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Sample records for a2 catalyzed acidolysis

  1. Phosphatidylcholine enrichment with medium chain fatty acids by immobilized phospholipase A(1) -catalyzed acidolysis.

    PubMed

    Ochoa, Angélica A; Hernández-Becerra, Josafat A; Cavazos-Garduño, Adriana; García, Hugo S; Vernon-Carter, Eduardo J

    2013-01-01

    Phospholipids are a biologically and industrially important class of compounds whose physical properties can be improved for diverse applications by substitution of medium-chain fatty acids for their native fatty acid chains. In this study, phosphatidylcholine (PC) was enriched with medium-chain fatty acids (MCFAs) by acidolysis with phospholipase A(1) (PLA(1) ) immobilized on Duolite A568. Response surface methodology was employed to evaluate the effects of the molar ratio of substrates (PC to free MCFAs), enzyme loading, and reaction temperature on the incorporation of free MCFAs into PC and on PC recovery. Enzyme loading and molar ratio of substrates contributed positively, but temperature negatively, to the incorporation of free MCFAs into PC. Increases in enzyme loading and the molar ratio of PC to free MCFAs led to increased incorporation of the latter into the former, but increased temperature had the opposite effect. By contrast, an increase in enzyme loading led to decreased PC recovery. Increased temperature had also a negative effect on PC recovery. Optimal conditions for maximum incorporation and PC recovery were molar ratio of PC to free MCFAs of 1:16, enzyme loading of 16%, and 50°C. Under these conditions, the incorporation of free MCFAs was 41% and the PC recovery was 53%. Copyright © 2012 American Institute of Chemical Engineers (AIChE).

  2. Lipase-catalyzed acidolysis of tripalmitin with hazelnut oil fatty acids and stearic acid to produce human milk fat substitutes.

    PubMed

    Sahin, Nese; Akoh, Casimir C; Karaali, Artemis

    2005-07-13

    Structured lipids (SLs) containing palmitic, oleic, stearic, and linoleic acids, resembling human milk fat (HMF), were synthesized by enzymatic acidolysis reactions between tripalmitin, hazelnut oil fatty acids, and stearic acid. Commercially immobilized sn-1,3-specific lipase, Lipozyme RM IM, obtained from Rhizomucor miehei was used as the biocatalyst for the enzymatic acidolysis reactions. The effects of substrate molar ratio, reaction temperature, and reaction time on the incorporation of stearic and oleic acids were investigated. The acidolysis reactions were performed by incubating 1:1.5:0.5, 1:3:0.75, 1:6:1, 1:9:1.25, and 1:12:1.5 substrate molar ratios of tripalmitin/hazelnut oil fatty acids/stearic acid in 3 mL of n-hexane at 55, 60, and 65 degrees C using 10% (total weight of substrates) of Lipozyme RM IM for 3, 6, 12, and 24 h. The fatty acid composition of reaction products was analyzed by gas-liquid chromatography (GLC). The fatty acids at the sn-2 position were identified after pancreatic lipase hydrolysis and GLC analysis. The results showed that the highest C18:1 incorporation (47.1%) and highest C18:1/C16:0 ratio were obtained at 65 degrees C and 24 h of incubation with the highest substrate molar ratio of 1:12:1.5. The highest incorporation of stearic acid was achieved at a 1:3:0.75 substrate molar ratio at 60 degrees C and 24 h. For both oleic and stearic acids, the incorporation level increased with reaction time. The SLs produced in this study have potential use in infant formulas.

  3. Lipase-catalyzed acidolysis of palm mid fraction oil with palmitic and stearic Fatty Acid mixture for production of cocoa butter equivalent.

    PubMed

    Mohamed, Ibrahim O

    2013-10-01

    Cocoa butter equivalent (CBE) was prepared by enzymatic acidolysis reaction of substrate consisting of refined palm mid fraction 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 composition of the five major triacylglycerols (TAGs) of the structured lipids was identified and quantified using cocoa butter certified reference material IRMM-801. The reaction resulted in production of cocoa butter equivalent with the TAGs' composition (1,3-dipalmitoyl-2-oleoyl-glycerol 30.7%, 1-palmitoyl-2-oleoyl-3-stearoyl-rac-glycerol 40.1%, 1-palmitoy-2,3- dioleoyl glycerol 9.0%, 1,3-distearoyl-2-oleoyl-glycerol 14.5 %, and 1-stearoyl-2,3-dioleoyl glycerol 5.7%) and with onset melting temperature of 31.6 °C and peak temperature of 40.4 °C which are close to those of cocoa butter. The proposed kinetics model for the acidolysis reaction presented the experimental data very well. The results of this research showed that palm mid fraction oil TAGs could be restructured to produce value added product such as CBE.

  4. Lipozyme RM IM-catalyzed acidolysis of Cinnamomum camphora seed oil with oleic acid to produce human milk fat substitutes enriched in medium-chain fatty acids.

    PubMed

    Zou, Xian-Guo; Hu, Jiang-Ning; Zhao, Man-Li; Zhu, Xue-Mei; Li, Hong-Yan; Liu, Xiao-Ru; Liu, Rong; Deng, Ze-Yuan

    2014-10-29

    In the present study, a human milk fat substitute (HMFS) enriched in medium-chain fatty acids (MCFAs) was synthesized through acidolysis reaction from Cinnamomum camphora seed oil (CCSO) with oleic acid in a solvent-free system. A commercial immobilized lipase, Lipozyme RM IM, from Rhizomucor miehei, was facilitated as a biocatalyst. Effects of different reaction conditions, including substrate molar ratio, enzyme concentration, reaction temperature, and reaction time were investigated using response surface methodology (RSM) to obtain the optimal oleic acid incorporation. After optimization, results showed that the maximal incorporation of oleic acid into HMFS was 59.68%. Compared with CCSO, medium-chain fatty acids at the sn-2 position of HMFS accounted for >70%, whereas oleic acid was occupied predominantly at the sn-1,3 position (78.69%). Meanwhile, triacylglycerol (TAG) components of OCO (23.93%), CCO (14.94%), LaCO (13.58%), OLaO (12.66%), and OOO (11.13%) were determined as the major TAG species in HMFS. The final optimal reaction conditions were carried out as follows: substrate molar ratio (oleic acid/CCSO), 5:1; enzyme concentration, 12.5% (w/w total reactants); reaction temperature, 60 °C; and reaction time, 28 h. The reusability of Lipozyme RM IM in the acidolysis reaction was also evaluated, and it was found that it could be reused up to 9 times without significant loss of activities. Urea inclusion method was used to separate and purify the synthetic product. As the ratio of HMFS/urea increased to 1:2, the acid value lowered to the minimum. In a scale-up experiment, the contents of TAG and total tocopherols in HMFS (modified CCSO) were 77.28% and 12.27 mg/100 g, respectively. All of the physicochemical indices of purified product were within food standards. Therefore, such a MCFA-enriched HMFS produced by using the acidolysis method might have potential application in the infant formula industry.

  5. Acidolysis of p-coumaric acid with omega-3 oils and antioxidant activity of phenolipid products in in vitro and biological model systems.

    PubMed

    Wang, Jiankang; Shahidi, Fereidoon

    2014-01-15

    Lipase-catalyzed acidolysis of p-coumaric acid with seal blubber oil (SBO) and menhaden oil (MHO) was carried out, followed by identification of major phenolipids in the resultant acidolysis mixture using high-performance liquid chromatography/mass spectrometry. Separation of phenolipid components from the resultant acidolysis mixture was achieved using flash column chromatography. The antioxidant activities of the phenolipids were examined in in vitro assays and biological model systems. The major phenolipids identified from acidolysis mixtures with both SBO and MHO included eight phenolic monoacylglycerols and eight phenolic diacylglycerols. Phenolipids derived from SBO and MHO generally showed good antioxidant potential in the systems tested. The prepared phenolipids exhibited high scavenging capacity toward 1,1-diphenyl-2-picrylhydrazyl (DPPH) and peroxyl radicals and displayed reducing power, strong inhibitory effect on bleaching of β-carotene, human low-density lipoprotein (LDL) cholesterol oxidation, as well as radical-induced DNA cleavage, thus suggesting that phenolipids derived from omega-3 oils may be used as potential stable products for health promotion and disease risk reduction.

  6. C5-hydroxylation of liquiritigenin is catalyzed selectively by CYP1A2.

    PubMed

    Wang, Ao-Xue; Hu, Ying; Liu, Hui-Xin; Qi, Xiao-Yi; Liu, Yong; Tu, Cai-Xia; Yang, Ling

    2011-05-01

    Liquiritigenin (7,4'-dihydroxyflavone), the primary active component of a traditional Chinese medicine Glycyrrhizae radix, has a wide range of pharmacological activities. Six oxidative metabolites of liquiritigenin (7,3',4'-trihydroxyflavone, a hydroxyl quinine metabolite, two A-ring dihydroxymetabolites, 7,4'-dihydroxyflavone, and 7-hydroxychromone) have been detected in rat liver microsomes (RLMs), and one CYP3A4-catalyzed metabolite (7,4'-dihydroxyflavone) has been identified in human liver microsomes (HLMs) recently. In this study, a novel mono-hydroxylated metabolite was detected in reaction catalyzed by HLMs, and was identified as 4',5,7-trihydroxyflavanone by comparing the tandem mass spectra and the chromatographic retention time with that of the standard compound. Significant difference in CL(int) (9-fold) was found between these two oxidative pathways of liquiritigenin, and C5-hydroxylation pathway was identified as the major oxidative metabolism of liquiritigenin. The study with chemical selective inhibitor, cDNA-expressed human CYPs, correlation assay, and kinetic study demonstrated that CYP1A2 was the specific isozyme responsible for the C5-hydroxylation metabolism of liquiritigenin in HLMs.

  7. Isolation of residual lignin from softwood kraft pulp. Advantages of the acetic acid acidolysis method.

    PubMed

    Lachenal, Dominique; Mortha, Gérard; Sevillano, Rose-Marie; Zaroubine, Michail

    2004-01-01

    Lignin in kraft pulp was extracted by enzymatic hydrolysis of the carbohydrates, acidolysis with dioxane-water-HCl (conventional method), and acidolysis with acetic acid-water-ZnCl2. The latter method was shown to extract lignin with a better yield than for conventional acidolysis and with a much lower content in impurities than for enzymatic hydrolysis. It was confirmed by 13C NMR analysis of the lignin samples that conventional hydrolysis modified the lignin polymer, causing the cleavage of some aryl-ether linkages. The cleavage was also observed on a model compound submitted to the same extraction conditions. In that respect, the acetic acid-water-ZnCl2 method was less damaging and consequently more suitable for analytical purposes.

  8. Acidolysis small molecular phenolic ether used as accelerator in photosensitive diazonaphthaquinone systems

    NASA Astrophysics Data System (ADS)

    Zhou, Haihua; Zou, Yingquan

    2006-03-01

    The photosensitive compounds in the photosensitive coatings of positive PS plates are the diazonaphthaquinone derivatives. Some acidolysis small molecular phenolic ethers, which were synthesized by some special polyhydroxyl phenols with vinyl ethyl ether, are added in the positive diazonaphthaquinone photosensitive composition to improve its sensitivity, composed with photo-acid-generators. The effects to the photosensitivity, anti-alkali property, anti-isopropyl alcohol property, dot resolution and line resolution of the coatings are studied with different additive percent of the special phenolic ethers. In the conventional photosensitive diazonaphthaquinone systems for positive PS plates, the photosensitivity is improved without negative effects to resolution, anti-alkali and anti-isopropyl alcohol properties when added about 5% of the special acidolysis phenolic ethers, EAAE or DPHE, composed with photo-acid-generators.

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

    PubMed Central

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

    2015-01-01

    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. PMID:25649189

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

    PubMed

    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.

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

    PubMed

    Nielsen, Henrik; Westhof, Eric; Johansen, Steinar

    2005-09-02

    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 by a transesterification reaction with the joining of the first and the third nucleotide of the messenger by a 2',5'-phosphodiester linkage. Thus, a group I-like ribozyme catalyzes an RNA branching reaction similar to the first step of splicing in group II introns and spliceosomal introns. The resulting short lariat, by forming a protective 5' cap, might have been useful in a primitive RNA world.

  12. Preparation of palm olein enriched with medium chain fatty acids by lipase acidolysis.

    PubMed

    Chnadhapuram, Mounika; Sunkireddy, Yella Reddy

    2012-05-01

    Medium chain (MC) fatty acids, caprylic (C8:0) and capric (C10:0) were incorporated into palm olein by 1,3-specific lipase acidolysis, up to 36% and 43%, respectively, when added as mixtures or individually after 24h. It was found that these acids were incorporated into palm olein at the expense of palmitic and oleic acids, the former being larger in quantity and reduction of 18:2 was negligible. The modified palm olein products showed reduction in higher molecular weight triacylglycerols (TGs) and increase in concentration of lower molecular weight TGs compared to those of palm olein. Fatty acids at sn-2 position in modified products were: C10:0, 4%; C16:0, 13%; C18:1, 66%; and C18:2, 15.4%. DSC results showed that the onset of melting and solids fat content were considerably reduced in modified palm olein products and no solids were found even at and below 10°C and also the onset of crystallisation was considerably lowered. The cloud point was reduced and iodine value dropped from 55.4 to 38 in modified palm olein. Thus, nutritionally superior palm olein was prepared by introducing MC fatty acids with reduced palmitic acid through lipase acidolysis.

  13. Enzyme-assisted acidolysis of borage (Borago officinalis L.) and evening primrose (Oenothera biennis L.) oils: incorporation of omega-3 polyunsaturated fatty acids.

    PubMed

    Senanayake, S P; Shahidi, F

    1999-08-01

    Lipase-catalyzed acidolysis of borage (Borago officinalis L.) and evening primrose (Oenothera biennisL.) oils with long-chain omega3 polyunsaturated fatty acids (PUFA), namely, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, was carried out in hexane, and the products were analyzed using gas chromatography. The most effective lipase for incorporation of omega3 PUFA into these oils was Pseudomonas sp. as compared to lipases from Mucor miehei and Candida antarctica. Response surface methodology was used to obtain a maximum yield of EPA+DHA incorporation while using the minimum amount of enzyme possible. The process variables studied were the amount of enzyme (150-350 units), reaction temperature (30-60 degrees C), and reaction time (6-30 h). All experiments were carried out according to a face-centered cube design. Under optimum conditions, incorporation of EPA+DHA was 35.5% in borage oil and 33. 6% in evening primrose oil. The modified borage and evening primrose oils containing gamma-linolenic acid, EPA, and DHA were successfully produced and may have potential health benefits.

  14. Quantum-dynamical picture of a multistep enzymatic process: reaction catalyzed by phospholipase A(2).

    PubMed Central

    Bała, P; Grochowski, P; Nowiński, K; Lesyng, B; McCammon, J A

    2000-01-01

    A quantum-classical molecular dynamics model (QCMD), applying explicit integration of the time-dependent Schrödinger equation (QD) and Newtonian equations of motion (MD), is presented. The model is capable of describing quantum dynamical processes in complex biomolecular systems. It has been applied in simulations of a multistep catalytic process carried out by phospholipase A(2) in its active site. The process includes quantum-dynamical proton transfer from a water molecule to histidine localized in the active site, followed by a nucleophilic attack of the resulting OH(-) group on a carbonyl carbon atom of a phospholipid substrate, leading to cleavage of an adjacent ester bond. The process has been simulated using a parallel version of the QCMD code. The potential energy function for the active site is computed using an approximate valence bond (AVB) method. The dynamics of the key proton is described either by QD or classical MD. The coupling between the quantum proton and the classical atoms is accomplished via Hellmann-Feynman forces, as well as the time dependence of the potential energy function in the Schrödinger equation (QCMD/AVB model). Analysis of the simulation results with an Advanced Visualization System revealed a correlated rather than a stepwise picture of the enzymatic process. It is shown that an sp(2)--> sp(3) configurational change at the substrate carbonyl carbon is mostly responsible for triggering the activation process. PMID:10968989

  15. Simplified Procedure for Recovery of Lignin Acidolysis Products for Determining the Lignin-Degrading Abilities of Microorganisms †

    PubMed Central

    Pometto, Anthony L.; Crawford, Don L.

    1985-01-01

    A simplified procedure for the identification and measurement of single-ring aromatic products of lignin acidolysis is described. The procedure employed a 6-h hydrolysis of spruce milled wood lignin in acidic dioxane at 87°C, followed by a series of organic extractions to recover acidolysis products which were quantified by gas chromatography of trimethylsilyl derivatives. Complex gel permeation chromatography procedures utilized by other workers were avoided in the modified procedure, but equivalent results were obtained. The simplified procedure was utilized to hydrolyze sound and actinomycete-decayed spruce milled wood lignins and was shown to be useful as a technique for the rapid screening of microorganisms for their ability to alter lignin. PMID:16346768

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

    PubMed

    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

  17. Acidolysis-based component mapping of glycosaminoglycans by reversed-phase high-performance liquid chromatography with off-line electrospray ionization-tandem mass spectrometry: evidence and tags to distinguish different glycosaminoglycans.

    PubMed

    Zhu, He; Chen, Xuan; Zhang, Xiao; Liu, Lili; Cong, Dapeng; Zhao, Xia; Yu, Guangli

    2014-11-15

    Diverse monosaccharide analysis methods have been established for a long time, but few methods are available for a complete monosaccharide analysis of glycosaminoglycans (GAGs) and certain acidolysis-resistant components derived from GAGs. In this report, a reversed-phase high-performance liquid chromatography (RP-HPLC) method with pre-column 1-phenyl-3-methyl-5-pyrazolone (PMP) derivatization was established for a complete monosaccharide analysis of GAGs. Good separation of glucosamine/mannosamine (GlcN/ManN) and glucuronic acid/iduronic acid (GlcA/IdoA) was achieved. This method can also be applied to analyze the acidolysis-resistant disaccharides derived from GAGs, and the sequences of these disaccharides were confirmed by electrospray ionization-collision-induced dissociation-tandem mass spectrometry (ESI-CID-MS/MS). These unique disaccharides could be used as markers to distinguish heparin/heparan sulfate (HP/HS), chondroitin sulfate/dermatan sulfate (CS/DS), and hyaluronic acid (HA).

  18. Oxidations of p-alkoxyacylanilides catalyzed by human cytochrome P450 1A2: structure-activity relationships and simulation of rate constants of individual steps in catalysis.

    PubMed

    Yun, C H; Miller, G P; Guengerich, F P

    2001-04-10

    Human cytochrome P450 (P450) 1A2 is involved in the oxidation of many important drugs and carcinogens. The prototype substrate phenacetin is oxidized to an acetol as well as the O-dealkylation product [Yun, C.-H., Miller, G. P., and Guengerich, F. P. (2000) Biochemistry 39, 11319-11329]. In an effort to improve rates of catalysis of P450 1A2 enzymes, we considered a set of p-alkoxyacylanilide analogues of phenacetin and found that variations in the O-alkyl and N-acyl substituents altered the rates of the two oxidation reactions and the ratio of acetol/phenol products. Moving one methylene group of phenacetin from the O-alkyl group to the N-acyl moiety increased rates of both oxidations approximately 5-fold and improved the coupling efficiency (oxidation products formed/NADPH consumed) from 6% to 38%. Noncompetitive kinetic deuterium isotope effects of 2-3 were measured for all O-dealkylation reactions examined with wild-type P450 1A2 and the E225I mutant, which has 6-fold higher activity. A trend of decreasing kinetic deuterium isotope effect for E225I > wild-type > mutant D320A was observed for O-demethylation of p-methoxyacetanilide, which follows the trend for k(cat). The set of O-dealkylation and acetol formation results for wild-type P450 1A2 and the E225I mutant with several of the protiated and deuterated substrates were fit to a model developed for the basic catalytic cycle and a set of microscopic rate constants in which the only variable was the rate of product formation (substrate oxygenation, including hydrogen abstraction). In this model, k(cat) is considerably less than any of the microscopic rate constants and is affected by several individual rate constants, including the rate of formation of the oxygenating species, the rate of substrate oxidation by the oxygenating species, and the rates of generation of reduced oxygen species (H(2)O(2), H(2)O). This analysis of the effects of the individual rate constants provides a framework for consideration of

  19. Hydroxylation of aspartic acid in domains homologous to the epidermal growth factor precursor is catalyzed by a 2-oxoglutarate-dependent dioxygenase.

    PubMed Central

    Stenflo, J; Holme, E; Lindstedt, S; Chandramouli, N; Huang, L H; Tam, J P; Merrifield, R B

    1989-01-01

    3-Hydroxyaspartic acid and 3-hydroxyasparagine are two rare amino acids that are present in domains homologous to the epidermal growth factor precursor in vitamin K-dependent plasma proteins as well as in proteins that do not require vitamin K for normal biosynthesis. They are formed by posttranslational hydroxylation of aspartic acid and asparagine, respectively. The first epidermal growth factor-like domain in factor IX (residues 45-87) was synthesized with aspartic acid in position 64, replacing 3-hydroxyaspartic acid. It was used as substrate in a hydroxylase assay with rat liver microsomes as the source of enzyme and reaction conditions that satisfy the requirements of 2-oxoglutarate-dependent dioxygenases. The synthetic peptide stimulated the 2-oxoglutarate decarboxylation in contrast to synthetic, modified epidermal growth factor (Met-21 and His-22 deleted and Glu-24 replaced by Asp) and synthetic peptides corresponding to residues 60-71 in human factor IX. This indicates that the hydroxylase is a 2-oxoglutarate-dependent dioxygenase with a selective substrate requirement. Images PMID:2492106

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

    PubMed Central

    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

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

    SciTech Connect

    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

  2. Catalyzing RE Project Development

    SciTech Connect

    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.

  3. Muon Catalyzed Fusion

    NASA Technical Reports Server (NTRS)

    Armour, Edward A.G.

    2007-01-01

    Muon catalyzed fusion is a process in which a negatively charged muon combines with two nuclei of isotopes of hydrogen, e.g, a proton and a deuteron or a deuteron and a triton, to form a muonic molecular ion in which the binding is so tight that nuclear fusion occurs. The muon is normally released after fusion has taken place and so can catalyze further fusions. As the muon has a mean lifetime of 2.2 microseconds, this is the maximum period over which a muon can participate in this process. This article gives an outline of the history of muon catalyzed fusion from 1947, when it was first realised that such a process might occur, to the present day. It includes a description of the contribution that Drachrnan has made to the theory of muon catalyzed fusion and the influence this has had on the author's research.

  4. Catalyzed sodium chlorate candles

    NASA Technical Reports Server (NTRS)

    Malich, C. W.; Wydeven, T.

    1972-01-01

    The catalytic effect of cobalt powder on chlorate decomposition has been confirmed. Catalysis is enhanced by oxidation of the metal during burning. Catalysts other than cobalt compounds should also be effective; the complete elimination of fuel has shown that the oxidation of cobalt during decomposition is not a vital factor in the improved performance of catalyzed candles.

  5. Lipase-catalyzed preparation of human milk fat substitutes from palm stearin in a solvent-free system.

    PubMed

    Zou, Xiao-Qiang; Huang, Jian-Hua; Jin, Qing-Zhe; Liu, Yuan-Fa; Song, Zhi-Hua; Wang, Xing-Guo

    2011-06-08

    Human milk fat substitutes (HMFSs) were synthesized by lipozyme RM IM-catalyzed acidolysis of chemically interesterified palm stearin (mp = 58 °C) with mixed FAs from rapeseed oil, sunflower oil, palm kernel oil, stearic acid, and myristic acid in a solvent-free system. Response surface methodology (RSM) was used to model and optimize the reactions, and the factors chosen were reaction time, temperature, substrate molar ratio, and enzyme load. The optimal conditions generated from the models were as follows: reaction time, 3.4 h; temperature, 57 °C; substrate molar ratio, 14.6 mol/mol; and enzyme load, 10.7 wt % (by the weight of total substrates). Under these conditions, the contents of palmitic acid (PA) and PA at sn-2 position (sn-2 PA) were 29.7 and 62.8%, respectively, and other observed FAs were all within the range of FAs of HMF. The product was evaluated by the cited model, and a high score (85.8) was obtained, which indicated a high degree of similarity of the product to HMF.

  6. Catalyzed Ceramic Burner Material

    SciTech Connect

    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

  7. Antiproton catalyzed fusion

    SciTech Connect

    Morgan, D.L. Jr.; Perkins, L.J.; Haney, S.W.

    1995-05-15

    Because of the potential application to power production, it is important to investigate a wide range of possible means to achieve nuclear fusion, even those that may appear initially to be infeasible. In antiproton catalyzed fusion, the negative antiproton shields the repulsion between the positively charged nuclei of hydrogen isotopes, thus allowing a much higher level of penetration through the repulsive Coulomb barrier, and thereby greatly enhancing the fusion cross section. Because of their more compact wave function, the more massive antiprotons offer considerably more shielding than do negative muons. The effects of the shielding on fusion cross sections are most predominate, at low energies. If the antiproton could exist in the ground state with a nucleus for a sufficient time without annihilating, the fusion cross sections are so enhanced that at room temperature energies, values up to about 1,000 barns (that for d+t) would be possible. Unfortunately, the cross section for antiproton annihilation with the incoming nucleus is even higher. A model that provides an upper bound for the fusion to annihilation cross section for all relevant energies indicates that each antiproton will catalyze no more than about one fusion. Because the energy required to make one antiproton greatly exceeds the fusion energy that is released, this level of catalysis is far from adequate for power production.

  8. Hydroxide-catalyzed bonding

    NASA Technical Reports Server (NTRS)

    Gwo, Dz-Hung (Inventor)

    2003-01-01

    A method of bonding substrates by hydroxide-catalyzed hydration/dehydration involves applying a bonding material to at least one surface to be bonded, and placing the at least one surface sufficiently close to another surface such that a bonding interface is formed between them. A bonding material of the invention comprises a source of hydroxide ions, and may optionally include a silicate component, a particulate filling material, and a property-modifying component. Bonding methods of the invention reliably and reproducibly provide bonds which are strong and precise, and which may be tailored according to a wide range of possible applications. Possible applications for bonding materials of the invention include: forming composite materials, coating substrates, forming laminate structures, assembly of precision optical components, and preparing objects of defined geometry and composition. Bonding materials and methods of preparing the same are also disclosed.

  9. Iptycene synthesis: A new method for attaching a 2,3-anthracene moiety to the 9,10-positions of another anthracene moiety - Exceptional conditions for a Lewis acid catalyzed Diels-Alder reaction

    NASA Technical Reports Server (NTRS)

    Chen, Yong-Shing; Hart, Harold

    1989-01-01

    An efficient three-step method for appending a 2,3-anthracene moiety to the 9,10-positions of an existing anthracene moiety is described. The first step uses excess 1,4-anthraquinone (3 equiv) and aluminum chloride (6 equiv) to obtain the anthracene-quinone cycloadduct (omission of the AlCl3 resulted in no adduct). The resulting diketone was reduced to the corresponding diol (excess LiAlH4), which was dehydrated to the arene with phosphorus oxychloride and pyridine. Specific examples include the preparation of heptipycene 8 from pentiptycene 6 (66 percent overall yield) and a similar conversion of 8 to the noniptycene 13 (75 percent overall yield). The methodology led to a markedly improved synthesis of tritriptycene 9 and the first synthesis of undecaiptycene 14.

  10. Iptycene synthesis: A new method for attaching a 2,3-anthracene moiety to the 9,10-positions of another anthracene moiety - Exceptional conditions for a Lewis acid catalyzed Diels-Alder reaction

    NASA Technical Reports Server (NTRS)

    Chen, Yong-Shing; Hart, Harold

    1989-01-01

    An efficient three-step method for appending a 2,3-anthracene moiety to the 9,10-positions of an existing anthracene moiety is described. The first step uses excess 1,4-anthraquinone (3 equiv) and aluminum chloride (6 equiv) to obtain the anthracene-quinone cycloadduct (omission of the AlCl3 resulted in no adduct). The resulting diketone was reduced to the corresponding diol (excess LiAlH4), which was dehydrated to the arene with phosphorus oxychloride and pyridine. Specific examples include the preparation of heptipycene 8 from pentiptycene 6 (66 percent overall yield) and a similar conversion of 8 to the noniptycene 13 (75 percent overall yield). The methodology led to a markedly improved synthesis of tritriptycene 9 and the first synthesis of undecaiptycene 14.

  11. Oxygenase-Catalyzed Desymmetrization of N,N-Dialkyl-piperidine-4-carboxylic Acids**

    PubMed Central

    Rydzik, Anna M; Leung, Ivanhoe K H; Kochan, Grazyna T; McDonough, Michael A; Claridge, Timothy D W; Schofield, Christopher J

    2014-01-01

    γ-Butyrobetaine hydroxylase (BBOX) is a 2-oxoglutarate dependent oxygenase that catalyzes the final hydroxylation step in the biosynthesis of carnitine. BBOX was shown to catalyze the oxidative desymmetrization of achiral N,N-dialkyl piperidine-4-carboxylates to give products with two or three stereogenic centers. PMID:25164544

  12. DNA-Catalyzed Amide Hydrolysis

    PubMed Central

    Zhou, Cong; Avins, Joshua L.; Klauser, Paul C.; Brandsen, Benjamin M.; Lee, Yujeong; Silverman, Scott K.

    2016-01-01

    DNA catalysts (deoxyribozymes) for a variety of reactions have been identified by in vitro selection. However, for certain reactions this identification has not been achieved. One important example is DNA-catalyzed amide hydrolysis, for which a previous selection experiment instead led to DNA-catalyzed DNA phosphodiester hydrolysis. Subsequent efforts in which the selection strategy deliberately avoided phosphodiester hydrolysis led to DNA-catalyzed ester and aromatic amide hydrolysis, but aliphatic amide hydrolysis has been elusive. In the present study, we show that including modified nucleotides that bear protein-like functional groups (any one of primary amino, carboxyl, or primary hydroxyl) enables identification of amide-hydrolyzing deoxyribozymes. In one case, the same deoxyribozyme sequence without the modifications still retains substantial catalytic activity. Overall, these findings establish the utility of introducing protein-like functional groups into deoxyribozymes for identifying new catalytic function. The results also suggest the longer-term feasibility of deoxyribozymes as artificial proteases. PMID:26854515

  13. Iodine-Catalyzed Polysaccharide Esterification

    USDA-ARS?s Scientific Manuscript database

    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...

  14. Performance of catalyzed hydrazine in field applications

    SciTech Connect

    Allgood, T.B.

    1987-01-01

    The performance of newly developed oxygen scavengers for boilers is often compared to sulfite and hydrazine. Catalyzed hydrazine out-performs hydrazine and might be preferred when catalyzed sulfite cannot be used. Data from a Midwest Utility confirms that, under field conditions, catalyzed hydrazine out-performance hydrazine and carbohydrazine when feedwater oxygen and iron levels were critical. Catalyzed hydrazine might be preferred when high performance and economics are the primary concerns.

  15. Effects of dietary oxidized konjac glucomannan sulfates (OKGMS) and acidolysis-oxidized konjac glucomannan (A-OKGM) on the immunity and expression of immune-related genes of Schizothorax prenanti.

    PubMed

    Chen, Mingrui; Wang, Hongjie; Yan, Qiuping; Zheng, Qiaoran; Yang, Min; Lv, Zhenzhen; He, Mei; Feng, Limei; Zhao, Jiaqi; Tang, Tingting; Wu, Yinglong

    2016-09-01

    In the present study, konjac glucomannan (KGM) was degraded by H2O2, and then used trisulfonated sodium amine and HCl, individually, to obtain two kinds of derivatives: oxidized konjac glucomannan sulfates (OKGMS) and acidolysis-oxidized konjac glucomannan (A-OKGM). The effects of two OKGM modified products on the immune parameters and expressions of toll-like receptor 22 (TLR22), myeloid differentiation factor 88 (MyD88) and interferon regulatory factors 7 (IRF7) genes in Schizothorax prenanti were determined. The alternative haemolytic complement (ACH50) activity was found to be significantly increased by the OKGMS diets. The immunoglobulin M (IgM) level was significantly enhanced by the OKGMS diets. The lysozyme activity was significantly increased by both OKGMS and A-OKGM diets. The superoxide dismutase (T-SOD) activity in fish fed with all doses of OKGMS diets was significantly higher than that in fish fed with basal diet. The glutathione peroxidase (GSH-PX) activity in fish fed with 0.8% and 1.6% A-OKGM diets was significantly higher than control group. The malondialdehyde (MDA) level was significantly decreased by both OKGMS and A-OKGM diets. The 0.8% A-OKGM diet significantly up-regulated TLR22 gene expression in the head kidney and spleen. TLR22 gene expression was significantly promoted by all OKGMS diets in the mesonephros and liver. The MyD88 mRNA level in 1.6% A-OKGM group significantly increased in the head kidney. The low dose of OKGMS significantly induced the MyD88 gene expression in the mesonephros, gut and liver, while 0.8% A-OKGM group also showed a significantly enhanced MyD88 mRNA expression in the gut. High dose of OKGMS significantly increased the IRF7 mRNA expression in the mesonephros and spleen. Fish fed with low dose of A-OKGM showed significantly higher expression of IRF7 in the gut and liver. Present study suggested that OKGMS and A-OKGM can act as immunostimulant to improve the immune indexes and up-regulate the immune-related gene

  16. Enantioselective synthesis of SSR 241586 by using an organo-catalyzed Henry reaction.

    PubMed

    Cochi, Anne; Métro, Thomas-Xavier; Pardo, Domingo Gomez; Cossy, Janine

    2010-08-20

    An organo-catalyzed Henry reaction, applied to an alpha-keto ester, has allowed the enantioselective synthesis of SSR 241586, a 2,2-disubstituted morpholine active in the treatment of schizophrenia and irritable bowel syndrome (IBS).

  17. Gold-catalyzed domino reactions.

    PubMed

    Michelet, Véronique

    2015-01-01

    Gold-catalyzed reactions have appeared to be highly attractive tools for chemists to promote novel transformations to prepare elaborated structures from simple starting materials. This chapter presents selected and original examples of domino processes in the presence of gold catalysts, highlighting reports implying hydration, hydroxylation, and hydroamination as key starting point for cascade transformations. Domino processes implying 1,n-enynes, asymmetric domino transformations, and applications of all the presented processes in total synthesis are presented.

  18. Thermodynamics of Enzyme-Catalyzed Reactions Database

    National Institute of Standards and Technology Data Gateway

    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. Photodegradation of acidolysis lignin from BCMP.

    PubMed

    Azadfallah, Mohammad; Mirshokraei, Seyed Ahmad; Latibari, Ahmad Jahan

    2008-12-15

    A mild acidic dioxane extraction method was employed to isolate lignin from hardwood bleached chemimechanical pulp (BCMP). The isolated lignin was then purified and undergone elemental analysis. To study the photodegradation behavior, the lignin samples were impregnated onto the Whatman filter papers and irradiated with UV light for various periods. The photolyzed lignin was then recovered and analyzed by (1)H-NMR spectroscopy. Phenylpropane-based formula (C(9)) of CMP pulp lignin and the photolyzed samples were then established with elemental analysis and (1)H-NMR spectroscopy data. The results indicated that the benzaldehyde and benzoic acid type compounds were the main photodegradation products of BCMP lignin. The lignin photodegradation probably involved the degradation of phenylcoumaran units. Irradiation also increased the phenolic hydroxyl group content and decreased that of methoxyl groups, due to demethoxylation. The degrees of aromatic ring condensation were increased upon continuing the irradiation time, which imples the formation of condensed structures in photolyzed lignin.

  20. Iridium-Catalyzed Allylic Substitution

    NASA Astrophysics Data System (ADS)

    Hartwig, John F.; Pouy, Mark J.

    Iridium-catalyzed asymmetric allylic substitution has become a valuable method to prepare products from the addition of nucleophiles at the more substituted carbon of an allyl unit. The most active and selective catalysts contain a phosphoramidite ligand possessing at least one arylethyl substituent on the nitrogen atom of the ligand. In these systems, the active catalyst is generated by a base-induced cyclometalation at the methyl group of this substituent to generate an iridium metalacycle bound by the COD ligand of the [Ir(COD)Cl]2 precursor and one additional labile dative ligand. Such complexes catalyze the reactions of linear allylic esters with alkylamines, arylamines, phenols, alcohols, imides, carbamates, ammonia, enolates and enolate equivalents, as well as typical stabilized carbon nucleophiles generated from malonates and cyanoesters. Iridium catalysts for enantioselective allylic substitution have also been generated from phosphorus ligands with substituents bound by heteroatoms, and an account of the studies of such systems, along with a description of the development of iridium catalysts is included.

  1. Gold-catalyzed naphthalene functionalization

    PubMed Central

    Rivilla, Iván

    2011-01-01

    Summary The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO2Et (R = H, Me) from N2C(R)CO2Et 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. PMID:21647320

  2. Trypsin-Catalyzed Deltamethrin Degradation

    PubMed Central

    Xiong, Chunrong; Fang, Fujin; Chen, Lin; Yang, Qinggui; He, Ji; Zhou, Dan; Shen, Bo; Ma, Lei; Sun, Yan; Zhang, Donghui; Zhu, Changliang

    2014-01-01

    To explore if trypsin could catalyze the degradation of non-protein molecule deltamethrin, we compared in vitro hydrolytic reactions of deltamethrin in the presence and absence of trypsin with ultraviolet-visible (UV/Vis) spectrophotometry and gas chromatography-mass spectrometry (GC/MS). In addition, acute oral toxicity of the degradation products was determined in Wistar rats. The results show that the absorption peak of deltamethrin is around 264 nm, while the absorption peaks of deltamethrin degradation products are around 250 nm and 296 nm. In our GC setting, the retention time of undegraded deltamethrin was 37.968 min, while those of deltamethrin degradation products were 15.289 min and 18.730 min. The LD50 of deltamethrin in Wistar rats is 55 mg/kg, while that of deltamethrin degradation products is 3358 mg/kg in female rats and 1045 mg/kg in male rates (61-fold and 19-fold reductions in toxicity), suggesting that trypsin could directly degrade deltamethrin, which significantly reduces the toxicity of deltamethrin. These results expand people's understanding of the functions of proteases and point to potential applications of trypsin as an attractive agent to control residual pesticides in the environment and on agricultural products. PMID:24594869

  3. Trypsin-catalyzed deltamethrin degradation.

    PubMed

    Xiong, Chunrong; Fang, Fujin; Chen, Lin; Yang, Qinggui; He, Ji; Zhou, Dan; Shen, Bo; Ma, Lei; Sun, Yan; Zhang, Donghui; Zhu, Changliang

    2014-01-01

    To explore if trypsin could catalyze the degradation of non-protein molecule deltamethrin, we compared in vitro hydrolytic reactions of deltamethrin in the presence and absence of trypsin with ultraviolet-visible (UV/Vis) spectrophotometry and gas chromatography-mass spectrometry (GC/MS). In addition, acute oral toxicity of the degradation products was determined in Wistar rats. The results show that the absorption peak of deltamethrin is around 264 nm, while the absorption peaks of deltamethrin degradation products are around 250 nm and 296 nm. In our GC setting, the retention time of undegraded deltamethrin was 37.968 min, while those of deltamethrin degradation products were 15.289 min and 18.730 min. The LD50 of deltamethrin in Wistar rats is 55 mg/kg, while that of deltamethrin degradation products is 3358 mg/kg in female rats and 1045 mg/kg in male rates (61-fold and 19-fold reductions in toxicity), suggesting that trypsin could directly degrade deltamethrin, which significantly reduces the toxicity of deltamethrin. These results expand people's understanding of the functions of proteases and point to potential applications of trypsin as an attractive agent to control residual pesticides in the environment and on agricultural products.

  4. Advances in lipase-catalyzed esterification reactions.

    PubMed

    Stergiou, Panagiota-Yiolanda; Foukis, Athanasios; Filippou, Michalis; Koukouritaki, Maria; Parapouli, Maria; Theodorou, Leonidas G; Hatziloukas, Efstathios; Afendra, Amalia; Pandey, Ashok; Papamichael, Emmanuel M

    2013-12-01

    Lipase-catalyzed esterification reactions are among the most significant chemical and biochemical processes of industrial relevance. Lipases catalyze hydrolysis as well as esterification reactions. Enzyme-catalyzed esterification has acquired increasing attention in many applications, due to the significance of the derived products. More specifically, the lipase-catalyzed esterification reactions attracted research interest during the past decade, due to an increased use of organic esters in biotechnology and the chemical industry. Lipases, as hydrolyzing agents are active in environments, which contain a minimum of two distinct phases, where all reactants are partitioned between these phases, although their distribution is not fixed and changes as the reaction proceeds. The kinetics of the lipase-catalyzed reactions is governed by a number of factors. This article presents a thorough and descriptive evaluation of the applied trends and perspectives concerning the enzymatic esterification, mainly for biofuel production; an emphasis is given on essential factors, which affect the lipase-catalyzed esterification reaction. Moreover, the art of using bacterial and/or fungal strains for whole cell biocatalysis purposes, as well as carrying out catalysis by various forms of purified lipases from bacterial and fungal sources is also reviewed.

  5. Oligonucleotide formation catalyzed by mononucleotide matrices

    NASA Technical Reports Server (NTRS)

    Lohrmann, R.

    1982-01-01

    Pb(2+)-containing precipitates of mononucleotides form matrices which catalyze the self-condensation of nucleotide 5-prime-phosphorimidazolides and their condensation with nucleosides. The reactions exhibit base-pairing specificity between matrix nucleotide and substrate, and usually follow the Watson-Crick pairing rules. Although purine polynucleotides do not facilitate the oligomerization of pyrimidine nucleotide monomers in solution, it is interesting that purine-containing matrices do catalyze such a reaction. The significance of the results in the context of the prebiotic evolution of polynucleotides is discussed.

  6. Enantioselective, iridium-catalyzed monoallylation of ammonia.

    PubMed

    Pouy, Mark J; Stanley, Levi M; Hartwig, John F

    2009-08-19

    Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations.

  7. Oligonucleotide formation catalyzed by mononucleotide matrices

    NASA Technical Reports Server (NTRS)

    Lohrmann, R.

    1982-01-01

    Pb(2+)-containing precipitates of mononucleotides form matrices which catalyze the self-condensation of nucleotide 5-prime-phosphorimidazolides and their condensation with nucleosides. The reactions exhibit base-pairing specificity between matrix nucleotide and substrate, and usually follow the Watson-Crick pairing rules. Although purine polynucleotides do not facilitate the oligomerization of pyrimidine nucleotide monomers in solution, it is interesting that purine-containing matrices do catalyze such a reaction. The significance of the results in the context of the prebiotic evolution of polynucleotides is discussed.

  8. Iron catalyzed asymmetric oxyamination of olefins.

    PubMed

    Williamson, Kevin S; Yoon, Tehshik P

    2012-08-01

    The regioselective and enantioselective oxyamination of alkenes with N-sulfonyl oxaziridines is catalyzed by a novel iron(II) bis(oxazoline) complex. This process affords oxazolidine products that can be easily manipulated to yield highly enantioenriched free amino alcohols. The regioselectivity of this process is complementary to that obtained from the analogous copper(II)-catalyzed reaction. Thus, both regioisomers of enantioenriched 1,2-aminoalcohols can be obtained using oxaziridine-mediated oxyamination reactions, and the overall sense of regiochemistry can be controlled using the appropriate choice of inexpensive first-row transition metal catalyst.

  9. Attractor Explosions and Catalyzed Vacuum Decay

    SciTech Connect

    Green, Daniel; Silverstein, Eva; Starr, David

    2006-05-05

    We present a mechanism for catalyzed vacuum bubble production obtained by combining moduli stabilization with a generalized attractor phenomenon in which moduli are sourced by compact objects. This leads straightforwardly to a class of examples in which the Hawking decay process for black holes unveils a bubble of a different vacuum from the ambient one, generalizing the new endpoint for Hawking evaporation discovered recently by Horowitz. Catalyzed vacuum bubble production can occur for both charged and uncharged bodies, including Schwarzschild black holes for which massive particles produced in the Hawking process can trigger vacuum decay. We briefly discuss applications of this process to the population and stability of metastable vacua.

  10. Enantioselective, Iridium-Catalyzed Monoallylation of Ammonia

    PubMed Central

    Pouy, Mark J.; Stanley, Levi M.; Hartwig, John F.

    2009-01-01

    Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations. PMID:19722644

  11. Palladium catalyzed hydrogenation of bio-oils and organic compounds

    DOEpatents

    Elliott, Douglas C [Kennewick, WA; Hu, Jianli [Richland, WA; Hart,; Todd, R [Kennewick, WA; Neuenschwander, Gary G [Burbank, WA

    2011-06-07

    The invention provides palladium-catalyzed hydrogenations of bio-oils and certain organic compounds. Experimental results have shown unexpected and superior results for palladium-catalyzed hydrogenations of organic compounds typically found in bio-oils.

  12. Palladium catalyzed hydrogenation of bio-oils and organic compounds

    DOEpatents

    Elliott, Douglas C.; Hu, Jianli; Hart, Todd R.; Neuenschwander, Gary G.

    2008-09-16

    The invention provides palladium-catalyzed hydrogenations of bio-oils and certain organic compounds. Experimental results have shown unexpected and superior results for palladium-catalyzed hydrogenations of organic compounds typically found in bio-oils.

  13. Zeolite 5A Catalyzed Etherification of Diphenylmethanol

    ERIC Educational Resources Information Center

    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…

  14. Organic acids tunably catalyze carbonic acid decomposition.

    PubMed

    Kumar, Manoj; Busch, Daryle H; Subramaniam, Bala; Thompson, Ward H

    2014-07-10

    Density functional theory calculations predict that the gas-phase decomposition of carbonic acid, a high-energy, 1,3-hydrogen atom transfer reaction, can be catalyzed by a monocarboxylic acid or a dicarboxylic acid, including carbonic acid itself. Carboxylic acids are found to be more effective catalysts than water. Among the carboxylic acids, the monocarboxylic acids outperform the dicarboxylic ones wherein the presence of an intramolecular hydrogen bond hampers the hydrogen transfer. Further, the calculations reveal a direct correlation between the catalytic activity of a monocarboxylic acid and its pKa, in contrast to prior assumptions about carboxylic-acid-catalyzed hydrogen-transfer reactions. The catalytic efficacy of a dicarboxylic acid, on the other hand, is significantly affected by the strength of an intramolecular hydrogen bond. Transition-state theory estimates indicate that effective rate constants for the acid-catalyzed decomposition are four orders-of-magnitude larger than those for the water-catalyzed reaction. These results offer new insights into the determinants of general acid catalysis with potentially broad implications.

  15. Catalyzing curriculum evolution in graduate science education.

    PubMed

    Gutlerner, Johanna L; Van Vactor, David

    2013-05-09

    Strategies in life science graduate education must evolve in order to train a modern workforce capable of integrative solutions to challenging problems. Our institution has catalyzed such evolution through building a postdoctoral Curriculum Fellows Program that provides a collaborative and scholarly education laboratory for innovation in graduate training.

  16. Zeolite 5A Catalyzed Etherification of Diphenylmethanol

    ERIC Educational Resources Information Center

    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…

  17. Microorganisms detected by enzyme-catalyzed reaction

    NASA Technical Reports Server (NTRS)

    Vango, S. P.; Weetall, H. H.; Weliky, N.

    1966-01-01

    Enzymes detect the presence of microorganisms in soils. The enzyme lysozymi is used to release the enzyme catalase from the microorganisms in a soil sample. The catalase catalyzes the decomposition of added hydrogen peroxide to produce oxygen which is detected manometrically. The partial pressure of the oxygen serves as an index of the samples bacteria content.

  18. Palladium-catalyzed substitution of allylic fluorides.

    PubMed

    Hazari, Amaruka; Gouverneur, Véronique; Brown, John M

    2009-01-01

    As unusual substrates for the Tsuji-Trost allylation reaction, allylic fluorides are responsive to palladium-catalyzed substitution. Their activity towards this reaction fits in the series OCO(2)Me>OBz>F>OAc. The classic stereoretention mechanism that involves sequential inversions does not operate in this case. Several distinct cases are considered.

  19. Dual chemistry catalyzed by human acireductone dioxygenase.

    PubMed

    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.

  20. A convergent synthesis of the C1-C16 segment of goniodomin A via palladium-catalyzed organostannane-thioester coupling.

    PubMed

    Fuwa, Haruhiko; Nakajima, Motohiro; Shi, Jinglu; Takeda, Yoshiyuki; Saito, Tomoyuki; Sasaki, Makoto

    2011-03-04

    A convergent synthesis of the C1-C16 segment of goniodomin A, an actin-targeting marine polyether macrolide natural product, has been achieved via a 2-fold application of palladium-catalyzed organostannane-thioester coupling.

  1. Analytical rheology of metallocene-catalyzed polyethylenes

    NASA Astrophysics Data System (ADS)

    Shanbhag, Sachin; Takeh, Arsia

    2011-03-01

    A computational algorithm that seeks to invert the linear viscoelastic spectrum of single-site metallocene-catalyzed polyethylenes is presented. The algorithm uses a general linear rheological model of branched polymers as its underlying engine, and is based on a Bayesian formulation that transforms the inverse problem into a sampling problem. Given experimental rheological data on unknown single-site metallocene- catalyzed polyethylenes, it is able to quantitatively describe the range of values of weight-averaged molecular molecular weight, MW , and average branching density, bm , consistent with the data. The algorithm uses a Markov-chain Monte Carlo method to simulate the sampling problem. If, and when information about the molecular weight is available through supplementary experiments, such as chromatography or light scattering, it can easily be incorporated into the algorithm, as demonstrated. Financial support from NSF DMR 0953002.

  2. Cold fusion catalyzed by muons and electrons

    SciTech Connect

    Kulsrud, R.M.

    1990-10-01

    Two alternative methods have been suggested to produce fusion power at low temperature. The first, muon catalyzed fusion or MCF, uses muons to spontaneously catalyze fusion through the muon mesomolecule formation. Unfortunately, this method fails to generate enough fusion energy to supply the muons, by a factor of about ten. The physics of MCF is discussed, and a possible approach to increasing the number of MCF fusions generated by each muon is mentioned. The second method, which has become known as Cold Fusion,'' involves catalysis by electrons in electrolytic cells. The physics of this process, if it exists, is more mysterious than MCF. However, it now appears to be an artifact, the claims for its reality resting largely on experimental errors occurring in rather delicate experiments. However, a very low level of such fusion claimed by Jones may be real. Experiments in cold fusion will also be discussed.

  3. Horseradish-Peroxidase-Catalyzed Tyrosine Click Reaction.

    PubMed

    Sato, Shinichi; Nakamura, Kosuke; Nakamura, Hiroyuki

    2017-03-02

    The efficiency of protein chemical modification on tyrosine residues with N-methylluminol derivatives was drastically improved by using horseradish peroxidase (HRP). In the previous method, based on the use of hemin and H2 O2 , oxidative side reactions such as cysteine oxidation were problematic for functionalization of proteins selectively on tyrosine residues. Oxidative activation of N-methylluminol derivatives with a minimum amount of H2 O2 prevented the occurrence of oxidative side reactions under HRP-catalyzed conditions. As probes for HRP-catalyzed protein modification, N-methylluminol derivatives showed much higher efficiency than tyramide without inducing oligomerization of probe molecules. Tyrosine modification also proceeded in the presence of β-nicotinamide adenine dinucleotide (NADH, H2 O2 -free conditions).

