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  • Polymer and Materials Science  (112,478)
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  • Engineering General  (9,884)
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  • 101
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of poly(benzazoles) containing the bicyclo[2.2.2]octane moiety (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 277-281 
    Details
    ISSN: 0887-624X
    Keywords: poly(benzazoles) ; bicyclo[2.2.2]octane ; aromatization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(benzobisoxazoles) (PBOs), poly(benzobisthiazoles) (PBTs) and copolymers thereof containing the 2,5-dihydroxybicyclo[2.2.2]octane moiety have been prepared and studied. The homopolymers were synthesized by the polycondensation of 2,5-dihydroxybicyclo[2.2.2]octane-1,4-dicarboxylic acid with 4,6-diamino-1,3-benzenediol dihydrochloride or 2,5-diamino-1,4-benzenedithiol dihydrochloride in poly(phosphoric acid). Random and block copolymers (PBO-PBT) were also prepared. The polymers were characterized by solubility, X-ray diffraction, spectroscopy (infrared and solid-state 13C nuclear magnetic resonance), and thermal analysis such as differential scanning calorimetry and thermogravimetric analysis. Thermogravimetric analysis showed thermal stability of the polymers above 375°C in air and under argon atmosphere. The polymers exhibited high resistance to organic and inorganic solvents. The polymers were converted to the more stable aromatic polymers via dehydration and retro Diels-Alder reactions of the 2,5-dihydroxybicyclo[2.2.2]octyl moiety by pyrolysis. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 277-281, 1998
    Additional Material: 3 Ill.
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  • 102
    Electronic Resource
    Electronic Resource
    Photoinduced surface relief gratings in high-Tg main-chain azoaromatic polymer films (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 283-289 
    Details
    ISSN: 0887-624X
    Keywords: polyurea ; azoaromatic group ; surface relief grating ; holographic material ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have synthesized two classes of polyureas with mono- and bisazoaromatic groups in their main chains via reactions between isophorone diisocyanate and the corresponding diamines. Holographic gratings were fabricated on azoaromatic polyurea films prepared by spin-coating from solutions. The effect of high glass transition temperature and dipole moment of azo groups on the formation of gratings was investigated. Although the two polymers have relatively high glass transition temperatures (197 and 236°C), chromophore alignment was induced by laser beam irradiation at modest light intensities. Regularly spaced surface relief gratings on the polymer film were also recorded upon exposure to an interference pattern of two polarized argon laser beams. Erasure could be achieved by heating above Tg or by exposure to one of the beams in a manner similar to low-Tg side-chain azo polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 283-289, 1998
    Additional Material: 3 Ill.
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  • 103
    Electronic Resource
    Electronic Resource
    Synthesis and properties of nonlinear optical side chain soluble polyimides for photonics applications (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 301-307 
    Details
    ISSN: 0887-624X
    Keywords: polyimides ; electrooptics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aromatic polyimides with side chain nonlinear optical chromophores have been investigated through a facile two-step synthetic route. First, various poly(hydroxy imide)s have been synthesized by direct thermal imidization of diaminophenol dihydrochloride salt and aromatic dianhydride monomers. The resulting polyimides bearing phenolic hydroxy groups were found to react easily with the terminal hydroxy group on the chromophores via the Mitsunobu condensation to give corresponding polyimides with high optical nonlinearities and good solubility in common organic solvents. Detailed physical properties showed that these polyimides have a molecular weight (Mw) of 31,000 and high glass transition temperature above 220°C, ensuring a long-term alignment stability at elevated temperature. The electrooptic coefficients, r33, of the electrically poled polymer films were in the range 1.8-7.6 pm/V at 1.3 μm. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 301-307, 1998
    Additional Material: 3 Ill.
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  • 104
    Electronic Resource
    Electronic Resource
    Polymer grafting onto carbon black by use of TEMPO-terminated polystyrene with controlled molecular weight (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 3165-3172 
    Details
    ISSN: 0887-624X
    Keywords: carbon black ; surface grafting of polymer ; living radical polymerization ; TEMPO-terminated polystyrene ; radical trap ; dispersibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The grafting of polystyrene with controlled molecular weight and narrow molecular weight distribution onto the carbon black surface through the trapping of polymer radicals formed by the thermal dissociation of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-terminated polystyrene (PSt-TEMPO) by the carbon black surface was investigated. PSt-TEMPO was prepared by living radical polymerization of St with the benzoyl peroxide/TEMPO system. When PSt having no terminal TEMPO moiety was heated with carbon black, no grafting of PSt onto the surface was observed. On the contrary, by the heating of PSt-TEMPO with carbon black in m-xylene at 125°C, PSt with controlled molecular weight and narrow molecular weight distribution was grafted onto the surface: the percentage grafting of PSt (Mn = 3.2 × 103;Mw/Mn = 1.07) onto furnace black was determined to be 16.0%. On the basis of the above results, it is concluded that PSt radicals formed by the thermal dissociation of the C—ON bond between PSt and TEMPO are trapped by polycondensed aromatic rings of carbon black. The mole number of grafted PSt chains on the carbon black surface decreased with increasing molecular weight of PSt-TEMPO. PSt-grafted carbon black gave a stable colloidal dispersion in THF. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3165-3172, 1998
    Additional Material: 7 Ill.
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  • 105
    Electronic Resource
    Electronic Resource
    Ethene-propene copolymerization with the MgCl2-supported dichlorobis(4,4,4-trifluoro-1-phenyl- 1,3-butanedionato)titanium catalyst activated by an ordinary trialkylaluminum (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2735-2740 
    Details
    ISSN: 0887-624X
    Keywords: Ti(BFA)2Cl2/MgCl2 catalyst (BFA = 4,4,4-trifluoro-1-phenyl-1,3-butanedione) ; activation by trialkylaluminum with or without diisopropyldimethoxysilane ; copolymerization of ethene with propene ; homogeneity of active species ; homogeneity of copolymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Ti(BFA)2Cl2/MgCl2-Al(C2H5)3 catalyst (BFA = 4,4,4-trifluoro-1-phenyl-1,3-butanedione) modified by DIPDMS (diisopropyldimethoxysilane), which had been proved to yield an extremely high isotactic polypropene in high selectivity, was tested for the copolymerization of ethene with propene. The analysis of resulting copolymers by CFC (cross fractionation chromatography) indicated the formation of a small quantity of ethene-rich copolymers as a byproduct, suggesting that the catalyst possesses not only Ti(III) species but a small portion of Ti(II) species. Whereas, the same catalyst without being modified by an external donor selectively yielded propene-rich random copolymers resulting from Ti(III) species in high yields. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2735-2740, 1998
    Additional Material: 5 Ill.
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  • 106
    Electronic Resource
    Electronic Resource
    Styrene-assisted free radical grafting of glycidyl methacrylate onto polyethylene in the melt (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2763-2774 
    Details
    ISSN: 0887-624X
    Keywords: free radical grafting ; glycidyl methacrylate ; polyethylene ; styrene ; reactive extrusion ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycidyl methacrylate (GMA) is a very useful monomer as it bears an epoxy group which is capable of reacting with various other functional groups. However, its melt free radical grafting reactivity onto a polymer backbone is low. In this study, we show that the use of styrene (St) as a comonomer greatly promotes both GMA's grafting yield and grafting rate onto polyethylene (PE). It is proposed that, in the presence of St, the dominant mechanism of the free radical grafting of GMA onto PE is that St reacts first with PE secondary macroradicals and the resulting styryl macroradicals then copolymerize with GMA leading to grafted GMA. We also show that the contribution of St is not related to an improved solubility of GMA in the molten PE. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2763-2774, 1998
    Additional Material: 20 Ill.
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  • 107
    Electronic Resource
    Electronic Resource
    Highly branched radial block copolymers via dendritic initiation of aliphatic polyesters (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2793-2798 
    Details
    ISSN: 0887-624X
    Keywords: highly branched radial block copolymers ; dendritic initiation ; alipatic polyesters ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Living ring opening polymerization of ε-caprolactone initiated from the numerous chain-end hydroxymethyl groups of the analogous dendrimeric and hyperbranched polyesters derived from 2,2-bis(hydroxymethyl) propionic acid is described. By controlling the size of the dendritic macromolecule and the molar ratio of ε-caprolactone, a variety of highly branched radial block copolymers are obtained. Comparison of the results obtained for the dendrimeric and hyperbranched initiators demonstrates that the reactivity of the chain-end hydroxymethyl groups in the dendrimer are significantly greater than in the isomeric hyperbranched case. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2793-2798, 1998
    Additional Material: 2 Ill.
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  • 108
    Electronic Resource
    Electronic Resource
    Stimuli-responsive polymers. III. Poly(aryl ether ketone amide)s with reversible trans- ↔ cis-4,4′-azobenzene and fixed 2,2′-binaphthyl kinking elements in the main chainDuPont contribution no. 7761. (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2827-2837 
    Details
    ISSN: 0887-624X
    Keywords: stimuli-responsive polymers ; trans-cis isomerization ; NMR spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low-temperature polycondensation of trans-azobenzene-4,4′-dicarbonyl chloride with (S)-(-)-1,1′-binaphthyl-2,2′-diamine and/or 1,4-bis(3-aminophenoxy-4′-benzoyl)benzene afforded a new series of poly(aryl ether ketone amide)s with both fixed and photoinducible kinking elements positioned randomly along the main chain. In their lower energy, trans-azobenzene configurations, the orange, film-forming materials were amorphous, highly tractable, and thermally stable under air or nitrogen up to about 420°C. Variants endowed with higher loadings of the bent binaphthyl monomer were soluble in a variety of organic solvent media including THF and acetone. The introduction of cis-azobenzene backbone kinks into these materials was carried out by irradiating the polymer solutions with near-UV light. Up to 70% of the azobenzene moieties in these polymers were capable of assuming the higher energy cis-configuration, thus greatly increasing the number of bent or kinked sites positioned along each polymer backbone. In solution, reverse cis → trans isomerization reactions were triggered thermally and were quantitatively tracked by both optical absorbance and 1H NMR spectroscopies. Activation parameters calculated for cis → trans reorganization of the polymer backbone were not dependent upon the chemical composition or molecular weight of the polymers but did exhibit a small dependence upon the nature of the solvent medium used to conduct the isomerization experiment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2827-2837, 1998
    Additional Material: 7 Ill.
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  • 109
    Electronic Resource
    Electronic Resource
    Crosslinkable fluorinated poly(arylene ethers) bearing phenyl ethynyl moiety for low-loss polymer optical waveguide devices (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2881-2887 
    Details
    ISSN: 0887-624X
    Keywords: fluorinated poly(arylene ether) ; phenyl ethynyl ; polymer optical waveguide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crosslinkable fluorinated poly(arylene ethers) (FPAE-Fn-PEP) with high transparency and high thermal stability have been investigated for low-loss optical waveguide materials. FPAE-Fn-PEP bearing phenyl ethynyl moiety at the polymer chain end were synthesized by the reaction of 4,4′-(hexafluoro-isopropylidene)diphenol with an excess decafluorobiphenyl, followed by the reaction of 4-phenyl ethynyl phenol. The Mns and Mw/Mns of the polymers determined by GPC with polystyrene standard were in the range of 6200 to 19,400 and 1.4 to 2.04, respectively. The resulting polymers were thermally crosslinked at 320°C for 2 h. The cured polymers show good chemical resistance and high thermal stability up to 510°C under nitrogen. The refractive indices of their films were controlled between 1.495 and 1.530 at 1.55 μm by adjusting molecular weight. A single-mode channel waveguide made of FPAE-F20-PEP was fabricated by conventional photolithography and O2 reactive ion etching (RIE). The propagation loss of the channel waveguide was measured and found to be less than 0.2 dB/cm at 1.55 μm. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2881-2887, 1998
    Additional Material: 4 Ill.
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  • 110
    Electronic Resource
    Electronic Resource
    Synthesis of polymers with pendant hydroxyl groups by polyaddition of bis(oxetane)s with dithiols (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2873-2880 
    Details
    ISSN: 0887-624X
    Keywords: polyaddition ; bis(oxetane) ; aromatic dithiol ; catalyst ; quaternary onium salt ; crown ether complex ; new reactive polymer ; pendant primary hydroxyl group ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition reaction of (3-methyl-3-oxetanyl)methyl acetate (MOMA) with bis(4-mercaptophenyl) sulfide (BMPS) was examined in certain organic solvents. When the reaction of MOMA with BMPS was performed without any catalyst in hexamethylphosphoric triamide (HMPA) and N-methyl-2-pyrrolidone (NMP) at 130°C for 24 h, conversions of the corresponding adduct were 96 and 36%, respectively, which was confirmed by 1H-NMR spectra. On the other hand, when the reaction was carried out using tetraphenylphosphonium bromide (TPPB) as a catalyst under the same conditions, conversions of the adduct were 96 and 81% in HMPA and NMP, respectively. This result shows that although the addition reaction of oxetane compound with aromatic dithiol proceeds without any catalyst in HMPA, the reaction was strongly enhanced by adding TPPB in NMP. On the basis of the above results, polyadditions of bis((3-methyl-3-oxetanyl)methyl) terephthalate (BMOT) and bis((3-ethyl-3-oxetanyl)methyl) terephthalate with BMPS were performed using TPPB as the catalyst in NMP at 130°C for 24 h. As a result, the corresponding high molecular weight polymers 1 (Mn = 22,400) and 2 (Mn = 12,800) with pendant primary hydroxyl groups were obtained in 83 and 89% yields without any gel products, respectively. Furthermore, a low molecular weight oligomer was obtained from the polyaddition of BMOT with aliphatic dithiol, bis(mercaptomethyl)benzene, under the same reaction conditions. The catalytic activity on the polyaddition of BMOT with BMPS was also examined, and it was found that thermally stable TPPB and crown ether complexes at the reaction temperature (130°C) have higher catalytic activity than tetrabutylammonium bromide and tetrabutylphosphonium bromide to produce polymer 1 with high molecular weight. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2873-2880, 1998
    Additional Material: 1 Ill.
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  • 111
    Electronic Resource
    Electronic Resource
    Fractal notation for nearly-symmetrical dendrimers (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2979-2983 
    Details
    ISSN: 0887-624X
    Keywords: dendrimer ; nomenclature ; fractal ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dendrimeric and related molecules that have the same atomic connectivity from exterior to core, P-C1-J1-C2- … Z (P peripheral group, J juncture, C connector, Z core) can be described completely by a highly compact fractal notation, which is of the general form PfJ1,J2 … (C1.C2 …)Z. In this paper, we show how to describe molecules that deviate slightly from the symmetry of a related parent molecule, by use of parenthetic expressions (iX), (dX), and (YrX) which designate atoms or molecular groups that are inserted, deleted, or replaced by other groups in the parent. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2979-2983, 1998
    Additional Material: 1 Tab.
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  • 112
    Electronic Resource
    Electronic Resource
    Polyketomalonate by catalytic oxidation of glycerol over a CeBiPt catalyst. II (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2995-2995 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
    Additional Material: 1 Ill.
