An Engineered Cholesterol Oxidase Catalyses Enantioselective Oxidation of Non-steroidal Secondary Alcohols

The enantioselective oxidation of 2° alcohols to ketones is an important reaction in synthetic chemistry, especially if it can be achieved using O₂-driven alcohol oxidases under mild reaction conditions. However to date, oxidation of secondary alcohols using alcohol oxidases has focused on activated benzylic or allylic substrates, with unactivated secondary alcohols showing poor activity. Here we show that cholesterol oxidase (EC 1.1.3.6) could be engineered for activity towards a range of aliphatic, cyclic, acyclic, allylic and benzylic secondary alcohols. Additionally, since the variants demonstrated high (S)-selectivity, deracemisation reactions were performed in the presence of ammonia borane to obtain enantiopure (R)-alcohols.     

Kinetic Monte Carlo simulation of the elementary electrochemistry in a hydrogen-powered solid oxide fuel cell

A hydrogen-powered solid oxide fuel cell (SOFC), with a Pt cathode and a Ni anode, is modeled with a kinetic Monte Carlo (KMC) simulation technique. A series of reversible elementary steps are adopted from experiments and theories for simulating the oxygen reduction reaction near the cathode-electrolyte interface and the hydrogen-oxidation mechanism near the anode-electrolyte interface. By studying the change in the ionic current density, the sensitivity of the kinetic parameters is analyzed, and the influence of various operating conditions and different material properties are also explored. The results show that the dominant elementary process is the oxygen incorporation into the yttria-stabilized zirconia (YSZ) electrolyte at the cathode. Increasing the applied bias voltage, operating temperature, and relative permittivity of the YSZ, but reducing the thickness of the YSZ enhance the ionic current density and improve the efficiency of the SOFC.     

Mercury,selenium, PCBs and fatty acids in fresh and canned fish available on the Slovenian market

In order to contribute to the general understanding of the risks and benefits of consuming fish and fish products, total mercury (THg), monomethylmercury (MeHg), polychlorinated biphenyls (PCBs), selenium (Se), n-3 and n-6 fatty acids were determined in fresh and canned fish on the Slovenian market. Furthermore, the mercury exposure of pregnant women in Slovenia was assessed by determining total mercury (THg) in hair, and through fresh and canned fish consumption obtained by a food frequency questionnaire. Based on the frequency of fish consumption and levels of MeHg, THg and PCBs determined in the present study, it can be concluded that fish available on the Slovenian market do not represent a health risk. It was also confirmed that fish are important sources of selenium and n-3 fatty acids.     

Analysis of gateway congestion in interconnected high-speed localnetworks

The effects of congestion on performance in interconnected high-speed local networks are investigated. The system studied uses network adapters as gateways to connect distributed local networks through a high-performance network link. Throughput measurements were determined by simulations of various combinations of link speeds, gateway buffering capacities, and local network traffic loads. The performance effects of several high-speed, local-network, bus-access protocols are investigated. Simulation model parameters are based on measurements of HYPERchannel networks     

Synthesis of sex pheromones of lesser peachtree borer and peachtree borer

The sex pheromones produced by females of the lesser peachtree borer,Synanthedon pictipes (Grote and Robinson), and the peachtree borer,Synanthedon exitiosa (Say), (E,Z)- and (Z,Z)-3,13-octadecadien-1-ol acetate, respectively, were synthesized from 1,8-dichlorooctane, lithium acetylide, and ethylene oxide. In the course of the synthesis a new carbon-oxygen cleavage reaction of homopropargylic acetals was found, and the stereochemistry of the dissolving metal reductions of acetylenic alcohols was investigated.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of that product by the USDA.     

GABA and glutamate depolarize cortical progenitor cells and inhibit DNA synthesis

We have found that, during the early stages of cortical neurogenesis, both GABA and glutamate depolarize cells in the ventricular zone of rat embryonic neocortex. In the ventricular zone, glutamate acts on AMPA/kainate receptors, while GABA acts on GABAA receptors. GABA induces an inward current at resting membrane potentials, presumably owing to a high intracellular Cl- concentration maintained by furosemide-sensitive Cl- transport. GABA and glutamate also produce increases in intracellular Ca2+ in ventricular zone cells, in part through activation of voltage-gated Ca2+ channels. Furthermore, GABA and glutamate decrease the number of embryonic cortical cells synthesizing DNA. Depolarization with K+ similarly decreases DNA synthesis, suggesting that the neurotransmitters act via membrane depolarization. Applied alone, GABAA and AMPA/kainate receptor antagonists increase DNA synthesis, indicating that endogenously released amino acids influence neocortical progenitors in the cell cycle. These results demonstrate a novel role for amino acid neurotransmitters in regulating neocortical neurogenesis.     

Linear subdivision is strictly a polynomial phenomenon

In this paper we give an elementary proof that polynomial curves are the only differentiable curves which permit subdivision by simple linear techniques. Subdivision methods for rational polynomial curves are also discussed.     

Influence of linoleic acid,pH and HRT on anaerobic microbial populations and metabolic shifts in ASBRs during dark hydrogen fermentation of lignocellulosic sugars

In this study, controlling an anaerobic microbial community to increase the hydrogen (H₂) yield during the degradation of lignocelluosic sugars was accomplished by adding linoleic acid (LA) at low pH and reducing the hydraulic retention time (HRT) of an anaerobic sequencing batch reactor (ASBR). At pH 5.5 and a 1.7 d HRT, the maximum H₂ yield for LA treated cultures fed glucose or xylose reached 2.89 ± 0.18 mol mol⁻¹ and 1.94 ± 0.17 mol mol⁻¹, respectively. The major soluble metabolites at pH 5.5 with a 1.7 day HRT differed between the control and LA treated cultures. A metabolic shift toward H₂ production resulted in increased hydrogenase activity in both the xylose (13%) and glucose (34%) fed LA treated cultures relative to the controls. In addition, the Clostridia population and the H₂ yield were elevated in cultures treated with LA. A flux balance analysis for the LA treated cultures showed a reduction in homoacetogenic activity which was associated with reducing the Bacteriodes levels from 12% to 5% in the glucose fed cultures and 16% to 10% in the xylose fed cultures. Strategies for controlling the homoacetogens and optimal hydrogen production from glucose and xylose are proposed.     

Impact of culture source and linoleic acid (C18:2) on biohydrogen production from glucose under mesophilic conditions

Genomic and statistical methods were used to demonstrate the effects of linoleic acid (LA) on hydrogen (H₂) production in mixed anaerobic cultures from two sources (designated as A and B). The microbial composition of the control cultures CA and CB were statistically different. Bacteroidaceae (26%) and Clostridiaceae (10%) dominated CA whereas Clostridiaceae (33%) and Bacteroidaceae (10%) dominated CB. Homoacetogens directed 42% of the electron equivalents to acetate production and decreased the H₂ yield by 50% in CA compared to CB. The maximum H₂ yields (3.11 ± 0.02 and 3.11 ± 0.07 mol H₂ mol⁻¹ glucose in LA-treated cultures ALA and BLA, respectively) were statistically the same. Cultures ALA and BLA followed the acetate-butyrate pathway while CA and CB followed propionate and homoacetogenic pathways. LA-treated and control cultures were statistically different based on the type and quantity of metabolites; the differences were also confirmed by principal component analysis (PCA).