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Sample records for a2 catalyzed acidolysis

  1. Synthesis of structured phospholipids by immobilized phospholipase A2 catalyzed acidolysis

    DEFF Research Database (Denmark)

    Vikbjerg, Anders Falk; Vikbjerg, Anders Falk; Xu, Xuebing

    2007-01-01

    Acyl modification of the sn-2 position in phospholipids (PLs) was conducted by acidolysis reaction using immobilized phospholipase A2 (PLA2) as the catalyst. In the first stage we screened different carriers for their ability to immobilize PLA2. Several carriers were able to fix the enzyme...

  2. Lipase-catalyzed acidolysis of canola oil with caprylic acid to produce medium-, long- and medium-chain-type structured lipids

    DEFF Research Database (Denmark)

    Wang, Yingyao; Xia, Luan; Xu, Xuebing

    2012-01-01

    Lipase-catalyzed acidolysis of canola oil with caprylic acid was performed to produce structured lipids (SLs) containing medium-chain fatty acid (M) at position sn-1,3 and long-chain fatty acid (L) at the sn-2 position in a solvent-free system. Six commercial lipases from different sources were...... screened for their ability to incorporate caprylic acid into the canola oil. The sn-1,3 regiospecificity toward the glycerol backbone of canola oil of the lipases with relatively higher acidolysis activity was compared by investigating the fatty acid profiles of the products. The results showed...

  3. Synthesis of structured triacylglycerols containing caproic acid by lipase-catalyzed acidolysis: Optimization by response surface methodology

    DEFF Research Database (Denmark)

    Zhou, D.Q.; Xu, Xuebing; Mu, Huiling

    2001-01-01

    Production in a batch reactor with a solvent-free system of structured triacylglycerols containing short-chain fatty acids by Lipozyme RM IM-catalyzed acidolysis between rapeseed oil and caproic acid was optimized using response surface methodology (RSM). Reaction time (t(r)), substrate ratio (S......-r), enzyme load (E-1, based on substrate), water content (W-c, based on enzyme), and reaction temperature (T-e), the five most important parameters for the reaction, were chosen for the optimization. The range of each parameter was selected as follows: t(r) = 5-17 h; E-1 = 6-14 wt %; T-e = 45-65 degreesC; S......-incorporated structured triacylglycerols were also evaluated. The optimal reaction conditions for the incorporation of caproic acid and the content of di-incorporated structured triacylglycerols were as follows: t(r) = 17 h; 8, = 5; E-1 = 14 wt %; W-c = 10 wt %; T-e = 65 degreesC. At these conditions, products with 55...

  4. Use of immobilized phospholipase A1-catalyzed acidolysis for the production of structured phosphatidylcholine with an elevated conjugated linoleic acid content

    Energy Technology Data Exchange (ETDEWEB)

    Baeza-Jimenez, R.; Gonzalez-Rodriguez, J.; Kim, I. H.; Gracia, H. S.; Otero, C.

    2012-11-01

    Structured phosphatidylcholine (SPC) was successfully produced via immobilized phospholipase A1 (PLA1) catalyzed acidolysis of phosphatidylcholine (PC) with conjugated linoleic acid (CLA). The effects of enzyme loading (2, 5, 10, 15 and 20%, with respect to the weight of substrates), temperature (20, 30, 40, 50 and 60 degree centigrade) and the molar ratio of substrates (1:2, 1:4, 1:6, 1:8 and 1:10, PC/CLA) were evaluated to maximize the incorporation of CLA into PC. The maximum incorporation of CLA achieved was ca. 90% for 24 h of reaction at 50 degree centigrade and 200 rpm, using a 1:4 substrate molar ratio and an enzyme loading of 15%. (Author) 30 refs.

  5. Synthesis of 1,3-dioleoyl-2-arachidonoylglycerol-rich structured lipids by lipase-catalyzed acidolysis of microbial oil from Mortierella alpina.

    Science.gov (United States)

    Abed, Sherif M; Zou, Xiaoqiang; Ali, Abdelmoneim H; Jin, Qingzhe; Wang, Xingguo

    2017-11-01

    Microbial oils (MOs) have gained widespread attention due to their functional lipids and health promoting properties. In this study, 1,3-dioleoyl-2-arachidonoylglycerol-rich structured lipids (SLs) were produced from MO and oleic acid (OA) via solvent-free acidolysis catalyzed by Lipozyme RM IM. Under the optimal conditions, the content of unsaturated fatty acids (UFAs) increased from 60.63 to 84.00%, while the saturated fatty acids (SFAs) content decreased from 39.37 to 16.00% at sn-1,3 positions in SLs. Compared with MO, arachidonic acid (ARA) content at the sn-2 position of SLs accounted for 49.71%, whereas OA was predominantly located at sn-1,3 positions (47.05%). Meanwhile, the most abundant triacylglycerol (TAG) species in SLs were (18:1-20:4-18:1), (20:4-20:4-18:1), (18:1-18:2-18:1), (18:1-18:2-18:0) and (24:0-20:4-18:1) with a relative content of 18.79%, 11.94%, 6.07%, 5.75% and 4.84%, respectively. Such novel SLs with improved functional properties enriched with UFAs are highly desirable and have the potential to be used in infant formula. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. Parameters affecting incorporation and by-product formation during the production of structured phospholipids by lipase-catalyzed acidolysis in solvent free system

    DEFF Research Database (Denmark)

    Vikbjerg, Anders Falk; Mu, Huiling; Xu, Xuebing

    2005-01-01

    By-product formation is a serious problem in the lipase-catalyzed acyl exchange of phospholipids (PL). By-products are formed due to parallel hydrolysis reactions and acyl migration in the reaction system. A clear elucidation of these side reactions is important for practical operation in order...... the influence of major factors and their relationships on a number of responses reflecting the turnover of main reactions as well as side reactions. The five factors, including enzyme dosage, reaction time, reaction temperature, substrate ratio (mol/mol caprylic acid/ PC) and water addition, were varied...... at three levels with two star points. All parameters besides water addition had an effect on the incorporation of caprylic acid into PC and lysophosphatidylcholine (LPC). Reaction time and enzyme dosage showed increased effect on incorporation into PC, while substrate ratio and reaction temperature showed...

  7. Comparison of linoleic and conjugated linoleic acids in enzymatic acidolysis of tristearin

    DEFF Research Database (Denmark)

    Yang, Tiankui; Xu, Xuebing; Li, L.T.

    2001-01-01

    The acyl incorporation and migration of linoleic and conjugated linoleic acids in enzymatic acidolysis were compared in a solvent-free system. Two systems were used in the Lipozyme RM IM-catalyzed acidolysis at 60C temperature and 5% by weight enzyme load (based on substrates). One included...... with gas chromatography, pancreatic lipase hydrolysis, and high performance liquid chromatography. Both acyl incorporation and migration of linoleic acid were faster than those of conjugated linoleic acid. At 5 h reaction, there were 13.0% LLL, 46.5% LSL, 27.7% LSS, and 5.6% SSS in the product for a system...... tristearin (SSS) and linoleic (L) or conjugated linoleic (cL) acids (1:6, mol/mol). The other was between tristearin and the mixture of linoleic and conjugated linoleic acids (1:3:3, mol/mol/mol). Acyl incorporation and migration together with triacylglycerol composition of the products were monitored...

  8. Synthesis of cocoa butter triacylglycerols using a model acidolysis system

    Directory of Open Access Journals (Sweden)

    Göǧüş, Fahrettin

    2008-12-01

    Full Text Available The effects of reaction parameters such as substrate mole ratio, reaction temperature, enzyme load, water content and reaction time were studied in a model enzymatic acidolysis system. Palmitic and stearic acids were incorporated into triolein (OOO under the catalysis of sn-1,3 specific lipase to produce the three major triacylglycerols (TAGs in cocoa butter (CB, namely, 1,3-dipalmitoyl-2-oleoyl--glycerol (POP, 1(3-palmitoyl-3(1-stearoyl-2-oleoyl-glycerol (POS and 1,3distearoyl-2-oleoyl-glycerol (SOS. TAG contents of the reaction products were analyzed by High Performance Liquid Chromatograph (HPLC.The best results (15.2% POP, 30.4% POS, 15.2 % SOS were obtained at 1:3:3 (OOO:palmitic acid:stearic acid substrate mole ratio and reaction parameters: time 10 h, temperature 45 oC, enzyme load 20 %, water content 5 %. The results obtained in this model system might be used for the optimization and application of lipase catalyzed acidolysis reactions in natural systems to produce cocoa butter equivalents (CBEs.El efecto de parámetros de reacción como el ratio molar de sustratos, carga de enzima, contenido de agua o temperatura de reacción fueron estudiados en un sistema modelo de acidolisis para la síntesis de triglicéridos disaturados. Los ácidos grasos palmítico y esteárico se incorporaron a la molécula de trioleína (OOO mediante la catálisis con una li-pasa sn-1,3 específica para producir los tres triglicéridos (TAGs mayoritarios de la manteca de cacao (CB: 1,3-dipalmitil-2-oleoil glicerol (POP, 1(3-palmitil-3(1-estearil-2glicerol (POS and 1,3-diestearil-2-oleoil glicerol (SOS. Los TAGs producidos en cada reacción se analizaron por cromatografía líquida de alta eficacia (HPLC. Los mejores resultados (15.2 %, POP, 30.4 % POS, 15.2 % SOS se obtuvieron empleando la relación molar de sustratos 1:3:3 (OOO: ácido palmítico:ácido esteárico y los parámetros de reacción: tiempo 10h, temperatura 45 °C, carga de enzima 20

  9. Lipase-Catalyzed Modification of Canola Oil with Caprylic Acid

    DEFF Research Database (Denmark)

    Wang, Yingyao; Luan, Xia; Xu, Xuebing

    Lipase-catalyzed acidolysis of canola oil with caprylic acid was performed to produce structured lipids. Six commercial lipases from different sources were screened for their ability to incorporate the caprylic acid into the canola oil. The positional distribution of FA on the glycerol backbone...

  10. Acidolysis hydrocarbon characteristics and significance of sediment samples from the ODP drilling legs of gas hydrate

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    Xun Sun

    2012-07-01

    Full Text Available To study on the significance and basis of acidolysis index to China marine gas hydrate exploring, since 2006, 111 samples derived from Leg 164 and 204 of the Ocean Drilling Program (ODP were analyzed in the experiment center of China Petroleum Exploration Research Institute to obtain data on acidolysis hydrocarbon index and methane carbon isotopes by the gas chromatography (GC of PE AutoSystem XL and isotope mass spectrometer (IRMS of Finnigan MAT251. Through these, we study the reliability of the acidolysis method and characterize the gas hydrate potential. The results show that the acidolysis hydrocarbon index has a stable correspondence with the Gas Hydrate Stability Zone (GHSZ in the ODP, and that there are clear abnormal signs in shallow samples that might reliably reflect the existence of authigenic carbonate caused by hydrocarbon migration from bottom hydrate. We therefore propose that the ability to characterize the acidolysis hydrocarbon is crucial to submarine gas hydrate exploration in China.

  11. Monitoring of monooctanoyl phosphatidylcholine synthesis by enzymatic acidolysis between soybean phosphatidylcholine and caprylic acid by thin-layer chromatography with a flame ionization detector

    DEFF Research Database (Denmark)

    Vikbjerg, Anders Falk; Mu, Huiling; Xu, Xuebing

    2005-01-01

    Thin-layer chromatography with flame ionization detector (TLC-FID) method was used for monitoring the production of structured phospholipids (ML-type: L-long chain fatty acids; M-medium chain fatty acids) by enzyme-catalyzed acidolysis between soybean phosphatidylcholine (PC) and caprylic acid....... It was found that the structured PC fractionated into 2-3 distinct bands on both plate thin layer chromatography (TLC) and Chromarod TLC. These 3 bands represented PC of LL-type, ML-type and MM-type, respectively. The TLC-FID method was applied in the present study to examine the influence of enzyme dosage...

  12. Prediction of a model enzymatic acidolysis system using neural networks

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    Güven, Aytaç

    2008-12-01

    Full Text Available A model for the acidolysis of trinolein and palmitic acid under the catalysis of immobilized sn-1,3 specific lipase was presented in this study. A neural networks (NN based model was developed for the prediction of the concentrations of the major reaction products of this reaction (1-palmitoyl-2,3-oleoyl-glycerol (POO 1,3-dipalmitoyl-2-oleoyl-glycerol (POP and triolein (OOO. Substrate ratio (SR, reaction temperature (T and reaction time (t were used as input parameters. The optimal architecture of the proposed NN model, which consists of one input layer with three inputs, one hidden layer with seven neurons and one output layer with three outputs, wass able to predict the reaction products concentration with a mean square error (MSE of less than 1.5 and R2 of 0.999. and explicit formulation of the proposed NN is presented. Considerable good performance is achieved in modeling the acidolysis reaction using neuronal networks.En este estudio se presenta un modelo para la acidólisis de la trilinoleina y el ácido palmítico mediante la catálisis con una lipasa específica sn-1,3 inmovilizada. Un modelo basado en redes neuronales (NN ha sido desarrollado para la predicción de la concentración de los principales productos de esta reacción (1-palmitoil-2,3-oleoil-glicerol (POO, 1,3-dipalmitoil-2-oleoil-glicerol (POP y trioleina (OOO. Se han usado como parámetros de entrada: la proporción del sustrato (SR, la temperatura de reacción (T y el tiempo de reacción (t. La arquitectura óptima del modelo de NN propuesto, que consiste en una capa de entrada con tres entradas, una capa oculta con siete neuronas y una capa de salida con tres salidas, fue capaz de predecir la concentración de los productos de reacción con un error cuadrático medio (MSE de menos de 1.5 y una R2 de 0.999 . Se presenta una formulación explícita del modelo NN propuesto. Se obtienen muy buenos resultados en la predicción de la reacciones de acidólisis mediante el uso de

  13. Effects of antioxidants on the lipase-catalyzed acidolysis during production of structured lipids

    DEFF Research Database (Denmark)

    Xu, Xuebing; Timm Heinrich, Maike; Nielsen, Nina Skall

    2005-01-01

    due to the adsorption in the enzyme bed. The study shows that the addition of antioxidants before enzymatic reactions has no negative effects on the reaction progress. None of the antioxidants chosen had a significant positive effect on either the reaction process or the oxidative status...

  14. Theoretical study on the N-demethylation mechanism of theobromine catalyzed by P450 isoenzyme 1A2.

    Science.gov (United States)

    Tao, Jing; Kang, Yuan; Xue, Zhiyu; Wang, Yongting; Zhang, Yan; Chen, Qiu; Chen, Zeqin; Xue, Ying

    2015-09-01

    Theobromine, a widely consumed pharmacological active substance, can cause undesirable muscle stiffness, nausea and anorexia in high doses ingestion. The main N-demethylation metabolic mechanism of theobromine catalyzed by P450 isoenzyme 1A2 (CYP1A2) has been explored in this work using the unrestricted hybrid density functional method UB3LYP in conjunction with the LACVP(Fe)/6-31G (H, C, N, O, S, Cl) basis set. Single-point calculations including empirical dispersion corrections were carried out at the higher 6-311++G** basis set. Two N-demethylation pathways were characterized, i.e., 3-N and 7-N demethylations, which involve the initial N-methyl hydroxylation to form carbinolamines and the subsequent carbinolamines decomposition to yield monomethylxanthines and formaldehydes. Our results have shown that the rate-limiting N-methyl hydroxylation occurs via a hydrogen atom transfer (HAT) mechanism, which proceeds in a spin-selective mechanism (SSM) in the gas phase. The carbinolamines generated are prone to decomposition via the contiguous heteroatom-assisted proton-transfer. Strikingly, 3-N demethylation is more favorable than 7-N demethylation due to its lower free energy barrier and 7-methylxanthine therefore is the optimum product reported for the demethylation of theobromine catalyzed by CYP1A2, which are in good agreement with the experimental observation. This work has first revealed the detail N-demethylation mechanisms of theobromine at the theoretical level. It can offer more significant information for the metabolism of purine alkaloid. Copyright © 2015 Elsevier Inc. All rights reserved.

  15. Valuable ingredients and feed toxicity evaluation of Microcystis aeruginosa acidolysis product in mice.

    Science.gov (United States)

    Han, Shiqun; Zhou, Qing; Xu, Yudi; Vanogtrop, Floris; Guo, Qijin; Liu, Guofeng; Yan, Shaohua

    2015-10-01

    This research studied the extraction from Microcystis aeruginosa using hydrochloric acid method as a potentially valuable protein resource from eutrophic lakes. Amino acid composition, residual algal toxins, and heavy metals of the acidolysis product were studied. After 18 h of hydrochloric acid treatment, the product of M. aeruginosa contained 17 amino acids, 51.34% of total amino acid requirements, and 30.25% of the livestock and poultry essential amino acid (Eaa). The residual microcystin-LR (MC-LR) was 0.94 µg kg(-1), which was less than WHO drinking water limit of microcystins. The removal ratio of microcystins was higher than 99.99% during the process of hydrolysis. The concentration of heavy metals of the product was in compliance with feed standards. Furthermore, using Horn's method, Mouse Micronucleus Test and Sperm Shape Abnormality Test were conducted to study the forage safety of the product. Half lethal dose (LD50) of acidolysis product in mice was >9.09 g kg(-1) body weight, actually belonging to non-toxic grade. Every dose treatment did not significantly increase activities of alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and γ-glutamyltransferase (γ-GT). The results of both micronucleus test and sperm shape abnormality test were negative, which suggested the product with no mutagenicity and sperm malformation effects. This study indicated that the acidolysis product of M. aeruginosa was safe to be used as a feed ingredient. © 2015 by the Society for Experimental Biology and Medicine.

  16. Acidolysis of terebinth fruit oil with palmitic and caprylic acids in a recirculating packed bed reactor: optimization using response surface methodology

    Energy Technology Data Exchange (ETDEWEB)

    Koçak, D.; Keskin, H.; Fadiloglu, S.; Gögüs, F.

    2016-07-01

    The acidolysis reaction of terebinth fruit oil with caprylic and palmitic acid has been investigated. The reaction was catalyzed by lipase (Lipozyme IM from Rhizomucormiehei) and carried out in recirculating packed bed reactor. The effects of reaction parameters have been analyzed using response surface methodology. Reaction time (3.5–6.5 h), enzyme load (10–20%), substrate flow rate (4–8 mL·min−1 ) and substrate mole ratios (Terebinth oil : Palmitic acid : Caprylic acid, 1:1.83:1.22–1:3.07:2.05) were evaluated. The optimum reaction conditions were 5.9 h reaction time, 10% enzyme load, 4 mL·min−1 substrate flow rate and 1:3.10:2.07 substrate mole ratio. The structured lipid obtained at these optimum conditions had 52.23% desired triacylglycerols and a lower caloric value than that of terebinth fruit oil. The melting characteristics and microstructure of the structured lipid were similar to those of commercial margarine fat extracts. The results showed that the structured lipid had the highest oxidative stability among the studied fats. (Author)

  17. Monitoring of monooctanoylphosphatidylcholine synthesis by enzymatic acidolysis between soybean phosphatidylcholine and caprylic acid by thin-layer chromatography with a flame ionization detector.

    Science.gov (United States)

    Vikbjerg, Anders F; Mu, Huiling; Xu, Xuebing

    2005-05-18

    Thin-layer chromatography with a flame ionization detector (TLC-FID) was used for monitoring the production of structured phospholipids (ML type: L, long-chain fatty acids; M, medium-chain fatty acids) by enzyme-catalyzed acidolysis between soybean phosphatidylcholine (PC) and caprylic acid. It was found that the structured PC fractionated into two to three distinct bands on both plate thin-layer chromatography (TLC) and Chromarod TLC. These three bands represented PC of the LL type, ML type, and MM type, respectively. The TLC-FID method was applied in the present study to examine the influence of enzyme dosage, reaction temperature, solvent amount, reaction time, and substrate ratio (caprylic acid/PC, mol/mol) on formation of ML-type PC in a batch reactor with Thermomyces lanuginosa lipase as the catalyst. The formation of ML-type PC was dependent on all parameters examined except for the substrate ratio. The ML-type PC content increased with increasing enzyme dosage, reaction temperature, solvent amount, and reaction time. The substrate ratio had no significant effect on the formation of ML-type PC within the tested range (3-15 mol/mol). The formation of MM-type PC was observed in some experiments, indicating that acyl migration is taking place during reaction since the lipase is claimed to be 1,3-specific. The TLC-FID method offers a simple and cheap technique for elucidation of product and byproduct formation during enzyme-catalyzed reactions for production of phospholipids containing mixtures of long- and medium-chain fatty acids.

  18. Acidolysis of a lignin model: investigation of heterogeneous catalysis using Montmorillonite clay.

    Science.gov (United States)

    Bouxin, Florent; Baumberger, Stéphanie; Pollet, Brigitte; Haudrechy, Arnaud; Renault, Jean-Hugues; Dole, Patrice

    2010-01-01

    The use of heterogeneous conditions involving Montmorillonite K10 clay was investigated as a mild alternative to homogeneous acidolysis of a lignin model. Guaiacyl Dehydrogenation Oligomers (DHOs) synthesized by horseradish peroxidase were selected as starting material. Hydrolysis products were analyzed by gel permeation chromatography and by HPLC/mass spectrometry. Several experimental parameters were studied such as catalyst and substrate concentration, as well as reaction solvent composition in order to minimize high molar mass product formation generated by recombination mechanisms. In both catalytic modes, the best hydrolysis conditions were similar in terms of solvent composition with dioxane/water (90/10, v/v) and catalyst H(+) concentration of about 0.01 mol/L. Although the homogeneous catalysis generated only 28% of low molecular weight (LMW) products (monomers and dimers), clay catalysis generated 35%. In light of the qualitative analysis, both catalytic methods gave the same products, thus supporting similar hydrolysis mechanisms.

  19. Practical synthesis of 1,3-oleoyl 2-docosahexaenoylglycerol by lipase-catalyzed reactions: An evaluation of different reaction routes

    DEFF Research Database (Denmark)

    Zhang, Hong; Onal, G.; Wijesundera, C.

    2009-01-01

    Three new synthetic routes were critically evaluated for the lipase-catalyzed production of 1,3-oleoyl-2 docosahexaenoylglycerol (ODD) in relatively large-scale (approximately 200 g). First, the production of 1,3-diolein by the reaction of glycerol and oleic acid followed by incorporation...... of docosahexaenoic (DHA) ethyl ester at the sn-2 position was studied. 1,3-Diolein was produced in 68.3% and 84.6% yield when stoichiometric amounts of the Substrates were reacted at 25 degrees C for 8 h in the presence of 10% Novozym 435 and Lipozyme RM IM, respectively. Further increase in reaction temperature...... and time led to decrease in the 1,3-diolein yield. However, only a 9.4% yield of triacylglycerol was obtained in the subsequent reaction step when the 1,3-diolein was reacted with DHA ethyl ester in the presence of Novozym 435. Secondly, the feasibility of direct acidolysis was studied. Acidolysis...

  20. Acidolysis reactions lead to esterification of endogenous tocopherols and compromised oxidative stability of modified oils.

    Science.gov (United States)

    Hamam, Fayez; Shahidi, Fereidoon

    2006-09-20

    For the first time, a possible mechanism responsible, in part, for the removal of endogenous antioxidants through the formation of tocopheryl esters during acidolysis reactions is proposed and confirmed. Tocopherols in the oils were found to react with carboxylic acids present in the medium, thus leading to the formation of tocopheryl esters that do not render any stability to the resultant modified oils as they lack any free hydroxyl groups on the phenolic ring of the molecule. Tocopheryl oleate, used as a standard, was synthesized through the reaction of acyl chloride of oleic acid with alpha-tocopherol (m/z 695.5 as evidenced by mass spectrometry). Subsequently, lipase-assisted esterification of alpha-, gamma-, and delta-tocopherols with oleic acid was carried out, and corresponding tocopheryl esters were isolated. In a real acidolysis reaction system involving docosahexaenoic acid single-cell oil and capric acid, high-performance liquid chromatography-mass spectrometry analysis demonstrated the presence of several tocopheryl esters. These included tocopheryl esters of myristic acid, namely, alpha-tocopheryl myristate, m/z 641.1, gamma-tocopheryl myristate, m/z 627.1, and delta-tocopheryl myristate, m/z 613.1, as well as those of palmitic acid, namely, alpha-tocopheryl palmitate, m/z 669.1, gamma-tocopheryl palmitate, m/z 655.1, and delta-tocopheryl palmitate, m/z 641.1. The mixture also contained different species of tocopheryl oleates, namely, alpha-tocopheryl oleate, m/z 695.5, gamma-tocopheryl oleate, m/z 681.1, and delta-tocopheryl oleate, m/z 667.2. Esters produced from reactions of docosahexaenoic acid and tocopherols were also detected, namely, alpha-tocopheryl docosahexaenoate, m/z 738.7, and delta-tocopheryl docosahexaenoate, m/z 710.7.

  1. Quantitation of acyl migration during lipase-catalyzed acidolysis, and of the regioisomers of structured triacylglycerols formed

    DEFF Research Database (Denmark)

    Mu, Huiling; Kurvinen, J.P.; Kallio, H.

    2001-01-01

    degradation, and ranged from 39.0 to 48.7% and 0.6 to 9.3%, respectively. Quantitation of triacylglycerol molecular species was performed by ammonia negative ion chemical ionization (NICI) mass spectrometry (MS). The proportion of ACN (acyl carbon number) 34 species that contained one C-18 fatty acid and two...... C-8:0, in samples analyzed, varied from 12.5 to 23.2%. The selected regioisomers MLM and MML within the ACN 34 species group were quantified by NICI tandem MS (MS/MS) and were in the range of 97.1 to 98.4% and 1.6 to 2.9%, respectively. There was no correlation between the level of acyl migration...

  2. Cytochrome P450 102A2 Catalyzes Efficient Oxidation of Sodium Dodecyl Sulphate: A Molecular Tool for Remediation

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    Irene Axarli

    2010-01-01

    Full Text Available Bacterial cytochrome P450s (CYPs constitute an important family of monooxygenase enzymes that carry out essential roles in the metabolism of endogenous compounds and foreign chemicals. In the present work we report the characterization of CYP102A2 from B. subtilis with a focus on its substrate specificity. CYP102A2 is more active in oxidation of sodium dodecyl sulphate (SDS than any other characterized CYP. The effect of SDS and NADPH concentration on reaction rate showed nonhyperbolic and hyperbolic dependence, respectively. The enzyme was found to exhibit a bell-shaped curve for plots of activity versus pH, over pH values 5.9–8.5. The rate of SDS oxidation reached the maximum value approximately at pH 7.2 and the pH transition observed controlled by two pas in the acidic (pa=6.7±0.08 and basic (pa=7.3±0.06 pH range. The results are discussed in relation to the future biotechnology applications of CYPs.

  3. Fast microwave-assisted acidolysis: a new biorefinery approach for the zero-waste utilisation of lignocellulosic biomass to produce high quality lignin and fermentable saccharides.

    Science.gov (United States)

    Zhou, Long; Santomauro, Fabio; Fan, Jiajun; Macquarrie, Duncan; Clark, James; Chuck, Christopher J; Budarin, Vitaliy

    2017-09-21

    Generally, biorefineries convert lignocellulosic biomass into a range of biofuels and further value added chemicals. However, conventional biorefinery processes focus mainly on the cellulose and hemicellulose fractions and therefore produce only low quality lignin, which is commonly burnt to provide process heat. To make full use of the biomass, more attention needs to be focused on novel separation techniques, where high quality lignin can be isolated that is suitable for further valorisation into aromatic chemicals and fuel components. In this paper, three types of lignocellulosic biomass (softwood, hardwood and herbaceous biomass) were processed by microwave-assisted acidolysis to produce high quality lignin. The lignin from the softwood was isolated largely intact in the solid residue after acidolysis. For example, a 10 min microwave-assisted acidolysis treatment produced lignin with a purity of 93% and in a yield of 82%, which is superior to other conventional separation methods reported. Furthermore, py-GC/MS analysis proved that the isolated lignin retained the original structure of native lignin in the feedstock without severe chemical modification. This is a large advantage, and the purified lignin is suitable for further chemical processing. To assess the suitability of this methodology as part of a biorefinery system, the aqueous phase, produced after acidolysis of the softwood, was characterised and assessed for its suitability for fermentation. The broth contained some mono- and di-saccharides but mainly contained organic acids, oligosaccharides and furans. While this is unsuitable for S. cerevisiae and other common ethanol producing yeasts, two oleaginous yeasts with known inhibitor tolerances were selected: Cryptococcus curvatus and Metschnikowia pulcherrima. Both yeasts could grow on the broth, and demonstrated suitable catabolism of the oligosaccharides and inhibitors over 7 days. In addition, both yeasts were shown to be able to produce an oil

  4. Acidolysis of terebinth fruit oil with palmitic and caprylic acids in a recirculating packed bed reactor: optimization using response surface methodology

    Directory of Open Access Journals (Sweden)

    Koçak Yanık, D.

    2016-06-01

    Full Text Available The acidolysis reaction of terebinth fruit oil with caprylic and palmitic acid has been investigated. The reaction was catalyzed by lipase (Lipozyme IM from Rhizomucormiehei and carried out in recirculating packed bed reactor. The effects of reaction parameters have been analyzed using response surface methodology. Reaction time (3.5–6.5 h, enzyme load (10–20%, substrate flow rate (4–8 mL·min-1 and substrate mole ratios (Terebinth oil : Palmitic acid : Caprylic acid, 1:1.83:1.22–1:3.07:2.05 were evaluated. The optimum reaction conditions were 5.9 h reaction time, 10% enzyme load, 4 mL·min-1 substrate flow rate and 1:3.10:2.07 substrate mole ratio. The structured lipid obtained at these optimum conditions had 52.23% desired triacylglycerols and a lower caloric value than that of terebinth fruit oil. The melting characteristics and microstructure of the structured lipid were similar to those of commercial margarine fat extracts. The results showed that the structured lipid had the highest oxidative stability among the studied fats.Se ha investigado la reacción de acidolisis del aceite de pistacho con los ácidoscaprílico y palmítico. La reacción fue catalizada por la lipasa Lipozyme IM de Rhizomucormiehei y realizada mediante recirculación del reactor de lecho compacto. Los efectos de los parámetros de la reacción han sido analizados mediante el uso de la metodología de superficie de respuesta. El tiempo de reacción (3.5 hasta 6.5 h, la carga de enzima (10–20%, el caudal de sustrato (4–8 mL·min-1 relaciones molares de los sustrato (aceite de pistacho: ácido palmítico: ácido caprílico, 1: 1,83: 1,22–1: 3,07: 2,05 fueron evaluados. Las condiciones óptimas de reacción fueron 5,9 h de tiempo de reacción, el 10% de carga de la enzima, 4 mL·min-1 de caudal de sustrato y 1: 3,10: 2,07 de relación molar de sustratos. Los lípidos estructurados obtenidos en las condiciones óptimas tenías 52,23% de triacilgliceroles

  5. Medium chain and behenic acid incorporated structured lipids from sal, mango and kokum fats by lipase acidolysis.

    Science.gov (United States)

    Bebarta, Biranchi; M, Jhansi; Kotasthane, Pranitha; Sunkireddy, Yella Reddy

    2013-01-15

    Medium chain (MC) and behenic fatty acids were incorporated into kokum, sal and mango fats using 1,3-specific lipase catalysed acidolysis. The incorporation of fatty acids increased with increase in concentration of fatty acids and duration of reaction. The order of incorporation of fatty acids was C22:0>C10:0>C8:0, to the extent of 53%, 42.5%, 35.8%, respectively, after 16 h, using kokum as substrate. The same trend was observed with sal or mango fats as substrates though the percentages incorporated were different. The modified products with higher contents of MC were liquids with no solid fats, even at 0°C, and which showed low cloud point due to an increase in triacylglycerols containing lower chain fatty acids. The modified products after incorporating both MC and C22:0 showed long melting ranges and were suitable for use in bakery, confectionery, etc. as vanaspati substitutes. Copyright © 2012 Elsevier Ltd. All rights reserved.

  6. Enzymatic acidolysis of triolein with palmitic and caprylic acids: Optimization of reaction parameters by response surface methodology

    Directory of Open Access Journals (Sweden)

    Keskin, H.

    2012-09-01

    Full Text Available An acidolysis reaction of triolein with caprylic and palmitic acids was performed using immobilized sn-1,3 specific lipase from Mucor miehei to produce a reduced calorie spreadable structured lipid (SL. Response surface methodology was applied to model and optimize the reaction conditions using a four-factor five-level central composite rotatable design. The selected factors were time (10-24 h, enzyme load (10-25 wt%, substrate mole ratio (Triolein:Caprylic acid:Palmitic acid, (1:1:1-1:2.5:2.5 and temperature (45-60 °C. The produced SLs were compared to fat extracts of commercial margarine in terms of melting profile and solid fat content (SFC. SL with a melting peak of 42 °C and SFC of 40.69% at 0 °C was very similar to soft margarines. The caloric value of this SL was determined as 37.74 kJ/g, theoretically. The optimum reaction conditions were found as reaction time 14 h; substrate mole ratio 1:2.1:2.1; temperature 58 °C; and enzyme load 15 wt%. Under optimum conditions, the product contained 29.68% COC, 25.47% POC, and 3.80% POP.

    La reacción de acidolísis de la trioleina con los ácidos caprílico y palmítico se realizó utilizando lipasa inmovilizada Mucor miehei, específica de sn-1, 3, para producir una grasa de untar baja en calorías compuesta de lípidos estructurados (SL. La metodología de superficie de respuesta se aplica para modelar y optimizar las condiciones de reacción utilizando un factor-cuatro y nivel-cinco de diseño central compuesto. Los factores seleccionados fueron el tiempo (10-24 h, la carga de enzima (10-25% en peso, la relación molar de sustratos (Trioleína:Ácido Caprílico:Ácido Palmítico, (1:1:1-1:2.5:2.5 y la temperatura (45-60 °C. Los SLs producidos se compararon con extractos de grasa de margarina comercial en términos de perfil de fusión y contenido de grasa sólida (SFC. El SL con un pico de fusión a 42 °C y SFC de 40,69% a 0 °C era muy similar a las

  7. A Small Phospholipase A2-α from Castor Catalyzes the Removal of Hydroxy Fatty Acids from Phosphatidylcholine in Transgenic Arabidopsis Seeds1[OPEN

    Science.gov (United States)

    Bayon, Shen; Chen, Guanqun; Weselake, Randall J.; Browse, John

    2015-01-01

    Ricinoleic acid, an industrially useful hydroxy fatty acid (HFA), only accumulates to high levels in the triacylglycerol fraction of castor (Ricinus communis) endosperm, even though it is synthesized on the membrane lipid phosphatidylcholine (PC) from an oleoyl ester. The acyl chains of PC undergo intense remodeling through the process of acyl editing. The identities of the proteins involved in this process, however, are unknown. A phospholipase A2 (PLA2) is thought to be involved in the acyl-editing process. We show here a role for RcsPLA2α in the acyl editing of HFA esterified to PC. RcsPLA2α was identified by its high relative expression in the castor endosperm transcriptome. Coexpression in Arabidopsis (Arabidopsis thaliana) seeds of RcsPLA2α with the castor fatty acid hydroxylase RcFAH12 led to a dramatic decrease in seed HFA content when compared with RcFAH12 expression alone in both PC and the neutral lipid fraction. The low-HFA trait was heritable and gene dosage dependent, with hemizygous lines showing intermediate HFA levels. The low seed HFA levels suggested that RcsPLA2α functions in vivo as a PLA2 with HFA specificity. Activity assays with yeast (Saccharomyces cerevisiae) microsomes showed a high specificity of RcsPLA2α for ricinoleic acid, superior to that of the endogenous Arabidopsis PLA2α. These results point to RcsPLA2α as a phospholipase involved in acyl editing, adapted to specifically removing HFA from membrane lipids in seeds. PMID:25667315

  8. A small phospholipase A2-α from castor catalyzes the removal of hydroxy fatty acids from phosphatidylcholine in transgenic Arabidopsis seeds.

    Science.gov (United States)

    Bayon, Shen; Chen, Guanqun; Weselake, Randall J; Browse, John

    2015-04-01

    Ricinoleic acid, an industrially useful hydroxy fatty acid (HFA), only accumulates to high levels in the triacylglycerol fraction of castor (Ricinus communis) endosperm, even though it is synthesized on the membrane lipid phosphatidylcholine (PC) from an oleoyl ester. The acyl chains of PC undergo intense remodeling through the process of acyl editing. The identities of the proteins involved in this process, however, are unknown. A phospholipase A2 (PLA2) is thought to be involved in the acyl-editing process. We show here a role for RcsPLA2α in the acyl editing of HFA esterified to PC. RcsPLA2α was identified by its high relative expression in the castor endosperm transcriptome. Coexpression in Arabidopsis (Arabidopsis thaliana) seeds of RcsPLA2α with the castor fatty acid hydroxylase RcFAH12 led to a dramatic decrease in seed HFA content when compared with RcFAH12 expression alone in both PC and the neutral lipid fraction. The low-HFA trait was heritable and gene dosage dependent, with hemizygous lines showing intermediate HFA levels. The low seed HFA levels suggested that RcsPLA2α functions in vivo as a PLA2 with HFA specificity. Activity assays with yeast (Saccharomyces cerevisiae) microsomes showed a high specificity of RcsPLA2α for ricinoleic acid, superior to that of the endogenous Arabidopsis PLA2α. These results point to RcsPLA2α as a phospholipase involved in acyl editing, adapted to specifically removing HFA from membrane lipids in seeds. © 2015 American Society of Plant Biologists. All Rights Reserved.

  9. Maximizing content of Omega-3 (EPA and DHA) in the process of enzymatic acidolysis of canola oil and concentrated of long-chain polyunsaturated fatty acids (LCPUFA) in supercritical CO2 conditions

    OpenAIRE

    Cedano, José; Rodríguez, Alicia; Siche, Raúl

    2016-01-01

    The aim of this study was to optimize the content of EPA and DHA in the process of enzymatic acidolysis of canola oil and concentrated of long-chain polyunsaturated fatty acids (LCPUFA) in structured triacylglycerols (TAGs). For this purpose, nonspecific lipase B from Candida antarctica immobilized in a supercritical CO2 was used. Crude salmon oil obtained from the industrial byproducts was used to obtain LCPUFA concentrate. Initially, a LCPUFAs concentrate was obtained by basic hydrolysis an...

  10. Catalyzing RE Project Development

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Kate; Elgqvist, Emma; Walker, Andy; Cutler, Dylan; Olis, Dan; DiOrio, Nick; Simpkins, Travis

    2016-09-01

    This poster details how screenings done with REopt - NREL's software modeling platform for energy systems integration and optimization - are helping to catalyze the development of hundreds of megawatts of renewable energy.

  11. Rhodium Catalyzed Decarbonylation

    DEFF Research Database (Denmark)

    Garcia Suárez, Eduardo José; Kahr, Klara; Riisager, Anders

    2017-01-01

    Rhodium catalyzed decarbonylation has developed significantly over the last 50 years and resulted in a wide range of reported catalyst systems and reaction protocols. Besides experimental data, literature also includes mechanistic studies incorporating Hammett methods, analysis of kinetic isotope...... effects as well as computational studies of model systems, which give an indication of the scope of the process. In this chapter, fundamental applications of Rh-catalyzed decarbonylation reactions are surveyed and discussed, including cross-coupling reactions, tandem reactions, and alternative...

  12. Acidolysis of α-O-4 Aryl-Ether Bonds in Lignin Model Compounds: A Modeling and Experimental Study

    Energy Technology Data Exchange (ETDEWEB)

    Pelzer, Adam W.; Sturgeon, Matthew R.; Yanez, Abraham J.; Chupka, Gina; O’Brien, Marykate H.; Katahira, Rui; Cortright, Randy D.; Woods, Liz; Beckham, Gregg T.; Broadbelt, Linda J.

    2015-07-06

    Lignocellulosic biomass offers a vast, renewable resource for the sustainable production of fuels and chemicals. To date, a commonly employed approach to depolymerize the polysaccharides in plant cell walls employs mineral acids, and upgrading strategies for the resulting sugars are under intense development. Although the behavior of cellulose and hemicellulose is reasonably well characterized, a more thorough understanding of lignin depolymerization mechanisms in acid environments is necessary to predict the fate of lignin under such conditions and ultimately to potentially make lignin a viable feedstock. To this end, dilute acid hydrolysis experiments were performed on two lignin model compounds containing the a-O-4 ether linkage at two temperatures concomitant with dilute acid pretreatment. Both primary and secondary products were tracked over time, giving insight into the reaction kinetics. The only difference between the two model compounds was the presence or absence of a methyl group on the a-carbon, with the former being typical of native lignin. It was found that methylation of the a-carbon increases the rate of reaction by an order of magnitude. Density functional theory calculations were performed on a proposed mechanism initiated by a nucleophilic attack on the a-carbon by water with a commensurate protonation of the ether oxygen. The values for the thermodynamics and kinetics derived from these calculations were used as the basis for a microkinetic model of the reaction. Results from this model are in good agreement with the experimental kinetic data for both lignin model compounds and provide useful insight into the primary pathways of a-O-4 scission reactions in acid-catalyzed lignin depolymerization. The distribution of primary and secondary products is interpreted as a function of two barriers of formation exhibiting opposite trends upon methylation of the a-carbon (one barrier is lowered while the other is increased). Such insights will be needed

  13. Muon catalyzed fusion

    Energy Technology Data Exchange (ETDEWEB)

    Ishida, K. [Advanced Meson Science Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Nagamine, K. [Muon Science Laboratory, IMSS-KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Matsuzaki, T. [Advanced Meson Science Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Kawamura, N. [Muon Science Laboratory, IMSS-KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

    2005-12-15

    The latest progress of muon catalyzed fusion study at the RIKEN-RAL muon facility (and partly at TRIUMF) is reported. The topics covered are magnetic field effect, muon transfer to {sup 3}He in solid D/T and ortho-para effect in dd{mu} formation.

  14. Catalyzing alignment processes

    DEFF Research Database (Denmark)

    Lauridsen, Erik Hagelskjær; Jørgensen, Ulrik

    2004-01-01

    This paper describes how environmental management systems (EMS) spur the circulation of processes that support the constitution of environmental issues as specific environ¬mental objects and objectives. EMS catalyzes alignmentprocesses that produce coherence among the different elements involved...... time and in combination with other social processes establish more aligned and standardized environmental performance between countries. However, examples of the introduction of environmental management suggests that EMS’ only plays a minor role in developing the actual environmental objectives...

  15. Catalyzed Ceramic Burner Material

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, Amy S., Dr.

    2012-06-29

    Catalyzed combustion offers the advantages of increased fuel efficiency, decreased emissions (both NOx and CO), and an expanded operating range. These performance improvements are related to the ability of the catalyst to stabilize a flame at or within the burner media and to combust fuel at much lower temperatures. This technology has a diverse set of applications in industrial and commercial heating, including boilers for the paper, food and chemical industries. However, wide spread adoption of catalyzed combustion has been limited by the high cost of precious metals needed for the catalyst materials. The primary objective of this project was the development of an innovative catalyzed burner media for commercial and small industrial boiler applications that drastically reduce the unit cost of the catalyzed media without sacrificing the benefits associated with catalyzed combustion. The scope of this program was to identify both the optimum substrate material as well as the best performing catalyst construction to meet or exceed industry standards for durability, cost, energy efficiency, and emissions. It was anticipated that commercial implementation of this technology would result in significant energy savings and reduced emissions. Based on demonstrated achievements, there is a potential to reduce NOx emissions by 40,000 TPY and natural gas consumption by 8.9 TBtu in industries that heavily utilize natural gas for process heating. These industries include food manufacturing, polymer processing, and pulp and paper manufacturing. Initial evaluation of commercial solutions and upcoming EPA regulations suggests that small to midsized boilers in industrial and commercial markets could possibly see the greatest benefit from this technology. While out of scope for the current program, an extension of this technology could also be applied to catalytic oxidation for volatile organic compounds (VOCs). Considerable progress has been made over the course of the grant

  16. Iodine-Catalyzed Polysaccharide Esterification

    Science.gov (United States)

    A review is provided of the recent reports to use iodine-catalyzed esterification reaction to produce esters from polysaccharides. The process entails reaction of the polysaccharide with an acid anhydride in the presence of a catalytic level of iodine, and in the absence of additional solvents. T...

  17. Manganese-Catalyzed Aerobic Heterocoupling of Aryl Grignard Reagents

    DEFF Research Database (Denmark)

    Ghaleshahi, Hajar Golshahi; Antonacci, Giuseppe; Madsen, Robert

    2017-01-01

    An improved protocol has been developed for the MnCl2-catalyzed cross-coupling reaction of two arylmagnesium bromides under dioxygen. The reaction was achieved by using the Grignard reagents in a 2:1 ratio and 20 % of MnCl2. Very good yields of the heterocoupling product were obtained when the li...

  18. Thermodynamics of Enzyme-Catalyzed Reactions Database

    Science.gov (United States)

    SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

  19. Controlled enzyme catalyzed heteropolysaccharide degradation

    DEFF Research Database (Denmark)

    Rasmussen, Louise Enggaard

    of the progress of enzymatic hydrolysis of different xylan substrates was developed. The method relies on dividing the HPSEC elution profiles into fixed time intervals and utilizing the linear refractive index response (area under the curve) of defined standard compounds. In order to obtain optimal high......-performance size exclusion chromatography profiles, the method was designed using 0.1 M CH3COONa in both the mobile phase and as the sample solution. This was based on the systematic evaluation of the influence of the mobile phase, including the type, ionic strength and pH, on the refractive index detector...... response. A time study of the enzyme catalyzed hydrolysis of birchwood xylan and wheat bran by BsX was used as an example to demonstrate the workability of the new HPSEC method for obtaining progress curves describing the evolution in the product profile during enzyme catalysis. Flaxseed mucilage (FM) has...

  20. Gold-catalyzed naphthalene functionalization

    Directory of Open Access Journals (Sweden)

    Iván Rivilla

    2011-05-01

    Full Text Available The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenylimidazol-2-ylidene, M = Cu, 1a; M = Au, 1b, in the presence of one equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethylphenyl, catalyze the transfer of carbene groups: C(RCO2Et (R = H, Me from N2C(RCO2Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either from the formal insertion of the carbene unit into the aromatic C–H bond or from its addition to a double bond. In addition, no byproducts derived from carbene coupling were observed.

  1. Can laccases catalyze bond cleavage in lignin?

    DEFF Research Database (Denmark)

    Munk, Line; Sitarz, Anna Katarzyna; Kalyani, Dayanand

    2015-01-01

    these enzymes may help degrading lignin, using oxygen as the oxidant. Laccases can catalyze polymerization of lignin, but the question is whether and how laccases can directly catalyze modification of lignin via catalytic bond cleavage. Via a thorough review of the available literature and detailed...... illustrations of the putative laccase catalyzed reactions, including the possible reactions of the reactive radical intermediates taking place after the initial oxidation of the phenol-hydroxyl groups, we show that i) Laccase activity is able to catalyze bond cleavage in low molecular weight phenolic lignin...... model compounds; ii) For laccases to catalyze inter-unit bond cleavage in lignin substrates, the presence of a mediator system is required. Clearly, the higher the redox potential of the laccase enzyme, the broader the range of substrates, including o- and p-diphenols, aminophenols, methoxy...

  2. Phospholipase A2 Biochemistry

    OpenAIRE

    Burke, John E.; Dennis, Edward A.

    2008-01-01

    The phospholipase A2 (PLA2) superfamily consists of many different groups of enzymes that catalyze the hydrolysis of the sn-2 ester bond in a variety of different phospholipids. The products of this reaction, a free fatty acid, and lysophospholipid have many different important physiological roles. There are five main types of PLA2: the secreted sPLA2’s, the cytosolic cPLA2’s, the Ca2+ independent iPLA2’s, the PAF acetylhydrolases, and the lysosomal PLA2’s. This review focuses on the superfam...

  3. Vanadium-catalyzed deoxydehydration of glycols.

    Science.gov (United States)

    Chapman, Garry; Nicholas, Kenneth M

    2013-09-25

    A survey of several metavandate (VO3(-)) and chelated dioxovanadium derivatives shows that tetrabutylammonium dioxovanadium(V)dipicolinate most effectively catalyzes the deoxydehydration (DODH) of glycols to olefins in moderate to excellent yields with triphenylphosphine or sodium sulfite as reductants.

  4. Biodiesel production by enzyme-catalyzed transesterification

    OpenAIRE

    Stamenković Olivera S.; Lazić Miodrag L.; Veljković Vlada B.; Skala Dejan U.

    2005-01-01

    The principles and kinetics of biodiesel production from vegetable oils using lipase-catalyzed transesterification are reviewed. The most important operating factors affecting the reaction and the yield of alkyl esters, such as: the type and form of lipase, the type of alcohol, the presence of organic solvents, the content of water in the oil, temperature and the presence of glycerol are discussed. In order to estimate the prospects of lipase-catalyzed transesterification for industrial appli...

  5. Transition-metal catalyzed synthesis of Ketoprofen

    Directory of Open Access Journals (Sweden)

    Ramminger Carolina

    2000-01-01

    Full Text Available Transition metal-catalyzed reactions including carbonylations, hydrovinylations and hydrogenations have been applied in the synthesis of alpha-(3-benzoylphenylpropanoic acid (Ketoprofen. 3-Vinylbenzophenone was obtained from 3-bromobenzophenone by a Pd-catalyzed Heck coupling reaction. Pd-catalyzed carbonylation of this olefin gave the isopropyl alpha-(3-benzoylphenyl propionate in high yield (95% and with high regioselectivity (>99.5%. Ketoprofen was obtained in 90% yield by hydrolysis of the isopropyl ester. It was also obtained in two steps from 3-vinylbenzophenone by a Ni-catalyzed hydrovinylation selectively affording 3-(3'-benzoylphenyl-1-butene, followed by an oxidation. 3-Ethynylbenzophenone was obtained from 3-bromobenzophenone by Pd-catalyzed coupling reaction. By means of a Pd-catalyzed carbonylation, this alkyne was converted regioselectively (97% into methyl alpha-(3-benzoylphenyl acrylate (93% yield. Hydrolysis of the ester afforded the alpha-(3-benzoylphenylacrylic acid. Asymmetric hydrogenation of this acid to give (S-ketoprofen in 95% optical yield was achieved using a chiral Ru-(S-BINAP catalyst.

  6. Continuous Production of Structured Phospholipids in a Packed Red Reactor with Lipase from Thermomyces lanuginosa

    DEFF Research Database (Denmark)

    Vikbjerg, Anders Falk; Peng, Lifeng; Mu, Huiling

    2005-01-01

    The possibilities of producing structured phospholipids by lipase-catalyzed acidolysis between soybean phospholipids and caprylic acid were examined in continuous packed bed enzyme reactors. Acidolysis reactions were performed in both a solvent system and a solvent-free system with the commercial...

  7. Biodiesel production by enzyme-catalyzed transesterification

    Directory of Open Access Journals (Sweden)

    Stamenković Olivera S.

    2005-01-01

    Full Text Available The principles and kinetics of biodiesel production from vegetable oils using lipase-catalyzed transesterification are reviewed. The most important operating factors affecting the reaction and the yield of alkyl esters, such as: the type and form of lipase, the type of alcohol, the presence of organic solvents, the content of water in the oil, temperature and the presence of glycerol are discussed. In order to estimate the prospects of lipase-catalyzed transesterification for industrial application, the factors which influence the kinetics of chemically-catalysed transesterification are also considered. The advantages of lipase-catalyzed transesterification compared to the chemically-catalysed reaction, are pointed out. The cost of down-processing and ecological problems are significantly reduced by applying lipases. It was also emphasized that lipase-catalysed transesterification should be greatly improved in order to make it commercially applicable. The further optimization of lipase-catalyzed transesterification should include studies on the development of new reactor systems with immobilized biocatalysts and the addition of alcohol in several portions, and the use of extra cellular lipases tolerant to organic solvents, intracellular lipases (i.e. whole microbial cells and genetically-modified microorganisms ("intelligent" yeasts.

  8. Zeolite 5A Catalyzed Etherification of Diphenylmethanol

    Science.gov (United States)

    Cooke, Jason; Henderson, Eric J.; Lightbody, Owen C.

    2009-01-01

    An experiment for the synthetic undergraduate laboratory is described in which zeolite 5A catalyzes the room temperature dehydration of diphenylmethanol, (C[subscript 6]H[subscript 5])[subscript 2]CHOH, producing 1,1,1',1'-tetraphenyldimethyl ether, (C[subscript 6]H[subscript 5])[subscript 2]CHOCH(C[subscript 6]H[subscript 5])[subscript 2]. The…

  9. Enyne Metathesis Catalyzed by Ruthenium Carbene Complexes

    DEFF Research Database (Denmark)

    Poulsen, Carina Storm; Madsen, Robert

    2003-01-01

    Enyne metathesis combines an alkene and an alkyne into a 1,3-diene. The first enyne metathesis reaction catalyzed by a ruthenium carbene complex was reported in 1994. This review covers the advances in this transformation during the last eight years with particular emphasis on methodology...

  10. Mechanochemical ruthenium-catalyzed olefin metathesis.

    Science.gov (United States)

    Do, Jean-Louis; Mottillo, Cristina; Tan, Davin; Štrukil, Vjekoslav; Friščić, Tomislav

    2015-02-25

    We describe the development of a mechanochemical approach for Ru-catalyzed olefin metathesis, including cross-metathesis and ring-closing metathesis. The method uses commercially available catalysts to achieve high-yielding, rapid, room-temperature metathesis of solid or liquid olefins on a multigram scale using either no or only a catalytic amount of a liquid.

  11. Enzyme-Catalyzed Transetherification of Alkoxysilanes

    Directory of Open Access Journals (Sweden)

    Peter G. Taylor

    2013-01-01

    Full Text Available We report the first evidence of an enzyme-catalyzed transetherification of model alkoxysilanes. During an extensive enzymatic screening in the search for new biocatalysts for silicon-oxygen bond formation, we found that certain enzymes promoted the transetherification of alkoxysilanes when tert-butanol or 1-octanol were used as the reaction solvents.

  12. Dual chemistry catalyzed by human acireductone dioxygenase.

    Science.gov (United States)

    Deshpande, Aditi R; Pochapsky, Thomas C; Petsko, Gregory A; Ringe, Dagmar

    2017-03-01

    Acireductone dioxygenase (ARD) from the methionine salvage pathway of Klebsiella oxytoca is the only known naturally occurring metalloenzyme that catalyzes different reactions in vivo based solely on the identity of the divalent transition metal ion (Fe2+ or Ni2+) bound in the active site. The iron-containing isozyme catalyzes the cleavage of substrate 1,2-dihydroxy-3-keto-5-(thiomethyl)pent-1-ene (acireductone) by O2 to formate and the ketoacid precursor of methionine, whereas the nickel-containing isozyme uses the same substrates to catalyze an off-pathway shunt to form methylthiopropionate, carbon monoxide and formate. This dual chemistry was recently demonstrated in vitro by ARD from Mus musculus (MmARD), providing the first example of a mammalian ARD exhibiting metal-dependent catalysis. We now show that human ARD (HsARD) is also capable of metal-dependent dual chemistry. Recombinant HsARD was expressed and purified to obtain a homogeneous enzyme with a single transition metal ion bound. As with MmARD, the Fe2+-bound HsARD shows the highest activity and catalyzes on-pathway chemistry, whereas Ni2+, Co2+ or Mn2+ forms catalyze off-pathway chemistry. The thermal stability of the HsARD isozymes is a function of the metal ion identity, with Ni2+-bound HsARD being the most stable followed by Co2+ and Fe2+, and Mn2+-bound HsARD being the least stable. As with the bacterial ARD, solution NMR data suggest that HsARD isozymes can have significant structural differences depending upon the metal ion bound. © The Author 2017. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  13. Heterogeneously-Catalyzed Conversion of Carbohydrates

    Science.gov (United States)

    Vigier, Karine De Oliveira; Jérôme, François

    Polyfunctionality of carbohydrates and their low solubility in conventional organic solvents make rather complex their conversion to higher value added chemicals. Therefore, innovative processes are now strongly needed in order to increase the selectivity of these reactions. Here, we report an overview of the different heterogeneously-catalyzed processes described in the literature. In particular, hydrolysis, dehydration, oxidation, esterification, and etherification of carbohydrates are presented. We shall discuss the main structural parameters that need to be controlled and that permit the conversion of carbohydrates to bioproducts with good selectivity. The conversion of monosaccharides and disaccharides over solid catalysts, as well as recent advances in the heterogeneously-catalyzed conversion of cellulose, will be presented.

  14. Nickel-catalyzed carbocyanation of alkynes

    OpenAIRE

    Nakao, Yoshiaki; Hiyama, Tamejiro

    2008-01-01

    Nickel-catalyzed carbocyanation reaction of alkynes is described. Alkynes undergo aryl- and allylcyanation reaction in the presence of nickel-phosphine catalysts to give a wide range of substituted acrylonitriles in highly stereo-, regio-, and chemoselective manners. Lewis acid cocatalysts, such as AlMe3, AlMe2Cl, and BPh3, are found to promote the arylcyanation significantly. The cooperative catalysis of nickel and Lewis acid also allows the carbocyanation reaction using alkenyl and alkyl cy...