  4. Stop-catalyzed baryogenesis beyond the MSSM

    NASA Astrophysics Data System (ADS)

    Katz, Andrey; Perelstein, Maxim; Ramsey-Musolf, Michael J.; Winslow, Peter

    2015-11-01

    Nonminimal supersymmetric models that predict a tree-level Higgs mass above the minimal supersymmetric standard model (MSSM) bound are well motivated by naturalness considerations. Indirect constraints on the stop sector parameters of such models are significantly relaxed compared to the MSSM; in particular, both stops can have weak-scale masses. We revisit the stop-catalyzed electroweak baryogenesis (EWB) scenario in this context. We find that the LHC measurements of the Higgs boson production and decay rates already rule out the possibility of stop-catalyzed EWB. We also introduce a gauge-invariant analysis framework that may generalize to other scenarios in which interactions outside the gauge sector drive the electroweak phase transition.

  5. Rhodium-catalyzed restructuring of carbon frameworks.

    PubMed

    Murakami, Masahiro

    2010-10-01

    Metal-catalyzed reactions involving an elementary step which cleaves a carbon-carbon bond provide unique organic transformations. Restructuring reactions recently developed in our laboratory, through which the carbon framework of a starting substance is restructured into a totally different carbon framework, are discussed, with the possibility of applying such methods to the synthesis of natural products. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

  6. Nickel-Catalyzed Synthesis of Quinazolinediones.

    PubMed

    Beutner, Gregory L; Hsiao, Yi; Razler, Thomas; Simmons, Eric M; Wertjes, William

    2017-03-03

    A nickel(0)-catalyzed method for the synthesis of quinazolinediones from isatoic anhydrides and isocyanates is described. High-throughput ligand screening revealed that XANTPHOS was the optimal ligand for this transformation. Subsequent optimization studies, supported by kinetic analysis, significantly expanded the reaction scope. The reaction exhibits a case of substrate inhibition kinetics with respect to the isocyanate. Preliminary results on an asymmetric synthesis of atropisomeric quinazolinediones are reported.

  7. Antiproton catalyzed microfission/fusion propulsion

    NASA Technical Reports Server (NTRS)

    Chiang, Pi-Ren; Lewis, Raymond A.; Smith, Gerald A.; Newton, Richard; Dailey, James; Werthman, W. Lance; Chakrabarti, Suman

    1994-01-01

    Inertial confinement fusion (ICF) utilizing an antiproton catalyzed hybrid fission/fusion target is discussed as a potential energy source for interplanetary propulsion. A proof-of-principle experiment underway at Phillips Laboratory, Kirtland AFB and antiproton trapping experiments at CERN, Geneva, Switzerland, are presented. The ICAN propulsion concept is described and results of performance analyses are reviewed. Future work to further define the ICAN concept is outlined.

  8. Cu2+-catalyzed oxidative degradation of thyroglobulin.

    PubMed

    Lee, H J; Sok, D E

    2000-10-01

    Thyroglobulin (Tg) was subjected to metal-catalyzed oxidation, and the oxidative degradation was analyzed by SDS-polyacrylamide gel electrophoresis under reducing conditions. In contrast to no effect of hydrogen peroxide (H2O2) alone on the Tg degradation, the inclusion of Cu2+ (30 microM), in combination with 2 mM H2O2, caused a remarkable degradation of Tg, time- and concentration-dependent. The action of Cu2+ was not mimicked by Fe2+, suggesting that Tg may interact selectively with Cu2+. A similar degradation of Tg was also observed with Cu2+/ascorbate system, and the concentration of Cu2+ (5-10 microM), in combination with ascorbate, required for the effective degradation was smaller than that of Cu2+ (10-30 microM) in combination with H2O2. In support of involvement of H2O2 in the Cu2+/ascorbate action, catalase expressed a complete protection. However, hydroxyl radical scavengers such as dimethylsulfoxide or mannitol failed to prevent the oxidation of Tg whereas phenolic compounds, which can interact with Cu2+, diminished the oxidative degradation, presumably consistent with the mechanism for Cu2+-catalyzed oxidation of protein. Moreover, the amount of carbonyl groups in Tg was increased as the concentration (3-100 microM) of Cu2+ was enhanced, while the formation of acid-soluble peptides was not remarkable in the presence of Cu2+ up to 200 microM. In further studies, Tg pretreated with heat or trichloroacetic acid seemed to be somewhat resistant to Cu2+-catalyzed oxidation, implying a possible involvement of protein conformation in the susceptibility to the oxidation. Based on these observations, it is proposed that Tg could be degraded non-enzymatically by Cu2+-catalyzed oxidation.

  9. Metal Catalyzed Oligomerization Reactions of Organosiloxanes.

    DTIC Science & Technology

    1982-10-28

    metallacycle from a mixture of stereo- isomers of the starting disiloxane is observed. The catalytic activity of these complexes for the oligomeriza... catalysts were adsorbed on oxide supports. Although the goal of synthesizing stereoregular silicones has not yet been achieved, the results warrant further...implicated as intermediates in several transi- tion metal-catalyzed reactions, e.g. olefin metathesis . 1 3 Metallacycles are also probable

  10. Iron-catalyzed trifluoromethylation of enamide.

    PubMed

    Rey-Rodriguez, Romain; Retailleau, Pascal; Bonnet, Pascal; Gillaizeau, Isabelle

    2015-02-23

    Herein the first example of the iron(II)-catalyzed trifluoromethylation of enamide using mild and simple reaction conditions is reported. The method is cost-effective and uses the easy-to-handle Togni's reagent as the electrophilic CF3 source. This transformation is totally regioselective at the C3 position of enamides and exhibits broad substrate scope, good functional group tolerance and thus demonstrates its useful application in a late-stage fluorination strategy.

  11. Palladium-Catalyzed Fluorosulfonylvinylation of Organic Iodides.

    PubMed

    Zha, Gao-Feng; Zheng, Qinheng; Leng, Jing; Wu, Peng; Qin, Hua-Li; Sharpless, K Barry

    2017-03-29

    A palladium-catalyzed fluorosulfonylvinylation reaction of organic iodides is described. Catalytic Pd(OAc)2 with a stoichiometric amount of silver(I) trifluoroacetate enables the coupling process between either an (hetero)aryl or alkenyl iodide with ethenesulfonyl fluoride (ESF). The method is demonstrated in the successful syntheses of eighty-eight otherwise difficult to access compounds, in up to 99 % yields, including the unprecedented 2-heteroarylethenesulfonyl fluorides and 1,3-dienylsulfonyl fluorides.

  12. Nickel-catalyzed enantioselective arylation of pyridine†

    PubMed Central

    Lutz, J. Patrick; Chau, Stephen T.

    2016-01-01

    We report an enantioselective Ni-catalyzed cross coupling of arylzinc reagents with pyridiniumions formed in situ from pyridine and a chloroformate. This reaction provides enantioenriched 2-aryl-1,2-dihydropyridine products that can be elaborated to numerous piperidine derivatives with little or no loss in ee. This method is notable for its use of pyridine, a feedstock chemical, to build a versatile, chiral heterocycle in a single synthetic step. PMID:28058106

  13. Transition metal catalyzed transformations of unsaturated molecules

    SciTech Connect

    Not Available

    1989-01-01

    In this proposal, research in three areas of transition metal catalyzed transformations of small molecules is proposed. The first encompasses metal catalyzed processes for the synthesis of several classes of carbon monoxide containing polymers. This section describes plans for metal catalyzed synthesis of (a) new alternating copolymers of carbon monoxide and olefins, (b) block copolymers consisting of segments of the olefin homopolymer and the olefin- carbon monoxide alternating copolymer, and (c) polycarbonates, polyesters and polyamides. The second section involves the examination of the chemistry of metal complexes incorporating oxo and hydrocarbyl ligands as a model for the heterogeneous oxidation of olefins and alkanes by meal oxides. Specific plans are to mimic in solution two proposed key steps in the heterogeneous oxidations. These are (a) the heterolytic cleavage of an alkyl (or allyl) C-H bond that is assisted by an oxo group, and (a) the transfer of an oxo group to the resultant metal bound alkyl (or allyl) ligand. The third section concerned with the development of a hybrid catalyst system involving both homogeneous and heterogeneous components for the oxidative functionalization of alkanes. The basic idea is to employ a transition metal in the elemental state to activate C-H bonds of alkanes and form surface alkyl groups. An additional transition metal species will be present in solution which will serve to oxidize these surface alkyl groups to ultimately yield oxidatively functionalized organic products. 57 refs.

  14. Fe-catalyzed etching of graphene layers

    NASA Astrophysics Data System (ADS)

    Cheng, Guangjun; Calizo, Irene; Hight Walker, Angela; PML, NIST Team

    We investigate the Fe-catalyzed etching of graphene layers in forming gas. Fe thin films are deposited by sputtering onto mechanically exfoliated graphene, few-layer graphene (FLG), and graphite flakes on a Si/SiO2 substrate. When the sample is rapidly annealed in forming gas, particles are produced due to the dewetting of the Fe thin film and those particles catalyze the etching of graphene layers. Monolayer graphene and FLG regions are severely damaged and that the particles catalytically etch channels in graphite. No etching is observed on graphite for the Fe thin film annealed in nitrogen. The critical role of hydrogen indicates that this graphite etching process is catalyzed by Fe particles through the carbon hydrogenation reaction. By comparing with the etched monolayer and FLG observed for the Fe film annealed in nitrogen, our Raman spectroscopy measurements identify that, in forming gas, the catalytic etching of monolayer and FLG is through carbon hydrogenation. During this process, Fe particles are catalytically active in the dissociation of hydrogen into hydrogen atoms and in the production of hydrogenated amorphous carbon through hydrogen spillover.

  15. Imidazole catalyzes chlorination by unreactive primary chloramines.

    PubMed

    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. Imidazole catalyzes chlorination by unreactive primary chloramines

    PubMed Central

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

    2015-01-01

    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 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 upon [HIm]/[HOCl] and literature data. Acid catalysis again suggests that the actual chlorinating agent is HImCl+; consistent with this interpretation, MeIm markedly catalyzed fluorescein chlorination by HOCl

  17. Hydroarylation of arynes catalyzed by silver for biaryl synthesis.

    PubMed

    Lee, Nam-Kyu; Yun, Sang Young; Mamidipalli, Phani; Salzman, Ryan M; Lee, Daesung; Zhou, Tao; Xia, Yuanzhi

    2014-03-19

    A new biaryl synthesis via silver-catalyzed hydroarylation of arynes from acyclic building blocks with unactivated arenes in intra- and intermolecular manners has been developed. The previously observed Diels-Alder reactions of arynes with arene were not observed under the current silver-catalyzed conditions. Deuterium scrambling and DFT calculations suggest a stepwise electrophilic aromatic substitution mechanism through the formation of a Wheland-type intermediate followed by a water-catalyzed proton transfer in the final step of the hydroarylation.

  18. Ligand Intermediates in Metal-Catalyzed Reactions

    SciTech Connect

    Gladysz, John A.

    1999-07-31

    The longest-running goal of this project has been the synthesis, isolation, and physical chemical characterization of homogeneous transition metal complexes containing ligand types believed to be intermediates in the metal-catalyzed conversion of CO/H{sub 2}, CO{sub 2}, CH{sub 4}, and similar raw materials to organic fuels, feedstocks, etc. In the current project period, complexes that contain unusual new types of C{sub x}(carbide) and C{sub x}O{sub y} (carbon oxide) ligands have been emphasized. A new program in homogeneous fluorous phase catalysis has been launched as described in the final report.

  19. Copper-catalyzed asymmetric oxidation of sulfides.

    PubMed

    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. Iron-catalyzed aminohydroxylation of olefins.

    PubMed

    Williamson, Kevin S; Yoon, Tehshik P

    2010-04-07

    We have discovered that N-sulfonyl oxaziridines react with a broad range of olefins in the presence of iron salts to afford 1,3-oxazolidines. This process provides access to 1,2-aminoalcohols with the opposite sense of regioselectivity produced from the copper-catalyzed oxyamination previously reported by our laboratories. Thus, either regioisomeric form of 1,2-aminoalcohols can easily be obtained from the reaction of oxaziridines with olefins, and the sense of regioselectivity can be controlled by the appropriate choice of inexpensive, nontoxic, first-row transition-metal catalyst.

  1. Aluminum Hydride Catalyzed Hydroboration of Alkynes.

    PubMed

    Bismuto, Alessandro; Thomas, Stephen P; Cowley, Michael J

    2016-12-05

    An aluminum-catalyzed hydroboration of alkynes using either the commercially available aluminum hydride DIBAL-H or bench-stable Et3 Al⋅DABCO as the catalyst and H-Bpin as both the boron reagent and stoichiometric hydride source has been developed. Mechanistic studies revealed a unique mode of reactivity in which the reaction is proposed to proceed through hydroalumination and σ-bond metathesis between the resultant alkenyl aluminum species and HBpin, which acts to drive turnover of the catalytic cycle. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Silver-catalyzed late-stage fluorination.

    PubMed

    Tang, Pingping; Furuya, Takeru; Ritter, Tobias

    2010-09-01

    Carbon-fluorine bond formation by transition metal catalysis is difficult, and only a few methods for the synthesis of aryl fluorides have been developed. All reported transition-metal-catalyzed fluorination reactions for the synthesis of functionalized arenes are based on palladium. Here we present silver catalysis for carbon-fluorine bond formation. Our report is the first example of the use of the transition metal silver to form carbon-heteroatom bonds by cross-coupling catalysis. The functional group tolerance and substrate scope presented here have not been demonstrated for any other fluorination reaction to date.

  3. [Fragment reaction catalyzed by E. coli ribosomes].

    PubMed

    Kotusov, V V; Kukhanova, M K; Sal'nikova, N E; Nikolaeva, L V; Kraevskiĭ, A A

    1977-01-01

    It has been shown that 50S subunits of E. coli MRE-600 ribosomes catalyze the reaction of N-(formyl)-methionyl ester of adenosine 5'-phosphate acting as peptide donor, with Phe-tRNA or CACCA-Phe serving as a peptide acceptor. The reaction is stimulated by cytidine 5'phosphate and inhibited by lincomycin, puromycin and chloramphenicol. The obtained results show that the structure of the donor site of peptidyltransferase is completely assembled on the 50S subunit and 30S subunit is not required for its formation.

  4. Palladium-Catalyzed Arylation of Fluoroalkylamines

    PubMed Central

    Brusoe, Andrew T.; Hartwig, John F.

    2015-01-01

    We report the synthesis of fluorinated anilines by palladium-catalyzed coupling of fluoroalkylamines with aryl bromides and aryl chlorides. The products of these reactions are valuable because anilines typically require the presence of an electron-withdrawing substituent on nitrogen to suppress aerobic or metabolic oxidation, and the fluoroalkyl groups have steric properties and polarity distinct from those of more common electron-withdrawing amide and sulfonamide units. The fluoroalkylaniline products are unstable under typical conditions for C–N coupling reactions (heat and strong base). However, the reactions conducted with the weaker base KOPh, which has rarely been used in cross-coupling to form C–N bonds, occurred in high yield in the presence of a catalyst derived from commercially available AdBippyPhos and [Pd(allyl)Cl]2. Under these conditions, the reactions occur with low catalyst loadings (<0.50 mol % for most substrates) and tolerate the presence of various functional groups that react with the strong bases that are typically used in Pd-catalyzed C–N cross-coupling reactions of aryl halides. The resting state of the catalyst is the phenoxide complex, (BippyPhosPd(Ar)OPh); due to the electron-withdrawing property of the fluoroalkyl substituent, the turnover-limiting step of the reaction is reductive elimination to form the C–N bond. PMID:26065341

  5. Catalyzed D-D stellarator reactor

    SciTech Connect

    Sheffield, John; Spong, Donald A.

    2016-05-12

    The advantages of using the catalyzed deuterium-deuterium (D-D) approach for a fusion reactor—lower and less energetic neutron flux and no need for a tritium breeding blanket—have been evaluated in previous papers, giving examples of both tokamak and stellarator reactors. This paper presents an update for the stellarator example, taking account of more recent empirical transport scaling results and design studies of lower-aspect-ratio stellarators. We use a modified version of the Generic Magnetic Fusion Reactor model to cost a stellarator-type reactor. Recently, this model has been updated to reflect the improved science and technology base and costs in the magnetic fusion program. Furthermore, it is shown that an interesting catalyzed D-D, stellarator power plant might be possible if the following parameters could be achieved: R/ ≈ 4, required improvement factor to ISS04 scaling, FR = 0.9 to 1.15, <β> ≈ 8.0% to 11.5%, Zeff ≈ 1.45 plus a relativistic temperature correction, fraction of fast ions lost ≈ 0.07, Bm ≈ 14 to 16 T, and R ≈ 18 to 24 m.

  6. Catalyzed D-D stellarator reactor

    DOE PAGES

    Sheffield, John; Spong, Donald A.

    2016-05-12

    The advantages of using the catalyzed deuterium-deuterium (D-D) approach for a fusion reactor—lower and less energetic neutron flux and no need for a tritium breeding blanket—have been evaluated in previous papers, giving examples of both tokamak and stellarator reactors. This paper presents an update for the stellarator example, taking account of more recent empirical transport scaling results and design studies of lower-aspect-ratio stellarators. We use a modified version of the Generic Magnetic Fusion Reactor model to cost a stellarator-type reactor. Recently, this model has been updated to reflect the improved science and technology base and costs in the magnetic fusionmore » program. Furthermore, it is shown that an interesting catalyzed D-D, stellarator power plant might be possible if the following parameters could be achieved: R/ ≈ 4, required improvement factor to ISS04 scaling, FR = 0.9 to 1.15, <β> ≈ 8.0% to 11.5%, Zeff ≈ 1.45 plus a relativistic temperature correction, fraction of fast ions lost ≈ 0.07, Bm ≈ 14 to 16 T, and R ≈ 18 to 24 m.« less

  7. Palladium-Catalyzed Arylation of Fluoroalkylamines.

    PubMed

    Brusoe, Andrew T; Hartwig, John F

    2015-07-08

    We report the synthesis of fluorinated anilines by palladium-catalyzed coupling of fluoroalkylamines with aryl bromides and aryl chlorides. The products of these reactions are valuable because anilines typically require the presence of an electron-withdrawing substituent on nitrogen to suppress aerobic or metabolic oxidation, and the fluoroalkyl groups have steric properties and polarity distinct from those of more common electron-withdrawing amide and sulfonamide units. The fluoroalkylaniline products are unstable under typical conditions for C-N coupling reactions (heat and strong base). However, the reactions conducted with the weaker base KOPh, which has rarely been used in cross-coupling to form C-N bonds, occurred in high yield in the presence of a catalyst derived from commercially available AdBippyPhos and [Pd(allyl)Cl]2. Under these conditions, the reactions occur with low catalyst loadings (<0.50 mol % for most substrates) and tolerate the presence of various functional groups that react with the strong bases that are typically used in Pd-catalyzed C-N cross-coupling reactions of aryl halides. The resting state of the catalyst is the phenoxide complex, (BippyPhosPd(Ar)OPh); due to the electron-withdrawing property of the fluoroalkyl substituent, the turnover-limiting step of the reaction is reductive elimination to form the C-N bond.

  8. Catalyzed D-D stellarator reactor

    SciTech Connect

    Sheffield, John; Spong, Donald A.

    2016-05-12

    The advantages of using the catalyzed deuterium-deuterium (D-D) approach for a fusion reactor—lower and less energetic neutron flux and no need for a tritium breeding blanket—have been evaluated in previous papers, giving examples of both tokamak and stellarator reactors. This paper presents an update for the stellarator example, taking account of more recent empirical transport scaling results and design studies of lower-aspect-ratio stellarators. We use a modified version of the Generic Magnetic Fusion Reactor model to cost a stellarator-type reactor. Recently, this model has been updated to reflect the improved science and technology base and costs in the magnetic fusion program. Furthermore, it is shown that an interesting catalyzed D-D, stellarator power plant might be possible if the following parameters could be achieved: R/ ≈ 4, required improvement factor to ISS04 scaling, FR = 0.9 to 1.15, <β> ≈ 8.0% to 11.5%, Zeff ≈ 1.45 plus a relativistic temperature correction, fraction of fast ions lost ≈ 0.07, Bm ≈ 14 to 16 T, and R ≈ 18 to 24 m.

  9. Antibody-catalyzed anaerobic destruction of methamphetamine

    PubMed Central

    Xu, Yang; Hixon, Mark S.; Yamamoto, Noboru; McAllister, Laura A.; Wentworth, Anita D.; Wentworth, Paul; Janda, Kim D.

    2007-01-01

    Methamphetamine [(+)-2] abuse has emerged as a fast-rising global epidemic, with immunopharmacotherapeutic approaches being sought for its treatment. Herein, we report the generation and characterization of a monoclonal antibody, YX1-40H10, that catalyzes the photooxidation of (+)-2 into the nonpsychoactive compound benzaldehyde (14) under anaerobic conditions in the presence of riboflavin (6). Studies have revealed that the antibody facilitates the conversion of (+)-2 into 14 by binding the triplet photoexcited state of 6 in proximity to (+)-2. The antibody binds riboflavin (Kd = 180 μM), although this was not programmed into hapten design, and the YX1-40H10-catalyzed reaction is inhibited by molecular oxygen via the presumed quenching of the photoexcited triplet state of 6. Given that this reaction is another highlight in the processing of reactive intermediates by antibodies, we speculate that this process may have future significance in vivo with programmed immunoglobulins that use flavins as cofactors to destroy selectable molecular targets under hypoxic or even anoxic conditions. PMID:17360412

  10. Manganese Catalyzed C-H Halogenation.

    PubMed

    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-Mn(V)═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 formation. Indeed, this idea

  11. Manganese Catalyzed C–H Halogenation

    SciTech Connect

    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

  12. Structured lipids via lipase-catalyzed incorporation of eicosapentaenoic acid into borage (Borago officinalis L.) and evening primrose (Oenothera biennis L.) oils.

    PubMed

    Senanayake, S P J Namal; Shahidi, Fereidoon

    2002-01-30

    Enzymatic acidolysis of borage oil (BO) or evening primrose oil (EPO) with eicosapentaenoic acid (20:5n-3; EPA) was studied. Of the six lipases that were tested in the initial screening, nonspecific lipase PS-30 from Pseudomonas sp. resulted in the highest incorporation of EPA into both oils. This enzyme was further studied for the influence of enzyme load, temperature, time, type of organic solvent, and mole ratio of substrates. The products from the acidolysis reaction were analyzed by gas chromatography (GC). The highest incorporation of EPA in both oils occurred at 45-55 degrees C and at 150-250 enzyme activity units. One unit of lipase activity was defined as nanomoles of fatty acids (oleic acid equivalents) produced per minute per gram of enzyme. Time course studies indicated that EPA incorporation was increased up to 26.8 and 25.2% (after 24 h) in BO and EPO, respectively. Among the solvents examined, n-hexane served best for the acidolysis of EPA with both oils. The effect of the mole ratio of oil to EPA was studied from 1:1 to 1:3. As the mole ratio of EPA increased, the incorporation increased from 25.2-26.8 to 37.4-39.9% (after 24 h). The highest EPA incorporations of 39.9 and 37.4% in BO and EPO, respectively, occurred at the stoichiometric mole ratio of 1:3 for oil to EPA.

  13. Enantioselective Construction of Acyclic Quaternary Carbon Stereocenters: Palladium-Catalyzed Decarboxylative Allylic Alkylation of Fully Substituted Amide Enolates.

    PubMed

    Starkov, Pavel; Moore, Jared T; Duquette, Douglas C; Stoltz, Brian M; Marek, Ilan

    2017-07-19

    We report a divergent and modular protocol for the preparation of acyclic molecular frameworks containing newly created quaternary carbon stereocenters. Central to this approach is a sequence composed of a (1) regioselective and -retentive preparation of allyloxycarbonyl-trapped fully substituted stereodefined amide enolates and of a (2) enantioselective palladium-catalyzed decarboxylative allylic alkylation reaction using a novel bisphosphine ligand.

  14. Acid-Catalyzed Isomerization of Carvone to Carvacrol

    ERIC Educational Resources Information Center

    Kjonaas, Richard A.; Mattingly, Shawn P.

    2005-01-01

    The acid-catalyzed isomerization of carvone to carvacrol, first reported by Ritter and Ginsburg, is especially well suited with a permanent-magnet FT instrument. The acid-catalyzed isomerization of carvone to carvacrol produced a 61% yield after a three hour reflux with 30% aqueous sulfuric acid.

  15. ENVIRONMENTAL TECHNOLOGY VERIFICATION REPORT: ENVIROFUELS DIESEL FUEL CATALYZER FUEL ADDITIVE

    EPA Science Inventory

    EPA's Environmental Technology Verification Program has tested EnviroFuels diesel fuel additive, called the Diesel Fuel Catalyzer. EnviroFuels has stated that heavy-duty on and off road diesel engines are the intended market for the catalyzer. Preliminary tests conducted indicate...

  16. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    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…

  17. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    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…

  18. Acid-Catalyzed Isomerization of Carvone to Carvacrol

    ERIC Educational Resources Information Center

    Kjonaas, Richard A.; Mattingly, Shawn P.

    2005-01-01

    The acid-catalyzed isomerization of carvone to carvacrol, first reported by Ritter and Ginsburg, is especially well suited with a permanent-magnet FT instrument. The acid-catalyzed isomerization of carvone to carvacrol produced a 61% yield after a three hour reflux with 30% aqueous sulfuric acid.

  19. ENVIRONMENTAL TECHNOLOGY VERIFICATION REPORT: ENVIROFUELS DIESEL FUEL CATALYZER FUEL ADDITIVE

    EPA Science Inventory

    EPA's Environmental Technology Verification Program has tested EnviroFuels diesel fuel additive, called the Diesel Fuel Catalyzer. EnviroFuels has stated that heavy-duty on and off road diesel engines are the intended market for the catalyzer. Preliminary tests conducted indicate...

  20. RNA-Catalyzed RNA Ligation on an External RNA Template

    NASA Technical Reports Server (NTRS)

    McGinness, Kathleen E.; Joyce, Gerald F.

    2002-01-01

    Variants of the hc ligase ribozyme, which catalyzes ligation of the 3' end of an RNA substrate to the 5' end of the ribozyme, were utilized to evolve a ribozyme that catalyzes ligation reactions on an external RNA template. The evolved ribozyme catalyzes the joining of an oligonucleotide 3'-hydroxyl to the 5'-triphosphate of an RNA hairpin molecule. The ribozyme can also utilize various substrate sequences, demonstrating a largely sequence-independent mechanism for substrate recognition. The ribozyme also carries out the ligation of two oligonucleotides that are bound at adjacent positions on a complementary template. Finally, it catalyzes addition of mononucleoside '5-triphosphates onto the '3 end of an oligonucleotide primer in a template-dependent manner. The development of ribozymes that catalyze polymerase-type reactions contributes to the notion that an RNA world could have existed during the early history of life on Earth.

  1. Fabrication of catalyzed ion transport membrane systems

    DOEpatents

    Carolan, Michael Francis; Kibby, Charles Leonard

    2013-06-04

    Process for fabricating a catalyzed ion transport membrane (ITM). In one embodiment, an uncatalyzed ITM is (a) contacted with a non-reducing gaseous stream while heating to a temperature and for a time period sufficient to provide an ITM possessing anion mobility; (b) contacted with a reducing gaseous stream for a time period sufficient to provide an ITM having anion mobility and essentially constant oxygen stoichiometry; (c) cooled while contacting the ITM with the reducing gaseous stream to provide an ITM having essentially constant oxygen stoichiometry and no anion mobility; and (d) treated by applying catalyst to at least one of (1) a porous mixed conducting multicomponent metallic oxide (MCMO) layer contiguous with a first side of a dense layer of MCMO and (2) a second side of the dense MCMO layer. In another embodiment, these steps are carried out in the alternative order of (a), (d), (b), and (c).

  2. Enzyme-catalyzed, gas-phase reactions.

    PubMed

    Barzana, E; Klibanov, A M; Karel, M

    1987-06-01

    Dehydrated preparations of alcohol oxidase adsorbed on DEAE-cellulose vigorously catalyze a gas-phase oxidation of ethanol vapors with molecular oxygen. The gas-phase reaction is strongly dependent on the water activity of the system. The enzymatic activity is severely inhibited by the product hydrogen peroxide. This inhibition can be alleviated, however, by an addition of catalase or peroxidase to the dry preparation. Such dehydrated, bienzymic catalysts afford a complete and selective conversion of the substrate to acetaldehyde. Dry alcohol oxidase is much more thermostable than in aqueous solution. The results of this work suggest that dehydrated enzymes have potential applications in the analysis of gaseous compounds and in the development of novel gas-solid bioreactors.

  3. Dopant-Catalyzed Singlet Exciton Fission.

    PubMed

    Snamina, Mateusz; Petelenz, Piotr

    2017-01-04

    In acene-based molecular crystals, singlet exciton fission occurs through superexchange mediated by two virtual charge-transfer states. Hence, it is sensitive to their energies, which depend on the local environment. The crucial point is the balance between the charge-quadrupole interactions within the pair of molecules directly involved in the process and those with the surrounding crystal matrix, which are governed by local symmetry and may be influenced by breaking this symmetry. This happens, for example, in the vicinity of a vacancy or an impurity and in the latter case is complemented by polarization energy and potentially by dipolar contributions. Our model calculations indicate that the superexchange coupling is sensitive enough to these factors to enable fission to be catalyzed by judiciously designed dopant molecules. In favorable cases, dipolar dopants are expected to increase the fission rate by an order of magnitude.

  4. Rhodium-Catalyzed Alkene Difunctionalization with Nitrenes.

    PubMed

    Ciesielski, Jennifer; Dequirez, Geoffroy; Retailleau, Pascal; Gandon, Vincent; Dauban, Philippe

    2016-06-27

    The Rh(II) -catalyzed oxyamination and diamination of alkenes generate 1,2-amino alcohols and 1,2-diamines, respectively, in good to excellent yields and with complete regiocontrol. In the case of diamination, the intramolecular reaction provides an efficient method for the preparation of pyrrolidines, and the intermolecular reaction produces vicinal amines with orthogonal protecting groups. These alkene difunctionalizations proceed by aziridination followed by nucleophilic ring opening induced by an Rh-bound nitrene generated in situ, details of which were uncovered by both experimental and theoretical studies. In particular, DFT calculations show that the nitrogen atom of the putative [Rh]2 =NR metallanitrene intermediate is electrophilic and support an aziridine activation pathway by N⋅⋅⋅N=[Rh]2 bond formation, in addition to the N⋅⋅⋅[Rh]2 =NR coordination mode. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Palladium-Catalyzed Aminocarbonylation of Allylic Alcohols.

    PubMed

    Li, Haoquan; Neumann, Helfried; Beller, Matthias

    2016-07-11

    A benign and efficient palladium-catalyzed aminocarbonylation reaction of allylic alcohols is presented. The generality of this novel process is demonstrated by the synthesis of β,γ-unsaturated amides including aliphatic, cinnamyl, and terpene derivatives. The choice of ligand is crucial for optimal carbonylation processes: Whereas in most cases the combination of PdCl2 with Xantphos (L6) gave best results, sterically hindered substrates performed better in the presence of simple triphenylphosphine (L10), and primary anilines gave the best results using cataCXium® PCy (L8). The reactivity of the respective catalyst system is significantly enhanced by addition of small amounts of water. Mechanistic studies and control experiments revealed a tandem allylic alcohol amination/C-N bond carbonylation reaction sequence.

  6. Enzyme-catalyzed degradation of carbon nanomaterials

    NASA Astrophysics Data System (ADS)

    Kotchey, Gregg P.

    Carbon nanotubes and graphene, the nanoscale sp 2 allotropes of carbon, have garnered widespread attention as a result of their remarkable electrical, mechanical, and optical properties and the promise of new technologies that harness these properties. Consequently, these carbon nanomaterials (CNMs) have been employed for diverse applications such as electronics, sensors, composite materials, energy conversion devices, and nanomedicine. The manufacture and eventual disposal of these products may result in the release of CNMs into the environment and subsequent exposure to humans, animals, and vegetation. Given the possible pro-inflammatory and toxic effects of CNMs, much attention has been focused on the distribution, toxicity, and persistence of CNMs both in living systems and the environment. This dissertation will guide the reader though recent studies aimed at elucidating fundamental insight into the persistence of CNMs such as carbon nanotubes (CNTs) and graphene derivatives (i.e., graphene oxide and reduced graphene oxide). In particular, in-testtube oxidation/degradation of CNMs catalyzed by peroxidase enzymes will be examined, and the current understanding of the mechanisms underlying these processes will be discussed. Finally, an outlook of the current field including in vitro and in vivo biodegradation experiments, which have benefits in terms of human health and environmental safety, and future directions that could have implications for nanomedical applications such as imaging and drug delivery will be presented. Armed with an understanding of how and why CNMs undergo enzyme-catalyzed oxidation/biodegradation, researchers can tailor the structure of CNMs to either promote or inhibit these processes. For example, in nanomedical applications such as drug delivery, the incorporation of carboxylate functional groups could facilitate biodegradation of the nanomaterial after delivery of the cargo. Also, the incorporation of CNMs with defect sites in consumer

  7. Thermodynamic limitations on microbially catalyzed reaction rates

    NASA Astrophysics Data System (ADS)

    LaRowe, Douglas E.; Dale, Andrew W.; Amend, Jan P.; Van Cappellen, Philippe

    2012-08-01

    Quantification of global biogeochemical cycles requires knowledge of the rates at which microorganisms catalyze chemical reactions. In order for models that describe these processes to capture global patterns of change, the underlying formulations in them must account for biogeochemical transformations over seasonal and millennial time scales in environments characterized by different energy levels. Building on existing models, a new thermodynamic limiting function is introduced. With only one adjustable parameter, this function that can be used to model microbial metabolism throughout the range of conditions in which organisms are known to be active. The formulation is based on a comparison of the amount of energy available from any redox reaction to the energy required to maintain a membrane potential, a proxy for the minimum amount of energy required by an active microorganism. This function does not require species- or metabolism-specific parameters, and can be used to model metabolisms that capture any amount of energy. The utility of this new thermodynamic rate limiting term is illustrated by applying it to three low-energy processes: fermentation, methanogenesis and sulfate reduction. The model predicts that the rate of fermentation will be reduced by half once the Gibbs energy of the catalyzed reaction reaches -12 kJ (mol e-)-1, and then slowing exponentially until the energy yield approaches zero. Similarly, the new model predicts that the low energy yield of methanogenesis, -4 to -0.5 kJ (mol e-)-1, for a partial pressure of H2 between 11 and 0.6 Pa decreases the reaction rate by 95-99%. Finally, the new function's utility is illustrated through its ability to accurately model sulfate concentration data in an anoxic marine sediment.

  8. Convergent stereoselective synthesis of the visual pigment A2E.

    PubMed

    Sicre, Cristina; Cid, M Magdalena

    2005-12-08

    [chemical reaction: see text]. A stereoselective total synthesis of the visual pigment A2E has been achieved with use of palladium-catalyzed cross-coupling reactions in all key steps: a regioselective Suzuki or Negishi coupling of 2,4-dibromopyridine, a Sonogashira reaction, and a double Stille cross-coupling to complete the bispolyenyl skeleton.

  9. NEW CORDIERITE DIESEL PARTICULATE FILTERS FOR CATALYZED AND NON-CATALYZED APPLICATIONS

    SciTech Connect

    Merkel, G; Cutler, W; Tao, T Chiffey, A; Phillips, P; Twigg, M; Walker, A

    2003-08-24

    Cordierite diesel particulate filters provide an economical approach to diesel emissions control. However, further reduction in the pressure drop of catalyzed and non-catalyzed cordierite filters is desirable. In order to derive a fundamental understanding of the relationship between clean and sootloaded pressure drop and the pore microstructure of the ceramic, and to optimize the microstructure for filter performance, cordierite filters have been fabricated spanning an extended range in porosity, pore size distribution, and pore connectivity. Analysis of the results has been applied to the development of several new cordierite diesel particulate filters that possess a unique combination of high filtration efficiency, high strength, and very low clean and soot-loaded pressure drop. Furthermore, catalyst systems have been developed that result in a minimal pressure drop increase of the catalyzed filter. Optimization of porosity and cell geometry has enabled fabrication o f filters with either high or low thermal mass appropriate to the regeneration strategy employed for a given engine management system.

  10. Oxygenase-catalyzed ribosome hydroxylation occurs in prokaryotes and humans.

    PubMed

    Ge, Wei; Wolf, Alexander; Feng, Tianshu; Ho, Chia-hua; Sekirnik, Rok; Zayer, Adam; Granatino, Nicolas; Cockman, Matthew E; Loenarz, Christoph; Loik, Nikita D; Hardy, Adam P; Claridge, Timothy D W; Hamed, Refaat B; Chowdhury, Rasheduzzaman; Gong, Lingzhi; Robinson, Carol V; Trudgian, David C; Jiang, Miao; Mackeen, Mukram M; McCullagh, James S; Gordiyenko, Yuliya; Thalhammer, Armin; Yamamoto, Atsushi; Yang, Ming; Liu-Yi, Phebee; Zhang, Zhihong; Schmidt-Zachmann, Marion; Kessler, Benedikt M; Ratcliffe, Peter J; Preston, Gail M; Coleman, Mathew L; Schofield, Christopher J

    2012-12-01

    The finding that oxygenase-catalyzed protein hydroxylation regulates animal transcription raises questions as to whether the translation machinery and prokaryotic proteins are analogously modified. Escherichia coli ycfD is a growth-regulating 2-oxoglutarate oxygenase catalyzing arginyl hydroxylation of the ribosomal protein Rpl16. Human ycfD homologs, Myc-induced nuclear antigen (MINA53) and NO66, are also linked to growth and catalyze histidyl hydroxylation of Rpl27a and Rpl8, respectively. This work reveals new therapeutic possibilities via oxygenase inhibition and by targeting modified over unmodified ribosomes.

  11. Particle growth by acid-catalyzed heterogeneous reactions of organic carbonyls on preexisting aerosols.

    PubMed

    Jang, Myoseon; Carroll, Brian; Chandramouli, Bharadwaj; Kamens, Richard M

    2003-09-01

    Aerosol growth by the heterogeneous reactions of different aliphatic and alpha,beta-unsaturated carbonyls in the presence/absence of acidified seed aerosols was studied in a 2 m long flow reactor (2.5 cm i.d.) and a 0.5-m3 Teflon film bag under darkness. For the flow reactor experiments, 2,4-hexadienal, 5-methyl-3-hexen-2-one, 2-cyclohexenone, 3-methyl-2-cyclopentenone, 3-methyl-2-cyclohexenone, and octanal were studied. The carbonyls were selected based on their reactivity for acid-catalyzed reactions, their proton affinity, and their similarity to the ring-opening products from the atmospheric oxidation of aromatics. To facilitate acid-catalyzed heterogeneous hemiacetal/acetal formation, glycerol was injected along with inorganic seed aerosols into the flow reactor system. Carbonyl heterogeneous reactions were accelerated in the presence of acid catalysts (H2SO4), leading to higher aerosol yields than in their absence. Aldehydes were more reactive than ketones for acid-catalyzed reactions. The conjugated functionality also resulted in higher organic aerosol yieldsthan saturated aliphatic carbonyls because conjugation with the olefinic bond increases the basicity of the carbonyl leading to increased stability of the protonated carbonyl. Aerosol population was measured from a series of sampling ports along the length of the flow reactor using a scanning mobility particle sizer. Fourier transform infrared spectrometry of either an impacted liquid aerosol layer or direct reaction of carbonyls as a thin liquid layer on a zinc selenide FTIR disk was employed to demonstrate the direct transformation of chemical functional groups via the acid-catalyzed reactions. These results strongly indicate that atmospheric multifunctional organic carbonyls, which are created by atmospheric photooxidation reactions, can contribute significantly to secondary organic aerosol formation through acid-catalyzed heterogeneous reactions. Exploratory studies in 25- and 190-m3 outdoor chambers

  12. Peptide Bond Formation Mechanism Catalyzed by Ribosome.

    PubMed

    Świderek, Katarzyna; Marti, Sergio; Tuñón, Iñaki; Moliner, Vicent; Bertran, Juan

    2015-09-23

    In this paper we present a study of the peptide bond formation reaction catalyzed by ribosome. Different mechanistic proposals have been explored by means of Free Energy Perturbation methods within hybrid QM/MM potentials, where the chemical system has been described by the M06-2X functional and the environment by means of the AMBER force field. According to our results, the most favorable mechanism in the ribosome would proceed through an eight-membered ring transition state, involving a proton shuttle mechanism through the hydroxyl group of the sugar and a water molecule. This transition state is similar to that described for the reaction in solution (J. Am. Chem. Soc. 2013, 135, 8708-8719), but the reaction mechanisms are noticeably different. Our simulations reproduce the experimentally determined catalytic effect of ribosome that can be explained by the different behavior of the two environments. While the solvent reorganizes during the chemical process involving an entropic penalty, the ribosome is preorganized in the formation of the Michaelis complex and does not suffer important changes along the reaction, dampening the charge redistribution of the chemical system.

  13. Mechanisms of bacterially catalyzed reductive dehalogenation

    SciTech Connect

    Picardal, Flynn William

    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.

  14. Peptide Bond Formation Mechanism Catalyzed by Ribosome

    PubMed Central

    Świderek, Katarzyna; Marti, Sergio; Tuñón, Iñaki; Moliner, Vicent; Bertran, Juan

    2015-01-01

    In this paper we present a study of the peptide bond formation reaction catalyzed by ribosome. Different mechanistic proposals have been explored by means of Free Energy Perturbation methods within hybrid QM/MM potentials, where the chemical system has been described by the M06-2X functional and the environment by means of the AMBER force field. According to our results, the most favourable mechanism in the ribosome would proceed through an eight-membered ring transition state, involving a proton shuttle mechanism through the hydroxyl group of the sugar and a water molecule. This transition state is similar to that described for the reaction in solution (J. Am. Chem. Soc. 2013, 135, 8708–8719) but the reaction mechanisms are noticeable different. Our simulations reproduce the experimentally determined catalytic effect of ribosome that can be explained by the different behaviour of the two environments. While the solvent reorganizes during the chemical process involving an entropic penalty, the ribosome is preorganized in the formation of the Michaelis complex and does not suffer important changes along the reaction, dampening the charge redistribution of the chemical system. PMID:26325003

  15. Thioglycoside hydrolysis catalyzed by {beta}-glucosidase

    SciTech Connect

    Shen Hong; Byers, Larry D.

    2007-10-26

    Sweet almond {beta}-glucosidase (EC 3.2.1.21) has been shown to have significant thioglycohydrolase activity. While the K{sub m} values for the S- and O-glycosides are similar, the k{sub cat} values are about 1000-times lower for the S-glycosides. Remarkably, the pH-profile for k{sub cat}/K{sub m} for hydrolysis of p-nitrophenyl thioglucoside (pNPSG) shows the identical dependence on a deprotonated carboxylate (pK{sub a} 4.5) and a protonated group (pK{sub a} 6.7) as does the pH-profile for hydrolysis of the corresponding O-glycoside. Not surprisingly, in spite of the requirement for the presence of this protonated group in catalytically active {beta}-glucosidase, thioglucoside hydrolysis does not involve general acid catalysis. There is no solvent kinetic isotope effect on the enzyme-catalyzed hydrolysis of pNPSG.

  16. Toluene Monooxygenase-Catalyzed Epoxidation of Alkenes

    PubMed Central

    McClay, Kevin; Fox, Brian G.; Steffan, Robert J.

    2000-01-01

    Several toluene monooxygenase-producing organisms were tested for their ability to oxidize linear alkenes and chloroalkenes three to eight carbons long. Each of the wild-type organisms degraded all of the alkenes that were tested. Epoxides were produced during the oxidation of butene, butadiene, and pentene but not hexene or octadiene. A strain of Escherichia coli expressing the cloned toluene-4-monooxygenase (T4MO) of Pseudomonas mendocina KR1 was able to oxidize butene, butadiene, pentene, and hexene but not octadiene, producing epoxides from all of the substrates that were oxidized. A T4MO-deficient variant of P. mendocina KR1 oxidized alkenes that were five to eight carbons long, but no epoxides were detected, suggesting the presence of multiple alkene-degrading enzymes in this organism. The alkene oxidation rates varied widely (ranging from 0.01 to 0.33 μmol of substrate/min/mg of cell protein) and were specific for each organism-substrate pair. The enantiomeric purity of the epoxide products also varied widely, ranging from 54 to >90% of a single epoxide enantiomer. In the absence of more preferred substrates, such as toluene or alkenes, the epoxides underwent further toluene monooxygenase-catalyzed transformations, forming products that were not identified. PMID:10788354

  17. Iodide effects in transition metal catalyzed reactions.

    PubMed

    Maitlis, Peter M; Haynes, Anthony; James, Brian R; Catellani, Marta; Chiusoli, Gian Paolo

    2004-11-07

    The unique properties of I(-) allow it to be involved in several different ways in reactions catalyzed by the late transition metals: in the oxidative addition, the migration, and the coupling/reductive elimination steps, as well as in substrate activation. Most steps are accelerated by I(-)(for example through an increased nucleophilicity of the metal center), but some are retarded, because a coordination site is blocked. The "soft" iodide ligand binds more strongly to soft metals (low oxidation state, electron rich, and polarizable) such as the later and heavier transition metals, than do the other halides, or N- and O-centered ligands. Hence in a catalytic cycle that includes the metal in a formally low oxidation state there will be less tendency for the metal to precipitate (and be removed from the cycle) in the presence of I(-) than most other ligands. Iodide is a good nucleophile and is also easily and reversibly oxidized to I(2). In addition, I(-) can play key roles in purely organic reactions that occur as part of a catalytic cycle. Thus to understand the function of iodide requires careful analysis, since two or sometimes more effects occur in different steps of one single cycle. Each of these topics is illustrated with examples of the influence of iodide from homogeneous catalytic reactions in the literature: methanol carbonylation to acetic acid and related reactions; CO hydrogenation; imine hydrogenation; and C-C and C-N coupling reactions. General features are summarised in the Conclusions.

  18. A computational study of acid catalyzed aerosol reactions of atmospherically relevant epoxides.

    PubMed

    Piletic, Ivan R; Edney, Edward O; Bartolotti, Libero J

    2013-11-07

    Epoxides are important intermediates of atmospheric isoprene oxidation. Their subsequent reactions in the particle phase lead to the production of organic compounds detected in ambient aerosols. We apply density functional theory to determine the important kinetic factors that drive epoxide reactions in the particle phase. Specifically, the importance of acid catalysis and solvent polarity are investigated using a variety of epoxides and nucleophiles. The condensed phase is modeled using molecular clusters immersed in a dielectric continuum and a majority of the calculations are performed with the M062x density functional and the 6-311++G** basis set. Calculations of acid catalyzed epoxide hydrolysis transition states for simple primary, secondary and tertiary epoxides are consistent with an A-2 mechanism where the nucleophile (water) interacts with an epoxide carbon in the transition state. By applying transition state theory to this mechanism, the overall rate constants of epoxide reactions such as hydrolysis, organosulfate formation, organonitrate formation and oligomerization are determined. The calculations indicate that the acid catalyzed hydrolysis rate constant of 2-methyl-2,3-epoxybutane-1,4-diol (β-IEPOX--an isoprene epoxide produced under low NOx conditions) is approximately 30 times greater than 2-methyl-2,3-epoxypropanoic acid (MAE--methacrylic acid epoxide derived from isoprene and produced at high NOx concentrations). Furthermore, acid catalyzed organosulfate formation and epoxide oligomerization reactions are competitive and appear to be kinetically favorable over the hydrolysis of IEPOX.

  19. Base-catalyzed and cholinesterase-catalyzed hydrolysis of acetylcholine and optically active analogs.

    PubMed

    Schowen, K B; Smissman, E E; Stephen, W F

    1975-03-01

    The base- and cholinestrase-catalyzed hydrolyses of the following optically active analogs of acetylcholine were studied: 3 (a)-trimethylammonium-2(a)-acetoxy-trans-decalin iodide, threo- and erythro-alpha, beta-dimethylacetylcholine iodide, alpha-methylacetylcholine, and beta-methylacetylcholine. Evidence that the optimum dihedral +N-C-C-O angle in the transition state for acetylcholinesterase hydrolysis of acetylcholine analogs is positive and anticlinal is given. The data obtained suggest that acetylcholine undergoes a geometrically flexible mode of attachment to the enzyme.

  20. ENVIRONMENTAL ASSESSMENT OF THE BASE CATALYZED DECOMPOSITION (BCD) PROCESS

    EPA Science Inventory

    This report summarizes laboratory-scale, pilot-scale, and field performance data on BCD (Base Catalyzed Decomposition) and technology, collected to date by various governmental, academic, and private organizations.

  1. Diastereoselective Pt catalyzed cycloisomerization of polyenes to polycycles.

    PubMed

    Geier, Michael J; Gagné, Michel R

    2014-02-26

    Application of a tridentate NHC containing pincer ligand to Pt catalyzed cascade cyclization reactions has allowed for the catalytic, diastereoselective cycloisomerization of biogenic alkene terminated substrates to the their polycyclic counterparts.

  2. ENVIRONMENTAL ASSESSMENT OF THE BASE CATALYZED DECOMPOSITION (BCD) PROCESS

    EPA Science Inventory

    This report summarizes laboratory-scale, pilot-scale, and field performance data on BCD (Base Catalyzed Decomposition) and technology, collected to date by various governmental, academic, and private organizations.

  3. Rhodium-Catalyzed Dehydrogenative Borylation of Cyclic Alkenes

    PubMed Central

    Kondoh, Azusa; Jamison, Timothy F.

    2010-01-01

    A rhodium-catalyzed dehydrogenative borylation of cyclic alkenes is described. This reaction provides direct access to cyclic 1-alkenylboronic acid pinacol esters, useful intermediates in organic synthesis. Suzuki-Miyaura cross-coupling applications are also presented. PMID:20107646

  4. Pd-catalyzed arylation of chlorotrifluoroethylene using arylboronic acids.

    PubMed

    Yamamoto, Tetsuya; Yamakawa, Tetsu

    2012-07-06

    The palladium-catalyzed cross-coupling of chlorotrifluoroethylene and arylboronic acids proceeds in the presence of a base and H(2)O to provide α,β,β-trifluorostyrene derivatives in satisfactory yields.

  5. Amino acid salt catalyzed intramolecular Robinson annulation†‡

    PubMed Central

    Li, Pingfan; Yamamoto, Hisashi

    2009-01-01

    The silica gel absorbed amino acid salt catalyzed asymmetric intramolecular Robinson annulation reaction has been developed; up to 97% ee was obtained with this readily recoverable organocatalyst. PMID:19724802

  6. The Iron-Catalyzed Oxidation of Hydrazine by Nitric Acid

    SciTech Connect

    Karraker, D.G.

    2001-07-17

    To assess the importance of iron to hydrazine stability, the study of hydrazine oxidation by nitric acid has been extended to investigate the iron-catalyzed oxidation. This report describes those results.