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  • 113
    Electronic Resource
    Electronic Resource
    Nanoparticles from vesicles polymerization. II. Evaluation of their encapsulation capacity (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 3035-3043 
    Details
    ISSN: 0887-624X
    Keywords: nanoencapsulation ; tyrosine ; dyes ; poly(isodecyl acrylate) ; nanoparticles ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization of isodecyl acrylate (ISODAC) in vesicles of sodium di-2-ethylhexyl phosphate (SEHP) loaded with dyes or tyrosine was achieved. The study of the polymerization rate-conversion curve of the monomer confirmed that this polymerization was different from other polymerizations known, as it was proposed previously. Then the entrapment of hydrophilic molecules such as tyrosine or brilliant cresyl blue and lipophilic molecules such as sudan III into the nanoparticles was evaluated and confirmed by different methods. While tyrosine was not retained, brilliant cresyl blue and sudan III were entrapped inside nanoparticles. The size and the polarity of the molecules to be encapsulated, which are related to their diffusion coefficients and partition coefficients between water and the nanoparticle, seem to be the parameters responsible of the entrapment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3035-3043, 1998
    Additional Material: 7 Ill.
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  • 114
    Electronic Resource
    Electronic Resource
    Polymerization of propylene by metallocene and Ziegler-Natta mixed catalytic systems. Study of polypropylene properties (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 3063-3072 
    Details
    ISSN: 0887-624X
    Keywords: polypropylene ; metallocenes ; Ziegler-Natta ; catalysts ; polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Propylene was polymerized with metallocene and Ziegler-Natta mixed-catalytic systems to obtain reactor blends of metallocene and Ziegler-Natta-derived propylene homopolymers. The two catalytic systems are able to act jointly, providing individual polymers with different melting and crystallization temperatures. Compatibility between the components of the mixed-catalytic systems and the influence of the components on the polymerization process and on the properties of the reactor blends were studied. Thermal, mechanical, viscoelastic, rheological, and optical properties of the blends were tested and compared with those of conventional polypropylene grades. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3063-3072, 1998
    Additional Material: 5 Ill.
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  • 115
    Electronic Resource
    Electronic Resource
    Crosslinkable interpolymer complexes of novolac resin and poly(ethylene oxide) (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 401-411 
    Details
    ISSN: 0887-624X
    Keywords: novolac resin ; poly(ethylene oxide) ; interpolymer complexes ; crosslinkable ; polymer morphology ; thermal properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crosslinkable interpolymer complexes of novolac resin and poly(ethylene oxide) (PEO) were prepared by mutual mixing ethanol solutions of novolac and PEO. Fourier transform infrared (FTIR) studies revealed that the driving force for the formation of novolac/PEO complex is hydrogen bonding interaction between the hydroxyl groups of novolac and the ether oxygens of PEO. The morphology and thermal properties of the complexes before and after curing were investigated by optical microscopy and differential scanning calorimetry (DSC). It was found that the uncured novolac/PEO complexes had a single composition-dependent glass transition temperature (Tg). The curing with 15 wt % hexamine (HMTA) (relative to novolac content) resulted in disappearing of Tg behaviour for both the neat novolac and the novolac-rich complexes, owing to less mobility of the novolac chain segments. The melting temperature (Tm) and crystallization rate of the HMTA-cured novolac/PEO complexes decreased with increasing novolac content, and no Tm was observed for the cured complexes with PEO content less than 50%. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 401-411, 1998
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  • 116
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of liquid crystalline copolyester of 4-hydroxy-2,3,5,6-tetrafluorobenzoic acid with 6-hydroxy-2-naphthoic acid (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 413-419 
    Details
    ISSN: 0887-624X
    Keywords: liquid crystalline polymer ; polyarylates ; 4-hydroxy-2,3,5,6-tetrafluorobenzoic acid ; 6-hydroxy-2-naphthoic acid ; fine structure ; thermal property ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4-Hydroxy-2,3,5,6-tetrafluorobenzoic acid/6-hydroxy-2-naphthoic acid copolymers (FHBA/HNA copolymer) with different copolymer compositions were prepared and the influence of FHBA residue on the thermal properties and structures of the copolymers were investigated. Introduction of FHBA decreased the crystal/nematic phase transition temperatures(TCNs) of the FHBA/HNA copolymers. TCNs of the copolymers were in the temperature range between 200 and 250°C, depending on the copolymer composition. They are approximately 40°C lower than those of 4-hydroxybenzoic acid/HNA copolymers. FHBA/HNA copolymers exhibited low crystallinity, and annealing treatment hardly influenced the crystalline natures. FHBA residue possibly interferes with the recrystallization during annealing. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 413-419, 1998
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  • 117
    Electronic Resource
    Electronic Resource
    Syntheses of poly(siloxane)-supported zirconocene catalysts and application to olefin polymerizations (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 421-428 
    Details
    ISSN: 0887-624X
    Keywords: poly(siloxane)-supported zirconocene catalysts ; polymerizations of ethene and propene ; copolymerization of ethene with 1-octene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(siloxane)s with bisindenyl, bisfluorenyl, bis(1,2,3,4-tetramethylcyclopentadienyl), bis(2,4,7-trimethylindenyl) and monoindenylmethyl side groups were synthesized by condensation of the corresponding dichlorosilanes and water. For reference, diphenylsilanediol or hydroquinone was also employed in place of water. A series of poly(siloxane)-supported zirconocene catalysts were then prepared from these precursors and applied to ethene and propene polymerizations as well as to the copolymerization of ethene with 1-octene in the presence of methylalumoxane. The polymerization activity of the new supported metallocenes depends drastically upon the substituents in the siloxane backbone. The zirconocene catalysts supported on poly(bisindenylsiloxane) and poly(bisfluorenylsiloxane) give the highest activities for ethene and propene polymerizations, respectively. The weight-average molecular weights of the polymers are also markedly dependent upon the substituents. On the other hand, the molecular mass distributions (MMD) are generally not so sharp, suggesting that the active species formed in these supported catalysts are not uniform. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 421-428, 1998
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  • 118
    Electronic Resource
    Electronic Resource
    Living cationic polymerization of vinyl ethers with carboxylic acid/tin tetrahalide initiating systems. I. New initiating systems based on acetic acid and selection of Lewis acid and basic additive leading to living polymers with low polydispersity (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 3173-3185 
    Details
    ISSN: 0887-624X
    Keywords: cationic polymerization ; living polymerization ; vinyl ether ; initiator ; acetic acid ; tin tetrabromide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cationic polymerization of isobutyl vinyl ether (IBVE) with acetic acid (CH3COOH)/tin tetrahalide (SnX4: X = Cl, Br, I) initiating systems in toluene solvent at 0°C was investigated, and the reaction conditions for living polymerization of IBVE with the new initiating systems were established. Among these tin tetrahalides, SnBr4 was found to be the most suitable Lewis acid to obtain living poly(IBVE) with a narrow molecular weight distribution (MWD). The polymerization with the CH3COOH/SnBr4 system, however, was accompanied with the formation of a small amount of another polymer fraction of very broad MWD, probably due to the occurrence of an uncontrolled initiation by SnBr4 coupled with protonic impurity. Addition of 1,4-dioxane (1-1.25 vol %) or 2,6-di-tert-butylpyridine (0.1-0.6mM) to the polymerization mixture completely eliminated the uncontrolled polymer to give only the living polymer with very narrow MWD (Mw/Mn ≤ 1.1; Mw, weight-average molecular weight; Mn, number-average molecular weight). The Mn of the polymers increased in direct proportion to monomer conversion, continued to increase upon sequential addition of a fresh monomer feed, and was in good agreement with the calculated values assuming that one CH3COOH molecule formed one polymer chain. Along with these results, kinetic study and direct 1H-NMR observation of the living polymerization indicated that CH3COOH and SnBr4 act as so-called “initiator” and “activator”, respectively, and the living polymerization proceeds via an activation of the acetate dormant species. The basic additives such as 1,4-dioxane and 2,6-di-tert-butylpyridine would serve mainly as a “suppressor” of the uncontrolled initiation by SnBr4. The polymers produced after quenching the living polymerization with methanol possessed the acetate dormant terminal and they induced living polymerization of IBVE in conjunction with SnBr4 in the presence of 1,4-dioxane. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3173-3185, 1998
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    Poly(arylene ether)s and poly(arylene thioether)s containing the 1,2-dihydro-4-phenyl(2H)- phthalazinone moiety (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 455-460 
    Details
    ISSN: 0887-624X
    Keywords: poly(arylene ether)s ; poly(arylene thioether)s ; S-(N,N′-dimethylcarbamate) ; phthalazinone ; one-pot polymerization ; thermal stability ; heterocyclic ring ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of new high molecular weight poly(arylene ether)s containing the 1,2-dihydro-4-phenyl(2H)phthalazinone moiety have been synthesized. The inherent viscosities of these polymers are in the range of 0.33-0.64 dL/g. They are amorphous and readily soluble in chloroform, DMF, and DMAc. The glass transition temperatures of the polymers range from 241 to 320°C and the 5% weight loss temperatures in nitrogen atmosphere range from 473 to 517°C. The hydroxy group in the monomer 1,2-dihydro-4-(4-hydroxyphenyl)(2H)phthalazin-1-one has been selectively transformed into the N,N′-dimethylthiocarbamate group, which was then rearranged to give the S-(N,N′-dimethylcarbamate) group via the Newman-Kwart rearrangement reaction. A series of poly(arylene thioether)s containing the 1,2-dihydro-4-phenyl(2H)phthalazinone moiety have also been synthesized via two types of reactions, a N—C coupling reaction and a one-pot reaction between the S-(N,N′-dimethylcarbamate) and activated dihalo compounds, in diphenyl sulfone in the presence of a cesium carbonate and calcium carbonate mixture. These poly(arylene thioether)s also have high glass transition temperatures (ranging from 217-303°C) and high thermal stabilities. Compared with their poly(ether) analogs, the poly(arylene thioether)s have glass transition temperatures several degrees lower, which is attributed to the more flexible C—S—C bonds. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 455-460, 1998
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    Oxyethylene copolymers with chloromethyl and (alkylthio)methyl or (alkylsulfonyl)methyl side groups: Syntheses and Tg/composition relationships (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 495-504 
    Details
    ISSN: 0887-624X
    Keywords: copolymer ; glass transition temperature ; Fox equation ; sulfone ; thioether ; oxyethylene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New classes of copolymers, poly[oxy(chloromethyl)ethylene]/poly[oxy-((alkylthio)methyl)ethylene] copolymers (CE-ATEs), poly[oxy((alkylthio)methyl)-ethylene]s (ATEs), poly[oxy(chloromethyl)ethylene]/poly[oxy((alkylsulfonyl)meth-yl)ethylene] copolymers (CE-ASEs), and poly[oxy((alkylsulfonyl)methyl)ethylene]s (ASEs) have been made for the first time. The thioether-containing polymers (CE-ATEs and ATEs) were synthesized by reacting poly[oxy(chloromethyl)ethylene] (CE, poly(epichlorohydrin)) with different amounts of sodium alkanethiolates. The sulfone-containing polymers (CE-ASEs and ASEs) were synthesized by oxidizing the CE-ATEs and ATEs using m-chloroperoxybenzoic acid. The Fox equation, a linear relationship, fit the Tg/composition data for most CE-ATEs. The Tg's of the CE-ASEs showed positive deviations from those calculated using the Fox equation. The Johnston equation, in which steric and/or polar interactions between dissimilar monomeric units are considered by using TgAB (the Tg of the AB or BA dyad), fit the Tg/composition data for all copolymers in this study. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 495-504, 1998
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    Synthesis and characterization of interpenetrating polymer networks for nonlinear optics (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 553-561 
    Details
    ISSN: 0887-624X
    Keywords: interpenetrating networks ; nonlinear optics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two-component simultaneous interpenetrating networks (IPN) of thepoly(4′-[[2-(methylacryloxy)ethyl]ethylamino]-4-nitroazobenzene-co-methyl meth-acrylate) (PDR1MA-co-MMA)/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) system, the PDR1MA/PPO system and 4′-[[2-(acetoxy)ethyl]ethylamino]-4-nitroazo benzene (ACDR1) doped MMA/PPO system were synthesized and characterized. As studied by differential scanning calorimetry (DSC) the full IPNs of the PDR1MA-co-MMA/PPO system and the PDR1MA/PPO system showed a single Tg varying with the PPO composition. A single-phase morphology of the full IPNs was also indicated by scanning electron microscopy (SEM). Transparent films were cast onto clean microscopic glass slides and poled at 190°C for 1 h. The UV-VIS absorption spectra of the three IPN systems before and after curing and corona poling showed a shift in the maximum absorption due to the induced alignment of the nonlinear optical chromophores in the IPN systems. The absorption intensity of the full IPNs remained same after heating at 120°C for 72 h, indicating that the electric field-induced alignment is stable in the full IPN materials. Preliminary second harmonic generation (SHG) data on these IPNs are presented. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 553-561, 1998
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    Polymerization of ethylene using high-activity Ziegler-type catalysts: Active center determination (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 573-585 
    Details
    ISSN: 0887-624X
    Keywords: polymerization ; Ziegler-Natta ; catalysis ; active centers ; ethylene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The concentration of active centers of a high-activity magnesium chloride-supported Ziegler-Natta catalyst has been determined using three different methods. The initial active center concentration has been determined by quenching the reaction slurry with MeOT. To determine the concentration of the propagation species along the course of the polymerization the radio-tagging agent, 14CO, and the tagging agent, CS2, were used. CS2, was also investigated as a tagging agent of the growing chains, in a metallocene catalyst system. The results obtained were compared to obtain some insight about the reliability of each method and the kind of information each method can provide. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 573-585, 1998
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    Synthesis, hydrophilicity, and oxygen permeability of poly[(trimethylsilyl)propyne]-gr-poly(N,N-dimethylacrylamide) (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 603-610 
    Details
    ISSN: 0887-624X
    Keywords: poly[(trimethylsilyl)propyne] ; poly(N,N-dimethylacrylamide) ; graft copolymer ; oxygen permeability ; hydrophilicity ; water contact angle ; contact lens ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N,N-dimethylacrylamide (DMAA) was graft copolymerized on poly[(trimethylsilyl)propyne] (PTMSP) by single electron reduction of PTMSP with potassium naphthalenide (K-Naph), followed by anion polymerization of DMAA from the carbanion formed in the reduction. A hard and practically non-water-swelling PTMSP-gr-poly(DMAA) was obtained under the conditions using controlled amount of K-Naph and DMAA. The graft copolymer was characterized with regard to structure, number-averaged molecular weight, and the amount of grafting poly(DMAA) determined by the relative absorbance of the IR absorption band assigned to the C=O and SiC—H functionalities (AC=O/ASiC—H). The oxygen permeability and water contact angle (θ) of the graft copolymer were evaluated while varying the amount of grafting poly(DMAA). The graft copolymer proved to be highly oxygen permeable (165 Barrers) and hydrophilic (θ = 27°). Its transparency was also elucidated with UV-vis spectra. This graft copolymer was proposed as a promising candidate for use as a hard contact lens material. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 603-610, 1998
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    Polymers from multifunctional isocyanates 14. Alternating copolymers from isocyanato alkenes: Copolymerization of 2-propenyl isocyanate with trimethylsilyl methacrylate as electron acceptor monomer (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 611-616 
    Details
    ISSN: 0887-624X
    Keywords: alternating copolymerization ; free radical ; isopropenylisocyanate ; trimethylsilyl methacrylate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The copolymerization of 2-propenyl isocyanate (1) with trimethylsilyl methacrylate (2) has been investigated. 1 is an electron donor monomer with little tendency to undergo homopolymerization, while 2 is an electron acceptor monomer, capable of free radical homopolymerization. Polymerization to low conversion in benzene gave copolymers with preferential incorporation of 2 and a tendency towards alternating copolymers with increasing amounts of 1 in the feed (1 : 1.13 with a 9 : 1 feed ratio of monomers 1 : 2). The glass transition temperatures of the amorphous polymers are in the range from 100-70°C, with a Tg of poly(trimethylsilyl methacrylate) being 135°C. Desilylation occurs in the presence of water, causing an exothermal reaction above the glass transition temperature probably with formation of amides, a reaction that can be used for crosslinking. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 611-616, 1998