  15. Imidazole catalyzes chlorination by unreactive primary chloramines.

    Science.gov (United States)

    Roemeling, Margo D; Williams, Jared; Beckman, Joseph S; Hurst, James K

    2015-05-01

    Hypochlorous acid and simple chloramines (RNHCl) are stable biologically derived chlorinating agents. In general, the chlorination potential of HOCl is much greater than that of RNHCl, allowing it to oxidize or chlorinate a much wider variety of reaction partners. However, in this study we demonstrate by kinetic analysis that the reactivity of RNHCl can be dramatically promoted by imidazole and histidyl model compounds via intermediary formation of the corresponding imidazole chloramines. Two biologically relevant reactions were investigated--loss of imidazole-catalyzed chlorinating capacity and phenolic ring chlorination using fluorescein and the tyrosine analog, 4-hydroxyphenylacetic acid (HPA). HOCl reacted stoichiometrically with imidazole, N-acetylhistidine (NAH), or imidazoleacetic acid to generate the corresponding imidazole chloramines which subsequently decomposed. Chloramine (NH2Cl) also underwent a markedly accelerated loss in chlorinating capacity when NAH was present, although in this case N-α-acetylhistidine chloramine (NAHCl) did not accumulate, indicating that the catalytic intermediate must be highly reactive. Mixing HOCl with 1-methylimidazole (MeIm) led to very rapid loss in chlorinating capacity via formation of a highly reactive chlorinium ion (MeImCl(+)) intermediate; this behavior suggests that the reactive forms of the analogous imidazole chloramines are their conjugate acids, e.g., the imidazolechlorinium ion (HImCl(+)). HOCl-generated imidazole chloramine (ImCl) reacted rapidly with fluorescein in a specific acid-catalyzed second-order reaction to give 3'-monochloro and 3',5'-dichloro products. Equilibrium constants for the transchlorination reactions HOCl + HIm = H2O + ImCl and NH2Cl + HIm = NH3 + ImCl were estimated from the dependence of the rate constants on [HIm]/[HOCl] and literature data. Acid catalysis again suggests that the actual chlorinating agent is HImCl(+); consistent with this interpretation, MeIm markedly catalyzed

  16. Manganese-Catalyzed Aerobic Heterocoupling of Aryl Grignard Reagents

    DEFF Research Database (Denmark)

    Ghaleshahi, Hajar Golshahi; Antonacci, Giuseppe; Madsen, Robert

    2017-01-01

    An improved protocol has been developed for the MnCl2-catalyzed cross-coupling reaction of two arylmagnesium bromides under dioxygen. The reaction was achieved by using the Grignard reagents in a 2:1 ratio and 20 % of MnCl2. Very good yields of the heterocoupling product were obtained when...... the limiting Grignard reagent underwent little homocoupling under the reaction conditions. Arylmagnesium bromides that contain p-methoxy, p-(dimethylamino), p-fluoro, and p-chloro substituents were shown to afford high product yields in the cross-coupling reactions with a variety of substituted aryl Grignard...... reagents. Heterocyclic Grignard reagents, on the other hand, were less effective substrates for this transformation because of the rapid homocoupling of these reagents under the reaction conditions....

  17. Titanium catalyzed silicon nanowires and nanoplatelets

    Directory of Open Access Journals (Sweden)

    Mohammad A. U. Usman

    2013-03-01

    Full Text Available Silicon nanowires, nanoplatelets, and other morphologies resulted from silicon growth catalyzed by thin titanium layers. The nanowires have diameters down to 5 nm and lengths to tens of micrometers. The two-dimensional platelets, in some instances with filigreed, snow flake-like shapes, had thicknesses down to the 10 nm scale and spans to several micrometers. These platelets grew in a narrow temperature range around 900 celsius, apparently representing a new silicon crystallite morphology at this length scale. We surmise that the platelets grow with a faceted dendritic mechanism known for larger crystals nucleated by titanium silicide catalyst islands.

  18. Chiral Diamine-catalyzed Asymmetric Aldol Reaction

    Institute of Scientific and Technical Information of China (English)

    LI Hui; XU Da-zhen; WU Lu-lu; WANG Yong-mei

    2012-01-01

    A highly efficient catalytic system composed of a simple and commercially available chiral primary diamine (1R,2R)-cyclohexane-1,2-diamine(6) and trifluoroacetic acid(TFA) was employed for asymmetric Aldol reaction in i-PrOH at room temperature.A loading of 10%(molar fraction) catalyst 6 with TFA as a cocatalyst could catalyze the Aldol reactions of various ketones or aldehydes with a series of aromatic aldehydes,furnishing Aldol products in moderate to high yields(up to >99%) with enantioselectivities of up to >99% and diastereoselectivities of up to 99:1.

  19. Copper-catalyzed asymmetric oxidation of sulfides.

    Science.gov (United States)

    O'Mahony, Graham E; Ford, Alan; Maguire, Anita R

    2012-04-06

    Copper-catalyzed asymmetric sulfoxidation of aryl benzyl and aryl alkyl sulfides, using aqueous hydrogen peroxide as the oxidant, has been investigated. A relationship between the steric effects of the sulfide substituents and the enantioselectivity of the oxidation has been observed, with up to 93% ee for 2-naphthylmethyl phenyl sulfoxide, in modest yield in this instance (up to 30%). The influence of variation of solvent and ligand structure was examined, and the optimized conditions were then used to oxidize a number of aryl alkyl and aryl benzyl sulfides, producing sulfoxides in excellent yields in most cases (up to 92%), and good enantiopurities in certain cases (up to 84% ee).

  20. Biginelli Reaction Catalyzed by Copper Nanoparticles

    Science.gov (United States)

    Dewan, Manika; Kumar, Ajeet; Saxena, Amit; De, Arnab; Mozumdar, Subho

    2012-01-01

    We recently reported a novel synthesis of copper nanoparticles from copper sulphate utilizing the charge-compensatory effect of ionic liquid [bmim]BF4 and ethylene glycol. The nanoparticles were characterized and found to be stable for one year. Here we hypothesize that the stabilized nanoparticles should be able to catalyze one-pot multicomponent organic reactions. We show that the nanoparticles catalyzed Biginelli reaction at room temperature to give the product 3,4-dihydopyrimidinone (>90% yield in ∼15 minutes) from aldehydes, β-diketoester (ethylacetoacetate) and urea (or thiourea). ). Remarkably, such high yields and rapid kinetics was found to be independent of the electronic density on the reactant aryl-aldehyde. This was probably because even the surface-active particles reacted faster in the presence of ionic liquid as compared to conventional methods. The heterocyclic dihydropyrimidinones (DHPMs) and their derivatives are widely used in natural and synthetic organic chemistry due to their wide spectrum of biological and therapeutic properties (resulting from their antibacterial, antiviral, antitumor and anti-inflammatory activities. Our method has an easy work-up procedure and the nanoparticles could be recycled with minimal loss of efficiency. PMID:22912792

  1. Manganese Catalyzed C–H Halogenation

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wei; Groves, John T.

    2015-06-16

    The remarkable aliphatic C–H hydroxylations catalyzed by the heme-containing enzyme, cytochrome P450, have attracted sustained attention for more than four decades. The effectiveness of P450 enzymes as highly selective biocatalysts for a wide range of oxygenation reactions of complex substrates has driven chemists to develop synthetic metalloporphyrin model compounds that mimic P450 reactivity. Among various known metalloporphyrins, manganese derivatives have received considerable attention since they have been shown to be versatile and powerful mediators for alkane hydroxylation and olefin epoxidation. Mechanistic studies have shown that the key intermediates of the manganese porphyrin-catalyzed oxygenation reactions include oxo- and dioxomanganese(V) species that transfer an oxygen atom to the substrate through a hydrogen abstraction/oxygen recombination pathway known as the oxygen rebound mechanism. Application of manganese porphyrins has been largely restricted to catalysis of oxygenation reactions until recently, however, due to ultrafast oxygen transfer rates. In this Account, we discuss recently developed carbon–halogen bond formation, including fluorination reactions catalyzed by manganese porphyrins and related salen species. We found that biphasic sodium hypochlorite/manganese porphyrin systems can efficiently and selectively convert even unactivated aliphatic C–H bonds to C–Cl bonds. An understanding of this novel reactivity derived from results obtained for the oxidation of the mechanistically diagnostic substrate and radical clock, norcarane. Significantly, the oxygen rebound rate in Mn-mediated hydroxylation is highly correlated with the nature of the trans-axial ligands bound to the manganese center (L–MnV$=$O). Based on the ability of fluoride ion to decelerate the oxygen rebound step, we envisaged that a relatively long-lived substrate radical could be trapped by a Mn–F fluorine source, effecting carbon–fluorine bond

  2. Kinetics and mechanism of uncatalyzed and ruthenium(III)-catalyzed ...

    Indian Academy of Sciences (India)

    The effect of ionic strength on both uncatalyzed and catalyzed reactions was studied by varying the. NaClO4 concentration. The rate of uncatalyzed reaction was found to increase with increasing ionic strength, whereas the rate of catalyzed reaction decreases with the increase of ionic strength. Thus, the plot of ln kU.

  3. Toward Efficient Palladium-Catalyzed Allylic C-H Alkylation

    DEFF Research Database (Denmark)

    Jensen, Thomas; Fristrup, Peter

    2009-01-01

    Recent breakthroughs have proved that direct palladium (II)-catalyzed allylic C-H alkylation can be achieved. This new procedure shows that the inherent requirement for a leaving group in the Tsuji-Trost palladium-catalyzed allylic alkylation can be lifted. These initial reports hold great promise...

  4. Representing Rate Equations for Enzyme-Catalyzed Reactions

    Science.gov (United States)

    Ault, Addison

    2011-01-01

    Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

  5. [Thymidylate synthase-catalyzed reaction mechanism].

    Science.gov (United States)

    Rode, Wojciech; Jarmuńa, Adam

    2015-01-01

    Thymidylate synthase ThyA (EC 2.1.1.45;-encoded by the Tyms gene), having been for 60 years a molecular target in chemotherapy, catalyses the dUMP pyrimidine ring C(5) methylation reaction, encompassing a transfer of one-carbon group (the methylene one, thus at the formaldehyde oxidation level) from 6R-N5,10-methylenetetrahydrofolate, coupled with a reduction of this group to the methyl one, with concomitant generation of 7,8-dihydrofolate and thymidylate. New facts are presented, concerning (i) molecular mechanism of the catalyzed reaction, including the substrate selectivity mechanism, (ii) mechanism of inhibition by a particular inhibitor, N4-hydroxy-dCMP, (iii) structural properties of the enzyme, (iv) cellular localization, (v) potential posttranslational modifications of the enzyme protein and their influence on the catalytic properties and (vi) non-catalytic activities of the enzyme.

  6. Heterogeneously Catalyzed Oxidation Reactions Using Molecular Oxygen

    DEFF Research Database (Denmark)

    Beier, Matthias Josef

    with a carboxylic acid resulting in TONs of up to 2000. In the absence of the carboxylic acid, ceria inhibited the reaction exhibiting radical scavenger properties. Contrary to p-xylene, neither ethylbenzene nor cumene conversion was promoted by ceria even in the presence of a carboxylic acid. Substantial leaching......Heterogeneously catalyzed selective oxidation reactions have attracted a lot of attention in recent time. The first part of the present thesis provides an overview over heterogeneous copper and silver catalysts for selective oxidations in the liquid phase and compared the performance and catalytic...... that both copper and silver can function as complementary catalyst materials to gold showing different catalytic properties and being more suitable for hydrocarbon oxidation reactions. Potential opportunities for future research were outlined. In an experimental study, the potential of silver as a catalyst...

  7. Lipase-catalyzed production of lysophospholipids

    Directory of Open Access Journals (Sweden)

    Mnasri Taha

    2017-07-01

    Full Text Available Lysophospholipids, such as lysophosphatidic acid or lysophosphatidylcholine, are important bioactive lipids, involved in various normal and pathological cellular processes. They also have industrial and pharmaceutical uses such as emulsifiers or components of drug delivery systems. Lipases, which natural substrates are long chain triacylglycerols, are important biocatalysts for organic synthesis mainly due to their broad substrate specificity and their ability to display high catalytic activity in organic media. This paper describes the various lipase-catalyzed reactions implemented for the production of lysophospholipids. They include hydrolysis or alcoholysis of phospholipids and acylation of the glycerophosphoryl moiety. Special emphasis is made on our work dealing with the production of lysophospholipids rich in dososahexaenoic acid, an important dietary polyunsaturated fatty acid via the hydrolysis of phospholipids extracted from the microalga Isochrysis galbana.

  8. Catalyzed modified clean fractionation of switchgrass.

    Science.gov (United States)

    Cybulska, Iwona; Brudecki, Grzegorz P; Hankerson, Brett R; Julson, James L; Lei, Hanwu

    2013-01-01

    Switchgrass was used as a lignocellulosic feedstock for second generation ethanol production, after pretreatment using sulfuric acid-catalyzed modified clean fractionation based on NREL's (National Renewable Energy Laboratory) original procedure. Optimization of temperature, catalyst concentration and solvent composition was performed using Response Surface Methodology, and 59.03 ± 7.01% lignin recovery, 84.85 ± 1.34% glucose, and 44.11 ± 3.44% aqueous fraction xylose yields were obtained at 140.00 °C, 0.46% w/w catalyst concentration, 36.71% w/w ethyl acetate concentration, and 25.00% w/w ethanol concentration. The cellulose fraction did not inhibit the fermentation performance of Saccharomyces cerevisiae and resulted in an ethanol yield of 89.60 ± 2.1%. Copyright © 2012 Elsevier Ltd. All rights reserved.

  9. Mechanisms of bacterially catalyzed reductive dehalogenation

    Energy Technology Data Exchange (ETDEWEB)

    Picardal, Flynn William [Univ. of Arizona, Tucson, AZ (United States)

    1992-01-01

    Nine bacteria were tested for the ability to dehalogenate tetrachloromethane (CT), tetrachloroethene (PCE), and 1, 1, 1-trichloroethane (TCA) under anaerobic conditions. Three bacteria were able to reductively dehalogenate CT. Dehalogenation ability was not readily linked to a common metabolism or changes in culture redox potential. None of the bacteria tested were able to dehalogenate PCE or TCA. One of the bacteria capable of dehalogenating CT, Shewanella putrefaciens, was chosen as a model organism to study mechanisms of bacterially catalyzed reductive dehalogenation. The effect of a variety of alternate electron acceptors on CT dehalogenation ability by S. putrefaciens was determined. oxygen and nitrogen oxides were inhibitory but Fe (III), trimethylamine oxide, and fumarate were not. A model of the electron transport chain of S. putrefaciens was developed to explain inhibition patterns. A period of microaerobic growth prior to CT exposure increased the ability of S. putrefaciens to dehalogenate CT. A microaerobic growth period also increased cytochrome concentrations. A relationship between cytochrome content and dehalogenation ability was developed from studies in which cytochrome concentrations in S. putrefaciens were manipulated by changing growth conditions. Stoichiometry studies using 14C-CT suggested that CT was first reduced to form a trichloromethyl radical. Reduction of the radical to produce chloroform and reaction of the radical with cellular biochemicals explained observed product distributions. Carbon dioxide or other fully dehalogenated products were not found.

  10. Zinc catalyzed Guanylation reaction of Amines with Carbodiimides ...

    Indian Academy of Sciences (India)

    016-1096-y. Zinc catalyzed Guanylation reaction of Amines with Carbodiimides/. Isocyanate leading to Guanidines/Urea derivatives formation. JAYEETA BHATTACHARJEE, MITALI SACHDEVA, INDRANI BANERJEE and. TARUN K PANDA.

  11. Platinum-Catalyzed Selective Tin-Carbon Bond Formation

    NARCIS (Netherlands)

    Thoonen, Sander Hendrikus Lambertus

    2003-01-01

    In conclusion, two improved methods for the selective synthesis of monoorganotin trihalides were developed. The platinum-catalyzed Kocheshkov redistribution reaction of dialkyltin dichlorides with tin tetrachloride is the most interesting. Contrary to the other two methods described (the direct

  12. Aerobic Oxidation of Alcohols to Carbonyl Compounds Catalyzed by ...

    Indian Academy of Sciences (India)

    hydroxyphthalimide (NHPI) com- bined with cobalt porphyrin intercalated heterogeneous hybrid catalyst (CoTPP-Zn2Al-LDH) has been devel- oped. The results showed that this catalytic system can effectively catalyze the oxidation of alcohols to the.

  13. Hydrolysis of Toxic Natural Glucosides Catalyzed by Cyclodextrin Dicyanohydrins

    DEFF Research Database (Denmark)

    Bjerre, Jeannette; Nielsen, Erik Holm; Bols, Mikael

    2008-01-01

    The hydrolysis of toxic 7-hydroxycoumarin glucosides and other aryl and alkyl glucosides, catalyzed by modified a- and ß-cyclodextrin dicyanohydrins, was investigated using different UV, redox, or HPAEC detection assays. The catalyzed reactions all followed Michaelis-Menten kinetics, and an impre......The hydrolysis of toxic 7-hydroxycoumarin glucosides and other aryl and alkyl glucosides, catalyzed by modified a- and ß-cyclodextrin dicyanohydrins, was investigated using different UV, redox, or HPAEC detection assays. The catalyzed reactions all followed Michaelis-Menten kinetics...... degree of catalysis was also found for the toxic hydroxycoumarin esculin. A novel synthesized diaminomethyl ß-cyclodextrin showed a weak catalysis of p-nitrophenyl ß-D-glucopyranoside hydrolysis....

  14. Copper-Catalyzed Alkylation of Benzoxazoles with Secondary Alkyl Halides

    OpenAIRE

    Ren P; Salihu I; Scopelliti R.; Hu XL

    2012-01-01

    Copper catalyzed direct alkylation of benzoxazoles using nonactivated secondary alkyl halides has been developed. The best catalyst is a new copper(I) complex (1) and the reactions are promoted by bis[2 (NN dimethylamino)ethyl] ether.

  15. Dirhodium-catalyzed C-H arene amination using hydroxylamines

    National Research Council Canada - National Science Library

    Paudyal, Mahesh P; Adebesin, Adeniyi Michael; Burt, Scott R; Ess, Daniel H; Ma, Zhiwei; Kürti, László; Falck, John R

    2016-01-01

    .... Here, we present a mild dirhodium-catalyzed C-H amination for conversion of structurally diverse monocyclic and fused aromatics to the corresponding primary and N-alkyl arylamines using NH2/NH(alkyl)-O-(sulfonyl...

  16. Aerobic Oxidation of Alcohols to Carbonyl Compounds Catalyzed by ...

    Indian Academy of Sciences (India)

    NHPI) combined with cobalt porphyrin intercalated heterogeneous hybrid catalyst (CoTPP-Zn2Al-LDH) has been developed. The results showed that this catalytic system can effectively catalyze the oxidation of alcohols to thecorresponding ...

  17. Oxidations catalyzed by phenylacetone monooxygenase from Thermobifida fusca

    NARCIS (Netherlands)

    Gonzalo, Gonzalo de; Torres Pazmino, Daniel; Ottolina, Gianluca; Fraaije, Marco W.; Carrea, Giacomo

    2005-01-01

    Several organic sulfides, ketones and other organic systems have been tested as substrates in oxidation reactions catalyzed by the recently discovered phenylacetone monooxygenase from Thermobifida fusca. The biocatalytic properties of this Baeyer–Villiger monooxygenase have been studied, revealing

  18. Nickel-catalyzed direct synthesis of dialkoxymethane ethers

    Indian Academy of Sciences (India)

    catalyzed direct synthesis of dialkoxymethane ethers. MURUGAN SUBARAMANIAN ABHIJIT BERA BHAGAVATULA L V PRASAD EKAMBARAM BALARAMAN. RAPID COMMUNICATION Volume 129 Issue 8 August 2017 pp 1153-1159 ...

  19. Ni-catalyzed reductive addition of alkyl halides to isocyanides.

    Science.gov (United States)

    Wang, Bo; Dai, Yijing; Tong, Weiqi; Gong, Hegui

    2015-12-21

    This paper highlights Ni-catalyzed reductive trapping of secondary and tertiary alkyl radicals with both electron-rich and electron-deficient aryl isocyanides using zinc as the terminal reductant, affording 6-alkylated phenanthridine in good yields. The employment of carbene ligands necessitates the alkyl radical process, and represents the first utility in the Ni-catalyzed reductive conditions for the generation of unactivated alkyl radicals from the halide precursors.

  20. Hemoglobin and Red Blood Cells Catalyze Atom Transfer Radical Polymerization

    OpenAIRE

    Silva Tilana B.; Spulber Mariana; Kocik Marzena K.; Seidi Farzad; Charan Himanshu; Rother Martin; Sigg Severin J.; Renggli Kasper; Kali Gergely; Bruns Nico

    2013-01-01

    Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity i.e. they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N isopropylacrylamide (NIPAAm) poly(ethylene glycol) methyl ether acrylate (PEGA) and poly(ethylene glycol) methyl eth...

  1. Conservation Kickstart- Catalyzing Conservation Initiatives Worldwide

    Science.gov (United States)

    Treinish, G.

    2014-12-01

    Adventurers and Scientists for Conservation (ASC) is a nonprofit organization that collects environmental data to catalyze conservation initiatives worldwide. Adventure athletes have the skills and motivation to reach the most remote corners of the world. ASC utilizes those skills to provide the scientific community with data while providing the outdoor community with purpose beyond the personal high of reaching a summit or rowing across an ocean. We carefully select projects, choosing partnerships that will maximize the impact of ASC volunteers. Each project must have a clear path to a tangible conservation outcome and demonstrate a clear need for our brand of volunteers. We partner with government agencies, universities, and independant reseachers to kickstart data collection efforts around the world. Last year, through a partnership with the Olympic National Forest, 20 volunteers from the Seattle area set up and monitored camera traps in an effort to survey for costal Pacific marten. Our work led to the species' listing as "critically imperiled" with NatureServe. A partnership with the inaugural Great Pacific Race, engaging trans-Pacific rowing teams, searched for microplastics in the Pacific Ocean as part of our ongoing microplastics campaign. In a multi-year partnership with the American Prairie Reserve (APR), ASC volunteer crews live and work on the Reserve collecting wildlife data year round. The data we obtain directly informs the Reserve's wildlife management decisions. On this project, our crews have safely and effectively navigated temperature extremes from -30 degrees to 100+ degrees while traveling in a remote location. We are currently scouting projects in the Okavango Delta of Botswana and the rainforest of Suriname where we will be able to cover large amounts of area in a short periord of time. ASC is at the crossroads of the adventure and coservation science communities. Our approach of answering specific questions by using highly skilled and

  2. Catalyzed precipitation in Al-Cu-Si

    Science.gov (United States)

    Mitlin, D.; Morris, J. W.; Radmilovic, V.

    2000-11-01

    The work reported here concerns the effect of Si on the precipitation of θ' phase (metastable Al2Cu) during the isothermal aging of Al-2Cu-1 Si (wt pct). The binary alloys Al-2Cu and Al-1 Si were studied for comparison. Only two precipitate phases were detected: essentially pure Si in Al-1 Si and Al-2Cu-1 Si, and θ' (metastable Al2Cu) in Al-2Cu and Al-2Cu-1Si. On aging the ternary alloy at 225 °C, Si precipitates first and catalyzes the θ' phase. The precipitates in the ternary alloy are smaller, are more densely distributed, have lower aspect ratios, and coarsen more slowly than those in the binary Al-2Cu aged at the same temperature. While the shapes of individual θ' precipitates in binary Al-2Cu are strongly affected by the kinetic problem of nucleating growth ledges, which produces a significant scatter in the aspect ratio for samples of given thickness, the overall evolution of particle shape with size follows the predictions of the Khachaturyan-Hairapetyan (KH) thermoelastic theory, which reduces to κ= L/d ∞ √ L at large sizes. The KH theory provides an estimate for the interfacial tension of the broad Al- θ' interface of 85 to 96 mJ/m2, which is near the values for other low-energy interfaces in Al, such as the twin boundary energy (100 mJ/m2) and the antiphase boundary energy in δ' Al3Li (70 mJ/m2). Si and θ' precipitates in Al-2Cu-1 Si have a strong elastic interaction because of their compensating strain fields. This elastic interaction promotes the nucleation of θ' precipitates on Si, decreases the expected aspect ratio of θ', and inhibits coarsening. Finally, Si precipitation in ternary Al-2Cu-1 Si differs from that in binary Al-1 Si in that the Si precipitates are coarser, more equiaxed, and more extensively twinned. These changes appear to be effects of Cu, which increases the solubility of Si in Al and adsorbs on the Si-Al interface, promoting twinning by a “step-poisoning” effect at the interface.

  3. Synthesis of dimethyl gloiosiphone a by way of palladium-catalyzed domino cyclization.

    Science.gov (United States)

    Doi, Takayuki; Iijima, Yusuke; Takasaki, Masaru; Takahashi, Takashi

    2007-05-11

    The synthesis of a spiro[4.4]nonane skeleton by the palladium-catalyzed domino cyclization of a linear 7-methylene-2,10-undecadienyl acetate is described. The pi-allylpalladium intermediate underwent intramolecular alkene insertion with high intraannular diastereoselectivity, followed by intramolecular Heck-type cyclization, leading to a spiro[4.4]nonane system. Oxidation of the allylic ether moiety and transformation of the vinyl group to an exo-methylene unit provided 3, which is the known synthetic intermediate of dimethyl gloiosiphone A (2).

  4. Palladium-Catalyzed Modification of Unprotected Nucleosides, Nucleotides, and Oligonucleotides

    Directory of Open Access Journals (Sweden)

    Kevin H. Shaughnessy

    2015-05-01

    Full Text Available Synthetic modification of nucleoside structures provides access to molecules of interest as pharmaceuticals, biochemical probes, and models to study diseases. Covalent modification of the purine and pyrimidine bases is an important strategy for the synthesis of these adducts. Palladium-catalyzed cross-coupling is a powerful method to attach groups to the base heterocycles through the formation of new carbon-carbon and carbon-heteroatom bonds. In this review, approaches to palladium-catalyzed modification of unprotected nucleosides, nucleotides, and oligonucleotides are reviewed. Polar reaction media, such as water or polar aprotic solvents, allow reactions to be performed directly on the hydrophilic nucleosides and nucleotides without the need to use protecting groups. Homogeneous aqueous-phase coupling reactions catalyzed by palladium complexes of water-soluble ligands provide a general approach to the synthesis of modified nucleosides, nucleotides, and oligonucleotides.

  5. Graphene oxide catalyzed cis-trans isomerization of azobenzene

    Directory of Open Access Journals (Sweden)

    Dongha Shin

    2014-09-01

    Full Text Available We report the fast cis-trans isomerization of an amine-substituted azobenzene catalyzed by graphene oxide (GO, where the amine functionality facilitates the charge transfer from azobenzene to graphene oxide in contrast to non-substituted azobenzene. This catalytic effect was not observed in stilbene analogues, which strongly supports the existence of different isomerization pathways between azobenzene and stilbene. The graphene oxide catalyzed isomerization is expected to be useful as a new photoisomerization based sensing platform complementary to GO-based fluorescence quenching methods.

  6. New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Qinhua [Iowa State Univ., Ames, IA (United States)

    2004-12-19

    The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I2, ICl, PhSeCl, PhSCl and p-O2NC6H4SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellent yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement

  7. Cyclodextrin-Catalyzed Organic Synthesis: Reactions, Mechanisms, and Applications

    Directory of Open Access Journals (Sweden)

    Chang Cai Bai

    2017-09-01

    Full Text Available Cyclodextrins are well-known macrocyclic oligosaccharides that consist of α-(1,4 linked glucose units and have been widely used as artificial enzymes, chiral separators, chemical sensors, and drug excipients, owing to their hydrophobic and chiral interiors. Due to their remarkable inclusion capabilities with small organic molecules, more recent interests focus on organic reactions catalyzed by cyclodextrins. This contribution outlines the current progress in cyclodextrin-catalyzed organic reactions. Particular emphases are given to the organic reaction mechanisms and their applications. In the end, the future directions of research in this field are proposed.

  8. Recent advances in copper-catalyzed asymmetric coupling reactions

    Directory of Open Access Journals (Sweden)

    Fengtao Zhou

    2015-12-01

    Full Text Available Copper-catalyzed (or -mediated asymmetric coupling reactions have received significant attention over the past few years. Especially the coupling reactions of aryl or alkyl halides with nucleophiles became a very powerful tool for the formation of C–C, C–N, C–O and other carbon–heteroatom bonds as well as for the construction of heteroatom-containing ring systems. This review summarizes the recent progress in copper-catalyzed asymmetric coupling reactions for the formation of C–C and carbon–heteroatom bonds.

  9. Microbial-Catalyzed Biotransformation of Multifunctional Triterpenoids Derived from Phytonutrients

    Directory of Open Access Journals (Sweden)

    Syed Adnan Ali Shah

    2014-07-01

    Full Text Available Microbial-catalyzed biotransformations have considerable potential for the generation of an enormous variety of structurally diversified organic compounds, especially natural products with complex structures like triterpenoids. They offer efficient and economical ways to produce semi-synthetic analogues and novel lead molecules. Microorganisms such as bacteria and fungi could catalyze chemo-, regio- and stereospecific hydroxylations of diverse triterpenoid substrates that are extremely difficult to produce by chemical routes. During recent years, considerable research has been performed on the microbial transformation of bioactive triterpenoids, in order to obtain biologically active molecules with diverse structures features. This article reviews the microbial modifications of tetranortriterpenoids, tetracyclic triterpenoids and pentacyclic triterpenoids.

  10. Marine natural products targeting phospholipases A2.

    Science.gov (United States)

    Folmer, Florence; Jaspars, Marcel; Schumacher, Marc; Dicato, Mario; Diederich, Marc

    2010-12-15

    Phospholipases A(2) (PLA(2)s) form a family of enzymes catalyzing the hydrolysis of membrane phospholipids into arachidonic acid, which is the major precursor of pro-inflammatory eicosanoids. As a result, PLA(2)s have been considered as potential targets in anti-inflammatory drug discovery. Marine natural products are a rich source of bioactive compounds, including PLA(2) inhibitors. Here, we review the properties of marine PLA(2) inhibitors identified since the first discovery of PLA(2) inhibitory activity in the marine natural product manoalide in the mid 1980s. Copyright © 2010 Elsevier Inc. All rights reserved.

  11. Acid-, base-, and lewis-acid-catalyzed heterolysis of methoxide from an alpha-hydroxy-beta-methoxy radical: models for reactions catalyzed by coenzyme B12-dependent diol dehydratase.

    Science.gov (United States)

    Xu, Libin; Newcomb, Martin

    2005-11-11

    [Reaction: see text].A model for glycol radicals was employed in laser flash photolysis kinetic studies of catalysis of the fragmentation of a methoxy group adjacent to an alpha-hydroxy radical center. Photolysis of a phenylselenylmethylcyclopropane precursor gave a cyclopropylcarbinyl radical that rapidly ring opened to the target alpha-hydroxy-beta-methoxy radical (3). Heterolysis of the methoxy group in 3 gave an enolyl radical (4a) or an enol ether radical cation (4b), depending upon pH. Radicals 4 contain a 2,2-diphenylcyclopropane reporter group, and they rapidly opened to give UV-observable diphenylalkyl radicals as the final products. No heterolysis was observed for radical 3 under neutral conditions. In basic aqueous acetonitrile solutions, specific base catalysis of the heterolysis was observed; the pK(a) of radical 3 was determined to be 12.5 from kinetic titration plots, and the ketyl radical formed by deprotonation of 3 eliminated methoxide with a rate constant of 5 x 10(7) s(-1). In the presence of carboxylic acids in acetonitrile solutions, radical 3 eliminated methanol in a general acid-catalyzed reaction, and rate constants for protonation of the methoxy group in 3 by several acids were measured. Radical 3 also reacted by fragmentation of methoxide in Lewis-acid-catalyzed heterolysis reactions; ZnBr2, Sc(OTf)3, and BF3 were found to be efficient catalysts. Catalytic rate constants for the heterolysis reactions were in the range of 3 x 10(4) to 2 x 10(6) s(-1). The Lewis-acid-catalyzed heterolysis reactions are fast enough for kinetic competence in coenzyme B12 dependent enzyme-catalyzed reactions of glycols, and Lewis-acid-catalyzed cleavages of beta-ethers in radicals might be applied in synthetic reactions.

  12. Silver and gold nanocluster catalyzed reduction of methylene blue ...

    Indian Academy of Sciences (India)

    Abstract. Arsenic can be determined in parts-per-million (ppm) level by absorbance measurement. This method is based on the quantitative colour bleaching of the dye, methylene blue by arsine catalyzed by nanoparticles in micellar medium. The arsine has been generated in situ from sodium arsenate by NaBH4 reduction.

  13. Silver and gold nanocluster catalyzed reduction of methylene blue ...

    Indian Academy of Sciences (India)

    Unknown

    nanoparticles in micellar medium. The arsine has been generated in situ from sodium arsenate ... trolled use of arsenic containing pesticides, paints and pigments etc. Keeping an eye on this grave situation of ... levels using micelle catalyzed reaction (Pal et al 1998). The participation of silver or gold nanoparticle as catalyst.

  14. The 2010 Chemistry Nobel Prize: Pd (0)-Catalyzed Organic Synthesis

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 16; Issue 2. The 2010 Chemistry Nobel Prize: Pd(O)-Catalyzed Organic Synthesis. Gopalpur Nagendrappa Y C Sunil Kumar. General Article Volume 16 Issue 2 February 2011 pp 152-164 ...

  15. Bioepoxidation of isosafrol catalyzed by radish and turnip peroxidases

    African Journals Online (AJOL)

    Peroxidases (PODs) from radish (Raphanus sativus L.) and turnip (Brassica napus L.) were extracted and precipitated with ammonium sulfate using a simple, low cost and quick method. The activities of all steps performed by the vegetable PODs were measured via guaiacol assay. The epoxidation of isosafrol, catalyzed by ...

  16. Transfer hydrogenation reactions catalyzed by chiral half-sandwich ...

    Indian Academy of Sciences (India)

    oxidoreductases catalyze transfer hydrogenation of car- ... ruthenium(II) complexes containing (S)-N-substituted- ... 2. Experimental. 2.1 Materials and methods. All reactions and manipulations were routinely per- formed under a nitrogen atmosphere using standard. Schlenk techniques in oven-dried glassware. L-Proline,.

  17. Development of a Lewis Base Catalyzed Selenocyclization Reaction

    Science.gov (United States)

    Collins, William

    2009-01-01

    The concept of Lewis base activation of selenium Lewis acids has been effectively reduced to practice in the Lewis base catalyzed selenofunctionalization of unactivated olefins. In this reaction, the weakly acidic species, "N"-phenylselenyl succinimide, is cooperatively activated by the addition of a "soft" Lewis base donor (phosphine sulfides,…

  18. CU(II): catalyzed hydrazine reduction of ferric nitrate

    Energy Technology Data Exchange (ETDEWEB)

    Karraker, D.G.

    1981-11-01

    A method is described for producing ferrous nitrate solutions by the cupric ion-catalyzed reduction of ferric nitrate with hydrazine. The reaction is complete in about 1.5 hours at 40/sup 0/C. Hydrazoic acid is also produced in substantial quantities as a reaction byproduct.

  19. Platinum-catalyzed hydroformylation of terminal and internal octenes

    NARCIS (Netherlands)

    van Duren, R.; van der Vlugt, J.I.; Kooijman, H.|info:eu-repo/dai/nl/091208610; Spek, A.L.|info:eu-repo/dai/nl/156517566; Vogt, D.

    2007-01-01

    A brief historic overview of Pt/Sn-catalyzed hydroformylation as well as recent advances in the hydroformylation of internal alkenes is provided. This serves as background for the results obtained with the [Pt(Sixantphos)Cl2] system, for which the molecular structure and the spectroscopic data are

  20. Asymmetric gold-catalyzed lactonizations in water at room temperature**

    Science.gov (United States)

    Handa, Sachin; Lippincott, Daniel J.; Slack, Eric D.; Aue, Donald H.

    2014-01-01

    Asymmetric gold-catalyzed hydrocarboxylations are reported that show broad substrate scope. The hydrophobic effect associated with in situ-formed aqueous nanomicelles leads to good-to-excellent ee’s of product lactones. In-flask product isolation, along with recycling of the catalyst and reaction medium, combine to arrive at an especially environmentally friendly process. PMID:25124085

  1. Catalyzing new product adoption at the base of the pyramid

    NARCIS (Netherlands)

    Marinakis, Yorgos; Walsh, Steven Thomas; Harms, Rainer

    2016-01-01

    One of the more perplexing of the entrepreneurial issues at the Base of the Pyramid (BoP) is how to catalyze new product adoption by BoP consumers. Because S-shaped adoption dynamics are the result of cultural transmission bias, the question can be rephrased as, how can an entrepreneur overcome

  2. EFFICIENT SODIUM SELENATE-CATALYZED SYNTHESIS OF 3,4 ...

    African Journals Online (AJOL)

    Sodium selenate efficiently catalyzes the three-component Biginelli reaction of an aldehyde, a,β-keto ester and urea or thiourea under solvent-free conditions to afford the corresponding 3,4-dihydropyrimidin-2(1H)-ones or –thiones in excellent yields. KEY WORDS: Dihydropyrimidinones, Sodium selenate, Biginelli reaction, ...

  3. Base catalyzed transesterification of sunflower oil biodiesel | Ahmad ...

    African Journals Online (AJOL)

    Electric oil expeller was used for the extraction of crude oil. Base catalyzed transesterifiction process is applied for optimum yield (80%) of biodiesel. Fuel properties of sunflower oil biodiesel were compared with American Society for Testing and Materials (ASTM). Engine efficiency of biodiesel with reference to power, ...

  4. Comparison of lipase-catalyzed synthesis of cyclopentadecanolide ...

    African Journals Online (AJOL)

    Administrator

    2011-09-26

    Sep 26, 2011 ... hydroxy-pentadecanate is not. It was reported that, ultra- sonic technology had been widely used in bioreaction system and had achieved ideal results (Du et al., ..... Enantioselective synthesis of silicon- containing(R)-ketone cyanhydrin catalyzed by(R)-oxynitrilase from plum in an aqueous/organic biphasic ...

  5. Palladium-catalyzed selective acyloxylation using sodium perborate as oxidant.

    Science.gov (United States)

    Pilarski, Lukasz T; Janson, Pär G; Szabó, Kálmán J

    2011-03-04

    Sodium perborate (SPB), a principal component of washing powders, was employed as an inexpensive and eco-friendly oxidant in the palladium-catalyzed C-H acyloxylation of alkenes in excellent regio- and stereochemistry. The reactions used anhydrides as acyloxy sources. The method applies to both terminal and internal alkenes, and even benzylic C-H oxidation.

  6. Transition-Metal-Catalyzed Carbonylation of Methyl Acetate.

    Science.gov (United States)

    Polichnowski, S. W.

    1986-01-01

    Presents a study of the rhodium-catalyzed, ioding-promoted carbonylation of methyl acetate. This study provides an interesting contrast between the carbonylation of methyl acetate and the carbonylation of methanol when similar rhodium/iodine catalyst systems are used. (JN)

  7. Recent developments in gold-catalyzed cycloaddition reactions

    Directory of Open Access Journals (Sweden)

    Fernando López

    2011-08-01

    Full Text Available In the last years there have been extraordinary advances in the development of gold-catalyzed cycloaddition processes. In this review we will summarize some of the most remarkable examples, and present the mechanistic rational underlying the transformations.

  8. DNA strand exchange catalyzed by molecular crowding in PEG solutions

    KAUST Repository

    Feng, Bobo

    2010-01-01

    DNA strand exchange is catalyzed by molecular crowding and hydrophobic interactions in concentrated aqueous solutions of polyethylene glycol, a discovery of relevance for understanding the function of recombination enzymes and with potential applications to DNA nanotechnology. © 2010 The Royal Society of Chemistry.

  9. Amylase catalyzed synthesis of glycosyl acrylates and their polymerization

    NARCIS (Netherlands)

    Kloosterman, Wouter M.J.; Jovanovic, Danijela; Brouwer, Sander; Loos, Katja

    2014-01-01

    The enzymatic synthesis of novel (di)saccharide acrylates from starch and 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and 4-hydroxybutyl acrylate (2-HEA, 2-HEMA and 4-HBA) catalyzed by various commercially available amylase preparations is demonstrated. Both liquefaction and

  10. Significance of mineral salts in prebiotic RNA synthesis catalyzed by montmorillonite.

    Science.gov (United States)

    Joshi, Prakash C; Aldersley, Michael F

    2013-06-01

    The montmorillonite-catalyzed reactions of the 5'-phosphorimidazolide of adenosine used as a model generated RNA type oligomers. These reactions were found to be dependent on the presence of mineral salts. Whereas montmorillonite (pH 7) produced only dimers and traces of trimer in water, addition of sodium chloride (0.1-2.0 M) enhanced the chain length of oligomers to 10-mers as detected by HPLC. Maximum catalytic activity was observed with sodium chloride at a concentration between 0.8 and 1.2 M. This concentration of sodium chloride resembled its abundance in the ancient oceans (0.9-1.2 M). Magnesium chloride produced a similar effect but its joint action with sodium chloride did not produce any difference in the oligomer chain length. Therefore, Mg(2+) was not deemed necessary for generating longer oligomers. The effect of monovalent cations upon RNA chain length was: Li(+) > Na(+) > K(+). A similar effect was observed with the anions with enhanced oligomer length in the following order: Cl(-) > Br(-) > I(-). Thus, the smaller ions facilitated the formation of the longest oligomers. Inorganic salts that tend to salt out organic compounds from water and salts which show salt-in effects had no influence on the oligomerization process indicating that the montmorillonite-catalyzed RNA synthesis is not affected by either of these hydrophobic or hydrophilic interactions. A 2.3-fold decrease in the yield of cyclic dimer was observed upon increasing the sodium chloride concentration from 0.2 to 2.0 M. Inhibition of cyclic dimer formation is vital for increasing the yield of linear dimers and longer oligomers. In summary, sodium chloride is likely to have played an essential role in any clay mineral-catalyzed prebiotic RNA synthesis.

  11. Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

    KAUST Repository

    Vummaleti, Sai V. C.

    2015-11-13

    Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

  12. DNA Self-assembly Catalyzed by Artificial Agents.

    Science.gov (United States)

    Shi, Chao; Wang, Yifan; Zhang, Menghua; Ma, Cuiping

    2017-07-28

    Nucleic acids have been shown to be versatile molecules and engineered to produce various nanostructures. However, the poor rate of these uncatalyzed nucleic acid reactions has restricted the development and applications. Herein, we reported a novel finding that DNA self-assembly could be nonenzymatically catalyzed by artificial agents with an increasing dissociation rate constant K2. The catalytic role of several artificial agents in DNA self-assembly was verified by real-time fluorescent detection or agarose gel electrophoresis. We found that 20% PEG 200 could significantly catalyze DNA self-assembly and increase the reaction efficiency, such as linear hybridization chain reaction (HCR) and exponential hairpin assembly (EHA). Therefore, we foresee that a fast and efficient DNA self-assembly in structural DNA nanotechnology will be desirable.

  13. Mild and efficient cyanuric chloride catalyzed Pictet–Spengler reaction

    Directory of Open Access Journals (Sweden)

    Ashish Sharma

    2013-06-01

    Full Text Available A practical, mild and efficient protocol for the Pictet–Spengler reaction catalyzed by cyanuric chloride (trichloro-1,3,5-triazine, TCT is described. The 6-endo cyclization of tryptophan/tryptamine and modified Pictet–Spengler substrates with both electron-withdrawing and electron-donating aldehydes was carried out by using a catalytic amount of TCT (10 mol % in DMSO under a nitrogen atmosphere. TCT catalyzed the Pictet–Spengler reaction involving electron-donating aldehydes in excellent yield. Thus, it has a distinct advantage over the existing methodologies where electron-donating aldehydes failed to undergo 6-endo cyclization. Our methodology provided broad substrate scope and diversity. This is indeed the first report of the use of TCT as a catalyst for the Pictet–Spengler reaction.

  14. Copper-Catalyzed Alkoxycarbonylation of Alkanes with Alcohols.

    Science.gov (United States)

    Li, Yahui; Wang, Changsheng; Zhu, Fengxiang; Wang, Zechao; Dixneuf, Pierre H; Wu, Xiao-Feng

    2017-04-10

    Esters are important chemicals widely used in various areas, and alkoxycarbonylation represents one of the most powerful tools for their synthesis. In this communication, a new copper-catalyzed carbonylative procedure for the synthesis of aliphatic esters from cycloalkanes and alcohols was developed. Through direct activation of the Csp3 -H bond of alkanes and with alcohols as the nucleophiles, the desired esters were prepared in moderate-to-good yields. Paraformaldehyde could also be applied for in situ alcohol generation by radical trapping, and moderate yields of the corresponding esters could be produced. Notably, this is the first report on copper-catalyzed alkoxycarbonylation of alkanes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Hydroperoxide-dependent sulfoxidation catalyzed by soybean microsomes.

    Science.gov (United States)

    Blee, E; Durst, F

    1987-04-01

    The sulfoxidation of methiocarb, an aromatic-alkyl sulfide pesticide, catalyzed by soybean microsomes was found to be strongly stimulated in the presence of cumene and linoleic acid hydroperoxides. We have shown that this S-oxidation, which does not require cofactors such as NAD(P)H, is an hydroperoxide-dependent reaction: 18O2-labeling experiments demonstrated that the oxygen atom incorporated into the sulfoxide originated from hydroperoxides rather than from molecular oxygen. In the absence of exogenous hydroperoxides, soybean microsomes catalyzed methiocarb sulfoxide formation at a basal rate dependent on their endogenous hydroperoxides, especially those derived from free fatty acids. The nature of the sulfoxidase is discussed. Our results seem to rule out the participation of cytochrome P-450 in this oxidation, whereas the studied sulfoxidase presents some similarities to plant peroxygenase.

  16. Transition Metal Catalyzed Synthesis of Carboxylic Acids, Imines, and Biaryls

    DEFF Research Database (Denmark)

    Santilli, Carola; Madsen, Robert

    Dehydrogenative synthesis of carboxylic acids catalyzed by a ruthenium N- heterocycliccarbene complex. A new methodology for the synthesis of carboxylic acids from primary alcohols and hydroxide has been developed. The reaction is catalyzed by the ruthenium N-heterocycliccarbene complex [RuCl2(Ii......Pr)(p-cymene)] where dihydrogen is generated as the only by-product (Scheme i). The dehydrogenative reaction is performed in toluene, which allows for a simple isolation of the products by precipitation followed by extraction. Various substituted benzyl alcohols smoothly undergo the transformation. The fast conversion...... to the carboxylic acids can be explained by the involvement of a competing Cannizzaro reaction. The scope of the dehydrogenation was further extended to linear and branched saturated aliphatic alcohols, although longer reaction times are necessary to ensure complete substrate conversions. The kinetic isotope effect...

  17. Identification of the enzymes catalyzing metabolism of methoxyflurane.

    Science.gov (United States)

    Waskell, L; Canova-Davis, E; Philpot, R; Parandoush, Z; Chiang, J Y

    1986-01-01

    The hepatic microsomal metabolism of methoxyflurane in rabbits is markedly stimulated by treatment with phenobarbital. However, the increased rate of metabolism cannot be completely accounted for by the activity of the purified phenobarbital-inducible cytochrome P-450 isozyme 2, even in the presence of cytochrome b5. The discovery of a second hepatic phenobarbital-inducible cytochrome P-450, isozyme 5, led us to undertake experiments to determine in hepatic and pulmonary preparations the portion of microsomal metabolism of methoxyflurane catalyzed by cytochrome P-450 isozymes 2 and 5. We report herein that isozyme 2 accounts for 25% and 29%, respectively, of the O-demethylation of methoxyflurane in hepatic microsomes from untreated and phenobarbital-treated rabbits, and for 25% of the methoxyflurane metabolism in pulmonary microsomes. Results for isozyme 5 indicate that it catalyzes 19% and 27% of methoxyflurane metabolism in control and phenobarbital-induced liver, and 47% of O-demethylation in the lung. In summary, we demonstrate that methoxyflurane O-demethylation in lung, phenobarbital-induced liver, and control liver microsomes is catalyzed by cytochrome P-450 isozymes 2 and 5. Results with purified cytochrome P-450 isozyme 5 are consistent with those obtained using microsomal preparations. Furthermore, metabolism of methoxyflurane by purified isozyme 5 is markedly stimulated by cytochrome b5. A role for cytochrome b5 in cytochrome P-450 isozyme 5-catalyzed metabolism of methoxyflurane was also demonstrated in microsomes. Antibody to isozyme 5 was unable to inhibit methoxyflurane metabolism in the presence of maximally inhibiting concentrations of cytochrome b5 antibody.(ABSTRACT TRUNCATED AT 250 WORDS)

  18. Lipase-Catalyzed Kinetic Resolution of Aryltrimethylsilyl Chiral Alcohols

    Directory of Open Access Journals (Sweden)

    Leandro H. Andrade

    2011-11-01

    Full Text Available Lipase-catalyzed kinetic resolution of aryltrimethylsilyl chiral alcohols through a transesterification reaction was studied. The optimal conditions found for the kinetic resolution of m- and p-aryltrimethylsilyl chiral alcohols, led to excellent results, high conversions (c = 50%, high enantiomeric ratios (E > 200 and enantiomeric excesses for the remaining (S-alcohol and (R-acetylated product (>99%. However, kinetic resolution of o-aryltrimethylsilyl chiral alcohols did not occur under the same conditions applied to the other isomers.

  19. Polyoxometalate catalyzed ozonation of chemical pulps in organic solvent media

    OpenAIRE

    Shatalov, Anatoly A.; Pereira, Helena

    2009-01-01

    Polyoxometalate (POM) catalyzed ozonation of chemical pulps in organic solvent media was found to be particularly effective and selective environmentally benign bleaching approach providing a way for substantial increase in pulp brightness, viscosity and degree of delignification in comparison with other ozone-based bleaching techniques. A series of tested low-boiling polar aprotic and protic organic solvents showed awell-defined capacity for ozonation improvement in the presence ...

  20. Medium effect on cyclohexene hydrocarbomethoxylation catalyzed by ruthenium (III) chloride

    OpenAIRE

    Sevostyanova N.; Batashev S.

    2016-01-01

    This paper presents influence of some solvents on cyclohexene hydrocarbomethoxylation catalyzed by ruthenium(III) chloride. The objective of the work was contained in the determination of medium influence on the reaction rate and yield of product — methyl cyclohexanecarboxylate. The kinetic method was used as the main method of investigation. The gas–liquid chromatography method was used to analyze the reaction mass. Influence of methanol, toluene, acetone and water on the hydrocarmothoxy...

  1. Synthesis of Graphite Encapsulated Metal Nanoparticles and Metal Catalyzed Nanotubes

    Science.gov (United States)

    vanderWal, R. L.; Dravid, V. P.

    1999-01-01

    This work focuses on the growth and inception of graphite encapsulated metal nanoparticles and metal catalyzed nanotubes using combustion chemistry. Deciphering the inception and growth mechanism(s) for these unique nanostructures is essential for purposeful synthesis. Detailed knowledge of these mechanism(s) may yield insights into alternative synthesis pathways or provide data on unfavorable conditions. Production of these materials is highly desirable given many promising technological applications.

  2. Gold-catalyzed cyclization of allenyl acetal derivatives

    Directory of Open Access Journals (Sweden)

    Dhananjayan Vasu

    2013-08-01

    Full Text Available The gold-catalyzed transformation of allenyl acetals into 5-alkylidenecyclopent-2-en-1-ones is described. The outcome of our deuterium labeling experiments supports a 1,4-hydride shift of the resulting allyl cationic intermediates because a complete deuterium transfer is observed. We tested the reaction on various acetal substrates bearing a propargyl acetate, giving 4-methoxy-5-alkylidenecyclopent-2-en-1-ones 4 via a degradation of the acetate group at the allyl cation intermediate.

  3. Vanadium haloperoxidase-catalyzed bromination and cyclization of terpenes.

    Science.gov (United States)

    Carter-Franklin, Jayme N; Parrish, Jon D; Tschirret-Guth, Richard A; Little, R Daniel; Butler, Alison

    2003-04-02

    Marine red algae (Rhodophyta) are a rich source of bioactive halogenated natural products, including cyclic terpenes. The biogenesis of certain cyclic halogenated marine natural products is thought to involve marine haloperoxidase enzymes. Evidence is presented that vanadium bromoperoxidase (V-BrPO) isolated and cloned from marine red algae that produce halogenated compounds (e.g., Plocamium cartilagineum, Laurencia pacifica, Corallina officinalis) can catalyze the bromination and cyclization of terpenes and terpene analogues. The V-BrPO-catalyzed reaction with the monoterpene nerol in the presence of bromide ion and hydrogen peroxide produces a monobromo eight-membered cyclic ether similar to laurencin, a brominated C15 acetogenin, from Laurencia glandulifera, along with noncyclic bromohydrin, epoxide, and dibromoproducts; however, reaction of aqueous bromine with nerol produced only noncyclic bromohydrin, epoxide, and dibromoproducts. The V-BrPO-catalyzed reaction with geraniol in the presence of bromide ion and hydrogen peroxide produces two singly brominated six-membered cyclic products, analogous to the ring structures of alpha and beta snyderols, brominated sesquiterpenes from Laurencia, spp., along with noncyclic bromohydrin, epoxide, and dibromoproducts; again, reaction of geraniol with aqueous bromine produces only noncyclic bromohydrin, epoxide, and dibromoproducts. Thus, V-BrPO can direct the electrophilic bromination and cyclization of terpenes.

  4. Aluminum-catalyzed silicon nanowires: Growth methods, properties, and applications

    Energy Technology Data Exchange (ETDEWEB)

    Hainey, Mel F.; Redwing, Joan M. [Department of Materials Science and Engineering, Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

    2016-12-15

    Metal-mediated vapor-liquid-solid (VLS) growth is a promising approach for the fabrication of silicon nanowires, although residual metal incorporation into the nanowires during growth can adversely impact electronic properties particularly when metals such as gold and copper are utilized. Aluminum, which acts as a shallow acceptor in silicon, is therefore of significant interest for the growth of p-type silicon nanowires but has presented challenges due to its propensity for oxidation. This paper summarizes the key aspects of aluminum-catalyzed nanowire growth along with wire properties and device results. In the first section, aluminum-catalyzed nanowire growth is discussed with a specific emphasis on methods to mitigate aluminum oxide formation. Next, the influence of growth parameters such as growth temperature, precursor partial pressure, and hydrogen partial pressure on nanowire morphology is discussed, followed by a brief review of the growth of templated and patterned arrays of nanowires. Aluminum incorporation into the nanowires is then discussed in detail, including measurements of the aluminum concentration within wires using atom probe tomography and assessment of electrical properties by four point resistance measurements. Finally, the use of aluminum-catalyzed VLS growth for device fabrication is reviewed including results on single-wire radial p-n junction solar cells and planar solar cells fabricated with nanowire/nanopyramid texturing.

  5. Aluminum-catalyzed silicon nanowires: Growth methods, properties, and applications

    Science.gov (United States)

    Hainey, Mel F.; Redwing, Joan M.

    2016-12-01

    Metal-mediated vapor-liquid-solid (VLS) growth is a promising approach for the fabrication of silicon nanowires, although residual metal incorporation into the nanowires during growth can adversely impact electronic properties particularly when metals such as gold and copper are utilized. Aluminum, which acts as a shallow acceptor in silicon, is therefore of significant interest for the growth of p-type silicon nanowires but has presented challenges due to its propensity for oxidation. This paper summarizes the key aspects of aluminum-catalyzed nanowire growth along with wire properties and device results. In the first section, aluminum-catalyzed nanowire growth is discussed with a specific emphasis on methods to mitigate aluminum oxide formation. Next, the influence of growth parameters such as growth temperature, precursor partial pressure, and hydrogen partial pressure on nanowire morphology is discussed, followed by a brief review of the growth of templated and patterned arrays of nanowires. Aluminum incorporation into the nanowires is then discussed in detail, including measurements of the aluminum concentration within wires using atom probe tomography and assessment of electrical properties by four point resistance measurements. Finally, the use of aluminum-catalyzed VLS growth for device fabrication is reviewed including results on single-wire radial p-n junction solar cells and planar solar cells fabricated with nanowire/nanopyramid texturing.

  6. Asymmetric Stetter reactions catalyzed by thiamine diphosphate-dependent enzymes.

    Science.gov (United States)

    Kasparyan, Elena; Richter, Michael; Dresen, Carola; Walter, Lydia S; Fuchs, Georg; Leeper, Finian J; Wacker, Tobias; Andrade, Susana L A; Kolter, Geraldine; Pohl, Martina; Müller, Michael

    2014-12-01

    The intermolecular asymmetric Stetter reaction is an almost unexplored transformation for biocatalysts. Previously reported thiamine diphosphate (ThDP)-dependent PigD from Serratia marcescens is the first enzyme identified to catalyze the Stetter reaction of α,β-unsaturated ketones (Michael acceptor substrates) and α-keto acids. PigD is involved in the biosynthesis of the potent cytotoxic agent prodigiosin. Here, we describe the investigation of two new ThDP-dependent enzymes, SeAAS from Saccharopolyspora erythraea and HapD from Hahella chejuensis. Both show a high degree of homology to the amino acid sequence of PigD (39 and 51 %, respectively). The new enzymes were heterologously overproduced in Escherichia coli, and the yield of soluble protein was enhanced by co-expression of the chaperone genes groEL/ES. SeAAS and HapD catalyze intermolecular Stetter reactions in vitro with high enantioselectivity. The enzymes possess a characteristic substrate range with respect to Michael acceptor substrates. This provides support for a new type of ThDP-dependent enzymatic activity, which is abundant in various species and not restricted to prodigiosin biosynthesis in different strains. Moreover, PigD, SeAAS, and HapD are also able to catalyze asymmetric carbon-carbon bond formation reactions of aldehydes and α-keto acids, resulting in 2-hydroxy ketones.