  7. Pd-Catalyzed Decarbonylative Cross-Couplings of Aroyl Chlorides.

    PubMed

    Malapit, Christian A; Ichiishi, Naoko; Sanford, Melanie S

    2017-08-04

    This report describes a method for Pd-catalyzed decarbonylative cross-coupling that enables the conversion of carboxylic acid derivatives to biaryls, aryl amines, aryl ethers, aryl sulfides, aryl boronate esters, and trifluoromethylated arenes. The success of this transformation leverages the Pd(0)/Brettphos-catalyzed decarbonylative chlorination of aroyl chlorides, which can then participate in diverse cross-coupling reactions in situ using the same Pd catalyst.

  8. Nickel-Catalyzed Coupling of Alkenes, Aldehydes, and Silyl Triflates

    PubMed Central

    Ng, Sze-sze; Ho, Chun-Yu; Jamison, Timothy F.

    2011-01-01

    A full account of two recently developed nickel-catalyzed coupling reactions of alkenes, aldehydes and silyl triflates is presented. These reactions provide either allylic alcohol or homoallylic alcohol derivatives selectively, depending on the ligand employed. These processes are believed to be mechanistically distinct from Lewis acid-catalyzed carbonyl-ene reactions, and several lines of evidence supporting this hypothesis are discussed. PMID:16939275

  9. New mechanistic studies on the proline-catalyzed aldol reaction

    PubMed Central

    List, Benjamin; Hoang, Linh; Martin, Harry J.

    2004-01-01

    The mechanism of the proline-catalyzed aldol reaction has stimulated considerable debate, and despite limited experimental data, at least five different mechanisms have been proposed. Complementary to recent theoretical studies we have initiated an experimental program with the goal of clarifying some of the basic mechanistic questions concerning the proline-catalyzed aldol reaction. Here we summarize our discoveries in this area and provide further evidence for the involvement of enamine intermediates. PMID:15073330

  10. Acidolysis of Poly(4-Methyl-1,3-Dioxolane).

    DTIC Science & Technology

    1986-01-10

    it formed as a water azeotrope until distillate temperature reached 900. At this point more reactants (a 1:1 mixture ) were added and the reaction was...800 and finally with three 160 mL portions of water at 800. Toluene / water azeotrope was then distilled (1 atm) followed by distillation of the...in 480 mL toluene precooled to 00. The final tmperature was -80. The toluene solution was washed with 1 eq. potassium hydroxide in 160 niL water at

  11. Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies

    NASA Technical Reports Server (NTRS)

    Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

    1988-01-01

    The surface-catalyzed air oxidation reactions of fuel hydrazines were studied in a 6500-liter fluorocarbon-film chamber at 80 to 100 ppm concentrations. First-order rate constants for the reactions catalyzed by aluminum, water-damaged aluminum (Al/Al2O3), stainless steel 304L, galvanized steel and titanium plates with surface areas of 2 to 24 sq m were determined. With 23.8 sq m of Al/Al2O3 the surface-catalyzed air oxidation of hydrazine had a half-life of 2 hours, diimide (N2H2) was observed as an intermediate and traces of ammonia were present in the final product mixture. The Al/Al2O3 catalyzed oxidation of monomethylhydrazine yielded methyldiazine (HN = NCH3) as an intermediate and traces of methanol. Unsymmetrical dimethylhydrazine gave no detectable products. The relative reactivities of hydrazine, MMH and UDMH were 130 : 7.3 : 1.0, respectively. The rate constants for Al/Al2O3-catalyzed oxidation of hydrazine and MMH were proportional to the square of the surface area of the plates. Mechanisms for the surface-catalyzed oxidation of hydrazine and diimide and the formation of ammonia are proposed.

  12. Conservation Kickstart- Catalyzing Conservation Initiatives Worldwide

    NASA Astrophysics Data System (ADS)

    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

  13. Homologation of α-aryl amino acids through quinone-catalyzed decarboxylation/Mukaiyama-Mannich addition.

    PubMed

    Haugeberg, Benjamin J; Phan, Johnny H; Liu, Xinyun; O'Connor, Thomas J; Clift, Michael D

    2017-03-09

    A new method for amino acid homologation by way of formal C-C bond functionalization is reported. This method utilizes a 2-step/1-pot protocol to convert α-amino acids to their corresponding N-protected β-amino esters through quinone-catalyzed oxidative decarboxylation/in situ Mukaiyama-Mannich addition. The scope and limitations of this chemistry are presented. This methodology provides an alternative to the classical Arndt-Eistert homologation for accessing β-amino acid derivatives. The resulting N-protected amine products can be easily deprotected to afford the corresponding free amines.

  14. Synthesis of Allenamides by Copper-Catalyzed Coupling of Propargylic Bromides and Nitrogen Nucleophiles.

    PubMed

    Demmer, Charles S; Benoit, Emeline; Evano, Gwilherm

    2016-03-18

    An efficient and general synthesis of allenamides derived from oxazolidinones and hydantoins is reported. Upon activation with a combination of a copper catalyst and a 2,2'-bipyridine derivative in the presence of an inorganic base, propargylic bromides were found to be suitable reagents for the direct allenylation of nitrogen nucleophiles by a formal copper-catalyzed S(N)2' reaction. Besides the availability of the starting materials, notable features of this route to allenamides are its mild reaction conditions, the reaction being performed at room temperature in most cases, and its applicability to the preparation of mono-, di-, as well as trisubstituted allenamides.

  15. Base-Catalyzed Depolymerization of Biorefinery Lignins

    DOE PAGES

    Katahira, Rui; Mittal, Ashutosh; McKinney, Kellene; ...

    2016-01-12

    Lignocellulosic biorefineries will produce a substantial pool of lignin-enriched residues, which are currently slated to be burned for heat and power. Going forward, however, valorization strategies for residual solid lignin will be essential to the economic viability of modern biorefineries. To achieve these strategies, effective lignin depolymerization processes will be required that can convert specific lignin-enriched biorefinery substrates into products of sufficient value and market size. Base-catalyzed depolymerization (BCD) of lignin using sodium hydroxide and other basic media has been shown to be an effective depolymerization approach when using technical and isolated lignins relevant to the pulp and paper industry.more » Moreover, to gain insights in the application of BCD to lignin-rich, biofuels-relevant residues, here we apply BCD with sodium hydroxide at two catalyst loadings and temperatures of 270, 300, and 330 °C for 40 min to residual biomass from typical and emerging biochemical conversion processes. We obtained mass balances for each fraction from BCD, and characterized the resulting aqueous and solid residues using gel permeation chromatography, NMR, and GC–MS. When taken together, these results indicate that a significant fraction (45–78%) of the starting lignin-rich material can be depolymerized to low molecular weight, water-soluble species. The yield of the aqueous soluble fraction depends significantly on biomass processing method used prior to BCD. Namely, dilute acid pretreatment results in lower water-soluble yields compared to biomass processing that involves no acid pretreatment. We also find that the BCD product selectivity can be tuned with temperature to give higher yields of methoxyphenols at lower temperature, and a higher relative content of benzenediols with a greater extent of alkylation on the aromatic rings at higher temperature. Our study shows that residual, lignin-rich biomass produced from conventional and

  16. Hydroxymethylation beyond Carbonylation: Enantioselective Iridium-Catalyzed Reductive Coupling of Formaldehyde with Allylic Acetates via Enantiotopic π-Facial Discrimination.

    PubMed

    Garza, Victoria J; Krische, Michael J

    2016-03-23

    Chiral iridium complexes modified by SEGPHOS catalyze the 2-propanol-mediated reductive coupling of branched allylic acetates 1a-1o with formaldehyde to form primary homoallylic alcohols 2a-2o with excellent control of regio- and enantioselectivity. These processes, which rely on enantiotopic π-facial discrimination of σ-allyliridium intermediates, represent the first examples of enantioselective formaldehyde C-C coupling beyond aldol addition.

  17. 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.

    PubMed

    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.

  18. Cobalt-Catalyzed Alkylation of Aromatic Amines by Alcohols.

    PubMed

    Rösler, Sina; Ertl, Michael; Irrgang, Torsten; Kempe, Rhett

    2015-12-07

    The implementation of inexpensive, Earth-abundant metals in typical noble-metal-mediated chemistry is a major goal in homogeneous catalysis. A sustainable or green reaction that has received a lot of attention in recent years and is preferentially catalyzed by Ir or Ru complexes is the alkylation of amines by alcohols. It is based on the borrowing hydrogen or hydrogen autotransfer concept. Herein, we report on the Co-catalyzed alkylation of aromatic amines by alcohols. The reaction proceeds under mild conditions, and selectively generates monoalkylated amines. The observed selectivity allows the synthesis of unsymmetrically substituted diamines. A novel Co complex stabilized by a PN5 P ligand catalyzes the reactions most efficiently. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Divergent pathways lead to ESCRT-III-catalyzed membrane fission.

    PubMed

    Peel, Suman; Macheboeuf, Pauline; Martinelli, Nicolas; Weissenhorn, Winfried

    2011-04-01

    Endosomal sorting complexes required for transport (ESCRT) have been implicated in topologically similar but diverse cellular and pathological processes including multivesicular body (MVB) biogenesis, cytokinesis and enveloped virus budding. Although receptor sorting at the endosomal membrane producing MVBs employs the regulated assembly of ESCRT-0 followed by ESCRT-I, -II, -III and the vacuolar protein sorting (VPS)4 complex, other ESCRT-catalyzed processes require only a subset of complexes which commonly includes ESCRT-III and VPS4. Recent progress has shed light on the pathway of ESCRT assembly and highlights the separation of tasks of different ESCRT complexes and associated partners. The emerging picture suggests that among all ESCRT-catalyzed processes, divergent pathways lead to ESCRT-III assembly within the neck of a budding structure catalyzing membrane fission.

  20. Palladium-catalyzed modification of unprotected nucleosides, nucleotides, and oligonucleotides.

    PubMed

    Shaughnessy, Kevin H

    2015-05-22

    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.

  1. Highly efficient palladium-catalyzed hydrostannation of ethyl ethynyl ether.

    PubMed

    Andrews, Ian P; Kwon, Ohyun

    2008-12-08

    The palladium-catalyzed hydrostannation of acetylenes is widely exploited in organic synthesis as a means of forming vinyl stannanes for use in palladium-catalyzed cross-coupling reactions. Application of this methodology to ethyl ethynyl ether results in an enol ether that is challenging to isolate from the crude reaction mixture because of incompatibility with typical silica gel chromatography. Reported here is a highly efficient procedure for the palladium-catalyzed hydrostannation of ethyl ethynyl ether using 0.1% palladium(0) catalyst and 1.0 equiv of tributyltin hydride. The product obtained is a mixture of regioisomers that can be carried forward with exclusive reaction of the beta-isomer. This method is highly reproducible; relative to previously reported procedures, it is more economical and involves a more facile purification procedure.

  2. Metal-Catalyzed Asymmetric Michael Addition in Natural Product Synthesis.

    PubMed

    Hui, Chunngai; Pu, Fan; Xu, Jing

    2016-12-19

    Asymmetric catalysis for chiral compound synthesis is a rapidly growing field in modern organic chemistry. Asymmetric catalytic processes have been indispensable for the synthesis of enantioselective materials to meet demands from various fields. Michael addition has been used extensively for the construction of C-C bonds under mild conditions. With the discovery and development of organo- and metal-catalyzed asymmetric Michael additions, the synthesis of enantioselective and/or diastereoselective Michael adducts has become possible and increasingly prevalent in the literature. In particular, metal-catalyzed asymmetric Michael addition has been employed as a key reaction in natural product synthesis for the construction of contiguous quaternary stereogenic center(s), which is still a difficult task in organic synthesis. Previously reported applications of metal-catalyzed asymmetric Michael additions in natural product synthesis are presented here and discussed in depth.

  3. Stau-catalyzed big-bang nucleosynthesis reactions

    NASA Astrophysics Data System (ADS)

    Kamimura, Masayasu; Kino, Yasushi; Hiyama, Emiko

    2010-06-01

    We study the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X-) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X- particle has a lifetime of τX>~103 s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state and induces various types of reactions in which X- acts as a catalyst. Some of these X- catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements. We use a high-accuracy three-body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

  4. Phosphine-Catalyzed [4 + 2] Annulation: Synthesis of Cyclohexenes

    PubMed Central

    Tran, Yang S.

    2008-01-01

    Phosphine-catalyzed [4 + 2] annulations of α-alkylallenoates with activated olefins allow the efficient syntheses of cyclohexenes. Hexamethylphosphorous triamide (HMPT)-catalyzed [4 + 2] annulations of α-alkylallenoates with arylidenemalononitriles provided highly functionalized 5,5-dicyano-4,6-disubstituted cyclohex-1-enecarboxylates in excellent yields (77–98%) and moderate to high diastereoselectivities (1:2–12:1). Remarkably, the corresponding triarylphosphine-catalyzed [4 + 2] annulations of α-methylallenoate with arylidenemalononitriles manifested a polarity inversion of the 1,4-dipole synthon, providing 4,4-dicyano-5-substituted cyclohex-1-enecarboxylates in excellent yields (80–93%). The polarity inversion of α-alkylallenoates from one 1,4-dipole to another under phosphine catalysis presumably resulted from a change in the balance of the equilibrium between the phosphonium dienolate and the vinylogous phosphonium ylide intermediate. PMID:17914823

  5. Atom transfer and rearrangement reactions catalyzed by methyltrioxorhenium, MTO

    SciTech Connect

    Jacob, Josemon

    1999-05-10

    Methyltrioxorhenium (MTO) catalyzes the desulfurization of thiiranes by triphenylphosphine. Enormous enhancement in rate is observed when the catalyst is pretreated with hydrogen sulfide prior to the reaction. Using 2-mercaptomethylthiophenol as a ligand, the author synthesized several model complexes to study the mechanism of this reaction. With suitable model systems, they were able to show that the active catalyst is a Re(V) species. The reactions are highly stereospecific and very tolerant to functional groups. As part of the studies, he synthesized and crystallographically characterized the first examples of neutral terminal and bridging Re(V)sulfidocomplexes. Some of these complexes undergo fast oxygen atom transfer reactions with organic and inorganic oxidants. Studies on these model complexes led them to the discovery that MTO catalyzes the selective oxidation of thiols to disulfides. This report contains the Introduction; ``Chapter 6: Isomerization of Propargylic Alcohols to Enones and Enals Catalyzed by Methylrhenium Trioxide``; and Conclusions.

  6. Gold-Catalyzed Rearrangements and Beyond

    PubMed Central

    2013-01-01

    Cycloisomerizations of enynes are probably the most representative carbon–carbon bond forming reactions catalyzed by electrophilic metal complexes. These transformations are synthetically useful because chemists can use them to build complex architectures under mild conditions from readily assembled starting materials. However, these transformations can have complex mechanisms. In general, gold(I) activates alkynes in the presence of any other unsaturated functional group by forming an (η2-alkyne)–gold complex. This species reacts readily with nucleophiles, including electron-rich alkenes. In this case, the reaction forms cyclopropyl gold(I) carbene-like intermediates. These can come from different pathways depending on the substitution pattern of the alkyne and the alkene. In the absence of external nucleophiles, 1,n-enynes can form products of skeletal rearrangement in fully intramolecular reactions, which are mechanistically very different from metathesis reactions initiated by the [2 + 2] cycloaddition of a Grubbs-type carbene or other related metal carbenes. In this Account, we discuss how cycloisomerization and addition reactions of substituted enynes, as well as intermolecular reactions between alkynes and alkenes, are best interpreted as proceeding through discrete cationic intermediates in which gold(I) plays a significant role in the stabilization of the positive charge. The most important intermediates are highly delocalized cationic species that some chemists describe as cyclopropyl gold(I) carbenes or gold(I)-stabilized cyclopropylmethyl/cyclobutyl/homoallyl carbocations. However, we prefer the cyclopropyl gold(I) carbene formulation for its simplicity and mnemonic value, highlighting the tendency of these intermediates to undergo cyclopropanation reactions with alkenes. We can add a variety of hetero- and carbonucleophiles to the enynes in the presence of gold(I) in intra- or intermolecular reactions, leading to the corresponding adducts with

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

    PubMed Central

    Shah, Syed Adnan Ali; Tan, Huey Ling; Sultan, Sadia; Mohd Faridz, Muhammad Afifi Bin; Mohd Shah, Mohamad Azlan Bin; Nurfazilah, Sharifah; Hussain, Munawar

    2014-01-01

    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. PMID:25003642

  8. N-Heterocyclic-Carbene-Catalyzed Umpolung of Imines.

    PubMed

    Patra, Atanu; Mukherjee, Subrata; Das, Tamal Kanti; Jain, Shailja; Gonnade, Rajesh G; Biju, Akkattu T

    2017-03-01

    N-Heterocyclic carbene (NHC) catalysis has been widely used for the umpolung of aldehydes, and recently for the umpolung of Michael acceptors. Described herein is the umpolung of aldimines catalyzed by NHCs, and the reaction likely proceeds via aza-Breslow intermediates. The NHC-catalyzed intramolecular cyclization of aldimines bearing a Michael acceptor resulted in the formation of biologically important 2-(hetero)aryl indole 3-acetic-acid derivatives in moderate to good yields. The carbene generated from the bicyclic triazolium salt was found to be efficient for this transformation.

  9. Chromium(II)-catalyzed enantioselective arylation of ketones

    PubMed Central

    Wang, Gang; Sun, Shutao; Mao, Ying; Xie, Zhiyu

    2016-01-01

    The chromium-catalyzed enantioselective addition of carbo halides to carbonyl compounds is an important transformation in organic synthesis. However, the corresponding catalytic enantioselective arylation of ketones has not been reported to date. Herein, we report the first Cr-catalyzed enantioselective addition of aryl halides to both arylaliphatic and aliphatic ketones with high enantioselectivity in an intramolecular version, providing facile access to enantiopure tetrahydronaphthalen-1-ols and 2,3-dihydro-1H-inden-1-ols containing a tertiary alcohol. PMID:28144349

  10. Zirconium-Catalyzed Asymmetric Carboalumination of Unactivated Terminal Alkenes.

    PubMed

    Xu, Shiqing; Negishi, Ei-Ichi

    2016-10-18

    Carbometalation of alkenes with stereocontrol offers an important opportunity for asymmetric C-C bond formation. However, the scope of catalytic stereoselective carbometalation of alkenes had until recently been limited to electronically biased alkenes or those with the presence of directing groups or other auxiliary functionalities to overcome the challenge associated with regio- and stereoselectivity. Catalytic asymmetric carbometalation of unactivated alkenes on the other hand remained as a formidable challenge. To address this long-standing problem, we sought to develop Zr-catalyzed asymmetric carboalumination of alkenes (namely, ZACA reaction) encouraged by our discovery of Zr-catalyzed alkyne carboalumination in 1978. Zr-catalyzed methylalumination of alkynes (ZMA) shows high regioselectivity and nearly perfect stereoselectivity. Its mechanistic studies have revealed that the ZMA reaction involves acyclic carbometalation with "superacidic" bimetallic reagents generated by interaction between two Lewis acids, i.e., alkylalanes and 16-electron zirconocene derivatives through dynamic polarization and ate complexation, affectionately termed as the "two-is-better-than-one" principle. With the encouraging results of Zr-catalyzed carboalumination of alkynes in hand, we sought to develop its alkene version for discovering a catalytic asymmetric C-C bond-forming reaction by using alkylalanes and suitable chiral zirconocene derivatives, which would generate "superacidic" bimetallic species to promote the desired carbometalation of alkenes. However, this proved to be quite challenging. Three major competing side reactions occur, i.e., (i) β-H transfer hydrometalation, (ii) bimetallic cyclic carbometalation, and (iii) Ziegler-Natta polymerization. The ZACA reaction was finally discovered by employing Erker's (-)-(NMI)2ZrCl2 as the catalyst and chlorinated hydrocarbon as solvent to suppress the undesired side reactions mentioned above. The ZACA reaction has evolved as a

  11. Coalification by clay-catalyzed oligomerization of plant monomers

    SciTech Connect

    Orchin, M.; Wilson, R.M.

    1990-01-01

    The main objective of this research program is to devise laboratory methods to mimic the processes by which plants synthesize lignans, lignins and the processes by which these materials are transformed further by geochemical reactions catalyzed by certain clays to coal-like materials. We believe that the radical cation Diels-Alder reaction is one of the principal routes which transforms simple plant materials to coal-like substances and that such reactions may be catalyzed by clays that occur in the environment of the decaying plant materials. Progress is described.

  12. Molecular Mechanism by which One Enzyme Catalyzes Two Reactions

    NASA Astrophysics Data System (ADS)

    Nishimasu, Hiroshi; Fushinobu, Shinya; Wakagi, Takayoshi

    Unlike ordinary enzymes, fructose-1,6-bisphosphate (FBP) aldolase/phosphatase (FBPA/P) catalyzes two distinct reactions : (1) the aldol condensation of dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate to FBP, and (2) the dephosphorylation of FBP to fructose-6-phosphate. We solved the crystal structures of FBPA/P in complex with DHAP (its aldolase form) and FBP (its phosphatase form). The crystal structures revealed that FBPA/P exhibits the dual activities through a dramatic conformational change in the active-site architecture. Our findings expand the conventional concept that one enzyme catalyzes one reaction.

  13. New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

    SciTech Connect

    Huang, Qinhua

    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

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

    PubMed

    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.

  15. Umpolung of Michael acceptors catalyzed by N-heterocyclic carbenes.

    PubMed

    Fischer, Christian; Smith, Sean W; Powell, David A; Fu, Gregory C

    2006-02-08

    N-Heterocyclic carbenes can catalyze beta-alkylations of a range of alpha,beta-unsaturated esters, amides, and nitriles that bear pendant leaving groups to form a variety of ring sizes. In this process, the nucleophilic catalyst transiently transforms the normally electrophilic beta carbon into a nucleophilic site through an unanticipated addition-tautomerization sequence.

  16. Rh-Catalyzed Asymmetric Hydrogenation of 1,2-Dicyanoalkenes.

    PubMed

    Li, Meina; Kong, Duanyang; Zi, Guofu; Hou, Guohua

    2017-01-06

    A highly efficient enantioselective hydrogenation of 1,2-dicyanoalkenes catalyzed by the complex of rhodium and f-spiroPhos has been developed. A series of 1,2-dicyanoalkenes were successfully hydrogenated to the corresponding chiral 1,2-dicyanoalkanes under mild conditions with excellent enantioselectivities (up to 98% ee). This methodology provides efficient access to the asymmetric synthesis of chiral diamines.

  17. Total Synthesis of Gelsenicine via a Catalyzed Cycloisomerization Strategy

    PubMed Central

    Newcomb, Eric T.; Knutson, Phil C.; Pedersen, Blaine A.; Ferreira, Eric M.

    2016-01-01

    The first total synthesis of (±)-gelsenicine is reported. The synthetic route is highly efficient (13 steps), featuring (1) a pivotal metal-catalyzed isomerization/rearrangement process that forges the central core of the molecule and (2) two facile C–N bond-forming steps that establish the flanking heterocycles. PMID:26716762

  18. Synthesis of Cyclic Guanidines via Pd-Catalyzed Alkene Carboamination

    PubMed Central

    Zavesky, Blane P.; Babij, Nicholas R.; Fritz, Jonathan A.

    2013-01-01

    A new approach to the synthesis of substituted 5-membered cyclic guanidines is described. Palladium-catalyzed alkene carboamination reactions between acyclic N-allyl guanidines and aryl or alkenyl halides provide these products in good yield. This method allows access to a number of different cyclic guanidine derivatives in only two steps from readily available allylic amines. PMID:24147839

  19. N-heterocyclic carbene catalyzed direct carbonylation of dimethylamine.

    PubMed

    Li, Xiaonian; Liu, Kun; Xu, Xiaoliang; Ma, Lei; Wang, Hong; Jiang, Dahao; Zhang, Qunfeng; Lu, Chunshan

    2011-07-21

    N-Heterocyclic carbene (NHC) catalyzed direct carbonylation of dimethylamine leading to the formation of DMF was successfully accomplished under metal-free conditions. The catalytic efficiency was investigated and the turnover numbers can reach as high as >300. The possible mechanism was also proposed.

  20. Catalyzing Graduate Teaching Assistants' Laboratory Teaching through Design Research

    ERIC Educational Resources Information Center

    Bond-Robinson, Janet; Rodriques, Romola A. Bernard

    2006-01-01

    We report on a study of a laboratory teaching apprenticeship program designed to improve graduate teaching assistant (GTA) performance. To catalyze GTAs as laboratory teachers we constructed learning goals, synthesized previous literature into a design model and a developmental path, and built two instruments to measure 12 strategic pedagogical…

  1. Nickel-catalyzed decarboxylative carboamination of alkynes with isatoic anhydrides.

    PubMed

    Yoshino, Yasufumi; Kurahashi, Takuya; Matsubara, Seijiro

    2009-06-10

    An intermolecular nickel-catalyzed addition reaction in which isatoic anhydrides react with alkynes to afford substituted quinolones has been developed. A mechanistic rationale is proposed, implying oxidative addition of Ni(0) to a carbamate, which allows intermolecular addition to alkynes via decarboxylation.

  2. Cu(I)-Catalyzed Asymmetric Diamination of Conjugated Dienes

    PubMed Central

    Du, Haifeng; Zhao, Baoguo; Yuan, Weicheng; Shi, Yian

    2009-01-01

    A Cu(I)-catalyzed asymmetric diamination for a variety of conjugated dienes and a triene with encouraging ee’s has been effectively achieved using (R)-DTBM-SEGPHOS as chiral ligand and di-tert-butyldiaziridinone as nitrogen source. PMID:18763785

  3. Development of a Lewis Base Catalyzed Selenocyclization Reaction

    ERIC Educational Resources Information Center

    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,…

  4. Palladium-Catalyzed Synthesis of 9-Fluorenylidenes through Aryne Annulation

    PubMed Central

    Worlikar, Shilpa A.; Larock, Richard C.

    2009-01-01

    The palladium-catalyzed annulation of arynes by substituted ortho-halostyrenes produces substituted 9- fluorenylidenes in good yields. This methodology provides this important carbocyclic ring system in a single step, which involves the generation of two new carbon-carbon bonds, occurs under relatively mild reaction conditions and tolerates a variety of functional groups, including cyano, ester, aldehyde and ketone groups. PMID:19413328

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

    ERIC Educational Resources Information Center

    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)

  6. Acid-catalyzed dehydrogenation of amine-boranes

    DOEpatents

    Stephens, Frances Helen; Baker, Ralph Thomas

    2010-01-12

    A method of dehydrogenating an amine-borane using an acid-catalyzed reaction. The method generates hydrogen and produces a solid polymeric [R.sup.1R.sup.2B--NR.sup.3R.sup.4].sub.n product. The method of dehydrogenating amine-boranes may be used to generate H.sub.2 for portable power sources.

  7. Palladium-catalyzed direct arylation of indoles with cyclohexanones.

    PubMed

    Chen, Shanping; Liao, Yunfeng; Zhao, Feng; Qi, Hongrui; Liu, Saiwen; Deng, Guo-Jun

    2014-03-21

    A novel palladium catalyzed approach to 3-arylindoles was developed from indoles and cyclohexanones. Various cyclohexanones acted as aryl sources via an alkylation and dehydrogenation sequence using molecular oxygen as the hydrogen acceptor. This method showed good regioselectivity and afforded 3-arylindoles as the sole products.

  8. Palladium-catalyzed stereocontrolled vinylation of azoles and phenothiazine.

    PubMed

    Lebedev, Artyom Y; Izmer, Vyatcheslav V; Kazyul'kin, Denis N; Beletskaya, Irina P; Voskoboynikov, Alexander Z

    2002-02-21

    [reaction: see text] Vinylation of various azoles (pyrrole, indole, carbazole, and their derivatives) and phenothiazine with vinyl bromides catalyzed by palladium-phosphine complexes results in the respective N-vinylazoles in 30-99% yields. This reaction with cis- and trans-beta-bromostyrenes is stereospecific giving the respective products with full retention of configuration.

  9. Asymmetric gold-catalyzed lactonizations in water at room temperature.

    PubMed

    Handa, Sachin; Lippincott, Daniel J; Aue, Donald H; Lipshutz, Bruce H

    2014-09-26

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

  10. Silver-catalyzed protodecarboxylation of heteroaromatic carboxylic acids.

    PubMed

    Lu, Pengfei; Sanchez, Carolina; Cornella, Josep; Larrosa, Igor

    2009-12-17

    A simple and highly efficient protodecarboxylation procedure for a variety of heteroaromatic carboxylic acids catalyzed by Ag(2)CO(3) and AcOH in DMSO is described. This methodology can also perform the selective monoprotodecarboxylation of several aromatic dicarboxylic acids.

  11. Cu-Catalyzed Fluorination of Diaryliodonium Salts with KF

    PubMed Central

    Ichiishi, Naoko; Canty, Allan J.; Yates, Brian F.

    2014-01-01

    A mild Cu-catalyzed nucleophilic fluorination of unsymmetrical diaryliodonium salts with KF is described. This protocol preferentially fluorinates less sterically hindered aromatic rings. The reaction exhibits a broad substrate scope and proceeds with high chemoselectivity and functional group tolerance. DFT calculations implicate a CuI/CuIII catalytic cycle. PMID:24063629

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

    ERIC Educational Resources Information Center

    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)

  13. Cu(II) - Catalyzed Hydrazine Reduction of Ferrous Nitrate

    SciTech Connect

    Karraker, D.G.

    2001-10-15

    This report discusses the results of a study of catalyzed hydrazine reduction of ferrous nitrate. It is apparent that there is a substantial reaction between hydrazine and nitrate ion (or nitric acid) to produce HN3 during both the reduction of Fe(III) and during storage at room temperature.

  14. Copper-catalyzed asymmetric reduction of 3,3-diarylacrylonitriles.

    PubMed

    Lee, Daehyung; Yang, Youngmin; Yun, Jaesook

    2007-07-05

    CuH-catalyzed enantioselective conjugate reduction of 3,3-diaryl-substituted acrylonitriles is described. A range of 3-aryl-3-pyridylacrylonitriles were reduced with high levels of enantioselectivity under optimal conditions employing a copper/Josiphos complex in the presence of polymethylhydrosiloxane (PMHS).

  15. Palladium-catalyzed silylation of aryl chlorides with hexamethyldisilane.

    PubMed

    McNeill, Eric; Barder, Timothy E; Buchwald, Stephen L

    2007-09-13

    A method for the palladium-catalyzed silylation of aryl chlorides has been developed. The method affords desired product in good yield, is tolerant of a variety of functional groups, and provides access to a wide variety of aryltrimethylsilanes from commercially available aryl chlorides. Additionally, a one-pot procedure that converts aryl chlorides into aryl iodides has been developed.

  16. Copper-catalyzed radical carbooxygenation: alkylation and alkoxylation of styrenes.

    PubMed

    Liao, Zhixiong; Yi, Hong; Li, Zheng; Fan, Chao; Zhang, Xu; Liu, Jie; Deng, Zixin; Lei, Aiwen

    2015-01-01

    A simple copper-catalyzed direct radical carbooxygenation of styrenes is developed utilizing alkyl bromides as radical resources. This catalytic radical difunctionalization accomplishes both alkylation and alkoxylation of styrenes in one pot. A broad range of styrenes and alcohols are well tolerated in this transformation. The EPR experiment shows that alkyl halides could oxidize Cu(I) to Cu(II) in this transformation.

  17. Metal-Catalyzed Cleavage of tRNA[superscript Phe

    ERIC Educational Resources Information Center

    Kirk, Sarah R.; Silverstein, Todd P.; McFarlane Holman, Karen L.

    2008-01-01

    This laboratory project is one component of a semester-long advanced biochemistry laboratory course that uses several complementary techniques to study tRNA[superscript Phe] conformational changes induced by ligand binding. In this article we describe a set of experiments in which students assay metal-catalyzed hydrolysis of tRNA[superscript Phe]…

  18. Enantioselective N-heterocyclic carbene-catalyzed synthesis of trifluoromethyldihydropyridinones.

    PubMed

    Wang, Dong-Ling; Liang, Zhi-Qin; Chen, Kun-Quan; Sun, De-Qun; Ye, Song

    2015-06-05

    The enantioselective N-heterocyclic carbene-catalyzed [4 + 2] cyclocondensation of α-chloroaldehydes and trifluoromethyl N-Boc azadienes was developed, giving the corresponding 3,4-disubstituted-6-trifluoromethyldihydropyridin-2(1H)-ones in good yields with exclusive cis-selectivities and excellent enantioselectivities.

  19. Ruthenium-catalyzed C–H activation of thioxanthones

    PubMed Central

    Wagner, Danny

    2015-01-01

    Summary Thioxanthones – being readily available in one step from thiosalicylic acid and arenes – were used in ruthenium-catalyzed C–H-activation reaction to produce 1-mono- or 1,8-disubstituted thioxanthones in good to excellent yields. Scope and limitation of this reaction are presented. PMID:25977717

  20. Palladium-catalyzed synthesis of functionalized tetraarylphosphonium salts.

    PubMed

    Marcoux, David; Charette, André B

    2008-01-18

    An efficient method to synthesize functionalized tetraarylphosphonium salts is described. This palladium-catalyzed coupling reaction between aryl iodides, bromides, or triflates and triphenylphosphine generates phosphonium salts in high yields. The coupling is compatible with a variety of functional groups such as alcohols, ketones, aldehydes, phenols, and amides.

  1. Palladium(II)-catalyzed direct alkenylation of nonaromatic enamides.

    PubMed

    Gigant, Nicolas; Gillaizeau, Isabelle

    2012-07-06

    A mild and efficient method for the direct alkenylation of nonaromatic enamides was achieved through a palladium(II)-catalyzed C-H functionalization. The reaction scope includes cyclic and acyclic enamides and a range of activated alkenes. This approach represents the first successful direct C(3)-functionalization of nonaromatic cyclic enamides.

  2. Zinc-catalyzed cyclopropenation of alkynes via 2-furylcarbenoids.

    PubMed

    González, María J; López, Luis A; Vicente, Rubén

    2014-11-07

    An unprecedented cyclopropenation reaction of alkynes catalyzed by ZnCl2 is reported. While Simmons-Smith-type carbenoids failed in the [2 + 1]-cycloaddition with alkynes, the use of enynones as the carbene source enables the preparation of substituted 2-furyl cyclopropene derivatives with remarkable scope.

  3. Metal-Catalyzed Cleavage of tRNA[superscript Phe

    ERIC Educational Resources Information Center

    Kirk, Sarah R.; Silverstein, Todd P.; McFarlane Holman, Karen L.

    2008-01-01

    This laboratory project is one component of a semester-long advanced biochemistry laboratory course that uses several complementary techniques to study tRNA[superscript Phe] conformational changes induced by ligand binding. In this article we describe a set of experiments in which students assay metal-catalyzed hydrolysis of tRNA[superscript Phe]…

  4. Iron-Catalyzed Synthesis of Sulfur-Containing Heterocycles.

    PubMed

    Bosset, Cyril; Lefebvre, Gauthier; Angibaud, Patrick; Stansfield, Ian; Meerpoel, Lieven; Berthelot, Didier; Guérinot, Amandine; Cossy, Janine

    2016-10-13

    An iron-catalyzed synthesis of sulfur- and sulfone-containing heterocycles is reported. The method is based on the cyclization of readily available substrates and proceeded with high efficiency and diastereoselectivity. A variety of sulfur-containing heterocycles bearing moieties suitable for subsequent functionalization are prepared. Illustrative examples of such postcyclization modifications are also presented.

  5. Palladium-catalyzed enantioselective 1,1-fluoroarylation of aminoalkenes.

    PubMed

    He, Ying; Yang, Zhenyu; Thornbury, Richard T; Toste, F Dean

    2015-09-30

    The development of an enantioselective palladium-catalyzed 1,1-fluoroarylation of unactivated aminoalkenes is described. The reaction uses arylboronic acids as the arene source and Selectfluor as the fluorine source to generate benzylic fluorides in good yields with excellent enantioselectivities. This transformation, likely proceeding through an oxidative Heck mechanism, affords 1,1-difunctionalized alkene products.

  6. Palladium-Catalyzed Enantioselective 1,1-Fluoroarylation of Aminoalkenes

    PubMed Central

    2016-01-01

    The development of an enantioselective palladium-catalyzed 1,1-fluoroarylation of unactivated aminoalkenes is described. The reaction uses arylboronic acids as the arene source and Selectfluor as the fluorine source to generate benzylic fluorides in good yields with excellent enantioselectivities. This transformation, likely proceeding through an oxidative Heck mechanism, affords 1,1-difunctionalized alkene products. PMID:26378886

  7. Pd-catalyzed C-H fluorination with nucleophilic fluoride.

    PubMed

    McMurtrey, Kate B; Racowski, Joy M; Sanford, Melanie S

    2012-08-17

    The palladium-catalyzed C-H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed.

  8. Palladium(III)-Catalyzed Fluorination of Arylboronic Acid Derivatives

    PubMed Central

    Tang, Pingping; Murphy, Jennifer M.; Ritter, Tobias

    2013-01-01

    A practical, palladium-catalyzed synthesis of aryl fluorides from arylboronic acid derivatives is presented. The reaction is operationally simple and amenable to multi-gram-scale synthesis. Evaluation of the reaction mechanism suggests a single-electron-transfer pathway, involving a Pd(III) intermediate that has been isolated and characterized. PMID:24040932

  9. Palladium(III)-catalyzed fluorination of arylboronic acid derivatives.

    PubMed

    Mazzotti, Anthony R; Campbell, Michael G; Tang, Pingping; Murphy, Jennifer M; Ritter, Tobias

    2013-09-25

    A practical, palladium-catalyzed synthesis of aryl fluorides from arylboronic acid derivatives is presented. The reaction is operationally simple and amenable to multigram-scale synthesis. Evaluation of the reaction mechanism suggests a single-electron-transfer pathway, involving a Pd(III) intermediate that has been isolated and characterized.

  10. Development of a Lewis Base Catalyzed Selenocyclization Reaction

    ERIC Educational Resources Information Center

    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,…

  11. Ruthenium-catalyzed tertiary amine formation from nitroarenes and alcohols.

    PubMed

    Feng, Chao; Liu, Yong; Peng, Shengming; Shuai, Qi; Deng, Guojun; Li, Chao-Jun

    2010-11-05

    A highly selective ruthenium-catalyzed C-N bond formation was developed by using the hydrogen-borrowing strategy. Various tertiary amines were obtained efficiently from nitroarenes and primary alcohols. The reaction tolerates a wide range of functionalities. A tentative mechanism was proposed for this direct amination reaction of alcohols with nitroarenes.

  12. Palladium catalyzed alkoxy- and aminocarbonylation of vinyl tosylates.

    PubMed

    Reeves, Diana C; Rodriguez, Sonia; Lee, Heewon; Haddad, Nizar; Krishnamurthy, Dhileepkumar; Senanayake, Chris H

    2011-05-06

    The palladium catalyzed alkoxycarbonylation and aminocarbonylation of vinyl tosylates are described. A variety of ketone and aldehyde derived vinyl tosylates may be carbonylated in the presence of primary, secondary, and tertiary alcohols, or primary and secondary amines, to provide the corresponding esters and amides in good yields. The alkoxycarbonylation was applied to a short synthesis of isoguvacine.

  13. Catalyzing Graduate Teaching Assistants' Laboratory Teaching through Design Research

    ERIC Educational Resources Information Center

    Bond-Robinson, Janet; Rodriques, Romola A. Bernard

    2006-01-01

    We report on a study of a laboratory teaching apprenticeship program designed to improve graduate teaching assistant (GTA) performance. To catalyze GTAs as laboratory teachers we constructed learning goals, synthesized previous literature into a design model and a developmental path, and built two instruments to measure 12 strategic pedagogical…

  14. N-Heterocyclic Carbene-Catalyzed Convenient Benzonitrile Assembly.

    PubMed

    Jia, Qianfa; Wang, Jian

    2016-05-06

    The benzonitrile unit is widely found in natural products, pharmaceuticals, and agrochemicals. Synthesis of benzonitriles has received considerable interests from the chemical community over the last few decades. Present synthetic protocols mainly rely on the pre-existing benzene core to install a cyano moiety. A new NHC-catalyzed [4 + 2]-benzannulation protocol is reported to assemble the benzonitrile framework.

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

    PubMed

    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.

  16. Synthesis of benzimidazoles via iridium-catalyzed acceptorless dehydrogenative coupling.

    PubMed

    Sun, Xiang; Lv, Xiao-Hui; Ye, Lin-Miao; Hu, Yu; Chen, Yan-Yan; Zhang, Xue-Jing; Yan, Ming

    2015-07-21

    Iridium-catalyzed acceptorless dehydrogenative coupling of tertiary amines and arylamines has been developed. A number of benzimidazoles were prepared in good yields. An iridium-mediated C-H activation mechanism is suggested. This finding represents a novel strategy for the synthesis of benzimidazoles.

  17. Computational Studies on Cinchona Alkaloid-Catalyzed Asymmetric Organic Reactions.

    PubMed

    Tanriver, Gamze; Dedeoglu, Burcu; Catak, Saron; Aviyente, Viktorya

    2016-06-21

    Remarkable progress in the area of asymmetric organocatalysis has been achieved in the last decades. Cinchona alkaloids and their derivatives have emerged as powerful organocatalysts owing to their reactivities leading to high enantioselectivities. The widespread usage of cinchona alkaloids has been attributed to their nontoxicity, ease of use, stability, cost effectiveness, recyclability, and practical utilization in industry. The presence of tunable functional groups enables cinchona alkaloids to catalyze a broad range of reactions. Excellent experimental studies have extensively contributed to this field, and highly selective reactions were catalyzed by cinchona alkaloids and their derivatives. Computational modeling has helped elucidate the mechanistic aspects of cinchona alkaloid catalyzed reactions as well as the origins of the selectivity they induce. These studies have complemented experimental work for the design of more efficient catalysts. This Account presents recent computational studies on cinchona alkaloid catalyzed organic reactions and the theoretical rationalizations behind their effectiveness and ability to induce selectivity. Valuable efforts to investigate the mechanisms of reactions catalyzed by cinchona alkaloids and the key aspects of the catalytic activity of cinchona alkaloids in reactions ranging from pharmaceutical to industrial applications are summarized. Quantum mechanics, particularly density functional theory (DFT), and molecular mechanics, including ONIOM, were used to rationalize experimental findings by providing mechanistic insights into reaction mechanisms. B3LYP with modest basis sets has been used in most of the studies; nonetheless, the energetics have been corrected with higher basis sets as well as functionals parametrized to include dispersion M05-2X, M06-2X, and M06-L and functionals with dispersion corrections. Since cinchona alkaloids catalyze reactions by forming complexes with substrates via hydrogen bonds and long

  18. Reaction Pathway for Cocaine Hydrolase-Catalyzed Hydrolysis of (+)-Cocaine

    PubMed Central

    Yao, Yuan; Liu, Junjun; Zheng, Fang; Zhan, Chang-Guo

    2017-01-01

    A recently designed and discovered cocaine hydrolase (CocH), engineered from human butyrylcholinesterase (BChE), has been proven promising as a novel enzyme therapy for treatment of cocaine overdose and addiction because it is highly efficient in catalyzing hydrolysis of naturally occurring (−)-cocaine. It has been known that the CocH also has a high catalytic efficiency against (+)-cocaine, a synthetic enantiomer of cocaine. Reaction pathway and the corresponding free energy profile for the CocH-catalyzed hydrolysis of (+)-cocaine have been determined, in the present study, by performing first-principles pseudobond quantum mechanical/molecular mechanical (QM/MM)-free energy (FE) calculations. Acordingt to the QM/MM-FE results, the catalytic hydrolysis process is initiated by the nucleophilic attack on carbonyl carbon of (−)-cocaine benzoyl ester via hydroxyl oxygen of S198 side chain, and the second reaction step (i.e. dissociation of benzoyl ester) is rate-determining. This finding for CocH-catalyzed hydrolysis of (+)-cocaine is remarkably different from that for the (+)-cocaine hydrolysis catalyzed by bacterial cocaine esterase in which the first reaction step of the deacylation is associated with the highest free energy barrier (~17.9 kcal/mol). The overall free energy barrier (~16.0 kcal/mol) calculated for the acylation stage of CocH-catalyzed hydrolysis of (+)-cocaine is in good agreement with the experimental free energy barrier of ~14.5 kcal/mol derivated from the experimental kinetic data. PMID:28250715

  19. A Novel Metabolic Pathway for Glucose Production Mediated by α-Glucosidase-catalyzed Conversion of 1,5-Anhydrofructose*

    PubMed Central

    Kim, Young-Min; Saburi, Wataru; Yu, Shukun; Nakai, Hiroyuki; Maneesan, Janjira; Kang, Min-Sun; Chiba, Seiya; Kim, Doman; Okuyama, Masayuki; Mori, Haruhide; Kimura, Atsuo

    2012-01-01

    α-Glucosidase is in the glycoside hydrolase family 13 (13AG) and 31 (31AG). Only 31AGs can hydrate the d-glucal double bond to form α-2-deoxyglucose. Because 1,5-anhydrofructose (AF), having a 2-OH group, mimics the oxocarbenium ion transition state, AF may be a substrate for α-glucosidases. α-Glucosidase-catalyzed hydration produced α-glucose from AF, which plateaued with time. Combined reaction with α-1,4-glucan lyase and 13AG eliminated the plateau. Aspergillus niger α-glucosidase (31AG), which is stable in organic solvent, produced ethyl α-glucoside from AF in 80% ethanol. The findings indicate that α-glucosidases catalyze trans-addition. This is the first report of α-glucosidase-associated glucose formation from AF, possibly contributing to the salvage pathway of unutilized AF. PMID:22613728

  20. 4-Dimenthylaminopyridine or Acid-Catalyzed Synthesis of Esters: A Comparison

    ERIC Educational Resources Information Center

    van den Berg, Annemieke W. C.; Hanefeld, Ulf

    2006-01-01

    A set of highly atom-economic experiments was developed to highlight the differences between acid- and base-catalyzed ester syntheses and to introduce the principles of atom economy. The hydrochloric acid-catalyzed formation of an ester was compared with the 4-dimethylaminopyradine-catalyzed ester synthesis.

  1. 4-Dimenthylaminopyridine or Acid-Catalyzed Synthesis of Esters: A Comparison

    ERIC Educational Resources Information Center

    van den Berg, Annemieke W. C.; Hanefeld, Ulf

    2006-01-01

    A set of highly atom-economic experiments was developed to highlight the differences between acid- and base-catalyzed ester syntheses and to introduce the principles of atom economy. The hydrochloric acid-catalyzed formation of an ester was compared with the 4-dimethylaminopyradine-catalyzed ester synthesis.

  2. Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.

    ERIC Educational Resources Information Center

    Lombardo, Anthony

    1982-01-01

    Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

  3. Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.

    ERIC Educational Resources Information Center

    Lombardo, Anthony

    1982-01-01

    Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

  4. Nickel(0)-catalyzed cycloaddition copolymerization involving two diynes and carbon dioxide to poly(2-pyrone)

    SciTech Connect

    Tsuda, Tetsuo; Ooi, Osamu; Maruta, Ken-ichi )

    1993-08-01

    A copolymerizability order of five diynes, i.e., 3,11-tetradecadiyne (A), 2,6-octadiyne (B), 1,4-di(2-hexynyl)benzene (C), 1,3-di(2-hexynyl)benzene (D), and 1,7-cyclotridecadiyne (E), in the nickel(0)-catalyzed 1:1 cycloaddition copolymerization of the diyne with CO[sub 2] to the poly(2-pyrone) was determined by the nickel(0)-catalyzed copolymerization involving two diynes and CO[sub 2]. The copolymerizability order obtained by analyzing the copolymer composition using [sup 1]H NMR spectroscopy was A [gt] E [gt] B [gt] C [gt] D. This order was explained in terms of the steric hindrance exerted by the substituent on the terminal C[triple bond]C bond of the cooligomer or the copolymer to its cycloaddition along with mobility of its terminal C[triple bond]C bond moiety for the cycloaddition. An order of cycloaddition reactivity of the diyne, which is related to formation of the cooligomer, was determined by measuring the unreacted diyne in the copolymerization involving five diynes and CO[sub 2] using gas chromatography. The result was E [gt] B [gt] C [gt] D [gt] A. Thus high copolymerizability of diyne A is noteworthy.

  5. An optimized hydrogen target for muon catalyzed fusion

    NASA Astrophysics Data System (ADS)

    Gheisari, R.

    2011-04-01

    This paper deals with the optimization of the processes involved in muon catalyzed fusion. Muon catalyzed fusion ( μCF) is studied in all layers of the solid hydrogen structure H/0.1%T⊕D2⊕HD. The layer H/ T acts as an emitter source of energetic tμ atoms, due to the so-called Ramsauer-Townsend effect. These tμ atoms are slowed down in the second layer (degrader) and are forced to take place nuclear fusion in HD. The degrader affects time evolution of tμ atomic beam. This effect has not been considered until now in μCF-multilayered targets. Due to muon cycling and this effect, considerable reactions occur in the degrader. In our calculations, it is shown that the fusion yield equals 180±1.5. It is possible to separate events that overlap in time.

  6. Investigations into Transition Metal Catalyzed Arene Trifluoromethylation Reactions.

    PubMed

    Ye, Yingda; Sanford, Melanie S

    2012-09-01

    Trifluoromethyl-substituted arenes and heteroarenes are widely prevalent in pharmaceuticals and agrochemicals. As a result, the development of practical methods for the formation of aryl-CF3 bonds has become an active field of research. Over the past five years, transition metal catalyzed cross-coupling between aryl-X (X = halide, organometallic, or H) and various "CF3" reagents has emerged as a particularly exciting approach for generating aryl-CF3 bonds. Despite many recent advances in this area, current methods generally suffer from limitations such as poor generality, harsh reaction conditions, the requirement for stoichiometric quantities of metals, and/or the use of costly CF3 sources. This Account describes our recent efforts to address some of these challenges by: (1) developing aryl trifluoromethylation reactions involving high oxidation state Pd intermediates, (2) exploiting AgCF3 for C-H trifluoromethylation, and (3) achieving Cu-catalyzed trifluoromethylation with photogenerated CF3•.

  7. Cytochrome c catalyzes the in vitro synthesis of arachidonoyl glycine

    SciTech Connect

    McCue, Jeffrey M.; Driscoll, William J.; Mueller, Gregory P.

    2008-01-11

    Long chain fatty acyl glycines are an emerging class of biologically active molecules that occur naturally and produce a wide array of physiological effects. Their biosynthetic pathway, however, remains unknown. Here we report that cytochrome c catalyzes the synthesis of N-arachidonoyl glycine (NAGly) from arachidonoyl coenzyme A and glycine in the presence of hydrogen peroxide. The identity of the NAGly product was verified by isotope labeling and mass analysis. Other heme-containing proteins, hemoglobin and myoglobin, were considerably less effective in generating arachidonoyl glycine as compared to cytochrome c. The reaction catalyzed by cytochrome c in vitro points to its potential role in the formation of NAGly and other long chain fatty acyl glycines in vivo.

