Asymmetric addition of phenylacetylene to aromatic ketones catalyzed by zinc or titanium complexes with chiral hydroxysulfonamide

Various new chiral hydroxysulfonamide ligands (3a-3n, 4a-4d) were prepared. Compounds 3a, 3g, 3i, 3k-3n, 4a-4d could accelerate the reaction and reduce reaction time, and 3a, 3g, 3i, 3k-3n catalyzed the reaction without titanium. The results obtained were promising in terms of yields and enantiomeric excesses (3k up to 85% ee, 4a up to 83% ee).     

Influence of reaction conditions on the enantioselectivity of biocatalyzed C-C bond formations under high pressure conditions

Benzoylformate decarboxylase (BFD, EC 4.1.1.7) is a homotetrameric thiamine diphosphate (ThDP)-dependent enzyme which catalyzes the synthesis of chiral 2-hydroxyketones accepting a broad range of aldehydes as substrates. In this study the synthesis of 2-hydroxypropiophenone (2-HPP) from benzaldehyde and acetaldehyde was catalyzed by three BFD variants namely BFD F464I, BFD A460I and BFD A460I-F464I. This paper reports the effect of hydrostatic pressure up to 290 MPa when the reactions were carried out at different benzaldehyde concentrations (5-40 mM) as well as at different pH values (7.0-8.5). Acetaldehyde concentration was fixed at 400 mM in all biotransformations. Reactions performed at high benzaldehyde concentrations and at high hydrostatic pressures showed an increase in (R)-2-HPP formation catalyzed by all BFD variants. For BFD A460I-F464I we observed an increase in the ee of (R)-2-HPP up to 80%, whereas at atmospheric conditions this variant synthesizes (R)-2-HPP with an ee of only 50%. Alkaline conditions (up to pH 8.5) and high hydrostatic pressures resulted in an increase of (R)-2-HPP synthesis, especially in the case of BFD A460I and BFD F464I.     

Polymer-immobilized fluorinase: Recyclable catalyst for fluorination reactions

Polymer-immobilized fluorinase for the synthesis of 5′-fluoro-5′-deoxyadenosine (FDA) from S-adenosyl-l-methionine (SAM) and fluoride ion in aqueous media is described. The optimal composition of the poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) and the heterogeneous catalytic reaction conditions were developed to yield FDA in 49% within 150 min. In PET radiochemistry, using [¹⁸F]fluoride ion in [¹⁸O]H₂O obtained from the cyclotron, [¹⁸F]FDA was synthesized with 68% fluorination efficiency. The immobilized fluorinase was recycled for up to four runs with 80% of catalytic activity in the final cycle.     

Enantioselective catalytic reduction of ketoimines with trichlorosilane promoted by readily available chiral Lewis bases

The straightforward synthesis of a series of enantiomerically pure Lewis basic amides by simple condensation of commercially available enantiopure diamines with picolinic acid is reported. These compounds were shown to promote the enantioselective reduction of ketoimines with trichlorosilane. Working with the model substrate N-phenyl benzophenone imine, the new organocatalysts led to the formation of the corresponding amine, with excellent chemical efficiency (up to 99% chemical yield) and good stereoselectivity (up to 73% ee). Up to 83% of enantioselectivity was reached in the reduction of differently substituted imines.     

Electrostatic interactions in the hairpin ribozyme account for the majority of the rate acceleration without chemical participation by nucleobases

Molecular dynamics simulations using a combined quantum mechanical/molecular mechanical potential are used to determine the two-dimensional free energy profiles for the mechanism of RNA transphosphorylation in solution and catalyzed by the hairpin ribozyme. A mechanism is explored whereby the reaction proceeds without explicit chemical participation by conserved nucleobases in the active site. The ribozyme lowers the overall free energy barrier by up to 16 kcal/mol, accounting for the majority of the observed rate enhancement. The barrier reduction in this mechanism is achieved mainly by the electrostatic environment provided by the ribozyme without recruitment of active site nucleobases as acid or base catalysts. The results establish a baseline mechanism that invokes only the solvation and specific hydrogen-bonding interactions present in the ribozyme active site and provide a departure point for the exploration of alternate mechanisms where nucleobases play an active chemical role.     