  7. Mechanism of the reaction catalyzed by mandelate racemase. 3. Asymmetry in reactions catalyzed by the H297N mutant

    Energy Technology Data Exchange (ETDEWEB)

    Landro, J.A.; Kallarakal, A.T.; Ransom, S.C.; Gerlt, J.A.; Kozarich, J.W. (Univ. of Maryland, College Park (United States)); Neidhart, D.J. (Abbott Labs., Abbott Park, IL (United States)); Kenyon, G.L. (Univ. of California, San Francisco (United States))

    1991-09-24

    Two preceding papers suggest that the active site of mandelate racemase (MR) contains two distinct general acid/base catalysts: Lys 166, which abstracts the {alpha}-proton from (s)-mandelate, and His 297, which abstracts the {alpha}-proton from (R)-mandelate. In this paper the authors report on the properties of the mutant of MR in which His 297 has been converted to asparagine by site-directed mutagenesis (H297N). The structure of H297N, solved by molecular replacement at 2.2-{angstrom} resolution, reveals that no conformational alterations accompany the substitution. As expected, h297N has no detectable MR activity. However, H297N catalyzes the stereospecific elimination of bromide ion from racemic {rho}-(bromomethyl) mandelate to give {rho}-(methyl)-benzoylformate in 45% yield at a rate equal to that measured for wild-type enzyme. The pD dependence of the rate of the exchange reaction catalyzed by H297N reveals a pK{sub a} of 6.4 in D{sub 2}O which is assigned to Lys 166. These observations provide persuasive evidence that the reaction catalyzed by MR does, in fact, proceed via a two-base mechanism in which Lys 166 abstracts the {alpha}-proton from (S)-mandelate and His 297 abstracts the {alpha}-proton from (R)-mandelate. These studies demonstrate the power of site-directed mutagenesis in providing otherwise inaccessible detail about the mechanism of an enzyme-catalyzed reaction.

  8. Ammonia and hydrazine. Transition-metal-catalyzed hydroamination and metal-free catalyzed functionalization

    Energy Technology Data Exchange (ETDEWEB)

    Bertrand, Guy [Univ. of California, San Diego, CA (United States)

    2012-06-29

    high temperatures and long reaction times. To address this issue, we have developed several new families of carbon- and boron-based ligands, which are even better donors. The corresponding metal complexes (particularly gold, rhodium, iridium, and ruthenium) of all these species will be tested in the Markovnikov and anti-Markovnikov hydroamination of alkynes, allenes, and also alkenes with ammonia and hydrazine. We will also develop metal-free catalytic processes for the functionalization of ammonia and hydrazine. By possessing both a lone pair of electrons and an accessible vacant orbital, singlet carbenes resemble and can mimic the chemical behavior of transition metals. Our preliminary results demonstrate that specially designed carbenes can split the N–H bond of ammonia by an initial nucleophilic activation that prevents the formation of Lewis acid-base adducts, which is the major hurdle for the transition metal catalyzed functionalization of NH3. The use of purely organic compounds as catalysts will eliminate the major drawbacks of transition-metal-catalysis technology, which are the excessive cost of metal complexes (metal + ligands) and in many cases the toxicity of the metal.

  9. Gold-catalyzed cyclization reactions of allenol and alkynol derivatives.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro

    2014-03-18

    Although gold is chemically inert as a bulk metal, the landmark discovery that gold nanoparticles can be effective catalysts has opened up new and exciting research opportunities in the field. In recent years, there has been growth in the number of reactions catalyzed by gold complexes [gold(I) and gold(III)], usually as homogeneous catalysts, because they are soft Lewis acids. In addition, alkynes and allenes have interesting reactivities and selectivities, notably their ability to produce complex structures in very few steps. In this Account, we describe our work in gold catalysis with a focus on the formation of C-C and C-O bonds using allenes and alkynes as starting materials. Of these, oxa- and carbo-cyclizations are perhaps the best known and most frequently studied. We have divided those contributions into sections arranged according to the nature of the starting material (allene versus alkyne). Gold-catalyzed carbocyclizations in allenyl C2-linked indoles, allenyl-β-lactams, and allenyl sugars follow different mechanistic pathways. The cyclization of indole-tethered allenols results in the efficient synthesis of carbazole derivatives, for example. However, the compound produced from gold-catalyzed 9-endo carbocyclization of (aryloxy)allenyl-tethered 2-azetidinones is in noticeable contrast to the 5-exo hydroalkylation product that results from allenyl sugars. We have illustrated the unusual preference for the 4-exo-dig cyclization in allene chemistry, as well as the rare β-hydride elimination reaction, in gold catalysis from readily available α-allenols. We have also observed in γ-allenols that a (methoxymethyl)oxy protecting group not only masks a hydroxyl functionality but also exerts directing effects as a controlling unit in a gold-catalyzed regioselectivity reversal. Our recent work has also led to a combined experimental and computational study on regioselective gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled

  10. Acid-Catalyzed Preparation of Biodiesel from Waste Vegetable Oil: An Experiment for the Undergraduate Organic Chemistry Laboratory

    Science.gov (United States)

    Bladt, Don; Murray, Steve; Gitch, Brittany; Trout, Haylee; Liberko, Charles

    2011-01-01

    This undergraduate organic laboratory exercise involves the sulfuric acid-catalyzed conversion of waste vegetable oil into biodiesel. The acid-catalyzed method, although inherently slower than the base-catalyzed methods, does not suffer from the loss of product or the creation of emulsion producing soap that plagues the base-catalyzed methods when…

  11. Synthesis of sn-1 functionalized phospholipids as substrates for secretory phospholipase A2

    DEFF Research Database (Denmark)

    Linderoth, Lars; Peters, Günther H.J.; Jørgensen, K.

    2007-01-01

    Secretory phospholipase A2 (sPLA2) represents a family of small water-soluble enzymes that catalyze the hydrolysis of phospholipids in the sn-2 position liberating free fatty acids and lysophospholipids. Herein we report the synthesis of two new phospholipids (1 and 2) with bulky allyl-substituen......Secretory phospholipase A2 (sPLA2) represents a family of small water-soluble enzymes that catalyze the hydrolysis of phospholipids in the sn-2 position liberating free fatty acids and lysophospholipids. Herein we report the synthesis of two new phospholipids (1 and 2) with bulky allyl...

  12. The Acid Hydrolysis Mechanism of Acetals Catalyzed by a Supramolecular Assembly in Basic Solution

    Energy Technology Data Exchange (ETDEWEB)

    Pluth, Michael D.; Bergman, Robert G.; Raymond, Kenneth N.

    2008-09-24

    A self-assembled supramolecular host catalyzes the hydrolysis of acetals in basic aqueous solution. The mechanism of hydrolysis is consistent with the Michaelis-Menten kinetic model. Further investigation of the rate limiting step of the reaction revealed a negative entropy of activation ({Delta}S{double_dagger} = -9 cal mol{sup -1}K{sup -1}) and an inverse solvent isotope effect (k(H{sub 2}O)/k(D{sub 2}O) = 0.62). These data suggest that the mechanism of hydrolysis that takes place inside the assembly proceeds through an A-2 mechanism, in contrast to the A-1 mechanism operating in the uncatalyzed reaction. Comparison of the rates of acetal hydrolysis in the assembly with the rate of the reaction of unencapsulated substrates reveals rate accelerations of up to 980 over the background reaction for the substrate diethoxymethane.

  13. Development and industrial application of catalyzer for low-temperature hydrogenation hydrolysis of Claus tail gas

    Directory of Open Access Journals (Sweden)

    Honggang Chang

    2015-10-01

    Full Text Available With the implementation of more strict national environmental protection laws, energy conservation, emission reduction and clean production will present higher requirements for sulfur recovery tail gas processing techniques and catalyzers. As for Claus tail gas, conventional hydrogenation catalyzers are gradually being replaced by low-temperature hydrogenation catalyzers. This paper concentrates on the development of technologies for low-temperature hydrogenation hydrolysis catalyzers, preparation of such catalyzers and their industrial application. In view of the specific features of SO2 hydrogenation and organic sulfur hydrolysis during low-temperature hydrogenation, a new technical process involving joint application of hydrogenation catalyzers and hydrolysis catalyzers was proposed. In addition, low-temperature hydrogenation catalyzers and low-temperature hydrolysis catalyzers suitable for low-temperature conditions were developed. Joint application of these two kinds of catalyzers may reduce the inlet temperatures in the conventional hydrogenation reactors from 280 °C to 220 °C, at the same time, hydrogenation conversion rates of SO2 can be enhanced to over 99%. To further accelerate the hydrolysis rate of organic sulfur, the catalyzers for hydrolysis of low-temperature organic sulfur were developed. In lab tests, the volume ratio of the total sulfur content in tail gas can be as low as 131 × 10−6 when these two kinds of catalyzers were used in a proportion of 5:5 in volumes. Industrial application of these catalyzers was implemented in 17 sulfur recovery tail gas processing facilities of 15 companies. As a result, Sinopec Jinling Petrochemical Company had outstanding application performances with a tail gas discharging rate lower than 77.9 mg/m3 and a total sulfur recovery of 99.97%.

  14. Energy harvesting by implantable abiotically catalyzed glucose fuel cells

    Energy Technology Data Exchange (ETDEWEB)

    Kerzenmacher, S.; von Stetten, F. [Laboratory for MEMS Applications, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 106, D-79110 Freiburg (Germany); Ducree, J. [HSG-IMIT, Wilhelm-Schickard-Str. 10, D-78052 Villingen-Schwenningen (Germany); Zengerle, R. [Laboratory for MEMS Applications, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 106, D-79110 Freiburg (Germany); HSG-IMIT, Wilhelm-Schickard-Str. 10, D-78052 Villingen-Schwenningen (Germany)

    2008-07-15

    Implantable glucose fuel cells are a promising approach to realize an autonomous energy supply for medical implants that solely relies on the electrochemical reaction of oxygen and glucose. Key advantage over conventional batteries is the abundant availability of both reactants in body fluids, rendering the need for regular replacement or external recharging mechanisms obsolete. Implantable glucose fuel cells, based on abiotic catalysts such as noble metals and activated carbon, have already been developed as power supply for cardiac pacemakers in the late-1960s. Whereas, in vitro and preliminary in vivo studies demonstrated their long-term stability, the performance of these fuel cells is limited to the {mu}W-range. Consequently, no further developments have been reported since high-capacity lithium iodine batteries for cardiac pacemakers became available in the mid-1970s. In recent years research has been focused on enzymatically catalyzed glucose fuel cells. They offer higher power densities than their abiotically catalyzed counterparts, but the limited enzyme stability impedes long-term application. In this context, the trend towards increasingly energy-efficient low power MEMS (micro-electro-mechanical systems) implants has revived the interest in abiotic catalysts as a long-term stable alternative. This review covers the state-of-the-art in implantable abiotically catalyzed glucose fuel cells and their development since the 1960s. Different embodiment concepts are presented and the historical achievements of academic and industrial research groups are critically reviewed. Special regard is given to the applicability of the concept as sustainable micro-power generator for implantable devices. (author)

  15. A SABATH Methyltransferase from the moss Physcomitrella patens catalyzes

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Nan [ORNL; Ferrer, Jean-Luc [Universite Joseph Fourier, France; Moon, Hong S [Department of Plant Sciences, University of Tennessee; Kapteyn, Jeremy [Institute of Biological Chemistry, Washington State University; Zhuang, Xiaofeng [Department of Plant Sciences, University of Tennessee; Hasebe, Mitsuyasu [Laboratory of Evolutionary Biology, National Institute for Biology, 38 Nishigounaka; Stewart, Neal C. [Department of Plant Sciences, University of Tennessee; Gang, David R. [Institute of Biological Chemistry, Washington State University; Chen, Feng [University of Tennessee, Knoxville (UTK)

    2012-01-01

    Known SABATH methyltransferases, all of which were identified from seed plants, catalyze methylation of either the carboxyl group of a variety of low molecular weight metabolites or the nitrogen moiety of precursors of caffeine. In this study, the SABATH family from the bryophyte Physcomitrella patens was identified and characterized. Four SABATH-like sequences (PpSABATH1, PpSABATH2, PpSABATH3, and PpSABATH4) were identified from the P. patens genome. Only PpSABATH1 and PpSABATH2 showed expression in the leafy gametophyte of P. patens. Full-length cDNAs of PpSABATH1 and PpSABATH2 were cloned and expressed in soluble form in Escherichia coli. Recombinant PpSABATH1 and PpSABATH2 were tested for methyltransferase activity with a total of 75 compounds. While showing no activity with carboxylic acids or nitrogen-containing compounds, PpSABATH1 displayed methyltransferase activity with a number of thiols. PpSABATH2 did not show activity with any of the compounds tested. Among the thiols analyzed, PpSABATH1 showed the highest level of activity with thiobenzoic acid with an apparent Km value of 95.5 lM, which is comparable to those of known SABATHs. Using thiobenzoic acid as substrate, GC MS analysis indicated that the methylation catalyzed by PpSABATH1 is on the sulfur atom. The mechanism for S-methylation of thiols catalyzed by PpSABATH1 was partially revealed by homology-based structural modeling. The expression of PpSABATH1 was induced by the treatment of thiobenzoic acid. Further transgenic studies showed that tobacco plants overexpressing PpSABATH1 exhibited enhanced tolerance to thiobenzoic acid, suggesting that PpSABATH1 have a role in the detoxification of xenobiotic thiols.

  16. Palladium-Catalyzed Directed Halogenation of Bipyridine N-Oxides.

    Science.gov (United States)

    Zucker, Sina P; Wossidlo, Friedrich; Weber, Manuela; Lentz, Dieter; Tzschucke, C Christoph

    2017-06-02

    The palladium-catalyzed directed C-H halogenation of bipyridine N-oxides was investigated. Using NCS or NBS (N-chloro- or N-bromosuccinimide) and 5 mol % Pd(OAc)2 in chlorobenzene (0.10 molar) at 110 °C, pyridine-directed functionalization took place and 3-chloro- or 3-bromobipyridine N-oxides were obtained in high yields. The reaction is sensitive to steric hindrance by 4- and 6'-substituents. Only in the latter case, where coordination of palladium by the pyridine is hindered, 3'-halogenation directed by the N-oxide function was observed. The halogenated products were deoxygenated by PCl3 or PBr3.

  17. Zinc oxide catalyzed growth of single-walled carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Gao Fenglei, E-mail: jsxzgfl@sina.com [Nanomaterials and Chemistry Key Laboratory, Wenzhou University, Wenzhou 325027 (China); Zhang Lijie; Huang Shaoming [Nanomaterials and Chemistry Key Laboratory, Wenzhou University, Wenzhou 325027 (China)

    2010-02-01

    We demonstrate that zinc oxide can catalyze the growth of single-walled carbon nanotubes (SWNTs) with high efficiency by a chemical vapor deposition process. The zinc oxide nanocatalysts, prepared using a diblock copolymer templating method and characterized by atomic force microscopy (AFM), were uniformly spaced over a large deposition area with an average diameter of 1.7 nm and narrow size distribution. Dense and uniform SWNTs films with high quality were obtained by using a zinc oxide catalyst, as characterized by scanning electron microscopy (SEM), Raman spectroscopy, AFM, and high-resolution transmission electron microscopy (HRTEM).

  18. Polyoxometalates as mediators in the laccase catalyzed delignification

    OpenAIRE

    Balakshin, M. Yu.; Evtuguin, D. V.; Neto, C. Pascoal; Paulo, Artur Cavaco

    2001-01-01

    The polyoxometalate (POM)-laccase catalytic system was applied for the first time to aerobic delignification of kraft pulps at moderate (40-60 degreesC) temperatures. Laccase was found to readily catalyze the re-oxidation of different kinds of polyoxometalates, including those, which cannot be re-oxidized by dioxygen even at high temperatures (PMo11V1, SiW11V1. etc.). This allows a sequence of catalytic redox cycles similar to that in the laccase-mediator system (LMS) where electrons are tran...

  19. Ketone-catalyzed photochemical C(sp3)-H chlorination.

    Science.gov (United States)

    Han, Lei; Xia, Jibao; You, Lin; Chen, Chuo

    2017-06-29

    Photoexcited arylketones catalyze the direct chlorination of C(sp3)-H groups by N-chlorosuccinimide. Acetophenone is the most effective catalyst for functionalization of unactivated C-H groups while benzophenone provides better yields for benzylic C-H functionalization. Activation of both acetophenone and benzophenone can be achieved by irradiation with a household compact fluorescent lamp. This light-dependent reaction provides a better control of the reaction as compared to the traditional chlorination methods that proceed through a free radical chain propagation mechanism.

  20. Iodine - catalyzed prins cyclization of aliphatic and aromatic ketones

    Energy Technology Data Exchange (ETDEWEB)

    Kishore, K.R.; Reddy, K.; Silva Junior, Luiz F., E-mail: luizfsjr@iq.usp.br [Universidade de Sao Paulo (IQ/USP), SP (Brazil). Inst. de Quimica. Dept. de Quimica Fundamental

    2013-09-15

    Iodine-catalyzed Prins cyclization of homoallylic alcohols and ketones was investigated. Anhydrous conditions and inert atmosphere are not required in this metal-free protocol. The reaction of 2-(3,4-dihydronaphthalene-1-yl)propan-1-ol with six aliphatic symmetric ketones gave the desired products in 67-77% yield. Cyclization was performed with four aliphatic unsymmetric ketones, leading to corresponding pyrans in 66-76% yield. Prins cyclization was also accomplished with four aromatic ketones in 37-66% yield. Finally, Prins cyclization of the monoterpene isopulegol and acetone was successfully achieved. (author)

  1. Asymmetric Propargylation of Ketones using Allenylboronates Catalyzed by Chiral Biphenols

    Science.gov (United States)

    Barnett, David S.; Schaus, Scott E.

    2011-01-01

    Chiral biphenols catalyze the enantioselective asymmetric propargylation of ketones using allenylboronates. The reaction uses 10 mol % of 3,3′-Br2-BINOL as the catalyst and allenyldioxoborolane as the nucleophile, in the absence of solvent, and under microwave irradiation to afford the homopropargylic alcohol. The reaction products are obtained in good yields (60 – 98%) and high enantiomeric ratios (3:1 – 99:1). Diastereoselective propargylations using chiral racemic allenylboronates result in good diastereoselectivities (dr > 86:14) and enantioselectivities (er > 92:8) under the catalytic conditions. PMID:21732609

  2. Comparing Ru and Fe-catalyzed olefin metathesis

    KAUST Repository

    Poater, Albert

    2014-01-01

    Density functional theory calculations have been used to explore the potential of Fe-based complexes with an N-heterocyclic carbene ligand, as olefin metathesis catalysts. Apart from a less endothermic reaction energy profile, a small reduction in the predicted upper energy barriers (≈ 2 kcal mol -1) is calculated in the Fe catalyzed profile with respect to the Ru catalysed profile. Overall, this study indicates that Fe-based catalysts have the potential to be very effective olefin metathesis catalysts. This journal is © the Partner Organisations 2014.

  3. Zeolite-catalyzed isomerization of tetroses in aqueous medium

    DEFF Research Database (Denmark)

    Shunmugavel, Saravanamurugan; Riisager, Anders

    2014-01-01

    in water. Hence, the results demonstrate water to be a preferred solvent compared to lower alcohols for zeolite-catalyzed tetrose isomerization, which is opposite to what previously have been found for analogous pentose and hexose isomerization. A reuse study revealed further that H-USY(6) could be applied...... in at least five reaction runs with essentially unchanged activity and without significant aluminium leaching from the catalyst. The use of benign reaction conditions and an industrially pertinent solid catalyst in combination with water establishes a new, green tetrose isomerization protocol...

  4. Deoxyribonucleoside kinases: two enzyme families catalyze the same reaction.

    Science.gov (United States)

    Sandrini, Michael P B; Piskur, Jure

    2005-05-01

    Mammals have four deoxyribonucleoside kinases, the cytoplasmic (TK1) and mitochondrial (TK2) thymidine kinases, and the deoxycytidine (dCK) and deoxyguanosine (dGK) kinases, which salvage the precursors for nucleic acids synthesis. In addition to the native deoxyribonucleoside substrates, the kinases can phosphorylate and thereby activate a variety of anti-cancer and antiviral prodrugs. Recently, the crystal structure of human TK1 has been solved and has revealed that enzymes with fundamentally different origins and folds catalyze similar, crucial cellular reactions.

  5. Ruthenium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols

    DEFF Research Database (Denmark)

    Mazziotta, Andrea; Madsen, Robert

    2017-01-01

    Dehydrogenative decarbonylation of a primary alcohol involves the release of both dihydrogen and carbon monoxide to afford the one-carbon shorter product. The transformation has now been achieved with a ruthenium-catalyzed protocol by using the complex Ru(COD)Cl2 and the hindered monodentate ligand...... P(o-tolyl)3 in refluxing p-cymene. The reaction can be applied to both benzylic and long chain linear aliphatic alcohols. The intermediate aldehyde can be observed during the transformation, which is therefore believed to proceed through two separate catalytic cycles involving first dehydrogenation...... of the alcohol and then decarbonylation of the resulting aldehyde....

  6. Synthesis of Dihydrobenzofurans via Palladium-Catalyzed Heteroannulations

    Energy Technology Data Exchange (ETDEWEB)

    Rozhkov, Roman Vladimirovich [Iowa State Univ., Ames, IA (United States)

    2004-01-01

    Palladium-catalyzed heteroannulation of 1,3-dienes with 3-iodo-2-alkenols, and 2-iodo-2-alkenols, as well as their amino analogs, affords the corresponding cyclic ethers and amines respectively. The presence of a β-hydrogen in the vinylic halide results in β-hydride elimination giving the corresponding alkyne. The presence of a bulky group in the α-position of the vinylic halide results in failure or reduced amounts of annulation products. A chloride source, pyridine base and electron-rich phosphine are essential for this reaction.

  7. Reactivity of bromoselenophenes in palladium-catalyzed direct arylations

    Directory of Open Access Journals (Sweden)

    Aymen Skhiri

    2017-12-01

    Full Text Available The reactivity of 2-bromo- and 2,5-dibromoselenophenes in Pd-catalyzed direct heteroarylation was investigated. From 2-bromoselenophene, only the most reactive heteroarenes could be employed to prepare 2-heteroarylated selenophenes; whereas, 2,5-dibromoselenophene generally gave 2,5-di(heteroarylated selenophenes in high yields using both thiazole and thiophene derivatives. Moreover, sequential catalytic C2 heteroarylation, bromination, catalytic C5 arylation reactions allowed the synthesis of unsymmetrical 2,5-di(heteroarylated selenophene derivatives in three steps from selenophene.

  8. Palladium-Catalyzed alpha-Arylation of Tetramic Acids

    DEFF Research Database (Denmark)

    Storgaard, Morten; Dorwald, F. Z.; Peschke, B.

    2009-01-01

    A mild, racemization-free, palladium-Catalyzed alpha-arylation of tetramic acids (2,4-pyrrolidinediones) has been developed. Various amino acid-derived tetramic acids were cleanly arylated by treatment with 2 mol % of Pd(OAc)(2), 4 mol % of a sterically demanding biaryl phosphine, 2.3 equiv of K2...... no effect on their reactivity: both electron-rich and electron-poor aryl chlorides and bromides or triflates led to good yields. Ortho-substituted aryl halides and heteroaryl halides, however, did not undergo the title reaction....

  9. FBH1 Catalyzes Regression of Stalled Replication Forks

    DEFF Research Database (Denmark)

    Fugger, Kasper; Mistrik, Martin; Neelsen, Kai J

    2015-01-01

    DNA replication fork perturbation is a major challenge to the maintenance of genome integrity. It has been suggested that processing of stalled forks might involve fork regression, in which the fork reverses and the two nascent DNA strands anneal. Here, we show that FBH1 catalyzes regression...... of a model replication fork in vitro and promotes fork regression in vivo in response to replication perturbation. Cells respond to fork stalling by activating checkpoint responses requiring signaling through stress-activated protein kinases. Importantly, we show that FBH1, through its helicase activity...... a model whereby FBH1 promotes early checkpoint signaling by remodeling of stalled DNA replication forks....

  10. Muon-catalyzed fusion in deuterium at 3 K

    Energy Technology Data Exchange (ETDEWEB)

    Knowles, P.E.; Beer, G.A.; Mason, G.R.; Porcelli, T.A. [Victoria Univ., BC (Canada); Bailey, J.M. [EA Technology, Capenhurst (United Kingdom); Beveridge, J.L.; Marshall, G.M.; Mulhauser, F.; Olin, A. [British Columbia Univ., Vancouver, BC (Canada). TRIUMF Facility; Fujiwara, M.C. [British Columbia Univ., Vancouver, BC (Canada); Huber, T.M. [Gustavus Adolphus Coll., St. Peter, MN (United States); Jacot-Guillarmod, R. [Fribourg Univ. (Switzerland); Kammel, P. [Lawrence Berkeley Lab., CA (United States); Kim, S.K. [Jeonbuk National Univ. (Korea, Republic of); Kunselman, A.R. [Wyoming Univ., Laramie, WY (United States); Martoff, C.J. [Temple Univ., Philadelphia, PA (United States); Petitjean, C. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Zmeskal, J. [Oesterreichische Akademie der Wissenschaften, Vienna (Austria)

    1996-10-01

    Muon-catalyzed fusion in deuterium has traditionally been studied in gaseous and liquid targets. The TRIUMF solid hydrogen layer target system has been used to study the fusion reaction rates in the solid phase at a target temperature of 3 K. Both branches of the cycle were observed; neutrons by a liquid organic scintillator, and protons by a silicon detector located inside the target system. The effective molecular formation rate from the upper hyperfine state and the spin exchange rate have been measured, and information on the branching ratio parameters has been extracted. (orig.). 21 refs.

  11. Fe(II)/Fe(III)-Catalyzed Intramolecular Didehydro-Diels-Alder Reaction of Styrene-ynes.

    Science.gov (United States)

    Mun, Hyeon Jin; Seong, Eun Young; Ahn, Kwang-Hyun; Kang, Eun Joo

    2018-02-02

    The intramolecular didehydro-Diels-Alder reaction of styrene-ynes was catalyzed by Fe(II) and Fe(III) to produce various naphthalene derivatives under microwave heating conditions. Mechanistic calculations found that the Fe(II) catalyst activates the styrenyl diene in an inverse-electron-demand Diels-Alder reaction, and the consecutive dehydrogenation reaction can be promoted by either Fe(II)-catalyzed direct dehydrogenation or an Fe(III)-catalyzed rearomatization/dehydrogenation pathway.

  12. Organizational innovation: a comprehensive model for catalyzing organizational development and change in a rapidly changing world

    National Research Council Canada - National Science Library

    Steiber, Annika; Alänge, Sverker

    2015-01-01

    ..., especially the processes through which organizational innovations are created, diffused, and sustained. There is thus a need for a more comprehensive understanding of mechanisms catalyzing organizational development...

  13. Solid oxide fuel cell with internal reforming, catalyzed interconnect for use therewith, and methods

    Science.gov (United States)

    Liu, Di-Jia; Guan, Jie; Minh, Nguyen

    2010-06-08

    A catalyzed interconnect for an SOFC electrically connects an anode and an anodic current collector and comprises a metallic substrate, which provides space between the anode and anodic current collector for fuel gas flow over at least a portion of the anode, and a catalytic coating on the metallic substrate comprising a catalyst for catalyzing hydrocarbon fuel in the fuel gas to hydrogen rich reformate. An SOFC including the catalyzed anodic inter-connect, a method for operating an SOFC, and a method for making a catalyzed anodic interconnect are also disclosed.

  14. Electrochemical reduction of oxygen catalyzed by Pseudomonas aeruginosa

    Energy Technology Data Exchange (ETDEWEB)

    Cournet, Amandine [Universite de Toulouse, UPS, LU49, Adhesion bacterienne et formation de biofilms, 35 chemin des Maraichers, 31062 Toulouse Cedex 09 (France)] [Laboratoire de Genie Chimique CNRS UMR5503, 4 allee Emile Monso, BP 84234, 31432 Toulouse Cedex 04 (France); Berge, Mathieu; Roques, Christine [Universite de Toulouse, UPS, LU49, Adhesion bacterienne et formation de biofilms, 35 chemin des Maraichers, 31062 Toulouse Cedex 09 (France); Bergel, Alain [Laboratoire de Genie Chimique CNRS UMR5503, 4 allee Emile Monso, BP 84234, 31432 Toulouse Cedex 04 (France); Delia, Marie-Line, E-mail: marieline.delia@ensiacet.f [Laboratoire de Genie Chimique CNRS UMR5503, 4 allee Emile Monso, BP 84234, 31432 Toulouse Cedex 04 (France)

    2010-07-01

    Pseudomonas aeruginosa has already been shown to catalyze oxidation processes in the anode compartment of a microbial fuel cell. The present study focuses on the reverse capacity of the bacterium, i.e. reduction catalysis. Here we show that P. aeruginosa is able to catalyze the electrochemical reduction of oxygen. The use of cyclic voltammetry showed that, for a given range of potential values, the current generated in the presence of bacteria could reach up to four times the current obtained without bacteria. The adhesion of bacteria to the working electrode was necessary for the catalysis to be observed but was not sufficient. The electron transfer between the working electrode and the bacteria did not involve mediator metabolites like phenazines. The transfer was by direct contact. The catalysis required a certain contact duration between electrodes and live bacteria but after this delay, the metabolic activity of cells was no longer necessary. Membrane-bound proteins, like catalase, may be involved. Various strains of P. aeruginosa, including clinical isolates, were tested and all of them, even catalase-defective mutants, presented the same catalytic property. P. aeruginosa offers a new model for the analysis of reduction catalysis and the protocol designed here may provide a basis for developing an interesting tool in the field of bacterial adhesion.

  15. Catalyzed Synthesis of Zinc Clays by Prebiotic Central Metabolites.

    Science.gov (United States)

    Zhou, Ruixin; Basu, Kaustuv; Hartman, Hyman; Matocha, Christopher J; Sears, S Kelly; Vali, Hojatollah; Guzman, Marcelo I

    2017-04-03

    How primordial metabolic networks such as the reverse tricarboxylic acid (rTCA) cycle and clay mineral catalysts coevolved remains a mystery in the puzzle to understand the origin of life. While prebiotic reactions from the rTCA cycle were accomplished via photochemistry on semiconductor minerals, the synthesis of clays was demonstrated at low temperature and ambient pressure catalyzed by oxalate. Herein, the crystallization of clay minerals is catalyzed by succinate, an example of a photoproduced intermediate from central metabolism. The experiments connect the synthesis of sauconite, a model for clay minerals, to prebiotic photochemistry. We report the temperature, pH, and concentration dependence on succinate for the synthesis of sauconite identifying new mechanisms of clay formation in surface environments of rocky planets. The work demonstrates that seeding induces nucleation at low temperatures accelerating the crystallization process. Cryogenic and conventional transmission electron microscopies, X-ray diffraction, diffuse reflectance Fourier transformed infrared spectroscopy, and measurements of total surface area are used to build a three-dimensional representation of the clay. These results suggest the coevolution of clay minerals and early metabolites in our planet could have been facilitated by sunlight photochemistry, which played a significant role in the complex interplay between rocks and life over geological time.

  16. Ozonation of Indigo Carmine Catalyzed with Fe-Pillared Clay

    Directory of Open Access Journals (Sweden)

    Miriam Bernal

    2013-01-01

    Full Text Available The ozonation catalyzed by iron-pillared clays was studied. The degradation of dye indigo carmine (IC was elected as test reaction. Fe-pillared clays were synthesized by employing hydrolyzed FeCl3 solutions and bentonite. The pillared structure was verified by XRD and by XPS the oxidation state of iron in the synthesized material was established to be +2. By atomic absorption the weight percentage of iron was determined to be 16. The reaction was conducted in a laboratory scale up-flow bubble column reactor. From the studied variables the best results were obtained with a particle size of 60 microns, pH=3, ozone flow of 0.045 L/min, and catalyst concentration of 100 mg/L. IC was completely degraded and degradation rate was found to be double when using Fe-PILCS than with ozone alone. DQO reduction was also significantly higher with catalyzed than with noncatalyzed ozonation.

  17. Renalase does not catalyze the oxidation of catecholamines.

    Science.gov (United States)

    Beaupre, Brett A; Hoag, Matthew R; Moran, Graham R

    2015-08-01

    It is widely accepted that the function of human renalase is to oxidize catecholamines in blood. However, this belief is based on experiments that did not account for slow, facile catecholamine autoxidation reactions. Recent evidence has shown that renalase has substrates with which it reacts rapidly. The reaction catalyzed defines renalase as an oxidase, one that harvests two electrons from either 2-dihydroNAD(P) or 6-dihydroNAD(P) to form β-NAD(P)(+) and hydrogen peroxide. The apparent metabolic purpose of such a reaction is to avoid inhibition of primary dehydrogenase enzymes by these β-NAD(P)H isomers. This article demonstrates that renalase does not catalyze the oxidation of neurotransmitter catecholamines. Using high-performance liquid chromatography we show that there is no evidence of consumption of epinephrine by renalase. Using time-dependent spectrophotometry we show that the renalase FAD cofactor spectrum is unresponsive to added catecholamines, that adrenochromes are not observed to accumulate in the presence of renalase and that the kinetics of single turnover reactions with 6-dihydroNAD are unaltered by the addition of catecholamines. Lastly we show using an oxygen electrode assay that plasma renalase activity is below the level of detection and only when exogenous renalase and 6-dihydroNAD are added can dioxygen be observed to be consumed. Copyright © 2015 Elsevier Inc. All rights reserved.

  18. Time-dependent kinetic complexities in cholinesterase-catalyzed reactions.

    Science.gov (United States)

    Masson, P

    2012-10-01

    Cholinesterases (ChEs) display a hysteretic behavior with certain substrates and inhibitors. Kinetic cooperativity in hysteresis of ChE-catalyzed reactions is characterized by a lag or burst phase in the approach to steady state. With some substrates damped oscillations are shown to superimpose on hysteretic lags. These time dependent peculiarities are observed for both butyrylcholinesterase and acetylcholinesterase from different sources. Hysteresis in ChE-catalyzed reactions can be interpreted in terms of slow transitions between two enzyme conformers E and E'. Substrate can bind to E and/or E', both Michaelian complexes ES and Ε'S can be catalytically competent, or only one of them can make products. The formal reaction pathway depends on both the chemical structure of the substrate and the type of enzyme. In particular, damped oscillations develop when substrate exists in different, slowly interconvertible, conformational, and/or micellar forms, of which only the minor form is capable of binding and reacting with the enzyme. Biphasic pseudo-first-order progressive inhibition of ChEs by certain carbamates and organophosphates also fits with a slow equilibrium between two reactive enzyme forms. Hysteresis can be modulated by medium parameters (pH, chaotropic and kosmotropic salts, organic solvents, temperature, osmotic pressure, and hydrostatic pressure). These studies showed that water structure plays a role in hysteretic behavior of ChEs. Attempts to provide a molecular mechanism for ChE hysteresis from mutagenesis studies or crystallographic studies failed so far. In fact, several lines of evidence suggest that hysteresis is controlled by the conformation of His438, a key residue in the catalytic triad of cholinesterases. Induction time may depend on the probability of His438 to adopt the operative conformation in the catalytic triad. The functional significance of ChE hysteresis is puzzling. However, the accepted view that proteins are in equilibrium between

  19. Immobilization of Chiral Ferrocenyl Ligands on Silica Gel and their Testing in Pd-catalyzed Allylic Substitution and Rh-catalyzed Hydrogenation

    Directory of Open Access Journals (Sweden)

    Duncan J. Macquarrie

    2005-07-01

    Full Text Available Five different silica gels containing two chiral ferrocenyl ligands were prepared by various synthetic routes and tested in an enantioselective Pd(0-catalyzed allylic substitution and Rh-catalyzed hydrogenation. All the prepared anchored ligands were characterized by porosimetry data, DRIFTS spectra, thermal data and AAS. The aim of the work was to compare the influence of the carrier, surface properties and immobilization strategy on the performance of the catalyst.

  20. Kinetic study on the acid-catalyzed hydrolysis of cellulose to levulinic acid

    NARCIS (Netherlands)

    Girisuta, B.; Janssen, L. P. B. M.; Heeres, H. J.

    2007-01-01

    A variety of interesting bulk chemicals is accessible by the acid-catalyzed hydrolysis of cellulose. An interesting example is levulinic acid, a versatile precursor for fuel additives, polymers, and resins. A detailed kinetic study on the acid-catalyzed hydrolysis of cellulose to levulinic acid is

  1. Towards a methanol economy: Zeolite catalyzed production of synthetic fuels

    DEFF Research Database (Denmark)

    Mentzel, Uffe Vie

    The main focus of this thesis is zeolite catalyzed conversion of oxygenates to hydrocarbon fuels and chemicals. Furthermore, conversion of ethane to higher hydrocarbons has also been studied. After a brief introduction to the concept of “the methanol economy” in the first chapter, the second...... chapter is a literature study of Mobil’s “methanol to hydrocarbons” (MTH) process, giving an overview of the history of the process, the nature of the employed catalysts, and the reaction mechanism. In the third chapter, a series of experiments concerning co conversion of ethane and methanol over...... a commercial H-ZSM-5 zeolite impregnated with gallium and/or molybdenum is described. The object was to investigate if the presence of methanol in the feed could enhance the conversion of ethane, but in all cases the opposite is observed; the presence of methanol actually suppresses the conversion of ethane...

  2. Multistep enzyme catalyzed reactions for unnatural amino acids.

    Science.gov (United States)

    D'Arrigo, Paola; Tessaro, Davide

    2012-01-01

    The use of unnatural amino acids, particularly synthetic α-amino acids, for modern drug discovery research requires the availability of enantiomerically pure isomers. Starting from a racemate, one single enantiomer can be obtained using a deracemization process. The two more common strategies of deracemization are those obtained by stereoinversion and by dynamic kinetic resolution. Both techniques will be here described using as a substrate the D,L-3-(2-naphthyl)-alanine, a non-natural amino acid: the first one employing a multi-enzymatic redox system, the second one combining an hydrolytic enzyme together with a base-catalyzed substrate racemization. In both cases, the final product, L-3-(2-naphthyl)alanine, is recovered with good yield and excellent enantiomeric excess.

  3. Palladium-catalyzed anti-Markovnikov oxidation of terminal alkenes.

    Science.gov (United States)

    Dong, Jia Jia; Browne, Wesley R; Feringa, Ben L

    2015-01-12

    The palladium-catalyzed oxidation of alkenes, the Wacker-Tsuji reaction, is undoubtedly a classic in organic synthesis and provides reliable access to methyl ketones from terminal alkenes under mild reaction conditions. Methods that switch the selectivity of the reaction to provide the aldehyde product are desirable because of the access they provide to a valuable functional group, however such methods are elusive. Herein we survey both the methods which have been developed recently in achieving such selectivity and discuss common features and mechanistic insight which offers promise in achieving the goal of a general method for anti-Markovnikov-selective olefin oxidations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. WILDCAT: a catalyzed D-D tokamak reactor

    Energy Technology Data Exchange (ETDEWEB)

    Evans, K. Jr.; Baker, C.C.; Brooks, J.N.

    1981-11-01

    WILDCAT is a conceptual design of a catalyzed D-D, tokamak, commercial, fusion reactor. WILDCAT utilizes the beneficial features of no tritium breeding, while not extrapolating unnecessarily from existing D-T designs. The reactor is larger and has higher magnetic fields and plasma pressures than typical D-T devices. It is more costly, but eliminates problems associated with tritium breeding and has tritium inventories and throughputs approximately two orders of magnitude less than typical D-T reactors. There are both a steady-state version with Alfven-wave current drive and a pulsed version. Extensive comparison with D-T devices has been made, and cost and safety analyses have been included. All of the major reactor systems have been worked out to a level of detail appropriate to a complete, conceptual design.

  5. Cobalt catalyzed hydroesterification of a wide range of olefins

    Energy Technology Data Exchange (ETDEWEB)

    Van Rensburg, H.; Hanton, M.; Tooze, R.P.; Foster, D.F. [Sasol Technology UK, St Andrews (United Kingdom)

    2011-07-01

    Petrochemical raw materials are an essential raw material for the production of detergents with a substantial portion of synthetic fatty alcohols being produced via hydroformylation of oil or coal derived olefins. Carbonylation processes other than hydroformylation have to date not been commercially employed for the production of fatty esters or alcohols. In this document we highlight the opportunities of converting olefins to esters using cobalt catalyzed alkoxycarbonylation. This process is highly versatile and applicable to a wide range of olefins, linear or branched, alpha or internal in combination with virtually any chain length primary or secondary alcohol allowing the synthesis of a diverse array of compounds such as ester ethoxylated surfactants, methyl branched detergents, lubricants and alkyl propanoates. Furthermore, alkoxycarbonylation of a broad olefin/paraffin hydrocarbon range could be used to produce the corresponding broad cut detergent alcohols. (orig.)

  6. Mg-catalyzed autoclave synthesis of aligned silicon carbide nanostructures.

    Science.gov (United States)

    Xi, Guangcheng; Liu, Yankuan; Liu, Xiaoyan; Wang, Xiaoqing; Qian, Yitai

    2006-07-27

    In this article, a novel magnesium-catalyzed co-reduction route was developed for the large-scale synthesis of aligned beta-SiC one-dimensional (1D) nanostructures at relative lower temperature (600 degrees C). By carefully controlling the reagent concentrations, we could synthesize beta-SiC rodlike and needlelike nanostructures. The possible growth mechanism of the as-synthesized beta-SiC 1D nanostructures has been investigated. The structure and morphology of the as-synthesized beta-SiC nanostructures are characterized using X-ray diffraction, Fourier transform infrared absorption, and scanning and transmission electron microscopes. Raman and photoluminescence properties are also investigated at room temperature. The as-synthesized beta-SiC nanostructures exhibit strong shape-dependent field emission properties. Corresponding to their shapes, the as-synthesized nanorods and nanoneedles display the turn-on fields of 12, 8.4, and 1.8 V/microm, respectively.

  7. Specific miRNA Stabilization by Gld2-Catalyzed Monoadenylation

    Directory of Open Access Journals (Sweden)

    Andrea D’Ambrogio

    2012-12-01

    Full Text Available MicroRNAs (miRNAs are small, noncoding RNAs that inhibit translation and promote mRNA decay. The levels of mature miRNAs are the result of different rates of transcription, processing, and turnover. The noncanonical polymerase Gld2 has been implicated in the stabilization of miR-122, possibly through catalyzing 3′ monoadenylation; however, there is little evidence that this relationship is one of cause and effect. Here, we biochemically characterize Gld2’s involvement in miRNA monoadenylation and its effect on miRNA stability. We find that Gld2 directly monoadenylates and stabilizes specific miRNA populations in human fibroblasts and that sensitivity to monoadenylation-induced stability depends on nucleotides in the miRNA 3′ end. These results establish a mechanism of miRNA stability and resulting posttranscriptional gene regulation.

  8. Rhenium-catalyzed deoxydehydration of diols and polyols.

    Science.gov (United States)

    Dethlefsen, Johannes R; Fristrup, Peter

    2015-03-01

    The substitution of platform chemicals of fossil origin by biomass-derived analogues requires the development of chemical transformations capable of reducing the very high oxygen content of biomass. One such reaction, which has received increasing attention within the past five years, is the rhenium-catalyzed deoxydehydration (DODH) of a vicinal diol into an alkene; this is a model system for abundant polyols like glycerol and sugar alcohols. The present contribution includes a review of early investigations of stoichiometric reactions involving rhenium, diols, and alkenes followed by a discussion of the various catalytic systems that have been developed with emphasis on the nature of the reductant, the substrate scope, and mechanistic investigations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Manganese-Catalyzed Upgrading of Ethanol into 1-Butanol.

    Science.gov (United States)

    Fu, Shaomin; Shao, Zhihui; Wang, Yujie; Liu, Qiang

    2017-08-30

    Biomass-derived ethanol is an important renewable feedstock. Its conversion into high-quality biofuels is a promising route to replace fossil resources. Herein, an efficient manganese-catalyzed Guerbet-type condensation reaction of ethanol to form 1-butanol was explored. This is the first example of upgrading ethanol into higher alcohols using a homogeneous non-noble-metal catalyst. This process proceeded selectively in the presence of a well-defined manganese pincer complex at the parts per million (ppm) level. The developed reaction represents a sustainable synthesis of 1-butanol with excellent turnover number (>110 000) and turnover frequency (>3000 h(-1)). Moreover, mechanistic studies including control experiments, NMR spectroscopy, and X-ray crystallography identified the essential role of the "N-H moiety" of the manganese catalysts and the major reaction intermediates related to the catalytic cycle.

  10. Calcium-catalyzed pyrolysis of lignocellulosic biomass components.

    Science.gov (United States)

    Case, Paige A; Truong, Chi; Wheeler, M Clayton; DeSisto, William J

    2015-09-01

    The present study examines the effect of calcium pretreatment on pyrolysis of individual lignocellulosic compounds. Previous work has demonstrated that the incorporation of calcium compounds with the feedstock prior to pyrolysis has a significant effect on the oxygen content and stability of the resulting oil. The aim of this work was to further explore the chemistry of calcium-catalyzed pyrolysis. Bench-scale pyrolysis of biomass constituents, including lignin, cellulose and xylan is performed and compared to the oils produced from pyrolysis of the same components after calcium pretreatment. The resulting oils were analyzed by quantitative GC-MS and SEC. These analyses, together with data collected from previous work provide evidence which was used to develop proposed reaction pathways for pyrolysis of calcium-pretreatment biomass. Copyright © 2015 Elsevier Ltd. All rights reserved.

  11. Lactam hydrolysis catalyzed by mononuclear metallo-ß-bactamases

    DEFF Research Database (Denmark)

    Olsen, Lars; Antony, J; Ryde, U

    2003-01-01

    Two central steps in the hydrolysis of lactam antibiotics catalyzed by mononuclear metallo-beta-lactamases, formation of the tetrahedral intermediate and its breakdown by proton transfer, are studied for model systems using the density functional B3LYP method. Metallo-beta-lactamases have two metal...... coordinating to the zinc ion. Potential proton shuttles from the second (unoccupied) metal-binding site (water, Asp, or Cys) are included in some calculations. The calculated reaction barrier for formation of the tetrahedral intermediate is 13 kcal/mol, close to what is observed experimentally for the rate......-limiting step. The barrier for the breakdown of the intermediate is low, 0-10 kcal/mol, if it is assisted by a water molecule or by a Cys or Asp model. Thus, the results indicate that proton transfer is not rate-limiting, and that any of the residues from the second metal site may function as proton shuttle...

  12. Quinone-Catalyzed Selective Oxidation of Organic Molecules.

    Science.gov (United States)

    Wendlandt, Alison E; Stahl, Shannon S

    2015-12-01

    Quinones are common stoichiometric reagents in organic chemistry. Para-quinones with high reduction potentials, such as DDQ and chloranil, are widely used and typically promote hydride abstraction. In recent years, many catalytic applications of these methods have been achieved by using transition metals, electrochemistry, or O2 to regenerate the oxidized quinone in situ. Complementary studies have led to the development of a different class of quinones that resemble the ortho-quinone cofactors in copper amine oxidases and mediate the efficient and selective aerobic and/or electrochemical dehydrogenation of amines. The latter reactions typically proceed by electrophilic transamination and/or addition-elimination reaction mechanisms, rather than hydride abstraction pathways. The collective observations show that the quinone structure has a significant influence on the reaction mechanism and has important implications for the development of new quinone reagents and quinone-catalyzed transformations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. FBH1 Catalyzes Regression of Stalled Replication Forks

    Directory of Open Access Journals (Sweden)

    Kasper Fugger

    2015-03-01

    Full Text Available DNA replication fork perturbation is a major challenge to the maintenance of genome integrity. It has been suggested that processing of stalled forks might involve fork regression, in which the fork reverses and the two nascent DNA strands anneal. Here, we show that FBH1 catalyzes regression of a model replication fork in vitro and promotes fork regression in vivo in response to replication perturbation. Cells respond to fork stalling by activating checkpoint responses requiring signaling through stress-activated protein kinases. Importantly, we show that FBH1, through its helicase activity, is required for early phosphorylation of ATM substrates such as CHK2 and CtIP as well as hyperphosphorylation of RPA. These phosphorylations occur prior to apparent DNA double-strand break formation. Furthermore, FBH1-dependent signaling promotes checkpoint control and preserves genome integrity. We propose a model whereby FBH1 promotes early checkpoint signaling by remodeling of stalled DNA replication forks.

  14. Enantioselective aldol reactions catalyzed by chiral phosphine oxides.

    Science.gov (United States)

    Kotani, Shunsuke; Sugiura, Masaharu; Nakajima, Makoto

    2013-08-01

    The development of enantioselective aldol reactions catalyzed by chiral phosphine oxides is described. The aldol reactions presented herein do not require the prior preparation of the masked enol ethers from carbonyl compounds as aldol donors. The reactions proceed through a trichlorosilyl enol ether intermediate, formed in situ from carbonyl compounds, which then acts as the aldol donor. Phosphine oxides activate the trichlorosilyl enol ethers to afford the aldol adducts with high stereoselectivities. This procedure was used to realize a directed cross-aldol reaction between ketones and two types of double aldol reactions (a reaction at one/two α position(s) of a carbonyl group) with high diastereo- and enantioselectivities. Copyright © 2013 The Chemical Society of Japan and Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Urea- and Thiourea-Catalyzed Aminolysis of Carbonates.

    Science.gov (United States)

    Blain, Marine; Yau, Honman; Jean-Gérard, Ludivine; Auvergne, Rémi; Benazet, Dominique; Schreiner, Peter R; Caillol, Sylvain; Andrioletti, Bruno

    2016-08-23

    The aminolysis of (poly)carbonates by (poly)amines provides access to non-isocyanate polyurethanes (NIPUs) that are toxic-reagent-free analogues of polyurethanes (PUs). Owing to their low reactivity, the ring opening of cyclic carbonates requires the use of a catalyst. Herein, we report that the more available and cheaper ureas could advantageously be used for catalyzing the formation of NIPUs at the expense of the thiourea analogues. In addition, we demonstrate a medium-range pKa of the (thio)urea and an unqeual substitution pattern is critical for controlling the efficiency of the carbonate opening. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Vanadium bromoperoxidase-catalyzed biosynthesis of halogenated marine natural products.

    Science.gov (United States)

    Carter-Franklin, Jayme N; Butler, Alison

    2004-11-24

    Marine red algae (Rhodophyta) are a rich source of bioactive halogenated natural products. The biogenesis of the cyclic halogenated terpene marine natural products, in particular, has attracted sustained interest in part because terpenes are the biogenic precursors of many bioactive metabolites. The first enzymatic asymmetric bromination and cyclization of a terpene, producing marine natural products isolated from red algae, is reported. Vanadium bromoperoxidase (V-BrPO) isolated from marine red algae (species of Laurencia, Plocamium, Corallina) catalyzes the bromination of the sesquiterpene (E)-(+)-nerolidol producing alpha-, beta-, and gamma-snyderol and (+)-3beta-bromo-8-epicaparrapi oxide. alpha-Snyderol, beta-snyderol, and (+)-3beta-bromo-8-epicaparrapi oxide have been isolated from Laurencia obtusa, and each have also been isolated from other species of marine red algae. gamma-Snyderol is a proposed intermediate in other bicyclo natural products. Single diastereomers of beta-snyderol, gamma-snyderol, and mixed diastereomers of (+)-3beta-bromo-8-epicaparrapi oxide (de = 20-25%) are produced in the enzyme reaction, whereas two diastereomers of these compounds are formed in the synthesis with 2,4,4,6-tetrabromocyclohexa-2,5-dienone (TBCO). V-BrPO likely functions by catalyzing the two-electron oxidation of bromide ion by hydrogen peroxide producing a bromonium ion or equivalent in the active site that brominates one face of the terminal olefin of nerolidol. These results establish V-BrPO's role in the biosynthesis of brominated cyclic sesquiterpene structures from marine red algae for the first time.

  17. Hemoglobin and red blood cells catalyze atom transfer radical polymerization.

    Science.gov (United States)

    Silva, Tilana B; Spulber, Mariana; Kocik, Marzena K; Seidi, Farzad; Charan, Himanshu; Rother, Martin; Sigg, Severin J; Renggli, Kasper; Kali, Gergely; Bruns, Nico

    2013-08-12

    Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen, but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity, i.e., they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N-isopropylacrylamide (NIPAAm), poly(ethylene glycol) methyl ether acrylate (PEGA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were polymerized using organobromine initiators and the reducing agent ascorbic acid in acidic aqueous solution. In order to avoid chain transfer from polymer radicals to Hb's cysteine residues, the accessible cysteines were blocked by a reaction with a maleimide. The formation of polymers with bromine chain ends, relatively low polydispersity indices (PDI), first order kinetics and an increase in the molecular weight of poly(PEGA) and poly(PEGMA) upon conversion indicate that control of the polymerization by Hb occurred via reversible atom transfer between the protein and the growing polymer chain. For poly(PEGA) and poly(PEGMA), the reactions proceeded with a good to moderate degree of control. Sodium dodecyl sulfate (SDS) gel electrophoresis, circular dichroism spectroscopy, and time-resolved ultraviolet-visible (UV-vis) spectroscopy revealed that the protein was stable during polymerization, and only underwent minor conformational changes. As Hb and erythrocytes are readily available, environmentally friendly, and nontoxic, their ATRPase activity is a useful tool for synthetic polymer chemistry. Moreover, this novel activity enhances the understanding of Hb's redox chemistry in the presence of organobromine compounds.

  18. Gold-Catalyzed Cyclizations of Alkynol-Based Compounds: Synthesis of Natural Products and Derivatives

    Directory of Open Access Journals (Sweden)

    Pedro Almendros

    2011-09-01

    Full Text Available The last decade has witnessed dramatic growth in the number of reactions catalyzed by gold complexes because of their powerful soft Lewis acid nature. In particular, the gold-catalyzed activation of propargylic compounds has progressively emerged in recent years. Some of these gold-catalyzed reactions in alkynes have been optimized and show significant utility in organic synthesis. Thus, apart from significant methodology work, in the meantime gold-catalyzed cyclizations in alkynol derivatives have become an efficient tool in total synthesis. However, there is a lack of specific review articles covering the joined importance of both gold salts and alkynol-based compounds for the synthesis of natural products and derivatives. The aim of this Review is to survey the chemistry of alkynol derivatives under gold-catalyzed cyclization conditions and its utility in total synthesis, concentrating on the advances that have been made in the last decade, and in particular in the last quinquennium.

  19. An mRNA is capped by a 2', 5' lariat catalyzed by a group I-like ribozyme

    DEFF Research Database (Denmark)

    Nielsen, Henrik; Westhof, Eric; Johansen, Steinar

    2005-01-01

    Twin-ribozyme introns are formed by two ribozymes belonging to the group I family and occur in some ribosomal RNA transcripts. The group I-like ribozyme, GIR1, liberates the 5' end of a homing endonuclease messenger RNA in the slime mold Didymium iridis. We demonstrate that this cleavage occurs...

  20. Rh(I)-Catalyzed Direct Arylation of Pyridines and Quinolines

    Energy Technology Data Exchange (ETDEWEB)

    Berman, Ashley; Lewis, Jared; Bergman, Robert; Ellman, Jonathan

    2008-07-29

    The pyridine and quinoline nuclei are privileged scaffolds that occupy a central role in many medicinally relevant compounds. Consequently, methods for their expeditious functionalization are of immediate interest. However, despite the immense importance of transition-metal catalyzed cross-coupling for the functionalization of aromatic scaffolds, general solutions for coupling 2-pyridyl organometallics with aryl halides have only recently been presented. Direct arylation at the ortho position of pyridine would constitute an even more efficient approach because it eliminates the need for the stoichiometric preparation and isolation of 2-pyridyl organometallics. Progress towards this goal has been achieved by activation of the pyridine nucleus for arylation via conversion to the corresponding pyridine N-oxide or N-iminopyridinium ylide. However, this approach necessitates two additional steps: activation of the pyridine or quinoline starting material, and then unmasking the arylated product. The use of pyridines directly would clearly represent the ideal situation both in terms of cost and simplicity. We now wish to document our efforts in this vein, culminating in an operationally simple Rh(I)-catalyzed direct arylation of pyridines and quinolines. We recently developed an electron-rich Rh(I) system for catalytic alkylation at the ortho position of pyridines and quinolines with alkenes. Therefore, we initially focused our attention on the use of similarly electron-rich Rh(I) catalysts for the proposed direct arylation. After screening an array of electron-rich phosphine ligands and Rh(I) salts, only marginal yields (<20%) of the desired product were obtained. Much more efficient was an electron-poor Rh(I) system with [RhCl(CO){sub 2}]{sub 2} as precatalyst (Table 1). For the direct arylation of picoline with 3,5-dimethyl-bromobenzene, addition of P(OiPr){sub 3} afforded a promising 40% yield of the cross coupled product 1a (entry 1). The exclusion of phosphite

  1. Recent advances in osmium-catalyzed hydrogenation and dehydrogenation reactions.

    Science.gov (United States)

    Chelucci, Giorgio; Baldino, Salvatore; Baratta, Walter

    2015-02-17

    CONSPECTUS: A current issue in metal-catalyzed reactions is the search for highly efficient transition-metal complexes affording high productivity and selectivity in a variety of processes. Moreover, there is also a great interest in multitasking catalysts that are able to efficiently promote different organic transformations by careful switching of the reaction parameters, such as temperature, solvent, and cocatalyst. In this context, osmium complexes have shown the ability to catalyze efficiently different types of reactions involving hydrogen, proving at the same time high thermal stability and simple synthesis. In the catalytic reduction of C═X (X = O, N) bonds by both hydrogenation (HY) and transfer hydrogenation (TH) reactions, the most interest has been focused on homogeneous systems based on rhodium, iridium, and in particular ruthenium catalysts, which have proved to catalyze chemo- and stereoselective hydrogenations with remarkable efficiency. By contrast, osmium catalysts have received much less attention because they are considered less active on account of their slower ligand exchange kinetics. Thus, this area remained almost neglected until recent studies refuted these prejudices. The aim of this Account is to highlight the impressive developments achieved over the past few years by our and other groups on the design of new classes of osmium complexes and their applications in homogeneous catalytic reactions involving the hydrogenation of carbon-oxygen and carbon-nitrogen bonds by both HY and TH reactions as well as in alcohol deydrogenation (DHY) reactions. The work described in this Account demonstrates that osmium complexes are emerging as powerful catalysts for asymmetric and non-asymmetric syntheses, showing a remarkably high catalytic activity in HY and TH reactions of ketones, aldehydes, imines, and esters as well in DHY reactions of alcohols. Thus, for instance, the introduction of ligands with an NH function, possibly in combination with a

  2. Flame Synthesis Used to Create Metal-Catalyzed Carbon Nanotubes

    Science.gov (United States)

    VanderWal, Randy L.

