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Catalytic Action (catalytic + action)
Selected AbstractsCatalytic Action of a Single Water Molecule in a Proton-Migration Reaction,ANGEWANDTE CHEMIE, Issue 29 2010Yoshiyuki Matsuda Dr. Ein kleiner Schritt: Der Mechanismus der Protonenverschiebung in ionisiertem Aceton durch Wasser wurde IR-spektroskopisch untersucht. Im Anschluss an die Ionisation spaltet das Wassermolekül ein Proton von einer Methylgruppe des Acetonmoleküls ab und überträgt es auf die Carbonylgruppe (siehe Bild). [source] A Polymer-Bound Oxidovanadium(IV) Complex Prepared from an L -Cysteine-Derived Ligand for the Oxidative Amination of StyreneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2008Mannar R. Maurya Abstract The ligand H2sal-cys (I) derived from salicylaldehyde and L -cysteine has been covalently bonded to chloromethylated polystyrene cross-linked with 5,% divinylbenzene. Upon treatment with [VO(acac)2] in dimethylformamide (DMF) the polystyrene-bound ligand PS-H2sal-cys (II) gave the oxidovanadium(IV) complex, PS-[VO(sal-cys)·DMF] (1). The corresponding neat complex, [VO(sal-eta)]2 (2), has also been prepared similarly in methanol. These complexes have been characterised by IR, electronic, EPR spectroscopic studies, magnetic susceptibility measurements and thermal as well as scanning electron micrographs studies. Complex [VO(sal-eta)]2 exhibits a medium intensity band at 980 cm,1 in the IR spectrum due to ,(V=O) stretch. Broad features of the EPR spectrum for the neat complex along with magnetic susceptibility studies suggest the presence of antiferromagnetic exchange interaction between two vanadium centers in close proximity. Both complexes catalyze the oxidative amination of styrene, in mild basic conditions, with secondary amines (diethylamine, imidazole, and benzimidazole) and gave a mixture of two aminated products in good yields. Amongst the two aminated products, the anti-Markovnikov product is favored over the Markovnikov one due to the steric hindrance posed by the secondary amines. The polymer-anchored heterogeneous catalyst is free from leaching during catalytic action and recyclable.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] The Extraordinary Cocatalytic Action of Polymethylaluminoxane (MAO) in the Polymerization of Terminal Olefins by Metallocenes: Chemical Change in the Group 4 Metallocene Dimethyl Derivatives Induced by MAO,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2005John J. Eisch Abstract In the polymerization of olefins with Group 4 metallocene dichlorides or dimethyl derivatives as procatalysts the use of polymethylaluminoxane (MAO) as the cocatalyst, especially in extreme excess (102,103 times the metallocene equivalent), has been shown to have an extraordinary accelerating effect on the rate of olefin polymerization, when compared with the cocatalytic action of alkylaluminum halides. In attempts at explaining the greatly superior catalytic activity of MAO in olefin polymerization (the MAO conundrum), hypotheses have generally paralleled the steps involved in the cocatalytic action of RnAlCl3,n, namely the alkylation of Cp2MtCl2, ionization of Cp2Mt(R)Cl into the metallocenium cation, [Cp2Mt,R]+, and anion, [Rn,1AlCl4,n], and subsequent ion-pair separation. In order to understand any differences in catalytic action between such cocatalysts, we have studied the individual action of MAO (100 equiv.) and of MeAlCl2 (1,2 equiv.) on each of the Group 4 metallocene derivatives, Cp2TiCl2, Cp2ZrCl2, Cp2Ti(CH3)2 and Cp2Zr(CH3)2. With MeAlCl2 each of the metallocene derivatives appeared to form the cation, [Cp2Mt,CH3]+, with greater (Ti) or lesser (Zr) ease, because an alkyne such as diphenylacetylene was then found to insert into the Mt,CH3 bond stereoselectively. In striking contrast, treatment of each metallocene with MAO gave two reactions very different from MeAlCl2, namely a steady evolution of methane gas upon mixing and a finding upon hydrolytic workup that the diphenylacetylene present had undergone no insertion into the Mt,CH3 bond but instead had been reductively dimerized completely to (E,E)-1,2,3,4-tetraphenyl-1,3-butadiene. To account for this astonishing difference in chemical behavior between MAO and MeAlCl2 in their cocatalytic activation of Group 4 metallocenes to olefin polymerization, it is necessary to postulate a novel, unique sequence of reaction steps occurring between MAO and the metallocene. If one starts with the metallocene dichloride, then the free TMA present in the MAO would generate the Cp2Mt(CH3)2. This metallocene dimethyl derivative, complexed with an oligomeric MAO unit, would undergo a transfer-epimetallation with added olefin or acetylene to form a metallacyclopropane or metallacyclopropene, respectively. With added diphenylacetylene the resulting 2,3-diphenylmetallacyclopropene would be expected rapidly to insert a second alkyne to form the 2,3,4,5-tetraphenyl-1-metallacyclopentadiene. Simple hydrolysis of the latter intermediate would generate (E,E)-1,2,3,4-tetraphenyl-1,3-butadiene while