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Catalytic Units (catalytic + unit)
Selected AbstractsIncreased Efficacies of an Individual Catalytic Site in Clustered Multivalent Dendritic CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Govindasamy Jayamurugan Abstract In the studies reported so far on dendrimer-mediated catalysis, the efficacies of the catalytic units were studied and compared primarily across the generations. In order to identify the efficacy of an individual catalytic unit with respect to the number of such units present within a given generation, a series of catalysts were prepared within a generation. Dendrimers incorporated with phosphine-metal complexes were chosen for the study and as many as 11 catalysts within three generations were synthesized. The CC bond-forming reactions, namely, the Heck and the Suzuki coupling reactions, were then selected to study the catalytic efficiencies of the series of partially and fully phosphine-metal complex functionalized dendrimers. The efficacies of the formation of cinnamate and biphenyl, catalyzed by the dendritic catalysts, were compared. The comparative analyses show that an individual catalytic site is far more effective in its catalytic activity when presented in multiple numbers, i.e., in a multivalent dendritic system, than as a single unit within the same generation, i.e., in a monovalent dendritic system. The study identifies the beneficial effects of the multivalent presentation of the catalytic moieties, both within and across the dendrimer generations. [source] Expression of Epstein-Barr virus-encoded LMP1 and hTERT extends the life span and immortalizes primary cultures of nasopharyngeal epithelial cells,JOURNAL OF MEDICAL VIROLOGY, Issue 10 2010Yim-Ling Yip Abstract Cell immortalization is regarded as an early and pre-requisite step in tumor development. Defining the specific genetic events involved in cell immortalization may provide insights into the early events of carcinogenesis. Nasopharyngeal carcinoma is common among the Southern Chinese population. Epstein-Barr virus (EBV) infection is associated closely with nasopharyngeal carcinoma. The involvement of LMP1 (an EBV-encoded oncogene) has been implicated in the pathogenesis of nasopharyngeal carcinoma. In this study, LMP1 expression, in combination with ectopic expression of hTERT (catalytic unit of human telomerase), was shown to extend the life span of primary cultures of nasopharyngeal epithelial cells and facilitate the immortalization of one of the cell lines (NP446). This is the first report on the successful immortalization of nasopharyngeal epithelial cells involving LMP1. The events associated with the immortalization of nasopharyngeal epithelial cells by LMP1/hTERT were characterized. Expression of c-Myc, Bmi-1, and Id-1 were upregulated at an early stage of immortalization. At a later stage of immortalization, downregulation of p21 and p16 expression were observed. Upregulation of EGFR expression and activation of MAPK signaling pathway were observed in LMP1/hTERT -immortalized nasopharyngeal epithelial cells. The LMP1/hTERT -immortalized NP446 cells were non-tumorigenic in immunosuppressed nude mice and retained anchorage-dependent growth, suggesting that additional events are required for tumorigenic transformation. The ability of the EBV-encoded LMP1, in the presence of hTERT expression, to extend the life span and immortalize primary cultures of nasopharyngeal epithelial cells supports the involvement of EBV infection and its viral products in the early stage of pathogenesis of nasopharyngeal carcinoma. J. Med. Virol. 82:1711,1723, 2010. © 2010 Wiley-Liss, Inc. [source] Cooperative Activation in the Hydrolytic Kinetic Resolution of Epoxides by a Bis-Cobalt(III)salen-Calix[4]arene HybridADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Sander Abstract A chiral, bimetallic cobalt(III)salen-calix[4]arene hybrid structure was prepared and tested in the hydrolytic kinetic resolution (HKR) of racemic epoxides. Kinetic studies have revealed that the two catalytic units on the upper rim of the calixarene scaffold are able to activate the reactants in a cooperative and primarily intramolecular mode. High enantioselective behaviour was observed and besides, a higher stability was found for the bimetallic catalyst as compared to a monometallic reference complex. [source] Increased Efficacies of an Individual Catalytic Site in Clustered Multivalent Dendritic CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Govindasamy Jayamurugan Abstract In the studies reported so far on dendrimer-mediated catalysis, the efficacies of the catalytic units were studied and compared primarily across the generations. In order to identify the efficacy of an individual catalytic unit with respect to the number of such units present within a given generation, a series of catalysts were prepared within a generation. Dendrimers incorporated with phosphine-metal complexes were chosen for the study and as many as 11 catalysts within three generations were synthesized. The CC bond-forming reactions, namely, the Heck and the Suzuki coupling reactions, were then selected to study the catalytic efficiencies of the series of partially and fully phosphine-metal complex functionalized dendrimers. The efficacies of the formation of cinnamate and biphenyl, catalyzed by the dendritic catalysts, were compared. The comparative analyses show that an individual catalytic site is far more effective in its catalytic activity when presented in multiple numbers, i.e., in a multivalent dendritic system, than as a single unit within the same generation, i.e., in a monovalent dendritic system. The study identifies the beneficial effects of the multivalent presentation of the catalytic moieties, both within and across the dendrimer generations. [source] Elucidation of Architectural Requirements from a Spacer in Supported Proline-Based Catalysts of Enantioselective Aldol ReactionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Kerem Goren Abstract In order to delineate the properties of the spacer architecture responsible for the strong positive dendritic effect exhibited by polymer-supported proline-based catalysts, we prepared two series of polystyrene-bound model catalysts. The first series was based on a linear and partially dendritic spacers (of reduced branching and valency) imitating the length of the second generation spacer, while the second series was based on the first generation dendron spacer with one functional (proline-terminated) and one non-functional arm. Comparative studies of the model and original (fully dendritic) catalysts in the asymmetric aldol reaction of aromatic aldehydes with acetone disclose the features characteristic to the dendritic architecture, such as proximity between the terminal catalytic units and enhanced branching, as crucial for inducing higher yield and enantioselectivity in catalysis. [source] Dendritic Amplification of Stereoselectivity of a Prolinamide-Catalyzed Direct Aldol ReactionISRAEL JOURNAL OF CHEMISTRY, Issue 1 2009Kazuhiko Mitsui Isomeric "compact" and "expanded" dendrimers functionalized with L -prolinamide catalytic units at the periphery were compared as catalysts to monomer controls in the organocatalytic direct aldol condensation. A positive dendritic effect that amplifies the stereoselectivity of the direct aldol condensation was observed for dendrimers 3 and 4, compared with lower molecular weight catalysts L -prolinani-lide 1 and G1 dendron 2. The difference in the compactness between 3 and 4 appears to have less impact on the stereoselectivity than the preorganized multivalency of the dendritic catalysts. [source] Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysisJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2005Adi Dahan Abstract Dendrimers, the aesthetically beautiful macromolecules displaying a variety of potentially useful architecture-induced properties, are traditionally assembled in solution. However, since 1988, a number of dendritic structures have been assembled on insoluble organic and inorganic polymers, and thus dendronized supports have been formed. One of the major applications of these new materials is in the field of heterogeneous catalysis. Supported dendritic catalytic systems, bearing the catalytic units on the dendron periphery, have been examined in the last 5 years in such reactions as hydroformylation, Heck and other Pd-catalyzed CC bond formations, oxidation, and enantioselective addition to aldehydes. In the majority of these studies, substantial dendritic effects on the reactivity, selectivity, or recyclability of the catalysts were observed. Although a number of factors have been suggested as sources of the effects, it is most likely that the phenomenon has a multicomponent origin. Additional research, including a full determination of the effects and their causes, is likely to lead to markedly better heterogeneous catalytic systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 235,262, 2005 [source] | ||||||||||