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    In situ FTIR investigation of MMA plasmas, plasma-polymerized films, and reaction mechanisms (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 587-602 
    Details
    ISSN: 0887-624X
    Keywords: plasma polymerization ; methyl methacrylate ; in situ FTIR/ATR diagnostic ; in situ FTIR plasma diagnostic ; analysis of variance ; regression analysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methyl methacrylate (MMA) plasmas and plasma-polymerized methyl methacrylate (PPMMA) films were studied in situ with FTIR and FTIR/ATR (attenuated total reflection) in an r.f. capacitively coupled glow discharge. A statistically designed experiment was conducted by varying the r.f. power, process pressure, and MMA flow rate. MMA plasma fragments were identified from the gas-phase FTIR measurements. They include the intermediate species such as dimethylketene, formaldehyde, allene, and propene; small hydrocarbons such as acetylene, methane, and ethylene; and oxygenates such as carbon dioxide, carbon monoxide, and methanol. Statistical analysis techniques (correlation analysis, analysis of variance and regression analysis) were used on both gas and film data. Gas-phase reaction mechanisms are proposed, and the relationship between the gas and film data is investigated to understand the film deposition chemistry. The deposition rate is positively correlated to the relative concentrations of MMA fragments which are identified as the major film precursors in the deposition process. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 587-602, 1998
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    ABC triblock polymethacrylates: Group transfer polymerization synthesis of the ABC, ACB, and BAC topological isomers and solution characterization (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 617-631 
    Details
    ISSN: 0887-624X
    Keywords: group transfer polymerization ; methyl methacrylate ; (dimethylamino)-ethyl methacrylate ; tetrahydropyranyl methacrylate ; methacrylic acid ; ABC triblock copolymers ; polymethacrylates ; polyampholytes ; block sequence ; water-soluble copolymers ; micelles ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ABC triblock copolymers of methyl methacrylate (MMA), (dimethylamino)-ethyl methacrylate (DMAEMA), and tetrahydropyranyl methacrylate (THPMA) consisting of 12 units of each type of monomer were synthesized by group transfer polymerization (GTP). These were the three topological isomers with differentblock sequences: DMAEMA12-THPMA12-MMA12, DMAEMA12-MMA12-THPMA12, and THPMA12-DMAEMA12-MMA12. The molecular weights and molecular weight distributions of the copolymers were determined by gel permeation chromatography (GPC) in tetrahydrofuran, and their number-average degrees of polymerization and copolymer compositions were calculated by proton nuclear magnetic resonance spectroscopy (1H-NMR). These molecular weights and degrees of polymerization corresponded closely to the values expected from the monomer/initiator ratios. The polydispersities were low as expected for GTP, and ranged from 1.09 to 1.25. The three triblocks were chemically modified by converting the THPMA units to methacrylic acid (MAA) units either by thermolysis or acid hydrolysis. The resulting ABC triblock poly-ampholytes were characterized by 1H-NMR spectroscopy and hydrogen ion titration. Aqueous GPC studies in 1.0M NaCl at pH 8.5 showed that the triblock copolymers form micelles whose size depends on their block sequence. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 617-631, 1998
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    Plasma-polymerized polyaniline films: Synthesis and characterization (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 633-643 
    Details
    ISSN: 0887-624X
    Keywords: plasma polymerization ; polyaniline ; free radicals ; surface characterization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radio-frequency plasma polymerization technique was used to polymerize aniline onto polymer substrates including perfluorinated ethylene propylene copolymer. The plasma-polyaniline films were characterized by ultraviolet/visible absorption spectroscopy, Fourier transform infrared spectroscopy, electron spin resonance, X-ray photoelectron spectroscopy, scanning electron microscopy, and contact angle measurements. Preliminary conductivity measurements were also carried out. It was demonstrated that the chemical and physical characteristics of the plasma-polymerized poly-aniline films changed significantly with discharge conditions, indicating the possibility for tailoring the structure and properties of the polyaniline films by optimizing the discharge conditions. In particular, the contents of quinoid sequences and aliphatic crosslinking moieties were found to increase with increasing power input and/or discharge duration. By contrast, the number of free radicals trapped in the polyaniline films and their mobility were shown to increase with decreasing the power input and/or discharge duration within the plasma conditions covered in this study. Furthermore, a correlation was found between surface hydrophilicity of the resultant plasma-polyaniline films and the atomic ratio of C to N. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 633-643, 1998
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    Synthesis and properties of a novel perfluorononenyloxy group containing polyarylates (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 645-653 
    Details
    ISSN: 0887-624X
    Keywords: 5-(perfluorononenyloxy)isophthaloyl chloride ; high-temperature solution condensation ; polyarylates ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of novel perfluorononenyloxy group containing polyarylates were synthesized by a high-temperature solution condensation of 5-(perfluorononenyloxy)-isophthaloyl chloride (II) with various aromatic diols in o-dichlorobenzene. All the polyarylates were amorphous and readily soluble in many organic solvents such as o-chlorophenol, o-dichlorobenzene, chloroform, and polar aprotic solvents at room temperature or on heating. Transparent, tough, and flexible films of these polymers could be cast from the o-chlorophenol solutions. The polymers having inherent viscosity of 0.61-1.63 dL/g were obtained in quantitative yields. These polymers were thermally quite stable. The glass transition temperatures of these polyarylates were in the range of 219-242°C by DSC and 224-251°C by DMA, and the 10% weight loss temperatures in nitrogen and air were above 415 and 397°C, respectively. Moreover, these polymers maintained good mechanical properties (G′ ∼ 108 Pa) up to 220°C and had lower moisture absorption than common polyarylates. The dielectric constants of these polymers ranged from 3.23 to 3.75. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 645-653, 1998
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    Polymerization kinetics of photocurable acrylic resins (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 665-673 
    Details
    ISSN: 0887-624X
    Keywords: epoxyacrylate ; diacrylates ; photopolymerization ; kinetics ; synergistic effect ; temperature effect ; heteroatom effect ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization kinetics of photocurable compositions based on an epoxyacrylate oligomer and three analogous diacrylate monomers were investigated. The effects of the oligomer-to-monomer ratio, curing conditions, and monomer structure were considered. The polymerization is characterized by a synergistic effect observed in a wide temperature range and occurring for the polymerization rate both in air and Ar and for final conversions in air. The final conversion in Ar is determined by viscosity of a formulation. The presence of a heteroatom (S or O) in the ester group of the reactive diluent is beneficial for the polymerization course, especially in air atmosphere. The best results were obtained for the sulfur-containing monomer. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 665-673, 1998
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    Synthesis and properties of novel photosensitive polyimides containing chalcone moiety in the main chain (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 685-693 
    Details
    ISSN: 0887-624X
    Keywords: photoreactive polyimides ; chalcone-containing polymers ; photocrosslinking ; photosensitive ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two chalcone-derivative isomers, 4,4′-diaminochalcone (4DAC) and 3,3′-diaminochalcone (3DAC), were synthesized and used as monomers together with tetracarboxylic dianhydrides to prepare novel photosensitive polyimides that contain a chalcone moiety in the main chain. The polyimides were characterized and their photochemical behavior was investigated as thin films and in solutions with the aid of ultraviolet and infrared spectroscopy. Compared with 4DAC-based polyimides, the 3DAC-based polyimides exhibited lower glass transition temperatures and higher photocrosslinking rates of the carbon-carbon double bond as well as higher photosensitivities obtained from the exposure characteristic curves, suggesting that an increase in the photoreactivity of the 3DAC-based polyimides might arise from the improved flexibility of their backbones. The polyimide from 3DAC and 6FDA (2,2-bis[3,4-dicarboxypheny]hexa-fluoropropane dianhydride) showed a photosensitivity of 33 mJ/cm2 with a contrast of 1.5 upon light irradiation using a Xenon lamp. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 685-693, 1998
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    Mechanism of the immobilization of surfactants on polymeric surfaces by means of an argon plasma treatment: Influence of the chemical structure of surfactant and substrate (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1829-1846 
    Details
    ISSN: 0887-624X
    Keywords: surface modification ; argon plasma treatment ; poly(ethylene) ; poly(propylene) ; poly(cis-butadiene) ; carboxylic acid groups ; XPS ; SSIMS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this article, a study on the mechanism of the immobilization of surfactants on polymeric surfaces by means of an argon plasma treatment is described. The unsaturated surfactant sodium 10-undecenoate [C11(:)] and the saturated surfactant sodium dodecanoate (C12) were immobilized on poly(ethylene) (PE), poly(propylene) (PP), and poly(cis-butadiene) (PB) surfaces. This was accomplished by treating polymeric substrates that were coated with C11(:) or C12 with an argon plasma. Derivatization X-ray Photoelectron Spectroscopy (XPS) and Static Secondary Ion Mass Spectrometry (SSIMS) showed that during the plasma treatment surfactants were covalently coupled to the polymeric surfaces. The chemical structure of both the surfactant and the polymeric substrate influenced the immobilization efficiency. At an optimal treatment time of 5 s, about 28 and 6% of the initial amount of carboxylate groups in the precoated C11(:) and C12 layer, respectively, was retained at the PE surface. The immobilization efficiencies of C11(:) and C12 on PP were about 20 and 9%, respectively. The immobilization efficiency of C11(:) and C12 on PB were both about 7%. The results obtained in this study indicate that the immobilization proceeds via a radical mechanism. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1829-1846, 1998
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    A novel route to poly(2-hydroxyethyl methacrylate) and its amphiphilic block copolymers (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1865-1872 
    Details
    ISSN: 0887-624X
    Keywords: anionic polymerization ; poly(2-hydroxyethyl methacrylate) ; amphiphilic block copolymer ; poly(methyl methacrylate)-b-poly(2-hydroxyethyl methacrylate) ; poly(styrene)-b-poly(2-hydroxyethyl methacrylate) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The vinyl of the ester group of 2-vinyloxyethyl methacrylate was first selectively reacted with acetic acid to obtain 2-[1-(acetoxy)ethoxy]ethyl methacrylate (2). This protected monomer was subjected to anionic polymerization in tetrahydrofuran at -60°C in the presence of LiCl, using 1,1-diphenylhexyllithium as initiator. The molecular weight of the polymer could thus be controlled and a narrow molecular weight distribution obtained. The protecting group, 1-(acetoxy)ethyl, could be easily eliminated (by quenching the polymerization reaction with methanol and water) to generate poly(2-hydroxyethyl methacrylate) (poly(HEMA)). Block copolymers were also prepared by the sequential anionic polymerization of MMA and 2 or styrene and 2. They possess narrow molecular weight distributions, and controlled molecular weights and compositions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1865-1872, 1998
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    Chemical reactions occurring in the thermal treatment of PC/PMMA blends (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1873-1884 
    Details
    ISSN: 0887-624X
    Keywords: polycarbonate ; poly(methyl methacrylate) ; blends ; exchange reactions ; mass spectrometry ; thermal degradation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical reactions occurring in the thermal treatment of bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) blends have been investigated by nuclear magnetic resonance (NMR), mass spectrometry (MS), size exclusion chromatography (SEC), and thermogravimetry (TG). Our results suggest that in the melt-mixing of PC/PMMA blends, at 230°C, no exchange reactions occur and that only the depolymerization reaction of PMMA has been observed. In the presence of an ester-exchange catalyst (SnOBu2), an exchange reaction was found to occur at 230°C, but no trace of PC/PMMA graft copolymer has been observed. Instead, an exchange reaction between the monomer methyl methacrylate (MMA), generated in the unzipping of PMMA chains, and the carbonate groups of PC has been suggested. This is due to the diffusion of MMA at the interface or even into the PC domains, where it can react with PC producing low molar mass PC oligomers bearing methacrylate and methyl carbonate chain ends and leaving the undecomposed PMMA chains unaffected. The TG curves of PC/PMMA blends prepared by mechanical mixing and by casting from THF show two separated degradation steps corresponding to that of homopolymers. This behavior is different from that of a transparent film of PC/PMMA blend, obtained by solvent casting from DCB/CHCl3, which shows a single degradation step indicating that the degradation rate of PC is increased by the presence of PMMA in the blend. The thermal degradation products obtained by DPMS of this blend consist of methyl methacrylate (MMA), cyclic carbonates arising from the degradation of PMMA and PC, respectively, and a series of open chain bisphenol-A carbonate oligomers with methacrylate and methyl carbonate terminal groups. The presence of the latter compounds suggests a thermally activated exchange reaction occurring above 300°C between MMA and PC. The presence of bisphenol-A carbonate oligomers bearing methyl ether end groups, generated by a thermally activated decarboxylation of the methyl carbonate end groups of PC, has also been observed among the pyrolysis products. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1873-1884, 1998
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    Polymerization of N-carbazolylacetylene by various transition metal catalysts and polymer properties (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2489-2492 
    Details
    ISSN: 0887-624X
    Keywords: N-carbazolylacetylene ; substituted acetylene ; transition metal catalyst ; metathesis polymerization ; substituted polyacetylene ; thermal stability ; third-order susceptibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Carbazolylacetylene (CzA) was polymerized in the presence of various transition metal catalysts including WCl6, MoCl5, [Rh(NBD)Cl]2, and Fe(acac)3 to give polymers in good yields. The polymers produced with W catalysts were dark purple solids and soluble in organic solvents such as toluene, chloroform, etc. The highest weight-average molecular weight of poly(CzA) reached about 4 × 104. In the UV-visible spectrum in CHCl3, poly(CzA) exhibited an absorption maximum around 550 nm (εmax = 4.0 × 103 M-1 cm-1) and the cutoff wavelength was 740 nm, showing a large red shift compared with that of poly(phenylacetylene) [poly(PA)]. Poly(CzA) began to lose weight in TGA under air at 310°C, being thermally more stable than poly(PA) and poly[3-(N-carbazolyl)-1-propyne]. Poly(CzA) showed a third-order susceptibility of 18 × 10-12 esu, which was 2 orders larger than that of poly(PA). © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2489-2492, 1998
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    Sequence and structure conservation in a protein core (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 358-366 
    Details
    ISSN: 0887-3585
    Keywords: homologous proteins ; superfamilies ; sequence conservation ; protein structure ; protein evolution ; sequence-structure relationships ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In order to study structural aspects of sequence conservation in families of homologous proteins, we have analyzed structurally aligned sequences of 585 proteins grouped into 128 homologous families. The conservation of a residue in a family is defined as the average residue similarity in a given position of aligned sequences. The residue similarities were expressed in the form of log-odd substitution tables that take into account the environments of amino acids in three-dimensional structures. The protein core is defined as those residues that have less then 7% solvent accessibility. The density of a protein core is described in terms of atom packing, which is investigated as a criterion for residue substitution and conservation. Although there is no significant correlation between sequence conservation and average atom packing around nonpolar residues such as leucine, valine and isoleucine, a significant correlation is observed for polar residues in the protein core. This may be explained by the hydrogen bonds in which polar residues are involved; the better their protection from water access the more stable should be the structure in that position. Proteins 33:358-366, 1998. © 1998 Wiley-Liss, Inc.
