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Total Turnover Number (total + turnover_number)
Selected AbstractsStabilized and Immobilized Bacillus subtilis Arginase for the Biobased Production of Nitrogen-Containing ChemicalsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Abstract L -Ornithine could serve as an intermediate in the biobased production of 1,4-diaminobutane from L -arginine. Using the concept of biorefinery, L -arginine could become widely available from biomass waste streams via the nitrogen storage polypeptide cyanophycin. Selective hydrolysis of L -arginine to L -ornithine is difficult to perform chemically, therefore the stabilization and immobilization of Bacillus subtilis arginase (EC,3.5.3.1) was studied in a continuously stirred membrane reactor system. Initial pH of the substrate solution, addition of L -aspartic acid and reducing agents all appeared to have an effect on the operational stability of B. subtilis arginase. A remarkably good operational stability (total turnover number, TTN=1.13,108) at the pH of arginine free base (pH,11.0) was observed, which was further improved with the addition of sodium dithionite to the substrate solution (TTN>1,109). B. subtilis arginase was successfully immobilized on three commercially available epoxy-activated supports. Immobilization on Sepabeads EC-EP was most promising, resulting in a recovered activity of 75% and enhanced thermostability. In conclusion, the stabilization and immobilization of B. subtilis arginase has opened up possibilities for its application in the biobased production of nitrogen-containing chemicals as an alternative to the petrochemical production. [source] Continuous Hydrogen Generation from Formic Acid: Highly Active and Stable Ruthenium CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Albert Boddien Abstract The ruthenium-catalyzed decomposition of formic acid was investigated with respect to continuous hydrogen generation and long-term stability of the catalytic systems. A highly active and stable system is presented, which was studied in batch and continuous modes for up to two months. The optimized catalyst system containing N,N -dimethyl- n -hexylamine with an in situ generated catalyst from (benzene)ruthenium dichloride dimer [RuCl2(benzene)]2 and 6 equivalents of 1,2-bis(diphenylphosphino)ethane (dppe) reached at room temperature a total turnover number (TON) of approximatly 260,000 with average turnover frequency (TOF) of about 900,h,1. Only hydrogen and carbon dioxide were detected in the produced gas mixture which makes this system applicable for direct use in fuel cells. [source] Bioreactors Based on Monolith-Supported Ionic Liquid Phase for Enzyme Catalysis in Supercritical Carbon DioxideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2007Pedro Lozano Abstract Bioreactors with covalently supported ionic liquid phases (SILP) were prepared as polymeric monoliths based on styrene,divinylbenzene or 2-hydroxyethyl methacrylate,ethylene dimethacrylate, and with imidazolium units loadings ranging from 54.7 to 39.8,% wt IL per gram of polymer. The SILPs were able to absorb Candida antarctica lipase B (CALB), leading to highly efficient and robust heterogeneous biocatalysts. The bioreactors were prepared as macroporous monolithic mini-flow systems and tested for the continuous flow synthesis of citronellyl propionate in supercritical carbon dioxide (scCO2) by transesterification. The catalytic activity of these mini-flow-bioreactors remained practically unchanged for seven operational cycles of 5,h each in different supercritical conditions. The best results were obtained when the most hydrophobic monolith, M-SILP- 8 -CALB, was assayed at 80,°C and 10,MPa, reaching a total turnover number (TON) of 35.8×104 mol product/mol enzyme. The results substantially exceeded those obtained for packed-bed reactors with supported silica-CALB-Si-4 catalyst under the same experimental conditions. [source] Application of immobilized bovine enterokinase in repetitive fusion protein cleavage for the production of mucin 1BIOTECHNOLOGY JOURNAL, Issue 11 2009Tina Kubitzki Abstract Bovine enterokinase is a serine protease that catalyzes the hydrolysis of peptide bonds and plays a key role in mammalian metabolism. Because of its high specificity towards the amino acid sequence (Asp)4 -Lys, enterokinase