    2001-01-01

    Metal-catalyzed carbon nanotubes are highly ordered carbon structures of nanoscale dimensions. They may be thought of as hollow cylinders whose walls are formed by single atomic layers of graphite. Such cylinders may be composed of many nested, concentric atomic layers of carbon or only a single layer, the latter forming a single-walled carbon nanotube. This article reports unique results using a flame for their synthesis. Only recently were carbon nanotubes discovered within an arc discharge and recognized as fullerene derivatives. Today metal-catalyzed carbon nanotubes are of great interest for many reasons. They can be used as supports for the metal catalysts like those found in catalytic converters. Open-ended nanotubes are highly desirable because they can be filled by other elements, metals or gases, for battery and fuel cell applications. Because of their highly crystalline structure, they are significantly stronger than the commercial carbon fibers that are currently available (10 times as strong as steel but possessing one-sixth of the weight). This property makes them highly desirable for strengthening polymer and ceramic composite materials. Current methods of synthesizing carbon nanotubes include thermal pyrolysis of organometallics, laser ablation of metal targets within hydrocarbon atmospheres at high temperatures, and arc discharges. Each of these methods is costly, and it is unclear if they can be scaled for the commercial synthesis of carbon nanotubes. In contrast, flame synthesis is an economical means of bulk synthesis of a variety of aerosol materials such as carbon black. Flame synthesis of carbon nanotubes could potentially realize an economy of scale that would enable their use in common structural materials such as car-body panels. The top figure is a transmission electron micrograph of a multiwalled carbon nanotube. The image shows a cross section of the atomic structure of the nanotube. The dark lines are individual atomic layer planes of

  3. Bonding by Hydroxide-Catalyzed Hydration and Dehydration

    Science.gov (United States)

    Gwo, Dz-Hung

    2008-01-01

    A simple, inexpensive method for bonding solid objects exploits hydroxide-catalyzed hydration and dehydration to form silicate-like networks in thin surface and interfacial layers between the objects. The method can be practiced at room temperature or over a wide range of temperatures. The method was developed especially to enable the formation of precise, reliable bonds between precise optical components. The bonds thus formed exhibit the precision and transparency of bonds formed by the conventional optical-contact method and the strength and reliability of high-temperature frit bonds. The method also lends itself to numerous non-optical applications in which there are requirements for precise bonds and/or requirements for bonds, whether precise or imprecise, that can reliably withstand severe environmental conditions. Categories of such non-optical applications include forming composite materials, coating substrates, forming laminate structures, and preparing objects of defined geometry and composition. The method is applicable to materials that either (1) can form silicate-like networks in the sense that they have silicate-like molecular structures that are extensible into silicate-like networks or (2) can be chemically linked to silicate-like networks by means of hydroxide-catalyzed hydration and dehydration. When hydrated, a material of either type features surface hydroxyl (-OH) groups. In this method, a silicate-like network that bonds two substrates can be formed either by a bonding material alone or by the bonding material together with material from either or both of the substrates. Typically, an aqueous hydroxide bonding solution is dispensed and allowed to flow between the mating surfaces by capillary action. If the surface figures of the substrates do not match precisely, bonding could be improved by including a filling material in the bonding solution. Preferably, the filling material should include at least one ingredient that can be hydrated to

  4. Synthesis of Pyridobenzazepines Using a One-Pot Rh/Pd-Catalyzed Process.

    Science.gov (United States)

    Lam, Heather; Tsoung, Jennifer; Lautens, Mark

    2017-06-16

    In recent years, our group has been developing multicatalytic reactions for the synthesis of biologically relevant heterocyclic compounds. An efficient dual-metal catalyzed reaction of electron-deficient o-chlorovinylpyridines with o-aminophenylboronic esters to access pyridobenzazepines is described. Combining a RhI-catalyzed arylation followed by a Pd0-catalyzed C-N coupling, in a one-pot procedure, provides a simplified method to access heterocycles without workup and purification after each step. The substrate scope encompasses a variety of N-H and N-alkylated pyridobenzazepine variants with yields up to 93%.

  5. Kinetics of Platinum-Catalyzed Decomposition of Hydrogen Peroxide

    Science.gov (United States)

    Vetter, Tiffany A.; Colombo, D. Philip, Jr.

    2003-07-01

    CIBA Vision Corporation markets a contact lens cleaning system that consists of an AOSEPT disinfectant solution and an AOSEPT lens cup. The disinfectant is a buffered 3.0% m/v hydrogen peroxide solution and the cup includes a platinum-coated AOSEPT disc. The hydrogen peroxide disinfects by killing bacteria, fungi, and viruses found on the contact lenses. Because the concentration of hydrogen peroxide needed to disinfect is irritating to eyes, the hydrogen peroxide needs to be neutralized, or decomposed, before the contact lenses can be used again. A general chemistry experiment is described where the kinetics of the catalyzed decomposition of the hydrogen peroxide are studied by measuring the amount of oxygen generated as a function of time. The order of the reaction with respect to the hydrogen peroxide, the rate constant, and the energy of activation are determined. The integrated rate law is used to determine the time required to decompose the hydrogen peroxide to a concentration that is safe for eyes.

  6. Catalyzed steam gasification of biomass. Phase II. Final research report

    Energy Technology Data Exchange (ETDEWEB)

    Hooverman, R.H.

    1979-05-01

    The Wright-Malta gasification process is characterized by low-temperature, catalyzed steam gasification in a pressurized rotary kiln. Fresh biomass moves slowly and continuously through the kiln, where it is gradually heated to around 1200/sup 0/F in an atmosphere of 300 psi steam. During its traverse, pyrolysis and reaction of steam with the nascent char convert nearly all of the organic solids to the gaseous phase. The volatile pyrolysis products pass through the kiln co-currently with the solids and are similarly cracked and steam-reformed within the kiln to fixed gases. Heat for the gasification process is provided by sensible heat recovered from the product gas and the wood decomposition exotherm, making the process inherently very energy-efficient. This report summarizes the work done during the experimental, laboratory-scale phase of development of the W-M biomass gasification process. Two bench-scale experimental gasifiers were constructed and tested: the ''minikiln'', a batch-feed, rotating autoclave; and the ''biogasser'', a stationary, continuous-feed, tubular reactor with zone heating and auger transport. Studies were carried out in these reactors to determine the extent of conversion of biomass solids to gas, and the makeup of the product gas, over a wide range of process conditions. The process variables that were investigated included reactor pressure and temperature, catalyst type and concentration, moisture content and type of biomass feed.

  7. Clay-catalyzed reactions of coagulant polymers during water chlorination

    Science.gov (United States)

    Lee, J.-F.; Liao, P.-M.; Lee, C.-K.; Chao, H.-P.; Peng, C.-L.; Chiou, C.T.

    2004-01-01

    The influence of suspended clay/solid particles on organic-coagulant reactions during water chlorination was investigated by analyses of total product formation potential (TPFP) and disinfection by-product (DBP) distribution as a function of exchanged clay cation, coagulant organic polymer, and reaction time. Montmorillonite clays appeared to act as a catalytic center where the reaction between adsorbed polymer and disinfectant (chlorine) was mediated closely by the exchanged clay cation. The transition-metal cations in clays catalyzed more effectively than other cations the reactions between a coagulant polymer and chlorine, forming a large number of volatile DBPs. The relative catalytic effects of clays/solids followed the order Ti-Mont > Fe-Mont > Cu-Mont > Mn-Mont > Ca-Mont > Na-Mont > quartz > talc. The effects of coagulant polymers on TPFP follow the order nonionic polymer > anionic polymer > cationic polymer. The catalytic role of the clay cation was further confirmed by the observed inhibition in DBP formation when strong chelating agents (o-phenanthroline and ethylenediamine) were added to the clay suspension. Moreover, in the presence of clays, total DBPs increased appreciably when either the reaction time or the amount of the added clay or coagulant polymer increased. For volatile DBPs, the formation of halogenated methanes was usually time-dependent, with chloroform and dichloromethane showing the greatest dependence. ?? 2003 Elsevier Inc. All rights reserved.

  8. Cu-catalyzed enantioselective allylic alkylation with organolithium reagents.

    Science.gov (United States)

    Hornillos, Valentín; Guduguntla, Sureshbabu; Fañanás-Mastral, Martín; Pérez, Manuel; Bos, Pieter H; Rudolph, Alena; Harutyunyan, Syuzanna R; Feringa, Ben L

    2017-03-01

    This protocol describes a method for the catalytic enantioselective synthesis of tertiary and quaternary carbon stereogenic centers, which are widely present in pharmaceutical and natural products. The method is based on the direct reaction between organolithium compounds, which are cheap, readily available and broadly used in chemical synthesis, and allylic electrophiles, using chiral copper catalysts. The methodology involves the asymmetric allylic alkylation (AAA) of allyl bromides, chlorides and ethers with organolithium compounds using catalyst systems based on Cu-Taniaphos and Cu-phosphoramidites. The protocol contains a complete description of the reaction setup, a method based on 1 H-NMR, gas chromatography-mass spectrometry (GC-MS) and chiral HPLC for assaying the regioselectivity and enantioselectivity of the product, and isolation, purification and characterization procedures. Six Cu-catalyzed AAA reactions between different organolithium reagents and allylic systems are detailed in the text as representative examples of these procedures. These reactions proceed within 1-10 h, depending on the nature of the allylic substrate (bromide, chloride, or ether and disubstituted or trisubstituted) or the chiral ligand used (Taniaphos or phosphoramidite). However, the entire protocol, including workup and purification, generally requires an additional 4-7 h to complete.

  9. Iodine-Catalyzed Prins Cyclization of Homoallylic Alcohols and Aldehydes

    Directory of Open Access Journals (Sweden)

    Luiz F. Silva

    2013-09-01

    Full Text Available The iodine-catalyzed Prins cyclization of homoallylic alcohols and aldehydes was investigated under metal-free conditions and without additives. Anhydrous conditions and inert atmosphere are not required. The reaction of 2-(3,4-dihydronaphthalen-1-ylpropan-1-ol and 21 aldehydes (aliphatic and aromatic in CH2Cl2 in the presence of 5 mol % of iodine gave 1,4,5,6-tetrahydro-2H-benzo[f]isochromenes in 54%–86% yield. Under similar conditions, the Prins cyclization of six alcohols containing an endocyclic double bond (primary, secondary, or tertiary led to dihydropyrans in 52%–91% yield. The acyclic homoallylic alcohols gave 4-iodo-tetrahydropyran in 29%–41% yield in the presence of 50 mol % of iodine. This type of substrate is the main limitation of the methodology. The relative configuration of the products was assigned by NMR and X-ray analysis. The mechanism and the ratio of the products are discussed, based on DFT calculations.

  10. Cyanation of arenes via iridium-catalyzed borylation.

    Science.gov (United States)

    Liskey, Carl W; Liao, Xuebin; Hartwig, John F

    2010-08-25

    We report a method to conduct one-pot meta cyanation of arenes by iridium-catalyzed C-H borylation and copper-mediated cyanation of the resulting arylboronate esters. This process relies on a method to conduct the cyanation of arylboronic esters, and conditions for this new transformation are reported. Conditions for the copper-mediated cyanation of arylboronic acids are also reported. By the resulting sequence of borylation and cyanation, 1,3-disubstituted and 1,2,3-trisubstituted arenes and heteroarenes containing halide, ketone, ester, amide, and protected alcohol functionalities are converted to the corresponding meta-substituted aryl nitriles. The utility of this methodology is demonstrated through the conversion of a protected 2,6-disubstituted phenol to 4-cyano-2,6-dimethylphenol, which is an intermediate in the synthesis of the pharmaceutical etravirine. The utility of the method is further demonstrated by the conversion of 3-chloro-5-methylbenzonitrile, produced through the one-pot C-H borylation and cyanation sequence, to the corresponding 3,5-disubstituted aldehydes, ketones, amides, carboxylic acids, tetrazoles, and benzylamines.

  11. Base-catalyzed depolymerization of lignin : separation of monomers

    Energy Technology Data Exchange (ETDEWEB)

    Vigneault, A. [Sherbrooke Univ., PQ (Canada). Dept. of Chemical Engineering; Johnson, D.K. [National Renewable Energy Laboratory, Golden, CO (United States); Chornet, E. [Sherbrooke Univ., PQ (Canada). Dept. of Chemical Engineering; National Renewable Energy Laboratory, Golden, CO (United States)

    2007-12-15

    Biofuels produced from residual lignocellulosic biomass range from ethanol to biodiesel. The use of lignin for the production of alternate biofuels and green chemicals has been studied with particular emphasis on the structure of lignin and its oxyaromatic nature. In an effort to fractionate lignocellulosic biomass and valorize specific constitutive fractions, the authors developed a strategy for the separation of 12 added value monomers produced during the hydrolytic base catalyzed depolymerization (BCD) of a Steam Exploded Aspen Lignin. The separation strategy was similar to vanillin purification to obtain pure monomers, but combining more steps after the lignin depolymerization such as acidification, batch liquid-liquid-extraction (LLE), followed by vacuum distillation, liquid chromatography (LC) and crystallization. The purpose was to develop basic data for an industrial size process flow diagram, and to evaluate both the monomer losses during the separation and the energy requirements. Experimentally testing of LLE, vacuum distillation and flash LC in the laboratory showed that batch vacuum distillation produced up to 4 fractions. Process simulation revealed that a series of 4 vacuum distillation columns could produce 5 distinct monomer streams, of which 3 require further chromatography and crystallization operations for purification. 22 refs., 4 tabs., 8 figs.

  12. Broadening the scope of glycosyltransferase-catalyzed sugar nucleotide synthesis.

    Science.gov (United States)

    Gantt, Richard W; Peltier-Pain, Pauline; Singh, Shanteri; Zhou, Maoquan; Thorson, Jon S

    2013-05-07

    We described the integration of the general reversibility of glycosyltransferase-catalyzed reactions, artificial glycosyl donors, and a high throughput colorimetric screen to enable the engineering of glycosyltransferases for combinatorial sugar nucleotide synthesis. The best engineered catalyst from this study, the OleD Loki variant, contained the mutations P67T/I112P/T113M/S132F/A242I compared with the OleD wild-type sequence. Evaluated against the parental sequence OleD TDP16 variant used for screening, the OleD Loki variant displayed maximum improvements in k(cat)/K(m) of >400-fold and >15-fold for formation of NDP-glucoses and UDP-sugars, respectively. This OleD Loki variant also demonstrated efficient turnover with five variant NDP acceptors and six variant 2-chloro-4-nitrophenyl glycoside donors to produce 30 distinct NDP-sugars. This study highlights a convenient strategy to rapidly optimize glycosyltransferase catalysts for the synthesis of complex sugar nucleotides and the practical synthesis of a unique set of sugar nucleotides.

  13. Production of Chemoenzymatic Catalyzed Monoepoxide Biolubricant: Optimization and Physicochemical Characteristics

    Directory of Open Access Journals (Sweden)

    Jumat Salimon

    2012-01-01

    Full Text Available Linoleic acid (LA is converted to per-carboxylic acid catalyzed by an immobilized lipase from Candida antarctica (Novozym 435. This per-carboxylic acid is only intermediate and epoxidized itself in good yields and almost without consecutive reactions. Monoepoxide linoleic acid 9(12-10(13-monoepoxy 12(9-octadecanoic acid (MEOA was optimized using D-optimal design. At optimum conditions, higher yield% (82.14 and medium oxirane oxygen content (OOC (4.91% of MEOA were predicted at 15 μL of H2O2, 120 mg of Novozym 435, and 7 h of reaction time. In order to develop better-quality biolubricants, pour point (PP, flash point (FP, viscosity index (VI, and oxidative stability (OT were determined for LA and MEOA. The results showed that MEOA exhibited good low-temperature behavior with PP of −41°C. FP of MEOA increased to 128°C comparing with 115°C of LA. In a similar fashion, VI for LA was 224 generally several hundred centistokes (cSt more viscous than MEOA 130.8. The ability of a substance to resist oxidative degradation is another important property for biolubricants. Therefore, LA and MEOA were screened to measure their OT which was observed at 189 and 168°C, respectively.

  14. Thinking Differently: Catalyzing Innovation in Healthcare and Beyond.

    Science.gov (United States)

    Samet, Kenneth A; Smith, Mark S

    2016-01-01

    Convenience, value, access, and choice have become the new expectations of consumers seeking care. Incorporating these imperatives and navigating an expanded competitive landscape are necessary for the success of healthcare organizations-today and in the future-and require thinking differently than in the past.Innovation must be a central strategy for clinical and business operations to be successful. However, the currently popular concept of innovation is at risk of losing its power and meaning unless deliberate and focused action is taken to define it, adopt it, embrace it, and embed it in an organization's culture. This article details MedStar Health's blueprint for establishing the MedStar Institute for Innovation (MI2), which involved recognizing the sharpened need for innovation, creating a single specific entity to catalyze innovation across the healthcare organization and community, discovering the untapped innovation energy already residing in its employee base, and moving nimbly into the white space of possibility.Drawing on MedStar's experience with MI2, we offer suggestions in the following areas for implementing an innovation institute in a large healthcare system:We offer healthcare and business leaders a playbook for identifying and unleashing innovation in their organizations, at a time when innovation is at an increased risk of being misunderstood or misdirected but remains absolutely necessary for healthcare systems and organizations to flourish in the future.

  15. Muon catalyzed fusion in 3-K solid deuterium

    Energy Technology Data Exchange (ETDEWEB)

    Knowles, P.E.; Beer, G.A.; Mason, G.R.; Porcelli, T.A. [Department of Physics, University of Victoria, Victoria, British Columbia, V8W2Y2 (CANADA); Adamczak, A. [Institute of Nuclear Physics, Radzikowskiego 152, 31-342, Krakow (Poland); Bailey, J.M. [Chester Technology, 15 Farbaily Close, Chester CH47QH (England); Beveridge, J.L.; Marshall, G.M.; Olin, A. [TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T2A3 (CANADA); Fujiwara, M.C. [Department of Physics, University of British Columbia, Vancouver British Columbia, V6T2A6 (CANADA); Huber, T.M. [Department of Physics, Gustavus Adolphus College, St. Peter, Minnesota 56082 (United States); Jacot-Guillarmod, R.; Mulhauser, F. [Institut de Physique, Universite de Fribourg, CH-1700 Fribourg (Switzerland); Kammel, P.; Zmeskal, J. [Institute for Medium Energy Physics, Austrian Academy of Sciences, A-1090 Vienna (Austria); Kim, S.K. [Department of Physics, Jeonbuk National University, Jeonju City 560-756, South (Korea); Kunselman, A.R. [Department of Physics, University of Wyoming, Laramie, Wyoming 82071 (United States); Martoff, C.J. [Department of Physics, Temple University, Philadelphia, Pennsylvania 19122 (United States); Petitjean, C. [Paul Scherrer Institut, CH-5232 Villigen (Switzerland)

    1997-09-01

    Muon catalyzed fusion in deuterium traditionally has been studied in gaseous and liquid targets. The TRIUMF solid-hydrogen-layer target system has been used to study the fusion reaction rates in the solid phase of D{sub 2} at a target temperature of 3 K. Products of two distinct branches of the reaction were observed: neutrons by a liquid organic scintillator and protons by a silicon detector located inside the target system. The effective molecular formation rate from the upper hyperfine state of {mu}d and the hyperfine transition rate have been measured: {tilde {lambda}}{sub (3)/(2)}=2.71(7){sub stat}(32){sub syst}{mu}s{sup {minus}1} and {tilde {lambda}}{sub (3)/(2)(1)/(2)}=34.2(8){sub stat}(1){sub syst}{mu}s{sup {minus}1}. The molecular formation rate is consistent with other recent measurements, but not with the theory for isolated molecules. The discrepancy may be due to incomplete thermalization, an effect that was investigated by Monte Carlo calculations. Information on branching ratio parameters for the s and p wave d+d nuclear interaction has been extracted. {copyright} {ital 1997} {ital The American Physical Society}

  16. A review on production of biodiesel using catalyzed transesterification

    Science.gov (United States)

    Dash, Santosh Kumar; Lingfa, Pradip

    2017-07-01

    Biodiesel is arguably an important fuel for compression ignition engine as far as sustainability and environmental issues are concerned. It can be produced from both edible and non-edible vegetable oils and animal fats. Owing to higher viscosity, the utilization of crude vegetable oil is not advisable as it results engine failure. For reducing the viscosity and improving the other fuel characteristics comparable to that of diesel fuel, different approaches have been developed. However, transesterification process is very reliable, less costly and easy method compared to other methods. Due to more free fatty acids content in most of the non-edible vegetable oils, a pretreatment is employed to convert the acids to ester, then transesterified with suitable alcohol. Primarily yield of biodiesel depends upon the molar ratio of oil/alcohol, reaction temperature, reaction time, amount of catalyst, type of catalyst, stirring speed. Both homogeneous and heterogeneous catalysts are used for synthesis purposes. Heterogeneous catalysts are less costly, environmental benign and can be derived from natural resources. Enzymatic catalysts are more environmental benign than heterogeneous catalysts but are costly, which hinders its widespread research and utilization. This article reviews the results of prominent works and researches in the field of production of biodiesel via catalyzed transesterification process.

  17. Polycyclization Enabled by Relay Catalysis: One-Pot Manganese-Catalyzed C-H Allylation and Silver-Catalyzed Povarov Reaction.

    Science.gov (United States)

    Chen, Shi-Yong; Li, Qingjiang; Liu, Xu-Ge; Wu, Jia-Qiang; Zhang, Shang-Shi; Wang, Honggen

    2017-06-09

    In this study, a Mn I /Ag I -based relay catalysis process is described for the one-pot synthesis of polycyclic products by a formal [3+2] and [4+2] cycloaddition reaction cascade. A manganese(I) complex catalyzed the first example of directed C-H allylation with allenes, setting the stage for an in situ Povarov cyclization catalyzed by silver(I). The reaction proceeds with high bond-forming efficiency (three C-C bonds), broad substrate scope, high regio- and stereoselectivity, and 100 % atom economy. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Total Synthesis of Enantiopure (+)-γ -Lycorane Using Highly Efficient Pd-Catalyzed Asymmetric Allylic Alkylation

    Science.gov (United States)

    Chapsal, Bruno D.; Ojima, Iwao

    2008-01-01

    Highly efficient short total synthesis of γ -lycorane (>99% ee, 41% overall yield) was achieved by using the asymmetric allylic alkylation in the key step catalyzed by palladium complexes with novel chiral biphenol-based monodentate phosphoramidite ligands. PMID:16562900

  19. Total Synthesis of Enantiopure (+)-γ -Lycorane Using Highly Efficient Pd-Catalyzed Asymmetric Allylic Alkylation

    OpenAIRE

    Chapsal, Bruno D.; OJIMA, IWAO

    2006-01-01

    Highly efficient short total synthesis of γ -lycorane (>99% ee, 41% overall yield) was achieved by using the asymmetric allylic alkylation in the key step catalyzed by palladium complexes with novel chiral biphenol-based monodentate phosphoramidite ligands.

  20. Oxovanadium(v)-catalyzed oxidative biaryl synthesis from organoborate under O2.

    Science.gov (United States)

    Mizuno, Hidenori; Sakurai, Hidehiro; Amaya, Toru; Hirao, Toshikazu

    2006-12-28

    Oxidative ligand coupling of organoborates was catalyzed by VO(OEt)Cl(2) under oxygen atmosphere, which provides a versatile method for the selective synthesis of symmetrical or unsymmetrical biaryls.

  1. Heterogeneous base-catalyzed methanolysis of vegetable oils: State of art

    Directory of Open Access Journals (Sweden)

    Miladinović Marija R.

    2010-01-01

    Full Text Available Today, homogeneous base-catalyzed methanolysis is most frequently used method for industrial biodiesel production. High requirements for the quality of feedstocks and the problems related to a huge amount of wastewaters have led to the development of novel biodiesel production technologies. Among them, the most important is heterogeneous base-catalyzed methanolysis, which has been intensively investigated in the last decade in order to develop new catalytic systems, to optimize the reaction conditions and to recycle catalysts. These studies are a base for developing continuous biodiesel production on industrial scale in near future. The present work summarizes up-to-date studies on biodiesel production by heterogeneous base-catalyzed methanolysis. The main goals were to point out the application of different base compounds as catalysts, the methods of catalyst preparation, impregnation on carriers and recycling as well as the possibilities to improve existing base-catalyzed biodiesel production processes and to develop novel ones.

  2. on the elementary steps of acid zeolite catalyzed amination of light alcohols

    NARCIS (Netherlands)

    Veefkind, V.A.; Lercher, J.A.

    1999-01-01

    Potential elementary reaction steps in solid acid catalyzed amination of light alcohols are critically compared using hydrogen mordenite as (model) catalyst and the open mechanistic questions have been addressed. Transient kinetic experiments combined with in situ infrared spectroscopy and isotopic

  3. Triflic acid catalyzed oxidative lactonization and diacetoxylation of alkenes using peroxyacids as oxidants.

    Science.gov (United States)

    Kang, Yan-Biao; Gade, Lutz H

    2012-02-03

    A clean and efficient diacetoxylation reaction of alkenes catalyzed by triflic acid using commercially available peroxyacids as the oxidants has been developed. This method was also applied in oxidative lactonizations of unsaturated carboxylic acids in good to high yields.

  4. Vanadium-Catalyzed Enantioselective Desymmetrization of meso-Secondary Allylic Alcohols and Homoallylic Alcohols

    OpenAIRE

    Li, Zhi; Zhang, Wei; Hisashi Yamamoto, H.

    2008-01-01

    Vanadium-catalyzed epoxidation has extended substrate scope. In addition to various bis-allylic alcohols, bis-homoallylic alcohols can also be desymmetrized using our Vanadium-Bis-hydroxamic acid complexes.

  5. Structural basis for Diels-Alder ribozyme-catalyzed carbon-carbon bond formation

    Science.gov (United States)

    Serganov, Alexander; Keiper, Sonja; Malinina, Lucy; Tereshko, Valentina; Skripkin, Eugene; Höbartner, Claudia; Polonskaia, Anna; Phan, Anh Tuân; Wombacher, Richard; Micura, Ronald; Dauter, Zbigniew; Jäschke, Andres; Patel, Dinshaw J

    2015-01-01

    The majority of structural efforts addressing RNA’s catalytic function have focused on natural ribozymes, which catalyze phosphodiester transfer reactions. By contrast, little is known about how RNA catalyzes other types of chemical reactions. We report here the crystal structures of a ribozyme that catalyzes enantioselective carbon-carbon bond formation by the Diels-Alder reaction in the unbound state and in complex with a reaction product. The RNA adopts a λ-shaped nested pseudoknot architecture whose preformed hydrophobic pocket is precisely complementary in shape to the reaction product. RNA folding and product binding are dictated by extensive stacking and hydrogen bonding, whereas stereoselection is governed by the shape of the catalytic pocket. Catalysis is apparently achieved by a combination of proximity, complementarity and electronic effects. We observe structural parallels in the independently evolved catalytic pocket architectures for ribozyme- and antibody-catalyzed Diels-Alder carbon-carbon bond-forming reactions. PMID:15723077

  6. Organizational innovation: verifying a comprehensive model for catalyzing organizational development and change

    National Research Council Canada - National Science Library

    Steiber, Annika; Alänge, Sverker

    2015-01-01

    .... Previous research has identified a need for a more comprehensive framework that will aid in better understanding of the mechanisms catalyzing organizational development and change. Steiber and Alänge (Triple Helix 2(9):1–25, 2015...

  7. Sulfenamide catalyzed oxidation of alcohols to the corresponding carbonyl compounds with anhydrous chloramine-T.

    Science.gov (United States)

    Kitagawa, Hideo; Mukaiyama, Teruaki

    2002-09-01

    N-tert-Butylbenzenesulfenamide (1) catalyzed oxidation of various alcohols with stoichiometric amount of anhydrous chloramines-T (2) proceeded smoothly at room temperature to afford the corresponding carbonyl compounds in good yields.

  8. Pd-Catalyzed C-H Bond Functionalization on the Indole and Pyrrole Nucleus

    Science.gov (United States)

    Beck, Elizabeth M.; Gaunt, Matthew J.

    This review details recent developments in the Pd-catalyzed C-H bond arylation and alkenylation of indoles and pyrroles, aromatic heterocycles that are frequently displayed in natural products and medicinal agents.

  9. Enantioconvergent synthesis by sequential asymmetric Horner-Wadsworth-Emmons and palladium-catalyzed allylic substitution reactions

    DEFF Research Database (Denmark)

    Pedersen, Torben Møller; Hansen, E. Louise; Kane, John

    2001-01-01

    A new method for enantioconvergent synthesis has been developed. The strategy relies on the combination of an asymmetric Horner-Wadsworth-Emmons (HWE) reaction and a palladium-catalyzed allylic substitution. Different $alpha@-oxygen-substituted, racemic aldehydes were initially transformed...... by asymmetric HWE reactions into mixtures of two major $alpha@,$beta@-unsaturated esters, possessing opposite configurations at their allylic stereocenters as well as opposite alkene geometry. Subsequently, these isomeric mixtures of alkenes could be subjected to palladium-catalyzed allylic substitution...

  10. Synthesis of highly substituted pyrroles via a multimetal-catalyzed rearrangement-condensation-cyclization domino approach.

    Science.gov (United States)

    Binder, Jörg T; Kirsch, Stefan F

    2006-05-11

    [reaction: see text] In a convenient one-pot process, easily accessed propargyl vinyl ethers and aromatic amines are effectively converted into tetra- and pentasubstituted 5-methylpyrroles which can further be transformed into 5-formylpyrroles via IBX-mediated oxidation. The cascade reaction proceeds through a silver(I)-catalyzed propargyl-Claisen rearrangement, an amine condensation, and a gold(I)-catalyzed 5-exo-dig heterocyclization.

  11. Mo-catalyzed asymmetric olefin metathesis in target-oriented synthesis: Enantioselective synthesis of (+)-africanol

    Science.gov (United States)

    Weatherhead, Gabriel S.; Cortez, G. A.; Schrock, Richard R.; Hoveyda, Amir H.

    2004-01-01

    Catalytic asymmetric ring-opening metathesis (AROM) provides an efficient method for the synthesis of a variety of optically enriched small organic molecules that cannot be easily prepared by alternative methods. The development of Mo-catalyzed AROM transformations that occur in tandem with ring-closing metathesis are described. The utility of the Mo-catalyzed AROM/ring-closing metathesis is demonstrated through an enantioselective approach to the synthesis of (+)-africanol. PMID:15056762

  12. Degradation of acid red 14 by silver ion-catalyzed peroxydisulfate oxidation in an aqueous solution

    OpenAIRE

    RASOULIFARD, Mohammad Hossein; MOHAMMADI, Seied Mohammad Mahdi DOUST

    2014-01-01

    Silver ion (Ag1+)-catalyzed peroxydisulfate was studied for the degradation of acid red 14 (AR-14) in an aqueous medium. The effect of different parameters, such as temperature, peroxydisulfate concentration, and dye and Ag1+ concentrations, were investigated. Application of Ag1+-catalyzed peroxydisulfate, as an advanced oxidation process, introduces an effectual method for wastewater treatment. An accelerated reaction using S2O82- to destroy dyes can be achieved via chemical activat...

  13. One-pot gold-catalyzed synthesis of 3-silylethynyl indoles from unprotected o-alkynylanilines

    Directory of Open Access Journals (Sweden)

    Jérôme Waser

    2011-05-01

    Full Text Available The Au(III-catalyzed cyclization of 2-alkynylanilines was combined in a one-pot procedure with the Au(I-catalyzed C3-selective direct alkynylation of indoles using the benziodoxolone reagent TIPS-EBX to give a mild, easy and straightforward entry to 2-substituted-3-alkynylindoles. The reaction can be applied to unprotected anilines, was tolerant to functional groups and easy to carry out (RT, and requires neither an inert atmosphere nor special solvents.

  14. Hydrogen generation from aqueous acid-catalyzed hydrolysis of sodium borohydride

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyun Jae [Clean Fuels and Catalysis Program, The EMS Energy Institute, and Department of Energy and Mineral Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); Shin, Kyoung-Jin; Kim, Hyun-Jong; Han, M.K. [Surface technology team, Korea Institute of Industrial Technology (KITECH), Incheon 406-840 (Korea, Republic of); Kim, Hansung; Shul, Yong-Gun [Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Jung, Kyeong Taek [Cheil Industries Co. LTD, 437-711 (Korea, Republic of)

    2010-11-15

    In this study, the hydrogen feed from both Ru-catalyzed and organic acid-catalyzed hydrolysis of NaBH{sub 4} was studied in terms of hydrogen generation rate and integrated PEMFC performance. Hydrogen feed generated from the conventional Ru-catalyzed hydrolysis of NaBH{sub 4} caused a drastic loss of PEMFC performance. It was found that the presence of sodium ion in hydrogen feed was a main factor that increased the interfacial resistance of fuel cell and, consequently, reduced the performance. Acid-catalyzed hydrolysis with powder form of NaBH{sub 4} was adopted in order to minimize the detrimental effect of sodium ion. The hydrogen feed from acid-catalyzed hydrolysis was quite dry so that even water vapor, the carrier of sodium ion, was not detected after condensation of hydrogen feed. It was confirmed by the several experiments that the hydrogen release rate can be controlled by varying the injection rate and concentration of aqueous acid. Various organic acids were employed in the production of hydrogen and found that acidity, acid type and chemical structure are also important factors on hydrolysis of NaBH{sub 4}. The performance from the integrated acid-catalyzed hydrogen generation system with PEMFC was quite stable and no significant loss was observed contrary to that from the integrated Ru-catalyzed hydrogen generation system-PEMFC test. This result also clarified that the detrimental effect of sodium ion could be removed by minimizing the water vapor in this manner. Based on the experiment of acid-catalyzed hydrolysis, a small-scale hydrogen-generating device was designed and fabricated, from which hydrogen release was controlled by the acid concentration and injection rate of aqueous acid solution. (author)

  15. Coupled ferredoxin and crotonyl coenzyme A (CoA) reduction with NADH catalyzed by the butyryl-CoA dehydrogenase/Etf complex from Clostridium kluyveri.

    Science.gov (United States)

    Li, Fuli; Hinderberger, Julia; Seedorf, Henning; Zhang, Jin; Buckel, Wolfgang; Thauer, Rudolf K

    2008-02-01

    Cell extracts of butyrate-forming clostridia have been shown to catalyze acetyl-coenzyme A (acetyl-CoA)- and ferredoxin-dependent formation of H2 from NADH. It has been proposed that these bacteria contain an NADH:ferredoxin oxidoreductase which is allosterically regulated by acetyl-CoA. We report here that ferredoxin reduction with NADH in cell extracts from Clostridium kluyveri is catalyzed by the butyryl-CoA dehydrogenase/Etf complex and that the acetyl-CoA dependence previously observed is due to the fact that the cell extracts catalyze the reduction of acetyl-CoA with NADH via crotonyl-CoA to butyryl-CoA. The cytoplasmic butyryl-CoA dehydrogenase complex was purified and is shown to couple the endergonic reduction of ferredoxin (E0' = -410 mV) with NADH (E0' = -320 mV) to the exergonic reduction of crotonyl-CoA to butyryl-CoA (E0' = -10 mV) with NADH. The stoichiometry of the fully coupled reaction is extrapolated to be as follows: 2 NADH + 1 oxidized ferredoxin + 1 crotonyl-CoA = 2 NAD+ + 1 ferredoxin reduced by two electrons + 1 butyryl-CoA. The implications of this finding for the energy metabolism of butyrate-forming anaerobes are discussed in the accompanying paper.

  16. Coupled Ferredoxin and Crotonyl Coenzyme A (CoA) Reduction with NADH Catalyzed by the Butyryl-CoA Dehydrogenase/Etf Complex from Clostridium kluyveri▿ †

    Science.gov (United States)

    Li, Fuli; Hinderberger, Julia; Seedorf, Henning; Zhang, Jin; Buckel, Wolfgang; Thauer, Rudolf K.

    2008-01-01

    Cell extracts of butyrate-forming clostridia have been shown to catalyze acetyl-coenzyme A (acetyl-CoA)- and ferredoxin-dependent formation of H2 from NADH. It has been proposed that these bacteria contain an NADH:ferredoxin oxidoreductase which is allosterically regulated by acetyl-CoA. We report here that ferredoxin reduction with NADH in cell extracts from Clostridium kluyveri is catalyzed by the butyryl-CoA dehydrogenase/Etf complex and that the acetyl-CoA dependence previously observed is due to the fact that the cell extracts catalyze the reduction of acetyl-CoA with NADH via crotonyl-CoA to butyryl-CoA. The cytoplasmic butyryl-CoA dehydrogenase complex was purified and is shown to couple the endergonic reduction of ferredoxin (E0′ = −410 mV) with NADH (E0′ = −320 mV) to the exergonic reduction of crotonyl-CoA to butyryl-CoA (E0′ = −10 mV) with NADH. The stoichiometry of the fully coupled reaction is extrapolated to be as follows: 2 NADH + 1 oxidized ferredoxin + 1 crotonyl-CoA = 2 NAD+ + 1 ferredoxin reduced by two electrons + 1 butyryl-CoA. The implications of this finding for the energy metabolism of butyrate-forming anaerobes are discussed in the accompanying paper. PMID:17993531

  17. The mechanism for iron-catalyzed alkene isomerization in solution

    Energy Technology Data Exchange (ETDEWEB)

    Sawyer, Karma R.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Harris, Charles B.

    2008-05-27

    Here we report nano- through microsecond time-resolved IR experiments of iron-catalyzed alkene isomerization in room-temperature solution. We have monitored the photochemistry of a model system, Fe(CO){sub 4}({eta}{sup 2}-1-hexene), in neat 1-hexene solution. UV-photolysis of the starting material leads to the dissociation of a single CO to form Fe(CO){sub 3}({eta}{sup 2}-1-hexene), in a singlet spin state. This CO loss complex shows a dramatic selectivity to form an allyl hydride, HFe(CO){sub 3}({eta}{sup 3}-C{sub 6}H{sub 11}), via an internal C-H bond-cleavage reaction in 5-25 ns. We find no evidence for the coordination of an alkene molecule from the bath to the CO loss complex, but do observe coordination to the allyl hydride, indicating that it is the key intermediate in the isomerization mechanism. Coordination of the alkene ligand to the allyl hydride leads to the formation of the bis-alkene isomers, Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) and Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2}. Because of the thermodynamic stability of Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) over Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2} (ca. 12 kcal/mol), nearly 100% of the alkene population will be 2-alkene. The results presented herein provide the first direct evidence for this mechanism in solution and suggest modifications to the currently accepted mechanism.

  18. A review on biodiesel production using catalyzed transesterification

    Energy Technology Data Exchange (ETDEWEB)

    Leung, Dennis Y.C.; Wu, Xuan; Leung, M.K.H. [Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong (China)

    2010-04-15

    Biodiesel is a low-emissions diesel substitute fuel made from renewable resources and waste lipid. The most common way to produce biodiesel is through transesterification, especially alkali-catalyzed transesterification. When the raw materials (oils or fats) have a high percentage of free fatty acids or water, the alkali catalyst will react with the free fatty acids to form soaps. The water can hydrolyze the triglycerides into diglycerides and form more free fatty acids. Both of the above reactions are undesirable and reduce the yield of the biodiesel product. In this situation, the acidic materials should be pre-treated to inhibit the saponification reaction. This paper reviews the different approaches of reducing free fatty acids in the raw oil and refinement of crude biodiesel that are adopted in the industry. The main factors affecting the yield of biodiesel, i.e. alcohol quantity, reaction time, reaction temperature and catalyst concentration, are discussed. This paper also described other new processes of biodiesel production. For instance, the Biox co-solvent process converts triglycerides to esters through the selection of inert co-solvents that generates a one-phase oil-rich system. The non-catalytic supercritical methanol process is advantageous in terms of shorter reaction time and lesser purification steps but requires high temperature and pressure. For the in situ biodiesel process, the oilseeds are treated directly with methanol in which the catalyst has been preciously dissolved at ambient temperatures and pressure to perform the transesterification of oils in the oilseeds. This process, however, cannot handle waste cooking oils and animal fats. (author)

  19. Enzyme catalyzed reactions: from experiment to computational mechanism reconstruction.

    Science.gov (United States)

    Srividhya, Jeyaraman; Mourão, Márcio A; Crampin, Edmund J; Schnell, Santiago

    2010-02-01

    The traditional experimental practice in enzyme kinetics involves the measurement of substrate or product concentrations as a function of time. Advances in computing have produced novel approaches for modeling enzyme catalyzed reactions from time course data. One example of such an approach is the selection of appropriate chemical reactions that best fit the data. A common limitation of this approach resides in the number of chemical species considered. The number of possible chemical reactions grows exponentially with the number of chemical species, which makes difficult to select reactions that uniquely describe the data and diminishes the efficiency of the methods. In addition, a method's performance is also dependent on several quantitative and qualitative properties of the time course data, of which we know very little. This information is important to experimentalists as it could allow them to setup their experiments in ways that optimize the network reconstruction. We have previously described a method for inferring reaction mechanisms and kinetic rate parameters from time course data. Here, we address the limitations in the number of chemical reactions by allowing the introduction of information about chemical interactions. We also address the unknown properties of the input data by determining experimental data properties that maximize our method's performance. We investigate the following properties: initial substrate-enzyme concentration ratios; initial substrate-enzyme concentration variation ranges; number of data points; number of different experiments (time courses); and noise. We test the method using data generated in silico from the Michaelis-Menten and the Hartley-Kilby reaction mechanisms. Our results demonstrate the importance of experimental design for time course assays that has not been considered in experimental protocols. These considerations can have far reaching implications for the computational mechanism reconstruction process

  20. Copper-catalyzed azide alkyne cycloaddition polymer networks

    Science.gov (United States)

    Alzahrani, Abeer Ahmed

    The click reaction concept, introduced in 2001, has since spurred the rapid development and reexamination of efficient, high yield reactions which proceed rapidly under mild conditions. Prior to the discovery of facile copper catalysis in 2002, the thermally activated azide-alkyne or Huisgen cycloaddition reaction was largely ignored following its discovery in large part due to its slow kinetics, requirement for elevated temperature and limited selectivity. Now, arguably, the most prolific and capable of the click reactions, the copper-catalyzed azide alkyne cycloaddition (CuAAC) reaction is extremely efficient and affords exquisite control of the reaction. The orthogonally and chemoselectivity of this reaction enable its wide utility across varied scientific fields. Despite numerous inherent advantages and widespread use for small molecule synthesis and solution-based polymer chemistry, it has only recently and rarely been utilized to form polymer networks. This work focuses on the synthesis, mechanisms, and unique attributes of the CuAAC reaction for the fabrication of functional polymer networks. The photo-reduction of a series of copper(II)/amine complexes via ligand metal charge transfer was examined to determine their relative efficiency and selectivity in catalyzing the CuAAC reaction. The aliphatic amine ligands were used as an electron transfer species to reduce Cu(II) upon irradiation with 365 nm light while also functioning as an accelerating agent and as protecting ligands for the Cu(I) that was formed. Among the aliphatic amines studied, tertiary amines such as triethylamine (TEA), tetramethyldiamine (TMDA), N,N,N',N",N"-pentamethyldiethylenetriamine (PMDTA), and hexamethylenetetramine (HMTETA) were found to be the most effective. The reaction kinetics were accelerated by increasing the PMDETA : Cu(II) ratio with a ratio of ligand to Cu(II) of 4:1 yielding the maximum conversion in the shortest time. The sequential and orthogonal nature of the photo

  1. Purification and deodorization of structured lipids by short path distillation

    DEFF Research Database (Denmark)

    Xu, Xuebing; Jacobsen, Charlotte; Nielsen, Nina Skall

    2002-01-01

    Purification of structured lipids (SL), produced from lipase- catalyzed acidolysis of rapeseed oil and capric acid, and deodorization of randomized SL, produced from chemical randomization of fish oil and tricaprin, were studied in a bench-scale short path distillation (SPD). SL obtained from...

  2. Ruthenium-Catalyzed Ammonia Borane Dehydrogenation: Mechanism and Utility.

    Science.gov (United States)

    Zhang, Xingyue; Kam, Lisa; Trerise, Ryan; Williams, Travis J

    2017-01-17

    One of the greatest challenges in using H2 as a fuel source is finding a safe, efficient, and inexpensive method for its storage. Ammonia borane (AB) is a solid hydrogen storage material that has garnered attention for its high hydrogen weight density (19.6 wt %) and ease of handling and transport. Hydrogen release from ammonia borane is mediated by either hydrolysis, thus giving borate products that are difficult to rereduce, or direct dehydrogenation. Catalytic AB dehydrogenation has thus been a popular topic in recent years, motivated both by applications in hydrogen storage and main group synthetic chemistry. This Account is a complete description of work from our laboratory in ruthenium-catalyzed ammonia borane dehydrogenation over the last 6 years, beginning with the Shvo catalyst and resulting ultimately in the development of optimized, leading catalysts for efficient hydrogen release. We have studied AB dehydrogenation with Shvo's catalyst extensively and generated a detailed understanding of the role that borazine, a dehydrogenation product, plays in the reaction: it is a poison for both Shvo's catalyst and PEM fuel cells. Through independent syntheses of Shvo derivatives, we found a protective mechanism wherein catalyst deactivation by borazine is prevented by coordination of a ligand that might otherwise be a catalytic poison. These studies showed how a bidentate N-N ligand can transform the Shvo into a more reactive species for AB dehydrogenation that minimizes accumulation of borazine. Simultaneously, we designed novel ruthenium catalysts that contain a Lewis acidic boron to replace the Shvo -OH proton, thus offering more flexibility to optimize hydrogen release and take on more general problems in hydride abstraction. Our scorpionate-ligated ruthenium species (12) is a best-of-class catalyst for homogeneous dehydrogenation of ammonia borane in terms of its extent of hydrogen release (4.6 wt %), air tolerance, and reusability. Moreover, a synthetically

  3. Mechanistic Comparison Between Pd-Catalyzed Ligand Directed C-H Chlorination and C-H Acetoxylation

    Science.gov (United States)

    Stowers, Kara J.; Sanford, Melanie S.

    2009-01-01

    This communication describes detailed investigations of the mechanism of the Pd-catalyzed C-H chlorination and acetoxylation of 2-ortho-tolylpyridine. Under the conditions examined, both reactions proceed via rate limiting cyclopalladation. However, substrate and catalyst order as well as Hammett data indicate that the intimate mechanism of cyclopalladation differs significantly between PdCl2-catalyzed chlorination and Pd(OAc)2-catalyzed acetoxylation. PMID:19754074

  4. Carbon dioxide reduction to methane and coupling with acetylene to form propylene catalyzed by remodeled nitrogenase.

    Science.gov (United States)

    Yang, Zhi-Yong; Moure, Vivian R; Dean, Dennis R; Seefeldt, Lance C

    2012-11-27

    A doubly substituted form of the nitrogenase MoFe protein (α-70(Val)(→Ala), α-195(His→Gln)) has the capacity to catalyze the reduction of carbon dioxide (CO(2)) to yield methane (CH(4)). Under optimized conditions, 1 nmol of the substituted MoFe protein catalyzes the formation of 21 nmol of CH(4) within 20 min. The catalytic rate depends on the partial pressure of CO(2) (or concentration of HCO(3)(-)) and the electron flux through nitrogenase. The doubly substituted MoFe protein also has the capacity to catalyze the unprecedented formation of propylene (H(2)C = CH-CH(3)) through the reductive coupling of CO(2) and acetylene (HC≡CH). In light of these observations, we suggest that an emerging understanding of the mechanistic features of nitrogenase could be relevant to the design of synthetic catalysts for CO(2) sequestration and formation of olefins.

  5. Carbon dioxide reduction to methane and coupling with acetylene to form propylene catalyzed by remodeled nitrogenase

    Science.gov (United States)

    Yang, Zhi-Yong; Moure, Vivian R.; Dean, Dennis R.; Seefeldt, Lance C.

    2012-01-01

    A doubly substituted form of the nitrogenase MoFe protein (α-70Val→Ala, α-195His→Gln) has the capacity to catalyze the reduction of carbon dioxide (CO2) to yield methane (CH4). Under optimized conditions, 1 nmol of the substituted MoFe protein catalyzes the formation of 21 nmol of CH4 within 20 min. The catalytic rate depends on the partial pressure of CO2 (or concentration of HCO3−) and the electron flux through nitrogenase. The doubly substituted MoFe protein also has the capacity to catalyze the unprecedented formation of propylene (H2C = CH-CH3) through the reductive coupling of CO2 and acetylene (HC≡CH). In light of these observations, we suggest that an emerging understanding of the mechanistic features of nitrogenase could be relevant to the design of synthetic catalysts for CO2 sequestration and formation of olefins. PMID:23150564

  6. Enantioselective [3+3] atroposelective annulation catalyzed by N-heterocyclic carbenes

    KAUST Repository

    Zhao, Changgui

    2018-02-05

    Axially chiral molecules are among the most valuable substrates in organic synthesis. They are typically used as chiral ligands or catalysts in asymmetric reactions. Recent progress for the construction of these chiral molecules is mainly focused on the transition-metal-catalyzed transformations. Here, we report the enantioselective NHC-catalyzed (NHC: N-heterocyclic carbenes) atroposelective annulation of cyclic 1,3-diones with ynals. In the presence of NHC precatalyst, base, Lewis acid and oxidant, a catalytic C–C bond formation occurs, providing axially chiral α-pyrone−aryls in moderate to good yields and with high enantioselectivities. Control experiments indicated that alkynyl acyl azoliums, acting as active intermediates, are employed to atroposelectively assemble chiral biaryls and such a methodology may be creatively applied to other useful NHC-catalyzed asymmetric transformations.

  7. Catalyzing Transdisciplinarity: A Systems Ethnography of Cancer-Obesity Comorbidity and Risk Coincidence.

    Science.gov (United States)

    Graham, S Scott; Harley, Amy; Kessler, Molly M; Roberts, Laura; DeVasto, Dannielle; Card, Daniel J; Neuner, Joan M; Kim, Sang-Yeon

    2017-05-01

    Effectively addressing wicked health problems, that is, those arising from complex multifactorial biological and socio-economic causes, requires transdisciplinary action. However, a significant body of research points toward substantial difficulties in cultivating transdisciplinary collaboration. Accordingly, this article presents the results of a study that adapts Systems Ethnography and Qualitative Modeling (SEQM) in response to wicked health problems. SEQM protocols were designed to catalyze transdisciplinary responses to national defense concerns. We adapted these protocols to address cancer-obesity comorbidity and risk coincidence. In so doing, we conducted participant-observations and interviews with a diverse range of health care providers, community health educators, and health advocacy professionals who target either cancer or obesity. We then convened a transdisciplinary conference designed to catalyze a coordinated response. The findings offer productive insights into effective ways of catalyzing transdisciplinarity in addressing wicked health problems action and demonstrate the promise of SEQM for continued use in health care contexts.

  8. DFT study of the molybdenum-catalyzed deoxydehydration of vicinal diols.

    Science.gov (United States)

    Lupp, Daniel; Christensen, Niels Johan; Dethlefsen, Johannes R; Fristrup, Peter

    2015-02-16

    The mechanism of the molybdenum-catalyzed deoxydehydration (DODH) of vicinal diols has been investigated using density functional theory. The proposed catalytic cycle involves condensation of the diol with an Mo(VI) oxo complex, oxidative cleavage of the diol resulting in an Mo(IV) complex, and extrusion of the alkene. We have compared the proposed pathway with several alternatives, and the results have been corroborated by comparison with the molybdenum-catalyzed sulfoxide reduction recently published by Sanz et al. and with experimental observations for the DODH itself. Improved understanding of the mechanism should expedite future optimization of molybdenum-catalyzed biomass transformations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. DFT Study of the Molybdenum-Catalyzed Deoxydehydration of Vicinal Diols

    DEFF Research Database (Denmark)

    Lupp, Daniel; Christensen, Niels Johan; Dethlefsen, Johannes Rytter

    2015-01-01

    The mechanism of the molybdenum-catalyzed deoxydehydration (DODH) of vicinal diols has been investigated using density functional theory. The proposed catalytic cycle involves condensation of the diol with an MoVI oxo complex, oxidative cleavage of the diol resulting in an MoIV complex, and extru......The mechanism of the molybdenum-catalyzed deoxydehydration (DODH) of vicinal diols has been investigated using density functional theory. The proposed catalytic cycle involves condensation of the diol with an MoVI oxo complex, oxidative cleavage of the diol resulting in an MoIV complex......, and extrusion of the alkene. We have compared the proposed pathway with several alternatives, and the results have been corroborated by comparison with the molybdenum- catalyzed sulfoxide reduction recently published by Sanz et al. and with experimental observations for the DODH itself. Improved understanding...

  10. Using simple donors to drive the equilibria of glycosyltransferase-catalyzed reactions.

    Science.gov (United States)

    Gantt, Richard W; Peltier-Pain, Pauline; Cournoyer, William J; Thorson, Jon S

    2011-08-21

    We report that simple glycoside donors can drastically shift the equilibria of glycosyltransferase-catalyzed reactions, transforming NDP-sugar formation from an endothermic to an exothermic process. To demonstrate the utility of this thermodynamic adaptability, we highlight the glycosyltransferase-catalyzed synthesis of 22 sugar nucleotides from simple aromatic sugar donors, as well as the corresponding in situ formation of sugar nucleotides as a driving force in the context of glycosyltransferase-catalyzed reactions for small-molecule glycodiversification. These simple aromatic donors also enabled a general colorimetric assay for glycosyltransfer, applicable to drug discovery, protein engineering and other fundamental sugar nucleotide-dependent investigations. This study directly challenges the general notion that NDP-sugars are 'high-energy' sugar donors when taken out of their traditional biological context.

  11. The Manganese-Catalyzed Cross-Coupling Reaction and the Influence of Trace Metals

    DEFF Research Database (Denmark)

    Santilli, Carola; Beigbaghlou, Somayyeh Sarvi; Ahlburg, Andreas

    2017-01-01

    radical as an intermediate leading to the proposal of an SRN1 pathway for the coupling. The mechanistic information gave rise to suspicion about two previously published cross-coupling reactions catalyzed by manganese(II) salts. As a result, the coupling between aryl halides and organostannanes as well......The substrate scope of the MnCl2-catalyzed cross-coupling between aryl halides and Grignard reagents has been extended to several methyl-substituted aryl iodides by performing the reaction at elevated temperature in a microwave oven. A radical clock experiment revealed the presence of an aryl...... as between aryl halides and amines were revisited. Both reactions were found impossible to reproduce without the addition of small amounts of palladium or copper and are therefore not believed to be catalyzed by manganese....

  12. Biofuel-Promoted Polychlorinated Dibenzodioxin/furan Formation in an Iron-Catalyzed Diesel Particle Filter.

    Science.gov (United States)

    Heeb, Norbert V; Rey, Maria Dolores; Zennegg, Markus; Haag, Regula; Wichser, Adrian; Schmid, Peter; Seiler, Cornelia; Honegger, Peter; Zeyer, Kerstin; Mohn, Joachim; Bürki, Samuel; Zimmerli, Yan; Czerwinski, Jan; Mayer, Andreas

    2015-08-04

    Iron-catalyzed diesel particle filters (DPFs) are widely used for particle abatement. Active catalyst particles, so-called fuel-borne catalysts (FBCs), are formed in situ, in the engine, when combusting precursors, which were premixed with the fuel. The obtained iron oxide particles catalyze soot oxidation in filters. Iron-catalyzed DPFs are considered as safe with respect to their potential to form polychlorinated dibenzodioxins/furans (PCDD/Fs). We reported that a bimetallic potassium/iron FBC supported an intense PCDD/F formation in a DPF. Here, we discuss the impact of fatty acid methyl ester (FAME) biofuel on PCDD/F emissions. The iron-catalyzed DPF indeed supported a PCDD/F formation with biofuel but remained inactive with petroleum-derived diesel fuel. PCDD/F emissions (I-TEQ) increased 23-fold when comparing biofuel and diesel data. Emissions of 2,3,7,8-TCDD, the most toxic congener [toxicity equivalence factor (TEF) = 1.0], increased 90-fold, and those of 2,3,7,8-TCDF (TEF = 0.1) increased 170-fold. Congener patterns also changed, indicating a preferential formation of tetra- and penta-chlorodibenzofurans. Thus, an inactive iron-catalyzed DPF becomes active, supporting a PCDD/F formation, when operated with biofuel containing impurities of potassium. Alkali metals are inherent constituents of biofuels. According to the current European Union (EU) legislation, levels of 5 μg/g are accepted. We conclude that risks for a secondary PCDD/F formation in iron-catalyzed DPFs increase when combusting potassium-containing biofuels.

  13. Synthesis of Fluoroalkoxy Substituted Arylboronic Esters by Iridium-Catalyzed Aromatic C–H Borylation

    KAUST Repository

    Batool, Farhat

    2015-08-17

    The preparation of fluoroalkoxy arylboronic esters by iridium-catalyzed aromatic C–H borylation is described. The fluoroalkoxy groups employed include trifluoromethoxy, difluoromethoxy, 1,1,2,2-tetrafluoroethoxy, and 2,2-difluoro-1,3-benzodioxole. The borylation reactions were carried out neat without the use of a glovebox or Schlenk line. The regioselectivities available through the iridium-catalyzed C–H borylation are complementary to those obtained by the electrophilic aromatic substitution reactions of fluoroalkoxy arenes. Fluoroalkoxy arylboronic esters can serve as versatile building blocks.