  8. Ligand development in the Ni-catalyzed hydrocyanation of alkenes.

    PubMed

    Bini, Laura; Müller, Christian; Vogt, Dieter

    2010-11-28

    The addition of HCN to alkenes is a very useful reaction for the synthesis of functional organic substrates. Industrially the nickel-catalyzed hydrocyanation has gained considerable importance mainly because of the production of adiponitrile in the DuPont process. In this process the hydrocyanation of butadiene is carried out using aryl phosphite-modified nickel catalyst. Since the performance of organo-transition metal complexes is largely determined by the ligand environment of the metal, fundamental understanding and ligand development is of pivotal importance for any progress. This feature article gives an account of the development and application of different mono- and bidentate phosphorus-based ligands in the Ni-catalyzed hydrocyanation reaction of alkenes. Special attention will be paid to the development of insight and understanding of the ligand structural and electronic properties towards the improvement of the catalyst performance in terms of stability, activity, and selectivity.

  9. Cholera toxin can catalyze ADP-ribosylation of cytoskeletal proteins

    SciTech Connect

    Kaslow, H.R.; Groppi, V.E.; Abood, M.E.; Bourne, H.R.

    1981-11-01

    Cholera toxin catalyzes transfer of radiolabel from (/sup 32/P)NAD/sup +/ to several peptides in particulate preparations of human foreskin fibroblasts. Resolution of these peptides by two-dimensional gel electrophoresis allowed identification of two peptides of M/sub r/ = 42,000 and 52,000 as peptide subunits of a regulatory component of adenylate cyclase. The radiolabeling of another group of peptides (M/sub r/ = 50,000 to 65,000) suggested that cholera toxin could catalyze ADP-ribosylation of cytoskeletal proteins. This suggestion was confirmed by showing that incubation with cholera toxin and (/sup 32/P)NAD/sup +/ caused radiolabeling of purified microtubule and intermediate filament proteins.

  10. Asymmetric oxidoreductions catalyzed by alcohol dehydrogenase in organic solvents

    SciTech Connect

    Grunwald, J.; Wirz, B.; Scollar, M.P.; Klibanov, A.M.

    1986-10-15

    A methodology is developed for the use of alcohol dehydrogenase (and other NAD/sup +//NADH-dependent enzymes) as catalysts in organic solvents. The enzyme and the cofactor are deposited onto the surface of glass beads which are then suspended in a water-immiscible organic solvent containing the substrate. Both NADH and NAD/sup +/ are efficiently regenerated in such a system with alcohol dehydrogenase-catalyzed oxidation of ethanol and reduction of isobutyraldehyde, respectively; cofactor turnover numbers of 10/sup 5/ to greater than 10/sup 6/ have been obtained. With use of asymmetric oxidoreductions catalyzed by horse liver alcohol dehydrogenase in isopropyl ether, optically active (ee of 95 to 100%) alcohols and ketones have been prepared on a 1 to 10 mmol scale.

  11. Erythrocyte enzymes catalyze 1-nitropyrene and 3-nitrofluoranthene nitroreduction.

    PubMed

    Belisario, M A; Pecce, R; Garofalo, A; Sannolo, N; Malorni, A

    1996-04-15

    Nitroarenes are environmental contaminants produced during incomplete combustion processes. Nitroreduction, the most important pathway of nitroarene toxification, occurs mainly in the liver and intestine. In the present study, we show that human red cells may also possess the metabolic competence to reduce 1-nitropyrene (NP) and 3-nitrofluoranthene (NF), the nitroarenes chosen as model compounds, to their corresponding amino derivatives, 1-aminopyrene (AP) and 3-aminofluoranthene (AF). The requirement of the cofactor couple NADH/FMN suggests that erythrocyte nitroreductase activity occurs via one electron transfer. The presence of oxygen strongly inhibited the haemolysate-catalyzed nitroarene reduction, whether measured as amine formation or nitroarene disappearance. Intermediate reactive species, that bind covalently to haemoglobin and/or other erythrocyte proteins, are formed during nitroreduction catalyzed by human haemolysate. In fact, the reduced metabolites AP and AF were released after mild acid hydrolysis of red cell proteins exposed to NP and NF, thus suggesting that sulphinamide adducts have been formed.

  12. Copper-Catalyzed Intramolecular Oxidative Amination of Unactivated Internal Alkenes.

    PubMed

    Xiong, Peng; Xu, Fan; Qian, Xiang-Yang; Yohannes, Yared; Song, Jinshuai; Lu, Xin; Xu, Hai-Chao

    2016-03-18

    A copper-catalyzed oxidative amination of unactivated internal alkenes has been developed. The Wacker-type oxidative alkene amination reaction is traditionally catalyzed by a palladium through a mechanism involving aminopalladation and β-hydride elimination. Replacing the precious and scarce palladium with a cheap and abundant copper for this transformation has been challenging because of the difficulty associated with the aminocupration of internal alkenes. The combination of a simple copper salt, without additional ligand, as the catalyst and Dess-Martin periodinane as the oxidant, promotes efficiently the oxidative amination of allylic carbamates and ureas bearing di- and trisubstituted alkenes leading to oxazolidinones and imidazolidinones. Preliminary mechanistic studies suggested a hybrid radical-organometallic mechanism involving an amidyl radical cyclization to form the key C-N bond. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Rearrangement Reactions Catalyzed by Cytochrome P450s

    PubMed Central

    Ortiz de Montellano, Paul R.; Nelson, Sidney D.

    2010-01-01

    Cytochrome P450s promote a variety of rearrangement reactions both as a consequence of the nature of the radical and other intermediates generated during catalysis, and of the neighboring structures in the substrate that can interact either with the initial radical intermediates or with further downstream products of the reactions. This article will review several kinds of previously published cytochrome P450-catalyzed rearrangement reactions, including changes in stereochemistry, radical clock reactions, allylic rearrangements, “NIH” and related shifts, ring contractions and expansions, and cyclizations that result from neighboring group interactions. Although most of these reactions can be carried out by many members of the cytochrome P450 superfamily, some have only been observed with select P450s, including some reactions that are catalyzed by specific endoperoxidases and cytochrome P450s found in plants. PMID:20971058

  14. Cross-ligation and exchange reactions catalyzed by hairpin ribozymes.

    PubMed Central

    Komatsu, Y; Koizumi, M; Sekiguchi, A; Ohtsuka, E

    1993-01-01

    The negative strand of the satellite RNA of tobacco ringspot virus (sTobRV(-)) contains a hairpin catalytic domain that shows self-cleavage and self-ligation activities in the presence of magnesium ions. We describe here that the minimal catalytic domain can catalyze a cross-ligation reaction between two kinds of substrates in trans. The cross-ligated product increased when the reaction temperature was decreased during the reaction from 37 degrees C to 4 degrees C. A two-stranded hairpin ribozyme, divided into two fragments between G45 and U46 in a hairpin loop, showed higher ligation activity than the nondivided ribozyme. The two stranded ribozyme also catalyzed an exchange reaction of the 3'-portion of the cleavage site. Images PMID:8441626

  15. Palladium-Catalyzed Arylation of Alkyl Sulfenate Anions.

    PubMed

    Jia, Tiezheng; Zhang, Mengnan; Jiang, Hui; Wang, Carol Y; Walsh, Patrick J

    2015-11-04

    A unique palladium-catalyzed arylation of alkyl sulfenate anions is introduced that affords aryl alkyl sulfoxides in high yields. Due to the base sensitivity of the starting sulfoxides, sulfenate anion intermediates, and alkyl aryl sulfoxide products, the use of a mild method to generate alkyl sulfenate anions was crucial to the success of this process. Thus, a fluoride triggered elimination strategy was employed with alkyl 2-(trimethylsilyl)ethyl sulfoxides to liberate the requisite alkyl sulfenate anion intermediates. In the presence of palladium catalysts with bulky monodentate phosphines (SPhos and Cy-CarPhos) and aryl bromides or chlorides, alkyl sulfenate anions were readily arylated. Moreover, the thermal fragmentation and the base promoted elimination of alkyl sulfoxides was overridden. The alkyl sulfenate anion arylation exhibited excellent chemoselectivity in the presence of functional groups, such as anilines and phenols, which are also known to undergo palladium catalyzed arylation reactions.

  16. Temperature dependence of the thrombin-catalyzed proteolysis of prothrombin.

    PubMed

    Shi, Fang; Winzor, Donald J; Jackson, Craig M

    2004-07-01

    Measurement of the temperature-dependence of thrombin-catalyzed cleavage of the Arg(155)-Ser(156) and Arg(284)-Thr(285) peptide bonds in prothrombin and prothrombin-derived substrates has yielded Arrhenius parameters that are far too large for classical mechanistic interpretation in terms of a simple hydrolytic reaction. Such a difference from the kinetic behavior exhibited in trypsin- and chymotrypsin-catalyzed proteolysis of peptide bonds is attributed to contributions by enzyme exosite interactions as well as enzyme conformational equilibria to the magnitudes of the experimentally determined Arrhenius parameters. Although the pre-exponential factor and the energy of activation deduced from the temperature-dependence of rate constants for proteolysis by thrombin cannot be accorded the usual mechanistic significance, their evaluation serves a valuable role by highlighting the existence of contributions other than those emanating from simple peptide hydrolysis to the kinetics of proteolysis by thrombin and presumably other enzymes of the blood coagulation system.

  17. Hairpin ribozyme-catalyzed ligation in water-alcohol solutions.

    PubMed

    Vlassov, Alexander V; Johnston, Brian H; Kazakov, Sergei A

    2005-12-01

    The hairpin ribozyme (HPR) is a naturally existing RNA that catalyzes site-specific RNA cleavage and ligation. At 37 degrees C and in the presence of divalent metal ions (M(2+)), the HPR efficiently cleaves RNA substrates in trans. Here, we show that the HPR can catalyze efficient M(2+)-independent ligation in trans in aqueous solutions containing any of several alcohols, including methanol, ethanol, and isopropanol, and millimolar concentrations of monovalent cations. Ligation proceeds most efficiently in 60% isopropanol at 37 degrees C, whereas the reverse (cleavage) reaction is negligible under these conditions. We suggest that dehydration of the RNA is the key factor promoting HPR activity in water- alcohol solutions. Alcohol-induced ribozyme ligation may have practical applications.

  18. Thermodynamics of Enzyme-Catalyzed Reactions: Part 4. Lyases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.

    1995-09-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by the lyase class of enzymes have been compiled. For each reaction the following information is given: the reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement (temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used); the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it or any calculations for which the data have been used. The data from 106 references have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  19. Thermodynamics of Enzyme-Catalyzed Reactions: Part 2. Transferases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.

    1994-07-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by the transferase class of enzymes have been compiled. For each reaction the following information is given: the reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement [temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used]; the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it or any calculations for which the data have been used. The data from 285 references have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  20. Thermodynamics of Enzyme-Catalyzed Reactions. Part 3. Hydrolases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.

    1994-11-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by the hydrolase class of enzymes have been compiled. For each reaction the following information is given: The reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement [temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used]; the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it or any calculations for which the data have been used. The data from 145 references have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  1. Generalized rate equation for single-substrate enzyme catalyzed reactions.

    PubMed

    Kargi, Fikret

    2009-04-24

    The most widely used rate expression for single-substrate enzyme catalyzed reactions, namely the Michaelis-Menten kinetics is based upon the assumption that enzyme concentration is in excess of the substrate in the medium and the rate is mainly limited by the substrate concentration according to saturation kinetics. However, this is only a special case and the actual rate expression varies depending on the initial enzyme/substrate ratio (E(0)/S(0)). When the substrate concentration exceeds the enzyme concentration the limitation is due to low enzyme concentration and the rate increases with the enzyme concentration according to saturation kinetics. The maximum rate is obtained when the initial concentrations of the enzyme and the substrate are equal. A generalized rate equation was developed in this study and special cases were discussed for enzyme catalyzed reactions.

  2. Copper-Catalyzed Divergent Addition Reactions of Enoldiazoacetamides with Nitrones.

    PubMed

    Cheng, Qing-Qing; Yedoyan, Julietta; Arman, Hadi; Doyle, Michael P

    2016-01-13

    Catalyst-controlled divergent addition reactions of enoldiazoacetamides with nitrones have been developed. By using copper(I) tetrafluoroborate/bisoxazoline complex as the catalyst, a [3+3]-cycloaddition reaction was achieved with excellent yield and enantioselectivity under exceptionally mild conditions, which represents the first highly enantioselective base-metal-catalyzed vinylcarbene transformation. When the catalyst was changed to copper(I) triflate, Mannich addition products were formed in high yields with near exclusivity under otherwise identical conditions.

  3. Iron-Catalyzed gem-Specific Dimerization of Terminal Alkynes.

    PubMed

    Liang, Qiuming; Osten, Kimberly M; Song, Datong

    2017-03-13

    We report a gem-specific homo- and cross-dimerization of terminal alkynes catalyzed by a well-defined iron(II) complex containing Cp* and picolyl N-heterocyclic carbene (NHC) ligands, and featuring a piano-stool structure. This catalytic system requires no additives and is compatible with a broad range of substrates, including those with polar functional groups such as NH and OH.

  4. Pd-catalyzed nucleophilic fluorination of aryl bromides.

    PubMed

    Lee, Hong Geun; Milner, Phillip J; Buchwald, Stephen L

    2014-03-12

    On the basis of mechanism-driven reaction design, a Pd-catalyzed nucleophilic fluorination of aryl bromides and iodides has been developed. The method exhibits a broad substrate scope, especially with respect to nitrogen-containing heteroaryl bromides, and proceeds with minimal formation of the corresponding reduction products. A facilitated ligand modification process was shown to be critical to the success of the reaction.

  5. Pd-Catalyzed Nucleophilic Fluorination of Aryl Bromides

    PubMed Central

    2015-01-01

    On the basis of mechanism-driven reaction design, a Pd-catalyzed nucleophilic fluorination of aryl bromides and iodides has been developed. The method exhibits a broad substrate scope, especially with respect to nitrogen-containing heteroaryl bromides, and proceeds with minimal formation of the corresponding reduction products. A facilitated ligand modification process was shown to be critical to the success of the reaction. PMID:24559304

  6. Copper-catalyzed arylation of alkyl halides with arylaluminum reagents

    PubMed Central

    Shrestha, Bijay

    2015-01-01

    Summary We report a Cu-catalyzed coupling between triarylaluminum reagents and alkyl halides to form arylalkanes. The reaction proceeds in the presence of N,N,N’,N’-tetramethyl-o-phenylenediamine (NN-1) as a ligand in combination with CuI as a catalyst. This catalyst system enables the coupling of primary alkyl iodides and bromides with electron-neutral and electron-rich triarylaluminum reagents and affords the cross-coupled products in good to excellent yields. PMID:26734088

  7. Palladium-Catalyzed Synthesis of N-Aryl Carbamates

    PubMed Central

    Vinogradova, Ekaterina V.; Park, Nathaniel H.; Fors, Brett P.; Buchwald, Stephen L.

    2013-01-01

    An efficient synthesis of aryl carbamates was achieved by introducing alcohols into the reaction of palladium-catalyzed cross-coupling of ArX (X = Cl, OTf) with sodium cyanate. The use of aryl triflates as electrophilic components in this transformation allowed for an expanded substrate scope for direct synthesis of aryl isocyanates. This methodology provides direct access to major carbamate protecting groups, S-thiocarbamates, and diisocyanate precursors to polyurethane materials. PMID:23441814

  8. Biaryl Phosphine Ligands in Palladium-Catalyzed Amination

    PubMed Central

    Surry, David S.

    2012-01-01

    Palladium-catalyzed amination of aryl halides has undergone rapid development in the last 12 years. This has been largely driven by implementation of new classes of ligands. Biaryl phosphines have proven to provide especially active catalysts in this context. This review discusses the applications that these catalysts have found in C-N cross-coupling in heterocycle synthesis, pharmaceuticals, materials science and natural product synthesis. PMID:18663711

  9. Silver-Catalyzed C(sp(3))-H Chlorination.

    PubMed

    Ozawa, Jun; Kanai, Motomu

    2017-03-17

    A silver-catalyzed chlorination of benzylic, tertiary, and secondary C(sp(3))-H bonds was developed. The reaction proceeded with as low as 0.2 mol % catalyst loading at room temperature under air atmosphere with synthetically useful functional group compatibility. The regioselectivity and reactivity tendencies suggest that the chlorination proceeded through a radical pathway, but an intermediate alkylsilver species cannot be ruled out.

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

    NASA Technical Reports Server (NTRS)

    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.

  11. Lactoperoxidase-catalyzed activation of carcinogenic aromatic and heterocyclic amines.

    PubMed

    Gorlewska-Roberts, Katarzyna M; Teitel, Candee H; Lay, Jackson O; Roberts, Dean W; Kadlubar, Fred F

    2004-12-01

    Lactoperoxidase, an enzyme secreted from the human mammary gland, plays a host defensive role through antimicrobial activity. It has been implicated in mutagenic and carcinogenic activation in the human mammary gland. The potential role of heterocyclic and aromatic amines in the etiology of breast cancer led us to examination of the lactoperoxidase-catalyzed activation of the most commonly studied arylamine carcinogens: 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP), benzidine, 4-aminobiphenyl (ABP), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). In vitro activation was performed with lactoperoxidase (partially purified from bovine milk or human milk) in the presence of hydrogen peroxide and calf thymus DNA. Products formed during enzymatic activation were monitored by HPLC with ultraviolet and radiometric detection. Two of these products were characterized as hydrazo and azo derivatives by means of mass spectrometry. The DNA binding level of 3H- and 14C-radiolabeled amines after peroxidase-catalyzed activation was dependent on the hydrogen peroxide concentration, and the highest levels of carcinogen binding to DNA were observed at 100 microM H2O2. Carcinogen activation and the level of binding to DNA were in the order of benzidine > ABP > IQ > MeIQx > PhIP. One of the ABP adducts was identified, and the level at which it is formed was estimated to be six adducts/10(5) nucleotides. The susceptibility of aromatic and heterocyclic amines for lactoperoxidase-catalyzed activation and the binding levels of activated products to DNA suggest a potential role of lactoperoxidase-catalyzed activation of carcinogens in the etiology of breast cancer.

  12. Asymmetric Arylation of Imines Catalyzed by Heterogeneous Chiral Rhodium Nanoparticles.

    PubMed

    Yasukawa, Tomohiro; Kuremoto, Tatsuya; Miyamura, Hiroyuki; Kobayashi, Shu̅

    2016-06-03

    Asymmetric arylation of aldimines catalyzed by heterogeneous chiral rhodium nanoparticles has been developed. The reaction proceeded in aqueous media without significant decomposition of the imines by hydrolysis to afford chiral (diarylmethyl)amines in high yields with outstanding enantioselectivities. This catalyst system exhibited the highest turnover number (700) in heterogeneous catalysts reported to date for these reactions. The reusability of the catalyst was also demonstrated.

  13. A Simple Strategy for Glycosyltransferase-Catalyzed Aminosugar Nucleotide Synthesis

    PubMed Central

    Zhang, Jianjun; Singh, Shanteri; Hughes, Ryan R.; Zhou, Maoquan; Sunkara, Manjula; Morris, Andrew J.; Thorson, Jon S.

    2014-01-01

    A set of 2-chloro-4-nitrophenyl glucosamino/xylosaminosides were synthesized and assessed as potential substrates in the context of glycosyltransferase-catalyzed formation of the corresponding UDP/TDP-α-D-glucosamino-/xylosaminosugars and single vessel transglycosylation reactions with a model acceptor. This study highlights a robust platform for aminosugar nucleotide synthesis and reveals OleD Loki as a proficient catalyst for U/TDP-aminosugar synthesis and utilization. PMID:24677528

  14. A simple strategy for glycosyltransferase-catalyzed aminosugar nucleotide synthesis.

    PubMed

    Zhang, Jianjun; Singh, Shanteri; Hughes, Ryan R; Zhou, Maoquan; Sunkara, Manjula; Morris, Andrew J; Thorson, Jon S

    2014-03-21

    A set of 2-chloro-4-nitrophenyl glucosamino-/xylosaminosides were synthesized and assessed as potential substrates in the context of glycosyltransferase-catalyzed formation of the corresponding UDP/TDP-α-D-glucosamino-/xylosaminosugars and in single-vessel model transglycosylation reactions. This study highlights a robust platform for aminosugar nucleotide synthesis and reveals OleD Loki to be a proficient catalyst for U/TDP-aminosugar synthesis and utilization

  15. Silver-Catalyzed Decarboxylative Bromination of Aliphatic Carboxylic Acids.

    PubMed

    Tan, Xinqiang; Song, Tao; Wang, Zhentao; Chen, He; Cui, Lei; Li, Chaozhong

    2017-03-13

    The silver-catalyzed Hunsdiecker bromination of aliphatic carboxylic acids is described. With Ag(Phen)2OTf as the catalyst and dibromoisocyanuric acid as the brominating agent, various aliphatic carboxylic acids underwent decarboxylative bromination to provide the corresponding alkyl bromides under mild conditions. This method not only is efficient and general but also enjoys wide functional group compatibility. An oxidative radical mechanism involving Ag(II) intermediates is proposed.

  16. The gravitino-stau scenario after catalyzed big bang nucleosynthesis

    SciTech Connect

    Kersten, Joern; Schmidt-Hoberg, Kai E-mail: kai.schmidt-hoberg@ph.tum.de

    2008-01-15

    We consider the impact of catalyzed big bang nucleosynthesis on theories with a gravitino lightest superparticle and a charged slepton next-to-lightest superparticle. In models where the gravitino to gaugino mass ratio is bounded from below, such as gaugino-mediated supersymmetry breaking, we derive a lower bound on the gaugino mass parameter m{sub 1/2}. As a concrete example, we determine the parameter space of gaugino mediation that is compatible with all cosmological constraints.

  17. Ligand-Controlled Regiodivergent Copper-Catalyzed Alkylboration of Alkenes.

    PubMed

    Su, Wei; Gong, Tian-Jun; Lu, Xi; Xu, Meng-Yu; Yu, Chu-Guo; Xu, Zheng-Yang; Yu, Hai-Zhu; Xiao, Bin; Fu, Yao

    2015-10-26

    A novel copper-catalyzed regiodivergent alkylboration of alkenes with bis(pinacolato)diboron and alkyl halides has been developed. The regioselectivity of the alkylboration was controlled by subtle differences in the ligand structure. The reaction thus enables the practical, regiodivergent synthesis of two different alkyl boronic esters with complex structures from a single alkene. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Enantio- and Regioselective CuH-Catalyzed Hydroamination of Alkenes

    PubMed Central

    Zhu, Shaolin; Niljianskul, Nootaree; Buchwald, Stephen L.

    2013-01-01

    A highly enantio- and regioselective copper-catalyzed hydroamination reaction of alkenes has been developed using diethoxy(methyl)silane (DEMS) and esters of hydroxylamines. The process tolerates a wide variety of substituted styrenes, including trans-, cis-, and β,β-disubstituted styrenes to yield α–branched amines. In addition, aliphatic alkenes coupled to generate exclusively the anti-Markovnikov hydroamination products. PMID:24106781

  19. Ru-catalyzed stereoselective addition of imides to alkynes.

    PubMed

    Goossen, Lukas J; Blanchot, Mathieu; Brinkmann, Claus; Goossen, Käthe; Karch, Ralph; Rivas-Nass, Andreas

    2006-12-08

    A catalyst system formed in situ from bis(2-methylallyl)cycloocta-1,5-dieneruthenium(II) ((cod)Ru[met]2), a phosphine, and scandium(III) trifluoromethanesulfonate (Sc(OTf)3) was found to efficiently catalyze the anti-Markovnikov addition of imides to terminal alkynes, allowing mild and atom-economic synthesis of enimides. Depending on the phosphine employed, both the (E)- and the (Z)-isomer can be accessed stereoselectively.

  20. Cobalt-catalyzed formation of symmetrical biaryls and its mechanism.

    PubMed

    Moncomble, Aurélien; Le Floch, Pascal; Gosmini, Corinne

    2009-01-01

    Effective devotion: An efficient cobalt-catalyzed method devoted to the formation of symmetrical biaryls is described avoiding the preparation of organometallic reagents. Various aromatic halides functionalized by a variety of reactive group reagents are employed. Preliminary DFT calculations have shown that the involvement of a Co(I)/Co(III) couple is realistic at least in the case of 1,3-diazadienes as ligands (FG = functional group).

  1. Copper-catalyzed trifluoromethylation of trisubstituted allylic and homoallylic alcohols.

    PubMed

    Lei, Jian; Liu, Xiaowu; Zhang, Shaolin; Jiang, Shuang; Huang, Minhao; Wu, Xiaoxing; Zhu, Qiang

    2015-04-27

    An efficient copper-catalyzed trifluoromethylation of trisubstituted allylic and homoallylic alcohols with Togni's reagent has been developed. This strategy, accompanied by a double-bond migration, leads to various branched CF3-substituted alcohols by using readily available trisubstituted cyclic/acyclic alcohols as substrates. Moreover, for alcohols in which β-H elimination is prohibited, CF3-containing oxetanes are isolated as the sole product.

  2. Gold(I)-Catalyzed Enantioselective Ring Expansion of Allenylcyclopropanols

    PubMed Central

    Kleinbeck, Florian; Toste, F. Dean

    2009-01-01

    The asymmetric gold(I)-catalyzed ring expansion of 1-allenylcyclopropanols is described. The method provides synthetically valuable cyclobutanones with a vinyl-substituted quaternary stereogenic center in high enantioselectivities and yields. The method shows a broad substrate scope, tolerating protected alcohols and amines, alkenes, unsaturated esters and acetals. The reaction is easily adjustable to large scale synthesis, leading to product formation without significant loss of selectivity or yield with only 0.5 mol% catalyst loading. PMID:19530649

  3. Asymmetric Palladium-Catalyzed Directed Intermolecular Fluoroarylation of Styrenes

    PubMed Central

    2015-01-01

    A mild catalytic asymmetric direct fluoro-arylation of styrenes has been developed. The palladium-catalyzed three-component coupling of Selectfluor, a styrene and a boronic acid, provides chiral monofluorinated compounds in good yield and in high enantiomeric excess. A mechanism proceeding through a Pd(IV)-fluoride intermediate is proposed for the transformation and synthesis of an sp3 C–F bond. PMID:24617344

  4. Enzyme catalyzed biochemical production in a polydimethylsiloxane microreactor

    NASA Astrophysics Data System (ADS)

    Dickey, Cynthia K.; Elmore, Bill B.; Jones, Francis

    2000-08-01

    Study of an aqueous-phase reaction in an enzyme- catalyzedpolydimethylsiloxane (PDMS) microreactor is underway. In the present work, urease - an enzyme that catalyzes urea to ammonia and carbon dioxide has been immobilized within open microchannels of 450 micrometers (micrometers ) in diameter or less. Microchannels are templated within PDMS. Preliminary results demonstrate the proof of concept for conversion biochemicals via a PDMS-based microreactor system.

  5. N-heterocyclic carbene-catalyzed rearrangements of vinyl sulfones.

    PubMed

    Atienza, Roxanne L; Roth, Howard S; Scheidt, Karl A

    2011-01-01

    N-heterocyclic carbenes catalyze the rearrangement of 1,1-bis(arylsulfonyl)ethylene to the corresponding trans-1,2-bis(phenylsulfonyl) under mild conditions. Tandem rearrangement/cycloadditions have been developed to capitalize on this new process and generate highly substituted isoxazolines and additional heterocyclic compounds. Preliminary mechanistic studies support a new conjugate addition/Umpolung process involving the ejection and subsequent unusual re-addition of a sulfinate ion.

  6. Anisotropic Morphological Changes in Goethite during Fe(2+)-Catalyzed Recrystallization.

    PubMed

    Joshi, Prachi; Gorski, Christopher A

    2016-07-19

    When goethite is exposed to aqueous Fe(2+), rapid and extensive Fe atom exchange can occur between solid-phase Fe(3+) and aqueous Fe(2+) in a process referred to as Fe(2+)-catalyzed recrystallization. This process can lead to the structural incorporation or release of trace elements, which has important implications for contaminant remediation and nutrient biogeochemical cycling. Prior work found that the process did not cause major changes to the goethite structure or morphology. Here, we further investigated if and how goethite morphology and aggregation behavior changed temporally during Fe(2+)-catalyzed recrystallization. On the basis of existing literature, we hypothesized that Fe(2+)-catalyzed recrystallization of goethite would not result in changes to individual particle morphology or interparticle interactions. To test this, we reacted nanoparticulate goethite with aqueous Fe(2+) at pH 7.5 over 30 days and used transmission electron microscopy (TEM), cryogenic TEM, and (55)Fe as an isotope tracer to observe changes in particle dimensions, aggregation, and isotopic composition over time. Over the course of 30 days, the goethite particles substantially recrystallized, and the particle dimensions changed anisotropically, resulting in a preferential increase in the mean particle width. The temporal changes in goethite morphology could not be completely explained by a single mineral-transformation mechanism but rather indicated that multiple transformation mechanisms occurred concurrently. Collectively, these results demonstrate that the morphology of goethite nanoparticles does change during recrystallization, which is an important step toward identifying the driving force(s) of recrystallization.

  7. Enzyme catalyzed optofluidic biolaser for sensitive ion concentration detection

    NASA Astrophysics Data System (ADS)

    Gong, Chaoyang; Gong, Yuan; Oo, Maung Kyaw Khaing; Wu, Yu; Rao, Yunjiang; Fan, Xudong

    2016-12-01

    The enzyme horseradish peroxidase (HRP) has been extensively used in biochemistry for its ability to amplify a weak signal. By using HRP catalyzed substrate as the gain medium, we demonstrate sensitive ion concentration detection based on the optofluidic laser. The enzyme catalyzed reaction occurs in bulk solution inside a Fabry-Perot laser cavity, where the colorless, non-fluorescent 10-Acetyl-3,7-dihydroxyphenoxazine (ADHP) substrate is oxidized to produce highly fluorescent resorufin. Laser emission is achieved when pumped with the second harmonic wave of a Q-switched YAG laser. Further, we use sulfide anion (S2-) as an example to investigate the sensing performance of enzyme catalyzed optofluidic laser. The laser onset time difference between the sample to be tested and the reference is set to be the sensing output. Thanks to the amplification effects of both the enzymatic reaction and laser emission, we achieve a detection limit of 10 nM and a dynamic range of 3 orders of magnitude.

  8. Protection of Wood from Microorganisms by Laccase-Catalyzed Iodination

    PubMed Central

    Engel, J.; Thöny-Meyer, L.; Schwarze, F. W. M. R.; Ihssen, J.

    2012-01-01

    In the present work, Norway spruce wood (Picea abies L.) was reacted with a commercial Trametes versicolor laccase in the presence of potassium iodide salt or the phenolic compounds thymol and isoeugenol to impart an antimicrobial property to the wood surface. In order to assess the efficacy of the wood treatment, a leaching of the iodinated and polymerized wood and two biotests including bacteria, a yeast, blue stain fungi, and wood decay fungi were performed. After laccase-catalyzed oxidation of the phenols, the antimicrobial effect was significantly reduced. In contrast, the enzymatic oxidation of iodide (I−) to iodine (I2) in the presence of wood led to an enhanced resistance of the wood surface against all microorganisms, even after exposure to leaching. The efficiency of the enzymatic wood iodination was comparable to that of a chemical wood preservative, VP 7/260a. The modification of the lignocellulose by the laccase-catalyzed iodination was assessed by the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique. The intensities of the selected lignin-associated bands and carbohydrate reference bands were analyzed, and the results indicated a structural change in the lignin matrix. The results suggest that the laccase-catalyzed iodination of the wood surface presents an efficient and ecofriendly method for wood protection. PMID:22865075

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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.

  11. Protection of wood from microorganisms by laccase-catalyzed iodination.

    PubMed

    Schubert, M; Engel, J; Thöny-Meyer, L; Schwarze, F W M R; Ihssen, J

    2012-10-01

    In the present work, Norway spruce wood (Picea abies L.) was reacted with a commercial Trametes versicolor laccase in the presence of potassium iodide salt or the phenolic compounds thymol and isoeugenol to impart an antimicrobial property to the wood surface. In order to assess the efficacy of the wood treatment, a leaching of the iodinated and polymerized wood and two biotests including bacteria, a yeast, blue stain fungi, and wood decay fungi were performed. After laccase-catalyzed oxidation of the phenols, the antimicrobial effect was significantly reduced. In contrast, the enzymatic oxidation of iodide (I(-)) to iodine (I(2)) in the presence of wood led to an enhanced resistance of the wood surface against all microorganisms, even after exposure to leaching. The efficiency of the enzymatic wood iodination was comparable to that of a chemical wood preservative, VP 7/260a. The modification of the lignocellulose by the laccase-catalyzed iodination was assessed by the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique. The intensities of the selected lignin-associated bands and carbohydrate reference bands were analyzed, and the results indicated a structural change in the lignin matrix. The results suggest that the laccase-catalyzed iodination of the wood surface presents an efficient and ecofriendly method for wood protection.

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

    SciTech Connect

    Hainey, Mel F.; Redwing, Joan M.

    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.

  13. Enzyme-catalyzed biocathode in a photoelectrochemical biofuel cell

    NASA Astrophysics Data System (ADS)

    Yang, Jing; Hu, Donghua; Zhang, Xiaohuan; Wang, Kunqi; Wang, Bin; Sun, Bo; Qiu, Zhidong

    2014-12-01

    A novel double-enzyme photoelectrochemical biofuel cell (PEBFC) has been developed by taking glucose dehydrogenase (GDH) and horseradish peroxidase (HRP) as the enzyme of the photoanode and biocathode to catalyze the oxidation of glucose and the reduction of oxygen. A H2-mesoporphyrin IX is used as a dye for a TiO2 film electrode to fabricate a photoanode. The horseradish peroxidase (HRP) is immobilized on a glassy carbon (GC) electrode to construct a biocathode which is used to catalyze the reduction of oxygen in the PEBFC for the first time. The biocathode exhibits excellent electrocatalytic activity in the presence of O2. The performances of the PEBFC are obtained by current-voltage and power-voltage curves. The short-circuit current density (Isc), the open-circuit voltage (Voc), maximum power density (Pmax), fill factor (FF) and energy conversion efficiency (η) are 439 μA cm-2, 678 mV, 79 μW cm-2, 0.39 and 0.016%, respectively, and the incident photon-to-collected electron conversion efficiency (IPCE) is 32% at 350 nm. The Isc is higher than that of the PEBFC with Pt cathode, and the Voc is higher than that of the dye-sensitized solar cell or the enzyme-catalyzed biofuel cell operating individually, which demonstrates that the HRP is an efficient catalyst for the biocathode in the PEBFC.

  14. Stau-catalyzed big-bang nucleosynthesis reactions

    SciTech Connect

    Kamimura, Masayasu; Kino, Yasushi; Hiyama, Emiko

    2010-06-01

    We study the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X{sup -}) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X{sup -} particle has a lifetime of tau{sub X} > or approx. 10{sup 3} s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state and induces various types of reactions in which X{sup -} acts as a catalyst. Some of these X{sup -} catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements. We use a high-accuracy three-body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

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

    SciTech Connect

    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.

  18. Synthetic Study of Dragmacidin E: Construction of the Core Structure Using Pd-Catalyzed Cascade Cyclization and Rh-Catalyzed Aminoacetoxylation.

    PubMed

    Inoue, Naoya; Nakano, Shun-Ichi; Harada, Shingo; Hamada, Yasumasa; Nemoto, Tetsuhiro

    2017-03-03

    We developed a novel synthetic method of the core structure of dragmacidin E bearing a 7-membered ring-fused bis(indolyl)pyrazinone skeleton. Formation of the 7-membered ring-fused tricyclic indole skeleton was accomplished using a palladium-catalyzed Heck insertion-allylic amination cascade. Vicinal difunctionalization of the 7-membered ring was realized via a rhodium-catalyzed aminoacetoxylation.

  19. Efficient and selective synthesis of 6,7-Dehydrostipiamide via Zr-catalyzed asymmetric carboalumination and Pd-catalyzed cross-coupling of organozincs.

    PubMed

    Zeng, Xingzhong; Zeng, Fanxing; Negishi, Ei-ichi

    2004-09-16

    [structure: see text] 6,7-Dehydrostipiamide has been synthesized in 23% yield in 15 steps in the longest linear sequence through the application of the Zr-catalyzed asymmetric carboalumination and the Pd-catalyzed organozinc cross-coupling in addition to the Brown crotylboration, the Corey-Peterson olefination, and the Corey-Fuchs reaction for carbon-carbon bond formation.

  20. Asymmetric synthesis of dihydropyranones from ynones by sequential copper(I)-catalyzed direct aldol and silver(I)-catalyzed oxy-Michael reactions.

    PubMed

    Shi, Shi-Liang; Kanai, Motomu; Shibasaki, Masakatsu

    2012-04-16

    Ynones as diene surrogates: the asymmetric synthesis of enantiomerically enriched substituted dihydropyranones is described. The products are obtained in two steps by a copper(I)-catalyzed direct aldol reaction of ynones followed by a silver-catalyzed oxy-Michael reaction. This easy method is compatible with both aromatic and aliphatic substrates, and provides excellent chemoselectivity under mild reaction conditions.

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

    SciTech Connect

    Bertrand, Guy

    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.

  2. Iridium-Catalyzed Asymmetric Hydrogenation of Unsaturated Carboxylic Acids.

    PubMed

    Zhu, Shou-Fei; Zhou, Qi-Lin

    2017-04-04

    Chiral carboxylic acid moieties are widely found in pharmaceuticals, agrochemicals, flavors, fragrances, and health supplements. Although they can be synthesized straightforwardly by transition-metal-catalyzed enantioselective hydrogenation of unsaturated carboxylic acids, because the existing chiral catalysts have various disadvantages, the development of new chiral catalysts with high activity and enantioselectivity is an important, long-standing challenge. Ruthenium complexes with chiral diphosphine ligands and rhodium complexes with chiral monodentate or bidentate phosphorus ligands have been the predominant catalysts for asymmetric hydrogenation of unsaturated acids. However, the efficiency of these catalysts is highly substrate-dependent, and most of the reported catalysts require a high loading, high hydrogen pressure, or long reaction time for satisfactory results. Our recent studies have revealed that chiral iridium complexes with chiral spiro-phosphine-oxazoline ligands and chiral spiro-phosphine-benzylamine ligands exhibit excellent activity and enantioselectivity in the hydrogenation of α,β-unsaturated carboxylic acids, including α,β-disubstituted acrylic acids, trisubstituted acrylic acids, α-substituted acrylic acids, and heterocyclic α,β-unsaturated acids. On the basis of an understanding of the role of the carboxy group in iridium-catalyzed asymmetric hydrogenation reactions, we developed a carboxy-group-directed strategy for asymmetric hydrogenation of olefins. Using this strategy, we hydrogenated several challenging olefin substrates, such as β,γ-unsaturated carboxylic acids, 1,1-diarylethenes, 1,1-dialkylethenes, and 1-alkyl styrenes in high yield and with excellent enantioselectivity. All these iridium-catalyzed asymmetric hydrogenation reactions feature high turnover numbers (up to 10000) and turnover frequencies (up to 6000 h(-1)), excellent enantioselectivities (greater than 95% ee with few exceptions), low hydrogen pressure (<12 atm

  3. Energy harvesting by implantable abiotically catalyzed glucose fuel cells

    NASA Astrophysics Data System (ADS)

    Kerzenmacher, S.; Ducrée, J.; Zengerle, R.; von Stetten, F.

    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 μW-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.

  4. Molecular mechanism of Ca(2+)-catalyzed fusion of phospholipid micelles.

    PubMed

    Tsai, Hui-Hsu Gavin; Juang, Wei-Fu; Chang, Che-Ming; Hou, Tsai-Yi; Lee, Jian-Bin

    2013-11-01

    Although membrane fusion plays key roles in intracellular trafficking, neurotransmitter release, and viral infection, its underlying molecular mechanism and its energy landscape are not well understood. In this study, we employed all-atom molecular dynamics simulations to investigate the fusion mechanism, catalyzed by Ca(2+) ions, of two highly hydrated 1-palmitoyl-2-oleoyl-sn-3-phosphoethanolamine (POPE) micelles. This simulation system mimics the small contact zone between two large vesicles at which the fusion is initiated. Our simulations revealed that Ca(2+) ions are capable of catalyzing the fusion of POPE micelles; in contrast, we did not observe close contact of the two micelles in the presence of only Na(+) or Mg(2+) ions. Determining the free energy landscape of fusion allowed us to characterize the underlying molecular mechanism. The Ca(2+) ions play a key role in catalyzing the micelle fusion in three aspects: creating a more-hydrophobic surface on the micelles, binding two micelles together, and enhancing the formation of the pre-stalk state. In contrast, Na(+) or Mg(2+) ions have relatively limited effects. Effective fusion proceeds through sequential formation of pre-stalk, stalk, hemifused-like, and fused states. The pre-stalk state is the state featuring lipid tails exposed to the inter-micellar space; its formation is the rate-limiting step. The stalk state is the state where a localized hydrophobic core is formed connecting two micelles; its formation occurs in conjunction with water expulsion from the inter-micellar space. This study provides insight into the molecular mechanism of fusion from the points of view of energetics, structure, and dynamics. © 2013 Elsevier B.V. All rights reserved.

  5. A SABATH Methyltransferase from the moss Physcomitrella patens catalyzes

    SciTech Connect

    Zhao, Nan; Ferrer, Jean-Luc; Moon, Hong S; Kapteyn, Jeremy; Zhuang, Xiaofeng; Hasebe, Mitsuyasu; Stewart, Neal C.; Gang, David R.; Chen, Feng

    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.

  6. [Novel L-amino acid ligases catalyzing oligopeptide synthesis].

    PubMed

    Kino, Kuniki

    2010-11-01

    L-Amino acid ligase (EC 6.3.2.28) is a microbial enzyme catalyzing formation of an alpha-peptide bond from unprotected L-amino acids in an ATP-dependent manner. The YwfE protein from Bacillus subtilis 168 was the first reported L-amino acid ligase, and it synthesizes various dipeptides. Thereafter, several L-amino acid ligases were newly obtained by in silico analysis using the ATP-grasp motif. But these L-amino acid ligases synthesize only dipeptide and no longer peptide. A novel L-amino acid ligase capable of catalyzing oligopeptide synthesis is required to increase the variety of peptides. We have previously found a new member of L-amino acid ligase, RizA, from B. subtilis NBRC3134, a microorganism that produces the peptide-antibiotic rhizocticin. We newly found that a gene at approximately 9 kbp upstream of rizA encoded a novel L-amino acid ligase RizB. Recombinant RizB synthesized homo-oligomers of branched-chain amino acids consisting of 2 to 5 amino acids, and also synthesized various heteropeptides. RizB is the first reported L-amino acid ligase that catalyzes oligopeptide synthesis. In addition, we obtained L-amino acid ligases showing oligopeptide synthesis activities by in silico analysis using BLAST, which is a set of similarity search programs. These L-amino acid ligases showed low similarity in amino acid sequence, but commonly used branched-chain amino acids, such as RizB, as substrates. Furthermore, the spr0969 protein of Streptococcus pneumoniae synthesized longer peptides than those synthesized by RizB, and the BAD_1200 protein of Bifidobacteria adolescentis showed higher activity toward aromatic amino acids than toward branched-chain ones.

  7. On the Temperature Dependence of Enzyme-Catalyzed Rates.

    PubMed

    Arcus, Vickery L; Prentice, Erica J; Hobbs, Joanne K; Mulholland, Adrian J; Van der Kamp, Marc W; Pudney, Christopher R; Parker, Emily J; Schipper, Louis A

    2016-03-29

    One of the critical variables that determine the rate of any reaction is temperature. For biological systems, the effects of temperature are convoluted with myriad (and often opposing) contributions from enzyme catalysis, protein stability, and temperature-dependent regulation, for example. We have coined the phrase "macromolecular rate theory (MMRT)" to describe the temperature dependence of enzyme-catalyzed rates independent of stability or regulatory processes. Central to MMRT is the observation that enzyme-catalyzed reactions occur with significant values of ΔCp(‡) that are in general negative. That is, the heat capacity (Cp) for the enzyme-substrate complex is generally larger than the Cp for the enzyme-transition state complex. Consistent with a classical description of enzyme catalysis, a negative value for ΔCp(‡) is the result of the enzyme binding relatively weakly to the substrate and very tightly to the transition state. This observation of negative ΔCp(‡) has important implications for the temperature dependence of enzyme-catalyzed rates. Here, we lay out the fundamentals of MMRT. We present a number of hypotheses that arise directly from MMRT including a theoretical justification for the large size of enzymes and the basis for their optimum temperatures. We rationalize the behavior of psychrophilic enzymes and describe a "psychrophilic trap" which places limits on the evolution of enzymes in low temperature environments. One of the defining characteristics of biology is catalysis of chemical reactions by enzymes, and enzymes drive much of metabolism. Therefore, we also expect to see characteristics of MMRT at the level of cells, whole organisms, and even ecosystems.

  8. A Link between Protein Structure and Enzyme Catalyzed Hydrogen Tunneling

    NASA Astrophysics Data System (ADS)

    Bahnson, Brian J.; Colby, Thomas D.; Chin, Jodie K.; Goldstein, Barry M.; Klinman, Judith P.

    1997-11-01

    We present evidence that the size of an active site side chain may modulate the degree of hydrogen tunneling in an enzyme-catalyzed reaction. Primary and secondary kH/kT and kD/kT kinetic isotope effects have been measured for the oxidation of benzyl alcohol catalyzed by horse liver alcohol dehydrogenase at 25 degrees C. As reported in earlier studies, the relationship between secondary kH/kT and kD/kT isotope effects provides a sensitive probe for deviations from classical behavior. In the present work, catalytic efficiency and the extent of hydrogen tunneling have been correlated for the alcohol dehydrogenase-catalyzed hydride transfer among a group of site-directed mutants at position 203. Val-203 interacts with the opposite face of the cofactor NAD+ from the alcohol substrate. The reduction in size of this residue is correlated with diminished tunneling and a two orders of magnitude decrease in catalytic efficiency. Comparison of the x-ray crystal structures of a ternary complex of a high-tunneling (Phe-93 --> Trp) and a low-tunneling (Val-203 --> Ala) mutant provides a structural basis for the observed effects, demonstrating an increase in the hydrogen transfer distance for the low-tunneling mutant. The Val-203 --> Ala ternary complex crystal structure also shows a hyperclosed interdomain geometry relative to the wild-type and the Phe-93 --> Trp mutant ternary complex structures. This demonstrates a flexibility in interdomain movement that could potentially narrow the distance between the donor and acceptor carbons in the native enzyme and may enhance the role of tunneling in the hydride transfer reaction.

  9. Pd-catalyzed decarboxylative cross coupling of potassium polyfluorobenzoates with aryl bromides, chlorides, and triflates.

    PubMed

    Shang, Rui; Xu, Qing; Jiang, Yuan-Ye; Wang, Yan; Liu, Lei

    2010-03-05

    Pd-catalyzed decarboxylative cross coupling of potassium polyfluorobenzoates with aryl bromides, chlorides, and triflates is achieved by using diglyme as the solvent. The reaction is useful for synthesis of polyfluorobiaryls from readily accessible and nonvolatile polyfluorobenzoate salts. Unlike the Cu-catalyzed decarboxylation cross coupling where oxidative addition is the rate-limiting step, in the Pd-catalyzed version decarboxylation is the rate-limiting step.

  10. Gold/acid-co-catalyzed direct microwave-assisted synthesis of fused azaheterocycles from propargylic hydroperoxides.

    PubMed

    Alcaide, Benito; Almendros, Pedro; Quirós, M Teresa

    2014-03-17

    The gold-acid-co-catalyzed synthesis of nine series of fused azaheterocycles with structural diversity starting from the same synthons as readily available propargylic hydroperoxides and aromatic amines has been achieved. The overall tandem process consists in a gold-catalyzed hydroperoxide rearrangement/Michael reaction followed by a final acid-catalyzed cyclization. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Facile Rh(III)-Catalyzed Synthesis of Fluorinated Pyridines

    PubMed Central

    Chen, Shuming; Bergman, Robert G.; Ellman, Jonathan A.

    2015-01-01

    A Rh(III)-catalyzed C–H functionalization approach was developed for the preparation of multi-substituted 3-fluoropyridines from α-fluoro-α,β-unsaturated oximes and alkynes. Oximes substituted with aryl, heteroaryl and alkyl β-substituents were effective coupling partners, as were symmetrical and unsymmetrical alkynes with aryl and alkyl substituents. The first examples of coupling α,β-unsaturated oximes with terminal alkynes was also demonstrated and proceeded with uniformly high regioselectivity to provide single 3-fluoropyridine regioisomers. Reactions were also conveniently set up in air on the bench top. PMID:25992591

  12. Rhodium(NHC)-catalyzed O-arylation of aryl bromides.

    PubMed

    Kim, Hyun Jin; Kim, Min; Chang, Sukbok

    2011-05-06

    The first example of the rhodium-catalyzed O-arylation of aryl bromides is reported. While the right combination of rhodium species and N-heterocyclic carbene (NHC) offered an effective catalytic system enabling the arylation to proceed, the choice of NHC was determined to be most important. The developed O-arylation protocol has a wide range of substrate scope, high functional group tolerance, and flexibility allowing a complementary route to either N- or O-arylation depending on the choice of NHC.

  13. Synthesis of Dihydrobenzofurans via Palladium-Catalyzed Heteroannulations

    SciTech Connect

    Rozhkov, Roman Vladimirovich

    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.

  14. Complex Biotransformations Catalyzed by Radical S-Adenosylmethionine Enzymes*

    PubMed Central

    Zhang, Qi; Liu, Wen

    2011-01-01

    The radical S-adenosylmethionine (AdoMet) superfamily currently comprises thousands of proteins that participate in numerous biochemical processes across all kingdoms of life. These proteins share a common mechanism to generate a powerful 5′-deoxyadenosyl radical, which initiates a highly diverse array of biotransformations. Recent studies are beginning to reveal the role of radical AdoMet proteins in the catalysis of highly complex and chemically unusual transformations, e.g. the ThiC-catalyzed complex rearrangement reaction. The unique features and intriguing chemistries of these proteins thus demonstrate the remarkable versatility and sophistication of radical enzymology. PMID:21771780

  15. Some thoughts on the muon catalyzed fusion reactor

    SciTech Connect

    Takahashi, H.

    1986-01-01

    The design of the muon catalyzed fusion reactor is discussed. Some of the engineering challenges and critical research areas such as ..pi../sup -/ meson transport, beam entry single crystal window and coherent x-ray for stripping the muon from ..cap alpha.. particle, are considered. In order to reduce the tritium inventory and neutron wall loading, use of the laser technique for manipulating the d-t mixture is considered. The heterogeneous d-t mixture using the droplet or jet is discussed. 39 refs., 6 figs.

  16. Can Chlorine Anion Catalyze the Reaction fo HOCl with HCl?

    NASA Technical Reports Server (NTRS)

    Richardson, S. L.; Francisco, J. S.; Mebel, A. M.; Morokuma, K.