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    Extraction of geometrically similar substructures: Least-squares and Chebyshev fitting and the difference distance matrix (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 320-328 
    Details
    ISSN: 0887-3585
    Keywords: structural similarity ; optimal superposition ; common substructure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In analysis, comparison and classification of conformations of proteins, a common computational task involves extractions of similar substructures. Structural comparisons are usually based on either of two measures of similarity: the root-mean-square (r.m.s.) deviation upon optimal superposition, or the maximal element of the difference distance matrix. The analysis presented here clarifies the relationships between different measures of structural similarity, and can provide a basis for developing algorithms and software to extract all maximal common well-fitting substructures from proteins.Given atomic coordinates of two proteins, many methods have been described for extracting some substantial (if not provably maximal) common substructure with low r.m.s. deviation. This is a relatively easy task compared with the problem addressed here, i.e., that of finding all common substructures with r.m.s. deviation less than a prespecified threshold. The combinatorial problems associated with similar subset extraction are more tractable if expressed in terms of the maximal element of the difference distance matrix than in terms of the r.m.s. deviation. However, it has been difficult to correlate these alternative measures of structural similarity. The purpose of this article is to make this connection.We first introduce a third measure of structural similarity: the maximum distance between corresponding pairs of points after superposition to minimize this value. This corresponds to fitting in the Chebyshev norm. Properties of Chebyshev superposition are derived.We describe relationships between the r.m.s. and minimax (Chebyshev) deviations upon optimal superposition, and between the Chebyshev deviation and the maximal element of the difference distance matrix. Combining these produces a relationship between the r.m.s. deviation upon optimal superposition and the maximal element of the difference distance matrix. Based on these results, we can apply algorithms and software for finding subsets of the difference distance matrix for which all elements are less than a specified bound, either to select only subsets for which the r.m.s.deviation is less than or equal to a specified threshold, or to select subsets that include all subsets for which the r.m.s. deviation is less than or equal to a threshold. Proteins 33:320-328, 1998. © 1998 Wiley-Liss, Inc.
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    Flexible docking using tabu search and an empirical estimate of binding affinity (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 367-382 
    Details
    ISSN: 0887-3585
    Keywords: ligand-protein docking ; molecular recognition ; tabu search ; empirical scoring function ; binding affinity prediction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: This article describes the implementation of a new docking approach. The method uses a Tabu search methodology to dock flexibly ligand molecules into rigid receptor structures. It uses an empirical objective function with a small number of physically based terms derived from fitting experimental binding affinities for crystallographic complexes. This means that docking energies produced by the searching algorithm provide direct estimates of the binding affinities of the ligands. The method has been tested on 50 ligand-receptor complexes for which the experimental binding affinity and binding geometry are known. All water molecules are removed from the structures and ligand molecules are minimized in vacuo before docking. The lowest energy geometry produced by the docking protocol is within 1.5 Å root-mean square of the experimental binding mode for 86% of the complexes. The lowest energies produced by the docking are in fair agreement with the known free energies of binding for the ligands. Proteins 33:367-382, 1998. © 1998 Wiley-Liss, Inc.
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    Folding-unfolding energy change of a simple sphere model protein and an energy landscape of the folding process (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 408-416 
    Details
    ISSN: 0887-3585
    Keywords: protein folding ; potential energy curve ; two state model ; semi-empirical calculation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have calculated the free energy of a spherical model of a protein or part of a protein generated in the way of protein folding. Two spherical models are examined; one is a homogeneous model consisting of only one residue type - hydrophobic. The other is a heterogeneous model consisting of two residue types - strong hydrophobic and weak hydrophobic. Both models show a folding transition state, and the latter model reproduces the trend of the experimental folded-unfolded energy change. The heterogeneous model suggests that in the folding process of a protein of more than 70 residues, a specific region of the protein folds first to form a stable region, then the other residues follow the folding process. The energy landscape of folding of a small protein is approximately a funnel model, whereas a flatter energy landscape is suggested for larger proteins of more than 55-70 residues. Proteins 33:408-416, 1998. © 1998 Wiley-Liss, Inc.
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    Structural model for family 32 of glycosyl-hydrolase enzymes (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 383-395 
    Details
    ISSN: 0887-3585
    Keywords: glycosidases ; protein structure prediction ; correlated mutations ; sequence space ; phylogenic relationships ; threading ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A structural model is presented for family 32 of the glycosyl-hydrolase enzymes based on the beta-propeller fold. The model is derived from the common prediction of two different threading methods, TOPITS and THREADER. In addition, we used a correlated mutation analysis and prediction of active-site residues to corroborate the proposed model. Physical techniques (circular dichroism and differential scanning calorimetry) confirmed two aspects of the prediction, the proposed all-beta fold and the multi-domain structure. The most reliable three-dimensional model was obtained using the structure of neuraminidase (1nscA) as template. The analysis of the position of the active site residues in this model is compatible with the catalytic mechanism proposed by Reddy and Maley (J. Biol. Chem. 271:13953-13958, 1996), which includes three conserved residues, Asp, Glu, and Cys. Based on this analysis, we propose the participation of one more conserved residue (Asp 162) in the catalytic mechanism. The model will facilitate further studies of the physical and biochemical characteristics of family 32 of the glycosyl-hydrolases. Proteins 33:383-395, 1998. © 1998 Wiley-Liss, Inc.
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    Molecular dynamics simulations of epidermal growth factor and transforming growth factor-α structures in water (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 396-407 
    Details
    ISSN: 0887-3585
    Keywords: AMBER ; epidermal growth factor ; transforming growth factor-alpha ; conformation ; receptor binding ; domain movement ; weakly polar interaction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: AMBER v. 4.1 force field in 1.5 ns NPT molecular dynamics simulations of murine epidermal growth factor (mEGF), human epidermal growth factor (hEGF), and human transforming growth factor-α (hTGF-α) structures with explicit TIP3P solvation were used to investigate differences in backbone stability, changes in secondary structure, interdomain flexibility, and weakly polar interactions. Backbone root mean square deviations of sections of each peptide show that the most stable regions in mEGF and hEGF are the A-, B-, and C-loops, whereas the most stable regions in hTGF-α are the A- and B-loops. The secondary structure in the B-loops of mEGF and hEGF differ significantly from the nuclear magnetic resonance (NMR) structures of mEGF and hEGF. The position and type of turns in the B-loop of mEGF and hEGF increase the interstrand distance of the antiparallel β-sheets thereby disrupting their structure. The interdomain flexibility of simulated hTGF-α structure is greater than in either mEGF or hEGF. The φ, ψ dihedrals of hTGF-α occupy two distinct populations of phase space corresponding to either a C7eq or an α-helical conformation. This change in dihedral angle is stabilized by Phe15 with Arg42 and Phe17 with Arg42 N-π weakly polar interactions that are present only in hTGF-α but not in mEGF or hEGF. Proteins 33:396-407, 1998. © 1998 Wiley-Liss, Inc.
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    Analysis of domain motions by approximate normal mode calculations (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 417-429 
    Details
    ISSN: 0887-3585
    Keywords: protein energy surface ; crambin ; lysozyme ; ATCase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The identification of dynamical domains in proteins and the description of the low-frequency domain motions are one of the important applications of numerical simulation techniques. The application of these techniques to large proteins requires a substantial computational effort and therefore cannot be performed routinely, if at all. This article shows how physically motivated approximations permit the calculation of low-frequency normal modes in a few minutes on standard desktop computers. The technique is based on the observation that the low-frequency modes, which describe domain motions, are independent of force field details and can be obtained with simplified mechanical models. These models also provide a useful measure for rigidity in proteins, allowing the identification of quasi-rigid domains. The methods are validated by application to three well-studied proteins, crambin, lysozyme, and ATCase. In addition to being useful techniques for studying domain motions, the success of the approximations provides new insight into the relevance of normal mode calculations and the nature of the potential energy surface of proteins. Proteins 33:417-429, 1998. © 1998 Wiley-Liss, Inc.
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    Helix-helix packing angle preferences for finite helix axes (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 457-459 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Recently, James Bowie addressed the question of how to normalize correctly the distribution of observed helix-helix packing angles in proteins (Bowie, Nature Struct. Biol. 4:915-917, 1997). A hitherto unrealized yet significant bias toward crossed packing angles was revealed. However, the derived random reference distribution of packing angles requires that helices have to be assumed as infinite in length. Here, we complement Bowie's analysis by consideration of the more realistic case where helices are of finite length. As a result, the statistical bias toward near perpendicular packings appears to be even stronger. Proteins 33:457-459, 1998. © 1998 Wiley-Liss, Inc.
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    A homology model for the human theta-class glutathione transferase T1-1 (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 444-454 
    Details
    ISSN: 0887-3585
    Keywords: hGSTT1-1 ; homology modeling ; menaphthyl sulfate ; dichloromethane ; dehalogenase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A manual threading approach is used to model the human glutathione transferase T1-1 based on the coordinates of the related Theta class enzyme T2-2. The low level of sequence identity (about 20%), found in the C-terminal extension in conjunction with a relative deletion of about five residues makes this a challenging modeling problem. The C-terminal extension contributes to the active site of the molecule and is thus of particular interest for understanding the molecular mechanism of the enzyme. Manual docking of known substrates and non-substrates has implicated potential candidates for the T1-1 catalytic residues involved in the dehalogenation and epoxide-ring opening activities. These include the conserved Theta class residues Arg 107, Trp 115, and the conserved GSTT1 subclass residue His 176. Also, the residue at position 234 is implicated in the modulation of T1-1 activity with different substrates between species. Proteins 33:444-454, 1998. © 1998 Wiley-Liss, Inc.
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    Intersubunit hydrogen bond acts as a global molecular switch in Escherichia coli aspartate transcarbamoylase (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 430-443 
    Details
    ISSN: 0887-3585
    Keywords: pyrimidine biosynthesis ; protein crystallography ; allostery ; long-range interactions ; site-directed mutagenesis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Tyr 165 in the catalytic subunit of Escherichia coli aspartate transcarbamoylase (ATCase, EC 2.1.3.2) forms an intersubunit hydrogen bond in the T state with Glu 239 in the 240s loop of a second catalytic subunit, which is broken in the T to R transition. Substitution of Tyr 165 by Phe lowers substrate affinity by approximately an order of magnitude and alters the pH profile for enzyme function. We have determined the crystal structure of Y165F at 2.4 Å resolution by molecular replacement, using a wild-type T state structure as the probe, and refined it to an R value of 25.2%. The Y165F mutation induces a global conformational change that is in the opposite direction to the T to R transition and therefore results in an extreme T state. The two catalytic trimers move closer by ∼0.14 Å and rotate by ∼0.2°, in the opposite direction to the T→R rotation; the two domains of each catalytic chain rotate by ∼2.1°, also in the opposite direction to the T→R transition; and the 240s loop adopts a new conformation. Residues 229 to 236 shift by ∼2.4 Å so that the active site is more open. Residues 237 to 244 rotate by ∼24.1°, altering interactions within the 240s loop and at the C1-C4 and C1-R4 interfaces. Arg 167, a key residue in domain closure and interactions with L-Asp, swings out from the active site to interact with Tyr 197. This crystal structure is consistent with the functional properties of Y165F, expands our knowledge of the conformational repertoire of ATCase, and indicates that the canonical T state does not represent an extreme. Proteins 33:430-443, 1998. © 1998 Wiley-Liss, Inc.
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    A hierarchical method for generating low-energy conformers of a protein-ligand complex (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 475-495 
    Details
    ISSN: 0887-3585
    Keywords: docking ; landscape ; dynamics ; dielectric ; affinity ; binding ; methotrexate ; thermolysin ; dihydrofolate reductase ; HIV protease ; generalized Born ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A novel dynamical protocol for finding the low-energy conformations of a protein-ligand complex is described. The energy functions examined consist of an empirical force field with four different dielectric screening models; the generalized Born/surface area model also is examined. Application of the method to three complexes of known crystal structure provides insights into the energy functions used for selecting low-energy docked conformations and into the structure of the binding-energy surface. Evidence is presented that the local energy minima of a ligand in a binding site are arranged in a hierarchical fashion. This observation motivates the construction of a hierarchical docking algorithm that substantially enriches the population of ligand conformations close to the crystal conformation. The algorithm is also adapted to permit docking into a flexible binding site and preliminary tests of this method are presented. Proteins 33:475-495, 1998. © 1998 Wiley-Liss, Inc.
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    Energy landscape of a native protein: Jumping-among-minima model (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 496-517 
    Details
    ISSN: 0887-3585
    Keywords: energy landscape ; hierarchical conformational substates ; molecular dynamics ; normal mode analysis ; principal component analysis ; jumping-among-minima model ; human lysozyme ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have investigated energy landscape of human lysozyme in its native state by using principal component analysis and a model, jumping-among-minima (JAM) model. These analyses are applied to 1 nsec molecular dynamics trajectory of the protein in water. An assumption embodied in the JAM model allows us to divide protein motions into intra-substate and inter-substate motions. By examining intra-substate motions, it is shown that energy surfaces of individual conformational substates are nearly harmonic and mutually similar. As a result of principal component analysis and JAM model analysis, protein motions are shown to consist of three types of collective modes, multiply hierarchical modes, singly hierarchical modes, and harmonic modes. Multiply hierarchical modes, the number of which accounts only for 0.5% of all modes, dominate contributions to total mean-square atomic fluctuation. Inter-substate motions are observed only in a small-dimensional subspace spanned by the axes of multiplyhierarchical and singly hierarchical modes. Inter-substate motions have two notable time components: faster component seen within 200 psec and slower component. The former involves transitions among the conformational substates of the low-level hierarchy, whereas the latter involves transitions of the higher level substates observed along the first four multiply hierarchical modes. We also discuss dependence of the subspace, which contains conformational substates, on time duration of simulation. Proteins 33:496-517, 1998. © 1998 Wiley-Liss, Inc.