alternative workup with D2O would give the 1,4-dideuterio derivative of this butadiene. Both such expectations were confirmed by experiment. In the case of added olefin, similar metallacyclopropane and metallacyclopentane intermediates should be produced until ring opening of the latter five-membered ring leads to an open-chain zwitterion, a process having ample precedent in the research of Gerhard Erker. The solution to the MAO conundrum then, namely the extraordinary cocatalytic activity of MAO in olefin polymerization by metallocenes, lies in the unique catalytic activation of the Group 4 metallocene dimethyl derivative, which occurs by transfer-epimetallation of the olefin monomer by the Cp2Mt(CH3)2,MAO complex. The most advantageous Lewis acidic sites in the MAO,oligomeric mixture for such metallocene,MAO complexation are suggested to be terminal Me2Al,O,AlMe, segments of an open-chain oligomer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] The Synthesis and Reactivity of Group 4 Zwitterionic Complexes of the Type Mt+CH2AlCl3,: One-Component Stereoselective Polymerization and Oligomerization Catalysts for Olefins and AcetylenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2004John J. Eisch Abstract A reinvestigation of the interaction of TiCl4 with 2 equiv. of Me3Al in toluene between ,78 °C and 25 °C over 24 h has now established that the ultimate black product obtained is an associated zwitterion of the type [Ti+,CH2,AlCl3,]n, supported by multinuclear NMR spectroscopy and mass spectrometric and gasometric analyses of the gases evolved (CH4, H2) upon its protolysis. Chemical reactions of the zwitterion have corroborated specific aspects of its proposed structure: 1) its methylene character, by its transformation of benzophenone into 1,1-diphenylethylene; 2) its divalent titanium content, by the substantial reductive dimerization of benzophenone to tetraphenylethylene, and 3) its Lewis acidic Ti center, by its catalytic isomerization of trans -stilbene oxide to 1,1-diphenylacetaldehyde. Similar individual reactions of ZrCl4 or HfCl4 with Me3Al have led to the analogous zwitterions [Zr+,CH2,AlCl3,]n and [Hf+,CH2,AlCl3,]n, respectively. These zwitterions of Ti, Zr and Hf have been proven to be capable of the cyclotrimerization and/or polymerization of acetylenes with varying facility, as evidenced by their catalytic action on 1-hexyne, phenylacetylene, di- n -butylacetylene, and diphenylacetylene. Furthermore, all three zwitterions were able to polymerize ethylene, without any added cocatalyst, with an activity following the order Zr > Ti > Hf. The Ti and Zr zwitterions effected the stereoselective polymerization of propylene to yield 50% of isotactic polymer, and all three catalysts induced the polymerization of 1-hexene to yield 85% (Zr, Hf) or 100% (Ti) of isotactic polymer. These oligomerizations and stereoselective polymerizations of acetylenes and olefins can be rationalized through a model for the active site resembling a three-membered metallacyclopropa(e)nium ion intermediate formed from the attack of the Group 4 metal zwitterion on the unsaturated hydrocarbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Effect of Al2O3 and TiO2 nanoparticles and APP on thermal stability and flame retardance of PMMA,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2006A. Laachachi Abstract Ammonium polyphosphate (APP)-based additives and Al2O3 and TiO2 nanoparticles have been incorporated separately or combined at a 15,wt% global percentage in poly(methyl methacrylate) (PMMA). APP,based additive containing melamine phosphate has led to an intumescent behavior during cone calorimeter tests, whereas thermal stability was particularly improved by the use of the oxide nanoparticles. APP with melamine phosphate and Al2O3 combination allowed significant synergism on flame retardance to be achieved, owing to the catalytic action of alumina well-dispersed nanoparticles, which modified the decomposition pathway of PMMA and the formation of a charred and ceramized structure. Aggregation processes in the case of TiO2 seemed to limit the catalytic action of the surface and did not allow synergism for flame retardance to be observed. Copyright © 2006 John Wiley & Sons, Ltd. [source] Structure of native laccase from Trametes hirsuta at 1.8,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2009Konstantin M. Polyakov This paper describes the structural analysis of the native form of laccase from Trametes hirsuta at 1.8,Å resolution. This structure provides a basis for the elucidation of the mechanism of catalytic action of these ubiquitous proteins. The 1.8,Å resolution native structure provided a good level of structural detail compared with many previously reported laccase structures. A brief comparison with the active sites of other laccases is given. [source] Structures and molecular-dynamics studies of three active-site mutants of bovine pancreatic phospholipase A2ACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2008Shankar Prasad Kanaujia Phospholipase A2 hydrolyzes phospholipids at the sn -2 