    1997-01-01

    The reaction of HOCl + HCl -> Cl2 + H20 in the presence of Cl has been studied using ab initio methods. This reaction has been shown to have a high activation barrier of 46.5 kcal/mol. The chlorine anion, Cl- is found to catalyze the reaction, viz. two mechanisms. The first involves Cl- interacting through the concerted four-center transition state of the neutral reaction. The other mechanism involves the formation of a HCl-HOCl-Cl- intermediate which dissociates into Cl2 + Cl- + H20. The steps are found to have no barriers. The overall exothermicity is 15.5 kcal/mol.

  17. Iridium-Catalyzed Kinetic Asymmetric Transformations of Racemic Allylic Benzoates

    PubMed Central

    Stanley, Levi M.; Bai, Chen; Ueda, Mitsuhiro; Hartwig, John F.

    2010-01-01

    Versatile methods for iridium-catalyzed, kinetic asymmetric substitution of racemic, branched allylic esters are reported. These reactions occur with a variety of aliphatic, aryl, and heteroaryl allylic benzoates to form the corresponding allylic substitution products in high yields (74–96%) with good to excellent enantioselectivity (84–98% ee) with a scope that encompasses a range of anionic carbon and heteroatom nucleophiles. These kinetic asymmetric processes occur with distinct stereochemical courses for racemic aliphatic and aromatic allylic benzoates, and the high reactivity of branched allylic benzoates enables enantioselective allylic substitutions that are slow or poorly selective with linear allylic electrophiles. PMID:20552969

  18. Rhodium-catalyzed enantioselective cyclopropanation of electron deficient alkenes

    PubMed Central

    Wang, Hengbin; Guptill, David M.; Alvarez, Adrian Varela

    2013-01-01

    The rhodium-catalyzed reaction of electron-deficient alkenes with substituted aryldiazoacetates and vinyldiazoacetates results in highly stereoselective cyclopropanations. With adamantylglycine derived catalyst Rh2(S-TCPTAD)4, high asymmetric induction (up to 98% ee) can be obtained with a range of substrates. Computational studies suggest that the reaction is facilitated by weak interaction between the carbenoid and the substrate carbonyl but subsequently proceeds via different pathways depending on the nature of the carbonyl.. Acrylates and acrylamides result in the formation of cyclopropanation products while the use of unsaturated aldehydes and ketones results in the formation of epoxides. PMID:24049630

  19. Kinetics of acid-catalyzed cleavage of cumene hydroperoxide.

    PubMed

    Levin, M E; Gonzales, N O; Zimmerman, L W; Yang, J

    2006-03-17

    The cleavage of cumene hydroperoxide, in the presence of sulfuric acid, to form phenol and acetone has been examined by adiabatic calorimetry. As expected, acid can catalyze cumene hydroperoxide reaction at temperatures below that of thermally-induced decomposition. At elevated acid concentrations, reactivity is also observed at or below room temperature. The exhibited reactivity behavior is complex and is significantly affected by the presence of other species (including the products). Several reaction models have been explored to explain the behavior and these are discussed.

  20. Palladium-Catalyzed Carbonylation of sec- and tert-Alcohols.

    PubMed

    Dong, Kaiwu; Sang, Rui; Liu, Jie; Razzaq, Rauf; Franke, Robert; Jackstell, Ralf; Beller, Matthias

    2017-05-22

    A general palladium-catalyzed synthesis of linear esters directly from sec- and tert-alcohols is described. Compared to the classic Koch-Haaf reaction, which leads to branched products, this new transformation gives the corresponding linear esters in high yields and selectivity. Key for this protocol is the use of an advanced palladium catalyst system with L2 (py(t) bpx) as the ligand. A variety of aliphatic and benzylic alcohols can be directly used and the catalyst efficiency for the benchmark reaction is outstanding (turnover number up to 89 000). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Lipase-catalyzed aza-Michael reaction on acrylate derivatives.

    PubMed

    Steunenberg, Peter; Sijm, Maarten; Zuilhof, Han; Sanders, Johan P M; Scott, Elinor L; Franssen, Maurice C R

    2013-04-19

    A methodology has been developed for an efficient and selective lipase-catalyzed aza-Michael reaction of various amines (primary and secondary) with a series of acrylates and alkylacrylates. Reaction parameters were tuned, and under the optimal conditions it was found that Pseudomonas stutzeri lipase and Chromobacterium viscosum lipase showed the highest selectivity for the aza-Michael addition to substituted alkyl acrylates. For the first time also, some CLEAs were examined that showed a comparable or higher selectivity and yield than the free enzymes and other formulations.

  2. Iron-Catalyzed Cross-Coupling of Alkenyl Acetates.

    PubMed

    Gärtner, Dominik; Stein, André Luiz; Grupe, Sabine; Arp, Johannes; Jacobi von Wangelin, Axel

    2015-09-01

    Stable C-O linkages are generally unreactive in cross-coupling reactions which mostly employ more electrophilic halides or activated esters (triflates, tosylates). Acetates are cheap and easily accessible electrophiles but have not been used in cross-couplings because the strong C-O bond and high propensity to engage in unwanted acetylation and deprotonation. Reported herein is a selective iron-catalyzed cross-coupling of diverse alkenyl acetates, and it operates under mild reaction conditions (0 °C, 2 h) with a ligand-free catalyst (1-2 mol%).

  3. Cooperative Catalysis: Calcium and Camphorsulfonic Acid Catalyzed Cycloisomerization of Diynols.

    PubMed

    Rauser, Marian; Schroeder, Sebastian; Niggemann, Meike

    2015-11-02

    The first transition metal-free cycloisomerization of easily accessible diynols is presented as a novel approach to bicyclic 2H-pyrans. As a one-step protocol, the reaction proceeds in a single reaction cascade by intertwining mechanistic fragments borrowed from transition metal-catalyzed Claisen rearrangment of vinyl ethers with our own work on allenyl/propargyl cation rearrangements and a 6π-oxo-electrocylization. It is enabled by a new cooperative catalytic system that combines a simple Ca(2+) catalyst with camphorsulfonic acid. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Lipase-catalyzed synthesis of monoacylglycerol in a homogeneous system.

    PubMed

    Monteiro, Julieta B; Nascimento, Maria G; Ninow, Jorge L

    2003-04-01

    The 1,3-regiospecifique lipase, Lipozyme IM, catalyzed the esterification of lauric acid and glycerol in a homogeneous system. To overcome the drawback of the insolubility of glycerol in hexane, which is extensively used in enzymatic synthesis, a mixture of n-hexane/tert-butanol (1:1, v/v) was used leading to a monophasic system. The conversion of lauric acid into monolaurin was 65% in 8 h, when a molar ratio of glycerol to fatty acid (5:1) was used with the fatty acid at 0.1 M, and the phenomenon of acyl migration was minimized.

  5. Iridium(I)-Catalyzed Regio- and Enantioselective Allylic Amidation

    PubMed Central

    Singh, Om V.; Han, Hyunsoo

    2009-01-01

    Ir(I)-catalyzed intermolecular allylic amidation of ethyl allylic carbonates with soft nitrogen nucleophiles under completely “salt-free” conditions is described. A combination of [Ir(COD)Cl]2, a chiral phosphoramidite ligand L*, and DBU as a base in THF effects the reaction. The reaction appears to be quite general, accommodating a wide variety of R-groups and soft nitrogen nucleophiles, and proceeds with excellent regio- and enantioselectivities to afford the branched N-protected allylic amines. The developed reaction was conveniently utilized in the asymmetric synthesis of Boc protected α- and β-amino acids as well as (−)-cytoxazone. PMID:19554202

  6. Iridium-Catalyzed (Z)-Trialkylsilylation of Terminal Olefins

    PubMed Central

    Lu, Biao; Falck, J. R.

    2010-01-01

    A complex of commercial [Ir(OMe)(cod)]2 and 4,4-di-tert-butyl-2,2-bipyridine (dtbpy) catalyzes the Z-selective, dehydrative silylation of terminal alkenes, but not 1,2-disubstituted alkenes, with triethylsilane or benzyldimethylsilane in THF at 40 °C. Yields and Z-stereoselectivity were significantly improved by 2-norbornene, in contrast with other sacrificial alkenes. The reaction is compatible with many functional groups including epoxides, ketones, amides, alcohols, esters, halides, ketals and silanes. a,b-Unsaturated esters were unreactive. The reaction probably proceeds through a Heck-type mechanism. PMID:20136153

  7. Base-Catalyzed Depolymerization of Lignin: Separation of Monomers

    SciTech Connect

    Vigneault, A.; Johnson, D. K.; Chornet, E.

    2007-12-01

    In our quest for fractionating lignocellulosic biomass and valorizing specific constitutive fractions, we have developed a strategy for the separation of 12 added value monomers generated during the hydrolytic based-catalyzed depolymerization of a Steam Exploded Aspen Lignin. The separation strategy combines liquid-liquid-extraction (LLE), followed by vacuum distillation, liquid chromatography (LC) and crystallization. LLE, vacuum distillation and flash LC were tested experimentally. Batch vacuum distillation produced up to 4 fractions. Process simulation confirmed that a series of 4 vacuum distillation columns could produce 5 distinct monomer streams, 3 of which require further chromatography and crystallization for purification.

  8. Aminoacyl-RNA synthesis catalyzed by an RNA.

    PubMed

    Illangasekare, M; Sanchez, G; Nickles, T; Yarus, M

    1995-02-03

    An RNA has been selected that rapidly aminoacylates its 2'(3') terminus when provided with phenylalanyl-adenosine monophosphate. That is, the RNA accelerates the same aminoacyl group transfer catalyzed by protein aminoacyl-transfer RNA synthetases. The best characterized RNA reaction requires both Mg2+ and Ca2+. These results confirm a necessary prediction of the RNA world hypothesis and represent efficient RNA reaction (> or = 10(5) times accelerated) at a carbonyl carbon, exemplifying a little explored type of RNA catalysis.

  9. New modes for the osmium-catalyzed oxidative cyclization.

    PubMed

    Donohoe, Timothy J; Lindsay-Scott, Peter J; Parker, Jeremy S; Callens, Cedric K A

    2010-03-05

    The osmium-catalyzed oxidative cyclization of amino alcohol initiators formally derived from 1,4-dienes is an effective method for the construction of pyrrolidines, utilizing a novel reoxidant (4-nitropyridine N-oxide = NPNO). The cyclization of enantiopure syn- and anti-amino alcohols gives rise to enantiopure cis- and trans-2,5-disubstituted pyrrolidines, respectively. Moreover, the cyclization of bis-homoallylic amines bearing an exocyclic chelating group is shown to be a complementary method for trans-pyrrolidine formation.

  10. Synthesis of Optically Active Polystyrene Catalyzed by Monophosphine Pd Complexes.

    PubMed

    Jouffroy, Matthieu; Armspach, Dominique; Matt, Dominique; Osakada, Kohtaro; Takeuchi, Daisuke

    2016-07-11

    Cationic Pd(II) monophosphine complexes derived from α- and β-cyclodextrins (CDs) promote the homopolymerization of styrene under carbon monoxide pressure. Although reversible CO coordination takes place under catalytic conditions according to (13) C NMR studies with (13) C-enriched CO, both complexes catalyze the formation of CO-free styrene polymers. These macromolecules display optical activity as a result of the presence of stereoregular sequences within the overall atactic polymer. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Palladium-Catalyzed Enantioselective Decarboxylative Allylic Alkylation of Cyclopentanones.

    PubMed

    Craig, Robert A; Loskot, Steven A; Mohr, Justin T; Behenna, Douglas C; Harned, Andrew M; Stoltz, Brian M

    2015-11-06

    The first general method for the enantioselective construction of all-carbon quaternary centers on cyclopentanones by enantioselective palladium-catalyzed decarboxylative allylic alkylation is described. Employing the electronically modified (S)-(p-CF3)3-t-BuPHOX ligand, α-quaternary cyclopentanones were isolated in yields up to >99% with ee's up to 94%. Additionally, in order to facilitate large-scale application of this method, a low catalyst loading protocol was employed, using as little as 0.15 mol % Pd, furnishing the product without any loss in ee.

  12. Iridium-catalyzed (Z)-trialkylsilylation of terminal olefins.

    PubMed

    Lu, Biao; Falck, J R

    2010-03-05

    A complex of commercial [Ir(OMe)(cod)](2) and 4,4-di-tert-butyl-2,2-bipyridine (dtbpy) catalyzes the Z-selective, dehydrative silylation of terminal alkenes, but not 1,2-disubstituted alkenes, with triethylsilane or benzyldimethylsilane in THF at 40 degrees C. Yields and Z-stereoselectivity were significantly improved by 2-norbornene, in contrast with other sacrificial alkenes. The reaction is compatible with many functional groups including epoxides, ketones, amides, alcohols, esters, halides, ketals, and silanes. alpha,beta-Unsaturated esters were unreactive. The reaction probably proceeds through a Heck-type mechanism.

  13. Nickel-Catalyzed Allylic Substitution of Simple Alkenes

    PubMed Central

    Matsubara, Ryosuke; Jamison, Timothy F.

    2011-01-01

    This report describes a nickel-catalyzed allylic substitution process of simple alkenes whereby an important structural motif, a 1,4-diene, was prepared. A key for this success is the use of an appropriate Ni-phosphine complex and a stoichiometric amount of silyl triflate. Reactions of 1-alkyl-substituted alkenes consistently provided 1,1-disubstituted alkenes with high selectivity. Insight into the reaction mechanism as well as miscellaneous application of the developed catalytic process is also documented. PMID:21387565

  14. Palladium-Catalyzed Fluoroarylation of gem-Difluoroalkenes.

    PubMed

    Tang, Hai-Jun; Lin, Ling-Zhi; Feng, Chao; Loh, Teck-Peng

    2017-08-07

    A Pd-catalyzed fluoroarylation of gem-difluoroalkenes with aryl halides is reported. By taking advantage of the in situ generated α-CF3 -benzylsilver intermediates derived from the nucleophilic addition of silver fluoride to gem-difluoroalkenes, this strategy bypasses the use of a strong base, thus enabling a mild and general synthetic method for ready access to non-symmetric α,α-disubstituted trifluoroethane derivatives. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Direct metal-catalyzed regioselective functionalization of enamides.

    PubMed

    Gigant, Nicolas; Chausset-Boissarie, Laëtitia; Gillaizeau, Isabelle

    2014-06-16

    Enamides are stable enamine surrogates and provide key intermediates for the synthesis of small but complex nitrogen-containing compounds. Metal-catalyzed regioselective functionalization of enamides provides a rapid method to synthesize useful nitrogen containing heterocycles. This review discloses the recent progress made in the development of the C-H functionalization of enamides involving efficient and atom-economical routes. Syntheses of different heterocycles are classified based on the site reactivity of enamides and key mechanistic insights are given for each transformation.

  16. Copper-Catalyzed Azide–Alkyne Click Chemistry for Bioconjugation

    PubMed Central

    Presolski, Stanislav I.; Hong, Vu Phong; Finn, M.G.

    2012-01-01

    The copper-catalyzed azide-alkyne cycloaddition reaction is widely used for the connection of molecular entities of all sizes. A protocol is provided here for the process with biomolecules. Ascorbate is used as reducing agent to maintain the required cuprous oxidation state. Since these convenient conditions produce reactive oxygen species, five equivalents of a copper-binding ligand is used with respect to metal. The ligand both accelerates the reaction and serves as a sacrificial reductant, protecting the biomolecules from oxidation. A procedure is also described for testing the efficiency of the reaction under desired conditions for purposes of optimization, before expensive biological reagents are used. PMID:22844652

  17. Cobalt-Catalyzed Z-Selective Hydrosilylation of Terminal Alkynes.

    PubMed

    Teo, Wei Jie; Wang, Chao; Tan, Ye Wei; Ge, Shaozhong

    2017-03-07

    A cobalt-catalyzed Z-selective hydrosilylation of alkynes has been developed relying on catalysts generated from bench-stable Co(OAc)2 and pyridine-2,6-diimine (PDI) ligands. A variety of functionalized aromatic and aliphatic alkynes undergo this transformation, yielding Z-vinylsilanes in high yields with excellent selectivities (Z/E ratio ranges from 90:10 to >99:1). The addition of a catalytic amount of phenol effectively suppressed the Z/E-isomerization of the Z-vinylsilanes that formed under catalytic conditions.

  18. Ruthenium-Catalyzed meta-Selective C—H Bromination

    PubMed Central

    Teskey, Christopher J; Lui, Andrew Y W; Greaney, Michael F

    2015-01-01

    The first example of a transition-metal-catalyzed, meta-selective C–H bromination procedure is reported. In the presence of catalytic [{Ru(p-cymene)Cl2}2], tetrabutylammonium tribromide can be used to functionalize the meta C–H bond of 2-phenylpyridine derivatives, thus affording difficult to access products which are highly predisposed to further derivatization. We demonstrate this utility with one-pot bromination/arylation and bromination/alkenylation procedures to deliver meta-arylated and meta-alkenylated products, respectively, in a single step. PMID:26288217

  19. Transition-metal-catalyzed asymmetric allylic dearomatization reactions.

    PubMed

    Zhuo, Chun-Xiang; Zheng, Chao; You, Shu-Li

    2014-08-19

    Dearomatization reactions serve as powerful methods for the synthesis of highly functionalized, three-dimensional structures starting with simple planar aromatic compounds. Among processes of this type, catalytic asymmetric dearomatization (CADA) reactions are attractive owing to the large number of aromatic compounds that are readily available and the fact that they enable direct access to enantiopure polycycles and spirocycles, which frequently are key structural motifs in biologically active natural products and pharmaceuticals. However, as a consequence of their high stabilities, arenes only difficultly participate in dearomatization reactions that take place with high levels of enantioselectivity. Transition-metal-catalyzed asymmetric allylic substitution reactions have been demonstrated to be powerful methods for enantioselective formation of C-C and C-X (X = O, N, S, etc.) bonds. However, the scope of these processes has been explored mainly using soft carbon nucleophiles, some hard carbon nucleophiles such as enolates and preformed organometallic reagents, and heteroatom nucleophiles. Readily accessible aromatic compounds have been only rarely used directly as nucleophiles in these reactions. In this Account, we present the results of studies we have conducted aimed at the development of transition-metal-catalyzed asymmetric allylic dearomatization reactions. By utilizing this general process, we have devised methods for direct dearomatization of indoles, pyrroles, phenols, naphthols, pyridines, and pyrazines, which produce various highly functionalized structural motifs bearing all-carbon quaternary stereogenic centers in a straightforward manner. In mechanistic investigations of the dearomatization process, we found that the five-membered spiroindolenines serve as intermediates, which readily undergo stereospecific allylic migration to form corresponding tetrahydro-1H-carbazoles upon treatment with a catalytic amount of TsOH. It is worth noting that no

  20. Fe-catalyzed etching of exfoliated graphite through carbon hydrogenation

    PubMed Central

    Cheng, Guangjun; Calizo, Irene; Hacker, Christina A.; Richter, Curt A.; Hight Walker, Angela R.

    2016-01-01

    We present an investigation on Fe-catalyzed etching of graphite by dewetting Fe thin films on graphite in forming gas. Raman mapping of the etched graphite shows thickness variation in the etched channels and reveals that the edges are predominately terminated in zigzag configuration. X-ray diffraction and photoelectron spectroscopy measurements identify that the catalytic particles are Fe with the presence of iron carbide and iron oxides. The existence of iron carbide indicates that, in additional to carbon hydrogenation, carbon dissolution into Fe is also involved during etching. Furthermore, the catalytic particles can be re-activated upon a second annealing in forming gas. PMID:27840449

  1. Coalification by clay-catalyzed oligomerization of plant monomers

    SciTech Connect

    Orchin, M.; Wilson, R.M.

    1991-01-01

    The chemical structure'' of coal, if indeed there is one, remains an enigma. Over the years numerous chemists have integrated a host of experimental observations to generate various average'' structures which differ greatly. Our approach is to regard the structural question of coal as a problem in natural product chemistry. Our model is that of a macromolecular polymer initially synthesized from monomeric naturally-occuring hydroxy and methoxy substituted propenylbenzenes (C{sub 6}-C{sub 3} units), properly aligned to undergo oligomerization reactions via conventional organic reaction mechanisms, specifically Diels-Alder radical cation condensations, phenolic coupling, and proton-catalyzed isomerization and cyclization.

  2. Enantioselective palladium(0)-catalyzed Nazarov-type cyclization.

    PubMed

    Kitamura, Kei; Shimada, Naoyuki; Stewart, Craig; Atesin, Abdurrahman C; Ateşin, Tülay A; Tius, Marcus A

    2015-05-18

    A Pd(0)-catalyzed asymmetric Nazarov-type cyclization is described. The optimized ligand for the reaction incorporates a weakly coordinating pyridine ring into a TADDOL-derived phosphoramidite (TADDOL=α,α,α,α-tetraaryl-1,3-dioxolane-4,5-dimethanol). The reaction leads to the formation of cyclopentenones as single diastereoisomers that incorporate two contiguous asymmetric centers, one tertiary and one an all-carbon-atom quaternary stereocenter, in high yield and optical purity. It is noteworthy that the reaction does not require that substrates should be activated by aryl substituents. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Stereoselective synthesis of cyclohexanones via phase transfer catalyzed double addition of nucleophiles to divinyl ketones.

    PubMed

    Silvanus, Andrew C; Groombridge, Benjamin J; Andrews, Benjamin I; Kociok-Köhn, Gabriele; Carbery, David R

    2010-11-05

    Functionalized cyclohexanones are formed in excellent yield and diastereoselectivity from a phase transfer catalyzed double addition of active methylene pronucleophiles to nonsymmetrical divinyl ketones.

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

    SciTech Connect

    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.

  5. Recent Developments in Metal-Catalyzed Additions of Oxygen Nucleophiles to Alkenes and Alkynes

    NASA Astrophysics Data System (ADS)

    Hintermann, Lukas

    Progress in the field of metal-catalyzed redox-neutral additions of oxygen nucleophiles (water, alcohols, carboxylic acids, and others) to alkenes, alkynes, and allenes between 2001 and 2009 is critically reviewed. Major advances in reaction chemistry include development of chiral Lewis acid catalyzed asymmetric oxa-Michael additions and Lewis-acid catalyzed hydro-alkoxylations of nonactivated olefins, as well as further development of Markovnikov-selective cationic gold complex-catalyzed additions of alcohols or water to alkynes and allenes.

  6. Enhancement of photosensitivity in the alcohol-added ferroin-catalyzed Belousov-Zhabotinsky reaction system

    NASA Astrophysics Data System (ADS)

    Jiro, Abe; Kazuhisa, Matsuda; Masakazu, Taka; Yasuo, Shirai

    1995-10-01

    The observation of photoinduced image formation in the alcohol-added ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction is reported. It is found that alcohol acts as a reagent that reduces the activation energy both of the ferroin-catalyzed and the Ce-catalyzed BZ reaction system and enhances the photosensitivity. By comparing the photosensitivity and photoinduced image formation for the ferroin-catalyzed BZ system with and without alcohol, we concluded that the photosensitivity of this alcohol-added BZ reaction system is enhanced by the presence of alcohol. This enhancement of the photosensitivity was confirmed in other alcohols such as ethanol, 1-propanol and 2-propanol.

  7. Cytochromes P450 Catalyze the Reduction of α,β-Unsaturated Aldehydes

    PubMed Central

    Amunom, Immaculate; Dieter, Laura J.; Tamasi, Viola; Cai, Jan; Conklin, Daniel J.; Srivastava, Sanjay; Martin, Martha V.; Guengerich, F. Peter; Prough, Russell A.

    2011-01-01

    The metabolism of α,β-unsaturated aldehydes, e.g. 4-hydroxynonenal, involves oxidation to carboxylic acids, reduction to alcohols, and glutathionylation to eventually form mercapturide conjugates. Recently we demonstrated that P450s can oxidize aldehydes to carboxylic acids, a reaction previously thought to involve aldehyde dehydrogenase. When recombinant cytochrome P450 3A4 was incubated with 4-hydroxynonenal, O2, and NADPH, several products were produced, including 1,4-dihydroxynonene (DHN), 4-hydroxy-2-nonenoic acid (HNA), and an unknown metabolite. Several P450s catalyzed the reduction reaction in the order (human) P450 2B6 ≅ P450 3A4 > P450 1A2 > P450 2J2 > (mouse) P450 2c29. Other P450s did not catalyze the reduction reaction (human P450 2E1 & rabbit P450 2B4). Metabolism by isolated rat hepatocytes showed that HNA formation was inhibited by cyanamide, while DHN formation was not affected. Troleandomycin increased HNA production 1.6-fold while inhibiting DHN formation, suggesting that P450 3A11 is a major enzyme involved in rat hepatic clearance of 4-HNE. A fluorescent assay was developed using 9-anthracenealdehyde to measure both reactions. Feeding mice diet containing t-butylated hydroxyanisole increased the level of both activities with hepatic microsomal fractions, but not proportionally. Miconazole (0.5 mM) was a potent inhibitor of these microsomal reduction reactions, while phenytoin and α-naphthoflavone (both at 0.5 mM) were partial inhibitors, suggesting the role of multiple P450 enzymes. The oxidative metabolism of these aldehydes was inhibited >90% in an Ar or CO atmosphere, while the reductive reactions were not greatly affected. These results suggest that P450s are significant catalysts of reduction of α,β-unsaturated aldehydes in liver. PMID:21766881

  8. Cytochromes P450 catalyze the reduction of α,β-unsaturated aldehydes.

    PubMed

    Amunom, Immaculate; Dieter, Laura J; Tamasi, Viola; Cai, Jian; Conklin, Daniel J; Srivastava, Sanjay; Martin, Martha V; Guengerich, F Peter; Prough, Russell A

    2011-08-15

    The metabolism of α,β-unsaturated aldehydes, e.g., 4-hydroxynonenal, involves oxidation to carboxylic acids, reduction to alcohols, and glutathionylation to eventually form mercapturide conjugates. Recently, we demonstrated that P450s can oxidize aldehydes to carboxylic acids, a reaction previously thought to involve aldehyde dehydrogenase. When recombinant cytochrome P450 3A4 was incubated with 4-hydroxynonenal, O(2), and NADPH, several products were produced, including 1,4-dihydroxynonene (DHN), 4-hydroxy-2-nonenoic acid (HNA), and an unknown metabolite. Several P450s catalyzed the reduction reaction in the order (human) P450 2B6 ≅ P450 3A4 > P450 1A2 > P450 2J2 > (mouse) P450 2c29. Other P450s did not catalyze the reduction reaction (human P450 2E1 and rabbit P450 2B4). Metabolism by isolated rat hepatocytes showed that HNA formation was inhibited by cyanamide, while DHN formation was not affected. Troleandomycin increased HNA production 1.6-fold while inhibiting DHN formation, suggesting that P450 3A11 is a major enzyme involved in rat hepatic clearance of 4-HNE. A fluorescent assay was developed using 9-anthracenealdehyde to measure both reactions. Feeding mice a diet containing t-butylated hydroxyanisole increased the level of both activities with hepatic microsomal fractions but not proportionally. Miconazole (0.5 mM) was a potent inhibitor of these microsomal reduction reactions, while phenytoin and α-naphthoflavone (both at 0.5 mM) were partial inhibitors, suggesting the role of multiple P450 enzymes. The oxidative metabolism of these aldehydes was inhibited >90% in an Ar or CO atmosphere, while the reductive reactions were not greatly affected. These results suggest that P450s are significant catalysts of the reduction of α,β-unsaturated aldehydes in the liver.

  9. Efficient synthesis of frutinone A and its derivatives through palladium-catalyzed C - H activation/carbonylation.

    PubMed

    Shin, Yongje; Yoo, Changho; Moon, Youngtaek; Lee, Yunho; Hong, Sungwoo

    2015-04-01

    Frutinone A, a biologically active ingredient of an antimicrobial herbal extract, demonstrates potent inhibitory activity towards the CYP1A2 enzyme. A three-step total synthesis of frutinone A with an overall yield of 44 % is presented. The construction of the chromone-annelated coumarin core was achieved through palladium-catalyzed CH carbonylation of 2-phenolchromones. The straightforward synthetic route allowed facile substitutions around the frutinone A core and thus rapid exploration of the structure-activity relationship (SAR) profile of the derivatives. The inhibitory activity of the synthesized frutinone A derivatives were determined for CYP1A2, and ten compounds exhibited one-to-two digit nanomolar inhibitory activity towards the CYP1A2 enzyme.

  10. Search for muon catalyzed d 3He-fusion

    NASA Astrophysics Data System (ADS)

    Maev, E. M.; Balin, D. V.; Case, T.; Crowe, K. M.; Del Rosso, A.; Ganzha, V. A.; Hartmann, F. J.; Kozlov, S. M.; Lauss, B.; Maev, O. E.; Mühlbauer, M.; Mulhauser, F.; Petitjean, C.; Petrov, G. E.; Sadetsky, S. M.; Schapkin, G. N.; Schott, W.; Semenchuk, G. G.; Smirenin, Yu. V.; Soroka, M. A.; Vasiliev, A. A.; Vorobyov, A. A.; Voropaev, N. I.; Zmeskal, J.

    1999-06-01

    We report on the results of an experiment aimed at observing muon-catalyzed d 3He-fusion with a setup previously used for studies of the muon-catalyzed dd-fusion. The basic element of the setup is a high pressure ionization chamber operating as an active target. In this experiment the chamber was filled with an HD + 3He (5.6%) gas mixture at 13.2 bar pressure and 50 K temperature. These conditions were chosen as optimal for formation of the 3Heμd-molecules with a low level of background from the d-μ-d fusion. The chamber was exposed to the negative muon beam at PSI. During a 3-week data-taking period, 9.7 × 108 muon stops have been selected. The analysis of the data was able to determine a new upper limit for the d 3He-fusion rate in the 3Heμd-molecule (λf≤ 6× 104 s-1), which is more than three orders of magnitude lower than the previously existed limit.

  11. Laccase catalyzed covalent coupling of fluorophenols increases lignocellulose surface hydrophobicity.

    PubMed

    Kudanga, Tukayi; Prasetyo, Endry Nugroho; Widsten, Petri; Kandelbauer, Andreas; Jury, Sandra; Heathcote, Carol; Sipilä, Jussi; Weber, Hansjoerg; Nyanhongo, Gibson S; Guebitz, Georg M

    2010-04-01

    This work presents for the first time the mechanistic evidence of a laccase-catalyzed method of covalently grafting hydrophobicity enhancing fluorophenols onto Fagus sylvatica veneers. Coupling of fluorophenols onto complex lignin model compounds guaiacylglycerol beta-guaiacyl ether and syringylglycerol beta-guaiacyl ether was demonstrated by LC-MS and NMR. Laccase-mediated coupling increased binding of 4-[4-(trifluoromethyl)phenoxy]phenol (4,4-F3MPP) and 4-(trifluoromethoxy)phenol (4-F3MP) to veneers by 77.1% and 39.2%, respectively. XPS studies showed that laccase-catalyzed grafting of fluorophenols resulted in a fluorine content of 6.39% for 4,4-F3MPP, 3.01% for 4-F3MP and 0.26% for 4-fluoro-2-methylphenol (4,2-FMP). Grafting of the fluorophenols 4,2-FMP, 4-F3MP and 4,4-F3MPP led to a 9.6%, 28.6% and 65.5% increase in hydrophobicity, respectively, when compared to treatments with the respective fluorophenols in the absence of laccase, in good agreement with XPS data. Copyright 2009 Elsevier Ltd. All rights reserved.

  12. Chloride-catalyzed corrosion of plutonium in glovebox atmospheres

    SciTech Connect

    Burgess, M.; Haschke, J.M.; Allen, T.H.; Morales, L.A.; Jarboe, D.M.; Puglisi, C.V.

    1998-04-01

    Characterization of glovebox atmospheres and the black reaction product formed on plutonium surfaces shows that the abnormally rapid corrosion of components in the fabrication line is consistent with a complex salt-catalyzed reaction involving gaseous hydrogen chloride (HCl) and water. Analytical data verify that chlorocarbon and HCl vapors are presented in stagnant glovebox atmospheres. Hydrogen chloride concentrations approach 7 ppm at some locations in the glovebox line. The black corrosion product is identified as plutonium monoxide monohydride (PuOH), a product formed by hydrolysis of plutonium in liquid water and salt solutions at room temperature. Plutonium trichloride (PuCl{sub 3}) produced by reaction of HCl at the metal surface is deliquescent and apparently forms a highly concentrated salt solution by absorbing moisture from the glovebox atmosphere. Rapid corrosion is attributed to the ensuing salt-catalyzed reaction between plutonium and water. Experimental results are discussed, possible involvement of hydrogen fluoride (HF) is examined, and methods of corrective action are presented in this report.

  13. Mechanism of Water Oxidation Catalyzed by a Mononuclear Manganese Complex.

    PubMed

    Li, Ying-Ying; Ye, Ke; Siegbahn, Per E M; Liao, Rong-Zhen

    2016-12-07

    The design and synthesis of biomimetic Mn complexes to catalyze oxygen evolution is a very appealing goal because water oxidation in nature employs a Mn complex. Recently, the mononuclear Mn complex [LMn(II) (H2 O)2 ](2+) [1, L=Py2 N(tBu)2 , Py=pyridyl] was reported to catalyze water oxidation electrochemically at an applied potential of 1.23 V at pH 12.2 in aqueous solution. Density functional calculations were performed to elucidate the mechanism of water oxidation promoted by this catalyst. The calculations showed that 1 can lose two protons and one electron readily to produce [LMn(III) (OH)2 ](+) (2), which then undergoes two sequential proton-coupled electron-transfer processes to afford [LMn(V) OO](+) (4). The O-O bond formation can occur through direct coupling of the two oxido ligands or through nucleophilic attack of water. These two mechanisms have similar barriers of approximately 17 kcal mol(-1) . The further oxidation of 4 to generate [LMn(VI) OO](2+) (5), which enables O-O bond formation, has a much higher barrier. In addition, ligand degradation by C-H activation has a similar barrier to that for the O-O bond formation, and this explains the relatively low turnover number of this catalyst.

  14. Can proteins and crystals self-catalyze methyl rotations?

    SciTech Connect

    Smith, Jeremy C; Baudry, Jerome

    2005-10-01

    The {chi} (C{sub {alpha}}-C{sub {beta}}) torsional barrier in the dipeptide alanine (N-methyl-l-alanyl-N-methylamide) crystal was investigated using ab initio calculations at various levels of theory, molecular mechanics, and molecular dynamics. For one of the two molecules in the asymmetric unit the calculations suggest that rotation around the ? dihedral angle is catalyzed by the crystal environment, reducing by up to 2kT the torsional barrier in the crystal with respect to that in the gas phase. This catalytic effect is present at both low and room temperature and originates from a van der Waals destabilization of the minima in the methyl dihedral potential coming from the nonbonded environment of the side chain. Screening of a subset of the Protein Data Bank with a pharmacophore model reproducing the crystal environment around this side chain methyl identified a protein containing an alanine residue with an environment similar to that in the crystal. Calculations indicate that this ? torsional barrier is also reduced in the protein at low temperature but not at room temperature. This suggests that environment-catalyzed rotation of methyl groups can occur both in the solid phase and in native biological structures, though this effect might be temperature-dependent. The relevance of this catalytic effect is discussed in terms of its natural occurrence and its possible contribution to the low-frequency vibrational modes of molecules.

  15. Mechanistic Elucidation of Zirconium-Catalyzed Direct Amidation.

    PubMed

    Lundberg, Helena; Tinnis, Fredrik; Zhang, Jiji; Algarra, Andrés G; Himo, Fahmi; Adolfsson, Hans

    2017-02-15

    The mechanism of the zirconium-catalyzed condensation of carboxylic acids and amines for direct formation of amides was studied using kinetics, NMR spectroscopy, and DFT calculations. The reaction is found to be first order with respect to the catalyst and has a positive rate dependence on amine concentration. A negative rate dependence on carboxylic acid concentration is observed along with S-shaped kinetic profiles under certain conditions, which is consistent with the formation of reversible off-cycle species. Kinetic experiments using reaction progress kinetic analysis protocols demonstrate that inhibition of the catalyst by the amide product can be avoided using a high amine concentration. These insights led to the design of a reaction protocol with improved yields and a decrease in catalyst loading. NMR spectroscopy provides important details of the nature of the zirconium catalyst and serves as the starting point for a theoretical study of the catalytic cycle using DFT calculations. These studies indicate that a dinuclear zirconium species can catalyze the reaction with feasible energy barriers. The amine is proposed to perform a nucleophilic attack at a terminal η(2)-carboxylate ligand of the zirconium catalyst, followed by a C-O bond cleavage step, with an intermediate proton transfer from nitrogen to oxygen facilitated by an additional equivalent of amine. In addition, the DFT calculations reproduce experimentally observed effects on reaction rate, induced by electronically different substituents on the carboxylic acid.

  16. RNA catalyzes nuclear pre-mRNA splicing

    PubMed Central

    Fica, Sebastian M.; Tuttle, Nicole; Novak, Thaddeus; Li, Nan-Sheng; Lu, Jun; Koodathingal, Prakash; Dai, Qing; Staley, Jonathan P.; Piccirilli, Joseph A.

    2014-01-01

    SUMMARY In nuclear pre-messenger RNA splicing, introns are excised by the spliceosome, a multi-megadalton machine composed of both proteins and small nuclear RNAs (snRNAs). Over thirty years ago, following the discovery of self-splicing group II intron RNAs, the snRNAs were hypothesized to catalyze splicing. However, no definitive evidence for a role of either RNA or protein in catalysis by the spliceosome has been reported to date. By using metal rescue strategies, here we show that the U6 snRNA catalyzes both splicing reactions by positioning divalent metals that stabilize the leaving groups during each reaction. Strikingly, all of the U6 catalytic metal ligands we identified correspond to the ligands observed to position catalytic, divalent metals in crystal structures of a group II intron RNA. These findings indicate that group II introns and the spliceosome share common catalytic mechanisms, and likely common evolutionary origins. Our results demonstrate that RNA mediates catalysis within the spliceosome. PMID:24196718

  17. Firefly bioluminescence: a mechanistic approach of luciferase catalyzed reactions.

    PubMed

    Marques, Simone M; Esteves da Silva, Joaquim C G

    2009-01-01

    Luciferase is a general term for enzymes catalyzing visible light emission by living organisms (bioluminescence). The studies carried out with Photinus pyralis (firefly) luciferase allowed the discovery of the reaction leading to light production. It can be regarded as a two-step process: the first corresponds to the reaction of luciferase's substrate, luciferin (LH(2)), with ATP-Mg(2+) generating inorganic pyrophosphate and an intermediate luciferyl-adenylate (LH(2)-AMP); the second is the oxidation and decarboxylation of LH(2)-AMP to oxyluciferin, the light emitter, producing CO(2), AMP, and photons of yellow-green light (550- 570 nm). In a dark reaction LH(2)-AMP is oxidized to dehydroluciferyl-adenylate (L-AMP). Luciferase also shows acyl-coenzyme A synthetase activity, which leads to the formation of dehydroluciferyl-coenzyme A (L-CoA), luciferyl-coenzyme A (LH(2)-CoA), and fatty acyl-CoAs. Moreover luciferase catalyzes the synthesis of dinucleoside polyphosphates from nucleosides with at least a 3'-phosphate chain plus an intact terminal pyrophosphate moiety. The LH(2) stereospecificity is a particular feature of the bioluminescent reaction where each isomer, D-LH(2) or L-LH(2), has a specific function. Practical applications of the luciferase system, either in its native form or with engineered proteins, encloses the analytical assay of metabolites like ATP and molecular biology studies with luc as a reporter gene, including the most recent and increasing field of bioimaging.

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

    PubMed

    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.

  19. Mechanism of methane formation in potassium catalyzed carbon gasification

    SciTech Connect

    Mims, C.A.; Krajewski, J.J.

    1986-11-01

    The authors have performed a kinetics and isotope tracer study of the mechanism of CH/sub 4/ formation from a potassium catalyzed carbon during gasification in atmospheres containing H/sub 2/O, H/sub 2/, CO/sub 2/, and CO Temperatures from 925 to 1025 K and pressures up to 8 atm were studied. The authors found that although potassium salts catalyze the formation of CH/sub 4/, there is not a one-to-one correspondence between CH/sub 4/ and CO formation rates implying different sites for generation of the two products. At low gas phase carbon activity the CH/sub 4/ product is formed by direct hydrogenation of substrate carbon and not by secondary reaction of gas phase CO or CO/sub 2/. At higher gas phase carbon activities some CH/sub 4/ is produced from gas phase carbon oxides as a result of carbon deposition. In some cases the deposited carbon shows higher reactivity than the original carbon substrate so that this can be legitimately viewed as a secondary pathway.

  20. An antibody-catalyzed bimolecular Diels-Alder reaction

    SciTech Connect

    Braisted, A.C.; Schultz, P.G. )

    1990-09-26

    There exist over 1,500 known enzymes which carry out a vast array of chemical reactions with remarkable specificity and reaction rates. It is surprising then that there are no documented examples of enzyme-catalyzed pericyclic cycloaddition reactions, yet there are among the most powerful and commonly used reactions in synthetic organic chemistry. The most important of these is the Diels-Alder reaction of a diene with a dienophile, which provides a straightforward and highly stereospecific route to cyclohexene derivatives. Given the importance of this reaction in organic chemistry and its novel mechanism, it was of interest to ask whether a Diels-Alderase enzymatic catalyst could be evolved from an antibody combining site. Generation of antibodies to a structure that mimics the pericyclic transition state for a Diels-Alder reaction should result in an antibody combining site that lowers the entropy of activation {Delta}S{sup {double dagger}} by binding both the diene and the dienophile in a reactive conformation. The authors approach toward the design of a transition-state analogue involves incorporation of an ethano bridge, which locks the cyclohexene ring of hapten in a conformation that resembles the proposed pericyclic transition state for the Diels-Alder reaction of cisoid diene with dienophile. The authors now report that antibodies generated to the transition-state analogue catalyze the addition of the acyclic water-soluble diene to the maleimide derivative to give the cyclohexene product.

  1. Solution-solid-solid mechanism: superionic conductors catalyze nanowire growth.

    PubMed

    Wang, Junli; Chen, Kangmin; Gong, Ming; Xu, Bin; Yang, Qing

    2013-09-11

    The catalytic mechanism offers an efficient tool to produce crystalline semiconductor nanowires, in which the choice, state, and structure of catalysts are active research issues of much interest. Here we report a novel solution-solid-solid (SSS) mechanism for nanowire growth catalyzed by solid-phase superionic conductor nanocrystals in low-temperature solution. The preparation of Ag2Se-catalyzed ZnSe nanowires at 100-210 °C is exampled to elucidate the SSS model, which can be extendable to grow other II-VI semiconductor (e.g., CdSe, ZnS, and CdS) nanowires by the catalysis of nanoscale superionic-phase silver or copper(I) chalcogenides (Ag2Se, Ag2S, and Cu2S). The exceptional catalytic ability of these superionic conductors originates from their structure characteristics, known for high-density vacancies and fast mobility of silver or copper(I) cations in the rigid sublattice of Se(2-) or S(2-) ions. Insights into the SSS mechanism are provided based on the formation of solid solution and the solid-state ion diffusion/transport at solid-solid interface between catalyst and nanowire.

  2. Metal-Catalyzed Oxidation and Photo-oxidation of Glucagon.

    PubMed

    Zhang, Jian

    2016-08-01

    The oxidation of glucagon by the H2O2/Cu(2+) system and by simulated sunlight was studied using HPLC-MS methodologies. It was found that copper ion-catalyzed oxidation is much faster in the residue 1-12 region than in photo-oxidation, but it is slower than photo-oxidation in the residue 18-29 region. This difference is due to the unique feature of the primary sequence of glucagon. The residue 1-12 region contains His-1 and Asp-9 that can bind to Cu(2+) ions and catalyze the oxidation of His-1 and Tyr-10, while the residue 18-29 region lacks these charged residues near the liable Met-27 and Trp-25 and hence no catalysis by the neighboring groups occurs. Fragment (residue 13-17) was more stable than the other regions of the peptide toward photo-oxidation because it contains only one oxidizable residue, Tyr-13. These findings may help explain the mechanism of action of glucagon and provide some hints for the development of effective anti-diabetic drug molecules and stable glucagon formulations.

  3. Aldose Reductase-catalyzed Reduction of Aldehyde Phospholipids

    PubMed Central

    Srivastava, Sanjay; Spite, Matthew; Trent, John O.; West, Matthew B.; Ahmed, Yonis; Bhatnagar, Aruni

    2012-01-01

    SUMMARY Oxidation of unsaturated phospholipids results in the generation of aldehyde side chains that remain esterified to the phospholipid backbone. Such “core” aldehydes elicit immune responses and promote inflammation. However, the biochemical mechanisms by which phospholipid aldehydes are metabolized or detoxified are not well understood. In the studies reported here, we examined whether aldose reductase (AR), which reduces hydrophobic aldehydes, metabolizes phospholipid aldehydes. Incubation with AR led to the reduction of 5-oxovaleroyl, 7-oxo-5-heptenoyl, 5-hydroxy-6-oxo-caproyl, and 5-hydroxy-8-oxo-6-octenoyl phospholipids generated upon oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC). The enzyme also catalyzed the reduction of phospholipid aldehydes generated from the oxidation of 1-alkyl, and 1-alkenyl analogs of PAPC, and 1-palmitoyl-2-arachidonoyl phosphatidic acid or phosphoglycerol. Aldose reductase catalyzed the reduction of chemically synthesized 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphatidylcholine (POVPC) with a Km of 10 μM. Addition of POVPC to the culture medium led to incorporation and reduction of the aldehyde in COS-7 and THP-1 cells. Reduction of POVPC in these cells was prevented by the AR inhibitors sorbinil and tolrestat and was increased in COS-7 cells overexpressing AR. Together, these observations suggest that AR may be a significant participant in the metabolism of several structurally diverse phospholipid aldehydes. This metabolism may be a critical regulator of the pro-inflammatory and immunogenic effects of oxidized phospholipids. PMID:15465833

  4. Cu-Catalyzed Click Reaction in Carbohydrate Chemistry.

    PubMed

    Tiwari, Vinod K; Mishra, Bhuwan B; Mishra, Kunj B; Mishra, Nidhi; Singh, Anoop S; Chen, Xi

    2016-03-09

    Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences.

  5. Titanium-Catalyzed Silicon Nanostructures Grown by APCVD

    NASA Astrophysics Data System (ADS)

    Usman, Mohammad A. U.; Smith, Brady J.; Jackson, Justin B.; De Long, Matthew C.; Miller, Mark S.

    2015-01-01

    We report on growth of Ti-catalyzed silicon nanostructures (SNCs) through atmospheric-pressure chemical vapor deposition. An extensive growth study relating the growth condition parameters, including the partial pressure of SiCl4 gas, reaction temperature, and reaction time, was carried out to obtain insight into the growth regimes for the observed SNCs. Based on phase diagram analysis of Ti-Si alloy and growth rate analysis of the silicon nanowires (SNWs) and silicon nanoplatelets, we believe the growth mechanism to be strongly dependent on the thermodynamics of the system, exhibiting a delicate balance that can easily tip between the growth and etching regimes of the system. Three types of SNCs were observed frequently throughout the study: nanowires, nanoplatelets, and balls. Regimes for highly etched growth were also noted through growth conditions plots. Ti-catalyzed SNWs grown using SiCl4 gas strongly suggest growth occurring through a type of vapor-solid-solid (VSS) mechanism that is limited by diffusion through the solid-catalyst interface. On the other hand, the two-dimensional SNP morphologies suggest growth occurring through the twin-plane mechanism at the edges, at 10 nm to 100 nm scales, also through a similar, VSS mechanism.

  6. Lipase-catalyzed polyester synthesis – A green polymer chemistry

    PubMed Central

    Kobayashi, Shiro

    2010-01-01

    This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemo-enzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting ‘green polymer chemistry’. PMID:20431260

  7. Subtilisin-catalyzed resolution of N-acyl arylsulfinamides.

    PubMed

    Savile, Christopher K; Magloire, Vladimir P; Kazlauskas, Romas J

    2005-02-23

    We report the first biocatalytic route to sulfinamides (R-S(O)-NH2), whose sulfur stereocenter makes them important chiral auxiliaries for the asymmetric synthesis of amines. Subtilisin E did not catalyze hydrolysis of N-acetyl or N-butanoyl arylsulfinamides, but did catalyze a highly enantioselective (E > 150 favoring the (R)-enantiomer) hydrolysis of N-chloroacetyl and N-dihydrocinnamoyl arylsulfinamides. Gram-scale resolutions using subtilisin E overexpressed in Bacillus subtilis yielded, after recrystallization, three synthetically useful auxiliaries: (R)-p-toluenesulfinamide (42% yield, 95% ee), (R)-p-chlorobenzenesulfinamide (30% yield, 97% ee), and (R)-2,4,6-trimethylbenzenesulfinamide (30% yield, 99% ee). Molecular modeling suggests that the N-chloroacetyl and N-dihydrocinnamoyl groups mimic a phenylalanine moiety and thus bind the sulfinamide to the active site. Molecular modeling further suggests that enantioselectivity stems from a favorable hydrophobic interaction between the aryl group of the fast-reacting (R)-arylsulfinamide and the S1' leaving group pocket in subtilisin E.

  8. Study of microwave effects on the lipase-catalyzed hydrolysis.

    PubMed

    Chen, Chia-Chen; Reddy, P Muralidhar; Devi, C Shobha; Chang, Po-Chi; Ho, Yen-Peng

    2016-01-01

    The effect of microwave heating on lipase-catalyzed reaction remains controversial. It is not clear whether the reaction rate enhancements are purely due to thermal/heating effects or to non-thermal effects. Therefore, quantitative mass spectrometry was used to conduct accurate kinetic analysis of lipase-catalyzed hydrolysis of triolein by microwave and conventional heating. Commercial lipases from Candida rugosa (CRL), Porcine Pancreas (PPL), and Burkholderia cepacia (BCL) were used. Hydrolysis reactions were performed at various temperatures and pH levels, along with various amounts of buffer and enzymes. Hydrolysis product yields at each time point using an internal-standard method showed no significant difference between microwave and conventional heating conditions when the reaction was carried out at the same temperature. CRL showed optimum catalytic activity at 37 °C, while PPL and BCL had better activities at 50 °C. The phosphate buffer was found to give a better hydrolysis yield than the Tris-HCl buffer. Overall results prove that a non-thermal effect does not exist in microwave-assisted lipase hydrolysis of triolein. Therefore, conventional heating at high temperatures (e.g., 50 °C) can be also used to accelerate hydrolysis reactions.

  9. Thermodynamics of Enzyme-Catalyzed Reactions: Part 1. Oxidoreductases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.; Bell, Donna; Fazio, Kari; Anderson, Ellen

    1993-03-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by oxidoreductases have been compiled. For each reaction the following information is given: the reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement (temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used); the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it. The thermodynamic conventions pertinent to the tabulation of equilibrium data are discussed. A distinction is made between those thermodynamic quantities which pertain to the overall biochemical reaction and those which pertain to a reference reaction that involves specific species. The data from 205 references have been examined and evaluated. Chemical Abstract Service Registry Numbers have been assigned to the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participated.