Enantioselective Ethylation of Various Aldehydes Catalyzed by Readily Accessible Chiral Diols

Four chiral C₂‐symmetric diols were synthesized in a straightforward three‐step reaction and demonstrated excellent enantioselectivities and good overall yields. Their catalytic activities were examined via the addition of diethylzinc to various aldehydes. The enantioselective addition of diethylzinc to 2‐methoxybenzaldehyde gave the corresponding chiral secondary alcohol with high yields (up to 95%) and moderate to good enantiomeric excess (up to 88%). All synthesized ligands were evaluated in the addition of diethylzinc to various aldehydes in the presence of an additional metal such as Ti(IV) complexes. Chirality 28:593–598, 2016. © 2016 Wiley Periodicals, Inc.     

Enantioselective organocatalytic Michael addition of ketones to alkylidene malonates

Organocatalysts bearing sulfide or sulfone functions (1a-d) were studied for the direct asymmetric Michael addition of ketones and alkylidene malonates. The organocatalyst (S)-2-((naphthalen-2-ylthio)methyl)pyrrolidine, bearing a pyrrolidine and a sulfide moiety, showed a very high catalytic activity in the absence of additives. The reaction condition is mild, and the Michael adducts were obtained in very good enantioselectivities (up to 96%), diastereoselectivities (up to 95:5), and chemical yields (up to 95%).     

Enantioselective addition of phenylacetylene to N-aryl arylimines catalyzed by Cu(II)-pyridine containing N-tosylatedaminoimine ligand complex

Chiral tridentate N-tosylated pyridine-containing ligands were prepared and used in the Cu(II)-catalyzed enantioselective addition of phenylacetylene to N-aryl arylimines. Moderate to high enantioselectivities (up to 95% ee) were obtained in very mild reaction conditions.     

Asymmetric Michael reaction of aldehydes with β-nitroalkenes catalyzed by pyrrolidine-camphor derived organocatalysts bearing hydrogen-bond donors

Several pyrrolidine-camphor derived organocatalysts were designed and synthesized. These organocatalysts were used for direct Michael reaction of aldehydes with nitroalkenes to give the desired γ-nitrocarbonyl compounds in high yields (up to 99%), high diastereoselectivities (syn:anti up to 92:8), and good to excellent enantioselectivities (up to 94% ee). Possible transition-state model was also proposed for this asymmetric transformation, which may involve hydrogen-bond interactions between the nucleophilic enamine formed in situ and the nitroalkenes.     

Effect of extracellular enzyme activity on digestion performance of mesophilic UASB reactor treating high-strength municipal wastewater

Effect of extracellular enzyme activity on digestion performance of up-flow anaerobic sludge blanket (UASB) reactor was investigated for enhancement of anaerobic treatability of municipal wastewater. Two identical UASB reactors (9 L), namely Reactor-A (without enzyme addition) and Reactor-B (with enzyme addition), were simultaneously operated at mesophilic conditions (32 ± 2 °C) with a hydraulic retention time of 24 h. Preliminary test results showed that the highest total chemical oxygen demand (TCOD) removal were achieved with an extracellular enzyme dosage of 0.2 mL/L. In the activation period of the extracellular enzyme (on days 186–212), while Reactor-A removed up to 69.3% of TCOD and 55.9% of soluble chemical oxygen demand (SCOD), Reactor-B effectively removed up to 81.9% of TCOD and 72.2% of SCOD. The average VFA/alkalinity ratios were determined to be about 0.40 (±0.03) and 0.28 (±0.08) for Reactor-A and Reactor-B, respectively.     

Production of activated carbon from bagasse and rice husk by a single-stage chemical activation method at low retention times

The production of activated carbon from bagasse and rice husk by a single-stage chemical activation method in short retention times (30-60min) was examined in this study. The raw materials were subjected to a chemical pretreatment and were fed to the reactor in the form of a paste (75% moisture). Chemicals examined were ZnCl2, NaOH and H3PO4, for temperatures of 600, 700 and 800 degrees C. Of the three chemical reagents under evaluation only ZnCl2 produced activated carbons with high surface areas. BET surface areas for rice husk were up to 750m2/g for 1:1 ZnCl2:rice husk ratio. BET surface areas for bagasse were up to 674m2/g for 0.75:1 ZnCl2:bagasse ratio. Results were compared to regular two-stage physical activation methods.     