position to cleave the fatty-acid ester bond of l -glycerophospholipids. The catalytic dyad (Asp99 and His48) along with a nucleophilic water molecule is responsible for enzyme hydrolysis. Furthermore, the residue Asp49 in the calcium-binding loop is essential for controlling the binding of the calcium ion and the catalytic action of phospholipase A2. To elucidate the structural role of His48 and Asp49, the crystal structures of three active-site single mutants H48N, D49N and D49K have been determined at 1.9,Å resolution. Although the catalytically important calcium ion is present in the H48N mutant, the crystal structure shows that proton transfer is not possible from the catalytic water to the mutated residue. In the case of the Asp49 mutants, no calcium ion was found in the active site. However, the tertiary structures of the three active-site mutants are similar to that of the trigonal recombinant enzyme. Molecular-dynamics simulation studies provide a good explanation for the crystallographic results. [source] Syntheses of esters through poly(styrene sulfonic acid)/poly(vinyl alcohol) membrane reactorASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010Tadashi Uragami Abstract Cation exchange membranes prepared from poly(styrene sulfonic acid) (PSA) and poly(vinyl alcohol) (PVA) were cross-linked by both glyoxal and gultaraledehyde and cross-linked membranes furthermore were annealed. The ion exchange capacity of the resulting PSA/PVA membranes increased, and the water content and degree of swelling of PSA/PVA membrane decreased with increasing annealing time. The syntheses of esters from alcohol and acetic acid through various PSA/PVA membranes have been carried out in a diaphragm type cell consisting of two detachable parts in which the membrane was set in the middle of the two parts of cell. When an aqueous solution of alcohol and acetic acid on one part of cell and p -chloro benzene (Cl-Bz) on another part were set, esters formed by the catalytic action of PSA/PVA membrane increased on the Cl-Bz phase with time. These results support that the PSA/PVA membrane could perform both the reaction and separation. The formation of esters in this membrane reactor was a secondary reaction as well as general the esterification between alcohols and acids. The catalytic action in the esterification of the PSA/PVA membranes prepared by changing the ratio of PSA/PVA and the amount of casting solution was also investigated. The rate of esterification reaction was significantly dependent on the number of sulfonic acid group in the effective membrane volume. The rate of reaction per mEq SO3H increased with an increase of the degree of swelling of the membrane and decreasing membrane thickness. In the esterifications of methanol, ethanol and n -propanol with acetic acid, the reactivity through the PSA/PVA membrane was higher than that with HCl as catalyst. In that of n -butanol with acetic acid, however, it was vice versa. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Research on alkali-catalyzed gasification of coal black liquor slurry cokes made up by five different coals,ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007Kuang Jian-ping Abstract The black liquor from paper mills contains large quantities of sodium compounds and other organic matter, such as lignin and cellulose. The sodium compounds will provide the catalytic action in coal black liquor slurry (CBLS) gasification, while lignin and cellulose can enhance the heat value in the process of gasification. Five black liquor slurries were made from coals from different regions: Xin Wen, Huang Ling, Zao Zhuang, Shen Mu and Shen Hua. Alkali-catalyzed gasification experiments on the different samples of CBLS and coal water slurry (CWS) were made on a thermobalance and a fixed-bed reactor. The residues of gasification were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The results reveal that many mesopores and micropores exist on the surface of the CBLS coke, which play a key role in the catalytic gasification process, and sodium as a catalyst can quicken the gasification reaction rate. XRD shows that NaCl and sodium silicate are the main crystal components in dry samples of CBLS and CWS. The C-O stretching vibration peak shifting to a lower wavenumber means that the energy for the C-O stretching vibration in the CBLS carbon matrix decreases after partial gasification. Not only the coal rank but also the oxygen-containing groups and minerals influence coal coke's gasification activity. Of the five different CBLS, the gasification reactivity of CBLS made by the Huang Ling coal was found to be higher than that of the others. The higher the degree of coalification, the lower the activity of the coke. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Variable Stoichiometry during the Laccase-Catalyzed Oxidation of Aqueous PhenolBIOTECHNOLOGY PROGRESS, Issue 2 2007Selvia Kurniawati The oxidation of aqueous phenol through the catalytic action of laccase from Trametes versicolor was studied over a wide range of phenol concentrations and enzyme activities. The stoichiometric ratio, which is defined as the molar ratio of phenol transformed to oxygen consumed in the catalytic reaction, was found to increase with phenol concentration in the reaction mixture from a theoretical lower limit of 1 and to approach a theoretical upper limit of 4. A logistic equation was proposed to relate reaction stoichiometry to substrate concentration and was successfully used to relate these parameters over a range of phenol concentrations extending from approximately 0.15 to 8 mM. This expression was incorporated into two kinetic models in order to account for variations in reaction stoichiometry during the reaction and to extend the range over which the models may be accurately applied. The new models demonstrated an improved ability to predict concentrations of phenol and oxygen over time in a closed batch reaction system. [source] Reactions of Hydrogen Atoms with Met-Enkephalin and Related PeptidesCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Olivier Mozziconacci Abstract The reactions of hydrogen atoms with enkephalins and related peptides have been investigated by radiolytic methods in aqueous solutions and lipid vesicle suspensions. Pulse radiolysis experiments indicate that methionine residue (Met) is the main target. In Met-enkephalin (Tyr-Gly-Gly-Phe-Met) the attack of the hydrogen atom occurs to about 50,% on Met with formation of methanethiyl radical. The remaining percentage is divided roughly evenly between Tyr and Phe. With Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu) the site of attack is limited to Tyr and Phe. Using a peptide,liposome (that is, 1-palmitoyl-2-oleoyl phosphatidylcholine vesicles) model, the cis,trans isomerization of phospholipids could be detected due to the catalytic action of thiyl radicals. The radiation chemical yields of the H. and, consequently of CH3S. radical, was modulated by the experimental conditions and the nature of peptide. Large amounts of trans lipids observed in phosphate buffer vesicle suspensions indicated the efficient role of double-bond isomerization as marker of Met-containing peptide damage. [source] Proton Transfer in the Complex H3N,,,HCl Catalyzed by Encapsulation into a C60 CageCHEMPHYSCHEM, Issue 7 2009Fang Ma Dr. Abstract Caged up: In contrast to acid,base behavior in solution, single molecules of NH3 and HCl do not react to form the ion pair NH4+Cl, in isolation. Proton transfer occurs in the complex H3N,,,HCl inside the C60 cage, to form the ion pair NH4+Cl, under the catalytic action of C60 (see picture). We report proton transfer in the complex H3N,,,HCl to form the ion pair NH4+Cl,, which is favored inside the C60 cage according to quantum chemical calculations. The results show that the NH4+Cl,@C60 is stable with an interaction energy of ,2.78 kcal,mol,1. Compared with the complex H3N,,,HCl without proton transfer, it is found that the C60 cage plays the role of a catalyst for proton transfer. In NH4+Cl,@C60 a negative charge area in the C60 cage is near the cation NH4+ whereas a positive charge area is near the anion Cl,. Also, a confinement effect of the C60 cage is noticed, as the endohedral structure of NH4+Cl, is more compact than the structure of NH4+Cl, in the gas-phase complex. These findings indicate that the catalysis by the C60 cage comes from two effects: 1) electrostatic inducement between the C60 cage and endohedral molecules and 2) the confinement effect that compresses endohedral molecular structures inside the C60 cage. In the infrared spectrum, it is found that the confinement effect of the cage can cause large blue shifts of the N,H stretching vibrations in NH4+Cl,@C60 compared with those in the NH4+Cl,,,,H2O complex. [source] Global production networks, the developmental state and the articulation of Asia Pacific economies in the commercial aircraft industryASIA PACIFIC VIEWPOINT, Issue 3 2007John T. Bowen Jr. Abstract: Asia Pacific economies , particularly Japan, South Korea, China and Singapore , play a large and growing role in the commercial aircraft industry, despite the fact that the region has no major independent plane-maker. Instead, Asia has secured a significant position in the increasingly elaborate global production networks of Boeing and Airbus. The wider Asian significance in those networks has been fostered not only by the region's deep capital and human resource assets but also by the catalytic actions of developmental states in the region. Moreover, decades of rapid air traffic growth have made Asia a crucial market for Boeing and Airbus. In response, the American and European giants have been compelled to outsource more of their business to Asia in order to win sales and to design new airliners tailored to the needs of Asian customers. Together, the increased importance of Asia in both the design and the manufacture of commercial aircraft point to a future in which Asia will capture an ever-larger share of the value created in one of the world's most technologically sophisticated and strategically significant industries. [source] | ||||||||||