  14. Rationalizing Ring-Size Selectivity in Intramolecular Pd-Catalyzed Allylations of Resonance-Stabilized Carbanions

    DEFF Research Database (Denmark)

    Norrby, Per-Ola; Mader, Mary M.; Vitale, Maxime

    2003-01-01

    Computational methods were applied to the Pd-catalyzed intramolecular allylations of resonance-stabilized carbanions obtained from amide and ketone substrates, with the aim of rationalizing the endo- vs. exo-selectivity in the cyclizations. In addition, ester substrates were prepared and subjected...... to the Pd-catalyzed cyclization conditions, and were found to form lactones via exo attack. DFT calculations using BP86/LACVP*+level of theory with a CH2Cl2 solvation correction reproduce the relative transition state energies. The preference for exo-cyclization of the nitrogen-containing starting material...

  15. FeCl3 -Catalyzed Ring-Closing Carbonyl-Olefin Metathesis.

    Science.gov (United States)

    Ma, Lina; Li, Wenjuan; Xi, Hui; Bai, Xiaohui; Ma, Enlu; Yan, Xiaoyu; Li, Zhiping

    2016-08-22

    Exploiting catalytic carbonyl-olefin metathesis is an ongoing challenge in organic synthesis. Reported herein is an FeCl3 -catalyzed ring-closing carbonyl-olefin metathesis. The protocol allows access to a range of carbo-/heterocyclic alkenes with good efficiency and excellent trans diastereoselectivity. The methodology presents one of the rare examples of catalytic ring-closing carbonyl-olefin metathesis. This process is proposed to take place by FeCl3 -catalyzed oxetane formation followed by retro-ring-opening to deliver metathesis products. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Palladium(0)-catalyzed single and double isonitrile insertion: a facile synthesis of benzofurans, indoles, and isatins.

    Science.gov (United States)

    Senadi, Gopal Chandru; Hu, Wan-Ping; Boominathan, Siva Senthil Kumar; Wang, Jeh-Jeng

    2015-01-12

    A palladium(0)-catalyzed cascade process consisting of isonitrile insertion and α-Csp(3)-H cross-coupling can be achieved for the synthesis of benzofurans and indoles. The construction of isatins by a Pd-catalyzed cascade reaction incorporating double isonitrile insertion, amination, and hydrolysis has also been achieved. The key features of this work include diverse heterocycle synthesis, phosphine-ligand-free reaction conditions, a one-pot procedure, simple and commercially available starting materials, broad functional-group compatibility, and moderate to good reaction yields. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Kinetics of enzyme-catalyzed cross-linking of feruloylated arabinan from sugar beet

    DEFF Research Database (Denmark)

    Abang Zaidel, Dayang Norulfairuz; Arnous, Anis; Holck, Jesper

    2011-01-01

    the kinetics of HRP catalyzed cross-linking of FA esterified to α-(1,5)-linked arabinans are affected by the length of the arabinan chains carrying the feruloyl substitutions. The kinetics of the HRP-catalyzed cross-linking of four sets of arabinan samples from sugar beet pulp, having different molecular...... weights and hence different degrees of polymerization, were monitored by the disappearance of FA absorbance at 316 nm. MALDI-TOF/TOF-MS analysis confirmed that the sugar beet arabinans were feruloyl-substituted, and HPLC analysis verified that the amounts of diFAs increased when FA levels decreased...

  18. Silver-Catalyzed Dehydrogenative Synthesis of Carboxylic Acids from Primary Alcohols

    DEFF Research Database (Denmark)

    Ghalehshahi, Hajar Golshadi; Madsen, Robert

    2017-01-01

    A simple silver-catalyzed protocol has been developed for the acceptorless dehydrogenation of primary alcohols into carboxylic acids and hydrogen gas. The procedure uses 2.5 % Ag2 CO3 and 2.5-3 equiv of KOH in refluxing mesitylene to afford the potassium carboxylate which is then converted...... into the acid with HCl. The reaction can be applied to a variety of benzylic and aliphatic primary alcohols with alkyl and ether substituents, and in some cases halide, olefin, and ester functionalities are also compatible with the reaction conditions. The dehydrogenation is believed to be catalyzed by silver...

  19. Development of melamine modified urea formaldehyde resins based o nstrong acidic pH catalyzed urea formaldehyde polymer

    Science.gov (United States)

    Chung-Yun Hse

    2009-01-01

    To upgrade the performance of urea-formaldehyde (UF) resin bonded particleboards, melamine modified urea-formaldehyde (MUF) resins based on strong acidic pH catalyzed UF polymers were investigated. The study was conducted in a series of two experiments: 1) formulation of MUF resins based on a UF polymer catalyzed with strong acidic pH and 2) determination of the...

  20. A Palladium-Catalyzed Vinylcyclopropane (3 + 2) Cycloaddition Approach to the Melodinus Alkaloids

    KAUST Repository

    Goldberg, Alexander F. G.

    2011-08-19

    A palladium-catalyzed (3+2) cycloaddition of a vinylcyclopropane and a β-nitrostyrene is employed to rapidly assemble the cyclopentane core of the Melodinus alkaloids. The ABCD ring system of the natural product family is prepared in six steps from commercially available materials.

  1. xanthen-11-ones by ZnO Nanoparticles Catalyzed Three Co

    African Journals Online (AJOL)

    NICO

    tetrahydrobenzo[a]xanthen-11-ones by ZnO Nanoparticles. Catalyzed Three Component Coupling Reaction of. Aldehydes, 2-Naphthol and Dimedone. Javad Safaei-Ghomi and Mohammad Ali Ghasemzadeh. Department of Chemistry, Qom Branch, Islamic Azad University, Qom, Iran. Received 11 September 2013, revised ...

  2. A simple model for chiral amplification in the aminoalcohol-catalyzed reaction of aldehydes with dialkylzinc

    Directory of Open Access Journals (Sweden)

    IVAN GUTMAN

    1999-08-01

    Full Text Available A simple explanation is offered for the recently discovered chiral amplification in the alkylation reaction of benzaldehyde by means of dialkylzinc, catalyzed by (dimethylaminoisoborneol. The model presentd is similar to, yet somewhat simpler than, the model put forward by Noyori et al.

  3. Palladium-Catalyzed Enantioselective Addition of Two Distinct Nucleophiles across Alkenes Capable of Quinone Methide Formation

    OpenAIRE

    Jensen, Katrina H.; Pathak, Tejas P.; Zhang, Yang; Sigman, Matthew S.

    2009-01-01

    A sequential intramolecular-intermolecular enantioselective alkene difunctionalization reaction has been developed which is thought to proceed through Pd-catalyzed quinone methide formation. The synthesis of new chiral heterocyclic compounds with adjacent chiral centers is achieved in enantiomeric ratios up to 99:1 and diastereomeric ratios up to 10:1.

  4. Zn(OTf)2 catalyzed indolylation and pyrrolylation of isatins: Efficient ...

    Indian Academy of Sciences (India)

    praveenithya

    Zn(OTf)2 catalyzed indolylation and pyrrolylation of isatins: Efficient synthesis and biochemical assay of 3,3- di(heteroaryl)oxindoles. C PRAVEEN a. , S NARENDIRAN b. , P DHEENKUMAR a,c and P T PERUMAL a,. * a. Organic Chemistry Division, Central Leather Research Institute (CSIR), Adyar, Chennai. 600020 ...

  5. Nickel-Catalyzed Synthesis of Primary Aryl and Heteroaryl Amines via C–O Bond Cleavage

    KAUST Repository

    Yue, Huifeng

    2017-03-13

    A nickel-catalyzed protocol for the conversion of aryl and heteroaryl alcohol derivatives to primary and secondary aromatic amines via C(sp2)-O bond cleavage is described. The new amination protocol can be applied to a range of substrates bearing diverse functional groups and uses readily available benzophenone imines as an effective nitrogen source.

  6. Synthesis of 2-substituted tetraphenylenes via transition-metal-catalyzed derivatization of tetraphenylene

    Directory of Open Access Journals (Sweden)

    Shulei Pan

    2016-06-01

    Full Text Available A new strategy for the synthesis of 2-substituted tetraphenylenes through a transition-metal-catalyzed derivatization has been developed. Three types of functionalities, including OAc, X (Cl, Br, I and carbonyl, were introduced onto tetraphenylene, which allows the easy access to a variety of monosubstituted tetraphenylenes. These reactions could accelerate research on the properties and application of tetraphenylene derivatives.

  7. Monooxygenation of small hydrocarbons catalyzed by bacterial cytochrome p450s.

    Science.gov (United States)

    Shoji, Osami; Watanabe, Yoshihito

    2015-01-01

    Cytochrome P450s (P450s) catalyze the NAD(P)H/O2-dependent monooxygenation of less reactive organic molecules under mild conditions. The catalytic activity of bacterial P450s is very high compared with P450s isolated from animals and plants, and the substrate specificity of bacterial P450s is also very high. Accordingly, their catalytic activities toward nonnative substrates are generally low especially toward small hydrocarbons. However, mutagenesis approaches have been very successful for engineering bacterial P450s for the hydroxylation of small hydrocarbons. On the other hand, "decoy" molecules, whose structures are very similar to natural substrates, can be used to trick the substrate recognition of bacterial P450s, allowing the P450s to catalyze oxidation reactions of nonnative substrates without any substitution of amino acid residues in the presence of decoy molecules. Thus, the hydroxylation of small hydrocarbons such as ethane, propane, butane and benzene can be catalyzed by P450BM3, a long-alkyl-chain hydroxylase, using substrate misrecognition of P450s induced by decoy molecules. Furthermore, a number of H2O2-dependent bacterial P450s can catalyze the peroxygenation of a variety of nonnative substrates through a simple substrate-misrecognition trick, in which catalytic activities and enantioselectivity are dependent on the structure of decoy molecules.

  8. Mechanistic investigation of the gold-catalyzed aerobic oxidation of alcohols

    DEFF Research Database (Denmark)

    Fristrup, Peter; Johansen, Louise Bahn; Christensen, Claus Hviid

    2008-01-01

    The mechanism for the gold-catalyzed aerobic oxidation of alcohols was studied using a series of para-substituted benzyl alcohols (Hammett methodology). The competition experiments clearly show that the rate-determining step of the reaction involves the generation of a partial positive charge in ...

  9. HClO4-SiO2 catalyzed per-O-acetylation of carbohydrates.

    Science.gov (United States)

    Misra, Anup Kumar; Tiwari, Pallavi; Madhusudan, Soni Kamlesh

    2005-02-07

    An efficient per-O-acetylation of carbohydrates catalyzed by HClO4-SiO2 is reported using a stoichiometric quantity of acetic anhydride avoiding the use of pyridine and excess acetic anhydride under solvent-free conditions.

  10. Alloying Au surface with Pd reduces the intrinsic activity in catalyzing CO oxidation

    KAUST Repository

    Qian, Kun

    2016-03-30

    © 2016. Various Au-Pd/SiO2 catalysts with a fixed Au loading but different Au:Pd molar ratios were prepared via deposition-precipitation method followed by H2 reduction. The structures were characterized and the catalytic activities in CO oxidation were evaluated. The formation of Au-Pd alloy particles was identified. The Au-Pd alloy particles exhibit enhanced dispersions on SiO2 than Au particles. Charge transfer from Pd to Au within Au-Pd alloy particles. Isolated Pd atoms dominate the surface of Au-Pd alloy particles with large Au:Pd molar ratios while contiguous Pd atoms dominate the surface of Au-Pd alloy particles with small Au:Pd molar ratios. Few synergetic effect of Au-Pd alloy occurs on catalyzing CO oxidation under employed reaction conditions. Alloying Au with Pd reduces the intrinsic activity in catalyzing CO oxidation, and contiguous Pd atoms on the Au-Pd alloy particles are capable of catalyzing CO oxidation while isolated Pd atoms are not. These results advance the fundamental understandings of Au-Pd alloy surfaces in catalyzing CO oxidation.

  11. Modeling of mass transfer in combination with a homogeneously catalyzed reaction

    NARCIS (Netherlands)

    Hoorn, J.A.A.; Versteeg, G. F.

    The mass transfer rates of a gaseous reactant into a liquid where the reactions are catalyzed by homogeneous catalysts have been evaluated by the numerical solution of the diffusion-reaction equations according to Higbie's penetration theory. The concentration profiles as well as enhancement factors

  12. Manganese-Catalyzed C−H Functionalizations: Hydroarylations and Alkenylations Involving an Unexpected Heteroaryl Shift

    KAUST Repository

    Wang, Chengming

    2017-06-24

    A manganese-catalyzed regio- and stereoselective hydroarylation of allenes is reported. The C−H functionalization method provides access to various alkenylated indoles in excellent yields. Moreover, a hydroarylation/cyclization cascade involving an unexpected C−N bond cleavage and aryl shift has been developed, which provides a new synthetic approach to substituted pyrroloindolones.

  13. Nickel-Catalyzed Decarbonylative Silylation, Borylation, and Amination of Arylamides via a Deamidative Reaction Pathway

    KAUST Repository

    Rueping, Magnus

    2017-10-23

    A nickel-catalyzed decarbonylative silylation, borylation, and amination of amides has been developed. This new methodology allows the direct interconversion of amides to arylsilanes, arylboronates, and arylamines and enables a facile route for carbon–heteroatom bond formations in a straightforward and mild fashion.

  14. Preparation of fluorinated biaryls through direct palladium-catalyzed coupling of polyfluoroarenes with aryltrifluoroborates

    KAUST Repository

    Fang, Xin

    2013-07-01

    The direct palladium-catalyzed coupling of polyfluoroarenes with aryltrifluoroborates gave the desired products of fluorinated biaryls in good to excellent yields. A diverse set of important functional groups including methoxy, aldehyde, ester, nitro and halide can be well tolerated in the protocol. © 2013 Elsevier B.V. All rights reserved.

  15. Lipase/Ruthenium-Catalyzed Dynamic Kinetic Resolution of β-Hydroxyalkyl ferrocene Derivatives

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Han Ki; Ahn, Yang Soo [Pohang University of Science and Technology, Pohang (Korea, Republic of)

    2004-10-15

    An efficient dynamic kinetic resolution of racemic β-hydroxyalkyl ferrocene and 1,1'-bis(β-hydroxyalkyl)- ferrocene derivatives was achieved using lipase/ruthenium-catalyzed transesterification in the presence of an acyl donor. The racemic β-hydroxyalkyl ferrocene derivatives were successfully transformed to the corresponding chiral acetates of high optical purities in high yields.

  16. Atomistic Model for the Polyamide Formation from beta-Lactam Catalyzed by Candida antarctica Lipase B

    NARCIS (Netherlands)

    Baum, Iris; Elsaesser, Brigitta; Schwab, Leendert W.; Loos, Katja; Fels, Gregor; Elsässer, Brigitta

    Candida antarctica lipase B (CALB) is an established biocatalyst for a variety of transesterification, amidation, and polymerization. reactions. In contrast to polyesters, poly amides are not yet generally accessible via enzymatic polymerization. In this regard, an enzyme-catalyzed ring-opening

  17. Optimization of H2SO4-catalyzed hydrothermal pretreatment of rapeseed straw for bioconversion to ethanol

    DEFF Research Database (Denmark)

    Xuebin, Lu; Zhang, Y.; Angelidaki, Irini

    2009-01-01

    A central composite design of response surface method was used to optimize H2SO4-catalyzed hydrothermal pretreatment of rapeseed straw, in respect to acid concentration (0.5-2%), treatment time (5-20 min) and solid content (10-20%) at 180 degrees C. Enzymatic hydrolysis and fermentation were also...

  18. Biphenol-based phosphoramidite ligands for the enantioselective copper-catalyzed conjugate addition of diethylzinc.

    Science.gov (United States)

    Alexakis, Alexandre; Polet, Damien; Rosset, Stéphane; March, Sébastien

    2004-08-20

    Phosphoramidite ligands, based on ortho-substituted biphenols and a chiral amine, induce high enantioselectivities (ee's up to 99%) in the copper-catalyzed conjugate addition of dialkylzinc reagents to a variety of Michael acceptors. Particularly, the best reported ee's were obtained for acyclic nitroolefins. Copyright 2004 American Chemical Society

  19. Amino acid based phosphoramidite ligands for the rhodium-catalyzed asymmetric hydrogenation

    NARCIS (Netherlands)

    Breuil, P.A.R.; Reek, J.N.H.

    2009-01-01

    Two sets of amino acid based phosphoramidite ligands with either a BINOL backbone (S-b-1a-e and Rb-1a) or a flexible biphenol backbone (2a-c and 2f) were synthesized and evaluated in the rhodium-catalyzed hydrogenation of different functionalized alkenes: dimethyl itaconate (3), methyl

  20. Palladium(II)/Brønsted Acid-Catalyzed Enantioselective Oxidative Carbocyclization–Borylation of Enallenes**

    Science.gov (United States)

    Jiang, Tuo; Bartholomeyzik, Teresa; Mazuela, Javier; Willersinn, Jochen; Bäckvall, Jan-E

    2015-01-01

    An enantioselective oxidative carbocyclization–borylation of enallenes that is catalyzed by palladium(II) and a Brønsted acid was developed. Biphenol-type chiral phosphoric acids were superior co-catalysts for inducing the enantioselective cyclization. A number of chiral borylated carbocycles were synthesized in high enantiomeric excess. PMID:25808996

  1. GSTP1-1 stereospecifically catalyzes glutathione conjugation of ethacrynic acid

    NARCIS (Netherlands)

    Iersel, M.L.P.S. van; Lipzig, M.M.H. van; Rietjens, I.M.C.M.; Vervoort, J.; Bladeren, P.J. van

    1998-01-01

    Using 1H NMR two diastereoisomers of the ethacrynic acid glutathione conjugate (EASG) as well as ethacrynic acid (EA) could be distinguished and quantified individually. Chemically prepared EASG consists of equal amounts of both diastereoisomers. GSTP1-1 stereospecifically catalyzes formation of one

  2. Specifically Grafting Hematin on MPTS-Coated Carbon Nanotubes for Catalyzing the Oxidation of Aniline

    Directory of Open Access Journals (Sweden)

    Kunkun Zheng

    2016-08-01

    Full Text Available Catalysts supported on nanomaterials have been widely investigated for the treatment of hazardous materials. This work has developed a novel method for grafting hematin on nanomaterials for catalyzing the oxidation of aniline in order to remove aniline from wastewater. Magnetic multi-walled carbon nanotubes (M-MWCNTs were coated with a layer formed through the hydrolysis and condensation of 3-mercaptopropyltriethoxysilane (MPTS. Hematin was specifically grafted on the MPTS-coated M-MWCNTs through thiol-alkene reaction. Hematin-MPTS-M-MWCNTs were used to catalyze the oxidation of aniline, and a high efficiency has been obtained. Consecutive use of the conjugate of hematin-MPTS-M-MWCNTs has been investigated, and the activity has been retained to a significant extent after five reaction/cleaning cycles. The result demonstrates that hematin-MPTS-M-MWCNTs are efficient for catalyzing the oxidation of aniline. The methodology for the specific grafting of hematin is of general utility, it is an easy-to-operate method and can be extended to other supports. Potentially, hematin-MPTS-based conjugates have a widespread application in catalyzing the removal of aniline from wastewater.

  3. Enzyme-Catalyzed Synthesis of Saccharide Acrylate Monomers from Nonedible Biomass

    NARCIS (Netherlands)

    Kloosterman, Wouter M. J.; Brouwer, Sander; Loos, Katja

    Various cellulase preparations were found to catalyze the transglycosidation between cotton linters and 2-hydroxyethyl acrylate. The conversion and enzyme activity were found to be optimal in reaction mixtures that contained 5 vol% of the acrylate. The structures of the products were revealed by

  4. Kinetic Parameters for the Noncatalyzed and Enzyme-Catalyzed Mutarotation of Glucose Using a Blood Glucometer

    Science.gov (United States)

    Hardee, John R.; Delgado, Bryan; Jones, Wray

    2011-01-01

    The kinetic parameters for the conversion of alpha-D-glucose to beta-D-glucose were measured using a blood glucometer. The reaction order, rate constant, and Arrhenius activation energy are reported for the noncatalyzed reaction and turnover number and Michaelis constant are reported for the reaction catalyzed by porcine kidney mutarotase. The…

  5. Homocoupling of benzyl halides catalyzed by POCOP-nickel pincer complexes

    KAUST Repository

    Chen, Tao

    2012-08-01

    Two types of POCOP-nickel(II) pincer complexes were prepared by mixing POCOP pincer ligands and NiX 2 in toluene at reflux. The resulting nickel complexes efficiently catalyze the homocoupling reactions of benzyl halides in the presence of zinc. The coupled products were obtained in excellent to quantitative yields. © 2012 Elsevier Ltd. All rights reserved.

  6. Palladium(II) Acetate Catalyzed Reductive Heck Reaction of Enones; A Practical Approach

    NARCIS (Netherlands)

    Mannathan, Subramaniyan; Raoufmoghaddam, Saeed; Reek, Joost N. H.; de Vries, Johannes G.; Minnaard, Adriaan J.

    2015-01-01

    A surprisingly practical Pd(OAc)(2) or Pd(TFA)(2)-catalyzed reductive Heck reaction between aryl iodides and alpha,beta-unsaturated ketones is described using N,N-diisopropylethylamine (DIPEA, Hunigs base) as the reductant. In general, 1 mol% of Pd(OAc)(2) is sufficient to afford good yields using

  7. Practical and General Palladium-Catalyzed Synthesis of Ketones from Internal Olefins

    KAUST Repository

    Morandi, Bill

    2013-01-16

    Make it simple! A convenient and general palladium-catalyzed oxidation of internal olefins to ketones is reported. The transformation occurs at room temperature and shows wide substrate scope. Applications to the oxidation of seed-oil derivatives and a bioactive natural product (see scheme) are described, as well as intriguing mechanistic features.

  8. Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

    Directory of Open Access Journals (Sweden)

    Pedro Almendros

    2011-05-01

    Full Text Available New gold-catalyzed methods using the β-lactam scaffold have been recently developed for the synthesis of different sized heterocycles. This overview focuses on heterocyclization reactions of allenic and alkynic β-lactams which rely on the activation of the allene and alkyne component. The mechanism as well as the regio- and stereoselectivity of the cyclizations are also discussed.

  9. Palladium-Catalyzed Anti-Markovnikov Oxidation of Allylic Amides to Protected beta-Amino Aldehydes

    NARCIS (Netherlands)

    Dong, Jiajia; Harvey, Emma C.; Fananas-Mastral, Martin; Browne, Wesley R.; Feringa, Bernard

    2014-01-01

    A general method for the preparation of N-protected beta-amino aldehydes from allylic amines or linear allylic alcohols is described. Here the Pd(II)-catalyzed oxidation of N-protected allylic amines with benzoquinone is achieved in tBuOH under ambient conditions with excellent selectivity toward

  10. Rh(III-catalyzed directed C–H bond amidation of ferrocenes with isocyanates

    Directory of Open Access Journals (Sweden)

    Satoshi Takebayashi

    2012-10-01

    Full Text Available [RhCp*(OAc2(H2O] [Cp* = pentamethylcyclopentadienyl] catalyzed the C–H bond amidation of ferrocenes possessing directing groups with isocyanates in the presence of 2 equiv/Rh of HBF4·OEt2. A variety of disubstituted ferrocenes were prepared in high yields, or excellent diastereoselectivities.

  11. Metallocene-catalyzed alkene polymerization and the observation of Zr-allyls

    OpenAIRE

    Landis, Clark R.; Christianson, Matthew D.

    2006-01-01

    Single-site polymerization catalysts enable exquisite control over alkene polymerization reactions to produce new materials with unique properties. Knowledge of catalyst speciation and fundamental kinetics are essential for full mechanistic understanding of zirconocene-catalyzed alkene polymerization. Currently the effect of activators on fundamental polymerization steps is not understood. Progress in understanding activator effects requires determination of fundamental kinetics for zirconoce...

  12. Enantioselective Evans-Tishchenko Reduction of b-Hydroxyketone Catalyzed by Lithium Binaphtholate

    Directory of Open Access Journals (Sweden)

    Makoto Nakajima

    2011-06-01

    Full Text Available Lithium diphenylbinaphtholate catalyzed the enantioselective Evans-Tishchenko reduction of achiral b-hydroxyketones to afford monoacyl-protected 1,3-diols with high stereoselectivities. In the reaction of racemic b-hydroxyketones, kinetic optical resolution occurred in a highly stereoselective manner.

  13. Mechanism of Cytochrome P450 17A1-Catalyzed Hydroxylase and Lyase Reactions

    DEFF Research Database (Denmark)

    Bonomo, Silvia; Jorgensen, Flemming Steen; Olsen, Lars

    2017-01-01

    Cytochrome P450 17A1 (CYP17A1) catalyzes C17 hydroxylation of pregnenolone and progesterone and the subsequent C17–C20 bond cleavage (lyase reaction) to form androgen precursors. Compound I (Cpd I) and peroxo anion (POA) are the heme-reactive species underlying the two reactions. We have...

  14. Efficient TCT-catalyzed Synthesis of 1,5-Benzodiazepine Derivatives under Mild Conditions

    Directory of Open Access Journals (Sweden)

    Ching-Fa Yao

    2008-09-01

    Full Text Available 2,4,6-Trichloro-1,3,5-triazine (TCT efficiently catalyzed the condensation reactions between 1,2-diamines and various enolizable ketones to afford 1,5-benzodiazepines in good to excellent yields. Simple and mild reaction conditions, the use of a cheap catalyst and easy workup and isolation are notable features of this method.

  15. Laccase catalyzed grafting of-N-OH type mediators to lignin via radical-radical coupling

    DEFF Research Database (Denmark)

    Munk, Line; Punt, A. M.; Kabel, M. A.

    2017-01-01

    by laccases from Trametes versicolor and Pleurotus ostreatus by quantitative analysis of the reaction outcome by pyrolysis gas chromatography mass spectroscopy. The two laccases were equally efficient in catalyzing grafting, but only-N-OH type mediators grafted. HPI (N-hydroxyacetanilide) grafted 7-10 times...

  16. Cu(I)-catalyzed efficient synthesis of 2′-Triazolo-nucleoside conjugates

    DEFF Research Database (Denmark)

    Mathur, D.; Rana, N.; Olsen, Carl Erik

    2015-01-01

    A small library of thirty-two 2′-triazolyl uridine and 2′-triazolyl-5-methyluridine has been synthesized by Cu(I)-catalyzed condensation of 2′-azido-2′-deoxyuridine and 2′-azido-2′-deoxy-5-methyluridine with different alkynes and aryl propargyl ethers in almost quantitative yields. Triazolo...

  17. Enantioselective BINOL-phosphoric acid catalyzed Pictet-Spengler reactions of N-benzyltryptamine

    NARCIS (Netherlands)

    Sewgobind, N.V.; Wanner, M.J.; Ingemann, S.; de Gelder, R.; van Maarseveen, J.H.; Hiemstra, H.

    2008-01-01

    Optically active tetrahydro-beta-carbolines were synthesized via an (R)-BINOL-phosphoric acid-catalyzed asynunetric Pictet-Spengler reaction of N-benzyltryptamine with a series of aromatic and aliphatic aldehydes. The tetrahydro-beta-carbolines were obtained in yields ranging from 77% to 97% and

  18. Synthesis of 5-hydroxymethylfurfural (HMF) by acid catalyzed dehydration of glucose-fructose mixtures

    DEFF Research Database (Denmark)

    Pedersen, Asbjørn Toftgaard; Ringborg, Rolf Hoffmeyer; Grotkjær, Thomas

    2015-01-01

    allowing the use of the cheapest available source of fructose: high fructose corn syrup. The dehydration was catalyzed by hydrochloric acid and conducted in acetone-water mixtures, which ensured good selectivity towards HMF and eliminated precipitation of polymer by-products (insoluble humins). Through...

  19. The Isomerization of (-)-Menthone to (+)-Isomenthone Catalyzed by an Ion-Exchange Resin

    Science.gov (United States)

    Ginzburg, Aurora L.; Baca, Nicholas A.; Hampton, Philip D.

    2014-01-01

    A traditional organic chemistry laboratory experiment involves the acid-catalyzed isomerization of (-)-menthone to (+)-isomenthone. This experiment generates large quantities of organic and aqueous waste, and only allows the final ratio of isomers to be determined. A "green" modification has been developed that replaces the mineral acid…

  20. Laccase catalyzed grafting of-N-OH type mediators to lignin via radical-radical coupling

    NARCIS (Netherlands)

    Munk, L.; Punt, A.M.; Kabel, M.A.; Meyer, A.S.

    2017-01-01

    Lignin is an underexploited resource in biomass refining. Laccases (EC 1.10.3.2) catalyze oxidation of phenolic hydroxyls using O2 as electron acceptor and may facilitate lignin modification in the presence of mediators. This study assessed the reactivity of four different synthetic mediators by

  1. Syntheses of Calix[4]Pyrroles by Amberlyst-15 Catalyzed Cyclocondensations of Pyrrole with Selected Ketones

    Directory of Open Access Journals (Sweden)

    Tanuja Bisht

    2007-11-01

    Full Text Available A facile and efficient protocol is reported for the synthesis of calix[4]pyrrolesand N-confused calix[4]pyrroles in moderate to excellent yields by reaction of dialkyl orcycloalkyl ketones with pyrrole catalyzed by reusable AmberlystTM-15 under eco-friendlyconditions.

  2. Palladium(II) acetate catalyzed reductive Heck reaction of enones: a practical approach

    NARCIS (Netherlands)

    Mannathan, S.; Raoufmoghaddam, S.; Reek, J.N.H.; de Vries, J.G.; Minnaard, A.J.

    2016-01-01

    A surprisingly practical Pd(OAc)​2 or Pd(TFA)​2-​catalyzed reductive Heck reaction between aryl iodides and α,​β-​unsatd. ketones is described using N,​N-​diisopropylethylamine (DIPEA, Huenigs base) as the reductant. In general, 1 mol % of Pd(OAc)​2 is sufficient to afford good yields using

  3. Palladium(0)/NHC-Catalyzed Reductive Heck Reaction of Enones : A Detailed Mechanistic Study

    NARCIS (Netherlands)

    Raoufmoghaddam, Saeed; Mannathan, Subramaniyan; Minnaard, Adriaan J; de Vries, Johannes G; Reek, Joost N H

    2015-01-01

    We have studied the mechanism of the palladium-catalyzed reductive Heck reaction of para-substituted enones with 4-iodoanisole by using N,N-diisopropylethylamine (DIPEA) as the reductant. Kinetic studies and in situ spectroscopic analysis have provided a detailed insight into the reaction. Progress

  4. Palladium(0)​/NHC-​catalyzed reductive Heck reaction of enones: a detailed mechanistic study

    NARCIS (Netherlands)

    Raoufmoghaddam, S.; Mannathan, S.; Minnaard, A.J.; de Vries, J.G.; Reek, J.N.H.

    2015-01-01

    We have studied the mechanism of the palladium-​catalyzed reductive Heck reaction of para-​substituted enones with 4-​iodoanisole by using N,​N-​diisopropylethylamine (DIPEA) as the reductant. Kinetic studies and in situ spectroscopic anal. have provided a detailed insight into the reaction.

  5. Cobalt-Catalyzed Cross-Coupling of α-Bromo Amides with Grignard Reagents.

    Science.gov (United States)

    Barde, E; Guérinot, A; Cossy, J

    2017-11-17

    A cobalt-catalyzed cross-coupling between α-bromo amides and Grignard reagents is disclosed. The reaction is general and allows access to a large variety of α-aryl and β,γ-unsaturated amides. Some mechanistic investigations have been undertaken to determine the nature of the intermediate species.

  6. Palladium-Catalyzed Polyfluorophenylation of Porphyrins with Bis(polyfluorophenylzinc Reagents

    Directory of Open Access Journals (Sweden)

    Toshikatsu Takanami

    2013-10-01

    Full Text Available A facile and efficient method for the synthesis of pentafluorophenyl- and related polyfluorophenyl-substituted porphyrins has been achieved via palladium-catalyzed cross-coupling reactions of brominated porphyrins with bis(polyfluorophenylzinc reagents. The reaction is applicable to a variety of free-base bromoporphyrins, their metal complexes, and a number of bis(polyfluorophenylzinc reagents.

  7. Palladium-Catalyzed Enantioselective Three-Component Synthesis of α-Substituted Amines.

    Science.gov (United States)

    Beisel, Tamara; Manolikakes, Georg

    2015-06-19

    The first general palladium-catalyzed, enantioselective three-component synthesis of α-arylamines starting from sulfonamides, aldehydes, and arylboronic acids has been developed. These reactions generate a wide array of α-arylamines with high yields and enantioselectivities. Notably, this process is tolerant to air and moisture, providing an operationally simple approach for the synthesis of chiral α-arylamines.

  8. Highly enantioselective synthesis of chiral cyclic allylic amines via Rh-catalyzed asymmetric hydrogenation.

    Science.gov (United States)

    Zhou, Ming; Liu, Tang-Lin; Cao, Min; Xue, Zejian; Lv, Hui; Zhang, Xumu

    2014-07-03

    Highly regioselective and enantioselective asymmetric hydrogenation of cyclic dienamides catalyzed by an Rh-DuanPhos complex has been developed, which provides a readily accessible method for the synthesis of chiral cyclic allylic amines in excellent enantioselectivities (up to 99% ee). The products are valuable chiral building blocks and could be easily transformed to multisubstituted cyclohexane derivatives.

  9. The Lewis-acid-catalyzed synthesis of hyperbranched poly(glycerol-diacid)s in toluene

    Science.gov (United States)

    The first examples of monomeric glycerol-derived hyperbranched polyesters produced in a non-polar solvent system are reported here. The polymers were made by the Lewis acid (dibutyltin(IV)oxide)-catalyzed polycondensation of glycerol with either succinic acid (n (aliphatic chain length)=2), glutari...

  10. Large acceleration of a-chymotrypsin-catalyzed dipeptide formation by 18-crown-6 in organic solvents

    NARCIS (Netherlands)

    van Unen, D.J.; Engbersen, Johannes F.J.; Reinhoudt, David

    1998-01-01

    The effects of 18-crown-6 on the synthesis of peptides catalyzed by α-chymotrypsin are reported. Lyophilization of the enzyme in the presence of 50 equivalents of 18-crown-6 results in a 425-fold enhanced activity when the reaction between the 2-chloroethylester of N-acetyl-L-phenylalanine and

  11. Synthesis of polysubstituted pyrazoles by a platinum-catalyzed sigmatropic rearrangement/cyclization cascade.

    Science.gov (United States)

    Wen, Jia-Jie; Tang, Hai-Tao; Xiong, Kai; Ding, Zong-Cang; Zhan, Zhuang-Ping

    2014-11-21

    A highly efficient Pt-catalyzed [3,3] sigmatropic rearrangement/cyclization cascade of N-propargylhydrazones is reported. The process provides expedient access to a variety of highly functionalized pyrazoles. The substrate has good substituted group compatibility, and the bioactive 3-CF3 pyrazoles could be synthesized easily with this method.

  12. Synthetic Studies and Mechanistic Insight in Nickel-Catalyzed [4+2+1] Cycloadditions

    Science.gov (United States)

    Ni, Yike

    2008-01-01

    A new nickel-catalyzed procedure for the [4+2+1] cycloaddition of (trimethylsilyl)diazomethane with alkynes tethered to dienes has been developed. A broad range of unsaturated substrates participates in the sequence, and stereoselectivities are generally excellent. Stereochemical studies provided evidence for a mechanism that involves the [3,3]-sigmatropic rearrangement of divinylcyclopropanes. PMID:16492045

  13. Palladium-catalyzed carbonylative sonogashira coupling of aryl bromides using near stoichiometric carbon monoxide

    DEFF Research Database (Denmark)

    Neumann, Karoline T.; Laursen, Simon R.; Lindhardt, Anders T.

    2014-01-01

    A general procedure for the palladium-catalyzed carbonylative Sonogashira coupling of aryl bromides is reported, using near stoichiometric amounts of carbon monoxide. The method allows a broad substrate scope in moderate to excellent yields. The formed alkynone motive serves as a platform...

  14. Enzyme-catalyzed nucleophilic ring opening of Epoxides for the preparation of enantiopure tertiary alcohols

    NARCIS (Netherlands)

    Majeric Elenkov, Maja; Hoeffken, H. Wolfgang; Tang, Lixia; Hauer, Bernhard; Janssen, Dick B.

    2007-01-01

    The halohydrin dehalogenase from Agrobacterium radiobacter AD1 (HheC) catalyzes nucleophilic ring opening of epoxides with cyanide and azide. In the case of 2,2-disubstituted epoxides, this reaction proceeds with excellent enantioselectivity (E values up to > 200), which gives, by kinetic

  15. Enzyme-Catalyzed Nucleophilic Ring Opening of Epoxides for the Preparation of Enantiopure Tertiary Alcohols

    NARCIS (Netherlands)

    Majeric Elenkov, Maja; Hoeffken, H. Wolfgang; Tang, Lixia; Hauer, Bernhard; Janssen, Dick B.

    2007-01-01

    The halohydrin dehalogenase from Agrobacterium radiobacter AD1 (HheC) catalyzes nucleophilic ring opening of epoxides with cyanide and azide. In the case of 2,2-disubstituted epoxides, this reaction proceeds with excellent enantioselectivity (E values up to >200), which gives, by kinetic resolution,

  16. Monitoring lipase-catalyzed butterfat interesterification with rapesee oil by Fourier transform near-infrared spectroscopy

    DEFF Research Database (Denmark)

    Zhang, Hong; Mu, Huiling; Xu, Xuebing

    2006-01-01

    This work demonstrates the application of FT-NIR spectroscopy to monitor the enzymatic interesterification process for butterfat modification. The reactions were catalyzed by Lipozyme TL IM at 70 C for the blend of butterfat/rapeseed oil (70/30, w/w) in a packed-bed reactor. The blend and intere...

  17. Copper-catalyzed trifluoromethylation of arylsulfinate salts using an electrophilic trifluoromethylation reagent

    KAUST Repository

    Lin, Xiaoxi

    2013-03-01

    A copper-catalyzed method for the trifluoromethylation of arylsulfinates with Togni\\'s reagent has been developed, affording aryltrifluoromethylsulfones in moderate to good yields. A wide range of functional groups in arylsulfinates are compatible with the reaction conditions. © 2013 Elsevier Ltd. All rights reserved.

  18. A new manganese-mediated, cobalt-catalyzed three-component synthesis of (diarylmethylsulfonamides

    Directory of Open Access Journals (Sweden)

    Antoine Pignon

    2014-02-01

    Full Text Available The synthesis of (diarylmethylsulfonamides and related compounds by a new manganese-mediated, cobalt-catalyzed three-component reaction between sulfonamides, carbonyl compounds and organic bromides is described. This organometallic Mannich-like process allows the formation of the coupling products within minutes at room temperature. A possible mechanism, emphasizing the crucial role of manganese is proposed.

  19. Enantioselective Michael Addition of Malonates to Chalcone Derivatives Catalyzed by Dipeptide-derived Multifunctional Phosphonium Salts.

    Science.gov (United States)

    Cao, Dongdong; Fang, Guosheng; Zhang, Jiaxing; Wang, Hongyu; Zheng, Changwu; Zhao, Gang

    2016-10-21

    Highly enantioselective Michael addition of malonates to enones catalyzed by dipeptide-derived multifunctional phosphonium salts has been developed. The newly established catalytic system was characterized with its wide substrate scope featured with aliphatic aldehyde-derived enones and substituted malonates. The gram scale-up synthesis of adducts can also be successfully achieved under optimal conditions with both excellent yield and enantioselectivity.

  20. Selective Metal-Free Hydrosilylation of CO2 Catalyzed by Triphenylborane in Highly Polar, Aprotic Solvents.

    Science.gov (United States)

    Mukherjee, Debabrata; Sauer, Daniel F; Zanardi, Alessandro; Okuda, Jun

    2016-06-01

    Triphenylborane (BPh3 ) in highly polar, aprotic solvents catalyzes hydrosilylation of CO2 effectively under mild conditions to provide silyl formates with high chemoselectivity (>95 %) and without over-reduction. This system also promotes reductive hydrosilylation of tertiary amides as well as dehydrogenative coupling of silane with alcohols. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Visible-Light Photoredox-Catalyzed Coupling Reaction of Azoles with α-Carbamoyl Sulfides.

    Science.gov (United States)

    Jarrige, Lucie; Levitre, Guillaume; Masson, Géraldine

    2016-08-19

    A simple, straightforward strategy for the synthesis of N-substituted azoles is reported that involves a visible-light photoredox-catalyzed coupling reaction of azoles with α-carbamoyl sulfides. A variety of heterocyclic units, including pyrazoles, benzopyrazoles, benzoimidazoles, and purines, can be efficiently incorporated under mild reaction conditions in respectable yields.

  2. Highly selective formation of imines catalyzed by silver nanoparticles supported on alumina

    DEFF Research Database (Denmark)

    Mielby, Jerrik Jørgen; Poreddy, Raju; Engelbrekt, Christian

    2014-01-01

    The oxidative dehydrogenation of alcohols to aldehydes catalyzed by Ag nanoparticles supported on Al2O3 was studied. The catalyst promoted the direct formation of imines by tandem oxidative dehydrogenation and condensation of alcohols and amines. The reactions were performed under mild conditions...

  3. Memory effects in palladium-catalyzed allylic Alkylations of 2-cyclohexen-1-yl acetate

    DEFF Research Database (Denmark)

    Svensen, Nina; Fristrup, Peter; Tanner, David Ackland

    2007-01-01

    The objective of this work was to characterize the enantiospecificity of the allylic alkylation of enantioenriched 2-cyclohexen-1-yl acetate with the enolate ion of dimethyl malonate catalyzed by unsymmetrical palladium catalysts. The precatalysts employed were (eta(3)-allyl)PdLCl, where L...

  4. Pd-catalyzed Z-selective semihydrogenation of alkynes: determining the type of active species

    NARCIS (Netherlands)

    Drost, R.M.; Rosar, V.; Marta, S.D.; Lutz, M.; Demitri, N.; Milani, B.; de Bruin, B.; Elsevier, C.J.

    2015-01-01

    A protocol was developed to distinguish between well-defined molecular and nanoparticle-based catalysts for the Pd-catalyzed semihydrogenation reaction of alkynes to Z-alkenes. The protocol applies quantitative partial poisoning and dynamic light scattering methods, which allow the institution of

  5. Pd-Catalyzed Z-Selective Semihydrogenation of Alkynes : Determining the Type of Active Species

    NARCIS (Netherlands)

    Drost, Ruben M.; Rosar, Vera; Marta, Silvia Dalla; Lutz, Martin; Demitri, Nicola; Milani, Barbara; De Bruin, Bas; Elsevier, Cornelis J.

    2015-01-01

    A protocol was developed to distinguish between well-defined molecular and nanoparticle-based catalysts for the Pd-catalyzed semihydrogenation reaction of alkynes to Z-alkenes. The protocol applies quantitative partial poisoning and dynamic light scattering methods, which allow the institution of

  6. Room-temperature base-free copper-catalyzed trifluoromethylation of organotrifluoroborates to trifluoromethylarenes

    KAUST Repository

    Huang, Yuanyuan

    2012-12-01

    An efficient room temperature copper-catalyzed trifluoromethylation of organotrifluoroborates under the base free condition using an electrophilic trifluoromethylating reagent is demonstrated. The corresponding trifluoromethylarenes were obtained in good to excellent yields and the reaction tolerates a wide range of functional groups. © 2012 Elsevier Ltd. All rights reserved.

  7. Synthesis of trifluoromethylated acetylenes via copper-catalyzed trifluoromethylation of alkynyltrifluoroborates

    KAUST Repository

    Zheng, Huidong

    2012-12-01

    A new method for the synthesis of trifluoromethylated acetylenes is developed which involves the copper-catalyzed trifluoromethylation of alkynyltrifluoroborates with an electrophilic trifluoromethylating reagent. This method offers significant advantages such as efficiency and mild and base-free reaction conditions. A plausible mechanism is proposed. © 2012 Elsevier Ltd. All rights reserved.

  8. Copper-catalyzed enantioselective conjugate addition of organometallic reagents to acyclic dienones

    NARCIS (Netherlands)

    Sebesta, Radovan; Pizzuti, M. Gabriella; Minnaard, Adriaan J.; Feringa, Ben L.; Šebesta, Radovan

    The enantioselective, copper/phosphoramidite-catalyzed 1,4-addition of dialkylzinc reagents to acyclic dienones is described. The products of this reaction, obtained with enantioselectivities of up to 95%, can be further functionalized by a second conjugate addition, or employed in an enolate

  9. Palladium-Catalyzed Regioselective C8-H Amination of 1-Naphthylamine Derivatives with Aliphatic Amines.

    Science.gov (United States)

    Li, Zexian; Sun, Suyan; Qiao, Huijie; Yang, Fan; Zhu, Yu; Kang, Jianxun; Wu, Yusheng; Wu, Yangjie

    2016-09-16

    A simple and facile protocol for palladium-catalyzed picolinamide-directed C8-H amination of 1-naphthylamine derivatives with simple secondary aliphatic amines was developed, thereby providing a new route to 1,8-naphthalenediamine derivatives. It is noteworthy that the picolinamide moiety as a bidentate directing group may play a key role in this regioselective transformation.

  10. Ag-catalyzed InAs nanowires grown on transferable graphite flakes

    DEFF Research Database (Denmark)

    Meyer-Holdt, Jakob; Kanne, Thomas; Sestoft, Joachim E.

    2016-01-01

    on exfoliated graphite flakes by molecular beam epitaxy. Ag catalyzes the InAs nanowire growth selectively on the graphite flakes and not on the underlying InAs substrates. This allows for easy transfer of the flexible graphite flakes with as-grown nanowire ensembles to arbitrary substrates by a micro-needle...

  11. Gold(III)-catalyzed three-component coupling reaction (TCC) selective toward furans.

    Science.gov (United States)

    Li, Jian; Liu, Li; Ding, Dong; Sun, Jiangtao; Ji, Yangxuan; Dong, Jialing

    2013-06-07

    An efficient three-component coupling reaction toward a variety of furan derivatives has been developed. This cascade transformation proceeds via the gold-catalyzed coupling reaction of phenylglyoxal derivatives, secondary amines, and terminal alkynes, under the reaction conditions, that undergoes cyclization into the furan core.

  12. Catalyzing Mass Production of Solar Photovoltaic Cells Using University Driven Green Purchasing

    Science.gov (United States)

    Pearce, Joshua M.

    2006-01-01

    Purpose: The purpose of this paper is to explore the use of the purchase power of the higher education system to catalyze the economy of scale necessary to ensure market competitiveness for solar photovoltaic electricity. Design/methodology/approach: The approach used here was to first determine the demand necessary to construct "Solar City…

  13. Unexpected Reaction Pathway for butyrylcholinesterase-catalyzed inactivation of “hunger hormone” ghrelin

    Science.gov (United States)

    Yao, Jianzhuang; Yuan, Yaxia; Zheng, Fang; Zhan, Chang-Guo

    2016-02-01

    Extensive computational modeling and simulations have been carried out, in the present study, to uncover the fundamental reaction pathway for butyrylcholinesterase (BChE)-catalyzed hydrolysis of ghrelin, demonstrating that the acylation process of BChE-catalyzed hydrolysis of ghrelin follows an unprecedented single-step reaction pathway and the single-step acylation process is rate-determining. The free energy barrier (18.8 kcal/mol) calculated for the rate-determining step is reasonably close to the experimentally-derived free energy barrier (~19.4 kcal/mol), suggesting that the obtained mechanistic insights are reasonable. The single-step reaction pathway for the acylation is remarkably different from the well-known two-step acylation reaction pathway for numerous ester hydrolysis reactions catalyzed by a serine esterase. This is the first time demonstrating that a single-step reaction pathway is possible for an ester hydrolysis reaction catalyzed by a serine esterase and, therefore, one no longer can simply assume that the acylation process must follow the well-known two-step reaction pathway.

  14. A DFT study on the mechanism of palladium-catalyzed divergent ...

    Indian Academy of Sciences (India)

    gent reactions reported by Liang group. Here, we present a detailed DFT study on the mechanism of palladium-catalyzed reaction of enyne carbonates to give the corresponding vinylidenepyridines or vinyli- denepyrrolidines based on the experiment reported by. Liang et al. In the experimental studies, Pd(dba)2 was. 547 ...

  15. Mechanism of Laccase¿TEMPO-Catalyzed Oxidation of Benzyl Alcoho

    NARCIS (Netherlands)

    Tromp, Sander A.; Matijosyte, Inga; Sheldon, Roger A.; Arends, Isabel W.C.E.; Mul, Guido; Kreutzer, Michiel T.; Moulijn, Jacob A.; de Vries, Simon

    2010-01-01

    The oxidation of benzyl alcohol by air, catalyzed by the organocatalyst TEMPO and the enzyme laccase has been investigated. To establish the kinetically significant pathways and corresponding kinetic parameters, a series of experiments is conducted with synthesized stable oxidized and reduced forms

  16. α-Ketophosphonates as ester surrogates: isothiourea-catalyzed asymmetric diester and lactone synthesis.

    Science.gov (United States)

    Smith, Siobhan R; Leckie, Stuart M; Holmes, Reuben; Douglas, James; Fallan, Charlene; Shapland, Peter; Pryde, David; Slawin, Alexandra M Z; Smith, Andrew D

    2014-05-02

    Isothiourea HBTM-2.1 catalyzes the asymmetric Michael addition/lactonization of aryl- and alkenylacetic acids using α-keto-β,γ-unsaturated phosphonates as α,β-unsaturated ester surrogates, giving access to a diverse range of stereodefined lactones or enantioenriched functionalized diesters upon ring-opening.

  17. Palladium-Catalyzed Cross-Coupling Reactions of Perfluoro Organic Compounds

    Directory of Open Access Journals (Sweden)

    Masato Ohashi

    2014-09-01

    Full Text Available In this review, we summarize our recent development of palladium(0-catalyzed cross-coupling reactions of perfluoro organic compounds with organometallic reagents. The oxidative addition of a C–F bond of tetrafluoroethylene (TFE to palladium(0 was promoted by the addition of lithium iodide, affording a trifluorovinyl palladium(II iodide. Based on this finding, the first palladium-catalyzed cross-coupling reaction of TFE with diarylzinc was developed in the presence of lithium iodide, affording α,β,β-trifluorostyrene derivatives in excellent yield. This coupling reaction was expanded to the novel Pd(0/PR3-catalyzed cross-coupling reaction of TFE with arylboronates. In this reaction, the trifluorovinyl palladium(II fluoride was a key reaction intermediate that required neither an extraneous base to enhance the reactivity of organoboronates nor a Lewis acid additive to promote the oxidative addition of a C–F bond. In addition, our strategy utilizing the synergetic effect of Pd(0 and lithium iodide could be applied to the C–F bond cleavage of unreactive hexafluorobenzene (C6F6, leading to the first Pd(0-catalyzed cross-coupling reaction of C6F6 with diarylzinc compounds.

  18. Cobalt-Catalyzed Bis-alkynylation of Amides via Double C-H Bond Activation.

    Science.gov (United States)

    Landge, Vinod G; Jaiswal, Garima; Balaraman, Ekambaram

    2016-02-19

    The first example of cobalt-catalyzed selective bis-alkynylation of amides via double C-H bond activation with the directing assistance of a removable bidentate auxiliary is reported. The developed alkynylation strategy is simple, efficient, and tolerant of various functional groups including ether, amine, halides, and heterocyclic motifs. The reaction can be scaled up under mild conditions.

  19. Efficient copper-catalyzed benzylic amidation with anhydrous chloramine-T.

    Science.gov (United States)

    Bhuyan, Ranjana; Nicholas, Kenneth M

    2007-09-27

    Benzylic hydrocarbons are selectively converted to the corresponding sulfonamides by the [Cu(CH(3)CN)(4)]PF(6)-catalyzed reaction with anhydrous TolSO(2)NNaCl (chloramine-T). Under the same conditions, representative ethers are also alpha-amidated; olefins produce allyl sulfonamides, aziridines, and/or beta-chloro sulfonamides.

  20. Enantioselective Copper-Catalyzed Arylation-Driven Semipinacol Rearrangement of Tertiary Allylic Alcohols with Diaryliodonium Salts.

    Science.gov (United States)

    Lukamto, Daniel H; Gaunt, Matthew J

    2017-07-12

    A copper-catalyzed enantioselective arylative semipinacol rearrangement of allylic alcohols using diaryliodonium salts is reported. Chiral Cu(II)-bisoxazoline catalysts initiate an electrophilic alkene arylation, triggering a 1,2-alkyl migration to afford a range of nonracemic spirocyclic ketones with high yields, diastereo- and enantioselectivities.

  1. Beta-D-xylosidase from Selenomonas ruminantium: thermodynamics of enzyme-catalyzed and noncatalyzed reactions

    Science.gov (United States)

    Beta-D-xylosidase/alpha-L-arabinofuranosidase from Selenomonas ruminantium (SXA) is the most active enzyme known for catalyzing hydrolysis of 1,4-beta-D-xylooligosaccharides to D-xylose. Temperature dependence for hydrolysis of 4-nitrophenyl-beta-D-xylopyranoside (4NPX), 4-nitrophenyl-alpha-L-arabi...

  2. Silver-Catalyzed Synthesis of Diaryl Selenides by Reaction of Diaryl Diselenides with Aryl Boronic Acids.

    Science.gov (United States)

    Goldani, Bruna; Ricordi, Vanessa G; Seus, Natália; Lenardão, Eder J; Schumacher, Ricardo F; Alves, Diego

    2016-11-18

    We described herein our results on the silver-catalyzed synthesis of diaryl selenides via a cross-coupling reaction of diaryl diselenides with aryl boronic acids. The methodology is tolerant to electron-donor and electron-withdrawing groups at the substrates and the desired products were obtained in good to excellent yields.

  3. Disulfide Bond Oxidoreductase DsbA2 of Legionella pneumophila Exhibits Protein Disulfide Isomerase Activity

    OpenAIRE

    Kpadeh, Zegbeh Z.; Jameson-Lee, Max; Anthony J. Yeh; Chertihin, Olga; Shumilin, Igor A.; Dey, Rafik; Day, Shandra R.; Hoffman, Paul S.

    2013-01-01

    The extracytoplasmic assembly of the Dot/Icm type IVb secretion system (T4SS) of Legionella pneumophila is dependent on correct disulfide bond (DSB) formation catalyzed by a novel and essential disulfide bond oxidoreductase DsbA2 and not by DsbA1, a second nonessential DSB oxidoreductase. DsbA2, which is widely distributed in the microbial world, is phylogenetically distinct from the canonical DsbA oxidase and the DsbC protein disulfide isomerase (PDI)/reductase of Escherichia coli. Here we s...

  4. C-H Bond Oxidation Catalyzed by an Imine-Based Iron Complex: A Mechanistic Insight.

    Science.gov (United States)

    Olivo, Giorgio; Nardi, Martina; Vìdal, Diego; Barbieri, Alessia; Lapi, Andrea; Gómez, Laura; Lanzalunga, Osvaldo; Costas, Miquel; Di Stefano, Stefano

    2015-11-02

    A family of imine-based nonheme iron(II) complexes (LX)2Fe(OTf)2 has been prepared, characterized, and employed as C-H oxidation catalysts. Ligands LX (X = 1, 2, 3, and 4) stand for tridentate imine ligands resulting from spontaneous condensation of 2-pycolyl-amine and 4-substituted-2-picolyl aldehydes. Fast and quantitative formation of the complex occurs just upon mixing aldehyde, amine, and Fe(OTf)2 in a 2:2:1 ratio in acetonitrile solution. The solid-state structures of (L1)2Fe(OTf)(ClO4) and (L3)2Fe(OTf)2 are reported, showing a low-spin octahedral iron center, with the ligands arranged in a meridional fashion. (1)H NMR analyses indicate that the solid-state structure and spin state is retained in solution. These analyses also show the presence of an amine-imine tautomeric equilibrium. (LX)2Fe(OTf)2 efficiently catalyze the oxidation of alkyl C-H bonds employing H2O2 as a terminal oxidant. Manipulation of the electronic properties of the imine ligand has only a minor impact on efficiency and selectivity of the oxidative process. A mechanistic study is presented, providing evidence that C-H oxidations are metal-based. Reactions occur with stereoretention at the hydroxylated carbon and selectively at tertiary over secondary C-H bonds. Isotopic labeling analyses show that H2O2 is the dominant origin of the oxygen atoms inserted in the oxygenated product. Experimental evidence is provided that reactions involve initial oxidation of the complexes to the ferric state, and it is proposed that a ligand arm dissociates to enable hydrogen peroxide binding and activation. Selectivity patterns and isotopic labeling studies strongly suggest that activation of hydrogen peroxide occurs by heterolytic O-O cleavage, without the assistance of a cis-binding water or alkyl carboxylic acid. The sum of these observations provides sound evidence that controlled activation of H2O2 at (LX)2Fe(OTf)2 differs from that occurring in biomimetic iron catalysts described to date.

  5. Lipase-catalyzed synthesis of cocoa butter equivalent from palm olein and saturated fatty acid distillate from palm oil physical refinery.

    Science.gov (United States)

    Mohamed, Ibrahim O

    2012-11-01

    Cocoa butter equivalent was prepared by enzymatic acidolysis reaction of substrate consisting of refined palm olein oil and palmitic-stearic fatty acid mixture. The reactions were performed in a batch reactor at a temperature of 60 °C in an orbital shaker operated at 160 RPM. Different mass ratios of substrates were explored and the compositions of the five major triacylglycerol (TAG) of the structured lipids were identified and quantified using cocoa butter-certified reference material IRMM-801. The reaction resulted in production of cococa butter equivent with TAG compostion (POP 26.6 %, POS 42.1, POO 7.5, SOS 18.0 %, and SOO 5.8 %) and melting temperature between 34.7 and 39.6 °C which is close to that of the cocoa butter. The result of this research demonstrated the potential use of saturated fatty acid distillate (palmitic and stearic fatty acids) obtained from palm oil physical refining process into a value-added product.