Enhanced Stability and Thickness‐Independent Oxygen Evolution Electrocatalysis of Heterostructured Anodes with Buried Epitaxial Bilayers

Achieving high oxygen evolution reaction (OER) activity while maintaining performance stability is a key challenge for designing perovskite structure oxide OER catalysts, which are often unstable in alkaline environments transforming into an amorphous phase. While the chemical and structural transformation occurring during electrolysis at the electrolyte–catalyst interface is now regarded as a crucial factor influencing OER activity, here, using La_0.7Sr_0.3CoO_3?δ (LSCO) as an active OER catalyst, the critical influence of buried layers on the oxidation current stability in nanoscopically thin, chemically and structurally evolving, catalyst layers is revealed. The use of epitaxial thin films is demonstrated to engineer both depletion layer widths and chemical stability of the catalyst support structure resulting in heterostructured anodes that maintain facile transport kinetics across the electrolyte–anode interface for atomically thin (2–3 unit cells) LSCO catalyst layers and greatly enhanced oxidation current stability as the perovskite structure OER catalysts chemically and structurally transform. This work opens up an approach to design robust and active heterostructured anodes with dynamically evolving ultrathin OER electrocatalyst layers for future green fuel technologies such as conformal coatings of high‐density 3D anode topologies for water splitting.     

Asymmetric catalysis 87. Enantioselective allylation of 1,5-dimethylbarbituric acid with Pd catalysts and new optically active PN ligands

The new PN ligands 5, 6 and 7 were prepared by Schiff base condensation of 2-formylphenyl(diphenyl)phosphine (1) with the optically active amines (R)-(−)-2-aminobutanol (2), (S)-(+)-2-aminobutanol (3) and (1S,2S)-2-amino- 1-phenyl-1,3-propanediol (4). These new ligands were used in the Pd catalysed allylation of 1,5-dimethylbarbituric acid with allylacetate. 5-Allyl-1,5-dimethylbarbituric acid was obtained with an optical induction of up to 12.7% ee.     

Acylation of sucrose with vinyl esters using immobilized hydrolases: demonstration that chemical catalysis may interfere with enzymatic catalysis

The acylation of sucrose with vinyl laurate in dimethylsulfoxide was catalyzed by Celite (28% conversion in 24 h at 40 °C, 150 mg catalyst ml^–1), Eupergit C (11% conversion in 24 h at 60 °C, 150 mg catalyst/ml), and even the simple Na₂HPO₄ (17% conversion in 24 h at 40 °C, 20 mg catalyst ml^–1). These chemical acylations must therefore be taken into account in acylations of hydroxyl-containing compounds with enol esters in polar solvents using immobilized enzymes.     

Synthesis of Novel Chiral Tridentate Schiff‐Base Ligands and Their Applications in Catalytic Asymmetric Henry Reaction

A series of chiral tridentate Schiff‐bases were prepared and used as ligands in the catalytic asymmetric Henry reaction. Under the optimal conditions, a variety of arylaldehydes were smoothly converted into corresponding adducts with high yields (up to 98%) and excellent enantioselectivities (up to 97% ee). Chirality 26: 780–783, 2014. © 2014 Wiley Periodicals, Inc.     

Fractionation of Heavy Metals in Mine Tailings Amended with Composted Manure

This study evaluated the effect of composted cow manure (CCM) on the chemical fractionation and retention degree of heavy metals (HMs) in mine tailings from Zimapán, México. In a greenhouse experiment, mine tailings from three deposits were incubated for 3 months; experimental units were placed in a PVC container, where increasing doses of CCM were applied. HM pseudo-total concentrations, HM extractions with ethylenediaminetetraacetic acid (EDTA, 0.05 M), and a sequential chemical extraction (SCE) were carried out. The HM concentrations were determined by atomic absorption spectrophotometry. The pseudo-total concentrations of Pb, Cu, Cd, and Ni found were up to 1506, 206, 27, and 23 mg kg^?1, respectively; extractable Pb was up to 42%; 21% for Cu; 51% for Cd; and 16% of Ni of the pseudo-total concentrations of each metal. Treatment with 12% of CCM in mine tailing decreased EDTA-extractable HM concentrations, while the SCE revealed a decrease in exchangeable fraction and an increase in the organic fraction of HM. A positive correlation between CCM application and organic fractions of HMs was found, although the highest increasements were recorded in the organic fraction.     