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    Patterns of protein-fold usage in eight microbial genomes: A comprehensive structural census (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 518-534 
    Details
    ISSN: 0887-3585
    Keywords: structure databank ; superfold ; protein structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Eight microbial genomes are compared in terms of protein structure. Specifically, yeast, H. influenzae, M. genitalium, M. jannaschii, Synechocystis, M. pneumoniae, H. pylori, and E. coli are compared in terms of patterns of fold usage - whether a given fold occurs in a particular organism. Of the ∼340 soluble protein folds currently in the structure databank (PDB), 240 occur in at least one of the eight genomes, and 30 are shared amongst all eight. The shared folds are depleted in all-helical structure and enriched in mixed helix-sheet structure compared to the folds in the PDB. The top-10 most common of the shared 30 are enriched in superfolds, uniting many non-homologous sequence families, and are especially similar in overall architecture - eight having helices packed onto a central sheet. They are also very different from the common folds in the PBD, highlighting databank biases. Folds can be ranked in terms of expression as well as genome duplication. In yeast the top-10 most highly expressed folds are considerably different from the most highly duplicated folds. A tree can be constructed grouping genomes in terms of their shared folds. This has a remarkably similar topology to more conventional classifications, based on very different measures of relatedness. Finally, folds of membrane proteins can be analyzed through transmembrane-helix (TM) prediction. All the genomes appear to have similar usage patterns for these folds, with the occurrence of a particular fold falling off rapidly with increasing numbers of TM-elements, according to a “Zipf-like” law. This implies there are no marked preferences for proteins with particular numbers of TM-helices (e.g. 7-TM) in microbial genomes. Further information pertinent to this analysis is available at http://bioinfo.mbb.yale.edu/genome. Proteins 33:518-534, 1998. © 1998 Wiley-Liss, Inc.
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    The slow step of folding of Staphylococcus aureus PC1 β-lactamase involves the collapse of a surface loop rate limited by the Trans to Cis isomerization of a non-proline peptide bond (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 550-557 
    Details
    ISSN: 0887-3585
    Keywords: mutagenesis ; c.d. spectroscopy ; unfolding ; Ω-loop ; molten-globule ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We wished to test the hypothesis that the non proline cis to trans isomerization of the peptide bond at position 167 in the S. aureus β-lactamase PC1 exerts a significant controlling effect on the folding pathway of this enzyme. The previous data presented in support of this hypothesis could not rule out the effect of factors unrelated to non-proline cis/trans isomerization. We have used the plasmid pET9d to direct soluble overproduction of the S. aureus β-lactamase PC1 and a site-directed mutant (Ile 167 to Pro) in Escherichia coli. Following purification the proteins were subjected to a comparative analysis of the kinetics of unfolding and refolding using the techniques of near- and far-UV circular dichroism spectroscopy and fluorescence spectroscopy in conjunction with “double-jump” experiments. Results show that the fully-unfolded I167P mutant enzyme retains 20% of molecules in a fast-refolding form and that slower-refolding molecules fold faster than the recombinant wild-type enzyme. The final stage of folding involves folding of the Ω-loop into a conformation essential for enzymatic activity. In support of the original hypothesis, the folding of this Ω-loop is rate limited by the isomerization of the Glu 166-Ile 167 peptide bond. Proteins 33:550-557, 1998. © 1998 Wiley-Liss, Inc.
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    Domain motions in bacteriophage T4 lysozyme: A comparison between molecular dynamics and crystallographic data (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 31 (1998), S. 116-127 
    Details
    ISSN: 0887-3585
    Keywords: molecular dynamics ; X-ray crystallography ; essential dynamics ; lysozyme ; hinge bending ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A comparison of a series of extended molecular dynamics (MD) simulations of bacteriophage T4 lysozyme in solvent with X-ray data is presented. Essential dynamics analyses were used to derive collective fluctuations from both the simulated trajectories and a distribution of crystallographic conformations. In both cases the main collective fluctuations describe domain motions. The protein consists of an N- and C-terminal domain connected by a long helix. The analysis of the distribution of crystallographic conformations reveals that the N-terminal helix rotates together with either of these two domains. The main domain fluctuation describes a closure mode of the two domains in which the N-terminal helix rotates concertedly with the C-terminal domain, while the domain fluctuation with second largest amplitude corresponds to a twisting mode of the two domains, with the N-terminal helix rotating concertedly with the N-terminal domain. For the closure mode, the difference in hinge-bending angle between the most open and most closed X-ray structure along this mode is 49 degrees. In the MD simulation that shows the largest fluctuation along this mode, a rotation of 45 degrees was observed. Although the twisting mode has much less freedom than the closure mode in the distribution of crystallographic conformations, experimental results suggest that it might be functionally important. Interestingly, the twisting mode is sampled more extensively in all MD simulations than it is in the distribution of X-ray conformations. Proteins 31:116-127, 1998. © 1998 Wiley-Liss, Inc.
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    Homology modeling of an RNP domain from a human RNA-binding protein: Homology-constrained energy optimization provides a criterion for distinguishing potential sequence alignments (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 558-566 
    Details
    ISSN: 0887-3585
    Keywords: Drosophila melanogaster couch potato protein ; Werner's syndrome ; restrained molecular dynamics ; simulated annealing ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have recently described an automated approach for homology modeling using restrained molecular dynamics and simulated annealing procedures (Li et al, Protein Sci., 6:956-970,1997). We have employed this approach for constructing a homology model of the putative RNA-binding domain of the human RNA-binding protein with multiple splice sites (RBP-MS). The regions of RBP-MS which are homologous to the template protein snRNP U1A were constrained by “homology distance constraints,” while the conformation of the non-homologous regions were defined only by a potential energy function. A full energy function without explicit solvent was employed to ensure that the calculated structures have good conformational energies and are physically reasonable. The effects of misalignment of the unknown and the template sequences were also explored in order to determine the feasibility of this homology modeling method for distinguishing possible sequence alignments based on considerations of the resulting conformational energies of modeled structures. Differences in the alignments of the unknown and the template sequences result in significant differences in the conformational energies of the calculated homology models. These results suggest that conformational energies and residual constraint violations in these homology-constrained simulated annealing calculations can be used as criteria to distinguish between correct and incorrect sequence alignments and chain folds. Proteins 33:558-566, 1998. © 1998 Wiley-Liss, Inc.
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    Structural basis of increased resistance to thermal denaturation induced by single amino acid substitution in the sequence of β-glucosidase A from Bacillus polymyxa (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 567-576 
    Details
    ISSN: 0887-3585
    Keywords: bacterial cellobiase ; mutated β-glucosidase ; family 1 ; thermoresistance ; X-ray structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The increasing development of the biotechnology industry demands the design of enzymes suitable to be used in conditions that often require broad resistance against adverse conditions. β-glucosidase A from Bacillus polymyxa is an interesting model for studies of protein engineering. This is a well-characterized enzyme, belonging to glycosyl hydrolase family 1. Its natural substrate is cellobiose, but is also active against various artificial substrates. In its native state has an octameric structure. Its subunit conserves the general (α/β)8 barrel topology of its family, with the active site being in a cavity defined along the axis of the barrel. Using random-mutagenesis, we have identified several mutations enhancing its stability and it was found that one them, the E96K substitution, involved structural changes. The crystal structure of this mutant has been determined by X-ray diffraction and compared with the native structure. The only difference founded between both structures is a new ion pair linking Lys96 introduced at the N-terminus of helix α2, to Asp28, located in one of the loops surrounding the active-site cavity. The new ion pair binds two segments of the chain that are distant in sequence and, therefore, this favorable interaction must exert a determinant influence in stabilizing the tertiary structure. Furthermore, analysis of the crystallographic isotropic temperature factors reveals that, as a direct consequence of the introduced ion pair, an unexpected decreased mobility of secondary structure units of the barrel which are proximal to the site of mutation is observed. However, this effect is observed only in the surrounding of one of the partners forming the salt bridge and not around the other. These results show that far-reaching effects can be achieved by a single amino acid replacement within the protein structure. Consequently, the identification and combination of a few single substitutions affecting stability may be sufficient to obtain a highly resistant enzyme, suitable to be used under extreme conditions. Proteins 33:567-576, 1998. © 1998 Wiley-Liss, Inc.
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  • 152
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    Mass spectrometry (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 1-2 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: No abstract.
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  • 153
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    Kinetics and interaction studies between cytochrome c3 and Fe-only hydrogenase from Desulfovibrio vulgaris hildenborough (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 590-600 
    Details
    ISSN: 0887-3585
    Keywords: [Fe] hydrogenase ; protein-protein interaction ; BIAcore analysis ; crystallization ; cooperativity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Hydrogenases from Desulfovibrio are found to catalyze hydrogen uptake with low potential multiheme cytochromes, such as cytochrome c3, acting as acceptors. The production of Fe-only hydrogenase from Desulfovibrio vulgaris Hildenborough was improved with respect to the growth phase and media to determine the best large-scale bacteria growth conditions. The interaction and electron transfer from Fe-only hydrogenase to multiheme cytochrome has been studied in detail by both BIAcore and steady-state measurements. The electron transfer between [Fe] hydrogenase and cytochrome c3 appears to be a cooperative phenomenon (h = 1.37). This behavior could be related to the conductivity properties of multihemic cytochromes. An apparent dissociation constant was determined (2 × 10-7 M). The importance of the cooperativity for contrasting models proposed to describe the functional role of the hydrogenase/cytochrome c3 complex is discussed. Presently, the only determined structure is from [NiFe] hydrogenase and there are no obvious similarities between [NiFe] and [Fe] hydrogenase. Furthermore, no crystallographic data are available concerning [Fe] hydrogenase. The first results on crystallization and X-ray crystallography are reported. Proteins 33:590-600, 1998. © 1998 Wiley-Liss, Inc.
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  • 154
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    Surface properties of adipocyte lipid-binding protein: Response to lipid binding, and comparison with homologous proteins (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 577-589 
    Details
    ISSN: 0887-3585
    Keywords: electrostatics ; accessible surface area ; fatty acid binding proteins ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Adipocyte lipid-binding protein (ALBP) is one of a family of intracellular lipid-binding proteins (iLBPs) that bind fatty acids, retinoids, and other hydrophobic ligands. The different members of this family exhibit a highly conserved three-dimensional structure; and where structures have been determined both with (holo) and without (apo) bound lipid, observed conformational changes are extremely small (Banaszak, et al., 1994, Adv. Prot. Chem. 45, 89; Bernlohr, et al., 1997, Annu. Rev. Nutr. 17, 277). We have examined the electrostatic, hydrophobic, and water accessible surfaces of ALBP in the apo form and of holo forms with a variety of bound ligands. These calculations reveal a number of previously unrecognized changes between apo and holo ALBP, including: 1) an increase in the overall protein surface area when ligand binds, 2) expansion of the binding cavity when ligand is bound, 3) clustering of individual residue exposure increases in the area surrounding the proposed ligand entry portal, and 4) ligand-binding dependent variation in the topology of the electrostatic potential in the area surrounding the ligand entry portal. These focused analyses of the crystallographic structures thus reveal a number of subtle but consistent conformational and surface changes that might serve as markers for differential targeting of protein-lipid complexes within the cell. Most changes are consistent from ligand to ligand, however there are some ligand-specific changes. Comparable calculations with intestinal fatty-acid-binding protein and other vertebrate iLBPs show differences in the electrostatic topology, hydrophobic topology, and in localized changes in solvent exposure near the ligand entry portal. These results provide a basis toward understanding the functional and mechanistic differences among these highly structurally homologous proteins. Further, they suggest that iLBPs from different tissues exhibit one of two predominant end-state structural distributions of the ligand entry portal. Proteins 33:577-589, 1998. © 1998 Wiley-Liss, Inc.
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  • 155
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    Structural models of the bovine papillomavirus E5 protein (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 601-612 
    Details
    ISSN: 0887-3585
    Keywords: platelet-derived growth factor receptor ; E5 protein ; bovine papillomavirus ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The bovine papillomavirus E5 protein is thought to be a type II integral membrane protein that exists as a disulfide-linked homodimer in transformed cells. Polarized-infrared measurements show that the E5 dimer in membrane bilayers is largely α-helical and has a transmembrane orientation. Computational searches of helix-helix conformations reveal two possible low-energy dimer structures. Correlation of these results with previous mutagenesis studies on the E5 protein suggests how the E5 dimer may serve as a molecular scaffold for dimerization and ligand-independent activation of the PDGF-β receptor. We propose that on each face of the E5 dimer a PDGF-β receptor molecule interacts directly with Gln17 from one E5 monomer and with Asp33 from the other E5 monomer. This model accounts for the requirement of Gln17 and Asp33 for complex formation and explains genetic results that dimerization of the E5 protein is essential for cell transformation. Proteins 33:601-612, 1998. © 1998 Wiley-Liss, Inc.
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  • 156
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    Dissection of multi-protein complexes using mass spectrometry: Subunit interactions in transthyretin and retinol-binding protein complexes (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 3-11 
    Details
    ISSN: 0887-3585
    Keywords: mass spectrometry ; time-of-flight ; nanoflow electrospray ; transthyretin ; retinol binding protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Complexes formed between transthyretin and retinol-binding protein prevent loss of retinol from the body through glomerular filtration. The interactions between these proteins have been examined by electrospray ionization combined with time-of-flight mass analysis. Conditions were found whereby complexes of these proteins, containing from four to six protein molecules with up to two ligands, are preserved in the gas phase. Analysis of the mass spectra of these multimeric species gives the overall stoichiometry of the protein subunits and provides estimates for solution dissociation constants of 1.9 ± 1.0 × 10-7 M for the first and 3.5 ± 1.0 × 10-5 M for the second retinol-binding protein molecule bound to a transthyretin tetramer. Dissociation of these protein assemblies within the gas phase of the mass spectrometer shows that each retinol-binding protein molecule interacts with three transthyretin molecules. Mass spectral analysis illustrates not only a correlation with solution behavior and crystallographic data of a closely related protein complex but also exemplifies a general method for analysis of multi-protein assemblies. Proteins Suppl. 2:3-11, 1998. © 1998 Wiley-Liss, Inc.
