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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of the acyclic biscystine peptide S,S′-bis(Boc-Cys-Ala-OMe) has been studied in the solid state by x-ray diffraction, and in solution by1H- and13C-nmr, ir, and CD methods. The peptide molecule has a twofold rotation symmetry and adopts an intramolecular antiparallel β-sheet structure in the solid state. The two antiparallel extended strands are stabilized by two hydrogen bonds between the Boc CO and Ala NH groups [N⃛O 2.964 (3) Å, O⃛HN 2.11 (3) Å, and NH⃛O angle 162 (3)°]. The disulfide bridge has a right-handed conformation with the torsion angle CβSSCβ = 95.8 (2)°. In solution the presence of a twofold rotation symmetry in the molecule is evident from the1H- and13C-nmr spectra. 1H-nmr studies, using solvent and temperature dependencies of NH chemical shifts, paramagnetic radical induced line broadening, and rate of deuterium-hydrogen exchange effects on NH resonances, suggest that Ala NH is solvent shielded and intramolecularly hydrogen bonded in CDCl3 and in (CD3)2SO. Nuclear Overhauser effects observed between Cys CαH and Ala NH protons and ir studies provide evidence of the occurrence of antiparallel β-sheet structure in these solvents. The CD spectra of the peptide in organic solvents are characteristic of those observed for cystine peptides that have been shown to adopt antiparallel β-sheet structures.
    Additional Material: 8 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 11 (1967), S. 1325-1331 
    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: Aliphatic polybenzoxazoles, polybenzothiazoles, and polybenzimidazoles have been prepared by three methods: in poly(phosphoric acid), by the polyamide precursor, and by melt polymerization. The melt polymerization method was found to be the most satisfactory. All of the aliphatic heterocyclic polymers had excellent thermal stability, resistance to alkaline hydrolysis, high glass transition temperatures, and a high degree of flexibility. The only class of polymer found having any degree of solubility, however, was the polybenzimidazoles. Aliphatic polybenzimidazole films were prepared by solution casting. These films were found to be extremely flexible at ambient and cryogenic temperatures. The films were unaffected by alkaline hydrolysis, even in an oxidizing medium. A molding prepared from the aliphatic polybenzimidazole had excellent physical properties at both cryogenic and room temperature.
    Additional Material: 5 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 6 (1962), S. 184-192 
    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: (1) The prognosis for adhesives uieful up to an hour at 1000°F., in air, is good. (2) Organic adhesives based on phenolic and silicone-phenolic resins are more capable than expected of usefulness at 1000°F. (3) Preparation of semiinorganic adhesives by reaction of heat stable organic polymers with inorganic reagents is feasible. (4) The prospect appears excellent for the achievement of adhesives to be used for 1000 hr. at 500°F., in air, on steel. (5) Despite research on 2000°F. adhesives, effort is still urgently needed on materials for use at lower temperatures. (6) Perhaps the area with the most serious shortage of information and research is the development and testing of adhesives for use at 180-500°F. for periods of three to five years. Both military and civilian agencies are planning the construction of supersonic transports which need such structural adhesives.
    Additional Material: 11 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 15 (1976), S. 1267-1281 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A very low-angle light-scattering photometer is described with respect to optical features, scattering cell, correction factors, and absolute calibration in the angular range 2°-35°. An improved microfiltration apparatus was used to obtain essentially dust-free aqueous solutions for very low-angle light scattering. The instrument was calibrated with silicotungstic acid, an absolute molecular-weight standard, and the calibration was confirmed with the use of several secondary standards.Very low-angle light-scattering measurements were made to determine the weight-average molecular weight M̄r and z-average radius of gyration Rg,z of a commerical preparation of calf-thymus DNA. Microfiltration of the solutions allowed measurements down to 6°. The value M̄r = 20.0 × 106 obtained by extrapolating 6°-9° data to 0° is more than three times that from 30°-75° data (6.38 × 106) but ∼20% smaller than that from 10-35° data (23.7 × 106). The experimental errors in M̄r and Rg,z are estimated to be ±8% and ±14%, respectively. Combined 6°-75° data from two photometers fit well a theoretical scattering curve for a model wormlike coil of the same M̄r as the DNA sample.
    Additional Material: 7 Ill.