  6. Homologous Pairing Activities of Two Rice RAD51 Proteins, RAD51A1 and RAD51A2

    Science.gov (United States)

    Ikawa, Shukuko; Mimida, Naozumi; Shimizu, Takeshi; Toki, Seiichi; Ichikawa, Hiroaki; Shibata, Takehiko; Kurumizaka, Hitoshi

    2013-01-01

    In higher eukaryotes, RAD51 functions as an essential protein in homologous recombination and recombinational repair of DNA double strand breaks. During these processes, RAD51 catalyzes homologous pairing between single-stranded DNA and double-stranded DNA. Japonica cultivars of rice (Oryza sativa) encode two RAD51 proteins, RAD51A1 and RAD51A2, whereas only one RAD51 exists in yeast and mammals. However, the functional differences between RAD51A1 and RAD51A2 have not been elucidated, because their biochemical properties have not been characterized. In the present study, we purified RAD51A1 and RAD51A2, and found that RAD51A2 robustly promotes homologous pairing in vitro. RAD51A1 also possesses homologous-pairing activity, but it is only about 10% of the RAD51A2 activity. Both RAD51A1 and RAD51A2 bind to ssDNA and dsDNA, and their DNA binding strictly requires ATP, which modulates the polymer formation activities of RAD51A1 and RAD51A2. These findings suggest that although both RAD51A1 and RAD51A2 have the potential to catalyze homologous pairing, RAD51A2 may be the major recombinase in rice. PMID:24124491

  7. Homologous pairing activities of two rice RAD51 proteins, RAD51A1 and RAD51A2.

    Directory of Open Access Journals (Sweden)

    Yuichi Morozumi

    Full Text Available In higher eukaryotes, RAD51 functions as an essential protein in homologous recombination and recombinational repair of DNA double strand breaks. During these processes, RAD51 catalyzes homologous pairing between single-stranded DNA and double-stranded DNA. Japonica cultivars of rice (Oryza sativa encode two RAD51 proteins, RAD51A1 and RAD51A2, whereas only one RAD51 exists in yeast and mammals. However, the functional differences between RAD51A1 and RAD51A2 have not been elucidated, because their biochemical properties have not been characterized. In the present study, we purified RAD51A1 and RAD51A2, and found that RAD51A2 robustly promotes homologous pairing in vitro. RAD51A1 also possesses homologous-pairing activity, but it is only about 10% of the RAD51A2 activity. Both RAD51A1 and RAD51A2 bind to ssDNA and dsDNA, and their DNA binding strictly requires ATP, which modulates the polymer formation activities of RAD51A1 and RAD51A2. These findings suggest that although both RAD51A1 and RAD51A2 have the potential to catalyze homologous pairing, RAD51A2 may be the major recombinase in rice.

  8. Dirhodium(II)-Catalyzed Sulfide Oxygenations: Catalyst Removal by Coprecipitation with Sulfoxides.

    Science.gov (United States)

    Zhao, Lili; Zhang, Hongyang; Wang, Yuanhua

    2016-01-04

    The dirhodium(II) carboxylate complex Rh2(esp)2 (esp = α,α,α',α'-tetramethyl-1,3-benzenedipropanoate) was shown to catalyze the sulfoxidation of organic sulfides using tert-butyl hydroperoxide as the oxidant. Due to the unique structure of Rh2(esp)2 and its stable Rh2(II,II) catalyst resting state, the rhodium catalyst is able to precipitate as a Rh2(esp)2-sulfoxide complex following the reaction which makes separation of the catalyst from the products very convenient. The precipitated Rh2(esp)2-sulfoxide complexes could be reused to catalyze sulfide oxygenation reactions without considerable loss of activity. Mechanistic studies suggest that the axial ligands fine-tune the redox potential of the dirhodium(II,II) compounds and determine the predominant catalyst species in the oxidation reaction.

  9. Optimization of the Enzyme-Catalyzed Transesterification of Hungarian Sunflower Oil with High Oleic Acid Content

    Energy Technology Data Exchange (ETDEWEB)

    Kovacs, Sandor; Krar, Marton; Hancsok, Jenoe (Univ. of Pannonia, Dept. of Hydrocarbon and Coal Processing, H-8201 Veszprem (Hungary)). e-mail: kovacss@almos.uni-pannon.hu

    2008-10-15

    In our research work we defined the optimum parameters (temperature, methanol to triglyceride molar ratio, reaction time, number of methanol feeds, and the amount of Candia Antarctica lipase) of the enzyme-catalyzed transesterification of properly pre-treated high oleic acid containing sunflower oil. The oleic acid content of the previously mentioned sunflower oil was present in the structure of the triglycerides. Characteristics of the produced sunflower oil methyl esters were evaluated according to the requirements of the EN 14214 standard. Our experimental results indicated that enzyme-catalyzed transesterification could be successfully used for the conversion of high oleic sunflower oils, since we have found proper combination of process parameters resulting in high yield (>99%) of monoesters. The applied enzyme can be separated after the transesterification and used again. The glycerine - because its reaction inhibiting effect - was separated continuously by membrane separation

  10. Single wire radial junction photovoltaic devices fabricated using aluminum catalyzed silicon nanowires

    Science.gov (United States)

    Ke, Y.; Wang, X.; Weng, X. J.; Kendrick, C. E.; Yu, Y. A.; Eichfeld, S. M.; Yoon, H. P.; Redwing, J. M.; Mayer, T. S.; Habib, Y. M.

    2011-11-01

    Single nanowire radial junction solar cell devices were fabricated using Si nanowires synthesized by Al-catalyzed vapor-liquid-solid growth of the p + core (Al auto-doping) and thin film deposition of the n + -shell at temperatures below 650 °C. Short circuit current densities of ~ 11.7 mA cm - 2 were measured under 1-sun AM1.5G illumination, showing enhanced optical absorption. The power conversion efficiencies were limited to junction shunt leakage promoted by the high p + /n + doping. This demonstration of a radial junction device represents an important advance in the use of Al-catalyzed Si nanowire growth for low cost photovoltaics.

  11. Applications of Palladium-Catalyzed C–N Cross-Coupling Reactions

    Science.gov (United States)

    2016-01-01

    Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts. PMID:27689804

  12. Ruthenium-Catalyzed Transformations of Alcohols: Mechanistic Investigations and Methodology Development

    DEFF Research Database (Denmark)

    Makarov, Ilya; Madsen, Robert; Fristrup, Peter

    The mechanism of the ruthenium-catalyzed dehydrogenative synthesis of amides from alcohols and amines was studied in detail by employing the combination of experimental and theoretical techniques. The Hammett study revealed that a small positive charge is formed at the benzylic position in the tr......The mechanism of the ruthenium-catalyzed dehydrogenative synthesis of amides from alcohols and amines was studied in detail by employing the combination of experimental and theoretical techniques. The Hammett study revealed that a small positive charge is formed at the benzylic position....... It was shown that tin-Beta zeolite was only capable of producing crotonaldehyde in low yields. Several other heterogeneous catalysts were tested (Al-Beta, Ti-Beta, Sn-MCM-41, ts-1) but none of them demonstrated substantially higher activity in the studied transformation....

  13. Rubber muscle actuation with pressurized CO2 from enzyme-catalyzed urea hydrolysis

    Science.gov (United States)

    Sutter, Thomas M.; Dickerson, Matthew B.; Creasy, Terry S.; Justice, Ryan S.

    2013-09-01

    A biologically inspired pneumatic pressure source was designed and sized to supply high pressure CO2(g) to power a rubber muscle actuator. The enzyme urease served to catalyze the hydrolysis of urea, producing CO2(g) that flowed into the actuator. The actuator’s power envelope was quantified by testing actuator response on a custom-built linear-motion rig. Reaction kinetics and available work density were determined by replacing the actuator with a double-action piston and measuring volumetric gas generation against a fixed pressure on the opposing piston. Under the conditions investigated, urease catalyzed the generation of up to 0.81 MPa (117 psi) of CO2(g) in the reactor headspace within 18 min, and the evolved gas produced a maximum work density of 0.65 J ml-1.

  14. Palladium-catalyzed asymmetric Heck arylation of 2,3-dihydrofuran--effect of prolinate salts.

    Science.gov (United States)

    Morel, Adam; Silarska, Ewelina; Trzeciak, Anna M; Pernak, Juliusz

    2013-01-28

    Chiral ionic liquids (CILs) containing L-prolinate and L-lactate anions and non-chiral quaternary ammonium cations were employed in the palladium catalyzed enantioselective Heck arylation of 2,3-dihydrofuran with aryl iodides (iodobenzene, 4-iodotoluene, 2-iodoanisole, 4-iodoanisole, 4-iodoacetophenone). In all the reactions 2-aryl-2,3-dihydrofuran (3) was obtained as the main product with the yield up to 52% at the total conversion reaching 83%. Product 3, 2-phenyl-2,3-dihydrofuran, was obtained with excellent enantioselectivity (>99% ee) in a 6 h reaction with tetrabutylammonium L-prolinate. In the proposed homogeneous reaction Pd(0) nanoparticles are considered as a resting state of the catalyst and a source of soluble palladium species catalyzing the Heck reaction. The yield and stereoselectivity of the Heck reaction are strongly influenced by the kind of non-chiral cations present in CILs.

  15. Mechanism and Selectivity of Cinchona Alkaloid Catalyzed [1,3]-Shifts of Allylic Trichloroacetimidates

    Science.gov (United States)

    Çelebi-Ölçüm, Nihan; Aviyente, Viktorya; Houk, K. N.

    2009-01-01

    Density Functional Theory calculations were used to investigate the [3,3]- and [1,3]-shifts of O-allylic trichloroacetimidates in the presence of cinchona alkaloids. Thermal [1,3]- and [3,3]-rearrangements proceed through concerted pseudopericyclic transition states to give the corresponding rearranged products. [1,3]-rearrangement is catalyzed via a double SN2' mechanism in which syn addition of the nucleophile is exclusively preferred in both steps. The catalyzed mechanism is favored by a 6.3 kcal/mol free energy difference compared to the alternative [3,3]-rearrangement pathway. The fast-reacting enantiomer is predicted to be determined by the availability of the H-bonding interaction between the catalyst and the substrate. PMID:19689147

  16. Aza Cope Rearrangement of Propargyl Enammonium Cations Catalyzed By a Self-Assembled `Nanozyme

    Energy Technology Data Exchange (ETDEWEB)

    Hastings, Courntey J.; Fiedler, Dorothea; Bergman, Robert G.; Raymond, Kenneth N.

    2008-02-27

    The tetrahedral [Ga{sub 4}L{sub 6}]{sup 12-} assembly (L = N,N-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene) encapsulates a variety of cations, including propargyl enammonium cations capable of undergoing the aza Cope rearrangement. For propargyl enammonium substrates that are encapsulated in the [Ga{sub 4}L{sub 6}]{sup 12-} assembly, rate accelerations of up to 184 are observed when compared to the background reaction. After rearrangement, the product iminium ion is released into solution and hydrolyzed allowing for catalytic turnover. The activation parameters for the catalyzed and uncatalyzed reaction were determined, revealing that a lowered entropy of activation is responsible for the observed rate enhancements. The catalyzed reaction exhibits saturation kinetics; the rate data obey the Michaelis-Menten model of enzyme kinetics, and competitive inhibition using a non-reactive guest has been demonstrated.

  17. Large-scale ruthenium- and enzyme-catalyzed dynamic kinetic resolution of (rac-1-phenylethanol

    Directory of Open Access Journals (Sweden)

    Bäckvall Jan-E

    2007-12-01

    Full Text Available Abstract The scale-up of the ruthenium- and enzyme-catalyzed dynamic kinetic resolution (DKR of (rac-1-phenylethanol (2 is addressed. The immobilized lipase Candida antarctica lipase B (CALB was employed for the resolution, which shows high enantioselectivity in the transesterification. The ruthenium catalyst used, (η 5-C5Ph5RuCl(CO2 1, was shown to possess very high reactivity in the "in situ" redox racemization of 1-phenylethanol (2 in the presence of the immobilized enzyme, and could be used in 0.05 mol% with high efficiency. Commercially available isopropenyl acetate was employed as acylating agent in the lipase-catalyzed transesterifications, which makes the purification of the product very easy. In a successful large-scale DKR of 2, with 0.05 mol% of 1, (R-1-phenylethanol acetate (3 was obtained in 159 g (97% yield in excellent enantiomeric excess (99.8% ee.

  18. NOx Catalyzed Pathway of Stratospheric Ozone Depletion: A Coupled Cluster Investigation.

    Science.gov (United States)

    Dutta, Achintya Kumar; Vaval, Nayana; Pal, Sourav

    2012-06-12

    We report a theoretical investigation on the NOx catalyzed pathways of stratospheric ozone depletion using highly accurate coupled cluster methods. These catalytic reactions represent a great challenge to state-of-the-art ab initio methods, while their mechanisms remain unclear to both experimentalists and theoreticians. In this work, we have used the so-called "gold standard of quantum chemistry," the CCSD(T) method, to identify the saddle points on NOx-based reaction pathways of ozone hole formation. Energies of the saddle points are calculated using the multireference variants of coupled cluster methods. The calculated activation energies and rate constants show good agreement with available experimental results. Tropospheric precursors to stratospheric NOx radicals have been identified, and their potential importance in stratospheric chemistry has been discussed. Our calculations resolve previous conflicts between ab initio and experimental results for a trans nitro peroxide intermediate, in the NOx catalyzed pathway of ozone depletion.

  19. Iridium- and Ruthenium-Catalyzed N-alkylation of Amines with Alcohols and Amines

    DEFF Research Database (Denmark)

    Lorentz-Petersen, Linda Luise Reeh

    experiments of the iridium catalyzed reactions revealed that the Voigt isomerization of the α-imino alcohol intermediate to the corresponding α-imino ketone plays a significant role. Synthesis of indoles Anilines and vicinal diols were reacted in the presence of a ruthenium complex (RuCl3 with PPh3...... catalysts have been employed for the N-alkylation of amines with either alcohols or amines. Synthesis of secondary amines Self-condensation of primary amines afforded secondary amines in good to high yields. The reaction is catalyzed by the commercially available [Cp*IrCl2]2 complex. The procedure...... is environmentally benign as it is performed in the absence of both solvent and additives and the only by-product is ammonia. Additionally, the work-up procedure is a simple distillation of the product directly from the reaction mixture. Synthesis of piperazines In the Madsen group it has previously been...

  20. Probing the mechanism of 1,4-conjugate elimination reactions catalyzed by terpene synthases.

    Science.gov (United States)

    Faraldos, Juan A; Gonzalez, Veronica; Li, Amang; Yu, Fanglei; Köksal, Mustafa; Christianson, David W; Allemann, Rudolf K

    2012-12-26

    The reaction mechanisms of (E)-β-farnesene synthase (EBFS) and isoprene synthase (ISPS), enzymes that catalyze a formal regiospecific 1,4-conjugate elimination of hydrogen diphosphate from (E,E)-farnesyl and dimethylallyl diphosphate (FDP and DMADP) to generate the semiochemicals (E)-β-farnesene and isoprene, respectively, were probed with substrate analogs and kinetic measurements. The results support stepwise reaction mechanisms through analogous enzyme-bound allylic cationic intermediates. For EBFS, we demonstrate that the elimination reaction can proceed via the enzyme-bound intermediate trans-nerolidyl diphosphate, while for ISPS the intermediacy of 2-methylbut-3-enyl 2-diphosphate can be inferred from the product outcome when deuterated DMADPs are used as substrates. Possible implications derived from the mechanistic details of the EBFS-catalyzed reaction for the evolution of sesquiterpene synthases are discussed.

  1. Mechanistic insight into benzenethiol catalyzed amide bond formations from thioesters and primary amines

    DEFF Research Database (Denmark)

    Stuhr-Hansen, Nicolai; Bork, Nicolai; Strømgaard, Kristian

    2014-01-01

    The influence of arylthiols on cysteine-free ligation, i.e. the reaction between an alkyl thioester and a primary amine forming an amide bond, was studied in a polar aprotic solvent. We reacted the ethylthioester of hippuric acid with cyclohexylamine in the absence or presence of various quantities...... of thiophenol (PhSH) in a slurry of disodium hydrogen phosphate in dry DMF. Quantitative conversions into the resulting amide were observed within a few hours in the presence of equimolar amounts of thiophenol. Ab initio calculations showed that the reaction mechanism in DMF is similar to the well-known aqueous...... reaction mechanism. The energy barrier of the catalyzed amidation reaction is approximately 40 kJ mol(-1) lower than the non-catalyzed amidation reaction. At least partially this can be explained by a hydrogen bond from the amine to the π-electrons of the thiophenol, stabilizing the transition state...

  2. Lipase-catalyzed process for biodiesel production: protein engineering and lipase production.

    Science.gov (United States)

    Hwang, Hyun Tae; Qi, Feng; Yuan, Chongli; Zhao, Xuebing; Ramkrishna, Doraiswami; Liu, Dehua; Varma, Arvind

    2014-04-01

    Biodiesel is an environment-friendly and renewable fuel produced by transesterification of various feedstocks. Although the lipase-catalyzed biodiesel production has many advantages over the conventional alkali catalyzed process, its industrial applications have been limited by high-cost and low-stability of lipase enzymes. This review provides a general overview of the recent advances in lipase engineering, including both protein modification and production. Recent advances in biotechnology such as in protein engineering, recombinant methods and metabolic engineering have been employed but are yet to impact lipase engineering for cost-effective production of biodiesel. A summary of the current challenges and perspectives for potential solutions are also provided. © 2013 Wiley Periodicals, Inc.

  3. C-Alkylation of Ketones and Related Compounds by Alcohols: Transition-Metal-Catalyzed Dehydrogenation.

    Science.gov (United States)

    Huang, Fei; Liu, Zhuqing; Yu, Zhengkun

    2016-01-18

    Transition-metal-catalyzed C-alkylation of ketones and secondary alcohols, with alcohols, avoids use of organometallic or environmentally unfriendly alkylating agents by means of borrowing hydrogen (BH) or hydrogen autotransfer (HA) activation of the alcohol substrates. Water is formed as the only by-product, thus making the BH process atom-economical and environmentally benign. Diverse homogeneous and heterogeneous transition-metal catalysts, ketones, and alcohols can be used for this transformation, thus rendering the BH process promising for replacing those procedures that use traditional alkylating agents. This Minireview summarizes the advances during the last five years in transition-metal-catalyzed BH α-alkylation of ketones, and β-alkylation of secondary alcohols with alcohols. A discussion on the application of the BH strategy for C-C bond formation is included. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Acid-catalyzed ethanolysis of temazepam in anhydrous and aqueous ethanol solutions.

    Science.gov (United States)

    Yang, S K

    1994-06-01

    The benzodiazepines are a family of anxiolytic and hypnotic drugs. When taken concurrently with ethanol, a pharmacological interaction may occur, potentiating the central nervous system depression produced by either drug. In addition to this pharmacological interaction, this report describes a novel chemical reaction between temazepam (a 3-hydroxy-1,4-benzodiazepine) and ethanol under acidic conditions similar to those found in vivo, resulting in a 3-ethoxylated product. Optimal conditions, kinetics, equilibrium, and the mechanism of this acid-catalyzed ethanolysis are reported. The results raise the possibility that the ethanolysis reaction may occur in the stomach of people who consume alcohol and 3-hydroxy-1,4-benzodiazepine on a regular basis. The acid-catalyzed ethanol-drug reaction is a relatively unexplored area and may alter the pharmacological action of some drugs.

  5. Stabilization of oil-in-water emulsions by enzyme catalyzed oxidative gelation of sugar beet pectin

    DEFF Research Database (Denmark)

    Abang Zaidel, Dayang Norulfairuz; Chronakis, Ioannis S.; Meyer, Anne S.

    2013-01-01

    Enzyme catalyzed oxidative cross-linking of feruloyl groups can promote gelation of sugar beet pectin (SBP). It is uncertain how the enzyme kinetics of this cross-linking reaction are affected in emulsion systems and whether the gelation affects emulsion stability. In this study, SBP (2.5% w....../v) was mixed into an oil-in-water emulsion system (4.4% w/w oil, 0.22% w/w whey protein, pH 4.5). Two separate, identically composed, emulsion systems were prepared by different methods of preparation. The emulsions prepared separately and subsequently mixed with SBP (referred as Mix A) produced significantly...... larger average particle sizes than the emulsions in which the SBP was homogenized into the emulsion system during emulsion preparation (referred as Mix B). Mix B type emulsions were stable. Enzyme catalyzed oxidative gelation of SBP helped stabilize the emulsions in Mix A. The kinetics of the enzyme...

  6. Pd-Catalyzed regioselective C-H halogenation of quinazolinones and benzoxazinones.

    Science.gov (United States)

    Dabiri, Minoo; Farajinia Lehi, Noushin; Kazemi Movahed, Siyavash; Khavasi, Hamid Reza

    2017-08-07

    A Pd-catalyzed ortho-selective halogenation of benzoxazinone and quinazolinone scaffolds has been described employing N-halosuccinimide as both a halogen source and an oxidant reagent via C-H bond activation. This transformation shows high chemo- and regioselectivities and demonstrates a broad range of benzoxazinone and quinazolinone substrates with different functional groups and has been scaled up to the gram level.

  7. Gold-catalyzed formation of heterocycles - an enabling new technology for medicinal chemistry.

    Science.gov (United States)

    Shen, Hong C; Graham, Thomas H

    2013-01-01

    Gold-catalyzed transformations allow efficient access to a wide scope of heterocyclic structures that serve as building blocks and pharmacophores in medicinal chemistry. Compared with other transition metal and Lewis acid catalysis, gold catalysis presents mechanistic divergence, excellent functional group tolerance and/or operational advantages. Emergent applications of gold catalysis have played a key role in the synthesis of biologically active molecules including a drug candidate.

  8. Immobilized Ionic Liquid-Catalyzed Synthesis of Pyrano[3,2-b]indole Derivatives

    Directory of Open Access Journals (Sweden)

    Saman Damavandi

    2012-01-01

    Full Text Available An ionic liquid-catalyzed synthesis of 2-amino-4,5-dihydro-4-arylpyrano[3,2-b]indole-3-carbonitrile derivatives through a novel three-component condensation of 3-hydroxyindole, aromatic aldehydes and malononitrile in the presence of silica supported ionic liquid of [pmim]HSO4SiO2 (silica supported 1-methyl-3-(triethoxysilylpropylimidazolium hydrogensulfate as an efficient catalyst is described.

  9. Ruthenium(III Chloride Catalyzed Acylation of Alcohols, Phenols, and Thiols in Room Temperature Ionic Liquids

    Directory of Open Access Journals (Sweden)

    Mingzhong Cai

    2009-09-01

    Full Text Available Ruthenium(III chloride-catalyzed acylation of a variety of alcohols, phenols, and thiols was achieved in high yields under mild conditions (room temperature in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]. The ionic liquid and ruthenium catalyst can be recycled at least 10 times. Our system not only solves the basic problem of ruthenium catalyst reuse, but also avoids the use of volatile acetonitrile as solvent.

  10. Lipophilic (hydroxy)phenylacetates by solvent-free lipase-catalyzed esterification and transesterification in vacuo.

    Science.gov (United States)

    Weitkamp, Petra; Weber, Nikolaus; Vosmann, Klaus

    2008-07-09

    Various long-chain alkyl (hydroxy)phenylacetates were prepared in high yield by lipase-catalyzed transesterification of the corresponding short-chain alkyl hydroxyphenylacetates and fatty alcohols in equimolar ratios. The reactions were performed in vacuo at moderate temperatures in the absence of solvents and drying agents in direct contact with the reaction mixture. Immobilized lipase B from Candida antarctica (Novozym 435) was the most effective biocatalyst for the various transesterification reactions. Generally, Novozym 435-catalyzed transesterifications of short-chain alkyl (hydroxy)phenylacetates with long-chain alcohols led to higher conversions and enzyme activities than the corresponding esterifications. For example, the transesterification activity was up to 4-fold higher than the esterification activity for the formation of oleyl 4-hydroxy-3-methoxyphenylacetate using Novozym 435 as a biocatalyst. The relative transesterification activities were as follows: phenylacetate > 3-methoxyphenylacetate approximately 4-methoxyphenylacetate > 4-hydroxy-3-methoxyphenylacetate > 3-hydroxyphenylacetate approximately 4-hydroxyphenylacetate > 2-methoxyphenylacetate > 3,4-dihydroxyphenylacetate. With respect to the position of methoxy and hydroxy substituents, the transesterification activity of Novozym 435 decreased in the order meta approximately para > ortho. Compounds with inverse chemical structures, for example, tyrosyl oleate, were obtained by Novozym 435-catalyzed esterification and transesterification of fatty acids and their methyl esters, respectively, with 2-phenylethan-1-ols. In contrast to the transesterifications of short-chain alkyl (hydroxy)phenylacetates with fatty alcohols, higher conversions and enzyme activities were observed for the Novozym 435-catalyzed esterifications of (hydroxy)phenylethanols with long-chain fatty acids than the corresponding transesterifications with fatty acid methyl esters.

  11. Highly enantioselective Ag(i)-catalyzed [3 + 2] cycloaddition of azomethine ylides.

    Science.gov (United States)

    Longmire, James M; Wang, Bin; Zhang, Xumu

    2002-11-13

    A highly reactive Ag(I)-catalyzed [3 + 2] cycloaddition of azomethine ylides is founded using AgOAc as the catalytic precursor and phosphines as ligands. Using a new bis-ferrocenyl amide phosphine (FAP) as the ligand, we found that high enantioselectivities (up to 97% ee) have been achieved in the [3 + 2] cycloaddition of azomethine ylides. Up to four stereogenic centers can be established in this multicomponent coupling reaction from readily available materials such as aldehydes, aminoesters, and dipolarophiles.

  12. Surprisingly Mild Enolate-Counterion-Free Pd(0)-Catalyzed Intramolecular Allylic Alkylations

    DEFF Research Database (Denmark)

    Madec, David; Prestat, Guillaume; Martini, Elisabetta

    2005-01-01

    Palladium-catalyzed intramolecular allylic alkylations of unsaturated EWG-activated amides can take place under phase-transfer conditions or in the presence of a crown ether. These new reaction conditions are milder and higher yielding than those previously reported. A rationalization for such an...... for such an unexpected result is put forth and validated by DFT-B3LYP calculations. The results suggest cyclization via a counterion-free (E)-enolate TS....

  13. Spatially resolved Raman spectroscopy on indium-catalyzed core-shell germanium nanowires: size effects

    Energy Technology Data Exchange (ETDEWEB)

    Xiang, Y; Zardo, I; Garma, T; Heiss, M; Fontcuberta i Morral, A [Walter Schottky Institut, Physik Department, Technische Universitaet Muenchen, Am Coulombwall 3, D-85748 Garching (Germany); Cao, L Y; Brongersma, M L [Geballe Laboratory for Advanced Materials, 476 Lomita Mall, Stanford University, Stanford, CA 94305 (United States); Morante, J R; Arbiol, J [Departament d' Electronica, Universitat de Barcelona, 08028 Barcelona, CAT (Spain)

    2010-03-12

    The structure of indium-catalyzed germanium nanowires is investigated by atomic force microscopy, scanning confocal Raman spectroscopy and transmission electron microscopy. The nanowires are formed by a crystalline core and an amorphous shell. We find that the diameter of the crystalline core varies along the nanowire, down to few nanometers. Phonon confinement effects are observed in the regions where the crystalline region is the thinnest. The results are consistent with the thermally insulating behavior of the core-shell nanowires.

  14. Esterification of Oleic Acid for Biodiesel Production Catalyzed by SnCl2: A Kinetic Investigation

    OpenAIRE

    da Silva, Marcio J.; Cardoso, Abiney L.; Soraia Cristina Gonzaga Neves

    2008-01-01

    The production of biodiesel from low-cost raw materials which generally contain high amounts of free fatty acids (FFAs) is a valuable alternative that would make their production costs more competitive than petroleum-derived fuel. Currently, the production of biodiesel from this kind of raw materials comprises a two-stage process, which requires an initial acid-catalyzed esterification of the FFA, followed by a basecatalyzed transesterification of the triglycerides. Commonly, the acid H 2 SO ...

  15. Mild copper-catalyzed N-arylation of azaheterocycles with aryl halides

    NARCIS (Netherlands)

    Kuil, M.; Bekedam, E.K.; Visser, G.M.; Hoogenband, van den A.; Terpstra, J.W.; Kamer, P.C.J.; Leeuwen, P.W.N.M.; Strijdonck, G.P.F.

    2005-01-01

    A highly efficient copper(I)-catalyzed N-arylation of azaheterocycles with various aryl halides is reported. The N-arylation reaction can be carried out using as low as 0.5 mol % of (Cu(I)OTf)2¿PhH and 1.0 mol % of 4,7-dichloro-1,10-phenanthroline as the ligand. Furthermore, cheap and stable copper

  16. Post-Ugi gold-catalyzed diastereoselective domino cyclization for the synthesis of diversely substituted spiroindolines

    Directory of Open Access Journals (Sweden)

    Amit Kumar

    2013-10-01

    Full Text Available An Ugi four-component reaction of propargylamine with 3-formylindole and various acids and isonitriles produces adducts which are subjected to a cationic gold-catalyzed diastereoselective domino cyclization to furnish diversely substituted spiroindolines. All the reactions run via an exo-dig attack in the hydroarylation step followed by an intramolecular diastereoselective trapping of the imminium ion. The whole sequence is atom economic and the application of a multicomponent reaction assures diversity.

  17. Recent developments in copper-catalyzed radical alkylations of electron-rich π-systems

    Directory of Open Access Journals (Sweden)

    Kirk W. Shimkin

    2015-11-01

    Full Text Available Recently, a number of papers have emerged demonstrating copper-catalyzed alkylation reactions of electron-rich small molecules. The processes are generally thought to be related to long established atom-transfer radical reactions. However, unlike classical reactions, these new transformations lead to simple alkylation products. This short review will highlight recent advances in alkylations of nitronate anions, alkenes and alkynes, as well as discuss current mechanistic understanding of these novel reactions.

  18. Rhodium-Catalyzed Linear Codimerization and Cycloaddition of Ketenes with Alkynes

    Directory of Open Access Journals (Sweden)

    Teruyuki Kondo

    2010-06-01

    Full Text Available A novel rhodium-catalyzed linear codimerization of alkyl phenyl ketenes with internal alkynes to dienones and a novel synthesis of furans by an unusual cycloaddition of diaryl ketenes with internal alkynes have been developed. These reactions proceed smoothly with the same rhodium catalyst, RhCl(PPh33, and are highly dependent on the structure and reactivity of the starting ketenes.

  19. Chiral Diarylmethanes via Copper-Catalyzed Asymmetric Allylic Arylation with Organolithium Compounds.

    Science.gov (United States)

    Guduguntla, Sureshbabu; Hornillos, Valentín; Tessier, Romain; Fañanás-Mastral, Martín; Feringa, Ben L

    2016-01-15

    A highly enantioselective copper/N-heterocyclic carbene catalyzed allylic arylation with organolithium compounds is presented. The use of commercial or readily prepared aryllithium reagents in the reaction with allyl bromides affords a variety of chiral diarylvinylmethanes, comprising a privileged structural motif in pharmaceuticals, in high yields with good to excellent regio- and enantioselectivities. The versatility of this new transformation is illustrated in the formal synthesis of the marketed drug tolterodine (Detrol).

  20. Palladium-catalyzed, asymmetric Baeyer–Villiger oxidation of prochiral cyclobutanones with PHOX ligands

    KAUST Repository

    Petersen, Kimberly S.

    2011-06-01

    Described in this report is a general method for the conversion of prochiral 3-substituted cyclobutanones to enantioenriched γ-lactones through a palladium-catalyzed Baeyer-Villiger oxidation using phosphinooxazoline ligands in up to 99% yield and 81% ee. Lactones of enantiopurity ≥93% could be obtained through a single recrystallization step. Importantly, 3,3-disubtituted cyclobutanones produced enantioenriched lactones containing a β-quaternary center. © 2011 Elsevier Ltd. All rights reserved.

  1. Photoredox-Catalyzed Ketyl–Olefin Coupling for the Synthesis of Substituted Chromanols

    KAUST Repository

    Fava, Eleonora

    2016-07-21

    A visible light photoredox-catalyzed aldehyde olefin cyclization is reported. The method represents a formal hydroacylation of alkenes and alkynes and provides chromanol derivatives in good yields. The protocol takes advantage of the double role played by trialkylamines (NR3) which act as (i) electron donors for reducing the catalyst and (ii) proton donors to activate the substrate via a proton-coupled electron transfer. © 2016 American Chemical Society.

  2. Precision Synthesis of Functional Polysaccharide Materials by Phosphorylase-Catalyzed Enzymatic Reactions

    Directory of Open Access Journals (Sweden)

    Jun-ichi Kadokawa

    2016-04-01

    Full Text Available In this review article, the precise synthesis of functional polysaccharide materials using phosphorylase-catalyzed enzymatic reactions is presented. This particular enzymatic approach has been identified as a powerful tool in preparing well-defined polysaccharide materials. Phosphorylase is an enzyme that has been employed in the synthesis of pure amylose with a precisely controlled structure. Similarly, using a phosphorylase-catalyzed enzymatic polymerization, the chemoenzymatic synthesis of amylose-grafted heteropolysaccharides containing different main-chain polysaccharide structures (e.g., chitin/chitosan, cellulose, alginate, xanthan gum, and carboxymethyl cellulose was achieved. Amylose-based block, star, and branched polymeric materials have also been prepared using this enzymatic polymerization. Since phosphorylase shows a loose specificity for the recognition of substrates, different sugar residues have been introduced to the non-reducing ends of maltooligosaccharides by phosphorylase-catalyzed glycosylations using analog substrates such as α-d-glucuronic acid and α-d-glucosamine 1-phosphates. By means of such reactions, an amphoteric glycogen and its corresponding hydrogel were successfully prepared. Thermostable phosphorylase was able to tolerate a greater variance in the substrate structures with respect to recognition than potato phosphorylase, and as a result, the enzymatic polymerization of α-d-glucosamine 1-phosphate to produce a chitosan stereoisomer was carried out using this enzyme catalyst, which was then subsequently converted to the chitin stereoisomer by N-acetylation. Amylose supramolecular inclusion complexes with polymeric guests were obtained when the phosphorylase-catalyzed enzymatic polymerization was conducted in the presence of the guest polymers. Since the structure of this polymeric system is similar to the way that a plant vine twines around a rod, this polymerization system has been named

  3. Using Thin Film Targets for Muonic Atoms and Muon Catalyzed Fusion Studies

    OpenAIRE

    TRIUMF Munoic Hydrogen Collaboration; Fujiwara, M C; Adamczak, A.; Bailey, J.M.; Beer, G A; Beveridge, J. L.; Faifman, M. P.; Huber, T. M.; Kammel, P; Kim, S. K.; Knowles, P. E.; Kunselman, A. R.; Markushin, V. E.; Marshall, G. M.; Martoff, C. J.

    2000-01-01

    Studies of muonic atoms and muon catalyzed fusion have been conventionally done in a bulk target of gas, liquid or solid hydrogen isotopes. The use of thin film targets developed at TRIUMF have notable advantages in tackling some of the most important questions in the field, which could be further exploited at future high intensity muon sources. We review the technique of the thin film method with emphasis on recent results and a future proposal.

  4. Ruthenium-Catalyzed Olefin Metathesis after Tetra-n-butylammonium Fluoride-Mediated Desilylation

    Science.gov (United States)

    Osman, Sami

    2012-01-01

    One-pot procedures expedite organic synthesis but pose challenges in that many reagents must be compatible with each other. We discovered that the presence of nBu4NF hindered rutheniumcatalyzed olefin metathesis when nBu4NF-mediated desilylation and olefin metathesis were performed in one pot. This problem could be solved by the addition of (TMS)2O to remove fluoride anions in order to facilitate the ruthenium-catalyzed olefin metathesis. PMID:23269856

  5. Mutagenicity screening of reaction products from the enzyme-catalyzed oxidation of phenolic pollutants

    Energy Technology Data Exchange (ETDEWEB)

    Massey, I.J.; Aitken, M.D.; Ball, L.M.; Heck, P.E. (Univ. of North Carolina, Chapel Hill, NC (United States). Dept. of Environmental Sciences and Engineering)

    1994-11-01

    Phenol-oxidizing enzymes such as peroxidases, laccases, and mushroom polyphenol oxidase are capable of catalyzing the oxidation of a wide range of phenolic pollutants. Although the use of these enzymes in waste-treatment applications has been proposed by a number of investigators, little information exists on the toxicological characteristics of the oxidation products. The enzymes chloroperoxidase, horseradish peroxidase, lignin peroxidase, and mushroom polyphenol oxidase were used in this study to catalyze the oxidation of phenol, several mono-substituted phenols, and pentachlorophenol. Seventeen reaction mixtures representing selected combinations of enzyme and parent phenol were subjected to mutagenicity screening using the Ames Salmonella typhimurium plate incorporation assay; five selected mixtures were also incubated with the S9 microsomal preparation to detect the possible presence of promutagens. The majority of reaction mixtures tested were not directly mutagenic, and none of those tested with S9 gave a positive response. Such lack of mutagenicity of enzymatic oxidation products provides encouragement for establishing the feasibility of enzyme-catalyzed oxidation as a waste-treatment process. The only positive responses were obtained with reaction products from the lignin peroxidase-catalyzed oxidation of 2-nitrophenol and 4-nitrophenol. Clear positive responses were observed when strain TA100 was incubated with 2-nitrophenol reaction-product mixtures, and when strain TA98 was incubated with the 4-nitrophenol reaction mixture. Additionally, 2,4-dinitrophenol was identified as a reaction product from 4-nitrophenol, and preliminary evidence indicates that both 2,4- and 2,6-dinitrophenol are produced from the oxidation of 2-nitrophenol. Possible mechanism by which these nitration reactions occur are discussed.

  6. Base catalyzed synthesis of bicyclo[3.2.1]octane scaffolds.

    Science.gov (United States)

    Boehringer, Régis; Geoffroy, Philippe; Miesch, Michel

    2015-07-07

    The base-catalyzed reaction of achiral 1,3-cyclopentanediones tethered to activated olefins afforded in high yields bicyclo[3.2.1]octane-6,8-dione or bicyclo[3.2.1]octane-6-carboxylate derivatives bearing respectively three or five stereogenic centers. The course of the reaction is closely related to the reaction time and to the base involved in the reaction.

  7. Iron-Catalyzed C-O Bond Activation: Opportunity for Sustainable Catalysis.

    Science.gov (United States)

    Bisz, Elwira; Szostak, Michal

    2017-10-23

    Oxygen-based electrophiles have emerged as some of the most valuable cross-coupling partners in organic synthesis due to several major strategic and environmental benefits, such as abundance and potential to avoid toxic halide waste. In this context, iron-catalyzed C-O activation/cross-coupling holds particular promise to achieve sustainable catalytic protocols due to its natural abundance, inherent low toxicity, and excellent economic and ecological profile. Recently, tremendous progress has been achieved in the development of new methods for functional-group-tolerant iron-catalyzed cross-coupling reactions by selective C-O cleavage. These methods establish highly attractive alternatives to traditional cross-coupling reactions by using halides as electrophilic partners. In particular, new easily accessible oxygen-based electrophiles have emerged as substrates in iron-catalyzed cross-coupling reactions, which significantly broaden the scope of this catalysis platform. New mechanistic manifolds involving iron catalysis have been established; thus opening up vistas for the development of a wide range of unprecedented reactions. The synthetic potential of this sustainable mode of reactivity has been highlighted by the development of new strategies in the construction of complex motifs, including in target synthesis. The most recent advances in sustainable iron-catalyzed cross-coupling of C-O-based electrophiles are reviewed, with a focus on both mechanistic aspects and synthetic utility. It should be noted that this catalytic manifold provides access to motifs that are often not easily available by other methods, such as the assembly of stereodefined dienes or C(sp 2 )-C(sp 3 ) cross-couplings, thus emphasizing the synthetic importance of this mode of reactivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Supported gold nanoparticle-catalyzed hydration of alkynes under basic conditions.

    Science.gov (United States)

    Liang, Shengzong; Jasinski, Jacek; Hammond, Gerald B; Xu, Bo

    2015-01-02

    TiO2-supported nanosize gold particles catalyze the hydration of alkynes using morpholine as a basic cocatalyst. Unlike most homogeneous cationic gold catalysts, the TiO2-Au/morpholine system is weakly basic and is compatible with acid-sensitive functional groups (e.g., silyl ethers, ketals) or with a strongly coordinating group such as pyridine. What's more, this gold catalyst can be recycled by simple filtration and works well in flow reactors.

  9. The first characterization of free radicals formed from cellular COX-catalyzed peroxidation.

    Science.gov (United States)

    Gu, Yan; Xu, Yi; Law, Benedict; Qian, Steven Y

    2013-04-01

    Through free radical-mediated peroxidation, cyclooxygenase (COX) can metabolize dihomo-γ-linolenic acid (DGLA) and arachidonic acid (AA) to form well-known bioactive metabolites, namely, the 1-series of prostaglandins (PGs1) and the 2-series of prostaglandins (PGs2), respectively. Unlike PGs2, which are generally viewed as proinflammatory and procarcinogenic PGs, PGs1 may possess anti-inflammatory and anti-cancer activity. Previous studies using ovine COX along with spin trapping and the LC/ESR/MS technique have shown that certain exclusive free radicals are generated from different free radical reactions in DGLA and AA peroxidation. However, it has been unclear whether the differences were associated with the contrasting bioactivity of DGLA vs AA. The aim of this study was to refine the LC/MS and spin trapping technique to make it possible for the association between free radicals and cancer cell growth to be directly tested. Using a colon cancer cell line, HCA-7 colony 29, and LC/MS along with a solid-phase extraction, we were able to characterize the reduced forms of radical adducts (hydroxylamines) as the free radicals generated from cellular COX-catalyzed peroxidation. For the first time, free radicals formed in the COX-catalyzed peroxidation of AA vs DGLA and their association with cancer cell growth were assessed (cell proliferation via MTS and cell cycle distribution via propidium iodide staining) in the same experimental setting. The exclusive free radicals formed from the COX-catalyzed peroxidation of AA and DGLA were shown to be correlated with the cell growth response. Our results indicate that free radicals generated from the distinct radical reactions in COX-catalyzed peroxidation may represent the novel metabolites of AA and DGLA that correspond to their contrasting bioactivity. Copyright © 2012 Elsevier Inc. All rights reserved.

  10. Room-temperature Cu-catalyzed N-arylation of aliphatic amines in neat water.

    Science.gov (United States)

    Wang, Deping; Zheng, Yanwen; Yang, Min; Zhang, Fuxing; Mao, Fangfang; Yu, Jiangxi; Xia, Xiaohong

    2017-10-04

    A room-temperature and PTC-free copper-catalyzed N-arylation of aliphatic amines in neat water has been developed. Using a combination of CuI and 6,7-dihydroquinolin-8(5H)-one oxime as the catalyst and KOH as the base, a wide range of aliphatic amines are arylated with various aryl and heteroaryl halides to give the corresponding products in up to 95% yield.

  11. E1-catalyzed ubiquitin C-terminal amidation for the facile synthesis of deubiquitinase substrates.

    Science.gov (United States)

    Wang, Xiaoyan Aria; Kurra, Yadagiri; Huang, Ying; Lee, Yan-Jiun; Liu, Wenshe R

    2014-01-03

    Will Ub my partner? The ubiquitin (Ub)-activating enzyme (E1) was used to catalyze an amidation reaction to functionalize the C terminus of Ub with unique functional groups, such as thiol, azide, alkyne, and alkene groups, with high efficiency and yield (>90 %). These groups were then applied for the facile synthesis of fluorophore-conjugated ubiquitin and specifically conjugated diubiquitin substrates for deubiquitinases. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Crown ether catalyzed deuterium exchange in the synthesis of benzyl cyanides

    Energy Technology Data Exchange (ETDEWEB)

    Davis, B.

    1987-02-01

    Nucleophilic substitution of benzyl-type chlorides with cyanide ion in deuterochloroform, deuteroacetonitrile or deuterobenzene catalyzed by 18-crown-6 results in the introduction of deuterium onto the benzyl carbon. Benzyl cyanides are labelled by refluxing with cyanide ion and crown ether in deutero solvent. Two such exchanges in deuterochloroform produced greater than 90% incorporation. Side-chain labelled phenylethylamine, tryptamine and m- and p-tyramine were synthesized in this way.

  13. An Efficient Method for the N-Bromosuccinimide Catalyzed Synthesis of Indolyl-Nitroalkanes

    Directory of Open Access Journals (Sweden)

    Ching-Fa Yao

    2009-10-01

    Full Text Available An efficient and practical method for the synthesis of indolyl-nitroalkane derivatives catalyzed by N-bromosuccinimide is described. The generality of this method was demonstrated by synthesizing an array of diverse 3-substituted indole derivatives by the reaction of different β-nitrostyrenes with various substituted indoles. Simple reaction conditions accompanied by good yields of indolyl-nitroalkanes are the merits of this methodology.

  14. Palladium-Catalyzed One-Pot Approach to 3-(Diarylmethyleneoxindoles from Propiolamidoaryl Triflate

    Directory of Open Access Journals (Sweden)

    Dahye Lee

    2015-08-01

    Full Text Available 3-(Diarylmethyleneoxindoles have been synthesized from propiolamidoaryl triflate utilizing a palladium-catalyzed one-pot reaction consisting of three successive reactions: Sonogashira, Heck, and Suzuki-Miyaura. This method allows for the production of a complex skeleton of 3-(diarylmethyleneoxindole from propiolamidoaryl triflate using a commercially available aryl iodide and arylboronic acid in a simple and efficient way with moderate yield and stereoselectivity.

  15. Muon-catalyzed fusion experiment target and detector system. Preliminary design report

    Energy Technology Data Exchange (ETDEWEB)

    Jones, S.E.; Watts, K.D.; Caffrey, A.J.; Walter, J.B.

    1982-03-01

    We present detailed plans for the target and particle detector systems for the muon-catalyzed fusion experiment. Requirements imposed on the target vessel by experimental conditions and safety considerations are delineated. Preliminary designs for the target vessel capsule and secondary containment vessel have been developed which meet these requirements. In addition, the particle detection system is outlined, including associated fast electronics and on-line data acquisition. Computer programs developed to study the target and detector system designs are described.

  16. The role of hydrogen bonding in the enzymatic reaction catalyzed by HIV-1 protease

    OpenAIRE

    Trylska, Joanna; Grochowski, Paweł; McCammon, J. Andrew

    2004-01-01

    The hydrogen-bond network in various stages of the enzymatic reaction catalyzed by HIV-1 protease was studied through quantum-classical molecular dynamics simulations. The approximate valence bond method was applied to the active site atoms participating directly in the rearrangement of chemical bonds. The rest of the protein with explicit solvent was treated with a classical molecular mechanics model. Two possible mechanisms were studied, general-acid/general-base (GA/GB) with Asp 25 protona...

  17. Mechanistic studies on Au(I)-catalyzed [3,3]-sigmatropic rearrangements using cyclopropane probes.

    Science.gov (United States)

    Mauleón, Pablo; Krinsky, Jamin L; Toste, F Dean

    2009-04-01

    A comparative study of the Au(I)-catalyzed [3,3]-sigmatropic rearrangement of propargylic esters and propargyl vinyl ethers is described. Stereochemically defined cyclopropanes are employed as mechanistic probes to provide new synthetic and theoretical data concerning the reversibility of this type of rearrangement. Factors controlling the structure-reactivity relationship of Au(I)-coordinated allenes have been examined, thereby allowing for controlled access to orthogonal reactivity.

  18. Mechanistic Studies on Au(I)-Catalyzed [3,3]-Sigmatropic Rearrangements using Cyclopropane Probes

    OpenAIRE

    Mauleón, Pablo; Krinsky, Jamin L.; Toste, F Dean

    2009-01-01

    A comparative study of the Au(I)-catalyzed [3,3]-sigmatropic rearrangement of propargylic esters and propargyl vinyl ethers is described. Stereochemically defined cyclopropanes are employed as mechanistic probes to provide new synthetic and theoretical data concerning the reversibility of this type of rearrangement. Factors controlling the structure-reactivity relationship of Au(I)-coordinated allenes have been examined, thereby allowing for controlled access to orthogonal reactivity.

  19. Cobalt-catalyzed hydrogenation of esters to alcohols: unexpected reactivity trend indicates ester enolate intermediacy.

    Science.gov (United States)

    Srimani, Dipankar; Mukherjee, Arup; Goldberg, Alexander F G; Leitus, Gregory; Diskin-Posner, Yael; Shimon, Linda J W; Ben David, Yehoshoa; Milstein, David

    2015-10-12

    The atom-efficient and environmentally benign catalytic hydrogenation of carboxylic acid esters to alcohols has been accomplished in recent years mainly with precious-metal-based catalysts, with few exceptions. Presented here is the first cobalt-catalyzed hydrogenation of esters to the corresponding alcohols. Unexpectedly, the evidence indicates the unprecedented involvement of ester enolate intermediates. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Synthesis of oxindole from acetanilide via Ir(iii)-catalyzed C-H carbenoid functionalization.

    Science.gov (United States)

    Patel, Pitambar; Borah, Gongutri

    2016-12-22

    Herein we disclose the first report on the synthesis of oxindole derivatives from acetanilide via Ir(iii)-catalyzed intermolecular C-H functionalization with diazotized Meldrum's acid. A broad range of substituted anilides were found to react smoothly under the Ir(iii)-catalytic system to afford the corresponding N-protected oxindoles. The N-protecting groups, such as Ac, Bz or Piv, can be easily removed to furnish the oxindole. Various synthetic applications of the synthesized oxindole were also demonstrated.

  1. [Study on optimization of the hydrolysis process of dioscin catalyzed by hydrochloric acid].

    Science.gov (United States)

    Li, Qian; Gao, Xiang-Tao; Zhao, Wen-Lei; Liu, Xiu-Hua

    2008-07-01

    To study the optimization of hydrolysis process of dioscin catalyzed by hydrochloric acid. The effects of hydrochloric acid concentration, reaction temperature, reaction time and their interactions had been investigated using orthogonal design and single-factor experiments. The optimum hydrolysis conditions were as follows: reaction temperature 90 degrees C, reaction time 3h, hydrochloric acid concentration 2.0 mol/L. Hydrochloric acid concentration and reaction temperature should be controlled because of their remarkable influence on hydrolysis process.

  2. Asymmetric Iron-Catalyzed C-H Alkylation Enabled by Remote Ligand meta-Substitution.

    Science.gov (United States)

    Loup, Joachim; Zell, Daniel; Oliveira, João C A; Keil, Helena; Stalke, Dietmar; Ackermann, Lutz

    2017-11-06

    Highly enantioselective iron-catalyzed C-H alkylations by inner-sphere C-H activation were accomplished with ample scope. High levels of enantiocontrol proved viable through a novel ligand design that exploits a remote meta-substitution on N-heterocyclic carbenes within a facile ligand-to-ligand H-transfer C-H cleavage. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Rhodium-Catalyzed Cyanation of C(sp(2))-H Bond of Alkenes.

    Science.gov (United States)

    Chaitanya, Manthena; Anbarasan, Pazhamalai

    2015-08-07

    Efficient and selective rhodium-catalyzed cyanation of chelation-assisted C-H bonds of alkenes has been accomplished using environmentally benign N-cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS) as a cyanating reagent. The developed methodology tolerates various functional groups and allows the synthesis of diverse substituted acrylonitriles in good to excellent yields. Furthermore, the potential of the methodology was demonstrated through the formal synthesis of chlorpheniramine-based antagonist.

  4. Probing the Mechanism of 1,4-Conjugate Elimination Reactions Catalyzed by Terpene Synthases

    OpenAIRE

    Faraldos, Juan A.; Gonzalez, Veronica; Li, Amang; Yu, Fanglei; Köksal, Mustafa; Christianson, David W.; Allemann, Rudolf K.

    2012-01-01

    The reaction mechanisms of (E)-β-farnesene synthase (EBFS) and isoprene synthase (ISPS), enzymes that catalyze a formal regioespecific 1,4-conjugate elimination of hydrogen-diphosphate from (E, E)-farnesyl and dimethylallyl diphosphate (FDP and DMADP) to generate the semiochemicals (E)-β-farnesene and isoprene, respectively, were probed with substrate analogs and kinetic measurements. The results support stepwise reaction mechanisms through analogous enzyme-bound allylic cationic intermediate...

  5. γ-Alumina Nanoparticle Catalyzed Efficient Synthesis of Highly Substituted Imidazoles

    Directory of Open Access Journals (Sweden)

    Bandapalli Palakshi Reddy

    2015-10-01

    Full Text Available γ-Alumina nano particle catalyzed multi component reaction of benzil, arylaldehyde and aryl amines afforded the highly substituted 1,2,4,5-tetraaryl imidazoles with good to excellent yield in less reaction time under the sonication as well as the conventional methods. Convenient operational simplicity, mild conditions and the reusability of catalyst were the other advantages of this developed protocol.

  6. The intriguing modeling of cis–trans selectivity in ruthenium-catalyzed olefin metathesis

    Directory of Open Access Journals (Sweden)

    Luigi Cavallo

    2011-01-01

    Full Text Available In this study we have investigated computationally the origin of the cis–trans selectivity in the Ru-catalyzed cross metathesis (CM of a prototype monosubstituted olefin, i.e., propene. Our calculations suggest that the origin of the preferential formation of trans-olefins is in the product release step, which prevents the initially formed cis-olefin from escaping the metal, and returns it to the reaction pool until the trans-olefin is formed.

  7. Oligomerization of 10,16-Dihydroxyhexadecanoic Acid and Methyl 10,16-Dihydroxyhexadecanoate Catalyzed by Lipases

    OpenAIRE

    Daniel Arrieta-Baez; Georgina Sandoval; Manuel Jimenez-Estrada; L. Gerardo Zepeda-Vallejo; María Eugenia Jaramillo-Flores; Julia Cassani; M. Beatriz Gómez-Patiño

    2013-01-01

    The main monomer of tomato cuticle, 10,16-dihydroxyhexadecanoic acid (10,16-DHPA) and its methyl ester derivative (methyl-10,16-dihydroxyhexadecanote; methyl-10,16-DHHD), were used to study their oligomerization reactions catalyzed by five lipases: Candida antarctica lipase B (CAL-B), Rhizomucor miehei lipase (RM), Thermomyces lanuginosus lipase (TL), Pseudomonas cepacia lipase (PCL) and porcine pancreatic lipase (PPL). For 10,16-DHPA, optimum yields were obtained at 60 °C using toluene and 2...

  8. Palladium(II)-catalyzed regioselective arylation of naphthylamides with aryl iodides utilizing a quinolinamide bidentate system.

    Science.gov (United States)

    Huang, Lehao; Li, Qian; Wang, Chen; Qi, Chenze

    2013-04-05

    A palladium(II)-catalyzed quinolinamide-directed 8-arylation of 1-naphthylamides with aryl iodides is reported. The bidentate directing group (quinolinamide) proved to be crucial for a highly regioselective transformation. In addition, the amide directing group can be easily hydrolyzed under basic conditions to offer a range of 8-aryl-1-naphthylamine derivatives. The theoretical calculations suggest that the C-H arylation reaction proceeds through a sequential C-H activation/oxidative addition pathway.

  9. Silver(I)-Catalyzed C4-H Amination of 1-Naphthylamine Derivatives with Azodicarboxylates.

    Science.gov (United States)

    Zhu, Hongmei; Sun, Suyan; Qiao, Huijie; Yang, Fan; Kang, Jianxun; Wu, Yusheng; Wu, Yangjie

    2018-02-02

    A simple and efficient protocol for silver(I)-catalyzed picolinamide directed C4-H amination of 1-naphthylamine derivatives with readily available azodicarboxylates has been developed, demonstrating a new approach to 1,4-naphthalenediamine derivatives in high yields. Note that this reaction system could proceed under external-oxidant- and additive-free conditions (only requires 5 mol % of AgOAc as the catalyst in acetone).

  10. Advances in Metal-Catalyzed Cross-Coupling Reactions of Halogenated Quinazolinones and Their Quinazoline Derivatives

    Directory of Open Access Journals (Sweden)

    Malose Jack Mphahlele

    2014-10-01

    Full Text Available Halogenated quinazolinones and quinazolines are versatile synthetic intermediates for the metal-catalyzed carbon–carbon bond formation reactions such as the Kumada, Stille, Negishi, Sonogashira, Suzuki-Miyaura and Heck cross-coupling reactions or carbon-heteroatom bond formation via the Buchwald-Hartwig cross-coupling to yield novel polysubstituted derivatives. This review presents an overview of the application of these methods on halogenated quinazolin-4-ones and their quinazolines to generate novel polysubstituted derivatives.

  11. Palladium-Catalyzed Asymmetric Benzylic Substitution of Secondary Benzyl Carbonates with Nitrogen and Oxygen Nucleophiles.

    Science.gov (United States)

    Najib, Atifah; Hirano, Koji; Miura, Masahiro

    2017-05-05

    A Pd/(R)-BINAP-catalyzed asymmetric benzylic substitution of secondary benzyl carbonates with amides and amines proceeds to form the corresponding optically active benzylamines in good yields with a high enantiomeric ratio. The reaction occurs in a dynamic kinetic asymmetric transformation (DYKAT) manner. Additionally, the asymmetric Pd catalysis can also be applicable to phenol nucleophiles, thus delivering chiral ethers with acceptable yields and enantioselectivity.

  12. alpha-Ketophosphonates as ester surrogates : isothiourea-catalyzed asymmetric diester and lactone synthesis

    OpenAIRE

    Smith, Siobhan R.; Leckie, Stuart M.; Holmes, Reuben; Douglas, James; Fallan, Charlene; Shapland, Peter; Pryde, David; Slawin, Alexandra M. Z.; Smith, Andrew D.

    2014-01-01

    This work is in part supported by the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013) ERC Grant Agreement No. 279850 Isothiourea HBTM-2.1 catalyzes the asymmetric Michael addition/lactonization of aryl- and alkenylacetic acids using α-keto-β,γ-unsaturated phosphonates as α,β-unsaturated ester surrogates, giving access to a diverse range of stereodefined lactones or enantioenriched functionalized diesters upon ring-opening. Postprint Pe...

