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Active Monomers (active + monomer)
Selected AbstractsPolynorbornene with pentafluorophenyl imide side chain groups: Synthesis and sulfonationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2010Arlette A. Santiago Abstract The mixtures of exo-endo -monomers and isomerically pure endo -monomers of N -pentafluorophenyl-norbornene-5,6-dicarboximide (2a) and N -phenyl-norbornene-5,6-dicarboximide (2b) were synthesized and polymerized via ring opening metathesis polymerization using bis(tricyclohexylphosphine) benzylidene ruthenium (IV) dichloride (I) and tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene] ruthenium dichloride (II). Ring opening metathesis polymerization of mixtures of exo-endo -monomers (2a) and (2b) and pure endo - 2b gave the corresponding high molecular weights poly(N -pentafluorophenyl-norbornene-5,6-dicarboximide) (3a) and poly(N -phenyl-norbornene-5,6-dicarboximide) (3b). The isomerically pure endo - 2a did not polymerize by I in these conditions, since I is the least active catalyst and endo - 2a is the least active monomer because of the intramolecular complex formation between the Ru active center and the fluorine atom of ring-opened endo - 2a on the one hand and steric hindrances caused by the pentafluorinated ring on the other. The quantitative hydrogenation of the polymer 3a, at room temperature and 115 bar, was achieved by a Wilkinson's catalyst. The new polynorbornene bearing highly fluorinated sulfonic acid groups (5) was obtained by the reaction of the hydrogenated poly(N -pentafluorophenyl-norbornene-5,6-dicarboximide) (4) with sodium 4-hydroxybenzenesulfonate dihydrate. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2925,2933, 2010 [source] Direct Observation of , -Chloro- p -quinodimethane as the Real Monomer in the Gilch Polymerization Leading to Poly(p -phenylene vinylene)sMACROMOLECULAR RAPID COMMUNICATIONS, Issue 2 2007Jens Wiesecke Abstract It is the general consensus that in Gilch polymerizations the 1,4-bis(chloromethylene)benzene starting material first changes into p -quinodimethane intermediates which then act as the real monomers. However, direct observation of these intermediates has not been possible so far. This is because usually the p -quinodimethane auto-initiates its rapid radical polymerization instantaneously, keeping its concentration extremely low throughout the whole process. Here it is shown that, when the reaction is carried out at very low temperatures, the formation of p -quinodimethane still proceeds but chain growth is suppressed. Hence, the concentration of the active monomer reaches a level sufficient for NMR analysis. [source] Irregular dimerization of guanylate cyclase-activating protein 1 mutants causes loss of target activationFEBS JOURNAL, Issue 18 2004Ji-Young Hwang Guanylate cyclase-activating proteins (GCAPs) are neuronal calcium sensors that activate membrane bound guanylate cyclases (EC 4.6.1.2.) of vertebrate photoreceptor cells when cytoplasmic Ca2+ decreases during illumination. GCAPs contain four EF-hand Ca2+ -binding motifs, but the first EF-hand is nonfunctional. It was concluded that for GCAP-2, the loss of Ca2+ -binding ability of EF-hand 1 resulted in a region that is crucial for targeting guanylate cyclase [Ermilov, A.N., Olshevskaya, E.V. & Dizhoor, A.M. (2001) J. Biol. Chem.276, 48143,48148]. In this study we tested the consequences of mutations in EF-hand 1 of GCAP-1 with respect to Ca2+ binding, Ca2+ -induced conformational changes and target activation. When the nonfunctional first EF-hand in GCAP-1 is replaced by a functional EF-hand the chimeric mutant CaM,GCAP-1 bound four Ca2+ and showed similar Ca2+ -dependent changes in tryptophan fluorescence as the wild-type. CaM,GCAP-1 neither activated nor interacted with guanylate cyclase. Size exclusion chromatography revealed that the mutant tended to form inactive dimers instead of active monomers like the wild-type. Critical amino acids in EF-hand 1 of GCAP-1 are cysteine at position 29 and proline at position 30, as changing these to glycine was sufficient to cause loss of target activation without a loss of Ca2+ -induced conformational changes. The latter mutation also promoted dimerization of the protein. Our results show that EF-hand 1 in wild-type GCAP-1 is critical for providing the correct conformation for target activation. [source] Enantioseparation of doubly functionalized polar norbornenes by HPLC and their ruthenium-catalyzed ring-opening metathesis polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2010Yasushi Nishihara Abstract Doubly fuctionalized polar norbornenes bearing the cyano and ester groups in 2,3-positions are synthesized and enantiomers are separated by high performance liquid chromatography (HPLC) with a chiral stationary phase. These optically active monomers are polymerized by ruthenium carbene catalysts, and high yields of the polymers were obtained. The chiral monomer bearing ethyl ester gave an optically active polymer of lower, but opposite sign of optical rotation (monomer [,]D = +61.0°, polymer [,]D = ,3.1°). The circular dichroism (CD) of the obtained chiral polymers gave a Cotton effect. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 485,491, 2010 [source] Secretion of proteins with dimerization capacity by the haemolysin type I transport system of Escherichia coliMOLECULAR MICROBIOLOGY, Issue 4 2004Sofía Fraile Summary The tolerance of the haemolysin transport system (Hly) for exporting dimeric protein substrates to the supernatants of Escherichia coli cultures was examined. A strong dimerization domain (i.e. an amphipathic ,-helix capable of forming a leucine zipper in the yeast transcription factor GCN4) was inserted into an epitope-tagged version of the 23 kDa C-terminal secretion signal of haemolysin (EHlyA). The zipper-containing polypeptide (ZEHlyA) was effectively secreted by E. coli cells carrying the HlyBD transporter and accumulated in the culture media as a stable dimer as determined by gel filtration chromatography. In vivo protein cross-linking experiments and coexpression with a secretion-deficient derivative of ZEHlyA indicated that leucine zipper-dependent dimerization occurs following secretion. To test whether dimerization allows the correct folding of the secreted polypeptide, immunoglobulin VHH -domains obtained from camel antibodies were fused to EHlyA and ZEHlyA. Functional dimerization of the ZEHlyA hybrid was anticipated to increase the apparent binding affinity (i.e. avidity) of the VHH moiety, thus becoming an excellent reporter of correct protein folding and dimerization. Both VHH -EHlyA and VHH -ZEHlyA hybrids were quantitatively secreted and found in the extracellular medium as active monomers and dimers respectively. When compared with their monomeric counterparts, the dimeric VHH -ZEHlyA molecules showed superior binding properties to their cognate antigen, with a 10-fold increase in their avidity. These data reveal a non-anticipated permissiveness of the Hly type I transport machinery for the secretion of substrates with dimerization capacity. [source] | ||||||||||