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  • 157
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    GLASS: A tool to visualize protein structure prediction data in three dimensions and evaluate their consistency (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 30 (1998), S. 339-351 
    Details
    ISSN: 0887-3585
    Keywords: protein structure prediction ; ab initio methods ; fold recognition ; molecular graphics ; model evaluation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: When a protein sequence does not share any significant sequence similarity with a protein of known structure, homology modeling cannot be applied. However, many novel and interesting methods, such as secondary structure prediction, fold recognition, and prediction of long-range interactions, are being developed and have been shown to be reasonably successful in predicting protein structures from sequence data and evolutionary information. The a priori evaluation of the correctness of a prediction obtained by one of these methods is however often problematic. Consequently, it is important to use all available information provided by as many different methods as possible and all the available experimental data about the protein of interest, since the consistency of the results is indicative of the reliability of the prediction. Hence the need has arisen for suitable tools able to compare results provided by different methods and evaluate their consistency. We have therefore constructed GLASS, a general platform to read, visualize, compare, and evaluate prediction results from many different sources and to project these prediction results into three dimensions. In addition, GLASS allows the comparison of selected parameters calculated for a model with the distribution observed in real protein structures, thus providing an easy way to test new methods for evaluating the likelihood of different structural models. GLASS can be considered as a “workbench” for structural predictions useful to both experimentalists and theoreticians. Proteins 30:339-351, 1998. © 1998 Wiley-Liss, Inc.
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  • 158
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    IMPALA: A simple restraint field to simulate the biological membrane in molecular structure studies (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 30 (1998), S. 357-371 
    Details
    ISSN: 0887-3585
    Keywords: membrane ; protein ; structure ; prediction ; hydrophobicity ; computer ; magainin ; melittin ; 18A ; M2δ ; PGLa ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The lipid bilayer is crucial for the folding of integral membrane proteins. This article presents an empirical method to account for water-lipid interfaces in the insertion of molecules interacting with bilayers. The interactions between the molecule and the bilayer are described by restraint functions designed to mimic the membrane effect. These functions are calculated for each atom and are proportional to the accessible surface of the latter. The membrane is described as a continuous medium whose properties are varying along the axis perpendicular to the bilayer plane. The insertion is analyzed by a Monte Carlo procedure applied to the restraint functions. The method was successfully applied to small α peptides of known configurations. It provides insights of the behaviors of the peptide dynamics that cannot be obtained with statistical approaches (e.g., hydropathy analysis). Proteins 30:357-371, 1998. © 1998 Wiley-Liss, Inc.
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  • 159
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    Discrimination between native and intentionally misfolded conformations of proteins: ES/IS, a new method for calculating conformational free energy that uses both dynamics simulations with an explicit solvent and an implicit solvent continuum modelYury N. Vorobjev is on leave from the Novosibirsk Institute of Bioorganic Chemistry, Novosibirsk, Russia. (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 399-413 
    Details
    ISSN: 0887-3585
    Keywords: protein stability ; conformational free energy ; structure discrimination ; molecular dynamics ; molecular surface ; continuum solvent model ; continuum dielectric model ; boundary element method ; protein entropy ; quasi-harmonic approximation ; deliberately misfolded protein structures ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A new method for calculating the total conformational free energy of proteins in water solvent is presented. The method consists of a relatively brief simulation by molecular dynamics with explicit solvent (ES) molecules to produce a set of microstates of the macroscopic conformation. Conformational energy and entropy are obtained from the simulation, the latter in the quasi-harmonic approximation by analysis of the covariance matrix. The implicit solvent (IS) dielectric continuum model is used to calculate the average solvation free energy as the sum of the free energies of creating the solute-size hydrophobic cavity, of the van der Waals solute-solvent interactions, and of the polarization of water solvent by the solute's charges. The reliability of the solvation free energy depends on a number of factors: the details of arrangement of the protein's charges, especially those near the surface; the definition of the molecular surface; and the method chosen for solving the Poisson equation. Molecular dynamics simulation in explicit solvent relaxes the protein's conformation and allows polar surface groups to assume conformations compatible with interaction with solvent, while averaging of internal energy and solvation free energy tend to enhance the precision. Two recently developed methods - SIMS, for calculation of a smooth invariant molecular surface, and FAMBE, for solution of the Poisson equation via a fast adaptive multigrid boundary element - have been employed. The SIMS and FAMBE programs scale linearly with the number of atoms. SIMS is superior to Connolly's MS (molecular surface) program: it is faster, more accurate, and more stable, and it smooths singularities of the molecular surface. Solvation free energies calculated with these two programs do not depend on molecular position or orientation and are stable along a molecular dynamics trajectory. We have applied this method to calculate the conformational free energy of native and intentionally misfolded globular conformations of proteins (the EMBL set of deliberately misfolded proteins) and have obtained good discrimination in favor of the native conformations in all instances. Proteins 32:399-413, 1998. © 1998 Wiley-Liss, Inc.
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  • 160
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    Statistical mechanics of protein folding by exhaustive enumeration (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 425-437 
    Details
    ISSN: 0887-3585
    Keywords: theory of protein folding ; folding funnel ; folding thermodynamics ; folding kinetics ; conformation space ; sequence/structure compatibility ; thermal denaturation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: It is hard to construct theories for the folding of globular proteins because they are large and complicated molecules having enormous numbers of nonnative conformations and having native states that are complicated to describe. Statistical mechanical theories of protein folding are constructed around major simplifying assumptions about the energy as a function of conformation and/or simplifications of the representation of the polypeptide chain, such as one point per residue on a cubic lattice. It is not clear how the results of these theories are affected by their various simplifications. Here we take a very different simplification approach where the chain is accurately represented and the energy of each conformation is calculated by a not unreasonable empirical function. However, the set of amino acid sequences and allowed conformations is so restricted that it becomes computationally feasible to examine them all. Hence we are able to calculate melting curves for thermal denaturation as well as the detailed kinetic pathway of refolding. Such calculations are based on a novel representation of the conformations as points in an abstract 12-dimensional Euclidean conformation space. Fast folding sequences have relatively high melting temperatures, native structures with relatively low energies, small kinetic barriers between local minima, and relatively many conformations in the global energy minimum's watershed. In contrast to other folding theories, these models show no necessary relationship between fast folding and an overall funnel shape to the energy surface, or a large energy gap between the native and the lowest nonnative structure, or the depth of the native energy minimum compared to the roughness of the energy landscape. Proteins 32:425-437, 1998. © 1998 Wiley-Liss, Inc.
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  • 161
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    Full-matrix least-squares refinement of lysozymes and analysis of anisotropic thermal motion (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 30 (1998), S. 232-243 
    Details
    ISSN: 0887-3585
    Keywords: turkey lysozyme ; human lysozyme ; crystal structure ; protein structure ; structure refinement ; protein crystal ; atomic resolution ; rigid-body motion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Crystal structures of turkey egg lysozyme (TEL) and human lysozyme (HL) were refined by full-matrix least-squares method using anisotropic temperature factors. The refinement converged at the conventional R-values of 0.104 (TEL) and 0.115 (HL) for reflections with Fo 〉 0 to the resolution of 1.12 Å and 1.15 Å, respectively. The estimated r.m.s. coordinate errors for protein atoms were 0.031 Å (TEL) and 0.034 Å (HL). The introduction of anisotropic temperature factors markedly reduced the R-value but did not significantly affect the main chain coordinates. The degree of anisotropy of atomic thermal motion has strong positive correlation with the square of distance from the molecular centroid. The ratio of the radial component of thermal ellipsoid to the r.m.s. magnitude of three principal components has negative correlation with the distance from the molecular centroid, suggesting the domination of libration rather than breathing motion. The TLS model was applied to elucidate the characteristics of the rigid-body motion. The TLS tensors were determined by the least-squares fit to observed temperature factors. The profile of the magnitude of reproduced temperature factors by the TLS method well fitted to that of observed Beqv. However, considerable disagreement was observed in the shape and orientation of thermal ellipsoid for atoms with large temperature factors, indicating the large contribution of local motion. The upper estimate of the external motion, 67% (TEL) and 61% (HL) of Beqv, was deduced from the plot of the magnitude of TLS tensors determined for main chain atoms which were grouped into shells according to the distance from the center of libration. In the external motion, the translational portion is predominant and the contribution of libration and screw motion is relatively small. The internal motion, estimated by subtracting the upper estimate of the external motion from the observed temperature factor, is very similar between TEL and HL in spite of the difference in 54 of 130 amino acid residues and in crystal packing, being suggested to reflect the intrinsic internal motion of chicken-type lysozymes. Proteins 30:232-243, 1998. © 1998 Wiley-Liss, Inc.
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  • 162
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    Mapping the active site of factor Xa by selective inhibitors: An NMR and MD study (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 30 (1998), S. 264-274 
    Details
    ISSN: 0887-3585
    Keywords: factor Xa ; serine proteinases ; blood coagulation ; active site inhibitors ; transferred NOE ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The structure of two selective inhibitors, Ac-Tyr-Ile-Arg-Ile-Pro-NH2 and Ac-(4-Amino-Phe)-(Cyclohexyl-Gly)-Arg-NH2, in the active site of the blood clotting enzyme factor Xa was determined by using transferred nuclear Overhauser effect nuclear magnetic resonance (NMR) spectroscopy. They represent a family of peptidic inhibitors obtained by the screening of a vast combinatorial library. Each structure was first calculated by using standard computational procedures (distance geometry, simulated annealing, energy minimization) and then further refined by systematic search of the conformation of the inhibitor docked in the active site and repeating the simulated annealing and energy minimization. The final structure was optimized by molecular dynamics simulations of the inhibitor-complex in water. The NMR restraints were kept throughout the refinement. The inhibitors assume a compact, very well defined conformation, embedded into the substrate binding site not in the same way as a substrate, blocking thus the catalysis. The model allows to explain the mode of action, affinity, and specificity of the peptides and to map the active site. Proteins 30:264-279, 1998. © 1998 Wiley-Liss, Inc.
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    Flexible docking allowing induced fit in proteins: Insights from an open to closed conformational isomersThe opinions expressed in this article are those of the authors and do not reflect the views or policies of the DHHS or the U.S. Government. The mention of trade names, commercial products, or organizations does not imply endorsement of the U.S. Government. (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 159-174 
    Details
    ISSN: 0887-3585
    Keywords: molecular recognition ; flexible docking ; protein-ligand interaction ; induced fit ; structure-based drug design ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Here we dock a ligand onto a receptor surface allowing hinge-bending domain/substructural movements. Our approach mimics and manifests induced fit in molecular recognition. All angular rotations are allowed on the one hand, while a conformational space search is avoided on the other. Rather than dock each of the molecular parts separately with subsequent reconstruction of the consistently docked molecules, all parts are docked simultaneously while still utilizing the position of the hinge from the start. Like pliers closing on a screw, the receptor automatically closes on its ligand in the best surface-matching way. Movements are allowed either in the ligand or in the larger receptor, hence reproducing induced molecular fit. Hinge bending movements are frequently observed when molecules associate. There are numerous examples of open versus closed conformations taking place upon binding. Such movements are observed when the substrate binds to its respective enzyme. In particular, such movements are of interest in allosteric enzymes. The movements can involve entire domains, subdomains, loops, (other) secondary structure elements, or between any groups of atoms connected by flexible joints. We have implemented the hinges at points and at bonds. By allowing 3-dimensional (3-D) rotation at the hinge, several rotations about (consecutive or nearby) bonds are implicitly taken into account. Alternatively, if required, the point rotation can be restricted to bond rotation. Here we illustrate this hinge-bending docking approach and the insight into flexibility it provides on a complex of the calmodulin with its M13 ligand, positioning the hinges either in the ligand or in the larger receptor. This automated and efficient method is adapted from computer vision and robotics. It enables utilizing entire molecular surfaces rather than focusing a priori on active sites. Hence, allows attaining the overall optimally matching surfaces, the extent and type of motions which are involved. Here we do not treat the conformational flexibility of side-chains or of very small pieces of the molecules. Therefore, currently available methods addressing these issues and the method presented here, are complementary to each other, expanding the repertoire of computational docking tools foreseen to aid in studies of recognition, conformational flexibility and drug design. Proteins 32:159-174, 1998. © 1998 Wiley-Liss, Inc.
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    Effects of the T→R transition on the electrostatic properties of E. coli aspartate transcarbamylaseDr. Allewell was supported by the University of Minnesota. The facilities of the Minnesota Supercomputer Center were used for some calculations. (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 200-210 
    Details
    ISSN: 0887-3585
    Keywords: electrostatics ; allostery ; modeling ; signal transduction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Aspartate transcarbamylase is a large (310 kD), multisubunit protein that binds substrates cooperatively and undergoes a large change in quaternary structure when substrates bind. The forces that drive this transition are poorly understood. We evaluated the electrostatic component of these forces by using finite difference and multigrid methods to solve the nonlinear Poisson-Boltzmann equation for complexes of the enzyme with several substrates and substrate analogs. The results have been compared with calculations for the unliganded protein. While pK½ values of most ionizable residues fall within 3 pH units of values for model compounds, 31 have pK½ values that fall outside the range 0-17. Many of these residues are at the active site, where they interact with the highly charged substrate, in the 80s loop or 240s loop or interact with these loops. The pK½ values of eight ionizable residues related by the twofold molecular axes differ by more than 3 pH units, providing additional evidence for asymmetry within the crystal. As in the unliganded structure, a set of residues forms a network in which ionizable groups with Wij values greater than 2 kcal-m-1 are separated by distances greater than 5 Å. Some residues participate in this network in both the unliganded and N-phosphonacetyl-L-aspartate (PALA)-liganded structure, while others are found in only one structure. The network is more extensive in the PALA-liganded structure than in the unliganded structure, but consists of two separate networks in the two halves of the molecule. Proteins 32:200-210, 1998. © 1998 Wiley-Liss, Inc.
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    Functional protein domains from the thermally driven motion of polypeptide chains: A proposal (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 223-228 
    Details
    ISSN: 0887-3585
    Keywords: protein structure ; phosphorylation ; glycosylation ; protein-protein interactions ; regulation ; molecular springs ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: It is proposed that the thermally driven motion of certain polypeptide chains, including those that are part of an otherwise stable folded protein, produces time-averaged three-dimensional domains that confer unique functions to a protein. These domains may be controlled by collapsing the polypeptide into an enthalpically favored structure, or extending it into an entropically dominated form. In the extended form, these domains occupy a relatively large space, which may be used to regulate protein-protein interactions and confer mechanical properties to proteins. This “entropic bristle” model makes several predictions about the structure and properties of these domains, and the predictions are used to reevaluate a range of biophysical studies on proteins. The outcome of the analysis suggests that the entropic bristle can be used to explain a wide range of disparate and apparently unrelated experimental observations. Proteins 32:223-228, 1998. © 1998 Wiley-Liss, Inc.
