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Catalytic Behaviour (catalytic + behaviour)
Selected AbstractsImmobilisation of the Pyrphos Ligand on Soluble Hyperbranched Supports and Use in Rhodium-Catalysed Hydrogenation in Ionic LiquidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2009Jutta Abstract The immobilisation of the pyrphos ligand has been extended from highly symmetric dendrimers to less regular structured hyperbranched poly(ethylene imines). Cationic dendritic pyrphos-rhodium(norbornadiene) [pyrphos-Rh(NBD)] complexes have been synthesised using poly(propylene imine) (PPI) and poly(amido amine) (PAMAM) dendrimers as supports bearing between 4 and 64 potential catalytically active sites at their periphery as well as pyrphos-Rh(NBD) complexes tethered to hyperbranched poly(ethylene imines) carrying on average 9 to 139 functionalities located throughout the whole supporting structure. These immobilised systems have been used as catalysts for the hydrogenation of Z -methyl ,-acetamidocinnamate. With the PPI, PAMAM, and hyperbranched poly(ethylene imine)-bound pyrphos-Rh(NBD) omplexes as catalysts, hydrogenations were carried out in methanol, and a decrease in activity and selectivity was observed with increasing size of the macromolecular support. Furthermore, the polycationic catalysts were tested in a liquid/liquid-biphasic system consisting of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate {[BMIM] [BF4]} and isopropyl alcohol. Using the PPI-, PAMAM-, and PEI-immobilised systems, a strong negative "dendritic effect" with increasing molecular size was observed with respect to the catalytic activity, the stereoinduction, and the recyclability. The PPI-bound rhodium(I)-complexes of generations one and two showed good reusability; even after triple recycling, with no loss of activity or selectivity being noted. It has been demonstrated that in this case the catalytic behaviour of hyperbranched systems is essentially similar to that of the related dendritic model system. [source] Synthesis of CdS- and ZnS-modified bentonite nanoparticles and their applications to the degradation of eosin BJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2009M. Ghiaci Abstract BACKGROUND: In the present study, nanocomposites of cadmium sulphide (CdS) and zinc sulphide (ZnS) on a bentonite have been prepared via an in-situ precipitation route and their catalytic behaviour was evaluated in the degradation of eosin B. RESULTS: It was found that the basal space of bentonite increased from 1.23 to 1.49 nm after CdS or ZnS nanoparticles were deposited on layers of the bentonite. The resulting CdS,bentonite and ZnS,bentonite nanocomposites can degrade eosin B from aqueous solution after 2 h under UV irradiation. CONCLUSION: A soft method for in situ synthesis of monodispersed, CdS and ZnS nanoparticles, using a reverse micelle type procedure, is reported. The synthesized CdS- and ZnS,bentonite composites combined the adsorptive ability of bentonite and the catalytic degradation ability of CdS and ZnS to remove eosin B from its aqueous solution efficiently. Copyright © 2009 Society of Chemical Industry [source] Cyclohexene hydrogenation using Group VIII metal complexes as catalysts in heterogeneous and homogeneous conditionsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2001E Quiroga Abstract The stability and catalytic behaviour of a ruthenium complex with chloride and tridecylamine as ligands were studied. The hydrogenation of cyclohexene carried out in mild conditions, both in homogeneous and heterogeneous conditions, was used as a test reaction. FTIR and XPS results show that the active species is the complex itself, which is stable under the reaction conditions. XPS determination shows that the ruthenium complex is tetra-coordinated, suggesting that its formula is [RuCl2(NH2(CH2)12CH3)2]. This ruthenium complex supported on ,-Al2O3 is more active and sulfur-resistant than the same complex unsupported and even more than a nickel complex with the above mentioned ligands. The Ru complex, supported or not, is also more active and sulfur-resistant than a conventional Ru/,-Al2O3 catalyst evaluated in the same operational conditions. © 2001 Society of Chemical Industry [source] Regulation of the catalytic behaviour of L-form starch phosphorylase from sweet potato roots by proteolysisPHYSIOLOGIA PLANTARUM, Issue 4 2002Han-Min Chen Starch phosphorylase (SP) is an enzyme used for the reversible phosphorolysis of the ,-glucan in plant cells. When compared to its isoform in an animal cell, glycogen phosphorylase, a peptide containing 78 amino acids (L78) is inserted in the centre of the low-affinity type starch phosphorylase (L-SP). We found that the amino acid sequence of L78 had several interesting features including the presence of a PEST region, which serves as a signal for rapid degradation. Indeed, most L-SP molecules isolated from mature sweet potato roots were nicked in the middle of a molecule, but still retained their tertiary or quaternary structures, as well as full catalytic activity. The nicking sites on the L78 were identified by amino acid sequencing of these peptides, which also enabled us to propose a proteolytic process for L-SP. Enzyme kinetic studies of L-SP in the direction of starch synthesis indicated that the Km decreased during the proteolytic process when starch was used as the limiting substrate, but the Km for the other substrate (Glc-1-P) increased. On the other hand, the maximum velocities (Vmax) increased for both substrates. Mobility of the nicked L-SP was retarded on a native polyacrylamide gel containing soluble starch, indicating the increased affinity for starch. Results in this study suggested that L78 and its proteolytic modifications might play a regulatory role on the catalytic behaviour of L-SP in starch biosynthesis. [source] | ||||||||||