Reaction Conditions. (reaction + conditions)

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Distribution within Chemistry

Selected Abstracts

Bis(terdentate) Pyrazole/Pyridine Ligands: Synthesis, Crystal Structures and Magnetic Properties of Bridged Binuclear and Tetranuclear Copper(II) Complexes

Akhilesh Kumar Singh
Abstract A new binucleating bis(terdentate) ligand, 3,5-[3-bis(2-pyridyl)pyrazole-1-ylmethyl]pyrazole (HL2), was synthesized. Reaction of the deprotonated ligand L2 with hydrated CuII salts gives (,-pyrazolato)(,-hydroxido)-bridged binuclear and tetranuclear complexes [L2Cu2(,-OH)(ClO4)(MeCN)](ClO4) (2), [L2Cu2(dmf)2(,3 -OH)]2(ClO4)4·4dmf (3·4dmf) and [L2L,Cu2](ClO4)2 [4; HL, = 3-(2-pyridyl)pyrazole]. In these complexes, both ,-OH and ,3 -OH bridges were observed. This contrasts the situation for a dicopper(II) complex of the related bis(terdentate) ligand 3,5-bis[6(2,2,-dipyridyl)]pyrazole (HL1), {L1Cu2(OMe)(MeOH)[,1 - O -(NO3)]}{[Cu2(NO3)2(,-OMe)2]}0.5·MeOH (1·MeOH), where the shorter and more rigid ligand side arms enforce a larger Cu···Cu separation and the formation of a MeO,HOMe moiety within the bimetallic pocket. Molecular structures of all complexes were elucidated by X-ray crystallography. Variable-temperature magnetic susceptibility measurements (295,2 K) for powdered samples of complexes 2,4 reveal strong antiferromagnetic coupling between two copper centres. The magnitude of the coupling is discussed in view of the structural features. During the preparation of complex 4, partial ligand hydrolysis was also observed, but this strongly depends on the reaction conditions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

From Central to Axial to Central Chirality: Enantioselective Construction of the trans -4,5,9,10-Tetrahydroxy-9,10-dihydrophenanthrene System

Georgi Stavrakov
Abstract Enantioselective synthesis of the core trans -4,5,9,10-tetrahydroxy-9,10-dihydrophenanthrene parent system of the antibiotics benanimicin, pradimicin and FD 594 has been accomplished. The synthesis employs a chiral tether approach and makes use of efficient central to axial to central chirality transfer. Key to success was an "imine-directed" atropdiastereoselective Ullmann coupling under mild reaction conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Toward Diels,Alder Reactions on a Solid Support Using Polymer Bound N -Substituted 3-Hydroxy-4,4-dimethyl-2-pyrrolidinone Acrylate Derivatives

Rhalid Akkari
Abstract Several N -substituted 3-hydroxy-4,4-dimethyl-2-pyrrolidinone acrylate derivatives, selected to allow their attachment to a polymer, have been prepared and tested as dienophiles in the Diels,Alder reaction. The experiments, performed under TiCl4 catalysis in solution or the solid phase with isoprene and cyclopentadiene as dienes, pointed out the difficulties associated with some of these compounds that failed to give the corresponding cycloadduct. 13C NMR studies provided some evidence regarding the nature of the interactions between the acrylate compounds and TiCl4. It appears that the outcome of the reaction is dependent on the acrylate structure and that the 4-(3-hydroxy-4,4-dimethyl-2-oxopyrrolidin-1-yl)benzoic acid acrylate derivatives are highly efficient to give the cycloadduct in good yield and with high regio- or endoselectivity in both solution and solid-phase reaction conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Thiiranation of 2,-adamantylidene-9-benzonorbornenylidene using 4,4,-oligothiodimorpholine and brønsted acid