  10. Enzyme catalyzed electricity-driven water softening system.

    PubMed

    Arugula, Mary A; Brastad, Kristen S; Minteer, Shelley D; He, Zhen

    2012-12-10

    Hardness in water, which is caused by divalent cations such as calcium and magnesium ions, presents a major water quality problem. Because hard water must be softened before use in residential applications, there is great interest in the saltless water softening process because, unlike ion exchange softeners, it does not introduce additional ions into water. In this study, a saltless hardness removal driven by bioelectrochemical energy produced through enzymatic oxidation of glucose was proposed and investigated. Glucose dehydrogenase was coated on a carbon electrode to catalyze glucose oxidation in the presence of NAD⁺ as a cofactor/mediator and methylene green as an electrocatalyst. The results showed that electricity generation stimulated hardness removal compared with non-electricity conditions. The enzymatic water softener worked upon a 6h batch operation per day for eight days, and achieved an average hardness removal of 46% at a high initial concentration of 800 mg/L as CaCO₃. More hardness was removed at a lower initial concentration. For instance, at 200mg/L as CaCO₃ the enzymatic water softener removed 76.4±4.6% of total hardness. The presence of magnesium ions decreased hardness removal because of its larger hydrated radius than calcium ions. The enzymatic water softener removed 70-80% of total hardness from three actual hard water samples. These results demonstrated a proof-of-concept that enzyme catalyzed electricity generation can be used to soften hard water. Copyright © 2012 Elsevier Inc. All rights reserved.

  11. A comparative study of ozonation, iron coated zeolite catalyzed ozonation and granular activated carbon catalyzed ozonation of humic acid.

    PubMed

    Gümüş, Dilek; Akbal, Feryal

    2017-05-01

    This study compares ozonation (O3), iron coated zeolite catalyzed ozonation (ICZ-O3) and granular activated carbon catalyzed ozonation (GAC-O3) for removal of humic acid from an aqueous solution. The results were evaluated by the removal of DOC that specifies organic matter, UV254 absorbance, SUVA (Specific Ultraviolet Absorbance at 254 nm) and absorbance at 436 nm. When ozonation was used alone, DOC removal was 21.4% at an ozone concentration of 10 mg/L, pH 6.50 and oxidation time of 60 min. The results showed that the use of ICZ or GAC as a catalyst increased the decomposition of humic acid compared to ozonation alone. DOC removal efficiencies were 62% and 48.1% at pH 6.5, at a catalyst loading of 0.75 g/L, and oxidation time of 60 min for ICZ and GAC, respectively. The oxidation experiments were also carried out using <100 kDa and <50 kDa molecular size fractions of humic acid in the presence of ICZ or GAC. Catalytic ozonation also yielded better DOC and UV254 reduction in both <50 kDa and <100 kDa fractions of HA compared to ozonation. Copyright © 2017 Elsevier Ltd. All rights reserved.

  12. Enantioselective Total Synthesis of (−)-Nardoaristolone B via a Gold(I)-Catalyzed Oxidative Cyclization

    PubMed Central

    2015-01-01

    The first enantioselective total synthesis of (−)-nardoaristolone B is accomplished by the implementation of an enantio- and diastereoselective copper(I)-catalyzed conjugate addition/enolate trapping sequence and a gold(I)-catalyzed oxidative cyclization (intermolecular oxidant), employed for the first time in total synthesis. PMID:25563976

  13. Palladium-catalyzed carbonylation of o-iodoanilines for synthesis of isatoic anhydrides.

    PubMed

    Gao, Sha; Chen, Ming; Zhao, Mi-Na; Du, Wei; Ren, Zhi-Hui; Wang, Yao-Yu; Guan, Zheng-Hui

    2014-05-02

    A novel palladium-catalyzed oxidative double carbonylation of o-iodoanilines for the synthesis of isatoic anhydrides has been developed. The reaction employs readily available o-iodoanilines as the starting materials and proceeds under mild conditions. For extension, palladium-catalyzed oxidative carbonylation of anthranilic acids was developed for the synthesis of substituted isatoic anhydrides in high to excellent yields.

  14. Recent advances in chiral imino-containing ligands for metal-catalyzed asymmetric transformations.

    PubMed

    Chen, Xu; Lu, Zhan

    2017-03-21

    In this review, the recent applications of a variety of chiral imino-containing ligands classified by different types of metal-catalyzed asymmetric reactions are summarized. The progress made in this area would encourage us to design and synthesize more novel chiral imino-containing ligands, and explore their applications in metal-catalyzed asymmetric transformations.

  15. Copper-catalyzed aerobic oxidative synthesis of aryl nitriles from benzylic alcohols and aqueous ammonia.

    PubMed

    Tao, Chuanzhou; Liu, Feng; Zhu, Youmin; Liu, Weiwei; Cao, Zhiling

    2013-05-28

    Copper-catalyzed direct conversion of benzylic alcohols to aryl nitriles was realized using NH3(aq.) as the nitrogen source, O2 as the oxidant and TEMPO as the co-catalyst. Furthermore, copper-catalyzed one-pot synthesis of primary aryl amides from alcohols was also achieved.

  16. Copper-catalyzed cascade reactions of α,β-unsaturated esters with keto esters

    PubMed Central

    Wang, Chongnian; Li, Zengchang

    2015-01-01

    Summary A copper-catalyzed cascade reaction of α,β-unsaturated esters with keto esters is reported. It features a copper-catalyzed reductive aldolization followed by a lactonization. This method provides a facile approach to prepare γ-carboxymethyl-γ-lactones and δ-carboxymethyl-δ-lactones under mild reaction conditions. PMID:25815072

  17. Regioselective hydrothiolation of alkenes bearing heteroatoms with thiols catalyzed by palladium diacetate.

    PubMed

    Tamai, Taichi; Ogawa, Akiya

    2014-06-06

    In sharp contrast to many examples of transition-metal-catalyzed hydrothiolation of alkynes, the corresponding catalytic addition of thiols to alkenes has remained undeveloped. However, a novel Pd-catalyzed addition of thiols to alkenes bearing a heteroatom, such as oxygen and nitrogen, is found to proceed under mild conditions to give the corresponding Markovnikov adducts, regioselectively, in good yields.

  18. ROLE OF COPPER,ZINC-SUPEROXIDE DISMUTASE IN CATALYZING NITROTYROSINE FORMATION IN MURINE LIVER

    USDA-ARS?s Scientific Manuscript database

    The solely known function of Cu,Zn-superoxide dismutase (SOD1) is to catalyze the dismutation of superoxide anion into hydrogen peroxide. Our objective was to determine if SOD1 catalyzed murine liver protein nitration induced by acetaminophen (APAP) and lipopolysaccharide (LPS). Liver and plasma ...

  19. Gold-catalyzed cyclizations of alkynol-based compounds: synthesis of natural products and derivatives.

    PubMed

    Alcaide, Benito; Almendros, Pedro; Alonso, José M

    2011-09-13

    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.

  20. Degradation and transformation of atrazine under catalyzed ozonation process with TiO2 as catalyst.

    PubMed

    Yang, Yixin; Cao, Hongbin; Peng, Pai; Bo, Hongmiao

    2014-08-30

    Degradation of atrazine by heterogeneously catalyzed ozonation was carried out with TiO2 in the form of rutile as the catalyst. Some experimental factors such as catalyst dose, ozone dose and initial concentration of atrazine were investigated for their influence on catalyzed ozonation process. Although atrazine was effectively removed from aqueous solution by catalyzed ozonation process, the mineralization degree only reached 56% at the experimental conditions. Five transformation products were identified by GC/MS analysis. The degradation of atrazine involved de-alkylation, de-chlorination and de-amination. Diaminotriazine and 5-azauracil were the de-chlorinated and de-aminated products, respectively. The evolution of concentration of transformation products during catalyzed ozonation process was compared with uncatalyzed ozonation to show the degradation pathway. Toxicity tests based on the inhibition of the luminescence emitted by Vibrio fisheri indicated the detoxification of atrazine by catalyzed ozonation.

  1. Rh(II)-catalyzed Reactions of Diazoesters with Organozinc Reagents

    PubMed Central

    Panish, Robert; Selvaraj, Ramajeyam; Fox, Joseph M.

    2015-01-01

    Rh(II)-catalyzed reactions of diazoesters with organozinc reagents are described. Diorganozinc reagents participate in reactions with diazo compounds by two distinct, catalyst-dependent mechanisms. With bulky diisopropylethylacetate ligands, the reaction mechanism is proposed to involve initial formation of a Rh-carbene and subsequent carbozincation to give a zinc enolate. With Rh2(OAc)4, it is proposed that initial formation of an azine precedes 1,2-addition by an organozinc reagent. This straightforward route to the hydrazone products provides a useful method for preparing chiral quaternary α-aminoesters or pyrazoles via the Paul-Knorr condensation with 1,3-diketones. Crossover and deuterium labeling experiments provide evidence for the mechanisms proposed. PMID:26241081

  2. Transition-metal-catalyzed synthesis of phenols and aryl thiols

    PubMed Central

    Liu, Shasha

    2017-01-01

    Phenols and aryl thiols are fundamental building blocks in organic synthesis and final products with interesting biological activities. Over the past decades, substantial progress has been made in transition-metal-catalyzed coupling reactions, which resulted in the emergence of new methods for the synthesis of phenols and aryl thiols. Aryl halides have been extensively studied as substrates for the synthesis of phenols and aryl thiols. In very recent years, C–H activation represents a powerful strategy for the construction of functionalized phenols directly from various arenes. However, the synthesis of aryl thiols through C–H activation has not been reported. In this review, a brief overview is given of the recent advances in synthetic strategies for both phenols and aryl thiols. PMID:28405239

  3. The role of fluoride in montmorillonite-catalyzed RNA synthesis.

    PubMed

    Aldersley, Michael F; Joshi, Prakash C

    2014-05-01

    The montmorillonite-catalyzed reactions of the 5'-phosphorimidazolide of adenosine in the presence of fluoride were investigated to complete our study on the effect of salts on this type of reaction. Both anions and cations have been found to influence the oligomerization reactions of the activated nucleotides, being used here as a model system for pre-biotic RNA synthesis. However, in total contrast to the behavior of the activated nucleotides in the presence of montmorillonite and other salts, alkali metal fluorides did not yield any detectable oligomerization products except in very dilute (<0.005 M) solutions of fluoride. Instead, 5'-phosphorofluoridates were formed. Their identity was confirmed by a combination of HPLC, mass spectrometry, synthesis, and NMR.

  4. Palladium(II)-Catalyzed Enantioselective Reactions Using COP Catalysts.

    PubMed

    Cannon, Jeffrey S; Overman, Larry E

    2016-10-18

    Allylic amides, amines, and esters are key synthetic building blocks. Their enantioselective syntheses under mild conditions is a continuing pursuit of organic synthesis methods development. One opportunity for the synthesis of these building blocks is by functionalization of prochiral double bonds using palladium(II) catalysis. In these reactions, nucleopalladation mediated by a chiral palladium(II) catalyst generates a new heteroatom-substituted chiral center. However, reactions where nucleopalladation occurs with antarafacial stereoselectivity are difficult to render enantioselective because of the challenge of transferring chiral ligand information across the square-planar palladium complex to the incoming nucleophile. In this Account, we describe the development and use of enantiopure palladium(II) catalysts of the COP (chiral cobalt oxazoline palladacyclic) family for the synthesis of enantioenriched products from starting materials derived from prochiral allylic alcohols. We begin with initial studies aimed at rendering catalyzed [3,3]-sigmatropic rearrangements of allylic imidates enantioselective, which ultimately led to the identification of the significant utility of the COP family of Pd(II) catalysts. The first use of an enantioselective COP catalyst was reported by Richards' and our laboratories in 2003 for the enantioselective rearrangement of allylic N-arylimidates. Shortly thereafter, we discovered that the chloride-bridged COP dimer, [COP-Cl]2, was an excellent enantioselective catalyst for the rearrangement of (E)-allylic trichloroacetimidates to enantioenriched allylic trichloroacetamides, this conversion being the most widely used of the allylic imidate rearrangements. We then turn to discuss SN2' reactions catalyzed by the acetate-bridged COP dimer, [COP-OAc]2, which proceed by a unique mechanism to provide branched allylic esters and allylic phenyl ethers in high enantioselectivity. Furthermore, because of the unique nucleopalladation

  5. Measurements of muon-catalyzed dt fusion in solid HD

    NASA Astrophysics Data System (ADS)

    Porcelli, Tracy Ann

    1999-12-01

    The first measurement of muon catalyzed dt fusion ( dtm--> 4He + n + m- ) in solid HD at ~ 3 K has been performed. The theory describing the formation of the [(dtm)pe e] muonic molecule from the resonant reaction tm+HD-->[(dtm) pee] , a key process in the dt fusion cycle, can now be tested against the experimental results. Using an experimental technique which employs solid layers of hydrogen isotopes, the energy of molecular formation is determined via time of flight, and dt fusion time spectra in solid HD have been measured. The theory describing the resonant formation of the dtm muonic molecule is compared to the experimental results through Monte Carlo simulations. The energy dependent molecular formation rates calculated for HD at 3 K have been employed in the Monte Carlo with the resultant simulated fusion time spectra in fair agreement with the experimental results.

  6. Measurements of Muon Catalyzed dt Fusion in Solid HD

    NASA Astrophysics Data System (ADS)

    Porcelli, Tracy

    1999-05-01

    The first measurement of muon catalyzed dt fusion (dtμ arrow ^4He + n + μ^-) in solid HD at ~ 3 K has been performed. The theory describing the formation of the [(dtμ)pee)] muonic molecule from the resonant reaction tμ + HD arrow [(dtμ)pee], a key process in the dt fusion cycle, can now be tested against experimental results. Using an experimental technique which employs solid layers of hydrogen isotopes, the energy of molecular formation is determined via time of flight, and dt fusion time spectra in solid HD have been measured. The theory describing the resonant formation of the dtμ muonic molecule is compared to the experimental results through Monte Carlo simulations. The energy dependent molecular formation rates calculated for HD at 3 K have been employed in the Monte Carlo with the resultant fusion time spectra in fair agreement with the experimental results.

  7. Field Emission from Self-Catalyzed GaAs Nanowires.

    PubMed

    Giubileo, Filippo; Di Bartolomeo, Antonio; Iemmo, Laura; Luongo, Giuseppe; Passacantando, Maurizio; Koivusalo, Eero; Hakkarainen, Teemu V; Guina, Mircea

    2017-09-16

    We report observations of field emission from self-catalyzed GaAs nanowires grown on Si (111). The measurements were taken inside a scanning electron microscope chamber with a nano-controlled tungsten tip functioning as anode. Experimental data were analyzed in the framework of the Fowler-Nordheim theory. We demonstrate stable current up to 10(-7) A emitted from the tip of single nanowire, with a field enhancement factor β of up to 112 at anode-cathode distance d = 350 nm. A linear dependence of β on the anode-cathode distance was found. We also show that the presence of a Ga catalyst droplet suppresses the emission of current from the nanowire tip. This allowed for the detection of field emission from the nanowire sidewalls, which occurred with a reduced field enhancement factor and stability. This study further extends GaAs technology to vacuum electronics applications.

  8. Quinone-Catalyzed Selective Oxidation of Organic Molecules

    PubMed Central

    Wendlandt, Alison E.

    2016-01-01

    Lead In Quinones are common stoichiometric reagents in organic chemistry. High potential para-quinones, 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 efficient and selective aerobic and/or electrochemical dehydrogenation of amines. The latter reactions typically proceed via 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 have important implications for the development of new quinone reagents and quinone-catalyzed transformations. PMID:26530485

  9. Site-specific DNA transesterification catalyzed by a restriction enzyme

    PubMed Central

    Sasnauskas, Giedrius; Connolly, Bernard A.; Halford, Stephen E.; Siksnys, Virginijus

    2007-01-01

    Most restriction endonucleases use Mg2+ to hydrolyze phosphodiester bonds at specific DNA sites. We show here that BfiI, a metal-independent restriction enzyme from the phospholipase D superfamily, catalyzes both DNA hydrolysis and transesterification reactions at its recognition site. In the presence of alcohols such as ethanol or glycerol, it attaches the alcohol covalently to the 5′ terminus of the cleaved DNA. Under certain conditions, the terminal 3′-OH of one DNA strand can attack the target phosphodiester bond in the other strand to create a DNA hairpin. Transesterification reactions on DNA with phosphorothioate linkages at the target bond proceed with retention of stereoconfiguration at the phosphorus, indicating, uniquely for a restriction enzyme, a two-step mechanism. We propose that BfiI first makes a covalent enzyme–DNA intermediate, and then it resolves it by a nucleophilic attack of water or an alcohol, to yield hydrolysis or transesterification products, respectively. PMID:17267608

  10. Dirhodium Catalyzed C-H Arene Amination using Hydroxylamines

    PubMed Central

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

    2016-01-01

    Primary and N-alkyl arylamine motifs are key functional groups in pharmaceuticals, agrochemicals and functional materials as well as in bioactive natural products. However, there is a dearth of generally applicable methods for the direct replacement of aryl hydrogens with –NH2/-NH-alkyl moieties. 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 either NH2/NHalkyl-O-(sulfonyl)hydroxylamines as aminating agents; the relatively weak RSO2O-N bond functions as an internal oxidant. The methodology is operationally simple, scalable, and fast at or below ambient temperature, furnishing arylamines in moderate-to-good yields and with good regioselectivity. It can be readily extended to the synthesis of fused N-heterocycles. PMID:27609890

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

    PubMed

    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.

  12. Site-specific DNA transesterification catalyzed by a restriction enzyme.

    PubMed

    Sasnauskas, Giedrius; Connolly, Bernard A; Halford, Stephen E; Siksnys, Virginijus

    2007-02-13

    Most restriction endonucleases use Mg2+ to hydrolyze phosphodiester bonds at specific DNA sites. We show here that BfiI, a metal-independent restriction enzyme from the phospholipase D superfamily, catalyzes both DNA hydrolysis and transesterification reactions at its recognition site. In the presence of alcohols such as ethanol or glycerol, it attaches the alcohol covalently to the 5' terminus of the cleaved DNA. Under certain conditions, the terminal 3'-OH of one DNA strand can attack the target phosphodiester bond in the other strand to create a DNA hairpin. Transesterification reactions on DNA with phosphorothioate linkages at the target bond proceed with retention of stereoconfiguration at the phosphorus, indicating, uniquely for a restriction enzyme, a two-step mechanism. We propose that BfiI first makes a covalent enzyme-DNA intermediate, and then it resolves it by a nucleophilic attack of water or an alcohol, to yield hydrolysis or transesterification products, respectively.

  13. Trypsin-catalyzed oxygen-18 labeling for quantitative proteomics

    SciTech Connect

    Qian, Weijun; Petritis, Brianne O.; Nicora, Carrie D.; Smith, Richard D.

    2011-07-01

    Stable isotope labeling based on relative peptide/protein abundance measurements is commonly applied for quantitative proteomics. Recently, trypsin-catalyzed oxygen-18 labeling has grown in popularity due to its simplicity, cost-effectiveness, and its ability to universally label peptides with high sample recovery. In (18)O labeling, both C-terminal carboxyl group atoms of tryptic peptides can be enzymatically exchanged with (18)O, thus providing the labeled peptide with a 4 Da mass shift from the (16)O-labeled sample. Peptide (18)O labeling is ideally suited for generating a labeled "universal" reference sample used for obtaining accurate and reproducible quantitative measurements across large number of samples in quantitative discovery proteomics.

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

    PubMed

    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.

  15. Pd-Catalyzed Heterocycle Synthesis in Ionic Liquids

    NASA Astrophysics Data System (ADS)

    Li, Jianxiao; Jiang, Huanfeng

    Heterocyclic and fused heterocyclic compounds are ubiquitously found in natural products and biologically interesting molecules, and many currently marketed drugs hold heterocycles as their core structure. In this chapter, recent advances on Pd-catalyzed synthesis of heterocycles in ionic liquids (ILs) are reviewed. In palladium catalysis, ILs with different cations and anions are investigated as an alternative recyclable and environmentally benign reaction medium, and a variety of heterocyclic compounds including cyclic ketals, quinolones, quinolinones, isoindolinones, and lactones are conveniently constructed. Compared to the traditional methods, these new approaches have many advantages, such as environmentally friendly synthetic procedure, easy product and catalyst separation, recyclable medium, which make them have the potential applications in industry.

  16. Calcium-catalyzed pyrolysis of lignocellulosic biomass components.

    PubMed

    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.

  17. Asymmetric Allylboration of Acyl Imines Catalyzed by Chiral Diols

    PubMed Central

    Lou, Sha; Moquist, Philip N.; Schaus, Scott E.

    2008-01-01

    Chiral BINOL-derived diols catalyze the enantioselective asymmetric allylboration of acyl imines. The reaction requires 15 mol% of (S)-3,3′-Ph2-BINOL as the catalyst and allyldiisopropoxyborane as the nucleophile. The reaction products are obtained in good yields (75 – 94%) and high enantiomeric ratios (95:5 – 99.5:0.5) for aromatic and aliphatic imines. High diastereoselectivities (dr > 98:2) and enantioselectivities (er > 98:2) are obtained in the reactions of acyl imines with crotyldiisopropoxyboranes. This asymmetric transformation is directly applied to the synthesis of maraviroc, the selective CCR5 antagonist with potent activity against HIV-1 infection. Mechanistic investigations of the allylboration reaction including IR, NMR, and mass spectrometry study indicate that acyclic boronates are activated by chiral diols via exchange of one of the boronate alkoxy groups with activation of the acyl imine via hydrogen bonding. PMID:18020334

  18. Degradation of Akt using protein-catalyzed capture agents.

    PubMed

    Henning, Ryan K; Varghese, Joseph O; Das, Samir; Nag, Arundhati; Tang, Grace; Tang, Kevin; Sutherland, Alexander M; Heath, James R

    2016-04-01

    Abnormal signaling of the protein kinase Akt has been shown to contribute to human diseases such as diabetes and cancer, but Akt has proven to be a challenging target for drugging. Using iterative in situ click chemistry, we recently developed multiple protein-catalyzed capture (PCC) agents that allosterically modulate Akt enzymatic activity in a protein-based assay. Here, we utilize similar PCCs to exploit endogenous protein degradation pathways. We use the modularity of the anti-Akt PCCs to prepare proteolysis targeting chimeric molecules that are shown to promote the rapid degradation of Akt in live cancer cells. These novel proteolysis targeting chimeric molecules demonstrate that the epitope targeting selectivity of PCCs can be coupled with non-traditional drugging moieties to inhibit challenging targets. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

  19. Guide to Enantioselective Dirhodium(II)-Catalyzed Cyclopropanation with Aryldiazoacetates

    PubMed Central

    Chepiga, Kathryn M.; Qin, Changming; Alford, Joshua S.; Chennamadhavuni, Spandan; Gregg, Timothy M.; Olson, Jeremy P.

    2013-01-01

    Catalytic enantioselective methods for the generation of cyclopropanes has been of longstanding pharmaceutical interest. Chiral dirhodium(II) catalysts prove to be an effective means for the generation of diverse cyclopropane libraries. Rh2(R-DOSP)4 is generaally the most effective catalyst for asymmetric intermolecular cyclopropanation of methyl aryldiazoacetates with styrene. Rh2(S-PTAD)4 provides high levels of enantioinduction with ortho-substituted aryldiazoacetates. The less-established Rh2(R-BNP)4 plays a complementary role to Rh2(R-DOSP)4 and Rh2(S-PTAD)4 in catalyzing highly enantioselective cyclopropanation of 3- methoxy-substituted aryldiazoacetates. Substitution on the styrene has only moderate influence on the asymmetric induction of the cyclopropanation. PMID:24273349

  20. Guide to Enantioselective Dirhodium(II)-Catalyzed Cyclopropanation with Aryldiazoacetates.

    PubMed

    Chepiga, Kathryn M; Qin, Changming; Alford, Joshua S; Chennamadhavuni, Spandan; Gregg, Timothy M; Olson, Jeremy P; Davies, Huw M L

    2013-07-08

    Catalytic enantioselective methods for the generation of cyclopropanes has been of longstanding pharmaceutical interest. Chiral dirhodium(II) catalysts prove to be an effective means for the generation of diverse cyclopropane libraries. Rh2(R-DOSP)4 is generaally the most effective catalyst for asymmetric intermolecular cyclopropanation of methyl aryldiazoacetates with styrene. Rh2(S-PTAD)4 provides high levels of enantioinduction with ortho-substituted aryldiazoacetates. The less-established Rh2(R-BNP)4 plays a complementary role to Rh2(R-DOSP)4 and Rh2(S-PTAD)4 in catalyzing highly enantioselective cyclopropanation of 3- methoxy-substituted aryldiazoacetates. Substitution on the styrene has only moderate influence on the asymmetric induction of the cyclopropanation.

  1. Experimental investigation of muon-catalyzed t + t fusion

    SciTech Connect

    Bogdanova, L. N.; Bom, V. R.; Demin, A. M.; Demin, D. L.; Eijk, C. W. E. van; Filchagin, S. V.; Filchenkov, V. V.; Grafov, N. N. Grishechkin, S. K.; Gritsaj, K. I.; Konin, A. D.; Kuryakin, A. V.; Medved', S. V.; Musyaev, R. K.; Rudenko, A. I.; Tumkin, D. P.; Vinogradov, Yu. I.; Yukhimchuk, A. A.; Yukhimchuk, S. A.; Zinov, V. G.

    2009-02-15

    The muon-catalyzed fusion ({mu}CF) process in tritium was studied by the {mu}CF collaboration on the muon beam of the JINR Phasotron. The measurements were carried out with a liquid tritium target at the temperature 22 K and density approximately 1.25 of the liquid hydrogen density (LHD). Parameters of the {mu}CF cycle were determined: the tt{mu} muonic molecule formation rate {lambda}{sub tt{mu}} = 2.84(0.32) {mu}s{sup -1}, the tt{mu} fusion reaction rate {lambda}{sub f} = 15.6(2.0) {mu}s{sup -1}, and the probability of muon sticking to helium {omega}{sub tt}= 13.9(1.5)%. The results agree with those obtained earlier by other groups, but better accuracy was achieved due to our unique experimental method.

  2. Rhenium-catalyzed deoxydehydration of diols and polyols.

    PubMed

    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.

  3. Rh(II)-Catalyzed Reactions of Diazoesters with Organozinc Reagents.

    PubMed

    Panish, Robert; Selvaraj, Ramajeyam; Fox, Joseph M

    2015-08-21

    Rh(II)-catalyzed reactions of diazoesters with organozinc reagents are described. Diorganozinc reagents participate in reactions with diazo compounds by two distinct, catalyst-dependent mechanisms. With bulky diisopropylethyl acetate ligands, the reaction mechanism is proposed to involve initial formation of a Rh-carbene and subsequent carbozincation to give a zinc enolate. With Rh2(OAc)4, it is proposed that initial formation of an azine precedes 1,2-addition by an organozinc reagent. This straightforward route to the hydrazone products provides a useful method for preparing chiral quaternary α-aminoesters or pyrazoles via the Paul-Knorr condensation with 1,3-diketones. Crossover and deuterium labeling experiments provide evidence for the mechanisms proposed.

  4. WILDCAT: a catalyzed D-D tokamak reactor

    SciTech Connect

    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. Homogeneously catalyzed oxidation for the destruction of aqueous organic wastes

    SciTech Connect

    Leavitt, D.D.; Horbath, J.S.; Abraham, M.A. )

    1990-11-01

    Several organic species, specifically atrazine, 2,4-dichlorophenozyacetic acid, and biphenyl, were converted to CO{sub 2} and other non-harmful gases through oxidation catalyzed by inorganic acid. Nearly complete conversion was obtained through homogeneous liquid-phase oxidation with ammonium nitrate. The kinetics of reaction have been investigated and indicate parallel oxidation and thermal degradation of the oxidant. This results in a maximum conversion at an intermediate temperature. Increasing oxidant concentration accelerates the rate of conversion and shifts the location of the optimum temperature. Reaction at varying acid concentration revealed that conversion increased with an approximately linear relationship as the pH of the solution was increased. Conversion was increased to greater than 99% through the addition of small amounts of transition metal salts demonstrating the suitability of a treatment process based on this technology for wastestreams containing small quantities of heavy metals.

  6. Transition Metals Catalyzed Element-Cyano Bonds Activations

    PubMed Central

    Wang, Rui; Falck, John R.

    2014-01-01

    Cyano group as a versatile functionalized intermediate has been explored for several decades, as it readily transfers to many useful functionalization groups such as amine, amide, acid, etc., which make it possess high popularization and use value in organic synthesis. Reactions involved with element-cyano bond cleavage can provide not only a new cyano group but also a freshly functionalized skeleton in one-pot, consequently making it of high importance. The highlights reviewed herein include H-CN, Si-CN, C-CN, B-CN, Sn-CN, Ge-CN, S-CN, Halo-CN, N-CN, and O-CN bonds cleavages and will summarize progress in such an important research area. This review article will focus on transition metal catalyzed reactions involving element-cyano bond activation. PMID:25558119

  7. Lipase-catalyzed ethanolysis of borage oil: a kinetic study.

    PubMed

    Torres, Carlos F; Hill, Charles G; Otero, Cristina

    2004-01-01

    Ethanolysis of borage oil catalyzed by two commercial lipases (from Pseudomonas cepacia and Candida antarctica) was studied using two different methodologies. Multiresponse models derived from a generalized Michaelis-Menten mechanism were utilized to describe the rates of formation of ethyl esters of the primary fatty acids present in the precursor oil. The relative rate constants determined for each of the fatty acid residues indicated that both lipases discriminate against release of gamma-linolenic acid residues under the reaction conditions studied. However, both lipases also released some of the residues located at the sn-2 position, indicating that for the experimental conditions studied, both lipases are nonspecific. Moreover, inactivation of Novozym 435 was rapid. Because the half-life of this enzyme (ca. 2.2 h) is comparable to the half-life of the reaction, the intrinsic reaction rate and enzyme deactivation must both be considered in modeling the kinetics.

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

    PubMed

    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.

  9. Secondary kinase reactions catalyzed by yeast pyruvate kinase.

    PubMed

    Leblond, D J; Robinson, J L

    1976-06-07

    1. Yeast pyruvate kinase (EC 2.7.1.40) catalyzes, in addition to the primary, physiologically important reaction, three secondary kinase reactions, the ATP-dependent phosphorylations of fluoride (fluorokinase), hydroxylamine (hydroxylamine kinase) and glycolate (glycolate kinase). 2. These reactions are accelerated by fructose-1,6-bisphosphate, the allosteric activator of the primary reaction. Wth Mg2+ as the required divalent cation, none of these reactions are observed in the absence of fructose-biphosphate. With Mn2+, fructose-bisphosphate is required for the glycolate kinase reaction, but merely stimulates the other reactions. 3. The effect of other divalent cations and pH on three secondary kinase reactions was also examined. 4. Results are compared with those obtained from muscle pyruvate kinase and the implications of the results for the mechanism of the yeast enzyme are discussed.

  10. Enantioselective copper-catalyzed carboetherification of unactivated alkenes.

    PubMed

    Bovino, Michael T; Liwosz, Timothy W; Kendel, Nicole E; Miller, Yan; Tyminska, Nina; Zurek, Eva; Chemler, Sherry R

    2014-06-16

    Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein reported is a highly efficient copper-catalyzed cyclization of γ-unsaturated pentenols which terminates in C-C bond formation, a net alkene carboetherification. Both intra- and intermolecular C-C bond formations are demonstrated, thus yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition-state calculations support a cis-oxycupration stereochemistry-determining step. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Oligonucleotide synthesis catalyzed by the Zn/2+/ ion

    NASA Technical Reports Server (NTRS)

    Sawai, H.; Orgel, L. E.

    1975-01-01

    Results of experiments are reported in which Zn(2+) ion catalyzed the formation of oligonucleotides from nucleoside phosphorimidazolides in aqueous solution, even in the absence of a template. Specifically, the imidazolides (ImpU or ImpA) polymerized to form ImpApA, and pApA, pApApA, and pApApApA, or the analogous uracil compounds. In addition, the expected hydrolysis products of the hydrolysis of ImpA were formed (pA, imidazole). Judging from the ratio of pA(n) over pA (with and without zinc ion), this ion increased the efficiency of phosphodiester-bond formation by up to 10 times. Possible mechanisms for the reaction are tentatively proposed.

  12. Dissecting Anion Effects in Gold(I)-Catalyzed Intermolecular Cycloadditions

    PubMed Central

    Homs, Anna; Obradors, Carla; Lebœuf, David; Echavarren, Antonio M

    2014-01-01

    From a series of gold complexes of the type [t-BuXPhosAu(MeCN)]X (X=anion), the best results in intermolecular gold(I)-catalyzed reactions are obtained with the complex with the bulky and soft anion BAr4F− [BAr4F−=3,5-bis(trifluoromethyl)phenylborate] improving the original protocols by 10–30% yield. A kinetic study on the [2+2] cycloaddition reaction of alkynes with alkenes is consistent with an scenario in which the rate-determining step is the ligand exchange to generate the (η2-phenylacetylene)gold(I) complex. We have studied in detail the subtle differences that can be attributed to the anion in this formation, which result in a substantial decrease in the formation of unproductive σ,π-(alkyne)digold(I) complexes by destabilizing the conjugated acid formed. PMID:26190958

  13. Degradation of Akt Using Protein Catalyzed Capture Agents

    PubMed Central

    Das, Samir; Nag, Arundhati; Tang, Grace; Tang, Kevin; Sutherland, Alexander M.; Heath, James R.

    2016-01-01

    Abnormal signaling of the protein kinase Akt has been shown to contribute to human diseases such as diabetes and cancer, but Akt has proven to be a challenging target for drugging. Using iterative in situ click chemistry we recently developed multiple protein catalyzed capture (PCC) agents that allosterically modulate Akt enzymatic activity in a protein based assay. Here we utilize similar PCCs to exploit endogenous protein degradation pathways. We use the modularity of the anti-Akt PCCs to prepare Proteolysis Targeting Chimeric molecules (PROTACs) that are shown to promote the rapid degradation of Akt in live cancer cells. These novel PROTACs demonstrate that the epitope targeting selectivity of PCCs can be coupled with non-traditional drugging moieties to inhibit challenging targets. PMID:26880702

  14. Enantioselective Cyclizations of Silyloxyenynes Catalyzed by Cationic Metal Phosphine Complexes

    PubMed Central

    Brazeau, Jean-François; Zhang, Suyan; Colomer, Ignacio; Corkey, Britton K.; Toste, F. Dean

    2012-01-01

    The discovery of complementary methods for enantioselective transition-metal-catalyzed cyclization with silyloxyenynes has been accomplished using chiral phosphine ligands. Under palladium catalysis, 1,6-silyloxyenynes bearing a terminal alkyne led to the desired 5-membered ring with high enantioselectivities (up to 91% ee). As for reactions under cationic gold catalysis, 1,6- and 1,5-silyloxyenynes bearing an internal alkyne furnished the chiral cyclopentane derivatives with excellent enantiomeric excess (up to 94% ee). Modification of the substrate by incorporating an α,β-unsaturation led to the discovery of a tandem cyclization. Remarkably, using silyloxy-1,3-dien-7-ynes under gold catalysis conditions provided the bicyclic derivatives with excellent diastereo- and enantioselectivities (up to >20:1 dr and 99% ee). PMID:22296571

  15. Chemo- and Enantioselective Intramolecular Silver-Catalyzed Aziridinations.

    PubMed

    Ju, Minsoo; Weatherly, Cale D; Guzei, Ilia A; Schomaker, Jennifer M

    2017-08-07

    Asymmetric nitrene-transfer reactions are a powerful tool for the preparation of enantioenriched amine building blocks. Reported herein are chemo- and enantioselective silver-catalyzed aminations which transform di- and trisubstituted homoallylic carbamates into [4.1.0]-carbamate-tethered aziridines in good yields and with ee values of up to 92 %. The effects of the substrate, silver counteranion, ligand, solvent, and temperature on both the chemoselectivity and ee value were explored. Stereochemical models were proposed to rationalize the observed absolute stereochemistry of the aziridines, which undergo nucleophilic ring opening to yield enantioenriched amines with no erosion in stereochemical integrity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Reactions of ethyl diazoacetate catalyzed by methylrhenium trioxide

    SciTech Connect

    Zhu, Z.; Espenson, H.

    1995-11-03

    Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) has found wise use in catalysis, including the epoxidation and metathesis of olefins, aldehyde olefination, and oxygen transfer. Extensive reports have now appeared in the area of MTO-catalyzed substrate oxidations with hydrogen peroxide. Certain catalytic applications of MTO for organic reactions that do not utilize peroxide have now been realized. In particular, a catalytic amount of MTO with ethyl diazoacetate (EDA) will convert aromatic imines to aziridines and convert aldehydes and ketones to epoxides. The aziridine preparation proceeds in high yields under anaerobic conditions more conveniently than with existing methods. Compounds with a three-membered heterocyclic ring can be obtained with the EDA/MTO catalytic system. Aromatic imines undergo cycloaddition reactions to give aziridines under mild conditions.

  17. Decomposition of peracetic acid catalyzed by vanadium complexes

    SciTech Connect

    Makarov, A.P.; Gekhman, A.E.; Moiseev, I.I.; Polotryuk, O.Y.

    1986-02-01

    This paper studies the decomposition of peracetic acid (AcOOH) in acetic acid (AcOH) catalyzed by vanadium complexes. It is shown that peractic acid in acetic acid solutions of ammonium anadate decomposes with the predominant formation of 0/sub 2/ and small amounts of CO/sub 2/, the yield of which increases with increasing temperature and peracetic acid concentration. Both reactions proceed without the formation of free radicals in amounts detectable by ESR spectroscopy. The rate of oxygen release under conditions in which the formation of CO/sub 2/ is insignificant obeys a kinetic equation indicating the intermediate formation of a complex between V/sup 5 +/ ions and peracetic acid and the slow conversion of this complex into the observed products.

  18. Biocatalytic Asymmetric Phosphorylation Catalyzed by Recombinant Glycerate-2-Kinase.

    PubMed

    Hardt, Norman; Kinfu, Birhanu M; Chow, Jennifer; Schoenenberger, Bernhard; Streit, Wolfgang R; Obkircher, Markus; Wohlgemuth, Roland

    2017-08-04

    The efficient synthesis of pure d-glycerate-2-phosphate is of great interest due to its importance as an enzyme substrate and metabolite. Therefore, we investigated a straightforward one-step biocatalytic phosphorylation of glyceric acid. Glycerate-2-kinase from Thermotoga maritima was expressed in Escherichia coli, allowing easy purification. The selective glycerate-2-kinase-catalyzed phosphorylation was followed by (31) P NMR and showed excellent enantioselectivity towards phosphorylation of the d-enantiomer of glyceric acid. This straightforward phosphorylation reaction and subsequent product isolation enabled the preparation of enantiomerically pure d-glycerate 2-phosphate. This phosphorylation reaction, using recombinant glycerate-2-kinase, yielded d-glycerate 2-phosphate in fewer reaction steps and with higher purity than chemical routes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Chemical and genomic evolution of enzyme-catalyzed reaction networks.

    PubMed

    Kanehisa, Minoru

    2013-09-02

    There is a tendency that a unit of enzyme genes in an operon-like structure in the prokaryotic genome encodes enzymes that catalyze a series of consecutive reactions in a metabolic pathway. Our recent analysis shows that this and other genomic units correspond to chemical units reflecting chemical logic of organic reactions. From all known metabolic pathways in the KEGG database we identified chemical units, called reaction modules, as the conserved sequences of chemical structure transformation patterns of small molecules. The extracted patterns suggest co-evolution of genomic units and chemical units. While the core of the metabolic network may have evolved with mechanisms involving individual enzymes and reactions, its extension may have been driven by modular units of enzymes and reactions. Copyright © 2013 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  20. Oligonucleotide synthesis catalyzed by the Zn/2+/ ion

    NASA Technical Reports Server (NTRS)

    Sawai, H.; Orgel, L. E.

    1975-01-01

    Results of experiments are reported in which Zn(2+) ion catalyzed the formation of oligonucleotides from nucleoside phosphorimidazolides in aqueous solution, even in the absence of a template. Specifically, the imidazolides (ImpU or ImpA) polymerized to form ImpApA, and pApA, pApApA, and pApApApA, or the analogous uracil compounds. In addition, the expected hydrolysis products of the hydrolysis of ImpA were formed (pA, imidazole). Judging from the ratio of pA(n) over pA (with and without zinc ion), this ion increased the efficiency of phosphodiester-bond formation by up to 10 times. Possible mechanisms for the reaction are tentatively proposed.

  1. Iridium-catalyzed reductive nitro-Mannich cyclization.

    PubMed

    Gregory, Alex W; Chambers, Alan; Hawkins, Alison; Jakubec, Pavol; Dixon, Darren J

    2015-01-02

    A new chemoselective reductive nitro-Mannich cyclization reaction sequence of nitroalkyl-tethered lactams has been developed. Relying on the rapid and chemoselective iridium(I)-catalyzed reduction of lactams to the corresponding enamine, subsequent nitro-Mannich cyclization of tethered nitroalkyl functionality provides direct access to important alkaloid natural-product-like structures in yields up to 81 % and in diastereoselectivities that are typically good to excellent. An in-depth understanding of the reaction mechanism has been gained through NMR studies and characterization of reaction intermediates. The new methodology has been applied to the total synthesis of (±)-epi-epiquinamide in four steps. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Triethylenetetramine prevents insulin aggregation and fragmentation during copper catalyzed oxidation.

    PubMed

    Torosantucci, Riccardo; Weinbuch, Daniel; Klem, Robin; Jiskoot, Wim

    2013-08-01

    Metal catalyzed oxidation via the oxidative system Cu(2+)/ascorbate is known to induce aggregation of therapeutic proteins, resulting in enhanced immunogenicity. Hence, inclusion of antioxidants in protein formulations is of great interest. In this study, using recombinant human insulin (insulin) as a model, we investigated the ability of several excipients, in particular triethylenetetramine (TETA), reduced glutathione(GSH) and ethylenediamine tetraacetic acid (EDTA), for their ability to prevent protein oxidation, aggregation, and fragmentation. Insulin (1mg/ml) was oxidized with 40 μM Cu(2+) and 4mM ascorbic acid in absence or presence of excipients. Among the excipients studied, 1mM of TETA, EDTA, or GSH prevented insulin aggregation upon metal catalyzed oxidation (MCO) for 3h at room temperature, based on size exclusion chromatography (SEC). At lower concentration (100 μM), for 72 h at +4 °C, TETA was the only one to inhibit almost completely oxidation-induced insulin aggregation, fragmentation, and structural changes, as indicated by SEC, nanoparticle tracking analysis, light obscuration particle counting, intrinsic/extrinsic fluorescence, circular dichroism, and chemical derivatization. In contrast, GSH had a slight pro-oxidant effect, as demonstrated by the higher percentage of aggregates and a more severe structural damage, whereas EDTA offered substantially less protection. TETA also protected a monoclonal IgG1 against MCO-induced aggregation, suggesting its general applicability. In conclusion, TETA is a potential candidate excipient for inclusion in formulations of oxidation-sensitive proteins. Copyright © 2013 Elsevier B.V. All rights reserved.

  3. [Ru/AC catalyzed ozonation of recalcitrant organic compounds].

    PubMed

    Wang, Jian-Bing; Hou, Shao-Pei; Zhou, Yun-Rui; Zhu, Wan-Peng; He, Xu-Wen

    2009-09-15

    Ozonation and Ru/AC catalyzed ozonation of dimethyl phthalate (DMP), phenols and disinfection by-products precursors were studied. It shows that Ru/AC catalyst can obviously enhance the mineralization of organic compounds. In the degradation of DMP, TOC removal was 28.84% by ozonation alone while it was 66.13% by catalytic ozonation. In the oxidation of 23 kinds of phenols, TOC removals were 9.57%-56.08% by ozonation alone while they were 41.81%-82.32% by catalytic ozonation. Compared to ozonation alone, Ru/AC catalyzed ozonation was more effective for the reduction of disinfection by-products formation potentials in source water. The reduction of haloacetic acids formation potentials was more obvious than thichlomethane formation potentials. After the treatment by catalytic ozonation, the haloacetic acids formation potentials decreased from 144.02 microg/L to 58.50 microg/L, which was below the standard value of EPA. However ozonation alone could not make it reach the standard. The treatments of source water by BAC, O3 + BAC, O3/AC + BAC and Ru/AC + O3 + BAC were also studied. In the four processes, TOC removal was 3.80%, 20.14%, 27.45% and 48.30% respectively, COD removal was 4.37%, 27.22%, 39.91% and 50.00% respectively, UV254 removal was 8.16%, 62.24%, 67.03% and 84.95% respectively. Ru/AC + O3 + BAC process is more effective than the other processes for the removal of TOC, COD and UV254 and no ruthenium leaching observed in the solution. It is a promising process for the treatment of micro polluted source water.

  4. Acid-Catalyzed Hydration of anti-Sesquinorbornene.

    PubMed

    Slebocka-Tilk, H.; Brown, R. S.

    1996-11-15

    The acid-catalyzed hydration of anti-sesquinorbornene (1) has been studied at 25 degrees C in 20% DME/H(2)O from 0.001 M < [HC1] < 0.05 M. The second-order rate constant for hydration is 5.35 +/- 0.07 M(-)(1) s(-)(1) which can be compared with a value of 1.38 +/- 0.06 M(-)(1) s(-)(1) for ethyl vinyl ether determined under the same conditions. The solvent deuterium kinetic isotope effect for hydration of 1 is 2.7, and a plot of the observed second-order rate constant for the hydration in a mixed solvent system of H(2)O/D(2)O against the atom fraction of deuterium (n) is bowed upward. The reaction also shows marked buffer catalysis by formic, chloroacetic, and dichloroacetic acids, the Brønsted alpha being 1 for these three carboxylic acids: H(3)O(+) does not fit on this Brønsted line. A mechanism for the reaction is presented which is consistent with the generally accepted one for acid-catalyzed hydration of an alkene in which the rate-limiting step involves proton transfer from H(3)O(+) to the double bond. Whether attack of a second water on the developing carbocation occurs simultaneously with protonation cannot be ascertained from the data for 1, but if so, the extent of its C-OH(2) bond formation must be small enough that there is little change in the bonding of these O-H bonds.

  5. Human carbonyl reductase catalyzes reduction of 4-oxonon-2-enal.

    PubMed

    Doorn, Jonathan A; Maser, Edmund; Blum, Andreas; Claffey, David J; Petersen, Dennis R

    2004-10-19

    4-Oxonon-2-enal (4ONE) was demonstrated to be a product of lipid peroxidation, and previous studies found that it was highly reactive toward DNA and protein. The present study sought to determine whether carbonyl reductase (CR) catalyzes reduction of 4ONE, representing a potential pathway for metabolism of the lipid peroxidation product. Recombinant CR was cloned from a human liver cDNA library, expressed in Escherichia coli, and purified by metal chelate chromatography. Both 4ONE and its glutathione conjugate were found to be substrates for CR, and kinetic parameters were calculated. TLC analysis of reaction products revealed the presence of three compounds, two of which were identified as 4-hydroxynon-2-enal (4HNE) and 1-hydroxynon-2-en-4-one (1HNO). GC/MS analysis confirmed 4HNE and 1HNO and identified the unknown reaction product as 4-oxononanal (4ONA). Analysis of oxime derivatives of the reaction products via LC/MS confirmed the unknown as 4ONA. The time course for CR-mediated, NADPH-dependent 4ONE reduction and appearance of 4HNE and 1HNO was determined using HPLC, demonstrating 4HNE to be a major product and 1HNO and 4ONA to be minor products. Simulated structures of 4ONE in the active site of CR/NADPH calculated via docking experiments predict the ketone positioned as primary hydride acceptor. Results of the present study demonstrate that 4ONE is a substrate for CR/NADPH and the enzyme may represent a pathway for biotransformation of the lipid. Furthermore, these findings reveal that CR catalyzes hydride transfer selectively to the ketone but also to the aldehyde and C=C of 4ONE, resulting in 4HNE, 1HNO, and 4ONA, respectively.

  6. Multimethylation of Rickettsia OmpB Catalyzed by Lysine Methyltransferases*

    PubMed Central

    Abeykoon, Amila; Wang, Guanghui; Chao, Chien-Chung; Chock, P. Boon; Gucek, Marjan; Ching, Wei-Mei; Yang, David C. H.

    2014-01-01

    Methylation of rickettsial OmpB (outer membrane protein B) has been implicated in bacterial virulence. Rickettsial methyltransferases RP789 and RP027-028 are the first biochemically characterized methyltransferases to catalyze methylation of outer membrane protein (OMP). Methylation in OMP remains poorly understood. Using semiquantitative integrated liquid chromatography-tandem mass spectroscopy, we characterize methylation of (i) recombinantly expressed fragments of Rickettsia typhi OmpB exposed in vitro to trimethyltransferases of Rickettsia prowazekii RP027-028 and of R. typhi RT0101 and to monomethyltransferases of R. prowazekii RP789 and of R. typhi RT0776, and (ii) native OmpBs purified from R. typhi and R. prowazekii strains Breinl, RP22, and Madrid E. We found that in vitro trimethylation occurs at relatively specific locations in OmpB with consensus motifs, KX(G/A/V/I)N and KT(I/L/F), whereas monomethylation is pervasive throughout OmpB. Native OmpB from virulent R. typhi contains mono- and trimethyllysines at locations well correlated with methylation in recombinant OmpB catalyzed by methyltransferases in vitro. Native OmpBs from highly virulent R. prowazekii strains Breinl and RP22 contain multiple clusters of trimethyllysine in contrast to a single cluster in OmpB from mildly virulent R. typhi. Furthermore, OmpB from the avirulent strain Madrid E contains mostly monomethyllysine and no trimethyllysine. The native OmpB from Madrid E was minimally trimethylated by RT0101 or RP027-028, consistent with a processive mechanism of trimethylation. This study provides the first in-depth characterization of methylation of an OMP at the molecular level and may lead to uncovering the link between OmpB methylation and rickettsial virulence. PMID:24497633

  7. Metal ion catalyzed hydrolysis of ethyl p-nitrophenyl phosphate.

    PubMed

    Rawlings, J; Cleland, W W; Hengge, A C

    2003-01-01

    15N isotope effects in the nitro group and 18O isotope effects in the phenolic oxygen have been measured for the hydrolysis of ethyl p-nitrophenyl phosphate catalyzed by several metal ions. Co(III)-cyclen at pH 7, 50 degrees C, gave an 15N isotope effect of 0.12% and an 18O one of 2.23%, showing that P-O cleavage is rate limiting and the bond is approximately 50% broken in the transition state. The active catalyst is a dimer and the substrate is presumably coordinated to the open site of one Co(III), and is attacked by hydroxide coordinated to the other Co(III). Co(III)-tacn under the same conditions shows a similar 15N isotope effect (0.13%), but a smaller 18O one (0.8%). Zn(II)-cyclen at pH 8.5, 80 degrees C, gave an 15N isotope effect of 0.05% and an 18O one of 0.95%, suggesting an earlier transition state. The catalyst in this case is monomeric, and thus the substrate is coordinated to one position and attacked by a cis-coordinated hydroxide. Eu(III) at pH 6.5, 50 degrees C, shows a very large 15N isotope effect of 0.34% and a 1.6% 18O isotope effect. The large 15N isotope effect argues for a late transition state or Eu(III) interaction with the nitro group, and was also seen in Eu(III)-catalyzed hydrolysis of p-nitrophenyl phosphate.

