pathways of pollutants in field and laboratory microcosm studies.     

N,N-dimethylsulfamide as precursor for N-nitrosodimethylamine (NDMA) formation upon ozonation and its fate during drinking water treatment

Application and microbial degradation of the fungicide tolylfluanide gives rise to a new decomposition product named N,N-dimethylsulfamide (DMS). In Germany, DMS was found in groundwaters and surface waters with typical concentrations in the range of 100-1000 ng/L and 50-90 ng/L, respectively. Laboratory-scale and field investigations concerning its fate during drinking water treatment showed that DMS cannot be removed via riverbank filtration, activated carbon filtration, flocculation, and oxidation or disinfection procedures based on hydrogen peroxide, potassium permanganate, chlorine dioxide, or UV irradiation. Even nanofiltration does not provide a sufficient removal efficiency. During ozonation about 30-50% of DMS are converted to the carcinogenic N-nitrosodimethylamine (NDMA). The NDMA being formed is biodegradable and can at least partially be removed by subsequent biologically active drinking water treatment steps including sand or activated carbon filtration. Disinfection with hypochlorous acid converts DMS to so far unknown degradation products but not to NDMA or 1,1-dimethylhydrazine (UDMH).     

Comparison of nutritional value and microbiological status of new imported fish species on the German market

Proximate composition, fatty acid profile, other nutritional values and spoilage indicators were examined in the muscle meat of five species: barramundi (Lates calcarifer) from various origins, tilapia (Oreochromis spp.) of different qualities, cobia (Rachycentron canadum) and leather jacket (Aluterus monoceros) from the Pacific Ocean and Patagonian grenadier (Macruronus magellanicus) from South America. Lowest lipid contents (0.4% and 0.8%) were found in leather jacket and cobia. Leather jacket fillets had lowest protein (16.2%) and highest sodium chloride content (4.9%). Concentrations of ∑EPA + DHA were 0.1 g 100 g^?1 for tilapia and leather jacket, 0.2 g 100 g^?1 for barramundi and cobia and 0.7 g 100 g^?1 for Patagonian grenadier. Barramundi and tilapia were characterised by high taurine content (215 and 276 mg 100 g^?1 ww.), and cobia had only low levels (41 mg 100 g^?1 ww.). Iodine contents were low and selenium levels varied between 303 and 570 μg kg^?1 ww. No sign of spoilage was detected.     

甲基纤维素/羟丙基甲基纤维素替代阿拉伯胶在乳化香精中的应用

阿拉伯胶被认为是稀释水包油体系中最适用的胶体.一个典型的应用实例就是用阿拉伯胶将柑桔香精油制成水分散的乳状液,然后用在柑桔味的软饮料中.但是多年来,由于阿拉伯胶的主要生产地区非洲不可预测的气候波动以及政治动荡,阿拉伯胶的稳定供应得不到保证.本文研究了将甲基纤维素和羟丙基甲基纤维素应用在8%和12%的浓缩橙子油乳状液中以替代20%的阿拉伯胶,结果表明能够显著降低用量,并且能够在4个月以上的常温保藏状态下获得相当或更加的视觉和粘度的稳定性.将这种浓缩乳状液应用在冷灌装饮料(大部分的软饮料)中非常有效.     

Palladium‐Catalyzed C?H Bond Acetoxylation: An Approach to ortho‐Substituted Hydroxy[2.2]paracyclophane Derivatives

The palladium‐catalyzed direct C H bond acetoxylation of [2.2]paracyclophanes has been investigated. Various mono‐ and disubstituted [2.2]paracyclophanes were subjected to typical Sanford acetoxylation conditions. Oxime ethers, an oxime acetate, a pyridine, and a pyrazole with [2.2]paracyclophane cores underwent direct ortho‐acetoxylation in good to excellent yields using 1–5 mol% of palladium(II) acetate in combination with iodobenzene diacetate as oxidant. The reactions could be performed on a multigram scale, and the ortho‐acetoxylated [2.2]paracyclophanes were suitable for further functionalizations affording a hydroxy[2.2]paracyclophane derivative and a planar chiral benzoxazole.     

Scalability and locality of extrapolation methods on large parallel systems

Time‐dependent processes can often be modeled by systems of ordinary differential equations (ODEs). Solving such a system for a detailed model can be highly computationally intensive. We investigate explicit extrapolation methods for solving such systems efficiently on current highly parallel supercomputer systems with shared‐or distributed‐memory architecture. We analyze and compare the scalability of several parallelization variants, some of them using multiple levels of parallelization. For a large class of ODE systems, data access costs are reduced considerably by exploiting the special structure of the ODE system. Furthermore, by employing a pipeline‐like loop structure, the locality of memory references is increased for such systems resulting in a better utilization of the cache hierarchy. Runtime experiments show that the optimized implementations can deliver a high scalability. Copyright © 2011 John Wiley & Sons, Ltd.     

Dimethyl Sulfoxide/Potassium Hydroxide: A Superbase for the Transition Metal‐Free Preparation of Cross‐Coupling Products

Potassium hydroxide (KOH) in dimethyl sulfoxide (DMSO) forms a superbasic medium that allows one to access cross‐coupling products from reactions between aryl halides with various sulfur‐, oxygen‐ and nitrogen‐based nucleophiles under transition metal‐free conditions.