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    Role of quaternary structure in muscle creatine kinase stability: Tryptophan 210 is important for dimer cohesion (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 43-51 
    Details
    ISSN: 0887-3585
    Keywords: dimeric mutant protein ; conformational stability ; guanidinium hydrochloride equilibrium denaturation ; intermediate state ; molten globule ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A mutant of the dimeric rabbit muscle creatine kinase (MM-CK) in which tryptophan 210 was replaced has been studied to assess the role of this residue in dimer cohesion and the importance of the dimeric state for the native enzyme stability. Wild-type protein equilibrium unfolding induced by guanidine hydrochloride occurs through intermediate states with formation of a molten globule and a premolten globule. Unlike the wild-type enzyme, the mutant inactivates at lower denaturant concentration and the loss of enzymatic activity is accompanied by the dissociation of the dimer into two apparently compact monomers. However, the Stokes radius of the monomer increases with denaturant concentration as determined by size exclusion chromatography, indicating that, upon monomerization, the protein structure is destabilized. Binding of 8-anilinonaphthalene-1-sulfonate shows that the dissociated monomer exposes hydrophobic patches at its surface, suggesting that it could be a molten globule. At higher denaturant concentrations, both wild-type and mutant follow similar denaturation pathways with formation of a premolten globule around 1.5-M guanidine, indicating that tryptophan 210 does not contribute to a large extent to the monomer conformational stability, which may be ensured in the dimeric state through quaternary interactions. Proteins 32:43-51, 1998. © 1998 Wiley-Liss, Inc.
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    Testing a new Monte Carlo algorithm for protein folding (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 52-66 
    Details
    ISSN: 0887-3585
    Keywords: heteropolymers ; lattice models ; lattice polymers ; Monte Carlo ; protein folding ; protein structure prediction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We demonstrate that the recently proposed pruned-enriched Rosenbluth method (PERM) (Grassberger, Phys. Rev. E 56:3682, 1997) leads to extremely efficient algorithms for the folding of simple model proteins. We test it on several models for lattice heteropolymers, and compare it to published Monte Carlo studies of the properties of particular sequences. In all cases our method is faster than the previous ones, and in several cases we find new minimal energy states. In addition to producing more reliable candidates for ground states, our method gives detailed information about the thermal spectrum and thus allows one to analyze thermodynamic aspects of the folding behavior of arbitrary sequences. Proteins 32:52-66, 1998. © 1998 Wiley-Liss, Inc.
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    Design of proteins with hydrophobic and polar amino acids (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 80-87 
    Details
    ISSN: 0887-3585
    Keywords: proteins ; inverse design ; negative design ; numerical optimization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A two amino acid (hydrophobic and polar) scheme is used to perform the design on target conformations corresponding to the native states of 20 single chain proteins. Strikingly, the percentage of successful identification of the nature of the residues benchmarked against naturally occurring proteins and their homologues is around 75%, independent of the complexity of the design procedure. Typically, the lowest success rate occurs for residues such as alanine that have a high secondary structure functionality. Using a simple lattice model, we argue that one possible shortcoming of the model studied may involve the coarse-graining of the 20 kinds of amino acids into just two effective types. Proteins 32:80-87, 1998. © 1998 Wiley-Liss, Inc.
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    Can one predict protein stability? An attempt to do so for residue 133 of T4 lysozyme using a combination of free energy derivatives, PROFEC, and free energy perturbation methods (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 438-458 
    Details
    ISSN: 0887-3585
    Keywords: mutant T4 lysozyme ; S-2-amino-3-cyclopentylpropanoic acid ; free energy simulation ; protein stability ; packing interaction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Free energy derivatives, pictorial representation of free energy changes (PROFEC) and free energy perturbation methods were employed to suggest the modifications that may improve the stability of a mutant T4 lysozyme with a S-2-amino-3-cyclopentylpropanoic acid residue (Cpe) at position 133. The free energy derivatives and PROFEC methods were used to locate promising sites where modifications may be introduced. The effects of several candidate modifications on the enzyme's stability were analyzed by the free energy perturbation method. We found that this scheme is able to effectively suggest modifications that may increase the enzyme's stability. The modifications investigated are the introduction of a methyl, a tert-butyl or a trifluoromethyl group at the Cε2 position and a cyclopropyl group between the Cδ2 and Cε2 position on the cyclopentyl ring. The stereochemistry of the introduced groups (in the α or β configurations) was studied. Our calculations predict that the introduction of a methyl group in the α configuration or a cyclopropyl group in the β configuration will increase the stability of the enzyme; the introduction of the two groups in the other configurations and the other modifications will decrease the stability of the enzyme. The results indicate that packing interactions can strongly influence the stability of the enzyme. Proteins 32:438-458, 1998. © 1998 Wiley-Liss, Inc.
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    Multiple conformational states of a new hematopoietic cytokine (megakaryocyte growth and development factor): pH- and urea-induced denaturation (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 495-503 
    Details
    ISSN: 0887-3585
    Keywords: megakaryocyte growth and development factor ; thrombopoietin ; cytokine ; equilibrium denaturation ; conformation ; protein folding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The effect of pH and urea on the conformation of recombinant human megakaryocyte growth and development factor (rHuMGDF) was determined by circular dichroism, intrinsic fluorescence spectroscopy, and equilibrium ultracentrifugation. The conformation of rHuMGDF was dependent on pH and urea concentration. Multiple folding forms were evidenced by multiple pH-induced transitions and urea-induced equilibrium transitions that deviated from a simple two-state process. In neutral to alkaline pH, rHuMGDF exists as a monomer, but an acid-induced conformational state self-associates to form a soluble aggregate. A folding intermediate(s) was observed with a more stable secondary structure than tertiary structure and was dependent on the pH of the urea-induced denaturation. The differences in the stabilities of the folding states were most distinct in the pH range of 4.5 to 6.5. The presence of intermediates in the folding pathway of rHuMGDF are similar to findings of previous studies of related growth factors that share a common three-dimensional structure. Proteins 32:495-503, 1998. © 1998 Wiley-Liss, Inc.
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    Structural basis for specificity of papain-like cysteine protease proregions toward their cognate enzymes (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 504-514 
    Details
    ISSN: 0887-3585
    Keywords: cysteine protease ; zymogens ; inhibition ; caricain ; cathepsin L ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Synthetic peptides corresponding to the proregions of papain-like cysteine proteases have been shown to be good and selective inhibitors of their parental enzymes. The molecular basis for their selectivity, quite remarkable in some cases, is not fully understood. The recent determination of the crystal structures of three distinct papain-like cysteine protease zymogens allows detailed structural comparisons to be made. The reasons for the specificity shown by each proregion toward its cognate enzyme are explained in terms of the three-dimensional structure of the proregion and the interface between the mature enzyme and the proregion. These comparisons reveal that insertion and substitution of amino acids within the proregion cause major rearrangement of sidechains on the enzyme/proregion interface, allowing detailed surface and charge recognition. Proteins 32:504-514, 1998. © 1998 Wiley-Liss, Inc.
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    Analytical shape computation of macromolecules: I. molecular area and volume through alpha shape (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 1-17 
    Details
    ISSN: 0887-3585
    Keywords: solvent accessible surface ; molecular surface ; area and volume ; Delaunay complex ; alpha shape ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The size and shape of macromolecules such as proteins and nucleic acids play an important role in their functions. Prior efforts to quantify these properties have been based on various discretization or tessellation procedures involving analytical or numerical computations. In this article, we present an analytically exact method for computing the metric properties of macromolecules based on the alpha shape theory. This method uses the duality between alpha complex and the weighted Voronoi decomposition of a molecule. We describe the intuitive ideas and concepts behind the alpha shape theory and the algorithm for computing areas and volumes of macromolecules. We apply our method to compute areas and volumes of a number of protein systems. We also discuss several difficulties commonly encountered in molecular shape computations and outline methods to overcome these problems. Proteins 33:1-17, 1998. © 1998 Wiley-Liss, Inc.
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    Reactivation of the totally inactive pancreatic lipase RP1 by structure-predicted point mutationsThe key results were presented by C. Cambillau on September 20th, 1997 during the European meeting held at Como (Italy) on: “Lipases and lipids: structure, specificity and applications in biocatalysis.”A. Roussel and J. de Caro contributed in equal proportions to the present study. (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 32 (1998), S. 523-531 
    Details
    ISSN: 0887-3585
    Keywords: pancreatic juice ; pancreatic lipase ; glycerides ; X-ray structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Both classical pancreatic lipase (DPL) and pancreatic lipase-related protein 1 (DPLRP1) have been found to be secreted by dog exocrine pancreas. These two proteins were purified to homogeneity from canine pancreatic juice and no significant catalytic activity was observed with dog PLRP1 on any of the substrates tested: di- and tri-glycerides, phospholipids, etc. DPLRP1 was crystallized and its structure solved by molecular replacement and refined at a resolution of 2.10 Å. Its structure is similar to that of the classical PL structures in the absence of any inhibitors or micelles. The lid domain that controls the access to the active site was found to have a closed conformation. An amino-acid substitution (Ala 178 Val) in the DPLRP1 may result in a steric clash with one of the acyl chains observed in the structures of a C11 alkyl phosphonate inhibitor, a transition state analogue, bound to the classical PL. This substitution was suspected of being responsible for the absence of DPLRP1 activity. The presence of Val and Ala residues in positions 178 and 180, respectively, are characteristic of all the known PLRP1, whereas Ala and Pro residues are always present in the same positions in all the other members of the PL gene family. Introducing the double mutation Val 178 Ala and Ala 180 Pro into the human pancreatic RP1 (HPLRP1) gene yielded a well expressed and folded enzyme in insect cells. This enzyme is kinetically active on triglycerides. Our findings on DPLRP1 and HPLRP1 are therefore likely to apply to all the RP1 lipases. Proteins 32:523-531, 1998. © 1998 Wiley-Liss, Inc.
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    Predicting structural effects in HIV-1 protease mutant complexes with flexible ligand docking and protein side-chain optimization (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 295-310 
    Details
    ISSN: 0887-3585
    Keywords: molecular recognition ; Monte Carlo docking ; dead-end-elimination ; rotamer library ; correlated energy landscapes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We present a computational approach for predicting structures of ligand-protein complexes and analyzing binding energy landscapes that combines Monte Carlo simulated annealing technique to determine the ligand bound conformation with the dead-end elimination algorithm for side-chain optimization of the protein active site residues. Flexible ligand docking and optimization of mobile protein side-chains have been performed to predict structural effects in the V32I/I47V/V82I HIV-1 protease mutant bound with the SB203386 ligand and in the V82A HIV-1 protease mutant bound with the A77003 ligand. The computational structure predictions are consistent with the crystal structures of these ligand-protein complexes. The emerging relationships between ligand docking and side-chain optimization of the active site residues are rationalized based on the analysis of the ligand-protein binding energy landscape. Proteins 33:295-310, 1998. © 1998 Wiley-Liss, Inc.
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    Structure and dynamic properties of the single disulfide-deficient α-amylase inhibitor [C45A/C73A]tendamistat: An NMR study (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 285-294 
    Details
    ISSN: 0887-3585
    Keywords: 2D NMR spectroscopy ; assignment ; relaxation ; protein mutant ; disulfide bonds ; 13C natural abundance ; 15N isotope labeling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Covalent linkages such as disulfide bonds are important for the stabilization of proteins. In the present NMR study we compare the structure and the dynamics of the single disulfide-deficient variant C45A/C73A of the α-amylase inhibitor tendamistat and the wild-type protein, which contains two disulfide bonds (C11-C27 and C45-C73). Complete proton assignment was achieved by standard homonuclear 2D techniques for the variant. Chemical shift differences, intra-strand NOE effects and protected amide proton were used to compare the connectivity of the secondary structure elements of variant and wild-type. Dynamic properties of the wild-type protein were studied by 13Cα heteronuclear NOE experiments with carbon in natural abundance. 15N isotope labeling was necessary to obtain the relaxation parameters of the variant, because of sample degradation. The 15N resonance assignment was achieved by a 15N 3D-NOESY-HMQC. Removal of the C45-C73 bond by the C45A/C73A mutation has no influence upon the β-barrel structure of tendamistat beside very local changes at the mutation site. The relaxation data revealed only subtle differences between variant and wild-type on a subnanosecond time scale. Only the N-terminus and G62 in the connecting loop between the anti-parallel β-sheets showed an increased mobility. The results are discussed in respect to thermodynamic stability and the secretion efficiency of tendamistat. Proteins 33:285-294, 1998. © 1998 Wiley-Liss, Inc.