Yoshiaki Sugihara
On leaving 4,4,-dithiodimorpholine 6 powder undisturbed at room temperature over 10 years, it led to the formation of 4,4,-tetrathiodimorpholine 7. Reactions of 2,-adamantylidene-9-benzonorbornenyidene 1 with 6, 7, and 4,4,-thiodimorpholine 8 and a Brønsted acid in CH2Cl2 at room temperature proceeded to afford the corresponding thiiranes, 2 and 3. The order of reactivity of 4,4,-oligothiodimorpholines combined with a Brønsted acid is 7 > 6 > 8. The thiirane 3 was transformed to 1 and 2 under the reaction conditions. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:12,18, 2009; Published online in Wiley InterScience ( DOI 10.1002/hc.20505 [source]

Oxidative dehydrogenation of propane in a perovskite membrane reactor with multi-step oxygen insertion

AICHE JOURNAL, Issue 9 2010
Oliver Czuprat
Abstract A membrane reactor incorporating a hollow fiber with successive parts of oxygen permeable and passivated surface segments has been developed and was used for the oxidative dehydrogenation (DH) of propane. This membrane geometry allows a controlled oxygen feeding into the reactor over its axial length. In the oxidative DH, the thermodynamic limitation of propane DH can be overcome. By using this novel hollow fiber membrane reactor with a Pt/Sn/K DH catalyst, oxygen separation and propene formation could be established even at temperatures as low as 625°C with long-term stability. Combining the hollow fiber membrane and the DH catalyst, the highest propene selectivity of 75% was observed at a propane conversion of 26% and 625°C whereas the best propene yield of 36% was obtained at 675°C (48% propene selectivity). The performance of this reactor is evaluated by applying various reaction conditions. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Vinyl polymerization of norbornene by mono- and trinuclear nickel complexes with indanimine ligands

Guangrong Tang
Abstract A series of new indanimine ligands [ArNCC2H3(CH3)C6H2(R)OH] (Ar = Ph, R = Me (1), R = H (2), and R = Cl (3); Ar = 2,6- i -Pr2C6H3, R = Me (4), R = H (5), and R = Cl (6)) were synthesized and characterized. Reaction of indanimines with Ni(OAc)2·4H2O results in the formation of the trinuclear hexa(indaniminato)tri (nickel(II)) complexes Ni3[ArN = CC2H3(CH3)C6H2(R)O]6 (Ar = Ph, R = Me (7), R = H (8), and R = Cl (9)) and the mononuclear bis(indaniminato)nickel (II) complexes Ni[ArNCC2H3(CH3)C6H2(R)O]2 (Ar = 2,6- i -Pr2C6H3, R = Me (10), R = H (11), and R = Cl (12)). All nickel complexes were characterized by their IR, NMR spectra, and elemental analyses. In addition, X-ray structure analyses were performed for complexes 7, 10, 11, and 12. After being activated with methylaluminoxane (MAO), these nickel(II) complexes can polymerize norbornene to produce addition-type polynorbornene (PNB) with high molecular weight Mv (106 g mol,1), highly catalytic activities up to 2.18 × 107 gPNB mol,1 Ni h,1. Catalytic activities and the molecular weight of PNB have been investigated for various reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 489,500, 2008 [source]

Experimental techniques in high-vacuum anionic polymerization

David Uhrig
Abstract Experimental methods used in high-vacuum anionic polymerization are described in detail, with extensive illustrations to demonstrate proper procedures and techniques. These descriptions include construction and operation of the vacuum line, handling purification chemicals, ampulization techniques, short-path distillations, initiator synthesis, polymerization procedures, and linking reactions using chlorosilanes. A primary emphasis is placed on safety. We believe that this review of these methods will be useful to scientists working in the field of anionic polymerization and may also benefit other researchers in performing tasks requiring ultra-high-purity reaction conditions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6179,6222, 2005 [source]

Efficient Simultaneous Dry Removal of SO2 and NOx from Flue Gas over Copper-Based Catalytic Materials