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  • 5
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of the sugar moiety of 8-(N-fluoren-2-ylamino)-2′-deoxyguanosine in solution has been examined as a function of temperature by 1H-nmr spectroscopy. Analysis of coupling constants shows that lowering the temperature to -50°C in methanol shifts the conformational equilibrium of the sugar ring resulting in a C2′-endo conformation at a mole fraction of 0.97. The computed phase angle of pseudorotation and amplitude of pucker are 154° and 36°, respectively, with very little discrepancy between the five calculated coupling constants and coupling constants extrapolated from the temperature profiles. A computer program has been written enabling a three-state best-fit analysis. The three-state analysis indicates an equilibrium between C2′-endo, C3′-endo, and 04′-endo conformations. In aqueous solution, the computed mole fraction of the 04′-endo form is 0.18 at 30°C. The conformation associated with the sugar ring and the C4′—C5′ bond is compared to that of 2′-deoxyguanosine.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 5 (1961), S. 606-611 
    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: X-ray, γ-ray, and electron irradiations are used to graft vinylpyrrolidone, a dye acceptor molecule, to a synthetic fiber, polyacrylonitrile. Two processes are described. In one, doses of 10-60 krad are given to the polymer--aqueous monomer system at dose rates of 3-27 krad/min. In the other process, 0.2-3.0 Mrad is given the system at 0.5-90 Mrad/sec., followed by a heat treatment to elongate the graft side chain. Oxygen inhibits the grafting and various inorganic salts such as sulfates and phosphates enhance the grafting.
    Additional Material: 9 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 2 (1959), S. 192-197 
    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: The influences of caustic, zinc, by-product sulfur, and additives on the degree of swelling and the rate of neutralization of viscose are reported. A film technique showed a marked decrease in gel swell factors as the caustic concentration was increased from 5.5 to 7%. In the presence of zinc and by-product sulfur, the viscose additive retards the regeneration process and reduces the gel swell. On mixing various amounts of “white” and conventional viscoses, a minimum value in gel swell occurs with an equal mixture of “white” and regular viscoses. A similar relationship is obtained on adding a polyethylene oxide derivative or an amine to the viscose; namely, a minimum point is reached at 50-70% by-product sulfur, but in these cases as the by-product sulfur is increased to 100%, the gel swell values level off. The actual numerical values of the gel swells are considerably lower for the mixed viscoses which contain additives in comparison with those without an additive. A gradual retardation of the neutralization rate is observed as the amount of by-product sulfur is increased in viscoses containing a polyethylene oxide derivative. A mechanism explaining the retardation of neutralization rates and reduction of the gel swell is proposed, based on the formation of a coordination complex between the additive, zinc ions, by-product sulfur, and the xanthate.
    Additional Material: 4 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 5 (1961), S. 491-492 
    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: Various chemical additives are commonly used in viscose to reduce the swelling of the resultant fibers and films. It was found that inorganic sodium salts, introduced into the additive-containing viscose, alter the action of the additive. The following salts, listed in order of the values of gel swelling ratios obtained with them, interfere with the deswelling of the viscose during regeneration: citrate 〉 thiosulfate 〉 tartrate 〉 sulfate 〉 chloride = phosphate = thiocyanate 〉 acetate 〉 nitrate 〉 control. Sodium idodide did not affect the usual deswelling of the films, and sodium sulfide and sodium carbonate caused the films to deswell slightly more than the control sample. It was proposed that the effectiveness of the salts follows a Hofmeister or lyotropic series.
    Additional Material: 1 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 26 (1988), S. 1613-1625 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The symmetry of the orientational distribution function of dye molecules in stretched PVA films is studied using polarized fluorescence. The different symmetries are monitored by a simple experimental technique in which angle-resolved fluorescence depolarization ratios are measured. A uniaxial distribution of rhodamine 6G molecules is obtained on stretching the film at temperatures above 60°C. In contrast a biaxial distribution of trypaflavine molecules is found for stretch temperatures in the 50-115°C range. It is suggested that the hydrogen bonding between the PVA chains, and between the dye molecules and the PVA chains, influences the symmetry of the distribution upon stretching.
    Additional Material: 5 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 3351-3357 
    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: The condition for the inverse piezoelectric effect in polymers is discussed and a thermodynamic criteria is derived. The resulting expression is related to the electrical configuration of the polymer and several promising structures are proposed. A dynamical model of the piezoelectric effect is given, and expressions are derived for the compliance and electromechanical losses.
    Additional Material: 2 Ill.
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