Highly enantioselective asymmetric direct aldol reaction promoted by aziridine amides constructed on chiral terpene scaffold

Optically pure, diastereomeric aziridine amides built on the chiral skeletons of camphor, fenchone, and menthone have proven to be highly efficient ligands for enantioselective asymmetric direct aldol reaction in the presence of water and zinc triflate. Desired products were formed in moderate to high chemical yields (up to 95%) and with enantiomeric excess up to 99%. The influence of the stereogenic centers located at the aziridine subunit on the stereochemical course of the reaction is discussed.     

生物法合成尿苷二磷酸葡萄糖的研究进展

尿苷二磷酸葡萄糖(UDPG)是一种重要的糖类物质合成前体.生物法合成具有低成本、无污染和高立体选择性等传统化学法不具备的优势.利用纯酶催化的生物法以基于Leloir途径改进的一锅法、蔗糖合酶催化的两步法以及糖合成反应可逆催化等产UDPG,实现了UDPG的高产.全细胞催化法利用稳定的胞内酶系产UDPG,胞内生成的UDPG作为底物直接参与产物的催化合成,可行性高且成本更低.综述了酶法和全细胞催化法合成UDPG这两种最主要生物法的研究进展.     

Linear copolymeric poly(thia-alkanedioates) by lipase-catalyzed esterification and transesterification of 3,3'-thiodipropionic acid and its dimethyl ester with alpha,omega-alkanediols

Linear copolymeric polyesters (polyoxoesters) containing thioether functions [poly(3,3'-thiodipropionic acid-co-alpha,omega-alkanediols)] were formed in good yield by esterification of an equimolar mixture of 3,3'-thiodipropionic acid (4-thiaheptane-1,7-dioic acid) and 1,6-hexanediol (weight average molecular mass, M(W) >600 Da: approximately 81% after 6 h) or 1,12-dodecanediol (M(W) > 900 Da: approximately 90% after 6 h) catalyzed by immobilized lipase B from Candida antarctica (Novozym 435) for up to 336 h in moderate vacuo without a solvent or drying reagent in the reaction mixture. Poly (3,3'-thiodipropionic acid-co-1,6-hexanediol) and poly (3,3'-thiodipropionic acid-co-1,12-dodecanediol) were extracted from the reaction mixtures using tetrahydrofurane and precipitated from tetrahydrofurane-iso-hexane (1:1, v/v) at approximately 0 degrees C. The precipitate of poly(3,3'-thiodipropionic acid-co-1,6-hexanediol) showed a maximum molecular weight of 6 x 10(5) Da corresponding to a M(W) of approximately 24,200 Da and a degree of polymerization of up to 2,150 monomer units. The precipitated poly(3,3'-thiodipropionic acid-co-1,12-dodecanediol) showed a maximum molecular weight of 8 x 10(5) Da corresponding to a M(W) of approximately 27,200 Da and a maximum degree of polymerization of up to 2,200 monomer units. The chemical structures of both polyesters containing thioether functions were confirmed by chemical derivatization and NMR spectrometry. The chemical structures of various low-molecular weight reaction intermediates of the esterification of 3,3'-thiodipropionic acid with 1,6-hexanediol were elucidated by GC-MS.     

东方栓孔菌菌丝体生物吸附剂对染料的脱色作用及其吸附机制研究

利用东方栓孔菌Trametes orientalis菌丝体制得的生物吸附剂,对刚果红、结晶紫、铬天青、亚甲基蓝和中性红5种染料进行了脱色试验,对脱色效果较好的染料进行了影响因子优化,并通过红外光谱分析、化学修饰等方法研究其吸附作用的机制。结果显示：东方栓孔菌菌丝体生物吸附剂对结晶紫有相对较好的脱色效果;在优化的影响因子中,0%–3.0%（m/v）浓度范围内,盐度对染料脱色有促进作用;表面活性剂促使脱色率增加,吐温60浓度为1.5%（v/v）时脱色率可达83.84%;温度为43℃、初始pH为3.0、振荡培养10d后吸附率最高达91.54%。红外光谱分析及化学修饰结果表明菌丝体对染料的吸附作用主要是由它们之间的静电作用力所致。