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991.
Dr. Virginia M. Cangelosi Dr. Aniruddha Deb Prof. James E. Penner‐Hahn Prof. Vincent L. Pecoraro 《Angewandte Chemie (International ed. in English)》2014,53(30):7900-7903
Protein design will ultimately allow for the creation of artificial enzymes with novel functions and unprecedented stability. To test our current mastery of nature’s approach to catalysis, a ZnII metalloenzyme was prepared using de novo design. α3DH3 folds into a stable single‐stranded three‐helix bundle and binds ZnII with high affinity using His3O coordination. The resulting metalloenzyme catalyzes the hydration of CO2 better than any small molecule model of carbonic anhydrase and with an efficiency within 1400‐fold of the fastest carbonic anhydrase isoform, CAII, and 11‐fold of CAIII. 相似文献
992.
993.
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995.
Catherine Bianchi Bruno Grassl Bernard Franois Christine Dagron‐Lartigau 《Journal of polymer science. Part A, Polymer chemistry》2005,43(19):4337-4350
Water‐soluble and photoluminescent block copolymers [poly(ethylene oxide)‐block‐poly(p‐phenylene vinylene) (PEO‐b‐PPV)] were synthesized, in two steps, by the addition of α‐halo‐α′‐alkylsulfinyl‐p‐xylene from activated poly(ethylene oxide) (PEO) chains in tetrahydrofuran at 25 °C. This copolymerization, which was derived from the Vanderzande poly(p‐phenylene vinylene) (PPV) synthesis, led to partly converted PEO‐b‐PPV block copolymers mixed with unreacted PEO chains. The yield, length, and composition of these added sequences depended on the experimental conditions, namely, the order of reagent addition, the nature of the monomers, and the addition of an extra base. The addition of lithium tert‐butoxide increased the length of the PPV precursor sequence and reduced spontaneous conversion. The conversion into PPV could be achieved in a second step by a thermal treatment. A spectral analysis of the reactive medium and the composition of the resulting polymers revealed new evidence for an anionic mechanism of the copolymerization process under our experimental conditions. Moreover, the photoluminescence yields were strongly dependant on the conjugation length and on the solvent, with a maximum (70%) in tetrahydrofuran and a minimum (<1%) in water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4337–4350, 2005 相似文献
996.
Pieter L. H. Verlooy Koen Robeyns Luc Van Meervelt Christine E. A. Kirschhock Johan A. Martens 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(12):o619-o622
The title compound, 6C13H24N+·H2Si8O206−·44H2O, belongs to the class of cyclosilicate hydrates, which structurally can be positioned between the zeosils and the clathrate hydrates. [Si8O18(OH)2] cubes carrying six negative charges are located on crystallographic inversion centres and are surrounded by six adamantyltrimethylammonium cations. 相似文献
997.
Jenny Undin Peter Plikk Anna Finne‐Wistrand Ann‐Christine Albertsson 《Journal of polymer science. Part A, Polymer chemistry》2010,48(22):4965-4973
Radical ring‐opening polymerization has been efficiently used to copolymerize 2‐methylene‐1,3,6‐trioxocane (MTC) and 2‐methylene‐1,3‐dioxepane (MDO). The cyclic ketene acetal MTC was first synthesized and homopolymerized at different temperatures using either 2,2‐azobisisobutyronitrile or dicumyl peroxide as initiator. The polymerization mechanism was not temperature‐dependent, and the polymerization proceeded with 100% ring‐opening at all the temperatures evaluated. The structures of MTC and PMTC were verified by 1H‐nuclear magnetic resonance (NMR) and 13C‐NMR spectroscopies. A number‐average molecular weight of 6500 was obtained after 2 days at 70 °C in bulk, which was somewhat higher than the theoretical molecular weight. A significant amount of branching was detected from the high polydispersity index as well as the glass‐transition temperatures. The polyester‐ether was then successfully obtained by copolymerization of MTC with MDO. Different feed ratios and temperatures were used to map the reaction, and the copolymers were characterized by NMR, size exclusion chromatography, and differential scanning calorimetry. The amount of MTC within the polymer was independent of the feed ratio and always higher than the amount of MDO. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
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999.
Sofia Målberg Dildare Basalp Anna Finne‐Wistrand Ann‐Christine Albertsson 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1214-1219
The catalytic activities of Bi(III) acetate (Bi(OAc)3) and of creatinine towards the ring‐opening polymerization of L ‐lactide have been compared with those of a stannous (II) ethylhexanoate ((SnOct)2)‐based system and with those of a system catalyzed by enzymes. All four were suitable catalysts for the synthesis of high and moderate molecular weight poly(L ‐lactide)s and the differences in reactivity and efficiency have been studied. Linear and branched poly(L ‐lactide)s were synthesized using these bio‐safe initiators together with ethylene glycol, pentaerythritol, and myoinositol as coinitiators. The polymerizations were performed in bulk at 120 and 140 °C and different reactivities and molecular weights were achieved by adding different amounts of coinitiators. A molecular weight of 105,900 g/mol was achieved with 99% conversion in 5 h at 120 °C with a Bi(OAc)3‐based system. This system was comparable to Sn(Oct)2 at 140 °C. The reactivity of creatinine is lower than that of Bi(OAc)3 but higher compared with enzymes lipase PS (Pseudomonas fluorescens). A ratio of Sn(Oct)2Mo/Io 10,000:1 was needed to achieve a polymer with a reasonable low amount of tin residue in the precipitated polymer, and a system catalyzed by creatinine at 140 °C has a higher conversion rate than such a system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1214–1219, 2010 相似文献
1000.
Bruno Grignard Christine Jérôme Cédric Calberg Christophe Detrembleur Robert Jérôme 《Journal of polymer science. Part A, Polymer chemistry》2007,45(8):1499-1506
1H,1H,2H,2H‐Heptadecafluorodecyl acrylate (AC8) was polymerized by reversible addition–fragmentation chain transfer and copolymerized with 2‐hydroxyethyl acrylate with the formation of random and block copolymers, respectively. The kinetics of the (co)polymerization was monitored with 1H NMR spectroscopy and showed that the homopolymerization and random copolymerization of AC8 were under control. As a result of this control and the use of S‐1‐dodecyl‐S‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate as a chain‐transfer agent, the copolymer chains were end‐capped by an α‐carboxylic acid group. Moreover, the controlled polymerization of AC8 was confirmed by the successful synthesis of poly(1H,1H,2H,2H‐heptadecafluorodecyl acrylate)‐b‐poly(2‐hydroxyethyl acrylate) diblock copolymers, which were typically amphiphilic compounds. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1499–1506, 2007 相似文献