is a potential tool for the cleavage of fusion proteins, which are gaining more importance in biopharmaceutical production. A candidate for adaptive cancer immunotherapy is mucin 1, which is produced recombinantly as a fusion protein in CHO cells. Here, we present the first repetitive application of immobilized enterokinase for the cleavage of the mucin fusion protein. The immobilization enables a facile biocatalytic process due to simplified separation of the biocatalyst and the target protein. Immobilized enterokinase was applied in a maximum of 18 repetitive reactions. The enzyme utilization (total turnover number) was increased significantly 419-fold compared to unbound enzyme by both immobilization and optimization of process conditions. Slight enzyme inactivation throughout the reaction cycles was observed, but was compensated by adjusting the process time accordingly. Thus, complete fusion protein cleavage was achieved. Furthermore, we obtained isolated mucin 1 with a purity of more than 90% by applying a simple and efficient purification process. The presented results demonstrate enterokinase to be an attractive tool for fusion protein cleavage. [source] Homogeneous Stabilization of Pt Nanoparticles in Dendritic Core,Multishell Architectures: Application in Catalytic Hydrogenation Reactions and RecyclingCHEMCATCHEM, Issue 7 2010Juliane Keilitz Abstract Core,multishell architectures are a new approach to homogeneously stabilize metal nanoparticles for harsh conditions. Herein, we present the synthesis and stabilization of Pt nanoparticles in dendritic core,multishell polymers and their application in hydrogenation reactions. The successful recycling of the catalyst was demonstrated for the hydrogenation of methyl crotonate 1 and was either achieved by ultrafiltration or in a two-phase system for at least 14,cycles. Thereby, the total turnover number (TON) was increased to 22,000. In the recycling experiments, low metal leaching into the product (as low as 0.3,ppm) was detected. Additionally, the selective hydrogenation of isophorone 3 was investigated and selectivities of 99:1 for CC versus CO hydrogenation were achieved. [source] Catalytic Hydroxylation in Biphasic Systems using CYP102A1 MutantsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2005Steffen Abstract Cytochrome P450 monooxygenases are biocatalysts that hydroxylate or epoxidise a wide range of hydrophobic organic substrates. Their technical application is, however, limited to a small number of whole-cell processes. The use of the isolated P450 enzymes is believed to be impractical due to their low stability, stoichiometric need of the expensive cofactor NAD(P)H and low solubility of most substrates in aqueous media. We investigated the behaviour of an isolated bacterial monooxygenase (mutants of CYP102A1) in a biphasic reaction system supported by cofactor recycling with the NADP+ -dependent formate dehydrogenase from Pseudomonas sp 101. Using this experimental set-up cyclohexane, octane and myristic acid were hydroxylated. To reduce the process costs a novel NADH-dependent mutant of CYP102A1 was designed. For recycling of NADH an NAD+ -dependent FDH was used. The stability of the monooxygenase mutants under the reaction conditions in the biphasic system was quite high as revealed by total turnover numbers of up to 12,850 in the NADPH-dependent cyclohexane hydroxylation and up to 30,000 in the NADH-dependent myristic acid oxidation. [source] Highly Selective Biphasic Telomerization of Butadiene with Glycols: Scope and LimitationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11 2003Arno Behr Abstract Highly selective telomerization reactions of a number of short-chain glycol nucleophiles with 1,3-butadiene have been achieved in aqueous biphasic systems employing the water-soluble catalyst system Pd(acac)2/TPPTS. For all substrates the selectivity for the obtained monotelomers 5,7 reached ,95% whereas butadiene dimers 3, octadienols 4 and ditelomers like 2 were produced only in trace amounts. The order of reactivity is ethylene glycol>>1,3-propylene glycol , glycerol>1,4-butylene glycol, which is in agreement with generally observed trends. The scope and limitations of these reactions are discussed in terms of obtained yields and achievable catalyst productivities (total turnover numbers). [source] | ||||||||||