  13. Measuring sticking and stripping in muon-catalyzed dt fusion with multilayer thin films

    Energy Technology Data Exchange (ETDEWEB)

    Fujiwara, M.C.; Gete, E.; Stocki, T.J. [British Columbia Univ., Vancouver, BC (Canada); Bailey, J.M. [Chester Technology (United Kingdom); Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A.; Porcelli, T.A. [Victoria Univ., BC (Canada); Beveridge, J.L.; Marshall, G.M.; Mulhauser, F. [British Columbia Univ., Vancouver, BC (Canada). TRIUMF Facility; Huber, T.M. [Gustavus Adolphus Coll., St. Peter, MN (United States); Jacot-Guillarmod, R. [Fribourg Univ. (Switzerland); Kammel, P. [Lawrence Berkeley Lab., CA (United States); Kherani, N.P. [Ontario Hydro, Toronto, ON (Canada); Kim, S.K. [Jeonbuk National Univ., Jeonju City (Korea, Republic of); Kunselman, A.R. [Wyoming Univ., Laramie, WY (United States); Markushin, V.E. [Rossijskij Nauchnyj Tsentr ``Kurchatovskij Inst.``, Moscow (Russian Federation); Martoff, C.J. [Temple Univ., Philadelphia, PA (United States); Petitjean, C. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Zmeskal, J. [Oesterreichische Akademie der Wissenschaften, Vienna (Austria)

    1996-10-01

    We propose a direct measurement of muon sticking to alpha particles in muon-catalyzed dt fusion at a high density. Exploiting the features of a multilayer thin-film target developed at TRIUMF, the sticking is determined directly by detection of charged fusion products. Experimental separation of initial sticking and stripping may become possible for the first time. Monte Carlo simulations, as well as preliminary results of test measurements are described. (orig.). 26 refs.

  14. Advantages and Limitations of Solid Layer Experiments in Muon Catalyzed Fusion

    Energy Technology Data Exchange (ETDEWEB)

    Marshall, G. M., E-mail: Glen.Marshall@triumf.ca [TRIUMF (Canada); Adamczak, A. [Institute of Nuclear Physics (Poland); Bailey, J. M. [Chester Technology (United Kingdom); Beveridge, J. L. [TRIUMF (Canada); Beer, G. A. [University of Victoria, Physics and Astronomy (Canada); Brewer, J. H. [University of British Columbia, Physics and Astronomy (Canada); Bystritsky, V. M. [Joint Institute for Nuclear Research (Russian Federation); Faifman, M. P. [Russian Research Center ' , Kurchatov Institute' (Russian Federation); Forster, B. M.; Fujiwara, M. C. [University of British Columbia, Physics and Astronomy (Canada); Huber, T. M. [Gustavus Adolphus College, Physics (United States); Jacot-Guillarmod, R. [University of Fribourg, Physics Department (Switzerland); Kammel, P. [Lawrence Berkeley National Laboratory (United States); Kendall, K. R. [TRIUMF (Canada); Kherani, N. P. [Ontario Hydro (Canada); Kim, S. K. [Jeonbuk National University (Korea, Republic of); Knowles, P. E. [University of Victoria, Physics and Astronomy (Canada); Kunselman, A. R. [Jeonbuk National University (Korea, Republic of); Maier, M. [University of Victoria, Physics and Astronomy (Canada); Markushin, V. E. [Paul Scherrer Institute (Switzerland)

    2001-12-15

    Since the discovery that muonic deuterium at energies near a few eV could travel distances of the order of 1 mm in condensed hydrogen, and in particular that muonic tritium and muonic deuterium could emerge from the surface of a solid hydrogen layer, the advantages of solid targets have enabled the study of several processes important in muon catalyzed fusion. A review of the results is presented, emphasizing the strengths and limitations of the use of solid hydrogen layer targets.

  15. Regioselective β-silylation of porphyrins via iridium-catalyzed C-H bond activation.

    Science.gov (United States)

    Sugita, Noriaki; Hayashi, Satoshi; Shibata, Masashi; Endo, Taiga; Noji, Masahiro; Takatori, Kazuhiko; Takanami, Toshikatsu

    2016-11-02

    An efficient approach to meso-unsubstituted β-silylporphyrins was developed through highly regioselective Ir-catalyzed C-H activation, in the presence of HSiMe(OSiMe3)2 as the Si source, from meso-unsubstituted porphyrins. Further transformations of the silyl group, such as oxidation, halogenation, and cross-coupling reactions, could be achieved under mild conditions, demonstrating the synthetic utility of β-silylporphyrins as a multipurpose synthon for fabricating porphyrin derivatives.

  16. Recent advances in transition metal-catalyzed C-H bond functionalization of ferrocene derivatives

    OpenAIRE

    López, L.Á. (Luis); López, Enol

    2016-01-01

    Transition metal-catalyzed C-H bond functionalizations of ferrocene derivatives have emerged in the last few years as a versatile tool in synthetic organometallic chemistry. These protocols offer significant advantages over more traditional approaches for the synthesis of functionalized ferrocene derivatives in terms of both atom- and step-economy. In this Perspective, we aim to showcase the state of the art in this 10 field, with special emphasis on recent asymmetric methodologie...

  17. Recent advances in copper-catalyzed C–H bond amidation

    Directory of Open Access Journals (Sweden)

    Jie-Ping Wan

    2015-11-01

    Full Text Available Copper catalysis has been known as a powerful tool for its ubiquitous application in organic synthesis. One of the fundamental utilities of copper catalysis is in the C–N bond formation by using carbon sources and nitrogen functional groups such as amides. In this review, the recent progress in the amidation reactions employing copper-catalyzed C–H amidation is summarized.

  18. C–H bond halogenation catalyzed or mediated by copper: an overview

    Directory of Open Access Journals (Sweden)

    Wenyan Hao

    2015-11-01

    Full Text Available Carbon–halogen (C–X bonds are amongst the most fundamental groups in organic synthesis, they are frequently and widely employed in the synthesis of numerous organic products. The generation of a C–X bond, therefore, constitutes an issue of universal interest. Herein, the research advances on the copper-catalyzed and mediated C–X (X = F, Cl, Br, I bond formation via direct C–H bond transformation is reviewed.

  19. Selective Palladium(II)-Catalyzed Carbonylation of Methylene β-C-H Bonds in Aliphatic Amines.

    Science.gov (United States)

    Cabrera-Pardo, Jaime R; Trowbridge, Aaron; Nappi, Manuel; Ozaki, Kyohei; Gaunt, Matthew J

    2017-09-18

    Palladium(II)-catalyzed C-H carbonylation reactions of methylene C-H bonds in secondary aliphatic amines lead to the formation of trans-disubstituted β-lactams in excellent yields and selectivities. The generality of the C-H carbonylation process is aided by the action of xantphos-based ligands and is important in securing good yields for the β-lactam products. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Rhodium-Catalyzed Asymmetric Hydrogenation of α,β-Unsaturated Carbonyl Compounds via Thiourea Hydrogen Bonding.

    Science.gov (United States)

    Wen, Jialin; Jiang, Jun; Zhang, Xumu

    2016-09-16

    The strategy of secondary interaction enables enantioselectivity for homogeneous hydrogenation. By introducing hydrogen bonding of substrates with thiourea from the ligand, α,β-unsaturated carbonyl compounds, such as amides and esters, are hydrogenated with high enantiomeric excess. The substrate scope for this chemical transformation is broad with various substituents at the β-position. Control experiments revealed that each unit of the ligand ZhaoPhos is irreplaceable. No nonlinear effect was observed for this Rh/ZhaoPhos-catalyzed asymmetric hydrogenation.

  1. Structural diversity of peroxidase-catalyzed oxidation products of o-methoxyphenols.

    Science.gov (United States)

    Antoniotti, Sylvain; Santhanam, Lakshmi; Ahuja, Disha; Hogg, Michael G; Dordick, Jonathan S

    2004-06-10

    [reaction: see text] The biocatalytic oxidation of o-methoxyphenolic compounds led to a variety of oligophenols (dimers to pentamers) and some of their oxidation products. The reaction was carried out in an aqueous medium at room temperature with hydrogen peroxide as the terminal oxidant in a facile and green route to potentially bioactive compounds. Detailed structural information on the products of peroxidase-catalyzed oxidation of o-methoxyphenols is presented for the first time.

  2. Lewis base catalyzed enantioselective allylic hydroxylation of Morita-Baylis-Hillman carbonates with water

    KAUST Repository

    Zhu, Bo

    2011-08-19

    A Lewis base catalyzed allylic hydroxylation of Morita-Baylis-Hillman (MBH) carbonates has been developed. Various chiral MBH alcohols can be synthesized in high yields (up to 99%) and excellent enantioselectivities (up to 94% ee). This is the first report using water as a nucleophile in asymmetric organocatalysis. The nucleophilic role of water has been verified using 18O-labeling experiments. © 2011 American Chemical Society.

  3. Transformation of cellulose and its derived carbohydrates into formic and lactic acids catalyzed by vanadyl cations.

    Science.gov (United States)

    Tang, Zhenchen; Deng, Weiping; Wang, Yanliang; Zhu, Enze; Wan, Xiaoyue; Zhang, Qinghong; Wang, Ye

    2014-06-01

    The transformation of cellulose or cellulose-derived carbohydrates into platform chemicals is the key to establish biomass-based sustainable chemical processes. The systems able to catalyze the conversion of cellulose into key chemicals in water without the consumption of hydrogen are limited. We report that simple vanadyl (VO(2+)) cations catalyze the conversions of cellulose and its monomer, glucose, into lactic acid and formic acid in water. We have discovered an interesting shift of the major product from formic acid to lactic acid on switching the reaction atmosphere from oxygen to nitrogen. Our studies suggest that VO(2+) catalyzes the isomerization of glucose to fructose, the retro-aldol fragmentation of fructose to two trioses, and the isomerization of trioses, which leads to the formation of lactic acid under anaerobic conditions. The oxidative cleavage of C-C bonds in the intermediates caused by the redox conversion of VO2(+)/VO(2+) under aerobic conditions results in formic acid and CO2. We demonstrate that the addition of an alcohol suppresses the formation of CO2 and enhances the formic acid yield significantly to 70-75 %. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Connecting observations of hematite (alpha-Fe2O3) growth catalyzed by Fe(II).

    Science.gov (United States)

    Rosso, Kevin M; Yanina, Svetlana V; Gorski, Christopher A; Larese-Casanova, Philip; Scherer, Michelle M

    2010-01-01

    Electron exchange between aqueous Fe(II) and structural Fe(III) in iron oxides and oxyhydroxides is important for understanding degradation of environmental pollutants through its apparent constitutive role underlying highly reactive "sorbed Fe(II)" and by catalyzing phase interconversion among these minerals. Although a mechanistic understanding of relationships between interfacial Fe(II)(ads)-Fe(III)(oxide) electron transfer, bulk electron conduction, Fe(II) release, and phase transformation behavior is emerging, much remains unclear, in part due to poorly interconnected investigations. The focus of this study is on reconciling two mutually similar observations of Fe(II)-catalyzed hematite growth documented spectroscopically and microscopically under substantially different chemical conditions. Here, we employ iron isotopic labeling to demonstrate that hematite grown on the (001) surface in Fe(II)-oxalate solution at pH 2.10 and 348 K has magnetic properties that closely correspond to those of hematite grown in Fe(II) solution at pH 7.4 and room temperature. The temperature evolution and extent of the Morin transition displayed in these two materials strongly suggest a mechanistic link involving trace structural Fe(II) incorporation into the growing hematite. Our findings indicate that Fe(II) catalyzed growth of hematite on hematite can occur under environmentally relevant conditions and may be due to bulk electron conduction previously demonstrated for hematite single crystals.

  5. Ultrasound assisted enzyme catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate.

    Science.gov (United States)

    Waghmare, Govind V; Vetal, Mangesh D; Rathod, Virendra K

    2015-01-01

    The present work illustrates the transesterification of glycerol to glycerol carbonate (GlyC) from dimethyl carbonate (DMC) using commercial immobilized lipase (Novozym 435) under ultrasonic irradiation. The experiments were performed in a batch reactor placed in an ultrasonic water bath using a sequence of experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading, duty cycle and ultrasound power on the conversion of glycerol to GlyC. It has been found that ultrasound-assisted lipase-catalyzed transesterification of glycerol would be a potential alternative to conventional alkali-catalyzed method, as high conversion (99.75%) was obtained at mild operating conditions: molar ratio of DMC to glycerol 3:1, catalyst amount of 13% (w/w), lower power input (100W), duty cycle 50% and temperature (60°C) in a relatively short reaction time (4h) using Novozym 435 as catalyst. Ultrasound reduces the reaction time up to 4h as compared to conventional stirring method (14h) catalyzed by Novozym 435. The repeated use of the catalyst under the optimum experimental condition resulted in decay in both enzyme activity and product conversion. Copyright © 2014 Elsevier B.V. All rights reserved.

  6. Constitutive modeling of the viscoelastic and viscoplastic responses of metallocene catalyzed polypropylene

    DEFF Research Database (Denmark)

    Drozdov, Aleksey; Christiansen, Jesper de Claville; Sanporean, Catalina-Gabriela

    2012-01-01

    Purpose – The purpose of this paper is to perform experimental investigation and constitutive modeling of the viscoelastic and viscoplastic behavior of metallocene catalyzed polypropylene (mPP) with application to lifetime assessment under conditions of creep rupture. Design/methodology/approach ......Purpose – The purpose of this paper is to perform experimental investigation and constitutive modeling of the viscoelastic and viscoplastic behavior of metallocene catalyzed polypropylene (mPP) with application to lifetime assessment under conditions of creep rupture. Design...... an arbitrary three-dimensional deformation with small strains, and its parameters are found fitting the observations. Findings – Crystalline structure and molecular architecture of polypropylene strongly affect its time and rate-dependent behavior. In particular, time-to-failure of metallocene catalyzed...... polypropylene under tensile creep noticeably exceeds that of isotactic polypropylene produced by the conventional Ziegler-Natta catalysis. Originality/value – Novel stress-strain relations are developed in viscoelastoplasticity of semi-crystalline polymers and applied to predict their mechanical behavior...

  7. Insights into hydrogen bond donor promoted fixation of carbon dioxide with epoxides catalyzed by ionic liquids.

    Science.gov (United States)

    Liu, Mengshuai; Gao, Kunqi; Liang, Lin; Wang, Fangxiao; Shi, Lei; Sheng, Li; Sun, Jianmin

    2015-02-28

    Catalytic coupling of carbon dioxide with epoxides to obtain cyclic carbonates is an important reaction that has been receiving renewed interest. In this contribution, the cycloaddition reaction in the presence of various hydrogen bond donors (HBDs) catalyzed by hydroxyl/carboxyl task-specific ionic liquids (ILs) is studied in detail. It was found that the activity of ILs could be significantly enhanced in the presence of ethylene glycol (EG), and EG/HEBimBr were the most efficient catalysts for the CO2 cycloaddition to propylene oxide. Moreover, the binary catalysts were also efficiently versatile for the CO2 cycloaddition to less active epoxides such as styrene oxide and cyclohexene oxide. Besides, the minimum energy paths for this hydrogen bond-promoted catalytic reaction were calculated using the density functional theory (DFT) method. The DFT results suggested that the ring-closing reaction was the rate-determining step in the HEBimBr-catalyzed cycloaddition reaction but the EG addition could remarkably reduce its energy barrier as the formation of a hydrogen bond between EG and the oxygen atom of epoxides led this process along the standard SN2 mechanism. As a result, the ring-opening reaction became the rate-determining step in the EG/HEBimBr-catalyzed cycloaddition reaction. The work reported herein helped the understanding and design of catalysts for efficient fixation of CO2 to epoxides via hydrogen bond activation.

  8. Fullerene-catalyzed reduction of azo derivatives in water under UV irradiation

    KAUST Repository

    Guo, Yong

    2012-09-27

    Metal-free fullerene (C60) was found to be an effective catalyst for the reduction of azo groups in basic aqueous solution under UV irradiation in the presence of NaBH4. Use of NaBH4 by itself is not sufficient to reduce the azo dyes without the assistance of a metal catalyst such as Pd and Ag. Experimental and theoretical results suggest that C 60 catalyzes this reaction by using its vacant orbital to accept the electron in the bonding orbital of azo dyes, which leads to the activation of the N=N bond. UV irradiation increases the ability of C60 to interact with electron-donor moieties in azo dyes. Filling a vacancy: Experimental and theoretical methods have been combined to show that C60-catalyzed reductions of azo compounds form aromatic amines under UV irradiation (see scheme). The obtained results show that C60 acts as an electron acceptor to catalyze the reduction of azo compounds, and the role of UV irradiation is to increase the ability of C60 to interact with electron-donor moieties in azo compounds. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Tyrosinase-catalyzed melanin as a contrast agent for photoacoustic tomography

    Science.gov (United States)

    Krumholz, Arie; Chavez, Sarah; Yao, Junjie; Fleming, Timothy; Gillanders, William E.; Wang, Lihong V.

    2011-03-01

    It is difficult to distinguish between tumor cells and surrounding cells without staining as is done in histology. We developed tyrosinase-catalyzed melanin as a reporter gene for photoacoustic tomography. Tyrosinase is the primary enzyme responsible for the production of melanin and alone is sufficient to produce melanin in non-melanogenic cells. Two cell lines were created: a stably transfected HeLa line and a transiently transfected 293 line. A phantom experiment was performed with the 293 transfected cells 48 hours post transfection and the results compared with oxygenated whole blood, B16 melanoma and 293 control cells. An in vivo experiment was performed using the transfected HeLa cells xenografted into a nude mouse ear, and then imaged. The results show strong contrast for tyrosinase-catalyzed melanin in both the 293 cells in the tube phantom as well as the in vivo result showing melanin in a nude mouse ear. Transfection increased expression in 293 cells 159 fold and image contrast compared to blood by as much as 50 fold. Due to the strong signal obtained at longer wavelengths and the decrease of blood signal at the same wavelengths, tyrosinase catalyzed melanin is a good candidate as a molecular imaging contrast agent for photoacoustic tomography.

  10. Structural Determinants of Alkyne Reactivity in Copper-Catalyzed Azide-Alkyne Cycloadditions

    Directory of Open Access Journals (Sweden)

    Xiaoguang Zhang

    2016-12-01

    Full Text Available This work represents our initial effort in identifying azide/alkyne pairs for optimal reactivity in copper-catalyzed azide-alkyne cycloaddition (CuAAC reactions. In previous works, we have identified chelating azides, in particular 2-picolyl azide, as “privileged” azide substrates with high CuAAC reactivity. In the current work, two types of alkynes are shown to undergo rapid CuAAC reactions under both copper(II- (via an induction period and copper(I-catalyzed conditions. The first type of the alkynes bears relatively acidic ethynyl C-H bonds, while the second type contains an N-(triazolylmethylpropargylic moiety that produces a self-accelerating effect. The rankings of reactivity under both copper(II- and copper(I-catalyzed conditions are provided. The observations on how other reaction parameters such as accelerating ligand, reducing agent, or identity of azide alter the relative reactivity of alkynes are described and, to the best of our ability, explained.

  11. Au(I/Au(III-catalyzed Sonogashira-type reactions of functionalized terminal alkynes with arylboronic acids under mild conditions

    Directory of Open Access Journals (Sweden)

    Deyun Qian

    2011-06-01

    Full Text Available A straightforward, efficient, and reliable redox catalyst system for the Au(I/Au(III-catalyzed Sonogashira cross-coupling reaction of functionalized terminal alkynes with arylboronic acids under mild conditions has been developed.

  12. The three transglycosylation reactions catalyzed by cyclodextrin glycosyltransferase from Bacillus circulans (strain 251) proceed via different kinetic mechanisms

    NARCIS (Netherlands)

    Veen, Bart A. van der; Alebeek, Gert-Jan W.M. van; Uitdehaag, Joost C.M.; Dijkstra, Bauke W.; Dijkhuizen, Lubbert

    Cyclodextrin glycosyltransferase (CGTase) catalyzes three transglycosylation reactions via a double displacement mechanism involving a covalent enzyme-intermediate complex (substituted-enzyme intermediate). Characterization of the three transglycosylation reactions, however, revealed that they

  13. Yttrium (III chloride catalyzed Mannich reaction: An efficient procedure for the synthesis of β-amino carbonyl compounds

    Directory of Open Access Journals (Sweden)

    Venkateswarlu Yekkirala

    2014-12-01

    Full Text Available Yttrium (III chloride catalyzed Mannich reaction of aldehydes with ketones and amines in acetonitrile at reflux temperature to give various β-amino carbonyl compounds in very good yields.

  14. Asymmetric hydroxyamination of oxindoles catalyzed by chiral bifunctional tertiary amine thiourea: construction of 3-amino-2-oxindoles with quaternary stereocenters.

    Science.gov (United States)

    Jia, Li-Na; Huang, Jun; Peng, Lin; Wang, Liang-Liang; Bai, Jian-Fei; Tian, Fang; He, Guang-Yun; Xu, Xiao-Ying; Wang, Li-Xin

    2012-01-14

    Chiral bifunctional tertiary amine thiourea was applied to catalyze the asymmetric hydroxyamination of 3-subsituted oxindoles with nitrosobenzene to construct 3-amino-2-oxindoles with quaternary stereocenters in good yields (up to 91%) and enantioselectivities (up to 90% ee).

  15. Copper(I)-catalyzed [3+1] cycloaddition of alkenyldiazoacetates and iminoiodinanes: easy access to substituted 2-azetines.

    Science.gov (United States)

    Barluenga, José; Riesgo, Lorena; Lonzi, Giacomo; Tomás, Miguel; López, Luis A

    2012-07-23

    The copper(I)-catalyzed reaction of alkenyldiazoacetates and iminoiodinanes affords functionalized azetine derivatives. This process is consistent with the formation of an aziridinyldiazoacetate intermediate, which gives rise to the four-membered heterocycles by metal-catalyzed ring expansion. The resulting azetine structure is a direct precursor of azeditine-2-carboxylic acid derivatives (EWG = electron-withdrawing group). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. A 11-Steps Total Synthesis of Magellanine through a Gold(I)-Catalyzed Dehydro Diels-Alder Reaction.

    Science.gov (United States)

    McGee, Philippe; Bétournay, Geneviève; Barabé, Francis; Barriault, Louis

    2017-05-22

    We have developed an innovative strategy for the formation of angular carbocycles via a gold(I)-catalyzed dehydro Diels-Alder reaction. This transformation provides rapid access to a variety of complex angular cores in excellent diastereoselectivities and high yields. The usefulness of this AuI -catalyzed cycloaddition was further demonstrated by accomplishing a 11-steps total synthesis of (±)-magellanine. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Mechanism of Rhodium-Catalyzed C-H Functionalization: Advances in Theoretical Investigation.

    Science.gov (United States)

    Qi, Xiaotian; Li, Yingzi; Bai, Ruopeng; Lan, Yu

    2017-11-07

    Transition-metal-catalyzed cross-coupling has emerged as an effective strategy for chemical synthesis. Within this area, direct C-H bond transformation is one of the most efficient and environmentally friendly processes for the construction of new C-C or C-heteroatom bonds. Over the past decades, rhodium-catalyzed C-H functionalization has attracted considerable attention because of the versatility and wide use of rhodium catalysts in chemistry. A series of C-X (X = C, N, or O) bond formation reactions could be realized from corresponding C-H bonds using rhodium catalysts. Various experimental studies on rhodium-catalyzed C-H functionalization reactions have been reported, and in tandem, mechanistic and computational studies have also progressed significantly. Since 2012, our group has performed theoretical studies to reveal the mechanism of rhodium-catalyzed C-H functionalization reactions. We have studied the changes in the oxidation state of rhodium and compared the Rh(I)/Rh(III) catalytic cycle to the Rh(III)/Rh(V) catalytic cycle using density functional theory calculation. The development of advanced computational methods and improvements in computing power make theoretical calculation a powerful tool for the mechanistic study of rhodium chemistry. Computational study is able to not only provide mechanistic insights but also explain the origin of regioselectivity, enantioselectivity, and stereoselectivity in rhodium-catalyzed C-H functionalization reactions. This Account summarizes our computational work on rhodium-catalyzed C-H functionalization reactions. The mechanistic study under discussion is divided into three main parts: C-H bond cleavage step, transformation of the C-Rh bond, and regeneration of the active catalyst. In the C-H bond cleavage step, computational results of four possible mechanisms, including concerted metalation-deprotonation (CMD), oxidative addition (OA), Friedel-Crafts-type electrophilic aromatic substitution (SEAr), and

  18. Annexin A2 and cancer

    DEFF Research Database (Denmark)

    Christensen, Maria V; Høgdall, Claus K; Jochumsen, Kirsten M

    2018-01-01

    Annexin A2 is a 36-kDa protein interfering with multiple cellular processes especially in cancer progression. The present review aimed to show the relations between Annexin A2 and cancer. A systematic search for studies investigating cancer and Annexin A2 expression was conducted using Pub......Med. Acute lymphoblastic leukaemia, acute promyelocytic leukaemia, clear cell renal cell carcinoma, breast, cervical, colorectal, endometrial, gastric cancer, glioblastoma, hepatocellular carcinoma, lung, multiple myeloma, oesophageal squamous cell carcinoma, ovarian cancer, pancreatic duct adenocarcinoma......, prostate cancer and urothelial carcinoma were evaluated. Annexin A2 expression correlates with resistance to treatment, binding to the bone marrow, histological grade and type, TNM-stage and shortened overall survival. The regulation of Annexin A2 is of interest due to its potential as target for a more...

  19. Synthetic scope and DFT analysis of the chiral binap–gold(I complex-catalyzed 1,3-dipolar cycloaddition of azlactones with alkenes

    Directory of Open Access Journals (Sweden)

    María Martín-Rodríguez

    2013-11-01

    Full Text Available The 1,3-dipolar cycloaddition between glycine-derived azlactones with maleimides is efficiently catalyzed by the dimeric chiral complex [(Sa-Binap·AuTFA]2. The alanine-derived oxazolone only reacts with tert-butyl acrylate giving anomalous regiochemistry, which is explained and supported by Natural Resonance Theory and Nucleus Independent Chemical Shifts calculations. The origin of the high enantiodiscrimination observed with maleimides and tert-butyl acrylate is analyzed using DFT computed at M06/Lanl2dz//ONIOM(b3lyp/Lanl2dz:UFF level. Several applications of these cycloadducts in the synthesis of new proline derivatives with a 2,5-trans-arrangement and in the preparation of complex fused polycyclic molecules are described.

  20. Resting state and elementary steps of the coupling of aryl halides with thiols catalyzed by alkylbisphosphine complexes of palladium.

    Science.gov (United States)

    Alvaro, Elsa; Hartwig, John F

    2009-06-10

    Detailed mechanistic studies on the coupling of aryl halides with thiols catalyzed by palladium complexes of the alkylbisphosphine ligand CyPF-(t)Bu (1-dicyclohexylphosphino-2-di-tert-butylphosphinoethylferrocene) are reported. The elementary steps that constitute the catalytic cycle, i.e. oxidative addition, transmetalation and reductive elimination, have been studied, and their relative rates are reported. Each of the steps of the catalytic process occurs at temperatures that are much lower than those required for the reactions catalyzed by a combination of palladium precursors and CyPF-(t)Bu. To explain these differences in rates between the catalytic and stoichiometric reactions, studies were conducted to identify the resting state of the catalyst of the reactions catalyzed by a combination of Pd(OAc)(2) and CyPF-(t)Bu, a combination of Pd(dba)(2) and CyPF-(t)Bu, or the likely intermediate Pd(CyPF-(t)Bu)(Ar)(Br). These data show that the major palladium complex in each case lies off of the catalytic cycle. The resting state of the reactions catalyzed by Pd(OAc)(2) and CyPF-(t)Bu was the palladium bis-thiolate complex [Pd(CyPF-(t)Bu)(SR)(2)] (R = alkyl or aryl). The resting state in reactions catalyzed by Pd(2)(dba)(3) and CyPF-(t)Bu was the binuclear complex [Pd(CyPF-(t)Bu)](2)(mu(2),eta(2)-dba) (9). The resting states of reactions of both aromatic and aliphatic thiols catalyzed by [Pd(CyPF-(t)Bu)(p-tolyl)(Br)] (3a) were the hydridopalladium thiolate complexes [Pd(CyPF-(t)Bu)(H)(SR)] (R= alkyl and aryl). All these palladium species have been prepared independently, and the mechanisms by which they enter the catalytic cycle have been examined in detail. These features of the reaction catalyzed by palladium and CyPF-(t)Bu have been compared with those of reactions catalyzed by the alkylbisphosphine DiPPF and Pd(OAc)(2) or Pd(dba)(2). Our data indicate that the resting states of these reactions are similar to each other and that our mechanistic conclusions about

  1. CYP703 is an ancient cytochrome P450 in land plants catalyzing in-chain hydroxylation of lauric acid to provide building blocks for sporopollenin synthesis in pollen.

    Science.gov (United States)

    Morant, Marc; Jørgensen, Kirsten; Schaller, Hubert; Pinot, Franck; Møller, Birger Lindberg; Werck-Reichhart, Danièle; Bak, Søren

    2007-05-01

    CYP703 is a cytochrome P450 family specific to land plants. Typically, each plant species contains a single CYP703. Arabidopsis thaliana CYP703A2 is expressed in the anthers of developing flowers. Expression is initiated at the tetrad stage and restricted to microspores and to the tapetum cell layer. Arabidopsis CYP703A2 knockout lines showed impaired pollen development and a partial male-sterile phenotype. Scanning electron and transmission electron microscopy of pollen from the knockout plants showed impaired pollen wall development with absence of exine. The fluorescent layer around the pollen grains ascribed to the presence of phenylpropanoid units in sporopollenin was absent in the CYP703A2 knockout lines. Heterologous expression of CYP703A2 in yeast cells demonstrated that CYP703 catalyzes the conversion of medium-chain saturated fatty acids to the corresponding monohydroxylated fatty acids, with a preferential hydroxylation of lauric acid at the C-7 position. Incubation of recombinant CYP703 with methanol extracts from developing flowers confirmed that lauric acid and in-chain hydroxy lauric acids are the in planta substrate and product, respectively. These data demonstrate that in-chain hydroxy lauric acids are essential building blocks in sporopollenin synthesis and enable the formation of ester and ether linkages with phenylpropanoid units. This study identifies CYP703 as a P450 family specifically involved in pollen development.

  2. Role of surface chemistry in modified ACF (activated carbon fiber)-catalyzed peroxymonosulfate oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Shiying, E-mail: ysy@ouc.edu.cn [Key Laboratory of Marine Environment and Ecology, Ministry of Education, Qingdao 266100 (China); College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100 (China); Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering (MEGE), Qingdao 266100 (China); Li, Lei [College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100 (China); Xiao, Tuo [College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100 (China); China City Environment Protection Engineering Limited Company, Wuhan 430071 (China); Zheng, Di; Zhang, Yitao [College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100 (China)

    2016-10-15

    Highlights: • ACF can efficiently activate peroxymonosulfate to degrade organic pollutants. • Basic functional groups may mainly increase the adsorption capacity of ACF. • C1, N1, N2 have promoting effect on the ACF catalyzed PMS oxidation. • Modification by heat after nitric acid is also a way of ACF regeneration. - Abstract: A commercial activated carbon fiber (ACF-0) was modified by three different methods: nitration treatment (ACF-N), heat treatment (ACF-H) and heat treatment after nitration (ACF-NH), and the effects of textural and chemical properties on the ability of the metal-free ACF-catalyzed peroxymonosulfate (PMS) oxidation of Reactive Black 5 (RB5), an azo dye being difficultly adsorbed onto ACF, in aqueous solution were investigated in this work. Surface density of functional groups, surface area changes, surface morphology and the chemical state inside ACF samples were characterized by Boehm titration, N{sub 2} adsorption, scanning electron microscopy in couple with energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), respectively. XPS spectra deconvolution was applied to figure out the importance of surface nitrogen-containing function groups. We found that π-π, pyridine and amine have promoting effect on the catalytic oxidation while the −NO{sub 2} has inhibitory effect on the ACF/PMS systems for RB5 destroy. Sustainability and renewability of the typical ACF-NH for catalytic oxidation of RB5 were also discussed in detail. Information about our conclusions are useful to control and improve the performance of ACF-catalyzed PMS oxidation for organic pollutants in wastewater treatment.

  3. A natural vanishing act: the enzyme-catalyzed degradation of carbon nanomaterials.

    Science.gov (United States)

    Kotchey, Gregg P; Hasan, Saad A; Kapralov, Alexander A; Ha, Seung Han; Kim, Kang; Shvedova, Anna A; Kagan, Valerian E; Star, Alexander

    2012-10-16

    Over the past three decades, revolutionary research in nanotechnology by the scientific, medical, and engineering communities has yielded a treasure trove of discoveries with diverse applications that promise to benefit humanity. With their unique electronic and mechanical properties, carbon nanomaterials (CNMs) represent a prime example of the promise of nanotechnology with applications in areas that include electronics, fuel cells, composites, and nanomedicine. Because of toxicological issues associated with CNMs, however, their full commercial potential may not be achieved. The ex vitro, in vitro, and in vivo data presented in this Account provide fundamental insights into the biopersistence of CNMs, such as carbon nanotubes and graphene, and their oxidation/biodegradation processes as catalyzed by peroxidase enzymes. We also communicate our current understanding of the mechanism for the enzymatic oxidation and biodegradation. Finally, we outline potential future directions that could enhance our mechanistic understanding of the CNM oxidation and biodegradation and could yield benefits in terms of human health and environmental safety. The conclusions presented in this Account may catalyze a rational rethinking of CNM incorporation in diverse applications. For example, armed with an understanding of how and why CNMs undergo enzyme-catalyzed oxidation and biodegradation, researchers can tailor the structure of CNMs to either promote or inhibit these processes. In nanomedical applications such as drug delivery, the incorporation of carboxylate functional groups could facilitate biodegradation of the nanomaterial after delivery of the cargo. On the other hand, in the construction of aircraft, a CNM composite should be stable to oxidizing conditions in the environment. Therefore, pristine, inert CNMs would be ideal for this application. Finally, the incorporation of CNMs with defect sites in consumer goods could provide a facile mechanism that promotes the

  4. Enzyme-catalyzed synthesis of saccharide acrylate monomers from nonedible biomass.

    Science.gov (United States)

    Kloosterman, Wouter M J; Brouwer, Sander G M; Loos, Katja

    2014-08-01

    Various cellulase preparations were found to catalyze the transglycosidation between cotton linters and 2-hydroxyethyl acrylate. The conversion and enzyme activity were found to be optimal in reaction mixtures that contained 5 vol % of the acrylate. The structures of the products were revealed by using TLC and (1) H and (13) C NMR spectroscopy. The enzyme-catalyzed reaction resulted in two products. The minor product originated from transglycosidation to hemicellulose and was found to be 2-(β-xylosyloxy)-ethyl acrylate. The major product was identified as 2-(β-glucosyloxy)-ethyl acrylate and the yield of the product was 5 wt % based on the amount of consumed cellulose. Glycosidation products with oligosaccharide moieties could not be detected in the reaction mixture. This result can be explained by the hydrolytic activities of the used cellulase preparation. Cellulase from Trichoderma reesei was found to possess, in addition to endoglucanase activity, cellobiosidase and β-glucosidase activities. Five other cellulase preparations from different origins were tested as well for catalysis of oligosaccharide acrylate synthesis. For most cellulase preparations the major transglycosidation product appeared to be 2-(β-glucosyloxy)-ethyl acrylate. Nevertheless, the endo-β-(1,4)-glucanase from Trichoderma longibrachiatum was found to catalyze the synthesis of 2-(β-cellobiosyloxy)-ethyl acrylate. Unlike the other cellulase preparations, endo-β-(1,4)-glucanase from T. longibrachiatum showed no detectable β-glucosidase activity and therefore oligosaccharide acrylate monomers were not further hydrolyzed into the monosaccharide acrylate 2-(β-glucosyloxy)-ethyl acrylate. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Treatment of hydrocarbon contamination under flow through conditions by using magnetite catalyzed chemical oxidation.

    Science.gov (United States)

    Usman, M; Faure, P; Lorgeoux, C; Ruby, C; Hanna, K

    2013-01-01

    Soil pollution by hydrocarbons (aromatic and aliphatic hydrocarbons) is a major environmental issue. Various treatments have been used to remove them from contaminated soils. In our previous studies, the ability of magnetite has been successfully explored to catalyze chemical oxidation for hydrocarbon remediation in batch slurry system. In the present laboratory study, column experiments were performed to evaluate the efficiency of magnetite catalyzed Fenton-like (FL) and activated persulfate (AP) oxidation for hydrocarbon degradation. Flow-through column experiments are intended to provide a better representation of field conditions. Organic extracts isolated from three different soils (an oil-contaminated soil from petrochemical industrial site and two soils polluted by polycyclic aromatic hydrocarbon (PAH) originating from coking plant sites) were spiked on sand. After solvent evaporation, spiked sand was packed in column and was subjected to oxidation using magnetite as catalyst. Oxidant solution was injected at a flow rate of 0.1 mL min(-1) under water-saturated conditions. Organic analyses were performed by GC-mass spectrometry, GC-flame ionization detector, and micro-Fourier transform infrared spectroscopy. Significant abatement of both types of hydrocarbons (60-70 %) was achieved after chemical oxidation (FL and AP) of organic extracts. No significant by-products were formed during oxidation experiment, underscoring the complete degradation of hydrocarbons. No selective degradation was observed for FL with almost similar efficiency towards all hydrocarbons. However, AP showed less reactivity towards higher molecular weight PAHs and aromatic oxygenated compounds. Results of this study demonstrated that magnetite-catalyzed chemical oxidation can effectively degrade both aromatic and aliphatic hydrocarbons (enhanced available contaminants) under flow-through conditions.

  6. Ru(III) catalyzed permanganate oxidation of aniline at environmentally relevant pH.

    Science.gov (United States)

    Zhang, Jing; Zhang, Ying; Wang, Hui; Guan, Xiaohong

    2014-07-01

    Ru(III) was employed as catalyst for aniline oxidation by permanganate at environmentally relevant pH for the first time. Ru(III) could significantly improve the oxidation rate of aniline by 5-24 times with its concentration increasing from 2.5 to 15 μmol/L. The reaction of Ru(III) catalyzed permanganate oxidation of aniline was first-order with respect to aniline, permanganate and Ru(III), respectively. Thus the oxidation kinetics can be described by a third-order rate law. Aniline degradation by Ru(III) catalyzed permanganate oxidation was markedly influenced by pH, and the second-order rate constant (ktapp) decreased from 643.20 to 2.67 (mol/L)⁻¹sec⁻¹ with increasing pH from 4.0 to 9.0, which was possibly due to the decrease of permanganate oxidation potential with increasing pH. In both the uncatalytic and catalytic permanganate oxidation, six byproducts of aniline were identified in UPLC-MS/MS analysis. Ru(III), as an electron shuttle, was oxidized by permanganate to Ru(VI) and Ru(VII), which acted the co-oxidants for decomposition of aniline. Although Ru(III) could catalyze permanganate oxidation of aniline effectively, dosing homogeneous Ru(III) into water would lead to a second pollution. Therefore, efforts would be made to investigate the catalytic performance of supported Ru(III) toward permanganate oxidation in our future study. Copyright © 2014. Published by Elsevier B.V.

  7. Highly enantioselective synthesis of γ-, δ-, and ε-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)-Cu- or Pd-catalyzed cross-coupling.

    Science.gov (United States)

    Xu, Shiqing; Oda, Akimichi; Kamada, Hirofumi; Negishi, Ei-ichi

    2014-06-10

    Despite recent advances of asymmetric synthesis, the preparation of enantiomerically pure (≥99% ee) compounds remains a challenge in modern organic chemistry. We report here a strategy for a highly enantioselective (≥99% ee) and catalytic synthesis of various γ- and more-remotely chiral alcohols from terminal alkenes via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)-Cu- or Pd-catalyzed cross-coupling. ZACA-in situ oxidation of tert-butyldimethylsilyl (TBS)-protected ω-alkene-1-ols produced both (R)- and (S)-α,ω-dioxyfunctional intermediates (3) in 80-88% ee, which were readily purified to the ≥99% ee level by lipase-catalyzed acetylation through exploitation of their high selectivity factors. These α,ω-dioxyfunctional intermediates serve as versatile synthons for the construction of various chiral compounds. Their subsequent Cu-catalyzed cross-coupling with various alkyl (primary, secondary, tertiary, cyclic) Grignard reagents and Pd-catalyzed cross-coupling with aryl and alkenyl halides proceeded smoothly with essentially complete retention of stereochemical configuration to produce a wide variety of γ-, δ-, and ε-chiral 1-alkanols of ≥99% ee. The MαNP ester analysis has been applied to the determination of the enantiomeric purities of δ- and ε-chiral primary alkanols, which sheds light on the relatively undeveloped area of determination of enantiomeric purity and/or absolute configuration of remotely chiral primary alcohols.

  8. Synthesis of alpha-tetrasubstituted triazoles by copper-catalyzed silyl deprotection/azide cycloaddition

    Directory of Open Access Journals (Sweden)

    Zachary L. Palchak

    2015-08-01

    Full Text Available Propargylamines are popular substrates for triazole formation, but tetrasubstituted variants have required multistep syntheses involving stoichiometric amounts of metal. A recent cyclohexanone–amine–silylacetylene coupling forms silyl-protected tetrasubstituted propargylamines in a single copper-catalyzed step. The development of the tandem silyl deprotection–triazole formation reported herein offers rapid access to alpha-tetrasubstituted triazoles. A streamlined two-step approach to this uncommon class of hindered triazoles will accelerate exploration of their therapeutic potential. The superior activity of copper(II triflate in the formation of triazoles from sensitive alkyne substrates extends to simple terminal alkynes.

  9. Stereochemistry of phospho group transfer catalyzed by a mutant alkaline phosphatase

    Energy Technology Data Exchange (ETDEWEB)

    Butler-Ransohoff, J.E.; Kendall, D.A.; Freeman, S.; Knowles, J.R.; Kaiser, E.T.

    1988-06-28

    The stereochemical course of the phospho group transfer catalyzed by mutant (S102C) alkaline phosphatase from Escherichia coli was investigated by using /sup 31/P nuclear magnetic resonance spectroscopy. Transphosphorylation from 4-nitrophenyl (R/sub P/)-/sup 17/O, /sup 16/O, /sup 18/O)phosphate to (S)-propane-1,2-diol occurs with overall retention of configuration at phosphorus. This result is consistent with the view that the hydrolysis of substrates by this mutant enzyme proceeds by way of a covalent phosphoenzyme intermediate in the same manner as the wild-type alkaline phosphatase.

  10. Continuous-Flow Processes in Heterogeneously Catalyzed Transformations of Biomass Derivatives into Fuels and Chemicals

    Directory of Open Access Journals (Sweden)

    Antonio A. Romero

    2012-07-01

    Full Text Available Continuous flow chemical processes offer several advantages as compared to batch chemistries. These are particularly relevant in the case of heterogeneously catalyzed transformations of biomass-derived platform molecules into valuable chemicals and fuels. This work is aimed to provide an overview of key continuous flow processes developed to date dealing with a series of transformations of platform chemicals including alcohols, furanics, organic acids and polyols using a wide range of heterogeneous catalysts based on supported metals, solid acids and bifunctional (metal + acidic materials.

  11. Enzyme-Catalyzed Modifications of Polysaccharides and Poly(ethylene glycol

    Directory of Open Access Journals (Sweden)

    H. N. Cheng

    2012-06-01

    Full Text Available Polysaccharides are used extensively in various industrial applications, such as food, adhesives, coatings, construction, paper, pharmaceuticals, and personal care. Many polysaccharide structures need to be modified in order to improve their end-use properties; this is mostly done through chemical reactions. In the past 20 years many enzyme-catalyzed modifications have been developed to supplement chemical derivatization methods. Typical reactions include enzymatic oxidation, ester formation, amidation, glycosylation, and molecular weight reduction. These reactions are reviewed in this paper, with emphasis placed on the work done by the authors. The polymers covered in this review include cellulosic derivatives, starch, guar, pectin, and poly(ethylene glycol.

  12. Synthesis of (-)-Piperitylmagnolol Featuring ortho-Selective Deiodination and Pd-Catalyzed Allylation.

    Science.gov (United States)

    Ikoma, Atsushi; Ogawa, Narihito; Kondo, Daiki; Kawada, Hiroki; Kobayashi, Yuichi

    2016-05-06

    A 1,4-addition strategy using an enone and a copper reagent was studied for the synthesis of (-)-piperitylmagnolol. A MOM-protected biphenol copper reagent was added to BF3·OEt2-activated 4-isopropylcyclohexenone, whereas 1,4-addition of protected monophenol reagents possessing an allyl group was found to be unsuccessful. The allyl group was later attached to the p-,p'-diiodo-biphenol ring by Pd-catalyzed coupling with allylborate. The aforementioned iodide was synthesized using a new method for ortho-selective deiodination of o-,p-diiodophenols.

  13. Scope and mechanism in palladium-catalyzed isomerizations of highly substituted allylic, homoallylic, and alkenyl alcohols.

    Science.gov (United States)

    Larionov, Evgeny; Lin, Luqing; Guénée, Laure; Mazet, Clément

    2014-12-03

    Herein we report the palladium-catalyzed isomerization of highly substituted allylic alcohols and alkenyl alcohols by means of a single catalytic system. The operationally simple reaction protocol is applicable to a broad range of substrates and displays a wide functional group tolerance, and the products are usually isolated in high chemical yield. Experimental and computational mechanistic investigations provide complementary and converging evidence for a chain-walking process consisting of repeated migratory insertion/β-H elimination sequences. Interestingly, the catalyst does not dissociate from the substrate in the isomerization of allylic alcohols, whereas it disengages during the isomerization of alkenyl alcohols when additional substituents are present on the alkyl chain.

  14. Origins of Enantioselectivity during Allylic Substitution Reactions Catalyzed by Metallacyclic Iridium Complexes

    Science.gov (United States)

    Madrahimov, Sherzod T.; Hartwig, John F.

    2012-01-01

    In depth mechanistic studies of iridium catalyzed regioselective and enantioselective allylic substitution reactions are presented. A series of cyclometallated allyliridium complexes that are kinetically and chemically competent to be intermediates in the allylic substitution reactions was prepared and characterized by 1D and 2D NMR spectroscopies and solid state structural analysis. The rates of epimerization of the less thermodynamically stable diastereomeric allyliridium complexes to the thermodynamically more stable allyliridium stereoisomers were measured. The rates of nucleophilic attack by aniline and by N-methylaniline on the isolated allyliridium complexes were also measured. Attack on the thermodynamically less stable allyliridium complex was found to be orders of magnitude faster than attack on the thermodynamically more stable complex, yet the major enantiomer of the catalytic reaction is formed from the more stable diastereomer. Comparison of the rates of nucleophilic attack to the rates of epimerization of the diastereomeric allyliridium complexes containing a weakly-coordinating counterion showed that nucleophilic attack on the less stable allyliridium species is much faster than conversion of the less stable isomer to the more stable isomer. These observations imply that Curtin-Hammett conditions are not met during iridium catalyzed allylic substitution reactions by η3-η1-η3 interconversion. Rather, these data imply that when these conditions exist for this reaction, they are created by reversible oxidative addition and the high selectivity of this oxidative addition step to form the more stable diastereomeric allyl complex leads to the high enantioselectivity. The stereochemical outcome of the individual steps of allylic substitution was assessed by reaction of deuterium-labeled substrates. The reaction was shown to occur by oxidative addition with inversion of configuration, followed by an outer sphere nucleophilic attack that leads to a second

  15. Palladium-catalyzed cross-coupling reactions of aryl boronic acids with aryl halides in water.

    Science.gov (United States)

    Wang, Shaoyan; Zhang, Zhiqiang; Hu, Zhizhi; Wang, Yue; Lei, Peng; Chi, Haijun

    2009-01-01

    An efficient Suzuki cross-coupling reaction using a variety of aryl halides in neat water was developed. The Pd-catalyzed reaction between aryl bromides or chlorides and phenyl boronic acids was compatible with various functional groups and affords biphenyls in good to excellent yields without requirement of organic cosolvents. The air stability and solubility in water of the palladium-phosphinous acid complexes were considered to facilitate operation of the coupling reaction and product isolation. The reaction conditions including Pd catalyst selection, temperature, base and catalyst recoverability were also investigated.

  16. Role of Diffusion in the Kinetics of Reversible Enzyme-catalyzed Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Szabo, Attila [National Institute of Digestive and Kidney Diseases, Maryland (United States); Zhou, Huan Xiang [Florida State University, Florida (United States)

    2012-03-15

    The accurate expression for the steady-state velocity of an irreversible enzyme-catalyzed reaction obtained by Shin and co-workers (J. Chem. Phys. 2001, 115, 1455) is generalized to allow for the rebinding of the product. The amplitude of the power-law (t{sup -1/2}) relaxation of the free- and bound-enzyme concentrations to steady-state values is expressed in terms of the steady-state velocity and the intrinsic (chemical) rate constants. This result is conjectured to be exact, even though our expression for the steady-state velocity in terms of microscopic parameters is only approximate

  17. In situ enzymatic removal of orthophosphate by the nucleoside phosphorylase catalyzed phosphorolysis of nicotinamide riboside.

    Science.gov (United States)

    Shriver, J W; Sykes, B D

    1982-09-01

    An enzymatic orthophosphate removal system is described which can be effectively used to continuously remove orthophosphate from biochemical samples. The phosphorolysis of nicotinamide riboside is catalyzed by calf spleen nucleoside phosphorylase to give ribose-1-PO4 and nicotinamide along with a proton. At pH 8 the production of ribose-1-PO4 from orthophosphate is essentially quantitative. This reaction can be monitored optically or by 31P nuclear magnetic resonance (NMR). Equations are given for determining the time required to remove a given amount of phosphate from a typical NMR sample with a known amount of nucleoside phosphorylase. The effects of a competing orthophosphate-producing reaction are considered.

  18. The mechanism of the phosphine-free palladium-catalyzed hydroarylation of alkynes

    DEFF Research Database (Denmark)

    Ahlquist, Mårten Sten Gösta; Fabrizi, G.; Cacchi, S.

    2006-01-01

    The mechanism of the Pd-catalyzed hydroarylation and hydrovinylation reaction of alkynes has been studied by a combination of experimental and theoretical methods (B3LYP), with an emphasis on the phosphine-free version. The regioselectivity of the hydroarylation and hydrovinylation shows unexpected...... differences, which could be attributed mainly to the higher steric demand of the cyclohexenyl group as compared to the phenyl group. Hydroarylation of alpha,beta-acetylenic carbonyl substrates yields a very unusual anti-Michael selectivity, which is shown to result from reaction of the nonconjugated double...

  19. [Development of novel methods for synthesis of heterocyclic compounds catalyzed by transition metals in fluorinated alcohols].

    Science.gov (United States)

    Saito, Akio

    2008-08-01

    New possibilities for catalytic syntheses of lactone derivatives and nitrogen-containing heterocyclic compounds in fluorinated alcohols are described. The cationic Rh(I) catalyst in fluorinated alcohol solvents (hexafluoroisopropanol: HFIP, trifluoroethanol: TFE) brought about not only mild cycloaddition reactions of ester-tethered compounds but also a facile formation of indole derivatives by the aromatic amino-Claisen rearrangement of N-propargyl aniline derivatives. The use of HFIP as an additive exerted a remarkable effect on the Pictet-Spengler reaction catalyzed by the fluorinated surfactant-combined Brønsted acid catalyst in water.

  20. Biomimetic oxidation of carbamazepine with hydrogen peroxide catalyzed by a manganese porphyrin

    Energy Technology Data Exchange (ETDEWEB)

    Neves, Claudia M.B.; Simoes, Mario M.Q.; Domingues, Fernando M.J.; Neves, M. Graca P.M.S.; Cavaleiro, Jose A.S., E-mail: msimoes@ua.pt [Dept. de Quimica, QOPNA, Universidade de Aveiro (Portugal)

    2012-07-01

    This laboratory project is planned for an undergraduate chemistry laboratory in which students prepare a manganese porphyrin able to mimic the oxidative metabolism of carbamazepine, one of the most frequently prescribed drugs in the treatment of epilepsy. The in vitro oxidation of carbamazepine results in the formation of the corresponding 10,11-epoxide, the main in vivo metabolite. The reaction is catalyzed by manganese porphyrin in the presence of H{sub 2}O{sub 2}, an environmentally-friendly oxidant. Through this project students will develop their skills in organic synthesis, coordination chemistry, chromatographic techniques such as TLC and HPLC, UV-visible spectrophotometry, and NMR spectroscopy. (author)

  1. Nickel-Catalyzed Cross-Coupling of Organolithium Reagents with (Hetero)Aryl Electrophiles.

    Science.gov (United States)

    Heijnen, Dorus; Gualtierotti, Jean-Baptiste; Hornillos, Valentín; Feringa, Ben L

    2016-03-14

    Nickel-catalyzed selective cross-coupling of aromatic electrophiles (bromides, chlorides, fluorides and methyl ethers) with organolithium reagents is presented. The use of a commercially available nickel N-heterocyclic carbene (NHC) complex allows the reaction with a variety of (hetero)aryllithium compounds, including those prepared via metal-halogen exchange or direct metallation, whereas a commercially available electron-rich nickel-bisphosphine complex smoothly converts alkyllithium species into the corresponding coupled product. These reactions proceed rapidly (1 h) under mild conditions (room temperature) while avoiding the undesired formation of reduced or homocoupled products. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. A new approach to ferrocene derived alkenes via copper-catalyzed olefination

    Directory of Open Access Journals (Sweden)

    Vasily M. Muzalevskiy

    2015-11-01

    Full Text Available A new approach to ferrocenyl haloalkenes and bis-alkenes was elaborated. The key procedure involves copper catalyzed olefination of N-unsubstituted hydrazones, obtained from ferrocene-containing carbonyl compounds and hydrazine, with polyhaloalkanes. The procedure is simple, cheap and could be applied for the utilization of environmentally harmful polyhalocarbons. The cyclic voltammetry study of the representative examples of the synthesized ferrocenyl alkenes shows the strong dependence of the cathodic behavior on the amount of vinyl groups: while for the monoalkene containing molecules no reduction is seen, the divinyl products are reduced in several steps.

  3. Process Technology for Immobilized LipaseProcess Technology for Immobilized Lipase-catalyzed

    DEFF Research Database (Denmark)

    Xu, Yuan

    , most applications remain in the production of high-value fine chemicals, primarily because of the expense of introducing new technology. In particular lipasecatalyzed synthesis has already achieved efficient operations for high-value products and more interesting now is to establish opportunities......-catalyzed transesterification is that it is multi-phasic system. The by-product glycerol can potentially impose inhibitory effects on immobilized lipases and likewise the un-dissolved ethanol can inhibit the lipase. The options for addressing these issues can be used as the basis for selecting the biocatalyst and the reactor...

  4. In vivo and in vitro olefin cyclopropanation catalyzed by heme enzymes

    Energy Technology Data Exchange (ETDEWEB)

    Coelho, Pedro S.; Brustad, Eric M.; Arnold, Frances H.; Wang, Zhan; Lewis, Jared C.

    2016-11-15

    The present invention provides methods for catalyzing the conversion of an olefin to any compound containing one or more cyclopropane functional groups using heme enzymes. In certain aspects, the present invention provides a method for producing a cyclopropanation product comprising providing an olefinic substrate, a diazo reagent, and a heme enzyme; and admixing the components in a reaction for a time sufficient to produce a cyclopropanation product. In other aspects, the present invention provides heme enzymes including variants and fragments thereof that are capable of carrying out in vivo and in vitro olefin cyclopropanation reactions. Expression vectors and host cells expressing the heme enzymes are also provided by the present invention.

  5. Abnormal gas sensing characteristics arising from catalyzed morphological changes of ionsorbed oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Xue Xinyu; Chen Zhaohui; Ma Chunhua; Xing Lili [College of Sciences, Northeastern University, Shenyang 110004 (China); Chen Yujin [College of Sciences, Harbin Engineering University, Harbin 150001 (China); Wang Yanguo; Wang Taihong, E-mail: xuexinyu@mail.neu.edu.cn [Micro-Nano Technologies Research Center, Hunan University, Changsha 410082 (China)

    2010-02-10

    Abnormal gas sensing characteristics are observed at low temperature in uniformly loaded Pt-SnO{sub 2} nanorod gas sensors. The sensors operated at 200 deg. C exhibit opposite variations of resistances, and the change of resistance decreases with increasing ethanol concentration. In contrast, the sensors operated at 300 deg. C show regular behavior and the sensitivity is extremely high. Such behaviors are ascribed to Pt-catalyzed morphological changes of ionsorbed oxygen at low temperature. The present results are the bases for further investigating the effect of ionsorbed oxygen morphologies on gas sensing.

  6. Investigation of acetic acid-catalyzed hydrothermal pretreatment on corn stover

    DEFF Research Database (Denmark)

    Xu, Jian; Thomsen, Mette Hedegaard; Thomsen, Anne Belinda

    2010-01-01

    Acetic acid (AA)-catalyzed liquid hot water (LHW) pretreatments on raw corn stover (RCS) were carried out at 195 °C at 15 min with the acetic acid concentrations between 0 and 400 g/kg RCS. After pretreatment, the liquor fractions and water-insoluble solids (WIS) were collected separately...... xylan recovery of 81.82% was observed by the pretreatment with 10 g AA/kg RCS. The toxic test on liquors showed that the inhibition effect happened to Baker's yeast when the acetic acid used in the pretreatment was higher than 100 g/kg RCS. The WIS obtained from the pretreatment with 15 g and 30 g...