  8. Cyclic peptide formation catalyzed by an antibody ligase

    PubMed Central

    Smithrud, David B.; Benkovic, Patricia A.; Benkovic, Stephen J.; Roberts, Victoria; Liu, Josephine; Neagu, Irina; Iwama, Seiji; Phillips, Barton W.; Smith, Amos B.; Hirschmann, Ralph

    2000-01-01

    Cyclic hexapeptides represent a class of compounds with important, diverse biological activities. We report herein that the antibody 16G3 catalyzes the cyclization of d-Trp-Gly-Pal-Pro-Gly-Phe⋅p-nitrophenyl ester (8a) to give c-(d-Trp-Gly-Pal-Pro-Gly-l-Phe) (11a). The antibody does not, however, catalyze either epimerization or hydrolysis. The resulting rate enhancement of the cyclization by 16G3 (22-fold) was sufficient to form the desired product in greater than 90% yield. In absolute rate terms, the turnover of 16G3 is estimated to be 2 min−1. The background rate of epimerization of 8a was reduced from 10 to 1% and hydrolysis from 50 to 4% in the presence of 16G3. As expected, the catalytic effects of 16G3 were blocked by the addition of an amount of the hapten equal to twice the antibody concentration. We also synthesized three diastereomers of 8a: the d-Trp1-d-Phe6 (8b), l-Trp1-l-Phe6 (8c), and l-Trp1-d-Phe6 (8d) hexapeptides as well as d-Trp′-l-Trp6 (12) and d-Phe′-l-Phe6 (13). As expected, the rate enhancement by 16G3 was greatest for 8a, because the stereochemistry of Trp1 and Phe6 matches that of the corresponding residues on the hapten used to induce the biosynthesis of 16G3. A model of the variable domain of 16G3 was generated from the primary sequence using the antibody structural database to guide the model construction. The resulting model provided support for some previously proposed interpretations of the kinetic data, while providing valuable new insights for others. PMID:10688882

  9. The General Base in the Thymidylate Synthase Catalyzed Proton Abstraction

    PubMed Central

    Ghosh, Ananda K.; Islam, Zahidul; Krueger, Jonathan; Abeysinghe, Don Thelma; Kohen, Amnon

    2015-01-01

    The enzyme thymidylate synthase (TSase), an important chemotherapeutic drug target, catalyzes the formation of 2′-deoxythymidine-5′-monophosphate (dTMP), a precursor of one of the DNA building blocks. TSase catalyzes a multi-step mechanism that includes the abstraction of a proton from the C5 of the substrate 2′-deoxyuridine-5′-monophosphate (dUMP). Previous studies on ecTSase proposed that an active-site residue, Y94 serves the role of the general base abstracting this proton. However, since Y94 is neither very basic, nor connected to basic residues, nor located close enough to the pyrimidine proton to be abstracted, the actual identity of this base remains enigmatic. Based on crystal structures, an alternative hypothesis is that the nearest potential proton-acceptor of C5 of dUMP is a water molecule that is part of a hydrogen bond (H-bond) network comprised of several water molecules and several protein residues including H147, E58, N177, and Y94. Here, we examine the role of the residue Y94 in the proton abstraction step by removing its hydroxyl group (Y94F mutant). We investigated the effect of the mutation on the temperature dependence of intrinsic kinetic isotope effects (KIEs) and found that these KIEs are more temperature dependent than those of the wild-type enzyme (WT). These results suggest that the phenolic –OH of Y94 is a component of the transition state for the proton abstraction step. The findings further support the hypothesis that no single functional group is the general base, but a network of bases and hydroxyls (from water molecules and tyrosine) sharing H-bonds across the active site can serve the role of the general base to remove the pyrimidine proton. PMID:25912171

  10. Activity of formylphosphate in the reaction catalyzed by formyltetrahydrofolate synthetase

    SciTech Connect

    Jahansouz, H.; Kofron, J.L.; Smithers, G.W.; Himes, R.H.; Reed, G.H.

    1986-05-01

    Formylphosphate (FP), a putative enzyme-bound intermediate in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase, was synthesized from formylfluoride and Pi. Measurement of hydrolysis rates by /sup 31/P NMR showed that FP is very unstable with a half-life of 48 min at 20/sup 0/C and pH 7. At pH 7 hydrolysis occurs with O-P bond cleavage as shown by /sup 18/O incorporation from /sup 18/O-H/sub 2/O into Pi. The substrate activity of FP was tested in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase isolated from Clostridium cylindrosporum. MgATP + H/sub 4/folate + HCOO/sup -/ in equilibrium MgADP + Pi +N/sup 10/-formylH/sub 4/folate FP supports the reaction in both the forward and reverse directions. Thus, N/sup 10/-formylH/sub 4/folate is produced from H/sub 4/-folate and FP but only if ADP is present, and ATP is produced from FP and ADP but only if H/sub 4/folate is present. The requirements for H/sub 4/folate in the synthesis of ATP from ADP and FP and for ADP in the synthesis of N/sup 10/-formylH/sub 4/folate from FP and H/sub 4/folate, are consistent with past kinetic and isotope exchange studies which showed that the reaction proceeds by a sequential mechanism and that all three substrates must be present for any reaction to occur.

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

    PubMed

    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.

  12. New metal catalyzed syntheses of nanostructured boron nitride and alkenyldecaboranes

    NASA Astrophysics Data System (ADS)

    Chatterjee, Shahana

    The goals of the research described in this dissertation were two-fold. The first goal was to develop new methods, employing metal-catalyzed chemical vapor deposition reactions of molecular polyborane precursors, for the production of boron nitride nanostructured materials, including both boron nitride nanotubes (BNNTs) and boron nitride nanosheets (BNNS). The second goal was to develop new systematic metal-catalyzed reactions for polyboranes that would facilitate their functionalization for possible biomedical and/or materials applications. The syntheses of multi- and double-walled BNNTs were achieved with the aid of a floating nickel catalyst via the catalytic chemical vapor deposition (CCVD) of borazine (B3N3H6) or decaborane (B10H14) molecular precursors in ammonia atmospheres, with each precursor having its own advantages. While borazine is a single-source precursor containing both boron and nitrogen, the decaborane-based syntheses required the additional step of reaction with ammonia. However, the higher observed BNNT yields and the ease of handling and commercial availability of decaborane are distinct advantages. The BNNTs derived from both precursors were crystalline with highly ordered structures. The BNNTs grown at 1200 ºC from borazine were mainly double walled, with lengths up to 0.2 µm and ˜2 nm diameters. The BNNTs grown at 1200-1300 ºC from decaborane were double- and multi-walled, with the double-walled nanotubes having ˜2 nm inner diameters and the multi-walled nanotubes (˜10 walls) having ˜4-5 nm inner diameters and ˜12-14 nm outer diameters. BNNTs grown from decaborane at 1300 ºC were longer, averaging ˜0.6 µm, whereas those grown at 1200 ºC had average lengths of ˜0.2 µm. The BNNTs were characterized using scanning and transmission electron microscopies (SEM and TEM), and electron energy loss spectroscopy (EELS). This floating catalyst method now provides a catalytic and potentially scalable route to BNNTs with low defect density

  13. Cyclobutene vs 1,3-Diene Formation in the Gold-Catalyzed Reaction of Alkynes with Alkenes: The Complete Mechanistic Picture.

    PubMed

    de Orbe, M Elena; Amenós, Laura; Kirillova, Mariia S; Wang, Yahui; López-Carrillo, Verónica; Maseras, Feliu; Echavarren, Antonio M

    2017-08-02

    The intermolecular gold(I)-catalyzed reaction between arylalkynes and alkenes leads to cyclobutenes by a [2 + 2] cycloaddition, which takes place stepwise, first by formation of cyclopropyl gold(I) carbenes, followed by a ring expansion. However, 1,3-butadienes are also formed in the case of ortho-substituted arylalkynes by a metathesis-type process. The corresponding reaction of alkenes with aryl-1,3-butadiynes, ethynylogous to arylalkynes, leads exclusively to cyclobutenes. A comprehensive mechanism for the gold(I)-catalyzed reaction of alkynes with alkenes is proposed on the basis of density functional theory calculations, which shows that the two pathways leading to cyclobutenes or dienes are very close in energy. The key intermediates are cyclopropyl gold(I) carbenes, which have been independently generated by retro-Buchner reaction from stereodefined 1a,7b-dihydro-1H-cyclopropa[a]naphthalenes.

  14. Determination of Proanthocyanidin A2 Content in Phenolic Polymer Isolates by Reversed-Phase High Performance Liquid Chromatography

    USDA-ARS?s Scientific Manuscript database

    This article summarizes the development of an analytical method for the determination of proanthocyanidin (PAC) A2 in phenolic polymer isolates following acid-catalyzed degradation in the presence of excess phloroglucinol. Isolates from cranberry juice concentrate (CJC) were extensively characterize...

  15. Gold-Catalyzed Benzylic Azidation of Phthalans and Isochromans and Subsequent FeCl3-Catalyzed Nucleophilic Substitutions.

    PubMed

    Asai, Shota; Yabe, Yuki; Goto, Ryota; Nagata, Saori; Monguchi, Yasunari; Kita, Yasuyuki; Sajiki, Hironao; Sawama, Yoshinari

    2015-01-01

    The benzylic positions of the phthalan and isochroman derivatives (1) as benzene-fused cyclic ethers effectively underwent gold-catalyzed direct azidation using trimethylsilylazide (TMSN3) to give the corresponding 1-azidated products (2) possessing the N,O-acetal partial structure. The azido group of the N,O-acetal behaved as a leaving group in the presence of catalytic iron(III) chloride, and 1-aryl or allyl phthalan and isochroman derivatives were obtained by nucleophilic arylation or allylation, respectively. Meanwhile, a double nucleophilic substitution toward the 1-azidated products (2) occurred at the 1-position using indole derivatives as a nucleophile accompanied by elimination of the azido group and subsequent ring opening of the cyclic ether nucleus produced the bisindolylarylmethane derivatives.

  16. Gold-catalyzed cyclization of (ortho-alkynylphenylthio)silanes: intramolecular capture of the vinyl-Au intermediate by the silicon electrophile.

    PubMed

    Nakamura, Itaru; Sato, Takuma; Terada, Masahiro; Yamamoto, Yoshinori

    2007-09-27

    The gold-catalyzed cyclization of (ortho-alkynylphenylthio)silanes 1 produced the corresponding 3-silylbenzo[b]thiophenes 2 in good to excellent yields. For example, the reaction of [2-(1-pentynyl)phenylthio]triisopropylsilane 1a, [2-(p-anisylethynyl)phenylthio]triisopropylsilane 1e, and [2-(phenylethynyl)phenylthio]triisopropylsilane 1g in the presence of 2 mol % of AuCl in toluene at 45 degrees C gave 2a, 2e, and 2g in 98, 99, and 97% yields, respectively. This reaction proceeds through intramolecular capture of the vinyl-Au intermediate by the silicon electrophile, so-called silyldemetalation.

  17. Differential inhibition of CYP1-catalyzed regioselective hydroxylation of estradiol by berberine and its oxidative metabolites.

    PubMed

    Chang, Yu-Ping; Huang, Chiung-Chiao; Shen, Chien-Chang; Tsai, Keng-Chang; Ueng, Yune-Fang

    2015-10-01

    Berberine is a pharmacologically active alkaloid present in widely used medicinal plants, such as Coptis chinensis (Huang-Lian). The hormone estradiol is oxidized by cytochrome P450 (CYP) 1B1 to primarily form the genotoxic metabolite 4-hydroxyestradiol, whereas CYP1A1 and CYP1A2 predominantly generate 2-hydroxyestradiol. To illustrate the effect of berberine on the regioselective oxidation of estradiol, effects of berberine and its metabolites on CYP1 activities were studied. Among CYP1s, CYP1B1.1, 1.3 (L432V), and 1.4 (N453S)-catalyzed 4-hydroxylation were preferentially inhibited by berberine. Differing from the competitive inhibition of CYP1B1.1 and 1.3, N453S substitution in CYP1B1 allowed a non-competitive or mixed-type pattern. An N228T in CYP1B1 highly decreased its activity and preference to 4-hydroxylation. A reverse mutation of T223N in CYP1A2 retained its 2-hydroxylation preference, but enhanced its inhibition susceptibility to berberine. Compared with berberine, metabolites demethyleneberberine and thalifendine caused weaker inhibition of CYP1A1 and CYP1B1 activities. Unexpectedly, thalifendine was more potent than berberine in the inhibition of CYP1A2, in which case an enhanced interaction through polar hydrogen-π bond was predicted from the docking analysis. These results demonstrate that berberine preferentially inhibits the estradiol 4-hydroxylation activity of CYP1B1 variants, suggesting that 4-hydroxyestradiol-mediated toxicity might be reduced by berberine, especially in tissues/tumors highly expressing CYP1B1.

  18. Metal ion-catalyzed nucleic acid alkylation and fragmentation.

    PubMed

    Browne, Kenneth A

    2002-07-10

    Nucleic acid microarrays are a growing technology in which high densities of known sequences are attached to a substrate in known locations (addressed). Hybridization of complementary sequences leads to a detectable signal such as an electrical impulse or fluorescence. This combination of sequence addressing, hybridization, and detection increases the efficiency of a variety of genomic disciplines including those that profile genetic expression, search for single nucleotide polymorphisms (SNPs), or diagnose infectious diseases by sequencing portions of microbial or viral genomes. Incorporation of reporter molecules into nucleic acids is essential for the sensitive detection of minute amounts of nucleic acids on most types of microarrays. Furthermore, polynucleic acid size reduction increases hybridization because of increased diffusion rates and decreased competing secondary structure of the target nucleic acids. Typically, these reactions would be performed as two separate processes. An improvement to past techniques, termed labeling-during-cleavage (LDC), is presented in which DNA or RNA is alkylated with fluorescent tags and fragmented in the same reaction mixture. In model studies with 26 nucleotide-long RNA and DNA oligomers using ultraviolet/visible and fluorescence spectroscopies as well as high-pressure liquid chromatography and mass spectrometry, addition of both alkylating agents (5-(bromomethyl)fluorescein, 5- or 6-iodoacetamidofluorescein) and select metal ions (of 21 tested) to nucleic acids in aqueous solutions was critical for significant increases in both labeling and fragmentation, with >or=100-fold increases in alkylation possible relative to metal ion-free reactions. Lanthanide series metal ions, Pb(2+), and Zn(2+) were the most reactive ions in terms of catalyzing alkylation and fragmentation. While oligonucleotides were particularly susceptible to fragmentation at sites containing phosphorothioate moieties, labeling and cleavage reactions

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

    PubMed

    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

  20. Fundamentals of heterogeneously catalyzed reactions of environmental importance

    NASA Astrophysics Data System (ADS)

    Deshmukh, Subodh Shrinivas

    Reaction kinetics and spectroscopic characterization are valuable tools for understanding heterogeneously catalyzed chemical reactions. The objective of this work was to apply the tools of catalysis and reaction kinetics to understand the fundamentals of chemical surface phenomena for environmentally important reactions. This thesis presents our work in two areas of catalytic reactions for pollution abatement---"chlorofluorocarbon (CFC) treatment chemistry" and "sulfur-tolerant auto exhaust catalysts." The ozone depletion potential of CFCs has resulted in a great interest in the academic and industrial communities to find replacements for these chemicals. Hydrofluorocarbons (HFCs) are amongst the best "environmentally benign" candidates for CFC replacement. One selective pathway for the synthesis of HFCs is via the hydrodechlorination of CFCs. This route has the added benefit of destroying harmful CFC stockpiles and converting them into more useful chemicals. The work in Chapter 3 shows that parallel hydrogenation pathways starting from a common CF2 species can explain the formation of the products CH2F2 and CH4 for the hydrodechlorination of CF2Cl2 over Pd/AlF3. Transient kinetics experiments using C2H4 as a trapping agent for surface carbenes have provided evidence for the presence of CH2 species on the catalyst surface during this reaction. The absence of either coupling products or trapped products containing F suggests that the rate of hydrogenation of surface CF2 species is faster than that of surface CH2 species. Another important class of CFC reactions is oxide-catalyzed disproportionations to control the number and position of halogen atoms in the CFC/HFC molecule. Chapter 4 combines the use of reaction kinetics tools and spectroscopic characterization techniques to understand the adsorption and reaction of CF3CFCl 2 over gamma-Al2O3. The CF3CFCl 2 reaction over gamma-Al2O3 lead to a modification of the gamma-Al2O3 surface due to fluorination and the

  1. High power density yeast catalyzed microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Ganguli, Rahul

    Microbial fuel cells leverage whole cell biocatalysis to convert the energy stored in energy-rich renewable biomolecules such as sugar, directly to electrical energy at high efficiencies. Advantages of the process include ambient temperature operation, operation in natural streams such as wastewater without the need to clean electrodes, minimal balance-of-plant requirements compared to conventional fuel cells, and environmentally friendly operation. These make the technology very attractive as portable power sources and waste-to-energy converters. The principal problem facing the technology is the low power densities compared to other conventional portable power sources such as batteries and traditional fuel cells. In this work we examined the yeast catalyzed microbial fuel cell and developed methods to increase the power density from such fuel cells. A combination of cyclic voltammetry and optical absorption measurements were used to establish significant adsorption of electron mediators by the microbes. Mediator adsorption was demonstrated to be an important limitation in achieving high power densities in yeast-catalyzed microbial fuel cells. Specifically, the power densities are low for the length of time mediator adsorption continues to occur. Once the mediator adsorption stops, the power densities increase. Rotating disk chronoamperometry was used to extract reaction rate information, and a simple kinetic expression was developed for the current observed in the anodic half-cell. Since the rate expression showed that the current was directly related to microbe concentration close to the electrode, methods to increase cell mass attached to the anode was investigated. Electrically biased electrodes were demonstrated to develop biofilm-like layers of the Baker's yeast with a high concentration of cells directly connected to the electrode. The increased cell mass did increase the power density 2 times compared to a non biofilm fuel cell, but the power density

  2. Selenide-Catalyzed Stereoselective Construction of Tetrasubstituted Trifluoromethylthiolated Alkenes with Alkynes.

    PubMed

    Wu, Jin-Ji; Xu, Jia; Zhao, Xiaodan

    2016-10-17

    The efficient regio- and stereoselective construction of tetrasubstituted alkenes is challenging and very important. For this purpose, we have developed an efficient approach to synthesize tetrasubstituted trifluoromethylthiolated alkenes from simple alkynes in excellent regio- and stereoselectivities by selenide-catalyzed multicomponent coupling. Using this method, trifluoromethylthiolated alkenyl triflates and arenes were achieved. In particular, the triflates could be further converted into carbofunctionalized alkenes by palladium-catalyzed cross-coupling reactions. Our method provides a new pathway for the construction of trifluoromethylthiolated tricarboalkenes. This work presents the first example of selenide-catalyzed trifluoromethylthiolation of alkynes and enables the challenging functionalizations of alkynes.

  3. Effective alkaline metal-catalyzed oxidative delignification of hybrid poplar

    SciTech Connect

    Bhalla, Aditya; Bansal, Namita; Stoklosa, Ryan J.; Fountain, Mackenzie; Ralph, John; Hodge, David B.; Hegg, Eric L.

    2016-02-09

    Background: Strategies to improve copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment of hybrid poplar were investigated. These improvements included a combination of increasing hydrolysis yields, while simultaneously decreasing process inputs through (i) more efficient utilization of H2O2 and (ii) the addition of an alkaline extraction step prior to the metal-catalyzed AHP pretreatment. We hypothesized that utilizing this improved process could substantially lower the chemical inputs needed during pretreatment. Results: Hybrid poplar was pretreated utilizing a modified process in which an alkaline extraction step was incorporated prior to the Cu-AHP treatment step and H2O2 was added batch-wise over the course of 10 h. Our results revealed that the alkaline pre-extraction step improved both lignin and xylan solubilization, which ultimately led to improved glucose (86 %) and xylose (95 %) yields following enzymatic hydrolysis. An increase in the lignin solubilization was also observed with fed-batch H2O2 addition relative to batch-only addition, which again resulted in increased glucose and xylose yields (77 and 93 % versus 63 and 74 %, respectively). Importantly, combining these strategies led to significantly improved sugar yields (96 % glucose and 94 % xylose) following enzymatic hydrolysis. In addition, we found that we could substantially lower the chemical inputs (enzyme, H2O2, and catalyst), while still maintaining high product yields utilizing the improved Cu-AHP process. This pretreatment also provided a relatively pure lignin stream consisting of ≥90 % Klason lignin and only 3 % xylan and 2 % ash following precipitation. Two-dimensional heteronuclear single-quantum coherence (2D HSQC) NMR and size-exclusion chromatography demonstrated that the solubilized lignin was high molecular weight (Mw ≈ 22,000 Da) and only slightly oxidized relative to lignin

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

    NASA Technical Reports Server (NTRS)

    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

  5. Bonding by Hydroxide-Catalyzed Hydration and Dehydration

    NASA Technical Reports Server (NTRS)

    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

  6. Effective alkaline metal-catalyzed oxidative delignification of hybrid poplar

    DOE PAGES

    Bhalla, Aditya; Bansal, Namita; Stoklosa, Ryan J.; ...

    2016-02-09

    Background: Strategies to improve copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment of hybrid poplar were investigated. These improvements included a combination of increasing hydrolysis yields, while simultaneously decreasing process inputs through (i) more efficient utilization of H2O2 and (ii) the addition of an alkaline extraction step prior to the metal-catalyzed AHP pretreatment. We hypothesized that utilizing this improved process could substantially lower the chemical inputs needed during pretreatment. Results: Hybrid poplar was pretreated utilizing a modified process in which an alkaline extraction step was incorporated prior to the Cu-AHP treatment step and H2O2 was added batch-wise over the course of 10more » h. Our results revealed that the alkaline pre-extraction step improved both lignin and xylan solubilization, which ultimately led to improved glucose (86 %) and xylose (95 %) yields following enzymatic hydrolysis. An increase in the lignin solubilization was also observed with fed-batch H2O2 addition relative to batch-only addition, which again resulted in increased glucose and xylose yields (77 and 93 % versus 63 and 74 %, respectively). Importantly, combining these strategies led to significantly improved sugar yields (96 % glucose and 94 % xylose) following enzymatic hydrolysis. In addition, we found that we could substantially lower the chemical inputs (enzyme, H2O2, and catalyst), while still maintaining high product yields utilizing the improved Cu-AHP process. This pretreatment also provided a relatively pure lignin stream consisting of ≥90 % Klason lignin and only 3 % xylan and 2 % ash following precipitation. Two-dimensional heteronuclear single-quantum coherence (2D HSQC) NMR and size-exclusion chromatography demonstrated that the solubilized lignin was high molecular weight (Mw ≈ 22,000 Da) and only slightly oxidized relative to lignin from untreated poplar. In conclusion: This study demonstrated that the fed

  7. Targeting Thromboxane A2 Receptor for Anti-Metastasis Therapy of Breast Cancer

    DTIC Science & Technology

    2011-09-01

    breast cancer metastasis. 2) Inhibition of thromboxane A2 production , either using TX synthase inhibitor or aspirin or other cyclooxygenase inhibitors...spectra reflected aberrant repair of 6-4 photoproducts and oxidative DNA damage. The 3’-5’ exonuclease was the principal enzymatic activity required...families of proteins: GEFs, guanine nucleotide exchange factors catalyze nucleotide exchange when activated by upstream signals; GAPs, GTPase-activating

  8. Synthesis and characterization of branched polymers from lipase-catalyzed trimethylolpropane copolymerizations.

    PubMed

    Kulshrestha, Ankur S; Gao, Wei; Fu, Hongyong; Gross, Richard A

    2007-06-01

    Lipase-catalyzed terpolymerizations were performed with the monomers trimethylolpropane (B3), 1,8-octanediol (B2), and adipic acid (A2). Polymerizations were performed in bulk, at 70 degrees C, for 42 h, using immobilized lipase B from Candida antartica (Novozyme-435) as a catalyst. To determine the substitution pattern of trimethylolpropane (TMP) in copolymers, model compounds with variable degrees of acetylation were synthesized. Inverse-gated 13C NMR spectra were recorded to first determine the chemical shift positions for mono-, di-, and trisubstituted TMP units and, subsequently, to determine substitution of TMP units along chains. Variation of TMP in the monomer feed gave copolymers with degrees of branching (DB) from 20% to 67%. In one example, a hyperbranched copolyester with 53 mol % TMP adipate units was formed in 80% yield, with Mw 14 100 (relative to polystyrene standards), Mw/Mn 5.3, and DB 36%. Thermal and crystalline properties of the copolyesters were studied by thermogravimetric analysis and differential scanning calorimetry.

  9. REACTION MECHANISMS OF 15-HYDROPEROXYEICOSATETRAENOIC ACID CATALYZED BY HUMAN PROSTACYCLIN AND THROMBOXANE SYNTHASES

    PubMed Central

    Yeh, Hui-Chun; Tsai, Ah-Lim; Wang, Lee-Ho

    2007-01-01

    Prostacyclin synthase (PGIS) and thromboxane synthase (TXAS) are atypical cytochrome P450s. They do not require NADPH or dioxygen for isomerization of prostaglandin H2 (PGH2) to produce prostacyclin (PGI2) and thromboxane A2 (TXA2). PGI2 and TXA2 have opposing actions on platelet aggregation and blood vessel tone. In this report, we use a lipid hydroperoxide, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), to explore the active site characteristics of PGIS and TXAS. The two enzymes transformed 15-HPETE not only into 13-hydroxy-14,15-epoxy-5,8,11-eicosatrienoic acid (13-OH-14,15-EET), like many microsomal P450s, but also to 15-ketoeicosatetraenoic acid (15-KETE) and 15-hydroxyeicosatetraenoic acid (15-HETE). 13-OH-14,15-EET and 15-KETE result from homolytic cleavage of the O–O bond, whereas 15-HETE results from heterolytic cleavage, a common peroxidase pathway. About 80% of 15-HPETE was homolytically cleaved by PGIS and 60% was homolytically cleaved by TXAS. The Vmax of homolytic cleavage is 3.5-fold faster than heterolytic cleavage for PGIS-catalyzed reactions (1100 min−1 vs. 320 min−1) and 1.4-fold faster for TXAS (170 min−1 vs. 120 min−1). Similar KM values for homolytic and heterolytic cleavages were found for PGIS (∼60 μM 15-HPETE) and TXAS (∼80 μM 15-HPETE), making PGIS a more efficient catalyst for the 15-HPETE reaction. PMID:17459323

  10. Self-catalyzed Growth of Large-Area Nanofilms of Two-Dimensional Carbon

    PubMed Central

    Qian, Xuemin; Liu, Huibiao; Huang, Changshui; Chen, Songhua; Zhang, Liang; Li, Yongjun; Wang, Jizheng; Li, Yuliang

    2015-01-01

    The graphdiyne (GD), a carbon allotrope with a 2D structure comprising benzene rings and carbon–carbon triple bonds, can be synthesized through cross-coupling on the surface of copper foil. The key problem is in understanding the dependence of layers number and properties, however, the controlled growth of the layers numbers of GD film have not been demonstrated, its controlled growth into large-area and high ordered films with different numbers of layers is still an important challenge. Here, we show that a new strategy for synthesizing GD films with 2D nanostructures on ZnO nanorod arrays through a combination of reduction and a self-catalyzed vapor–liquid–solid growth process, using GD powder as the vapor source and ZnO nanorod arrays as the substrate. HRTEM shows the distance between pairs of streaks being approximately 0.365 nm by different thicknesses of GD films. The approach enables us to construct large-area ordered semiconductive films with high-quality surfaces showing high conductivity (up to 2800 S cm−1). FETs were fabricated based on the well ordered films; we prepared and measured over 100 devices. Devices incorporating these well-ordered and highly conductive GD films exhibited field-effect mobility as high as 100 cm2 V−1 s−1. PMID:25583680

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

    USGS Publications Warehouse

    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.

  12. MEMS-Based Satellite Micropropulsion Via Catalyzed Hydrogen Peroxide Decomposition

    NASA Technical Reports Server (NTRS)

    Hitt, Darren L.; Zakrzwski, Charles M.; Thomas, Michael A.; Bauer, Frank H. (Technical Monitor)

    2001-01-01

    Micro-electromechanical systems (MEMS) techniques offer great potential in satisfying the mission requirements for the next generation of "micro-scale" satellites being designed by NASA and Department of Defense agencies. More commonly referred to as "nanosats", these miniature satellites feature masses in the range of 10-100 kg and therefore have unique propulsion requirements. The propulsion systems must be capable of providing extremely low levels of thrust and impulse while also satisfying stringent demands on size, mass, power consumption and cost. We begin with an overview of micropropulsion requirements and some current MEMS-based strategies being developed to meet these needs. The remainder of the article focuses the progress being made at NASA Goddard Space Flight Center towards the development of a prototype monopropellant MEMS thruster which uses the catalyzed chemical decomposition of high concentration hydrogen peroxide as a propulsion mechanism. The products of decomposition are delivered to a micro-scale converging/diverging supersonic nozzle which produces the thrust vector; the targeted thrust level approximately 500 N with a specific impulse of 140-180 seconds. Macro-scale hydrogen peroxide thrusters have been used for satellite propulsion for decades; however, the implementation of traditional thruster designs on a MEMS scale has uncovered new challenges in fabrication, materials compatibility, and combustion and hydrodynamic modeling. A summary of the achievements of the project to date is given, as is a discussion of remaining challenges and future prospects.

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

    PubMed

    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.

  14. Enzyme-Catalyzed Regioselective Modification of Starch Nanoparticles

    SciTech Connect

    Chakraborty, Soma; Sahoo, Bishwabhusan; Teraoka, Iwao; Miller, Lisa M.; Gross, Richard A.

    2004-12-13

    The selective esterification of starch nanoparticles was performed using as catalyst Candida antartica Lipase B (CAL-B) in its immobilized (Novozym 435) and free (SP-525) forms. The starch nanoparticles were made accessible for acylation reactions by formation of Aerosol-OT (AOT, bis(2-ethylhexyl)sodium sulfosuccinate) stabilized microemulsions. Starch nanoparticles in microemulsions were reacted with vinyl stearate, ε-caprolactone, and maleic anhydride at 40 °C for 48 h to give starch esters with degrees of substitution (DS) of 0.8, 0.6, and 0.4, respectively. Substitution occurred regioselectively at the C-6 position of the glucose repeat units. Infrared microspectroscopy (IRMS) revealed that AOT-coated starch nanoparticles diffuse into the outer 50 μm shell of catalyst beads. Thus, even though CAL-B is immobilized within a macroporous resin, CAL-B is sufficiently accessible to the starch nanoparticles. When free CAL-B was incorporated along with starch within AOT-coated reversed micelles, CAL-B was also active and catalyzed the acylation with vinyl stearate (24 h, 40 °C) to give DS = 0.5. After removal of surfactant from the modified starch nanoparticles, they were dispersed in DMSO or water and were shown to retain their nanodimensions.

  15. Kinetic modeling of Pt-catalyzed glycolaldehyde decomposition to syngas.

    PubMed

    Salciccioli, Michael; Vlachos, Dionisios G

    2012-05-10

    Fundamental knowledge of the elementary reaction mechanisms involved in oxygenate decomposition on transition metal catalysts can facilitate the optimization of future catalyst and reactor systems for biomass upgrade to fuels and chemicals. Pt-catalyzed decomposition of glycolaldehyde, as the smallest oxygenate with alcohol and aldehyde functionality, was studied via a DFT-based microkinetic model. It was found that two decomposition pathways exist. Under conditions of low hydrogen surface coverage, the initial C-H bond breaking reaction to HOCH(2)CO* is prevalent, while under conditions of high hydrogen coverage, the rather unexpected O-H bond forming reaction to HOCH(2)CHOH* is more active (subsequent decomposition is energetically favorable from HOCH(2)CHOH*). Our results indicate the possibility that (de)hydrogenation chemistry is rate-controlling in many small polyoxygenate biomass derivatives, and suitable catalysts are needed. Finally, DFT was used to understand the increased decomposition activity observed on the surface segregated Ni-Pt-Pt bimetallic catalyst. It was found that the initial O-H bond breaking of glycolaldehyde to OCH(2)CHO* has an activation barrier of just 0.21 eV. This barrier is lower than that of any glycolaldehyde consuming reaction on Pt. These computational predictions are in qualitative agreement with experimental results.

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

    PubMed Central

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

    2013-01-01

    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 kcat/Km 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. PMID:23610417

  17. Study of muon catalyzed dd-fusion in HD gas

    NASA Astrophysics Data System (ADS)

    Semenchuk, G. G.; Balin, D. V.; Case, T.; Crowe, K. M.; Ganzha, V. A.; Hartmann, F. J.; Kozlov, S. M.; Lauss, B.; Maev, E. M.; Mühlbauer, M.; Petitjean, C.; Petrov, G. E.; Sadetsky, S. M.; Schapkin, G. N.; Schott, W.; Smirenin, Yu. V.; Soroka, M. A.; Vasiliev, A. A.; Vorobyov, A. A.; Voropaev, N. I.; Zmeskal, J.

    1999-06-01

    The results of an experiment on muon catalyzed dd-fussion in HD gas are presented. The experiment was performed at the muon beam of PSI using a high-pressure ionization chamber filled with pure HD-gas of low D2 concentration on the level 1%, at temperatures 50, 150 and 300 K. The non-resonant character of ddμ-molecule formation on HD molecules was confirmed by measuring the ratio of yields of the two ddμ-fusion channels, R=Y(3He,n)/Y(3H,p), which proved to be close to unity. The ddμ formation rate was found to vary from λddμ-HD=0.05· 106 s-1 at T=50 K to λddμ-HD=0.12· 106 s-1 at T=300 K, in agreement with the theoretical prediction. A prominent peak at t<60 ns was observed in the time spectrum of fusion neutrons indicating a resonant contribution of ddμ formation from epithermal dμ atoms.

  18. Phase-transfer-catalyzed asymmetric synthesis of axially chiral anilides.

    PubMed

    Liu, Kun; Wu, Xiangfei; Kan, S B Jennifer; Shirakawa, Seiji; Maruoka, Keiji

    2013-12-01

    Catalytic asymmetric synthesis of axially chiral o-iodoanilides and o-tert-butylanilides as useful chiral building blocks was achieved by means of binaphthyl-modified chiral quaternary ammonium-salt-catalyzed N-alkylations under phase-transfer conditions. The synthetic utility of axially chiral products was demonstrated in various transformations. For example, axially chiral N-allyl-o-iodoanilide was transformed to 3-methylindoline by means of radical cyclization with high chirality transfer from axial chirality to C-centered chirality. Furthermore, stereochemical information on axial chirality in o-tert-butylanilides could be used as a template to control the stereochemistry of subsequent transformations. The transition-state structure of the present phase-transfer reaction was discussed on the basis of the X-ray crystal structure of ammonium anilide, which was prepared from binaphthyl-modified chiral ammonium bromide and o-iodoanilide. The chiral tetraalkylammonium bromide as a phase-transfer catalyst recognized the steric difference between the ortho substituents on anilide to obtain high enantioselectivity. The size and structural effects of the ortho substituents on anilide were investigated, and a wide variety of axially chiral anilides that possess various functional groups could be synthesized with high enantioselectivities. This method is the only general way to access a variety of axially chiral anilides in a highly enantioselective fashion reported to date. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Kinetics of phenolic polymerization catalyzed by peroxidase in organic media

    SciTech Connect

    Xu, Y.P.; Huang, G.L; Yu, Y.T.

    1995-07-05

    Phenolic polymerization was carried out by enzymatic catalysis in organic media, and its kinetics was studied by using high-pressure liquid chromatography (HPLC). Phenols and aromatic amines with electron-withdrawing groups could hardly be polymerized by HRP catalysis, but phenols and aromatic amines with electron-donating groups could easily by polymerized. The reaction rate of either the para-substituted substrate or meta-substituted substrate was higher than that of ortho-substituted substrate. When ortho-position of hydroxy group of phenols was occupied by an electron-donating group and if another electron-donating group occupied para-position of hydroxy group, the reaction rate increased. Horseradish peroxidase and lactoperoxidase could easily catalyze the polymerization, but chloroperoxidase and laccase failed to yield polymers. Metallic ions such as Mn{sup 2+}, Fe{sup 2+}, or Fe{sup 3+}, and Cu{sup 2+} could poison horseradish peroxidase to various extents, but ions such as Co{sup 2+}, Cd{sup 2+}, Zn{sup 2+}, and K{sup +} were not found to inhibit the reaction.

  20. Carbon-catalyzed gasification of organic feedstocks in supercritical water

    SciTech Connect

    Xu, X.; Matsumura, Y.; Stenberg, J.; Antal, M.J. Jr.

    1996-08-01

    Spruce wood charcoal, macadamia shell charcoal, coal activated carbon, and coconut shell activated carbon catalyze the gasification of organic compounds in supercritical water. Feedstocks studied in this paper include glycerol, glucose, cellobiose, whole biomass feedstocks (depithed bagasse liquid extract and sewage sludge), and representative Department of Defense (DoD) wastes (methanol, methyl ethyl ketone, ethylene glycol, acetic acid, and phenol). The effects of temperature, pressure, reactant concentration, weight hourly space velocity, and the type of catalyst on the gasification of glucose are reported. Complete conversion of glucose (22% by weight in water) to a hydrogen-rich synthesis gas was realized at a weight hourly space velocity (WHSV) of 22.2 h{sup {minus}1} in supercritical water at 600 C, 34.5 MPa. Complete conversions of the whole biomass feeds were also achieved at the same temperature and pressure. The destruction efficiencies for the representative DoD wastes were also high. Deactivation of the carbon catalyst was observed after 4 h of operation without swirl in the entrance region of the reactor, but the carbon gasification efficiency remained near 100% for more than 6 h when a swirl generator was employed in the entrance of the reactor.

  1. A review on production of biodiesel using catalyzed transesterification

    NASA Astrophysics Data System (ADS)

    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.

  2. Investigating antibody-catalyzed ozone generation by human neutrophils.

    PubMed

    Babior, Bernard M; Takeuchi, Cindy; Ruedi, Julie; Gutierrez, Abel; Wentworth, Paul

    2003-03-18

    Recent studies have suggested that antibodies can catalyze the generation of previously unknown oxidants including dihydrogen trioxide (H(2)O(3)) and ozone (O(3)) from singlet oxygen ((1)O(2)(*)) and water. Given that neutrophils have the potential both to produce (1)O(2)(*) and to bind antibodies, we considered that these cells could be a biological source of O(3). We report here further analytical evidence that antibody-coated neutrophils, after activation, produce an oxidant with the chemical signature of O(3). This process is independent of surface antibody concentration down to 50% of the resting concentration, suggesting that surface IgG is highly efficient at intercepting the neutrophil-generated (1)O(2)(*). Vinylbenzoic acid, an orthogonal probe for ozone detection, is oxidized by activated neutrophils to 4-carboxybenzaldehyde in a manner analogous to that obtained for its oxidation by ozone in solution. This discovery of the production of such a powerful oxidant in a biological context raises questions about not only the capacity of O(3) to kill invading microorganisms but also its role in amplification of the inflammatory response by signaling and gene activation.

  3. Temperature dependences of rate coefficients for electron catalyzed mutual neutralization.

    PubMed

    Shuman, Nicholas S; Miller, Thomas M; Friedman, Jeffrey F; Viggiano, Albert A; Maeda, Satoshi; Morokuma, Keiji

    2011-07-14

    The flowing afterglow technique of variable electron and neutral density attachment mass spectrometry (VENDAMS) has recently yielded evidence for a novel plasma charge loss process, electron catalyzed mutual neutralization (ECMN), i.e., A(+) + B(-) + e(-) → A + B + e(-). Here, rate constants for ECMN of two polyatomic species (POCl(3)(-) and POCl(2)(-)) and one diatomic species (Br(2)(-)) each with two monatomic cations (Ar(+)and Kr(+)) are measured using VENDAMS over the temperature range 300 K-500 K. All rate constants show a steep negative temperature dependence, consistent with that expected for a three body process involving two ions and an electron. No variation in rate constants as a function of the cation type is observed outside of uncertainty; however, rate constants of the polyatomic anions (~1 × 10(-18) cm(6) s(-1) at 300 K) are measurably higher than that for Br(2)(-) [(5.5 ± 2) × 10(-19) cm(6) s(-1) at 300 K].

  4. Temperature dependences of rate coefficients for electron catalyzed mutual neutralization

    SciTech Connect

    Shuman, Nicholas S.; Miller, Thomas M.; Friedman, Jeffrey F.; Viggiano, Albert A.; Maeda, Satoshi; Morokuma, Keiji

    2011-07-14

    The flowing afterglow technique of variable electron and neutral density attachment mass spectrometry (VENDAMS) has recently yielded evidence for a novel plasma charge loss process, electron catalyzed mutual neutralization (ECMN), i.e., A{sup +}+ B{sup -}+ e{sup -}{yields} A + B + e{sup -}. Here, rate constants for ECMN of two polyatomic species (POCl{sub 3}{sup -} and POCl{sub 2}{sup -}) and one diatomic species (Br{sub 2}{sup -}) each with two monatomic cations (Ar{sup +}and Kr{sup +}) are measured using VENDAMS over the temperature range 300 K-500 K. All rate constants show a steep negative temperature dependence, consistent with that expected for a three body process involving two ions and an electron. No variation in rate constants as a function of the cation type is observed outside of uncertainty; however, rate constants of the polyatomic anions ({approx}1 x 10{sup -18} cm{sup 6} s{sup -1} at 300 K) are measurably higher than that for Br{sub 2}{sup -}[(5.5 {+-} 2) x 10{sup -19} cm{sup 6} s{sup -1} at 300 K].

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

    PubMed

    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.

  6. Remote catalyzation for direct formation of graphene layers on oxides.

    PubMed

    Teng, Po-Yuan; Lu, Chun-Chieh; Akiyama-Hasegawa, Kotone; Lin, Yung-Chang; Yeh, Chao-Hui; Suenaga, Kazu; Chiu, Po-Wen

    2012-03-14

    Direct deposition of high-quality graphene layers on insulating substrates such as SiO(2) paves the way toward the development of graphene-based high-speed electronics. Here, we describe a novel growth technique that enables the direct deposition of graphene layers on SiO(2) with crystalline quality potentially comparable to graphene grown on Cu foils using chemical vapor deposition (CVD). Rather than using Cu foils as substrates, our approach uses them to provide subliming Cu atoms in the CVD process. The prime feature of the proposed technique is remote catalyzation using floating Cu and H atoms for the decomposition of hydrocarbons. This allows for the direct graphitization of carbon radicals on oxide surfaces, forming isolated low-defect graphene layers without the need for postgrowth etching or evaporation of the metal catalyst. The defect density of the resulting graphene layers can be significantly reduced by tuning growth parameters such as the gas ratios, Cu surface areas, and substrate-to-Cu distance. Under optimized conditions, graphene layers with nondiscernible Raman D peaks can be obtained when predeposited graphite flakes are used as seeds for extended growth. © 2012 American Chemical Society

  7. Feasibility of an antiproton catalyzed fission fragment rocket

    SciTech Connect

    Hdinger, D.S.

    1992-03-01

    The purpose of this project was to investigate the feasibility of an antiproton catalyzed fission fragment rocket (FFR). The FFR is characterized by the extraction of fission fragments from the fissile fuel, and the utilization of their kinetic energy for thrust generation. A significant drawback to previous FFR designs was the requirement to maintain a critical nuclear pile as the fission fragment source. The author examined the possibility of replacing the critical pile with a sub-critical pile driven by antiprotons. Recent experiments have revealed that antiprotons stimulate highly energetic fissions in {sup 238}U, with a neutron multiplicity of 13.7 neutrons per fission. This interaction was used as a throttled neutron source. The pile consisted of layers of fissile coated fibers which are designed to allow fission fragments to escape them, where the fragments collide with a fluid. The heated fluid is then ejected from the rocket to provide thrust. The calculations performed indicate that each antiproton injected into the pile can stimulate 8 or more fissions while maintaining a neutron multiplication of less than 0.4. Based on the results seen, the engine design presented is inadequate. Limitations introduced by the reaction fluid far outweigh the simplicity-of-design gained. Despite this, the basic idea of using the antiproton-U interaction as a source of spacecraft propulsion warrants further study.

  8. Temperature dependences of rate coefficients for electron catalyzed mutual neutralization

    NASA Astrophysics Data System (ADS)

    Shuman, Nicholas S.; Miller, Thomas M.; Friedman, Jeffrey F.; Viggiano, Albert A.; Maeda, Satoshi; Morokuma, Keiji

    2011-07-01

    The flowing afterglow technique of variable electron and neutral density attachment mass spectrometry (VENDAMS) has recently yielded evidence for a novel plasma charge loss process, electron catalyzed mutual neutralization (ECMN), i.e., A+ + B- + e- → A + B + e-. Here, rate constants for ECMN of two polyatomic species (POCl3- and POCl2-) and one diatomic species (Br2-) each with two monatomic cations (Ar+and Kr+) are measured using VENDAMS over the temperature range 300 K-500 K. All rate constants show a steep negative temperature dependence, consistent with that expected for a three body process involving two ions and an electron. No variation in rate constants as a function of the cation type is observed outside of uncertainty; however, rate constants of the polyatomic anions (˜1 × 10-18 cm6 s-1 at 300 K) are measurably higher than that for Br2- [(5.5 ± 2) × 10-19 cm6 s-1 at 300 K].

  9. Nickel-Catalyzed Cycloadditions of Unsaturated Hydrocarbons, Aldehydes, and Ketones

    PubMed Central

    Tekavec, Thomas N.

    2014-01-01

    The nickel-catalyzed cycloaddition of unsaturated hydrocarbons and carbonyls is reported. Diynes and enynes were used as coupling partners. Carbonyl substrates include both aldehdyes and ketones. Reactions of diynes and aldehydes afforded the [3, 3] electrocyclic ring-opened tautomers, rather than pyrans, in high yields. The cycloaddition reaction of enynes and aldehydes afforded two distinct products. A new carbon–carbon bond is formed, prior to a competitive β-hydrogen elimination of a nickel alkoxide, between the carbonyl carbon and either one of the carbons of the olefin or the alkyne. The steric hindrance of the enyne greatly affected the chemoselectivity of the cycloaddition of enynes and aldehydes. In some cases, dihydropyran was also formed. The scope of the cycloaddition reaction was expanded to include the coupling of enynes and ketones. No β-hydrogen elimination was observed in cycloaddition reaction of enynes and ketones. Instead, C–O bond-forming reductive elimination occurred exclusively to afford dihydropyrans in excellent yields. In all cases, complete chemoselectivity was observed; only dihydropyrans where the carbonyl carbon forms a carbon–carbon bond with a carbon of the olefin, rather than of the alkyne, were observed. All cycloaddition reactions occur at room temperature and employ nickel catalysts bearing the hindered 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or its saturated analogue, 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazolin-2-ylidene (SIPr). PMID:18318544

  10. The platinum-catalyzed decomposition of methanol: A deceptive demonstration

    SciTech Connect

    Coffing, D.L.; Wile, J.L. )

    1993-07-01

    The platinum-catalyzed gas-phase decomposition of methanol can be used for classroom demonstration in an exciting, interesting fashion. The platinum catalysts, after being heated until it glows, can be made to continue glowing for hours by suspending it over the methanol. This demonstration is useful in a classroom setting for several reasons. First it is more complicated than it appears initially, involving a reaction that is not immediately obvious and is, therefore, more challenging for students to understand. Second, the platinum illustrates the phenomenon of exothermic reactions in a distinctive and memorable way. Because the platinum foil has to be heated before the reactions will proceed, this demonstration also is a perfect example of the temperature dependence of [Delta]G in determining the spontaneity of a reaction. Finally, this demonstration can be used to explain the mutual interaction of two reactions. Because an explanation of this demonstration requires the use of many chemical concepts, it is an ideal activity for stimulating synthesis among students near the end of the course.

  11. Stereochemical course of enzyme-catalyzed aminopropyl transfer: spermidine synthase

    SciTech Connect

    Kullberg, D.W.; Orr, G.R.; Coward, J.K.

    1986-05-01

    The R and S enantionmers of S-adenosyl-3-(/sup 2/H)3-(methylthio)-1-propylamine (decarboxylated S-adenosylmethionine), previously synthesized in this laboratory, were incubated with (1,4-/sup 2/H/sub 4/)-putrescine in the presence of spermidine synthase from E. coli. The resulting chiral (/sup 2/H/sub 5/)spermidines were isolated and converted to their N/sub 1/,N/sub 7/-dibocspermidine-N/sub 4/-(1S,4R)-camphanamides. The derivatives were analyzed by 500 MHz /sup 1/H-NMR and the configuration of the chiral center assigned by correlation with the spectra of synthetic chiral (/sup 2/H/sub 3/)dibocspermidine camphanamide standards. The enzyme-catalyzed aminopropyl transfer was shown to occur with net retention of configuration, indicative of a double-displacement mechanism. This result concurs with that of a previous steady-state kinetics study of spermidine synthase isolated from E. coli, but contradicts the single-displacement mechanism suggested by a stereochemical analysis of chiral spermidines biosynthesized in E. coli treated with chirally deuterated methionines. It also indicates that this aminopropyltransferase is mechanistically distinct from the methyltransferases, which have been shown to act via a single-displacement mechanism (net inversion at -CH/sub 3/) in all cases studied to date.

  12. Dephenolization of industrial wastewaters catalyzed by polyphenol oxidase

    SciTech Connect

    Atlow, S.C.; Bonadonna-Aparo, L.; Klibanov, A.M.

    1984-01-01

    A new enzymatic method for the removal of phenols from industrial aqueous effluents has been developed. The method uses the enzyme polyphenol oxidase which oxidizes phenols to the corresponding o-quinones; the latter then undergo a nonenzymatic polymerization to form water-insoluble aggregates. Therefore, the enzyme in effect precipitates phenols from water. Polyphenol oxidase has been found to nearly completely dephenolize solutions of phenol in the concentration range from 0.01 to 1.0 g/L. The enzymatic treatment is effective over a wide range of pH and temperature; a crude preparation of polyphenol oxidase (mushroom extract) is as effective as a purified, commercially obtained version. In addition to phenol itself, polyphenol oxidase is capable of precipitating from water a number of substituted phenols (cresols, chlorophenols, naphthol, etc.). Also, even pollutants which are unreactive towards polyphenol oxidase can be enzymatically coprecipitated with phenol. The polyphenol oxidase treatment has been successfully used to dephenolize two different real industrial wastewater samples, from a plant producing triarylphosphates and from a coke plant. The advantage of the polyphenol oxidase dephenolization over the peroxidase-catalyzed one previously elaborated by the authors is that the former enzyme uses molecular oxygen instead of costly hydrogen peroxide (used by peroxidase) as an oxidant.

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

    PubMed

    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.