Gabriele Centi
The combined removal of SO2 (DeSOx) and NOx (DeNOx) from flue gas of power plants can be efficiently realized with a dry process using copper-based sorbent-catalysts which oxidize-adsorb SO2 in the form of an easily regenerable copper-sulphate and catalyze the reduction of NO in the presence of NH3/O2. This contribution reviews the results on this topic, discussing in particular the following main aspects: (i) Sorption and catalytic chemistry of the process, (ii) Development and features of the copper-based sorbent-catalyst. (iii) Optimization of the reaction conditions. (iv) Kinetic models of the sorption and catalytic behavior and role of the textural properties of the catalyst, (v) Flowsheet and economics of the process, (vi) Behavior in extended operations and life time cycles. The key features of the technology and its fields of application are also discussed. [source]

Removal of poly-histidine fusion tags from recombinant proteins purified by expanded bed adsorption

N. Abdullah
Abstract Enzymatic methods have been used to cleave the C- or N-terminus polyhistidine tags from histidine tagged proteins following expanded bed purification using immobilized metal affinity chromatography (IMAC). This study assesses the use of Factor Xa and a genetically engineered exopeptidase dipeptidyl aminopeptidase-1 (DAPase-1) for the removal of C-terminus and N-terminus polyhistidine tags, respectively. Model proteins consisting of maltose binding protein (MBP) having a C- or N-terminal polyhistidine tag were used. Digestion of the hexahistidine tag of MBP-His6 by Factor Xa and HT15-MBP by DAPase-1 was successful. The time taken to complete the conversion of MBP-His6 to MBP was 16 h, as judged by SDS,PAGE and Western blots against anti-His antibody. When the detagged protein was purified using subtractive IMAC, the yield was moderate at 71% although the overall recovery was high at 95%. Likewise, a yield of 79% and a recovery of 97% was obtained when digestion was performed with using "on-column" tag digestion. On-column tag digestion involves cleavage of histidine tag from polyhistidine tagged proteins that are still bound to the IMAC column. Digestion of an N-terminal polyhistidine tag from HT15-MBP (1 mg/mL) by the DAPase-I system was superior to the results obtained with Factor Xa with a higher yield and recovery of 99% and 95%, respectively. The digestion by DAPase-I system was faster and was complete at 5 h as opposed to 16 h for Factor Xa. The detagged MBP proteins were isolated from the digestion mixtures using a simple subtractive IMAC column procedure with the detagged protein appearing in the flowthrough and washing fractions while residual dipeptides and DAPase-I (which was engineered to exhibit a poly-His tail) were adsorbed to the column. FPLC analysis using a MonoS cation exchanger was performed to understand and monitor the progress and time course of DAPase-I digestion of HT15-MBP to MBP. Optimization of process variables such as temperature, protein concentration, and enzyme activity was developed for the DAPase-I digesting system on HT15-MBP to MBP. In short, this study proved that the use of either Factor Xa or DAPase-I for the digestion of polyhistidine tags is simple and efficient and can be carried out under mild reaction conditions. © 2005 Wiley Periodicals, Inc. [source]

Synergistic cellulose hydrolysis can be described in terms of fractal-like kinetics

Priit Väljamäe
Abstract A fractal-like kinetics model was used to describe the synergistic hydrolysis of bacterial cellulose by Trichoderma reesei cellulases. The synergistic action of intact cellobiohydrolase Cel7A and endoglucanase Cel5A at low enzyme-to-substrate ratios showed an apparent substrate inhibition consistent with a case where two-dimensional (2-D) surface diffusion of the cellobiohydrolase is rate-limiting. The action of Cel7A core and Cel5A was instead consistent with a three-dimensional (3-D) diffusion-based mode of action. The synergistic action of intact Cel7A was far superior to that of the core at a high enzyme-to-substrate ratio, but this effect was gradually reduced at lower enzyme-to-substrate ratios. The apparent fractal kinetics exponent h obtained by nonlinear fit of hydrolysis data to the fractal-like kinetics analogue of a first-order reaction was a useful empirical parameter for assessing the rate retardation and its dependence on the reaction conditions. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 254,257, 2003. [source]