  7. Polycyclic Aromatic Hydrocarbons via Iron(III)-Catalyzed Carbonyl-Olefin Metathesis.

    Science.gov (United States)

    McAtee, Christopher C; Riehl, Paul S; Schindler, Corinna S

    2017-03-01

    Polycyclic aromatic hydrocarbons are important structural motifs in organic chemistry, pharmaceutical chemistry, and materials science. The development of a new synthetic strategy toward these compounds is described based on the design principle of iron(III)-catalyzed carbonyl-olefin metathesis reactions. This approach is characterized by its operational simplicity, high functional group compatibility, and regioselectivity while relying on FeCl3 as an environmentally benign, earth-abundant metal catalyst. Experimental evidence for oxetanes as reactive intermediates in the catalytic carbonyl-olefin ring-closing metathesis has been obtained.

  8. Mechanistic Investigations of the Iron(III)-Catalyzed Carbonyl-Olefin Metathesis Reaction.

    Science.gov (United States)

    Ludwig, Jacob R; Phan, Susan; McAtee, Christopher C; Zimmerman, Paul M; Devery, James J; Schindler, Corinna S

    2017-08-09

    Iron(III)-catalyzed carbonyl-olefin ring-closing metathesis represents a new approach toward the assembly of molecules traditionally generated by olefin-olefin metathesis or olefination. Herein, we report detailed synthetic, spectroscopic, kinetic, and computational studies to determine the mechanistic features imparted by iron(III), substrate, and temperature to the catalytic cycle. These data are consistent with an iron(III)-mediated asynchronous, concerted [2+2]-cycloaddition to form an intermediate oxetane as the turnover-limiting step. Fragmentation of the oxetane via Lewis acid-activation results in the formation of five- and six-membered unsaturated carbocycles.

  9. Base-Catalyzed Depolymerization of Solid Lignin-Rich Streams Enables Microbial Conversion

    DEFF Research Database (Denmark)

    Rodriguez, Alberto; Salvachúa, Davinia; Katahira, Rui

    2017-01-01

    base-catalyzed depolymerization (BCD) using a process-relevant solid lignin stream produced via deacetylation, mechanical refining, and enzymatic hydrolysis to enable biological lignin conversion. BCD was conducted with the solid lignin substrate over a range of temperatures at two NaOH concentrations......, and the results demonstrate that the lignin can be partially extracted and saponified at temperatures as low as 60°C. At 120°C and 2% NaOH, the high extent of lignin solubility was accompanied by a considerable decrease in the lignin average molecular weight and the release of lignin-derived monomers including...

  10. Metal assisted catalyzed etched (MACE) black Si: optics and device physics.

    Science.gov (United States)

    Toor, Fatima; Miller, Jeffrey B; Davidson, Lauren M; Duan, Wenqi; Jura, Michael P; Yim, Joanne; Forziati, Joanne; Black, Marcie R

    2016-08-25

    Metal-assisted catalyzed etching (MACE) of silicon (Si) is a controllable, room-temperature wet-chemical technique that uses a thin layer of metal to etch the surface of Si, leaving behind various nano- and micro-scale surface features, including nanowires (NWs), that can be tuned to achieve various useful engineering goals, in particular with respect to Si solar cells. In this review, we introduce the science and technology of MACE from the literature, and provide an in-depth analysis of MACE to enhance Si solar cells, including the outlook for commercial applications of this technology.

  11. Cooperative Metal–Ligand Catalyzed Intramolecular Hydroamination and Hydroalkoxylation of Allenes Using a Stable Iron Catalyst

    KAUST Repository

    El-Sepelgy, Osama

    2018-01-18

    A new iron-catalyzed chemoselective intramolecular hydroamination and hydroalkoxylation of the readily available α-allenic amines and alcohols to valuable unsaturated 5-membered heterocycles, 2,3-dihydropyrrole and 2,3-dihydrofuran, is reported. Effective selectivity control is achieved by a metal–ligand cooperative activation of the substrates. The mild reaction conditions and the use of low amounts of an air and moisture stable iron catalyst allow for the hydrofunctionalization of a wide range of allenes bearing different functional groups in good yields in the absence of base or any sensitive additives.

  12. Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

    Directory of Open Access Journals (Sweden)

    Thibault E. Schmid

    2015-12-01

    Full Text Available The copper-catalyzed asymmetric conjugate addition (ACA of nucleophiles onto polyenic Michael acceptors represents an attractive and powerful methodology for the synthesis of relevant chiral molecules, as it enables in a straightforward manner the sequential generation of two or more stereogenic centers. In the last decade, various chiral copper-based catalysts were evaluated in combination with different nucleophiles and Michael acceptors, and have unambiguously demonstrated their usefulness in the control of the regio- and enantioselectivity of the addition. The aim of this review is to report recent breakthroughs achieved in this challenging field.

  13. Enantioselective Synthesis of Acyclic α-Quaternary Carboxylic Acid Derivatives through Iridium-Catalyzed Allylic Alkylation.

    Science.gov (United States)

    Shockley, Samantha E; Hethcox, J Caleb; Stoltz, Brian M

    2017-09-11

    The first highly enantioselective iridium-catalyzed allylic alkylation that provides access to products bearing an allylic all-carbon quaternary stereogenic center has been developed. The reaction utilizes a masked acyl cyanide (MAC) reagent, which enables the one-pot preparation of α-quaternary carboxylic acids, esters, and amides with a high degree of enantioselectivity. The utility of these products is further explored through a series of diverse product transformations. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Photoassisted Oxidation of Sulfides Catalyzed by Artificial Metalloenzymes Using Water as an Oxygen Source †

    Directory of Open Access Journals (Sweden)

    Christian Herrero

    2016-12-01

    Full Text Available The Mn(TpCPP-Xln10A artificial metalloenzyme, obtained by non-covalent insertion of Mn(III-meso-tetrakis(p-carboxyphenylporphyrin [Mn(TpCPP, 1-Mn] into xylanase 10A from Streptomyces lividans (Xln10A as a host protein, was found able to catalyze the selective photo-induced oxidation of organic substrates in the presence of [RuII(bpy3]2+ as a photosensitizer and [CoIII(NH35Cl]2+ as a sacrificial electron acceptor, using water as oxygen atom source.

  15. Palladium-catalyzed migratory insertion of isocyanides: an emerging platform in cross-coupling chemistry.

    Science.gov (United States)

    Vlaar, Tjøstil; Ruijter, Eelco; Maes, Bert U W; Orru, Romano V A

    2013-07-08

    Isocyanides have been important building blocks in organic synthesis since the discovery of the Ugi reaction and related isocyanide-based multicomponent reactions. In the past decade isocyanides have found a new application as versatile C1 building blocks in palladium catalysis. Palladium-catalyzed reactions involving isocyanide insertion offer a vast potential for the synthesis of nitrogen-containing fine chemicals. This Minireview discusses all the achievements in this emerging field. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Alumina-entrapped Ag catalyzed nitro compounds coupled with alcohols using borrowing hydrogen methodology.

    Science.gov (United States)

    Liu, Huihui; Chuah, Gaik Khuan; Jaenicke, Stephan

    2015-06-14

    Supported silver catalysts were reported for the first time to be able to catalyze the coupling reaction between nitroarenes and alcohols via the borrowing hydrogen scheme. The recyclable, non-leaching catalyst is synthesized by the entrapment method, which allows entrapping of silver nanoparticles in an alumina matrix. Alcohols, acting as the reducing agents for nitro-groups, alkylated the resultant amines smoothly over these silver catalysts giving a yield of >98% towards the N-substituted amines. In this process, multiple steps were realized in one-pot over a single catalyst with very high efficiency. It offers another clean and economic way to achieve amination of alcohols.

  17. Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols

    Directory of Open Access Journals (Sweden)

    Katrina Tait

    2016-10-01

    Full Text Available Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene derivatives using alcohol nucleophiles were investigated. The optimal conditions were found to be 10 mol % PdCl2(CH3CN2 in methanol, offering yields up to 92%. The reaction was successful using primary, secondary and tertiary alcohol nucleophiles and was compatible with a variety of substituents on cyclopropanated oxabenzonorbornadiene. With unsymmetrical C1-substituted cyclopropanated 7-oxabenzonorbornadienes, the regioselectivity of the reaction was excellent, forming only one regioisomer in all cases.

  18. Social Media as Catalyzer for Connected Health: Hype or Hope? Perspectives from IMIA Working Groups.

    Science.gov (United States)

    Fernandez-Luque, Luis; Vilmarlund, Vivian; Borycki, Elizabeth; Schulz, Stefan; Kuziemsky, Craig; Marschollek, Michael; Kulikowski, Casimir A

    2016-01-01

    The Internet and social media are becoming ubiquitous technologies that are transforming the health sector. Social media has become an avenue for accessing, creating and sharing health information among patients and healthcare professionals. Furthermore, social media has become a key feature in many eHealth solutions, including wearable technologies, Big Data solutions, eLearning systems, Serious Games, Medical imaging, etc. These hyper-connected technologies are facilitating a paradigm shift towards more connected health. In this panel, representatives of different IMIA Working Groups will explore how both hope and hype contribute to social media's catalyzing role in creating connected health solutions.

  19. Microwave Assisted Hydrolysis of Holocellulose Catalyzed with Sulfonated Char Derived from Lignin-Rich Residue

    Directory of Open Access Journals (Sweden)

    Kui Wang

    2015-01-01

    Full Text Available A microwave assisted green process has been developed for production of sugars through liquefying holocellulose catalyzed with sulfonated char derived from the lignin-rich residue produced during pretreatment of lignocellulose. Various reaction parameters including the hydrolysis temperature, hydrolysis time, catalyst content, and the ratio of water to feedstock were evaluated. The maximum sugars yield of 82.6% (based on the dry mass of holocellulose was obtained under the optimum reaction conditions. The sulfonated char showed superior catalytic performance to that of dilute sulfuric acid in converting holocellulose into sugars under microwave irradiation.

  20. In vivo and in vitro olefin cyclopropanation catalyzed by heme enzymes

    Science.gov (United States)

    Coelho, Pedro S; Brustad, Eric M; Arnold, Frances H; Wang, Zhan; Lewis, Jared C

    2015-03-31

    The present invention provides methods for catalyzing the conversion of an olefin to any compound containing one or more cyclopropane functional groups using heme enzymes. In certain aspects, the present invention provides a method for producing a cyclopropanation product comprising providing an olefinic substrate, a diazo reagent, and a heme enzyme; and admixing the components in a reaction for a time sufficient to produce a cyclopropanation product. In other aspects, the present invention provides heme enzymes including variants and fragments thereof that are capable of carrying out in vivo and in vitro olefin cyclopropanation reactions. Expression vectors and host cells expressing the heme enzymes are also provided by the present invention.

  1. Phosphonium Salts as Pseudohalides: Regioselective Nickel-Catalyzed Cross-Coupling of Complex Pyridines and Diazines.

    Science.gov (United States)

    Zhang, Xuan; McNally, Andrew

    2017-08-07

    Heterobiaryls are important pharmacophores that are challenging to prepare by traditional cross-coupling methods. An alternative approach is presented where pyridines and diazines are converted into heteroaryl phosphonium salts and coupled with aryl boronic acids. Nickel catalysts are unique for selective heteroaryl transfer, and the reaction has a broad substrate scope that includes complex pharmaceuticals. Phosphonium ions also display orthogonal reactivity in cross-couplings compared to halides, enabling chemoselective palladium- and nickel-catalyzed coupling sequences. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. A Radical Mechanism for the Vanadium-Catalyzed Deoxydehydration of Glycols

    OpenAIRE

    Vicente Poutás, Luis Carlos de; Castiñeira Reis, Marta; Sanz Díez, Roberto; Silva López, Carlos; Nieto Faza, Olalla

    2016-01-01

    We propose a novel mechanism for the deoxydehydration (DODH) reaction of glycols catalyzed by a [Bu4N][VO2(dipic)] complex (dipic = pyridine-2,6-dicarboxylate) using triphenylphosphine as a reducing agent. Using density functional theory, we have confirmed that the preferred sequence of reaction steps involves reduction of the V(V) complex by phosphine, followed by condensation of the glycol into a [VO(dipic)(-O-CH2CH2-O-)] V(III) complex (6), which then evolves to the alkene product, with re...

  3. Ruthenium-Catalyzed Methylation of Amines with Paraformaldehyde in Water under Mild Conditions.

    Science.gov (United States)

    van der Waals, Dominic; Heim, Leo E; Gedig, Christian; Herbrik, Fabian; Vallazza, Simona; Prechtl, Martin H G

    2016-09-08

    Methylated amines are highly important for a variety of pharmaceutical and agrochemical applications. Existing routes for their formation result in the production of large amounts of waste or require high reaction temperatures, both of which impact the ecological and economical footprint of the methodologies. Herein, we report the ruthenium-catalyzed reductive methylation of a range of aliphatic amines, using paraformaldehyde as both substrate and hydrogen source, in combination with water. This reaction proceeds under mild aqueous reaction conditions. Additionally the use of a secondary phase for catalyst retention and recycling has been investigated with promising results. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Gold-catalyzed direct alkynylation of tryptophan in peptides using TIPS-EBX

    Directory of Open Access Journals (Sweden)

    Gergely L. Tolnai

    2016-04-01

    Full Text Available The selective functionalization of peptides containing only natural amino acids is important for the modification of biomolecules. In particular, the installation of an alkyne as a useful handle for bioconjugation is highly attractive, but the use of a carbon linker is usually required. Herein, we report the gold-catalyzed direct alkynylation of tryptophan in peptides using the hypervalent iodine reagent TIPS-EBX (1-[(triisopropylsilylethynyl]-1,2-benziodoxol-3(1H-one. The reaction proceeded in 50–78% yield under mild conditions and could be applied to peptides containing other nucleophilic and aromatic amino acids, such as serine, phenylalanine or tyrosine.

  5. Iridium‐Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols with the Liberation of Syngas

    DEFF Research Database (Denmark)

    Olsen, Esben Paul Krogh; Madsen, Robert

    2012-01-01

    =cyclooctene) and racemic 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (rac‐BINAP) in a mesitylene solution saturated with water. A catalytic amount of lithium chloride was also added to improve the catalyst turnover. The reaction has been applied to a variety of primary alcohols and gives rise to products in good...... to excellent yields. Ethers, esters, imides, and aryl halides are stable under the reaction conditions, whereas olefins are partially saturated. The reaction is believed to proceed by two consecutive organometallic transformations that are catalyzed by the same iridium(I)–BINAP species. First, dehydrogenation...

  6. Cobalt carbonyl-catalyzed carbonylation of functionalized aziridines to versatile β-lactam building blocks.

    Science.gov (United States)

    Piens, Nicola; Van Hecke, Kristof; Vogt, Dieter; D'hooghe, Matthias

    2017-06-07

    The Co2(CO)8-catalyzed carbonylation of different classes of non-activated aziridines with diverse substitution patterns was investigated. Special attention was devoted to selectivity issues and reaction optimization. This study resulted in the regio- and stereospecific synthesis of 24 novel β-lactam target structures in high yields on a multigram scale. The synthetic potential of the newly obtained azetidin-2-ones was illustrated via ring-expansion, ring-closure, and/or side chain-functionalization protocols to provide a straightforward entry to novel pyrrolidines, C-fused bi- and tricyclic β-lactams and monocyclic carbapenem analogs.

  7. Selective Palladium(II)-Catalyzed Carbonylation of Methylene β-C-H Bonds in Aliphatic Amines.

    OpenAIRE

    Cabrera-Pardo, Jaime R; Trowbridge, Aaron; Nappi, Manuel; Ozaki, Kyohei; Gaunt, Matthew James

    2017-01-01

    Pd(II)-catalyzed C–H carbonylation of methylene C–H bonds in secondary aliphatic amines leads to the formation trans-disubstituted β-lactams in excellent yields and selectivities. The generality of the C–H carbonylation process is aided by the action of xantphos-based ligands and is important in securing good yields of the β-lactam products. EPSRC (EP/100548X/1), ERC (ERC-STG-259711), Royal Society (Wolfson Award), Marie Curie Foundation and Herchel Smith Foundation.

  8. Understanding the hydrolysis mechanism of ethyl acetate catalyzed by an aqueous molybdocene: a computational chemistry investigation.

    Science.gov (United States)

    Tílvez, Elkin; Cárdenas-Jirón, Gloria I; Menéndez, María I; López, Ramón

    2015-02-16

    A thoroughly mechanistic investigation on the [Cp2Mo(OH)(OH2)](+)-catalyzed hydrolysis of ethyl acetate has been performed using density functional theory methodology together with continuum and discrete-continuum solvation models. The use of explicit water molecules in the PCM-B3LYP/aug-cc-pVTZ (aug-cc-pVTZ-PP for Mo)//PCM-B3LYP/aug-cc-pVDZ (aug-cc-pVDZ-PP for Mo) computations is crucial to show that the intramolecular hydroxo ligand attack is the preferred mechanism in agreement with experimental suggestions. Besides, the most stable intermediate located along this mechanism is analogous to that experimentally reported for the norbornenyl acetate hydrolysis catalyzed by molybdocenes. The three most relevant steps are the formation and cleavage of the tetrahedral intermediate immediately formed after the hydroxo ligand attack and the acetic acid formation, with the second one being the rate-determining step with a Gibbs energy barrier of 36.7 kcal/mol. Among several functionals checked, B3LYP-D3 and M06 give the best agreement with experiment as the rate-determining Gibbs energy barrier obtained only differs 0.2 and 0.7 kcal/mol, respectively, from that derived from the experimental kinetic constant measured at 296.15 K. In both cases, the acetic acid elimination becomes now the rate-determining step of the overall process as it is 0.4 kcal/mol less stable than the tetrahedral intermediate cleavage. Apart from clarifying the identity of the cyclic intermediate and discarding the tetrahedral intermediate formation as the rate-determining step for the mechanism of the acetyl acetate hydrolysis catalyzed by molybdocenes, the small difference in the Gibbs energy barrier found between the acetic acid formation and the tetrahedral intermediate cleavage also uncovers that the rate-determining step could change when studying the reactivity of carboxylic esters other than ethyl acetate substrate specific toward molybdocenes or other transition metal complexes. Therefore

  9. Manganese-Catalyzed Cross-Coupling of Aryl Halides and Grignard Reagents by a Radical Mechanism

    DEFF Research Database (Denmark)

    Antonacci, Giuseppe; Ahlburg, Andreas; Fristrup, Peter

    2017-01-01

    The substrate scope and the mechanism have been investigated for the MnCl2-catalyzed cross-coupling reaction between aryl halides and Grignard reagents. The transformation proceeds rapidly and in good yield when the aryl halide component is an aryl chloride containing a cyano or an ester group...... in the para position or a cyano group in the ortho position. A range of other substituents gave no conversion of the aryl halide or led to the formation of side products. A broader scope was observed for the Grignard reagents, where a variety of alkyl- and arylmagnesium chlorides participated in the coupling...

  10. Kinetics of transesterification of methyl acetate and n-octanol catalyzed by cation exchange resins

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yong; Gao, Li; Li, Xiying; Mao, Liqun [Henan University, Kaifeng (China); Wei, Min [Henan University of Technology, Zhengzhou (China)

    2013-05-15

    The transesterification kinetics of methyl acetate with n-octanol to octyl acetate and methanol were studied using Amberlyst 15 as catalyst in a batch stirred reactor. The influence of the agitation speed, particle size, temperature, catalyst loading, and initial reactants molar ratio was investigated in detail. A pseudo-homogeneous (PH) kinetic model was applied to correlate the experimental data in the temperature range of 313.15 K to 328.15 K. The estimated kinetic parameters made the calculated results in good agreement with the experimental data. A kinetic model describing the transesterification reaction catalyzed by cation exchange resins was developed.

  11. Biomimetic oxidation of carbamazepine with hydrogen peroxide catalyzed by a manganese porphyrin

    Directory of Open Access Journals (Sweden)

    Cláudia M. B. Neves

    2012-01-01

    Full Text Available This laboratory project is planned for an undergraduate chemistry laboratory in which students prepare a manganese porphyrin able to mimic the oxidative metabolism of carbamazepine, one of the most frequently prescribed drugs in the treatment of epilepsy. The in vitro oxidation of carbamazepine results in the formation of the corresponding 10,11-epoxide, the main in vivo metabolite. The reaction is catalyzed by manganese porphyrin in the presence of H2O2, an environmentally-friendly oxidant. Through this project students will develop their skills in organic synthesis, coordination chemistry, chromatographic techniques such as TLC and HPLC, UV-visible spectrophotometry, and NMR spectroscopy.

  12. Ruthenium-Catalyzed Synthesis of 1,5-Dichlorides by Sequential Intermolecular Kharasch Reactions

    OpenAIRE

    Thommes, Katrin; Fernandez-Zumel, Mariano Alfonso; Buron, Charlotte; Godinat, Aurélien; Scopelliti, Rosario; Severin, Kay

    2011-01-01

    Sequential intermolecular atom transfer radical addition reactions of activated dichlorides Cl2CRR′ (R = CN, CO2Et, R′ = H, CN, CO2Et) with two olefins catalyzed by [Cp*RuCl2(PPh3)] in the presence Mg allow the synthesis of linear 1,5-dichlorides. Different olefins can be employed in the first and in the second addition reaction. The reaction products are interesting synthetic precursors as demonstrated by the synthesis of two cyclopentanes by Mg-induced dechlorination. The structure of trans...

  13. Phenanthrene Synthesis via Chromium-Catalyzed Annulation of 2-Biaryl Grignard Reagents and Alkynes.

    Science.gov (United States)

    Yan, Jianming; Yoshikai, Naohiko

    2017-11-22

    A chromium/2,2'-bipyridine-catalyzed annulation reaction of 2-biarylmagnesium reagents with alkynes is reported. The reaction is applicable to a variety of aryl- and/or alkyl-substituted internal alkynes as well as 2-biaryl and related Grignard reagents, thus affording phenanthrene derivatives in moderate to good yields. The reaction proceeds at the expense of excess alkyne as a hydrogen acceptor and thus does not need an external oxidant. Deuterium-labeling experiments shed light on the reaction mechanism, which likely involves multiple intramolecular C-H activation processes on chromium.

  14. Carbon isotope fractionation of 1,1,1-trichloroethane during base-catalyzed persulfate treatment

    Energy Technology Data Exchange (ETDEWEB)

    Marchesi, Massimo, E-mail: m2marche@uwaterloo.ca [Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Thomson, Neil R. [Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Aravena, Ramon [Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Sra, Kanwartej S. [Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Golder Associates Inc, Toronto, Ontario, Canada L5N 5Z7 (Canada); Otero, Neus; Soler, Albert [Departament de Cristal.lographia, Mineralogia i Diposits Minerals, Facultat de Geologia, Universitat de Barcelona, Barcelona, Spain 08028 (Spain)

    2013-09-15

    Highlights: • Treatability and C fractionation of 1,1,1-TCA by base-catalyzed S{sub 2}O{sub 8}{sup 2−} was studied. • The rate of degradation of 1,1,1-TCA increased with a higher OH{sup −}:S{sub 2}O{sub 8}{sup 2−} ratio. •Base-catalyzed S{sub 2}O{sub 8}{sup 2−} can potentially treat recalcitrant compound like 1,1,1-TCA. • An enrichment factor of −7.0‰ independent of the OH{sup −}:S{sub 2}O{sub 8}{sup 2−} ratio was obtained. • Carbon isotope can potentially be used to estimate the ISCO treatment efficacy. -- Abstract: The extent of carbon isotope fractionation during degradation of 1,1,1-trichloroethane (1,1,1-TCA) by a base-catalyzed persulfate (S{sub 2}O{sub 8}{sup 2−}) treatment system was investigated. Significant destruction of 1,1,1-TCA was observed at a pH of ∼12. An increase in the NaOH:S{sub 2}O{sub 8}{sup 2−} molar ratio from 0.2:1 to 8:1 enhanced the reaction rate of 1,1,1-TCA by a factor of ∼5 to yield complete (>99.9%) destruction. An average carbon isotope enrichment fractionation factor which was independent of the NaOH:S{sub 2}O{sub 8}{sup 2−} molar ratio of −7.0 ± 0.2‰ was obtained. This significant carbon isotope fractionation and the lack of dependence on changes in the NaOH:S{sub 2}O{sub 8}{sup 2−} molar ratio demonstrates that carbon isotope analysis can potentially be used in situ as a performance assessment tool to estimate the degradation effectiveness of 1,1,1-TCA by a base-catalyzed persulfate system.

  15. Palladium-Catalyzed Deaminative Phenanthridinone Synthesis from Aniline via C-H Bond Activation.

    Science.gov (United States)

    Yedage, Subhash L; Bhanage, Bhalchandra M

    2016-05-20

    This work reports palladium-catalyzed phenanthridinone synthesis using the coupling of aniline and amide by formation of C-C and C-N bonds in a one-pot fashion via dual C-H bond activation. It involves simultaneous cleavage of four bonds and the formation of two new bonds. The present protocol is ligand-free, takes place under mild reaction conditions, and is environmentally benign as nitrogen gas and water are the only side products. This transformation demonstrates a broad range of aniline and amide substrates with different functional groups and has been scaled up to gram level.

  16. Hydrodeoxygenation of fatty acid esters catalyzed by Ni on nano-sized MFI type zeolites

    Energy Technology Data Exchange (ETDEWEB)

    Schreiber, Moritz W.; Rodriguez-Niño, Daniella; Gutiérrez, Oliver Y.; Lercher, Johannes A.

    2016-01-01

    The impact of support morphology and composition on the intrinsic activity of Ni supported on MFI-type zeolite was explored in the hydrodeoxygenation of methyl stearate, tristearate, and algae oil (mixture of triglycerides). The nano-sized structure of the support (self-pillared nanosheets) is beneficial for the activity of the catalysts. Higher Ni dispersion and concomitant higher reaction rates were obtained on nano-structured supports than on zeolite with conventional morphology. Rates normalized to accessible Ni atoms (TOF), however, varied little with support morphology. Acidity of the support increases the rate of Ni-catalyzed C-O hydrogenolysis per surface metal site.

  17. Homologous Pairing Activities of Two Rice RAD51 Proteins, RAD51A1 and RAD51A2

    OpenAIRE

    Yuichi Morozumi; Ryohei Ino; Shukuko Ikawa; Naozumi Mimida; Takeshi Shimizu; Seiichi Toki; Hiroaki Ichikawa; Takehiko Shibata; Hitoshi Kurumizaka

    2013-01-01

    In higher eukaryotes, RAD51 functions as an essential protein in homologous recombination and recombinational repair of DNA double strand breaks. During these processes, RAD51 catalyzes homologous pairing between single-stranded DNA and double-stranded DNA. Japonica cultivars of rice (Oryza sativa) encode two RAD51 proteins, RAD51A1 and RAD51A2, whereas only one RAD51 exists in yeast and mammals. However, the functional differences between RAD51A1 and RAD51A2 have not been elucidated, because...

  18. Palladium(0)-Catalyzed Benzylic C(sp(3))-H Functionalization for the Concise Synthesis of Heterocycles and Its Applications.

    Science.gov (United States)

    Tsukano, Chihiro

    2017-01-01

    C-H functionalization reactions involve the activation of otherwise unreactive C-H bonds, and represent atom economical methods for the direct transformation of simple substrates to complex molecules. While transition metal-catalyzed C(sp(2))-H functionalization reactions are regularly used in synthesis, C(sp(3))-H functionalization is rarely applied to the synthesis of complex natural products because of the difficulties associated with controlling selectivity. With this in mind, we focused on the development of new palladium (Pd)(0)-catalyzed C(sp(3))-H functionalization reactions for the synthesis of complex molecules, resulting in several new methods capable of solving these problems. We initially developed a concise synthetic method for the facile construction of oxindoles and spirooxindoles via a Pd-catalyzed benzylic C(sp(3))-H functionalization reaction. This method was subsequently extended to the synthesis of various heterocycles, including 2-arylindoles, benzocarbazole, indolocarbazole, indoloquinazolinone, and indoloquinazolinedione, as well as the total synthesis of several pyrrolophenanthridine alkaloids without the need for any protecting groups. This method was also successfully applied to the synthesis of the right-hand fragment of benzohopane from tetrahydro-2H-fluorene, which was constructed by a Pd-catalyzed benzylic C(sp(3))-H functionalization. In this review, we provide a detailed discussion of our most recent investigations pertaining to Pd(0)-catalyzed benzylic C(sp(3))-H functionalization.

  19. Primuline Derivatives That Mimic RNA to Stimulate Hepatitis C Virus NS3 Helicase-catalyzed ATP Hydrolysis*

    Science.gov (United States)

    Sweeney, Noreena L.; Shadrick, William R.; Mukherjee, Sourav; Li, Kelin; Frankowski, Kevin J.; Schoenen, Frank J.; Frick, David N.

    2013-01-01

    ATP hydrolysis fuels the ability of helicases and related proteins to translocate on nucleic acids and separate base pairs. As a consequence, nucleic acid binding stimulates the rate at which a helicase catalyzes ATP hydrolysis. In this study, we searched a library of small molecule helicase inhibitors for compounds that stimulate ATP hydrolysis catalyzed by the hepatitis C virus (HCV) NS3 helicase, which is an important antiviral drug target. Two compounds were found that stimulate HCV helicase-catalyzed ATP hydrolysis, both of which are amide derivatives synthesized from the main component of the yellow dye primuline. Both compounds possess a terminal pyridine moiety, which was critical for stimulation. Analogs lacking a terminal pyridine inhibited HCV helicase catalyzed ATP hydrolysis. Unlike other HCV helicase inhibitors, the stimulatory compounds differentiate between helicases isolated from various HCV genotypes and related viruses. The compounds only stimulated ATP hydrolysis catalyzed by NS3 purified from HCV genotype 1b. They inhibited helicases from other HCV genotypes (e.g. 1a and 2a) or related flaviviruses (e.g. Dengue virus). The stimulatory compounds interacted with HCV helicase in the absence of ATP with dissociation constants of about 2 μm. Molecular modeling and site-directed mutagenesis studies suggest that the stimulatory compounds bind in the HCV helicase RNA-binding cleft near key residues Arg-393, Glu-493, and Ser-231. PMID:23703611

  20. Rotation of the exo-methylene group of (R)-3-methylitaconate catalyzed by coenzyme B(12)-dependent 2-methyleneglutarate mutase from Eubacterium barkeri.

    Science.gov (United States)

    Pierik, Antonio J; Ciceri, Daniele; Bröker, Gerd; Edwards, Christopher H; McFarlane, William; Winter, Joachim; Buckel, Wolfgang; Golding, Bernard T

    2002-11-27

    2-Methyleneglutarate mutase from the anaerobe Eubacterium (Clostridium) barkeri is an adenosylcobalamin (coenzyme B(12))-dependent enzyme that catalyzes the equilibration of 2-methyleneglutarate with (R)-3-methylitaconate. Two possibilities for the mechanism of the carbon skeleton rearrangement of the substrate-derived radical to the product-related radical are considered. In both mechanisms an acrylate group migrates from C-3 of 2-methyleneglutarate to C-4. In the "addition-elimination" mechanism this 1,2-shift occurs via an intermediate, a 1-methylenecyclopropane-1,2-dicarboxylate radical, in which the migrating acrylate is simultaneously attached to both C-3 and C-4. In the "fragmentation-recombination" mechanism the migrating group, a 2-acrylyl radical, becomes detached from C-3 before it starts bonding to C-4. In an attempt to distinguish between these two possibilities we have investigated the action of 2-methyleneglutarate mutase on the stereospecifically deuterated substrates (Z)-3-methyl[2'-(2)H(1)]itaconate and (Z)-3-[2'-(2)H(1),methyl-(2)H(3)]methylitaconate. The enzyme catalyzes the equilibration of both compounds with their corresponding E-isomers and with a 1:1 mixture of the corresponding (E)- and (Z)-2-methylene[2'-(2)H(1)]glutarates, as shown by monitoring of the reactions with (1)H and (2)H NMR. In the initial phase of the enzyme-catalyzed equilibration a significant excess (8-11%) of (E)-3-methyl[2'-(2)H(1)]itaconate over its equilibrium value was observed ("E-overshoot"). The E-overshoot was only 3-4% with (Z)-3-[2'-(2)H(1),methyl-(2)H(3)]methylitaconate because the presence of the deuterated methyl group raises the energy barrier from 3-methylitaconate to the corresponding radical. The overshoot is explained by postulating that the migrating acrylate group has to overcome an additional energy barrier from the state leading back to the substrate-derived radical to the state leading forward to the product-related radical. It is concluded that the

  1. Group XV phospholipase A2, a lysosomal phospholipase A2

    OpenAIRE

    Shayman, James A.; Kelly, Robert; Kollmeyer, Jessica; He, Yongqun; Abe, Akira

    2011-01-01

    A phospholipase A2 was identified from MDCK cell homogenates with broad specificity toward glycerophospholipids including phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylglycerol. The phospholipase has the unique ability to transacylate short chain ceramides. This phospholipase is calcium-independent, localized to lysosomes, and has an acidic pH optimum. The enzyme was purified from bovine brain and found to be a water-soluble glycoprotein consisting of a si...

  2. Formation of environmentally relevant polyhalogenated carbazoles from chloroperoxidase-catalyzed halogenation of carbazole.

    Science.gov (United States)

    Chen, Yanqiu; Lin, Kunde; Chen, Da; Wang, Kun; Zhou, Wenxiu; Wu, Yan; Huang, Xinwen

    2017-09-23

    Polyhalogenated carbazoles (PHCs) are a class of emerging organic contaminants that have received increasing concern due to their widespread distribution and dioxin-like toxicity. Although previous studies have suggested possible natural sources of PHCs in the environment, the formation pathways are poorly understood. Here we explored the production of PHCs from halogenation of carbazole in the presence of Br(-) and/or Cl(-) under the catalysis of chloroperoxidase (CPO) isolated from the marine fungus Caldariomyces fumago. Overall, a total of 25 congeners including mono-to tetra-substituted chlorinated, brominated, and mixed halogenated carbazoles (with substitution patterns of -BrCl, -BrCl2, -BrCl3, -Br2Cl, -Br2Cl2, and -Br3Cl) were produced from the reactions under various conditions. The PHC product profiles were apparently dependent on the halide concentrations. In the CPO-mediated chlorination of carbazole, 3-mono- and 3,6-dichlorocarbazoles predominated in the formation products. In addition to the less abundant mixed halogenated carbazoles (-Br2Cl), 1,3,6-tri- and 1,3,6,8-tetrabromocarbazoles were the dominant products in reactions containing both Br(-) and Cl(-). The CPO-catalyzed halogenation of carbazole could take place in pH 3-7, but the formation products were pH dependent. Results of this study suggest that CPO-catalyzed halogenation of carbazole may play an important role in the natural formation of PHCs. Copyright © 2017 Elsevier Ltd. All rights reserved.

  3. HLA-DM Focuses on Conformational Flexibility Around P1 Pocket to Catalyze Peptide Exchange.

    Science.gov (United States)

    Yin, Liusong; Stern, Lawrence J

    2013-10-17

    Peptides presented by major histocompatibility complex class II (MHCII) molecules to CD4+ T cells play a central role in the initiation of adaptive immunity. This antigen presentation process is characterized by the proteolytic cleavage of foreign and self proteins, and loading of the resultant peptides onto MHCII molecules. Loading and exchange of antigenic peptides is catalyzed by a non-classical MHCII molecule, HLA-DM. The impact of HLA-DM on epitope selection has been appreciated for a long time. However, the molecular mechanism by which HLA-DM mediates peptide exchange remains elusive. Here, we review recent efforts in elucidating how HLA-DM works, highlighted by two recently solved co-structures of HLA-DM bound to HLA-DO (a natural inhibitor of HLA-DM), or to HLA-DR1 (a common MHCII). In light of these efforts, a model for HLA-DM action in which HLA-DM utilizes conformational flexibility around the P1 pocket of the MHCII-peptide complex to catalyze peptide exchange is proposed.

  4. Reuse performance of granular-activated carbon and activated carbon fiber in catalyzed peroxymonosulfate oxidation.

    Science.gov (United States)

    Yang, Shiying; Li, Lei; Xiao, Tuo; Zhang, Jun; Shao, Xueting

    2017-03-01

    Recently, activated carbon was investigated as an efficient heterogeneous metal-free catalyst to directly activate peroxymonosulfate (PMS) for degradation of organic compounds. In this paper, the reuse performance and the possible deactivation reasons of granular-activated carbon (GAC) and activated carbon fiber (ACF) in PMS activation were investigated. As results indicated, the reusability of GAC, especially in the presence of high PMS dosage, was relatively superior to ACF in catalyzed PMS oxidation of Acid Orange 7 (AO7), which is much more easily adsorbed by ACF than by GAC. Pre-oxidation experiments were studied and it was demonstrated that PMS oxidation on ACF would retard ACF's deactivation to a big extent. After pre-adsorption with AO7, the catalytic ability of both GAC and ACF evidently diminished. However, when methanol was employed to extract the AO7-spent ACF, the catalytic ability could recover quite a bit. GAC and ACF could also effectively catalyze PMS to degrade Reactive Black 5 (RB5), which is very difficult to be adsorbed even by ACF, but both GAC and ACF have poor reuse performance for RB5 degradation. The original organic compounds or intermediate products adsorbed by GAC or ACF would be possibly responsible for the deactivation.

  5. Remote C−H Activation of Quinolines through Copper-Catalyzed Radical Cross-Coupling

    KAUST Repository

    Xu, Jun

    2016-01-12

    Achieving site selectivity in carbon-hydrogen (C-H) functionalization reactions is a formidable challenge in organic chemistry. Herein, we report a novel approach to activating remote C-H bonds at the C5 position of 8-aminoquinoline through copper-catalyzed sulfonylation under mild conditions. Our strategy shows high conversion efficiency, a broad substrate scope, and good toleration with different functional groups. Furthermore, our mechanistic investigations suggest that a single-electron-transfer process plays a vital role in generating sulfonyl radicals and subsequently initiating C-S cross-coupling. Importantly, our copper-catalyzed remote functionalization protocol can be expanded for the construction of a variety of chemical bonds, including C-O, C-Br, C-N, C-C, and C-I. These findings provide a fundamental insight into the activation of remote C-H bonds, while offering new possibilities for rational design of drug molecules and optoelectronic materials requiring specific modification of functional groups. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Rice cytochrome P450 MAX1 homologs catalyze distinct steps in strigolactone biosynthesis

    KAUST Repository

    Zhang, Yanxia

    2014-10-26

    Strigolactones (SLs) are a class of phytohormones and rhizosphere signaling compounds with high structural diversity. Three enzymes, carotenoid isomerase DWARF27 and carotenoid cleavage dioxygenases CCD7 and CCD8, were previously shown to convert all-trans-β-carotene to carlactone (CL), the SL precursor. However, how CL is metabolized to SLs has remained elusive. Here, by reconstituting the SL biosynthetic pathway in Nicotiana benthamiana, we show that a rice homolog of Arabidopsis More Axillary Growth 1 (MAX1), encodes a cytochrome P450 CYP711 subfamily member that acts as a CL oxidase to stereoselectively convert CL into ent-2\\'-epi-5-deoxystrigol (B-C lactone ring formation), the presumed precursor of rice SLs. A protein encoded by a second rice MAX1 homolog then catalyzes the conversion of ent-2\\'-epi-5-deoxystrigol to orobanchol. We therefore report that two members of CYP711 enzymes can catalyze two distinct steps in SL biosynthesis, identifying the first enzymes involved in B-C ring closure and a subsequent structural diversification step of SLs.

  7. The oxidation of chiral alcohols catalyzed by catalase in organic solvents

    Energy Technology Data Exchange (ETDEWEB)

    Magner, E.; Klibanov, A.M. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Chemistry

    1995-04-20

    The catalytic properties of bovine liver catalase have been investigated in organic solvents. In tetrahydrofuran, dioxane, and acetone (all containing 1% to 3% of water), the enzyme breaks down tert-butyl hydroperoxide several fold faster than in pure water. Furthermore, the rate of catalase-catalyzed production of tert-butanol from tert-butyl hydroperoxide increases more than 400-fold upon transition from aqueous buffer to ethanol as the reaction medium. The mechanistic rationale for this striking effect is that in aqueous buffer the rate-limiting step of the enzymatic process involves the reduction of catalase`s compound 1 by tert-butyl hydroperoxide. In ethanol, an additional step in the reaction scheme becomes available in which ethanol, greatly outcompeting the hydroperoxide, is oxidized by compound 1 regenerating the free enzyme. In solvents, such as acetonitrile or tetrahydrofuran, which themselves are not oxidizable by compound 1, catalase catalyzes the oxidation of numerous primary and secondary alcohols with tert-butyl hydroperoxide to the corresponding aldehydes or ketones. The enzymatic oxidation of some chiral alcohols (2,3-butanediol, citronellol, and menthol) under these conditions occurs enantioselectively. Examination of the enantioselectivity for the oxidation of 2,3-butanediol in a series of organic solvents reveals a considerable solvent dependence.

  8. Peroxidase-catalyzed oxidation of capsaicinoids: steady-state and transient-state kinetic studies.

    Science.gov (United States)

    Goodwin, Douglas C; Hertwig, Kristen M

    2003-09-01

    Capsaicinoids are the pungent compounds in Capsicum fruits (i.e., "hot" peppers). Peroxidases catalyze capsaicinoid oxidation and may play a central role in their metabolism. However, key kinetic aspects of peroxidase-catalyzed capsaicinoid oxidation remain unresolved. Using transient-state methods, we evaluated horseradish peroxidase compound I and II reduction by two prominent capsaicinoids (25 degrees C, pH 7.0). We determined rate constants approaching 2 x 10(7) and 5 x 10(5)M(-1)s(-1) for compound I and compound II reduction, respectively. We also determined k(app) values for steady-state capsaicinoid oxidation approaching 8 x 10(5)M(-1)s(-1) (25 degrees C, pH 7.0). Accounting for stoichiometry, these are in excellent agreement with constants for compound II reduction, suggesting that this reaction governs capsaicinoid-dependent peroxidase turnover. Ascorbate rapidly reduced capsaicinoid radicals, assisting in the determination of the kinetic constants reported. Because ascorbate accumulates in Capsicum fruits, it may also be an important determinant for capsaicinoid content and preservation in Capsicum fruits and related products.

  9. Identification of two alpha-ketoglutarate-dependent dioxygenases in extracts of Rhodotorula glutinis catalyzing deoxyuridine hydroxylation

    Energy Technology Data Exchange (ETDEWEB)

    Stubbe, J.

    1985-08-25

    Attempts to isolate deoxyuridine 2'-hydroxylase from Rhodotorula glutinis J. Biol. Chem. 258, 10551-10557) have led to the identification and partial purification of a newly recognized alpha-ketoglutarate-requiring oxygenase. This activity, designated deoxyuridine (uridine) 1'-hydroxylase, in the presence of iron and ascorbate, catalyzes the conversion of deoxyuridine (uridine), O2, and alpha-ketoglutarate to uracil, deoxyribonolactone (ribonolactone), CO2, and succinate. Incubation of (1'-TH)uridine with this activity results in time-dependent formation of uracil concomitant with production of CO2 and 3H2O. Also reported in this paper is the partial purification and characterization of the alpha-ketoglutarate-requiring enzyme, deoxyuridine 2'-hydroxylase. Incubation of (2'-alpha-TH)deoxyuridine with this activity results in concomitant production of uridine and 3H2O. Incubation with (2'-beta-TH) deoxyuridine results in the production of uridine whose specific activity is identical to that of the starting material. This enzyme catalyzes the conversion of deoxyuridine to uridine with retention of configuration. No isotope effect is observed on this transformation.

  10. Lipase catalyzed transesterification of ethyl butyrate synthesis inn-hexane- a kinetic study.

    Science.gov (United States)

    Devi, N Annapurna; Radhika, G B; Bhargavi, R J

    2017-08-01

    Kinetics of lipase catalyzed transesterification of ethyl caprate and butyric acid was investigated. The objective of this work was to propose a reaction mechanism and develop a rate equation for the synthesis of ethyl butyrate by transesterification using surfactant coated lipase from Candida rugosa . The reaction rate could be described in terms of Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both the substrates. The values of kinetic parameters computed were V max  = 2.861 μmol/min/mg; K m(acid)  = 0.0746 M; K m(ester)  = 0.125 M; K i acid = 0.450 M. This study indicated a competitive enzyme inhibition by butyric acid during lipase catalyzed transesterification reaction. Experimental observations had clearly indicated that the substrates as well as product act as dead-end inhibitors.

  11. Ultrasound assisted lipase catalyzed synthesis of cinnamyl acetate via transesterification reaction in a solvent free medium.

    Science.gov (United States)

    Tomke, Prerana D; Rathod, Virendra K

    2015-11-01

    Cinnamyl acetate is known for its use as flavor and fragrance material in different industries such as food, pharmaceutical, cosmetic etc. This work focuses on ultrasound assisted lipase (Novozym 435) catalyzed synthesis of cinnamyl acetate via transesterification of cinnamyl alcohol and vinyl acetate in non-aqueous, solvent free system. Optimization of various parameters shows that a higher yield of 99.99% can be obtained at cinnamyl alcohol to vinyl acetate ratio of 1:2 with 0.2% of catalyst, at 40°C and 150 rpm, with lower ultrasound power input of 50 W (Ultrasound intensity 0.81 W/cm(2)), at 25 kHz frequency, 50% duty cycle. Further, the time required for the maximum conversion is reduced to 20 min as compared to 60 min of conventional process. Similarly, the enzyme can be successfully reused seven times without loss of enzyme activity. Thus, ultrasound helps to enhance the enzyme catalyzed synthesis of flavors. Copyright © 2015 Elsevier B.V. All rights reserved.

  12. Highly efficient preparation of lipophilic hydroxycinnamates by solvent-free lipase-catalyzed transesterification.

    Science.gov (United States)

    Weitkamp, Petra; Vosmann, Klaus; Weber, Nikolaus

    2006-09-20

    Various medium- or long-chain alkyl cinnamates and hydroxycinnamates, including oleyl p-coumarate as well as palmityl and oleyl ferulates, were prepared in high yield by lipase-catalyzed transesterification of an equimolar mixture of a short-chain alkyl cinnamate and a fatty alcohol such as lauryl, palmityl, and oleyl alcohol under partial vacuum at moderate temperature in the absence of solvents and drying agents in direct contact with the reaction mixture. Immobilized lipase B from Candida antarctica was the most effective biocatalyst for the various transesterification reactions. Transesterification activity of this enzyme was up to 56-fold higher than esterification activity for the preparation of medium- and long-chain alkyl ferulates. The relative transesterification activities found for C. antarctica lipase were of the following order: hydrocinnamate > cinnamate > 4-hydroxyhydrocinnamate > 3-methoxycinnamate > 2-methoxycinnamate approximately 4-methoxycinnamate approximately 3-hydroxycinnamate > hydrocaffeate approximately 4-hydroxycinnamate > ferulate > 2-hydroxycinnamate > caffeate approximately sinapate. With respect to the position of the hydroxy substituents at the phenyl moiety, the transesterification activity of C. antarctica lipase B increased in the order meta > para > ortho. The immobilized lipases from Rhizomucor miehei and Thermomyces lanuginosus demonstrated moderate and low transesterification activity, respectively. Compounds with inverse chemical structure, that is, 3-phenylpropyl alkanoates such as 3-(4-hydroxyphenyl)propyl oleate and 3-(3,4-dimethoxyphenyl)propyl oleate, were obtained by C. antarctica lipase-catalyzed transesterification of fatty acid methyl esters with the corresponding 3-phenylpropan-1-ols in high yield, as well.

  13. A novel chemoenzymatic synthesis of propyl caffeate using lipase-catalyzed transesterification in ionic liquid.

    Science.gov (United States)

    Pang, Na; Gu, Shuang-Shuang; Wang, Jun; Cui, Hong-Sheng; Wang, Fang-Qin; Liu, Xi; Zhao, Xing-Yu; Wu, Fu-An

    2013-07-01

    Propyl caffeate has the highest antioxidant capacity in the caffeate alkyl esters family, but industrial production of propyl caffeate is hindered by low yields using either the chemical or enzymatic catalysis method. To set up a high-yield process for obtaining propyl caffeate, a novel chemoenzymatic synthesis method using lipase-catalyzed transesterification of an intermediate methyl caffeate or ethyl caffeate and 1-propanol in ionic liquid was established. The maximum propyl caffeate yield of 98.5% was obtained using lipase-catalyzed transesterification under the following optimal conditions: Novozym 435 as a biocatalyst, [Bmim][CF3SO3] as a medium, a molar ratio of methyl caffeate to 1-propanol of 1:5, a mass ratio of methyl caffeate to lipase of 1:20, and a reaction temperature of 60°C. The two-step conversion of caffeic acid to propyl caffeate via methyl caffeate is an efficient way to prepare propyl caffeate with an overall yield of 82.7%. Copyright © 2013 Elsevier Ltd. All rights reserved.

  14. Lipase-catalyzed biodiesel production with methyl acetate as acyl acceptor

    Energy Technology Data Exchange (ETDEWEB)

    Huang Ying; Yan Yunjun [School of Life Science and Technology, Huazhong Univ. of Science and Technology, Wuhan (China)

    2008-03-15

    Biodiesel is an alternative diesel fuel made from renewable biological resources. During the process of biodiesel production, lipase-catalyzed transesterification is a crucial step. However, current techniques using methanol as acyl acceptor have lower enzymatic activity; this limits the application of such techniques in large-scale biodiesel production. Furthermore, the lipid feedstock of currently available techniques is limited. In this paper, the technique of lipase-catalyzed transesterification of five different oils for biodiesel production with methyl acetate as acyl acceptor was investigated, and the transesterification reaction conditions were optimized. The operation stability of lipase under the obtained optimal conditions was further examined. The results showed that under optimal transesterification conditions, both plant oils and animal fats led to high yields of methyl ester: cotton-seed oil, 98%; rape-seed oil, 95%; soybean oil, 91%; tea-seed oil, 92%; and lard, 95%. Crude and refined cotton-seed oil or lard made no significant difference in yields of methyl ester. No loss of enzymatic activity was detected for lipase after being repeatedly used for 40 cycles (ca. 800 h), which indicates that the operational stability of lipase was fairly good under these conditions. Our results suggest that cotton-seed oil, rape-seed oil and lard might substitute soybean oil as suitable lipid feedstock for biodiesel production. Our results also show that our technique is fit for various lipid feedstocks both from plants and animals, and presents a very promising way for the large-scale biodiesel production. (orig.)

  15. Ultrasound-assisted lipase-catalyzed transesterification of soybean oil in organic solvent system.

    Science.gov (United States)

    Batistella, Luciane; Lerin, Lindomar A; Brugnerotto, Patrícia; Danielli, Angélica J; Trentin, Cláudia M; Popiolski, Ariana; Treichel, Helen; Oliveira, J Vladimir; de Oliveira, Débora

    2012-05-01

    This work reports the transesterification of soybean oil with ethanol using two commercial immobilized lipases under the influence of ultrasound irradiation. The experiments were performed in an ultrasonic water bath, following a sequence of experimental designs to assess the effects of temperature, enzyme and water concentrations, oil to ethanol molar ratio and output irradiation power on the reaction yield. Results show that ultrasound-assisted lipase-catalyzed transesterification of soybean oil with ethanol might be a potential alternative route to conventional alkali-catalyzed method, as high reaction yields (~90 wt.%) were obtained at mild irradiation power supply (~100 W), and temperature (60 °C) in a relatively short reaction time, 4h, using Lipozyme RM IM as catalyst. The repeated use of the catalyst under the optimum experimental condition resulted in a decay in both enzyme activity and product conversion after two cycles. The use of Novozym 435 led to lower conversions (about 57%) but the enzyme activity was stable after eight cycles of use, showing, however, a reduction in product conversion after the forth cycle. Copyright © 2011 Elsevier B.V. All rights reserved.

  16. Optimization of lipase-catalyzed transesterification of lard for biodiesel production using response surface methodology.

    Science.gov (United States)

    Huang, Ying; Zheng, Hai; Yan, Yunjun

    2010-01-01

    Biodiesel, an alternative diesel fuel made from renewable biological resources, has become more and more attractive recently. Combined use of two immobilized lipases with complementary position specificity instead of one lipase is a potential way to significantly reduce cost of lipase-catalyzed biodiesel production. In this study, the process of biodiesel production from lard catalyzed by the combined use of Novozym435 (non-specific) and Lipozyme TLIM (1,3-specific) was optimized by response surface methodology. The optimal reaction conditions were 0.04 of amount of lipase/oil (w/w), 0.49 of proportion of Novozym435/total lipases (w/w), 0.55 of quantity of tert-butanol/oil (v/v), 5.12 of quantity of methanol/oil (mol/mol), and 20 h of reaction time, by which 97.2% of methyl ester (ME) yield was attained, very close to the predicted value (97.6%). This optimal reaction condition could be true of other similar reactions with plant and animal oil resources; their ME yield could be higher than 95%. The lipases regenerated by washing with organic solvent after each reaction cycle could be continuously reused for 20 cycles without any loss of activity, exhibiting very high manipulation stability.

  17. Beta-D-xylosidase from Selenomonas ruminantium: catalyzed reactions with natural and artificial substrates.

    Science.gov (United States)

    Jordan, Douglas B

    2008-03-01

    Catalytically efficient beta-D-xylosidase from Selenomonas ruminantium (SXA) exhibits pK (a)s 5 and 7 (assigned to catalytic base, D14, and catalytic acid, E186) for k (cat)/K (m) with substrates 1,4-beta-D-xylobiose (X2) and 1,4-beta-D-xylotriose (X3). Catalytically inactive, dianionic SXA (D14(-)E186(-)) has threefold lower affinity than catalytically active, monoanionic SXA (D14(-)E186(H)) for X2 and X3, whereas D14(-)E186(-) has twofold higher affinity than D14(-)E186(H) for 4-nitrophenyl-beta-D-xylopyranoside (4NPX), and D14(-)E186(-) has no affinity for 4-nitrophenyl-alpha-L-arabinofuranoside. Anomeric isomers, alpha-D-xylose and beta-D-xylose, have similar affinity for SXA. 4-Nitrophenol competitively inhibits SXA-catalyzed hydrolysis of 4NPX. SXA steady-state kinetic parameters account for complete progress curves of SXA-catalyzed hydrolysis reactions.

  18. Quantifying Possible Routes for SpnF-Catalyzed Formal Diels-Alder Cycloaddition.

    Science.gov (United States)

    Medvedev, Michael G; Zeifman, Alexey A; Novikov, Fedor N; Bushmarinov, Ivan S; Stroganov, Oleg V; Titov, Ilya Yu; Chilov, Ghermes G; Svitanko, Igor V

    2017-03-22

    The Diels-Alder reaction is a cornerstone of modern organic synthesis. Despite this, it remains essentially inaccessible to biosynthetic approaches. Only a few natural enzymes catalyze even a formal [4 + 2] cycloaddition, and it remains uncertain if any of them proceed via the Diels-Alder mechanism. In this study, we focus on the [4 + 2] cycloaddition step in the biosynthesis of spinosyn A, a reaction catalyzed by SpnF enzyme, one of the most promising "true Diels-Alderase" candidates. The four currently proposed mechanisms (including the Diels-Alder one) for this reaction in water (as a first-order approximation of the enzymatic reaction) are evaluated by an exhaustive quantum mechanical search for possible transition states (728 were found in total). We find that the line between the recently proposed bis-pericyclic [J. Am. Chem. Soc. 2016, 138 (11), 3631] and Diels-Alder routes is blurred, and favorable transition states of both types may coexist. Application of the Curtin-Hammett principle, however, reveals that the bis-pericyclic mechanism accounts for ∼83% of the reaction flow in water, while the classical Diels-Alder mechanism contributes only ∼17%. The current findings provide a route for modeling this reaction inside the SpnF active site and inferring the catalytic architecture of possible Diels-Alderases.

  19. Biodiesel Production from Spent Fish Frying Oil Through Acid-Base Catalyzed Transesterification

    Directory of Open Access Journals (Sweden)

    Abdalrahman B. Fadhil

    2012-06-01

    Full Text Available Biodiesel fuels were prepared from a special type of frying oil namely spent fish frying oil through two step transesterification viz. acid-base catalyzed transesterification. Hydrochloric acid and potassium hydroxide with methanol were used for this purpose. The oil was pre-treated with (1.0 wt% HCl and methanol to reduce free fatty acids content of the oil. Then, conditions of the base catalyzed step such as base concentration, reaction temperature, methanol to oil molar ratio and reaction time were optimized. The study raveled that, 0.50% KOH w/w of oil; a 6:1 methanol to oil molar ratio; a reaction temperature of 60°C and a duration of 1h were the optimal conditions because they resulted in high biodiesel yield. Fuel properties of the products were assessed and found better than those of the parent oil. Furthermore, they met the specified limits according to the ASTM standards. Thin layer chromatography was used as a simple technique to monitor the transesterification of the oil. Blending of the optimal biodiesel sample with petro diesel using specified volume percentages was done as well. The results indicated that biodiesel had slight effect on the values of the assessed properties.

  20. Variables affecting the reactivity of acid-catalyzed transesterification of vegetable oil with methanol.

    Science.gov (United States)

    Furukawa, Shigeki; Uehara, Yoshihiro; Yamasaki, Hiroshi

    2010-05-01

    The dominant factors affecting the reactivity of acid-catalyzed transesterification of vegetable oil with methanol have been investigated. Effects of varying the acid catalyst species, surface active agent type and content were studied. Also, the effect of the type of oil was examined. Biodiesel fuel yields increased with the addition of sodium dodecylsulfonate as surface active agent because the mass transfer rates of protons and methanol to the oil phase through the oil-methanol interface were increased with increasing interfacial area. Evaluation of the reaction kinetics, based on changes in parent oils containing triglyceride or diglyceride showed that the activation energies were almost no change, but the frequency factors were 2210 and 9827mol(-1)min(-1), respectively. Therefore, it was concluded that a lower reactivity during acid-catalyzed transesterification with methanol was caused by a lower contact probability for oil, methanol and acid catalyst in the presence of an oil-methanol interface during the reaction. Copyright 2009 Elsevier Ltd. All rights reserved.