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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 31 (1998), S. 445-452 
    ISSN: 0887-3585
    Keywords: chorismate mutase ; activity ; allosteric ; electrostatics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The predicted active site of chorismate mutase of baker's yeast Saccharomyces cerevisiae has been studied by continuum electrostatics, molecular surface/volume calculations, and molecular modeling. Our study shows that despite being subject to an allosteric transition, the enzyme's active-site pocket neither decreased in volume nor deformed significantly in shape between the active R state and the inactive T state. We find that the polar atmosphere in the pocket is responsible for the enzyme's affinity. A single amino acid, Glu23, can adequately account for the atmospheric variation. This residue swings into the active-site pocket from the R state to the T state. In the R state, Glu23 on helix H2 doubly pairs with Arg204 and Lys208 of H11, which is packed against H2. In the T state, a slide occurs between H11 and H2 such that Glu23 can no longer interact with Lys208 and competes with Asp24 for interacting with Arg204. Consequently, Glu23 is found in the T state to couple with Arg157, an active-site residue critical to substrate binding. The tandem sliding of H11 in both monomers profoundly changes the interactions in the dimer interface. The loop between H11 and H12 demonstrates the largest conformational change. Hence, we establish a connection between the allosteric transition and the activity of the enzyme. The conformational change in the transition is suggested to propagate into the active-site pocket via a series of polar interactions that result in polarity reversal in the active-site pocket, which regulates the enzyme's activity. Proteins 31:445-452, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 7 (1996), S. 309-314 
    ISSN: 1042-7147
    Keywords: nonlinear optical polymer ; interpenetrating polymer network ; polyurethane ; polyacrylate ; chromophore ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Interpenetrating polymer networks (IPNs) based on polyurethane and polyacrylate-containing 4-(4'-nitrophenylazo) aniline chromophore groups were synthesized and characterized by infrared spectra, gel content and differential scanning calorimetry. Thin, transparent films of the IPNs were prepared by spin-coating, followed by thermal curing and corona poling. The poled IPN film shows very good optical properties and exhibits only one glass transition temperature. The second-order nonlinear optical (NLO) properties of the poled film were studied by visible light absorbance measurement according to one-dimensional rigid oriented gas model. The second-order nonlinear optical polarizability can reach 10-7 e.s.u. The poled IPN film of defined composition showed a good temporal stability of NLO properties at 120°C for more than 160 hr.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 60 (1996), S. 537-542 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two kinds of interpenetrating polymer networks (IPNs) containing 4-(4′-nitrophenyl-azo)aniline chromophore groups were synthesized. A polyacrylate network was prepared by polymerization of Dispersed Red-19 (DR-19) diacrylate, whereas an epoxy resin network was formed by reaction of Bisphenol A-type epoxy resin E44 with 4(4′-nitrophenylazo)-3-amino aniline. A polyurethane network was synthesized by reaction between (β-hydroxyl propyl acrylate-DR-1 methacrylate) copolymer and phenol-capped isocynate-terminated DR-19. IPNs based on polyacrylate/epoxy resin and IPNs based on polyurethane/epoxy resin were obtained by carrying out two corresponding kinds of reactions simultaneously. Both kinds of IPNs were characterized by gel content, IR spectra, and DSC. The first kind of IPNs exhibits two glass transition temperatures at 122 and 165°C, while the second kind of IPNs showed one broad glass transition temperature at 172°C. Thin and transparent poled films of both IPNs were prepared by spin-coating, followed by thermal curing and corona poling at 160°C for 1 h. The second-order nonlinear optical properties of the poled films were studied by a visible light absorbance measurement according to the one-dimensional rigid oriented gas model. The polyurethane/epoxy resin IPNs were more stable in dipole alignment than were the polyacrylate/epoxy resin IPNs at temperature higher than 120°C. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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