  14. Deoxycholic acid transformations catalyzed by selected filamentous fungi.

    PubMed

    Kollerov, V V; Lobastova, T G; Monti, D; Deshcherevskaya, N O; Ferrandi, E E; Fronza, G; Riva, S; Donova, M V

    2016-03-01

    More than 100 filamentous fungi strains, mostly ascomycetes and zygomycetes from different phyla, were screened for the ability to convert deoxycholic acid (DCA) to valuable bile acid derivatives. Along with 11 molds which fully degraded DCA, several strains were revealed capable of producing cholic acid, ursocholic acid, 12-keto-lithocholic acid (12-keto-LCA), 3-keto-DCA, 15β-hydroxy-DCA and 15β-hydroxy-12-oxo-LCA as major products from DCA. The last metabolite was found to be a new compound. The ability to catalyze the introduction of a hydroxyl group at the 7(α/β)-positions of the DCA molecule was shown for 32 strains with the highest 7β-hydroxylase activity level for Fusarium merismoides VKM F-2310. Curvularia lunata VKM F-644 exhibited 12α-hydroxysteroid dehydrogenase activity and formed 12-keto-LCA from DCA. Acremonium rutilum VKM F-2853 and Neurospora crassa VKM F-875 produced 15β-hydroxy-DCA and 15β-hydroxy-12-oxo-LCA, respectively, as major products from DCA, as confirmed by MS and NMR analyses. For most of the positive strains, the described DCA-transforming activity was unreported to date. The presented results expand the knowledge on bile acid metabolism by filamentous fungi, and might be suitable for preparative-scale exploitation aimed at the production of marketed bile acids. Copyright © 2016 Elsevier Inc. All rights reserved.

  15. Efficient, crosswise catalytic promiscuity among enzymes that catalyze phosphoryl transfer.

    PubMed

    Mohamed, Mark F; Hollfelder, Florian

    2013-01-01

    The observation that one enzyme can accelerate several chemically distinct reactions was at one time surprising because the enormous efficiency of catalysis was often seen as inextricably linked to specialization for one reaction. Originally underreported, and considered a quirk rather than a fundamental property, enzyme promiscuity is now understood to be important as a springboard for adaptive evolution. Owing to the large number of promiscuous enzymes that have been identified over the last decade, and the increased appreciation for promiscuity's evolutionary importance, the focus of research has shifted to developing a better understanding of the mechanistic basis for promiscuity and the origins of tolerant or restrictive specificity. We review the evidence for widespread crosswise promiscuity amongst enzymes that catalyze phosphoryl transfer, including several members of the alkaline phosphatase superfamily, where large rate accelerations between 10(6) and 10(17) are observed for both native and multiple promiscuous reactions. This article is part of a Special Issue entitled: Chemistry and mechanism of phosphatases, diesterases and triesterases.

  16. Transamidation of carboxamides catalyzed by Fe(III) and water.

    PubMed

    Becerra-Figueroa, Liliana; Ojeda-Porras, Andrea; Gamba-Sánchez, Diego

    2014-05-16

    The highly efficient transamidation of several primary, secondary, and tertiary amides with aliphatic and aromatic amines (primary and secondary) is described. The reaction is performed in the presence of a 5 mol % concentration of different hydrated salts of Fe(III), and the results show that the presence of water is crucial. The methodology was also applied to urea and phthalimide to demonstrate its versatility and wide substrate scope. An example of its use is an intramolecular application in the synthesis of 2,3-dihydro-5H-benzo[b]-1,4-thiazepin-4-one, which is the bicyclic core of diltiazem and structurally related drugs (Budriesi, R.; Cosimelli, B.; Ioan, P.; Carosati, E.; Ugenti, M. P.; Spisani, R. Curr. Med. Chem. 2007, 14, 279-287). A plausible mechanism that explains the role of water is proposed on the basis of experimental observations and previous mechanistic suggestions for transamidation reactions catalyzed by transition metals such as copper and aluminum. This methodology represents a significant improvement over other existing methods; it can be performed in air and with wet or technical grade solvents.

  17. Kinetics of Platinum-Catalyzed Decomposition of Hydrogen Peroxide

    NASA Astrophysics Data System (ADS)

    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.

  18. Palladium-Catalyzed Decarboxylative Asymmetric Allylic Alkylation of Enol Carbonates

    PubMed Central

    Trost, Barry M.; Xu, Jiayi; Schmidt, Thomas

    2009-01-01

    Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio- and enantio-selective process for the synthesis of ketones bearing either a quaternary or a tertiary α-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic di-substituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium enolates, the DAAA reaction proceeds through an “outer sphere” SN2 type of attack on the π-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the π-allylpalladium cation must serve as the counterion for the enolate, the enolate probably exists as a tight-ion-pair. This largely prevents the common side reactions of enolates associated with the equilibrium between different enolates. The much milder reaction conditions as well as the much broader substrate scope also represent the advantages of the DAAA reaction over the direct allylation of preformed metal enolates. PMID:19928805

  19. Predictive modeling of metal-catalyzed polyolefin processes

    NASA Astrophysics Data System (ADS)

    Khare, Neeraj Prasad

    2003-10-01

    This dissertation describes the essential modeling components and techniques for building comprehensive polymer process models for metal-catalyzed polyolefin processes. The significance of this work is that it presents a comprehensive approach to polymer process modeling applied to large-scale commercial processes. Most researchers focus only on polymerization mechanisms and reaction kinetics, and neglect physical properties and phase equilibrium. Both physical properties and phase equilibrium play key roles in the accuracy and robustness of a model. This work presents the fundamental principles and practical guidelines used to develop and validate both steady-state and dynamic simulation models for two large-scale commercial processes involving the Ziegler-Natta polymerization to produce high-density polyethylene (HDPE) and polypropylene (PP). It also provides a model for the solution polymerization of ethylene using a metallocene catalyst. Existing modeling efforts do not include physical properties or phase equilibrium in their calculations. These omissions undermine the accuracy and predictive power of the models. The forward chapters of the dissertation discuss the fundamental concepts we consider in polymer process modeling. These include physical and thermodynamic properties, phase equilibrium, and polymerization kinetics. The later chapters provide the modeling applications described above.

  20. Kinetics of acid base catalyzed transesterification of Jatropha curcas oil.

    PubMed

    Jain, Siddharth; Sharma, M P

    2010-10-01

    Out of various non-edible oil resources, Jatropha curcas oil (JCO) is considered as future feedstock for biodiesel production in India. Limited work is reported on the kinetics of transesterification of high free fatty acids containing oil. The present study reports the results of kinetic study of two-step acid base catalyzed transesterification process carried out at an optimum temperature of 65 °C and 50 °C for esterification and transesterification respectively under the optimum methanol to oil ratio of 3:7 (v/v), catalyst concentration 1% (w/w) for H₂SO₄ and NaOH. The yield of methyl ester (ME) has been used to study the effect of different parameters. The results indicate that both esterification and transesterification reaction are of first order with reaction rate constant of 0.0031 min⁻¹ and 0.008 min⁻¹ respectively. The maximum yield of 21.2% of ME during esterification and 90.1% from transesterification of pretreated JCO has been obtained.

  1. Toward antibody-catalyzed hydrolysis of organophosphorus poisons

    PubMed Central

    Vayron, Philippe; Renard, Pierre-Yves; Taran, Frédéric; Créminon, Christophe; Frobert, Yveline; Grassi, Jacques; Mioskowski, Charles

    2000-01-01

    We report here our preliminary results on the use of catalytic antibodies as an approach to neutralizing organophosphorus chemical weapons. A first-generation hapten, methyl-α-hydroxyphosphinate Ha, was designed to mimic the approach of an incoming water molecule for the hydrolysis of exceedingly toxic methylphosphonothioate VX (1a). A moderate protective activity was first observed on polyclonal antibodies raised against Ha. The results were further confirmed by using a mAb PAR 15 raised against phenyl-α-hydroxyphosphinate Hb, which catalyzes the hydrolysis of PhX (1b), a less toxic phenylphosphonothioate analog of VX with a rate constant of 0.36 M−1⋅min−1 at pH 7.4 and 25°C, which corresponds to a catalytic proficiency of 14,400 M−1 toward the rate constant for the uncatalyzed hydrolysis of 1b. This is a demonstration on the organophosphorus poisons themselves that mAbs can catalytically hydrolyze nerve agents, and a significant step toward the production of therapeutically active abzymes to treat poisoning by warfare agents. PMID:10860971

  2. Process Intensification in Base-Catalyzed Biodiesel Production

    SciTech Connect

    McFarlane, Joanna; Birdwell Jr, Joseph F; Tsouris, Costas; Jennings, Hal L

    2008-01-01

    Biodiesel is considered a means to diversify our supply of transportation fuel, addressing the goal of reducing our dependence on oil. Recent interest has resulted in biodiesel manufacture becoming more widely undertaken by commercial enterprises that are interested in minimizing the cost of feedstock materials and waste production, as well as maximizing the efficiency of production. Various means to accelerate batch processing have been investigated. Oak Ridge National Laboratory has experience in developing process intensification methods for nuclear separations, and this paper will discuss how technologies developed for very different applications have been modified for continuous reaction/separation of biodiesel. In collaboration with an industrial partner, this work addresses the aspect of base-catalyzed biodiesel production that limits it to a slow batch process. In particular, we have found that interfacial mass transfer and phase separation control the transesterification process and have developed a continuous two-phase reactor for online production of a methyl ester and glycerol. Enhancing the mass transfer has additional benefits such as being able to use an alcohol-to-oil phase ratio closer to stoichiometric than in conventional processing, hence minimizing the amount of solvent that has to be recycled and reducing post-processing clean up costs. Various technical issues associated with the application of process intensification technology will be discussed, including scale-up from the laboratory to a pilot-scale undertaking.

  3. Out of the fog: Catalyzing integrative capacity in interdisciplinary research.

    PubMed

    Piso, Zachary; O'Rourke, Michael; Weathers, Kathleen C

    2016-04-01

    Social studies of interdisciplinary science investigate how scientific collaborations approach complex challenges that require multiple disciplinary perspectives. In order for collaborators to meet these complex challenges, interdisciplinary collaborations must develop and maintain integrative capacity, understood as the ability to anticipate and weigh tradeoffs in the employment of different disciplinary approaches. Here we provide an account of how one group of interdisciplinary fog scientists intentionally catalyzed integrative capacity. Through conversation, collaborators negotiated their commitments regarding the ontology of fog systems and the methodologies appropriate to studying fog systems, thereby enhancing capabilities which we take to constitute integrative capacity. On the ontological front, collaborators negotiated their commitments by setting boundaries to and within the system, layering different subsystems, focusing on key intersections of these subsystems, and agreeing on goals that would direct further investigation. On the methodological front, collaborators sequenced various methods, anchored methods at different scales, validated one method with another, standardized the outputs of related methods, and coordinated methods to fit a common model. By observing the process and form of collaborator conversations, this case study demonstrates that social studies of science can bring into critical focus how interdisciplinary collaborators work toward an integrated conceptualization of study systems.

  4. Iron-catalyzed hydrogen production from formic acid.

    PubMed

    Boddien, Albert; Loges, Björn; Gärtner, Felix; Torborg, Christian; Fumino, Koichi; Junge, Henrik; Ludwig, Ralf; Beller, Matthias

    2010-07-07

    Hydrogen represents a clean energy source, which can be efficiently used in fuel cells generating electricity with water as the only byproduct. However, hydrogen generation from renewables under mild conditions and efficient hydrogen storage in a safe and reversible manner constitute important challenges. In this respect formic acid (HCO(2)H) represents a convenient hydrogen storage material, because it is one of the major products from biomass and can undergo selective decomposition to hydrogen and carbon dioxide in the presence of suitable catalysts. Here, the first light-driven iron-based catalytic system for hydrogen generation from formic acid is reported. By application of a catalyst formed in situ from inexpensive Fe(3)(CO)(12), 2,2':6'2''-terpyridine or 1,10-phenanthroline, and triphenylphosphine, hydrogen generation is possible under visible light irradiation and ambient temperature. Depending on the kind of N-ligands significant catalyst turnover numbers (>100) and turnover frequencies (up to 200 h(-1)) are observed, which are the highest known to date for nonprecious metal catalyzed hydrogen generation from formic acid. NMR, IR studies, and DFT calculations of iron complexes, which are formed under reaction conditions, confirm that PPh(3) plays an active role in the catalytic cycle and that N-ligands enhance the stability of the system. It is shown that the reaction mechanism includes iron hydride species which are generated exclusively under irradiation with visible light.

  5. Production of chemoenzymatic catalyzed monoepoxide biolubricant: optimization and physicochemical characteristics.

    PubMed

    Salimon, Jumat; Salih, Nadia; Abdullah, Bashar Mudhaffar

    2012-01-01

    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 H(2)O(2), 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.

  6. Hydrogen cycling of niobium and vanadium catalyzed nanostructured magnesium.

    PubMed

    Schimmel, H Gijs; Huot, Jacques; Chapon, Laurent C; Tichelaar, Frans D; Mulder, Fokko M

    2005-10-19

    The reaction of hydrogen gas with magnesium metal, which is important for hydrogen storage purposes, is enhanced significantly by the addition of catalysts such as Nb and V and by using nanostructured powders. In situ neutron diffraction on MgNb(0.05) and MgV(0.05) powders give a detailed insight on the magnesium and catalyst phases that exist during the various stages of hydrogen cycling. During the early stage of hydriding (and deuteriding), a MgH(1< x < 2) phase is observed, which does not occur in bulk MgH(2) and, thus, appears characteristic for the small particles. The abundant H vacancies will cause this phase to have a much larger hydrogen diffusion coefficient, partly explaining the enhanced kinetics of nanostructured magnesium. It is shown that under relevant experimental conditions, the niobium catalyst is present as NbH(1). Second, a hitherto unknown Mg-Nb perovskite phase could be identified that has to result from mechanical alloying of Nb and the MgO layer of the particles. Vanadium is not visible in the diffraction patterns, but electron micrographs show that the V particle size becomes very small, 2-20 nm. Nanostructuring and catalyzing the Mg enhance the adsorption speed that much that now temperature variations effectively limit the absorption speed and not, as for bulk, the slow kinetics through bulk MgH(2) layers.

  7. Mechanistic study of silver-catalyzed decarboxylative fluorination.

    PubMed

    Patel, Niki R; Flowers, Robert A

    2015-06-05

    The silver-catalyzed fluorination of aliphatic carboxylic acids by Selectfluor in acetone/water provides access to fluorinated compounds under mild and straightforward reaction conditions. Although this reaction provides efficient access to fluorinated alkanes from a pool of starting materials that are ubiquitous in nature, little is known about the details of the reaction mechanism. We report spectroscopic and kinetic studies on the role of the individual reaction components in decarboxylative fluorination. The studies presented herein provide evidence that Ag(II) is the intermediate oxidant in the reaction. In the rate-limiting step of the reaction, Ag(I)-carboxylate is oxidized to Ag(II) by Selectfluor. Substrate inhibition of the process occurs through the formation of a silver-carboxylate. Water is critical for solubilizing reaction components and ligates to Ag(I) under the reaction conditions. The use of donor ligands on Ag(I) provides evidence of oxidation to Ag(II) by Selectfluor. The use of sodium persulfate as an additive in the reaction as well as NFSI as a fluorine source further supports the generation of a Ag(II) intermediate; this data will enable the development of a more efficient set of reaction conditions for the fluorination.

  8. A Personal Adventure in Muon-Catalyzed Fusion

    NASA Astrophysics Data System (ADS)

    Jackson, John David

    2010-03-01

    Luis Alvarez and colleagues discovered muon-catalyzed fusion of hydrogen isotopes by chance in late 1956. On sabbatical leave at Princeton University during that year, I read the first public announcement of the discovery at the end of December in that well-known scientific journal, The New York Times. A nuclear theorist by prior training, I was intrigued enough in the phenomenon to begin some calculations. I describe my work here, my interaction with Alvarez, and a summary of the surprising developments, both before and after Alvarez’s discovery. The rare proton-deuteron ( p-d) fusion events in Alvarez’s liquid-hydrogen bubble chamber occurred only because of the natural presence of a tiny amount of deuterium (heavy hydrogen). Additionally, the fusion rate, once the proton-deuteron-muon ( pdμ - ) molecular ion has been formed, is sufficiently slow that only rarely does an additional catalytic act occur. A far different situation occurs for muons stopping in pure deuterium or a deuterium-tritium ( d- t) mixture where the fusion rates are many orders of magnitude larger and the molecular-formation rates are large compared to the muon’s decay rate. The intricate interplay of atomic, molecular, and nuclear science, together with highly fortuitous accidents in the molecular dynamics and the hope of practical application, breathed life into a seeming curiosity. A small but vigorous worldwide community has explored these myriad phenomena in the past 50 years.

  9. Primordial lithium abundance in catalyzed big bang nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Bird, Chris; Koopmans, Kristen; Pospelov, Maxim

    2008-10-01

    There exists a well-known problem with the Li7+Be7 abundance predicted by standard big bang nucleosynthesis being larger than the value observed in population II stars. The catalysis of big bang nucleosynthesis by metastable, τX≳103sec, charged particles X- is capable of suppressing the primordial Li7+Be7 abundance and making it consistent with the observations. We show that to produce the correct abundance, this mechanism of suppression places a requirement on the initial abundance of X- at temperatures of 4×108K to be on the order of or larger than 0.02 per baryon, which is within the natural range of abundances in models with metastable electroweak-scale particles. The suppression of Li7+Be7 is triggered by the formation of (Be7X-) compound nuclei, with fast depletion of their abundances by catalyzed proton reactions, and in some models by direct capture of X- on Be7. The combination of Li7+Be7 and Li6 constraints favors the window of lifetimes, 1000s≲τX≤2000s.

  10. Electrophoresis-chemiluminescence detection of phenols catalyzed by hemin.

    PubMed

    Shu, Lu; Zhu, Jinkun; Wang, Qingjiang; He, Pingang; Fang, Yuzhi

    2014-09-01

    Based on the catalytic activity of hemin, an efficient biocatalyst, an indirect capillary electrophoresis-chemiluminescence (CE-CL) detection method for phenols using a hemin-luminol-hydrogen peroxide system was developed. Through a series of static injection experiments, hemin was found to perform best in a neutral solution rather than an acidic or alkaline medium. Although halide ions such as Br(-) and F(-) could further enhance the CL signal catalyzed by hemin, it is difficult to apply these conditions to this CE-CL detection system because of the self-polymerization of hemin, as it hinders the CE process. The addition of concentrated ammonium hydroxide to an aqueous/dimethyl sulfoxide solution of hemin-luminol afforded a stable CE-CL baseline. The indirect CE-CL detection of five phenols using this method gave the following limits of detections: 4.8 × 10(-8) mol/L (o-sec-butylphenol), 4.9 × 10(-8) mol/L (o-cresol), 5.4 × 10(-8) mol/L (m-cresol), 5.3 × 10(-8) mol/L (2,4-dichlorophenol) and 7.1 × 10(-8) mol/L (phenol).

  11. Mild palladium-catalyzed selective monoarylation of nitriles.

    PubMed

    Wu, Lingyun; Hartwig, John F

    2005-11-16

    Two new palladium-catalyzed procedures for the arylation of nitriles under less basic conditions than previously reported have been developed. The selective monoarylation of acetonitrile and primary nitriles has been achieved using alpha-silyl nitriles in the presence of ZnF2. This procedure is compatible with a variety of functional groups, including cyano, keto, nitro, and ester groups, on the aryl bromide. The arylation of secondary nitriles occurred in high yield by conducting reactions with zinc cyanoalkyl reagents. These reaction conditions tolerated base-sensitive functional groups, such as ketones and esters. The combination of these two methods, one with alpha-silyl nitriles and one with zinc cyanoalkyl reagents, provides a catalytic route to a variety of benzylic nitriles, which have not only biological significance but utility as synthetic intermediates. The utility of these new coupling reactions has been demonstrated by a synthesis of verapamil, a clinically used drug for the treatment of heart disease, by a three-step route from commercial materials that allows convenient variation of the aryl group.

  12. Iodide-catalyzed ozonation of terpenes on aqueous surfaces

    NASA Astrophysics Data System (ADS)

    Enami, S.; Hayase, S.; Kawasaki, M.; Hoffmann, M. R.; Colussi, A. J.

    2011-12-01

    Biogenic terpenes are the dominant global source of volatile organic compounds (VOC) and secondary organic aerosols (SOA). Their atmospheric chemistry has therefore major direct and indirect impacts on global climate change. At the same time, it has become apparent that organic and inorganic iodine species of marine origin are ubiquitous in the troposphere. They are found over the open ocean (even in the absence of biogenic sources), the Antarctic coast, in rain, aerosols, ice, and snow, and participate in HOx/NOx cycles in the troposphere. Here we report that iodide catalyzes the ozonation of alpha-pinene on aqueous surfaces. Nebulizer-assisted online electrospray mass spectrometry of alpha-pinene solutions briefly exposed to gaseous ozone reveals that alpha-pinene, which is unreactive during 10 microsecond contact times, is converted into acids (e.g., pinonic acid) and previously unreported iodine-containing species in the presence of millimolar iodide. These newly found products were characterized by MS/MS in conjunction with isotope and kinetic studies, and may account for unidentified organoiodine species observed in recent field measurements.

  13. Copper-catalyzed enantioselective stereodivergent synthesis of amino alcohols

    PubMed Central

    Shi, Shi-Liang; Wong, Zackary L.; Buchwald, Stephen L.

    2016-01-01

    The chirality, or ‘handedness’, of a biologically active molecule can alter its physiological properties. For this reason, it is routine procedure in the drug discovery and development process to prepare and fully characterize all possible stereoisomers of a drug candidate for biological evaluation1,2. Despite many recent advances in asymmetric synthesis, the development of general and practical strategies to obtain all possible stereoisomers of an organic compound bearing multiple contiguous stereocenters remains a significant challenge3. In this manuscript, we report a stereodivergent copper-based approach for the expeditious construction of amino alcohols with high levels of chemo-, regio-, diastereo- and enantioselectivity. Specifically, these amino alcohol products were synthesized using the sequential copper hydride-catalyzed hydrosilylation and hydroamination of readily available enals and enones. This strategy provides a route to all possible stereoisomers of the amino alcohol products, which contain up to three contiguous stereocenters. Catalyst control and stereospecificity were simultaneously leveraged to attain exceptional control of the product stereochemistry. Beyond the utility of this protocol, the strategy demonstrated here should inspire the development of methods providing complete sets of stereoisomers for other valuable synthetic targets. PMID:27018656

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

    PubMed Central

    Salimon, Jumat; Salih, Nadia; Abdullah, Bashar Mudhaffar

    2012-01-01

    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. PMID:22346338

  15. Enzymatically catalyzed HES conjugation using microbial transglutaminase: Proof of feasibility.

    PubMed

    Besheer, Ahmed; Hertel, Thomas C; Kressler, Jörg; Mäder, Karsten; Pietzsch, Markus

    2009-11-01

    Polymer-drug and polymer-protein conjugates are promising candidates for the delivery of therapeutic agents. PEGylation, using poly(ethylene glycol) for the conjugation, is now the gold standard in this field, and some PEGylated proteins have successfully reached the market. Hydroxyethyl starch (HES) is a water-soluble, biodegradable derivative of starch that is currently being investigated as a substitute for PEG. So far, only chemical methods have been suggested for HES conjugation; however, these may have detrimental effects on proteins. Here, we report an enzymatic method for HES conjugation using a recombinant microbial transglutaminase (rMTG). The latter catalyzes the acyl transfer between the gamma-carboxamide group of a glutaminyl residue (acyl donors) and a variety of primary amines (acyl acceptors), including the amino group of lysine. HES was modified with N-carbobenzyloxy glutaminyl glycine (Z-QG) and hexamethylene diamine (HMDA) to act as acyl donor and acyl acceptor, respectively. Using (1)H NMR, the degree of modification with Z-QG and HMDA was found to be 4.6 and 3.9 mol%, respectively. Using SDS-PAGE, it was possible to show that the modified HES successfully coupled to test compounds, proving that it is accepted as a substrate by rMTG. Finally, the process described in this study is a simple, mild approach to produce fully biodegradable polymer-drug and polymer-protein conjugates. (c) 2009 Wiley-Liss, Inc. and the American Pharmacists Association

  16. Existence of efficient divalent metal ion-catalyzed and inefficient divalent metal ion-independent channels in reactions catalyzed by a hammerhead ribozyme

    PubMed Central

    Zhou, Jing-Min; Zhou, De-Min; Takagi, Yasuomi; Kasai, Yasuhiro; Inoue, Atsushi; Baba, Tadashi; Taira, Kazunari

    2002-01-01

    The hammerhead ribozyme is generally accepted as a well characterized metalloenzyme. However, the precise nature of the interactions of the RNA with metal ions remains to be fully defined. Examination of metal ion-catalyzed hammerhead reactions at limited concentrations of metal ions is useful for evaluation of the role of metal ions, as demonstrated in this study. At concentrations of Mn2+ ions from 0.3 to 3 mM, addition of the ribozyme to the reaction mixture under single-turnover conditions enhances the reaction with the product reaching a fixed maximum level. Further addition of the ribozyme inhibits the reaction, demonstrating that a certain number of divalent metal ions is required for proper folding and also for catalysis. At extremely high concentrations, monovalent ions, such as Na+ ions, can also serve as cofactors in hammerhead ribozyme-catalyzed reactions. However, the catalytic efficiency of monovalent ions is extremely low and, thus, high concentrations are required. Furthermore, addition of monovalent ions to divalent metal ion-catalyzed hammerhead reactions inhibits the divalent metal ion-catalyzed reactions, suggesting that the more desirable divalent metal ion–ribozyme complexes are converted to less desirable monovalent metal ion–ribozyme complexes via removal of divalent metal ions, which serve as a structural support in the ribozyme complex. Even though two channels appear to exist, namely an efficient divalent metal ion-catalyzed channel and an inefficient monovalent metal ion-catalyzed channel, it is clear that, under physiological conditions, hammerhead ribozymes are metalloenzymes that act via the significantly more efficient divalent metal ion-dependent channel. Moreover, the observed kinetic data are consistent with Lilley’s and DeRose’s two-phase folding model that was based on ground state structure analyses. PMID:12034824

  17. The importance of thyroglobulin structure in thyroid peroxidase-catalyzed conversion of diiodotyrosine to thyroxine.

    PubMed

    Lamas, L; Taurog, A

    1977-04-01

    We have previously demonstrated that thyroid peroxidase (TPO) not only catalyzes the iodination of thyroglobulin and other proteins, but that it also catalyzes the intramolecular conversion of DIT residues to T4 (coupling reaction). The present study was designed to determine whether the native structure of thyroglobulin contributes to the efficiency of TPO-catalyzed coupling. Two lines of evidence are presented in support of the view that the conformation of thyroglobulin is important for TPO-catalyzed coupling. The first was based on comparison of T4 yields in thyroglobulin and other proteins. The second involved the effect of guanidine pretreatment on T4 yields in thyroglobulin. Both types of experiment provided evidence that the native structure of thyroglobulin contributes to the efficiency of the coupling reaction. Specificity of thyroid peroxidase activity, on the other hand, does not appear to be of importance in the coupling reaction.

  18. On the Role of CO2 in NHC-Catalyzed Oxidation of Aldehydes

    PubMed Central

    Chiang, Pei-Chen; Bode, Jeffrey W.

    2011-01-01

    NHC-catalyzed oxidations using carbon dioxide as the stoichiometric oxidant have been carefully investigated. These studies support a secondary role of CO2 in suppressing side reactions and exogenous oxygen as the actual oxidant. PMID:21486084

  19. 53. VIEW LOOKING S.E. AT THE CATALYZER BUILDINGS, COOLING SHEDS ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    53. VIEW LOOKING S.E. AT THE CATALYZER BUILDINGS, COOLING SHEDS AND ABSORPTION BUILDINGS IN THE BACKGROUND. MAY 29, 1919. - United States Nitrate Plant No. 2, Reservation Road, Muscle Shoals, Muscle Shoals, Colbert County, AL

  20. Palladium-catalyzed allylic amination: a powerful tool for the enantioselective synthesis of acyclic nucleoside phosphonates.

    PubMed

    Azzouz, Mariam; Soriano, Sébastien; Escudero-Casao, Margarita; Matheu, M Isabel; Castillón, Sergio; Díaz, Yolanda

    2017-08-30

    Acyclic nucleoside phosphonates have been prepared in a straightforward manner and in high yields by an enantioselective palladium-catalyzed allylic substitution involving nucleic bases as nucleophiles followed by cross-metathesis reaction with diethyl allylphosphonate.

  1. Silver triflate-catalyzed tandem reaction of N'-(2-alkynylbenzylidene)hydrazide with pyridyne.

    PubMed

    Jiang, Lingyong; Yu, Xingxin; Fang, Bing; Wu, Jie

    2012-10-28

    A silver triflate-catalyzed tandem reaction of N'-(2-alkynylbenzylidene)hydrazide with pyridyne is presented. Different outcomes are obtained, depending on the pyridynes utilized in the transformation.

  2. PALLADIUM-CATALYZED OXIDATION OF STYRENE AND ALKENES IN PRESENCE OF IONIC LIQUIDS (WACKER REACTION)

    EPA Science Inventory

    The use of ionic liquids in various synthetic transformations is gaining significance due to the enhanced reaction rates, potential for recycling and compatibility with various organic compounds and organometallic catalysts. Palladium-catalyzed oxidation of styrene and other alk...

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

    PubMed Central

    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

  4. GREEN CATALYZED OXIDATION OF HYDROCARBONS IN ALTERNATIVE SOLVENT SYSTEMS GENERATED BY PARIS II

    EPA Science Inventory

    Green Catalyzed Oxidation of Hydrocarbons in Alternative Solvent Systems Generated by PARIS II

    Michael A. Gonzalez*, Thomas M. Becker, and Paul F. Harten; Sustainable Technology Division, Office of Research and Development; United States Environmental Protection Agency, 26...

  5. Silver-catalyzed PuO sub 2 dissolution with persulfate

    SciTech Connect

    Fisher, F D; Barney, G S; Cooper, T D; Duchsherer, M J

    1991-06-01

    This report consists of 14 slides and associated narrative for a presentation to be given at the 15th Annual Actinide Separations Conference on silver-catalyzed PuO{sub 2} dissolution with persulfate. (JL)

  6. Rhodium-Catalyzed Transannulation of 1,2,3-Triazoles with Nitriles

    PubMed Central

    Horneff, Tony; Chuprakov, Stepan; Chernyak, Natalia

    2009-01-01

    Stable and readily available 1-sulfonyl triazoles are converted to the corresponding imidazoles in good to excellent yields via a rhodium(II)-catalyzed reaction with nitriles. Rhodium iminocarbenoids are proposed intermediates. PMID:18855475

  7. Synthesis of Polycyclic Nitrogen Heterocycles via Cascade Pd-Catalyzed Alkene Carboamination/Diels-Alder Reactions.

    PubMed

    White, Derick R; Wolfe, John P

    2015-05-15

    Cascade Pd-catalyzed alkene carboamination/Diels-Alder reactions between bromodienes and amines bearing two pendant alkenes are described. These transformations generate 4 bonds, 3 rings, and 3-5 stereocenters to afford polycyclic nitrogen heterocycles with high diastereoselectivity.

  8. From the molecule to the mole: improving heterogeneous copper catalyzed click chemistry using single molecule spectroscopy.

    PubMed

    Wang, Bowen; Durantini, Javier; Decan, Matthew R; Nie, Jun; Lanterna, Anabel E; Scaiano, Juan C

    2016-12-22

    Single molecule spectroscopy (SMS) inspired the optimization of a heterogeneous 'click' catalyst leading to enhanced yields of the Cu-catalyzed reaction of azides with terminal alkynes. Changes in SMS data after optimization confirm the improvements in catalyst performance.

  9. GREEN CATALYZED OXIDATION OF HYDROCARBONS IN ALTERNATIVE SOLVENT SYSTEMS GENERATED BY PARIS II

    EPA Science Inventory

    Green Catalyzed Oxidation of Hydrocarbons in Alternative Solvent Systems Generated by PARIS II

    Michael A. Gonzalez*, Thomas M. Becker, and Paul F. Harten; Sustainable Technology Division, Office of Research and Development; United States Environmental Protection Agency, 26...

  10. Nickel-Catalyzed Borylation of Halides and Pseudo-Halides with Tetrahydroxydiboron [B2(OH)4

    PubMed Central

    Molander, Gary A.; Cavalcanti, Livia N.; García-García, Carolina

    2013-01-01

    Arylboronic acids are gaining increased importance as reagents and target structures in a variety of useful applications. Recently, the palladium-catalyzed synthesis of arylboronic acids employing the atom economical tetrahydroxydiboron (BBA) reagent has been reported. The high cost associated with palladium, combined with several limitations of both palladium and copper-catalyzed processes, prompted us to develop an alternative method. Thus, the nickel-catalyzed borylation of aryl and heteroaryl halides and pseudo-halides using tetrahydroxydiboron (BBA) has been formulated. The reaction proved to be widely functional group tolerant and applicable to a number of heterocyclic systems. To the best of our knowledge, the examples presented here represent the only effective Ni-catalyzed Miyaura borylations conducted at room temperature. PMID:23777538

  11. Highly enantioselective [4 + 2] cyclization of chloroaldehydes and 1-azadienes catalyzed by N-heterocyclic carbenes.

    PubMed

    Jian, Teng-Yue; Sun, Li-Hui; Ye, Song

    2012-11-14

    Highly functionalized dihydropyridinones were synthesized via the N-heterocyclic carbene-catalyzed enantioselective [4 + 2] annulation of α-chloroaldehydes and azadienes. Hydrogenation of the resulted dihydropyridinones afforded the corresponding piperidinones with high enantiopurity.

  12. A novel palladium-catalyzed hydroalkoxylation of alkenes with a migration of double bond.

    PubMed

    Tan, Jiajing; Zhang, Zuhui; Wang, Zhiyong

    2008-04-21

    A novel palladium-catalyzed addition of alcohols to olefins was developed, in which a migration of double bond was involved. By this new method, a variety of allylic ethers were prepared with moderate to high yields under mild conditions.

  13. PALLADIUM-CATALYZED OXIDATION OF STYRENE AND ALKENES IN PRESENCE OF IONIC LIQUIDS (WACKER REACTION)

    EPA Science Inventory

    The use of ionic liquids in various synthetic transformations is gaining significance due to the enhanced reaction rates, potential for recycling and compatibility with various organic compounds and organometallic catalysts. Palladium-catalyzed oxidation of styrene and other alk...

  14. Cascade dearomatization of N-substituted tryptophols via Lewis acid-catalyzed Michael reactions.

    PubMed

    Liu, Chuan; Zhang, Wei; Dai, Li-Xin; You, Shu-Li

    2012-09-21

    Lewis acid-catalyzed cascade dearomatization of N-substituted tryptophols via Michael addition reaction was developed. The generality of the method has been demonstrated by the synthesis of versatile furoindoline derivatives with a quaternary carbon center in good yields.

  15. Iron- and cobalt-catalyzed arylation of azetidines, pyrrolidines, and piperidines with Grignard reagents.

    PubMed

    Barré, Baptiste; Gonnard, Laurine; Campagne, Rémy; Reymond, Sébastien; Marin, Julien; Ciapetti, Paola; Brellier, Marie; Guérinot, Amandine; Cossy, Janine

    2014-12-05

    Iron- and cobalt-catalyzed cross-couplings between iodo-azetidines, -pyrrolidines, -piperidines, and Grignard reagents are disclosed. The reaction is efficient, cheap, chemoselective and tolerates a large variety of (hetero)aryl Grignard reagents.

  16. Iridium-catalyzed hydrogen transfer: synthesis of substituted benzofurans, benzothiophenes, and indoles from benzyl alcohols.

    PubMed

    Anxionnat, Bruno; Gomez Pardo, Domingo; Ricci, Gino; Rossen, Kai; Cossy, Janine

    2013-08-02

    An iridium-catalyzed hydrogen transfer has been developed in the presence of p-benzoquinone, allowing the synthesis of a diversity of substituted benzofurans, benzothiophenes, and indoles from substituted benzylic alcohols.

  17. Copper-catalyzed oxidative carbon-heteroatom bond formation: a recent update.

    PubMed

    Zhu, Xu; Chiba, Shunsuke

    2016-08-08

    This review updates recent advances in Cu-catalyzed (anaerobic) oxidative carbon-heteroatom bond formation on sp(3)- and sp(2)-C-H bonds as well as alkenes, classified according to the types of stoichiometric oxidants.

  18. Novel method for the synthesis of enamines by palladium catalyzed amination of alkenyl bromides.

    PubMed

    Barluenga, José; Fernández, M Alejandro; Aznar, Fernando; Valdés, Carlos

    2002-10-21

    The intermolecular palladium catalyzed cross-coupling reaction between secondary amines and alkenyl bromides is described for the first time, giving rise to enamines with very high yields and regioselectivity.

  19. Rhodium(III)-Catalyzed C-H Activation of Nitrones and Annulative Coupling with Nitroalkenes.

    PubMed

    Bai, Dachang; Jia, Qingqian; Xu, Teng; Zhang, Qiuqiu; Wu, Fen; Ma, Chaorui; Liu, Bingxian; Chang, Junbiao; Li, Xingwei

    2017-09-15

    Rh(III)-catalyzed synthesis of nitro-functionalized indenes has been realized via C-H activation of arylnitrones and annulation with nitroolefins. The reaction proceeded in moderate to high yields with good functional group tolerance under ambient atmosphere.

  20. Direct enantioselective aldol reactions catalyzed by a proline-thiourea host-guest complex.

    PubMed

    Reis, Omer; Eymur, Serkan; Reis, Barbaros; Demir, Ayhan S

    2009-03-07

    Proline-thiourea host-guest complex-catalyzed direct enantioselective aldol reactions have been developed, in which the catalytic activities were evaluated in the direct asymmetric aldol reactions of various aromatic aldehydes and cyclohexanone.

  1. Brønsted acid-catalyzed Nazarov cyclization of pyrrole derivatives accelerated by microwave irradiation.

    PubMed

    Bachu, Prabhakar; Akiyama, Takahiko

    2009-07-15

    The Brønsted acid-catalyzed Nazarov cyclization of pyrrole derivatives was developed. Microwave irradiation accelerated the Nazarov cyclization significantly at 40 degrees C to give cyclopenta[b]pyrrole derivatives in excellent yields with high trans selectivity.

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

    PubMed

    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.

  3. Ready Access to the Echinopines Skeleton via Gold(I)-Catalyzed Alkoxycyclizations of Enynes.

    PubMed

    Dorel, Ruth; Echavarren, Antonio M

    2016-09-16

    The [3,5,5,7] tetracyclic skeleton of echinopines has been stereoselectively accessed through a gold(I)-catalyzed alkoxycyclization of cyclopropyl-tethered 1,6-enynes. The key bicyclo[4.2.1]nonane core of the enyne precursors was readily assembled by means of a Co-catalyzed [6 + 2] cycloaddition. Furthermore, the attempted alkoxycyclization of 1,5-enyne substrates revealed an uncovered cyclopropyl rearrangement that gives rise to [3,6,5,7] tetracyclic structures.

  4. Palladium-catalyzed carbonylative Sonogashira coupling of aryl bromides via tert-butyl isocyanide insertion.

    PubMed

    Tang, Ting; Fei, Xiang-Dong; Ge, Zhi-Yuan; Chen, Zhong; Zhu, Yong-Ming; Ji, Shun-Jun

    2013-04-05

    A simple and efficient palladium-catalyzed carbonylative Sonogashira coupling via tert-butyl isocyanide insertion has been developed, which demonstrates the utility of isocyanides in intermolecular C-C bond construction. This methodology provides a novel pathway for the synthesis of alkynyl imines which can undergo simple silica gel catalyzed hydrolysis to afford alkynones. The approach is tolerant of a wide range of substrates and applicable to library synthesis.

  5. Ligand-controlled divergent formation of alkenyl- or allylboronates catalyzed by Pd, and synthetic applications.

    PubMed

    Martos-Redruejo, Alicia; López-Durán, Ruth; Buñuel, Elena; Cárdenas, Diego J

    2014-09-11

    The use of different ligands allows the preparation of either allyl- or alkenylboronates by Pd-catalyzed borylation of allylic carbonates containing alkyne groups. Unprecedented borylative cyclisation to alkenylboronates takes place with PCy3. The difficult dissociation of NHC ligands allows borylation of carbonates in the presence of alkynes. Oxidation, regioselective Suzuki coupling, as well as Au-catalyzed cycloisomerisation of boronates illustrate the potential synthetic applications of these reactions.

  6. Use of a palladium(II)-catalyzed oxidative kinetic resolution in synthetic efforts toward bielschowskysin.

    PubMed

    Meyer, Michael E; Phillips, John H; Ferreira, Eric M; Stoltz, Brian M

    2013-09-09

    Progress toward the cyclobutane core of bielshowskysin is reported. The core was thought to arise from a cyclopropane intermediate via a furan-mediated cyclopropane fragmentation, followed by a 1,4-Michael addition. The synthesis of the cyclopropane intermediate utilizes a Suzuki coupling reaction, an esterification with 2-diazoacetoacetic acid, and a copper catalyzed cyclopropanation. An alcohol intermediate within the synthetic route was obtained in high enantiopurity via a highly selective palladium(II)-catalyzed oxidative kinetic resolution (OKR).

  7. Ru-Catalyzed Dehydrogenative C-O Bond Formation with Anilines and Phenols.

    PubMed

    Heitz, Christophe; Jones, Alexander W; Oezkaya, Bünyamin S; Bub, Christina L; Louillat-Habermeyer, Marie-Laure; Wagner, Victoria; Patureau, Frederic W

    2016-12-12

    The Ru catalyzed cross-dehydrogenative C-O bond formation between anilines and phenols is described and discussed. The exclusive C-O versus C-N bond-formation selectivity, moreover in the absence of chelating-assisting directing groups and while leaving the N-H position untouched, is a remarkable feature of this metal-catalyzed radical cross-dehydrogenative coupling. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Fronts and pulses in an enzymatic reaction catalyzed by glucose oxidase

    PubMed Central

    Míguez, David G.; Vanag, Vladimir K.; Epstein, Irving R.

    2007-01-01

    Waves and patterns in living systems are often driven by biochemical reactions with enzymes as catalysts and regulators. We present a reaction–diffusion system catalyzed by the enzyme glucose oxidase that exhibits traveling wave patterns in a spatially extended medium. Fronts and pulses propagate as a result of the coupling between the enzyme-catalyzed autocatalytic production and diffusion of hydrogen ions. A mathematical model qualitatively explains the experimental observations. PMID:17420460

  9. Ready Access to the Echinopines Skeleton via Gold(I)-Catalyzed Alkoxycyclizations of Enynes

    PubMed Central

    2016-01-01

    The [3,5,5,7] tetracyclic skeleton of echinopines has been stereoselectively accessed through a gold(I)-catalyzed alkoxycyclization of cyclopropyl-tethered 1,6-enynes. The key bicyclo[4.2.1]nonane core of the enyne precursors was readily assembled by means of a Co-catalyzed [6 + 2] cycloaddition. Furthermore, the attempted alkoxycyclization of 1,5-enyne substrates revealed an uncovered cyclopropyl rearrangement that gives rise to [3,6,5,7] tetracyclic structures. PMID:27529429

  10. Cyclization strategies to polyenes using Pd(II)-catalyzed couplings of pinacol vinylboronates.

    PubMed

    Iafe, Robert G; Chan, Daniel G; Kuo, Jonathan L; Boon, Byron A; Faizi, Darius J; Saga, Tomomi; Turner, Jonathan W; Merlic, Craig A

    2012-08-17

    As a complement to Pd(0)-catalyzed cyclizations, seven Pd(II)-catalyzed cyclization strategies are reported. α,ω-Diynes are selectively hydroborated to bis(boronate esters), which cyclize under Pd(II)-catalysis producing a diverse array of small, medium, and macrocyclic polyenes with controlled E,E, Z,Z, or E,Z stereochemistry. Various functional groups are tolerated including aryl bromides, and applications are illustrated.

  11. Gold(I)-Catalyzed Enantioselective Synthesis of Benzopyrans via Rearrangement of Allylic Oxonium Intermediates

    PubMed Central

    Uemura, Minoru; Watson, Iain D. G.; Katsukawa, Mikimoto; Toste, F. Dean

    2009-01-01

    The first transition metal-catalyzed asymmetric carboalkoxylation reaction of propargyl esters is described. The (R)-MeO-DTBM-BIPHEP(AuCl)2-catalyzed reactions allows for the construction of benzopyrans containing quaternary stereocenters with excellent enantioselectivity. Experimental evidence supports a mechanism proceeding via the generation of a stabilized carbocation from an allylic oxonium intermediate, and subsequent trapping by a chiral allylgold(I) spieces. PMID:19236093

  12. Intermolecular Palladium-Catalyzed Oxidative Fluorocarbonylation of Unactivated Alkenes: Efficient Access to β-Fluorocarboxylic Esters.

    PubMed

    Qi, Xiaoxu; Yu, Feng; Chen, Pinhong; Liu, Guosheng

    2017-10-02

    A novel palladium-catalyzed intermolecular oxidative fluorocarbonylation of alkenes has been developed, in which employment of a cooperative process with electrophilic ArIF2 -meidated alkenes activation and palladium-catalyzed carbonylation is crucial for the successful catalytic transformation. The current transformation presents the first convenient method to generate β-fluorinated carboxylic acid derivatives under mild reaction conditions from simple alkenes with excellent regioselectivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Palladium-Catalyzed Dearomative Cyclocarbonylation by C-N Bond Activation.

    PubMed

    Yu, Hui; Zhang, Guoying; Huang, Hanmin

    2015-09-07

    A fundamentally novel approach to bioactive quinolizinones is based on the palladium-catalyzed intramolecular cyclocarbonylation of allylamines. [Pd(Xantphos)I2 ], which features a very large bite angle, has been found to facilitate the rapid carbonylation of azaarene-substituted allylamines into bioactive quinolizinones in good to excellent yields. This transformation represents the first dearomative carbonylation and is proposed to proceed by palladium-catalyzed CN bond activation, dearomatization, CO insertion, and a Heck reaction.

  14. Dihydrobiphenylenes through ruthenium-catalyzed [2+2+2] cycloadditions of ortho-alkenylarylacetylenes with alkynes.

    PubMed

    García-Rubín, Silvia; González-Rodríguez, Carlos; García-Yebra, Cristina; Varela, Jesús A; Esteruelas, Miguel A; Saá, Carlos

    2014-02-10

    A new synthetic route to dihydrobiphenylenes has been developed. The process involves a mild Ru(II) -catalyzed [2+2+2] dimerization of ortho-alkenylarylacetylenes or its more versatile variant, the Ru-catalyzed [2+2+2] cycloaddition of ortho-ethynylstyrenes with alkynes. Mechanistic aspects of this [2+2+2] cycloaddition are discussed. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Rhodium-Catalyzed Ketone Methylation Using Methanol Under Mild Conditions: Formation of α-Branched Products**

    PubMed Central

    Chan, Louis K M; Poole, Darren L; Shen, Di; Healy, Mark P; Donohoe, Timothy J

    2014-01-01

    The rhodium-catalyzed methylation of ketones has been accomplished using methanol as the methylating agent and the hydrogen-borrowing method. The sequence is notable for the relatively low temperatures that are required and for the ability of the reaction system to form α-branched products with ease. Doubly alkylated ketones can be prepared from methyl ketones and two different alcohols by using a sequential one-pot iridium- and rhodium-catalyzed process. PMID:24288297

  16. Nickel-Catalyzed Heck-Type Reactions of Benzyl Chlorides and Simple Olefins

    PubMed Central

    Matsubara, Ryosuke; Gutierrez, Alicia C.; Jamison, Timothy F.

    2011-01-01

    Nickel-catalyzed intermolecular benzylation and heterobenzylation of unactivated alkenes to provide functionalized allylbenzene derivatives is described. A wide range of both the benzyl chloride and alkene coupling partners are tolerated. In contrast to analogous palladium-catalyzed variants of this process, all reactions described herein employ electronically unbiased aliphatic olefins (including ethylene), proceed at room temperature and provide 1,1-disubstituted olefins over the more commonly observed 1,2-disubstituted olefins with very high selectivity. PMID:22066899

  17. Stereoselective synthesis of 2,5-disubstituted morpholines using a palladium-catalyzed hydroamination reaction.

    PubMed

    McGhee, Alicia; Cochran, Brian M; Stenmark, Torrey A; Michael, Forrest E

    2013-08-04

    A palladium-catalyzed hydroamination reaction is the key step in a stereoselective synthesis of 2,5-disubstituted and 2,3,5-trisubsituted morpholines from carbamate-protected aziridines. Aziridines are selectively attacked at the more substituted position by unsaturated alcohol nucleophiles using Lewis acid catalysts. Palladium-catalyzed hydroamination of the resulting aminoalkenes gives morpholines as a single diastereomer in excellent yield.

  18. An electrochemical nickel-catalyzed arylation of 3-amino-6-chloropyridazines.

    PubMed

    Sengmany, Stéphane; Vitu-Thiebaud, Arnaud; Le Gall, Erwan; Condon, Sylvie; Léonel, Eric; Thobie-Gautier, Christine; Pipelier, Muriel; Lebreton, Jacques; Dubreuil, Didier

    2013-01-18

    3-Amino-6-aryl- and 3-amino-6-heteroarylpyridazines have been obtained in generally good yield using a nickel-catalyzed electrochemical cross-coupling between 3-amino-6-chloropyridazines and aryl or heteroaryl halides at room temperature. Comparative experiments involving classical palladium-catalyzed reactions, such as Suzuki, Stille, or Negishi cross-couplings, reveal that the electrochemical method can constitute a reliable alternative tool for biaryl formation. A possible reaction mechanism is proposed on the basis of electrochemical analyses.

  19. Pt-catalyzed rearrangement of oxaspirohexanes to 3-methylenetetrahydrofurans: scope and mechanism.

    PubMed

    Malapit, Christian A; Chitale, Sampada M; Thakur, Meena S; Taboada, Rosa; Howell, Amy R

    2015-05-15

    A novel Pt-catalyzed rearrangement of oxaspirohexanes to 3-methylenetetrahydrofurans is reported. Mechanistic studies by (13)C-labeling experiments confirm oxidative addition of Pt(II) regioselectively to the least substituted carbon-carbon bond of the cyclopropane to form a platinacyclobutane intermediate. To our knowledge, this is the first alkoxy-substituted platinacyclobutane that has been observed spectroscopically. The scope and a proposed mechanism of this new Pt-catalyzed transformation are described.

  20. Multidirectional Synthesis of Substituted Indazoles via Iridium-Catalyzed C-H Borylation.

    PubMed

    Sadler, Scott A; Hones, Andrew C; Roberts, Bryan; Blakemore, David; Marder, Todd B; Steel, Patrick G

    2015-05-15

    In the absence of a steric directing group, iridium-catalyzed C-H borylation of N-protected indazoles occurs rapidly and selectively at C-3 and the resulting boronate esters can be utilized in a range of downstream conversions. The functional group tolerance of the iridium-catalyzed C-H borylation reaction enables simple and efficient multidirectional syntheses of substituted indazoles to be realized.