Detailed Structure–Function Correlations of Bacillus subtilis Acetolactate Synthase

Isobutanol is deemed to be a next‐generation biofuel and a renewable platform chemical. 1 Non‐natural biosynthetic pathways for isobutanol production have been implemented in cell‐based and in vitro systems with Bacillus subtilis acetolactate synthase (AlsS) as key biocatalyst. 2 – 6 AlsS catalyzes the condensation of two pyruvate molecules to acetolactate with thiamine diphosphate and Mg²⁺ as cofactors. AlsS also catalyzes the conversion of 2‐ketoisovalerate into isobutyraldehyde, the immediate precursor of isobutanol. Our phylogenetic analysis suggests that the ALS enzyme family forms a distinct subgroup of ThDP‐dependent enzymes. To unravel catalytically relevant structure‐function relationships, we solved the AlsS crystal structure at 2.3 Å in the presence of ThDP, Mg²⁺ and in a transition state with a 2‐lactyl moiety bound to ThDP. We supplemented our structural data by point mutations in the active site to identify catalytically important residues.     

Stereoselective Monoamine Oxidase‐Catalyzed Oxidative Aza‐Friedel–Crafts Reactions of meso‐Pyrrolidines in Aqueous Buffer

We disclose the highly diastereoselective combination of monoamine oxidase‐catalyzed oxidation of meso‐pyrrolidines and aza‐Friedel–Crafts reactions in aqueous buffer to give valuable enantioenriched 2‐substituted pyrrolidines in a formal double C H activation process. A range of secondary as well as tertiary amines were shown to be suitable substrates for the biocatalytic oxidation and subsequent addition of a variety of C‐nucleophiles.

     

Effect of processing parameters,antistiction coatings,and polymer type when injection molding microfeatures

Thermoplastic polyurethane (TPU) and silicon tooling with microscale features on its surface was employed to investigate the impact of three factors on the quality of injection molded microscale features: (1) optimized process parameters, (2) use of a more flexible thermoplastic material, and (3) used as an antistiction coating. The molded parts and tooling surface were characterized by atomic force, confocal, and scanning electron microscopy. Although both improved filling of the tooling trenches, higher mold temperatures significantly enhanced replication, but faster injection velocities contributed moderately to replication quality. With medium aspect ratio (2.3:1) trenches, the antistiction coating doubled depth ratios, enhanced the edge definition and flatness of the features, and significantly reduced tearing of the features during ejection. The flexibility of the TPU permitted easier part ejection and left less polymer residue on the tooling surface in comparison to polycarbonate and other thermoplastic polymers. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

用于电源、继电器和螺线管的协同式线路保护

在各种新型先进设备上实施协同式电路保护可有助于提高设备可靠性、减少元器件数量,并使其符合严格的安规要求。协同式方法能够帮助保护电源、继电器和螺线管,避免因线路故障或过载造成电流增大以及尖峰电压或暴露在稳态过压状态带来的危害。     

Iron porphyrin-based cathode catalysts for polymer electrolyte membrane fuel cells: Effect of NH3 and Ar mixtures as pyrolysis gases on catalytic activity and stability

Ten different catalysts were prepared by loading 66 wt% ClFeTMPP on N330, a furnace grade carbon black, and pyrolyzing this catalyst precursor for 10 min at 950 °C in a NH₃/Ar gas mixture with various NH₃ volume fractions (from 0% to 100%). The activity and stability of these catalysts were measured in a fuel cell and compared. The only stable catalyst, although the least active, among these was the one pyrolyzed in pure Ar. A notable leap in catalytic activity, but drop in stability, was observed for all catalysts pyrolyzed in gas mixtures containing NH₃, even with a mere volume fraction of 1.3% NH₃ in the pyrolysis gas mixture. Catalytic activities increased, while stability decreased with increasing volume fraction of NH₃. The physicochemical properties of these catalysts were correlated with their electrochemical behaviour observed in fuel cell tests. It was found that a volume fraction of only 1.3% NH₃ was enough to double the micropore surface area, the surface nitrogen and iron concentrations in the resulting catalyst. Since the active sites are believed to be of the Fe/N/C type, the sharp increase in catalytic activity with as little as 1.3% NH₃ is attributed to the concurrent increase in microporous surface area, N and Fe surface contents in these catalysts. The only property that apparently correlates with stability is the degree of graphitization of the catalyst, which was estimated either from either X-ray diffraction and Raman spectroscopy measurements. Lastly, it was found that the catalysts’ peroxide yield, resulting from the partial reduction of O₂, does not correlate with their degree of stability.     

Stability of anthocyanins in frozen and freeze-dried raspberries during long-term storage: in relation to glass transition

Abstract: Anthocyanins, natural plant pigments in the flavonoid group, are responsible for the red color and some of the nutraceutical benefits of raspberries. This study explores anthocyanin degradation in frozen and freeze‐dried raspberries during storage in relation to glass transition temperatures. Frozen raspberries were stored at ?80, ?35, and ?20 °C, while freeze‐dried raspberries were stored at selected water activity (a_w) values ranging from 0.05 to 0.75 at room temperature (23 °C) for more than a year. The characteristic glass transition temperatures (T′_g) of raspberries with high water content and glass transition temperature (T_g) of raspberries with small water content were determined using a differential scanning calorimeter. The pH differential method was used to determine the quantity of anthocyanins in frozen and freeze‐dried raspberries at selected time intervals. The total anthocyanins in raspberries fluctuated during 378 d of storage at ?20 and ?35, and ?80 °C. Anthocyanin degradation in freeze‐dried raspberries ranged from 27% to 32% and 78% to 89% at a_w values of 0.05 to 0.07 and 0.11 to 0.43, respectively, after 1 y. Anthocyanins were not detectable in freeze‐dried raspberries stored at a_w values of 0.53 to 0.75 after 270 d. First order and Weibull equations were used to fit the anthocyanin degradation in freeze‐dried raspberries. The 1^st‐order rate constant (k) of anthocyanin degradation ranged from 0.003 to 0.023 days^?1 at the selected water activities. Significant anthocyanin degradation occurred in both the glassy and rubbery states of freeze‐dried raspberries during long‐term storage. However, the rate of anthocyanin degradation in freeze‐dried raspberries stored in the glassy state was significantly smaller than the rate of anthocyanin degradation in the rubbery state.     

Factors affecting in vitro formation of tannin-protein complexes

In interaction of condensed tannins from Desmodium intortum and Lotus pedunculatus and tannic acid (hydrolysable tannin) with salivary mucoproteins (from sheep and goats), plant leaf proteins and bovine serum albumin were evaluated. These studies were carried out over a pH range of 2-0-9-0 and different inorganic ion conditions to simulate conditions in which dietary proteins would interact with tannins in a ruminant digestive tract. Insoluble tannin-protein interactions were found at pH 4–5–5–5 for bovine serum albumin and 3–5–5–5 for plant leaf protein. The present study showed that pH alone was not the sole determinant for tannin-protein complex formation, since tannin-protein complexation was found in the pH range 6-0–6-5 when different inorganic ions were added to the solutions. Insoluble complexes were not formed with salivary proteins, although precipitation by tannic acid was achieved at 5°C. This suggests that tannins may form soluble rather than insoluble complexes with salivary proteins. It was concluded that purified F1 leaf protein (the major protei occurring in leaf tissue) ought to be used as the test protein for evaluating tannin-protein interactions for in vitro assay procedures. Using this method it was calculated that 27–43% and 19–40% of available plant protein may interact with condensed tannins from Desmodium intortum and Lotus pedunculatus, respectively.