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    Gel formation in cationic polymerization of divinyl ethers. I. 1,4-Bis(2-vinyloxyethoxy)benzene (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 675-683 
    Details
    ISSN: 0887-624X
    Keywords: cationic polymerization ; vinyl ether ; divinyl ether ; crosslinking ; gelation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymerization of 1,4-bis(2-vinyloxyethoxy)benzene (CH2=C—O—CH2—CH2—O—C6H4—O—CH2CH2—O—C=CH2; 1) was investigated in CH2Cl2 at 0°C with the use of a variety of cationic initiators. SnCl4, SnBr4, AlEtCl2, and BF3OEt2 (strong Lewis acids) and CF3SO3H (a strong protonic acid) yielded crosslinked insoluble polymers immediately after the polymerizations were initiated. The binary initiating systems such as HCl/ZnCl2 and (C6H5O)2P(O)OH/ZnCl2 also produced insoluble poly(1)s. At the low initial concentration of ZnCl2, however, the (C6H5O)2P(O)OH/ZnCl2 system gave the soluble polymers quantitatively, and gelation occurred only when the reaction mixture was stored for a long time after complete consumption of the monomer. The content of the unreacted pendant vinyl ether groups of the soluble polymers decreased with monomer conversion, and almost all the pendant vinyl ether groups were consumed in the soluble polymer obtained at 100% monomer conversion; this may be ascribed to frequent occurrence of intramolecular crosslinking. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 675-683, 1998
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    Peroxide induced crosslinking and degradation of polyvinyl chloride (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 851-860 
    Details
    ISSN: 0887-624X
    Keywords: polyvinyl chloride ; peroxide modification ; crosslinking ; degradation ; electron spin resonance ; kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Peroxide induced crosslinking and degradation of polyvinyl chloride (PVC) were experimentally investigated using an on-line electron spin resonance (ESR) spectroscopy technique. The reaction variables included temperature, peroxide type and concentration. A single line ESR spectrum was observed with its peak-to-peak width decreasing during the reaction. The mechanism involved in the reaction was elucidated based on the radical information. The radical concentration versus reaction time profile exhibited two distinct regions: the chemically initiated reaction continued by the thermal initiation. The addition of peroxide induced and significantly enhanced the thermal initiated crosslinking and degradation. The radical concentration data coupled with the extent of dehydrochlorination gave an estimate of the rate constant of polyene propagation. A significant decrease of the rate constant was observed during the reaction. The gel content and swelling ratio were also measured to provide additional information to the reaction process. The initial gelation rate increased with the increase of temperature and/or peroxide concentration. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 851-860, 1998
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    BF3·OEt2-initiated polymerization of 2-methylene-1,3-dioxepanes (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 873-881 
    Details
    ISSN: 0887-624X
    Keywords: 2-methylene-1,3-dioxepane ; 4,7-dimethyl-2-methylene-1,3-dioxepane ; cyclic ketene acetal ; cationic polymerization ; ring-opening polymerization ; ring-retained polymerization ; copolymerization ; boron trifluoride etherate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: BF3·OEt2-initiated polymerizations of 2-methylene-1,3-dioxepane gave polymers composed of both ring-retained and ring-opened structures. The ring-opening content increased with an increase in polymerization temperature. Poly(4,7-dimethyl-2-methylene-1,3-dioxepane) propagated slower during BF3·OEt2-initiated polymerization and had a lower ring-opened content than poly(2-methylene-1,3-dioxepane). The type of acid initiator used also affected the amount of ring opening observed. Stronger acids gave less ring opening. Attempted BF3·OEt2-initiated copolymerizations of these seven-membered ring cyclic ketene acetals with isobutyl vinyl ether at room temperature resulted in formation of the two homopolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 873-881, 1998
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    Synthesis and properties of polyamidines (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 929-938 
    Details
    ISSN: 0887-624X
    Keywords: polyamidines ; chain conformation ; hydrogen bonds ; prototropic tautomerism ; thermal stability ; hydrolytic stability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymers with amidine groups —NH—CR=N— in the main chain were prepared by acid catalysed melt polycondensation of 4,4′-diaminodiphenyl methane (DAPM) with various orthoesters. The resulting polyamidines were characterized by 1H-, 13C- and 15N-NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TGA) and wide angle x-ray scattering (WAXS) measurements. The properties of the polyamidines are strongly determined by the substituent R on the amidine group. Some peculiarities of the polyformamidine (R=H) could be attributed to the conformation of the amidine group. Glass transition temperatures varied from 106 to 161°C depending on the substituent R. All polyamidines possessed good thermal stability up to 370°C and, with exception of the polyformamidine, good solubility in common solvents. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 929-938, 1998
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    Synthesis of a novel highly conjugated conducting polymer (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 949-953 
    Details
    ISSN: 0887-624X
    Keywords: conjugated polyacetylene ; acetylene derivative ; poly(HPB) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new conjugated polyacetylene derivative dehydrated poly(4-hydroxy-4-phenyl-1-butyne) [dehydrated poly(HPB)] was synthesized from poly(4-hydroxy-4-phenyl-1-butyne) [poly(HPB)], which was obtained by the polymerization of 4-hydroxy-4-phenyl-1-butyne. The resulting dehydrated poly(HPB) was soluble in common organic solvents. The dehydrated poly(HPB) was found to have extended conjugated polyene structure. The dehydrated poly(HPB) was thermally stable up to 300°C. The electrical conductivity of I2-doped dehydrated poly(HPB) was 10-2 S cm-1. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 949-953, 1998
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    Importance of active-site reactivity and reaction conditions in the preparation of hyperbranched polymers by self-condensing vinyl polymerization: Highly branched vs. linear poly[4-(chloromethyl)styrene] by metal-catalyzed “living” radical polymerization (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 955-970 
    Details
    ISSN: 0887-624X
    Keywords: hyperbranched ; self-condensing vinyl polymerization ; metal catalyzed ; living radical ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-condensing vinyl polymerization of 4-(chloromethyl)styrene using metal-catalyzed living radical polymerization catalyzed by the complex CuCl/2,2′-bipyridyl has been attempted. Given the unequal reactivity of the two potential propagating species in this system, a variety of polymerization conditions were tested to optimize the extent of branching in the products. Typical reaction conditions included polymerization in the bulk, or preferably in chlorobenzene solution, with catalyst to monomer ratios in the range 0.01-0.30, temperatures of 100-130°C, and reaction times from 0.1 to 32 h. Polymers with weight average molecular weights between 3 × 103 and 1.6 × 105 and different extents of branching are formed as evidenced by size-exclusion chromatography, light scattering, and NMR analysis of the reaction products. The influence of reaction conditions on the molecular weight and branching of the resulting polymers is discussed in detail. In sharp contrast to an earlier report, the weight of evidence suggests that, at a catalyst to monomer ratio of 0.01, an almost linear polymer is obtained, while a high catalyst to monomer ratio favors the formation of a branched structure. As a result of the unequal reactivity of the primary and secondary benzylic halide reactive sites, growth occurs by a modified self-condensing vinyl polymerization mechanism that involves incorporation of the largely linear vinyl-terminated fragments formed early on in the polymerization into the vinyl polymer, to afford an irregularly branched structure. Chemical transformations involving the numerous benzylic halide functionalities of the highly branched polymer have been investigated. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 955-970, 1998
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    Autoacceleration and inhibition: Free volume. Epoxy-amine kinetics (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1001-1016 
    Details
    ISSN: 0887-624X
    Keywords: free volume ; autoacceleration ; inhibition ; tertiary amines ; friction coefficient ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The epoxy-diamine cure process was studied. We found that the mechanism can be described in three steps: (i) initiation up to 20-25% of conversion. (ii) autoacceleration and (iii) inhibition. It has been observed that after the initiation there is a clear autoacceleration effect which has been explained in terms of free volume, considerations: the volume occupied by the products of reaction diminishes the available volume increasing the “local concentration” of the reactants and therefore the rate of reaction. The reaction was followed by FTIR (near infrared) as the main technique. We used a purified epoxy resin as well as phenyl glycidyl ether cured with m-xylenediamine. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1001-1016, 1998
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    Formation of quinoid fragments in vacuum-deposited poly-para-phenylene films: IR spectroscopy evidence (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1043-1052 
    Details
    ISSN: 0887-624X
    Keywords: poly-para-phenylene ; quinoid structure ; IR spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of vacuum-deposited poly-para-phenylene (PPP) films prepared from a high-molecular-weight PPP powder has been investigated by IR spectroscopy. It has been demonstrated that in IR spectra of PPP films exhibiting intense luminescence an extremely strong band at 1375 cm-1 is observed, which is not typical for currently known PPP modifications. Based on the IR spectral data, the model of formation of a PPP chain with quinoid fragments in the ground electronic state is proposed. The structure of defects that inevitably spring up during the benzenoid-quinoid transition is discussed. High intensity of the band at 1375 cm-1 is associated with the change in the order of the “defect” C—C bond between adjacent quinoid and benzenoid units. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1043-1052, 1998
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    Synthesis and characterization of new soluble polyamides based on 3,3′,5,5′-tetramethyl-2,2- bis[4-(4-aminophenoxy)phenyl]propane and various aromatic dicarboxylic acids (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1075-1080 
    Details
    ISSN: 0887-624X
    Keywords: 3,3′,5,5′-tetramethyl-2,2-bis[4-(4-aminophenoxy)phenyl]propane (TBAPP) ; direct polycondensation ; polyamides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of new soluble polyamides having isopropylidene- and methyl-substituted arylene ether moieties in the polymer chain were prepared by the direct polycondensation of 3,3′,5,5′-tetramethyl-2,2-bis[4-(4-aminophenoxy)phenyl]propane (TBAPP) and various aromatic dicarboxylic acids in N-methyl-2-pyrrolidinone (NMP) using triphenyl phosphite and pyridine as condensing agents. Polymers were produced with high yield and moderate to high inherent viscosities of 0.87-1.56 dL g-1. All the polymers could be readily dissolved in polar aprotic solvents such as NMP, N,N-dimethylacetamide and N,N-dimethylformamide, as well as less polar solvents such as m-cresol and pyridine. Some of them were even soluble in tetrahydrofuran. These polymers were solution-cast into transparent, flexible, tough films which were further characterized by x-ray and mechanical analysis. All of the polymers were amorphous and the polyamide films had a tensile strength range of 51-100 MPa, an elongation at break range of 4-11%, and a tensile modulus range of 1.90-2.53 GPa. These polyamides had glass transition temperatures between 188-255°C and 10% mass loss temperatures in the range of 439-468 and 454-483°C in nitrogen and air atmosphere, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1075-1080, 1998
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    New polar silane-PEO polyester complexes as polymer electrolytes (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1093-1106 
    Details
    ISSN: 0887-624X
    Keywords: ion-conducting polymers ; silicon ; synthesis ; stability ; conductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trifunctional carbosilanes containing hydroxy and cyano groups have been synthesized in good yields and incorporated into polyether-based electrolytes. The new linear and cross-linked modified PEOs have been characterized by DSC and conductivity measurements. The effect of silane content, the length of the PEO block, glycerol concentration, and temperature on glass transition temperature and conductivity of lithium salts complexes of these materials has been evaluated. The new materials showed improved conductivity (∼ 10-5 S cm-1) at ambient temperatures compared with unmodified polyethers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1093-1106, 1998
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    Synthesis and properties of poly(amide-imide)s based on the diimide-diacid condensed from 2,2′- bis(4-aminophenoxy)biphenyl and trimellitic anhydride (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1169-1177 
    Details
    ISSN: 0887-624X
    Keywords: poly(amide-imide)s ; 2,2′-bis(4-trimellitimidophenoxy) biphenyl ; solubility ; 2,2′-bis(4-aminophenoxy)biphenyl ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new dicarboxylic acid having a kinked structure was synthesized from the condensation of 2,2′-bis(4-aminophenoxy)biphenyl and trimellitic anhydride. A series of biphenyl-2,2′-diyl-containing aromatic poly(amide-imide)s having inherent viscosities of 0.23-0.94 dL/g was prepared by the triphenyl phosphite activated polycondensation from the diimide-diacid II with various aromatic diamines in a medium consisting of N-methyl-2-pyrrolidone (NMP), pyridine, and calcium chloride. Most of the resulting polymers showed an amorphous nature and were readily soluble in a variety of organic solvents including NMP and N,N-dimethylacetamide (DMAc). Transparent, flexible, and tough films of these polymers could be cast from DMAc or NMP solutions. The glass transition temperatures of these polymers were in the range of 227-261°C and the 10% weight loss temperatures were above 520°C in nitrogen. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1169-1177, 1998
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  • 187
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    Sulfonation of a poly(phenylquinoxaline) film (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1197-1199 
    Details
    ISSN: 0887-624X
    Keywords: sulfonation ; proton exchange membrane ; poly(phenylquinoxaline) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 188
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    Synthesis and cationic photopolymerization of 1-butenyl glycidyl ether (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1179-1187 
    Details
    ISSN: 0887-624X
    Keywords: 1-butenyl glycidyl ether ; photoinitiated cationic polymerization ; diaryliodonium salts ; cyclopolymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1-Butenyl glycidyl ether was prepared in high yield by the ruthenium-catalyzed isomerization of crotyl glycidyl ether. This ambifunctional monomer underwent facile photoinitiated cationic polymerization using diaryliodonium salts as photoinitiators. The progress of the polymerizations was followed using Fourier transform real-time infrared spectroscopy, and the reactivity of this monomer under various experimental conditions determined. A comparison of the rates of polymerization of the epoxy and vinyl ether groups suggested that the polymerization may take place by an intramolecular cyclization process that generates cyclic acetal units in the backbone of the polymer. It was further shown that crotyl glycidyl ether undergoes regioselective cationic ring-opening polymerization to give a polyether, and then isomerization was carried out to give an oligomer bearing reactive pendant 1-butenyl ether groups. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1179-1187, 1998
    Additional Material: 8 Ill.
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  • 189
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    Pulse radiolysis studies of poly(methyl methacrylate) containing pyrene (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1209-1215 
    Details
    ISSN: 0887-624X
    Keywords: poly(methyl methacrylate) ; pyrene ; pulse radiolysis ; radical ion decay ; ion recombination ; fluorescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A pulse radiolysis study of poly(methyl methacrylate) in the presence of pyrene has been carried out in the temperature range 100-295 K. The concentration of pyrene was changed from 10-3 to 10-1 mol dm-3. The absorption/emission spectra and kinetics of solute excited states and solute radical ions were investigated. It was found that pyrene excited states were formed as a result of their radical ion recombination in a time scale up to seconds. The decay of solute radical ions was influenced by photobleaching and can be described by a time-dependent rate constant. The activation energy of Py ions decay was temperature dependent and was equal to 35.7 and 1.2 kJ/mol for temperatures 〉Tγ and 〈Tγ, respectively, where Tγ ∼ 175 K represented the transition temperature responsible for γ-relaxation. The reaction mechanism was proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1209-1215, 1998
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  • 190
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    Anionic synthesis of aromatic amide and carboxyl functionalized polymers. Chain-end functionalization of poly(styryl)lithium with N,N-diisopropyl-4-(1-phenylethenyl)benzamide (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1233-1241 
    Details
    ISSN: 0887-624X
    Keywords: living anionic polymerization ; poly(styryl)lithium ; functionalization ; aromatic carboxylation ; N,N-diisopropylamide ; N,N-diisopropyl-4-(1-phenylethenyl)-benzamide ; substituted 1,1-diphenylethylenes ; functionalized polystyrene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel syntheses of N,N-diisopropyl-4-benzoylbenzamide, N,N-diisopropyl-4-(1-hydroxy-1-phenylethyl)benzamide, and N,N-diisopropyl-4-(1-phenylethenyl)benzamide (1) are described. ω-Amidopolystyrene (2) was synthesized in quantitative yields by the reaction of poly(styryl)lithium with stoichiometric amounts of N,N-diisopropyl-4-(1-phenylethenyl)benzamide (1) in toluene/tetrahydrofuran (4 : 1 v/v) at -78°C. Deblocking of the amide protecting group by acid hydrolysis quantitatively provides the corresponding aromatic carboxyl chain-end functionalized polystyrene (3). The functionalization agent and functionalized polymers were characterized by HPLC, thin-layer chromatography, size exclusion chromatography, vapor phase osmometry, spectroscopy (1H-NMR, 13C-NMR, and FTIR), potentiometry, and elemental analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1233-1241, 1998
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  • 191
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    Synthesis of novel polyaryl(ether-ketones) with tert-butyl pendent groupsDedicated to Prof. F. J. Baltaá Calleja on the occasion of his 60th birthday. (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1251-1256 
    Details
    ISSN: 0887-624X
    Keywords: ether ketones ; synthesis ; NMR ; thermal properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Linear polyaryl(ether ketones) containing tert-butyl pendent groups were prepared from aromatic hydrocarbons and aromatic diacid chlorides, both classes of monomers containing tert-butyl pendent groups. The polymers were prepared in high yield and high molecular weight by low-temperature precipitation polycondensation in 1,2-dichloroethane. The presence of meta-oriented moieties and bulky pendent groups played a beneficial role with regard to solubility, while the thermal transitions and thermal resistance were not greatly impaired relative to conventional all para-oriented polyaryl(ether-ketones). The current polyaryl(ether-ketones) showed glass transition temperatures in the range 170-240°C and decomposition temperatures, as measured by TGA, of about 500°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1251-1256, 1998
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  • 192
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    New polymer syntheses. XCVI. Star-shaped LC-polyesters derived from β-(4-hydroxyphenyl)propionic acid and 4-hydroxybenzoic acid (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1387-1395 
    Details
    ISSN: 0887-624X
    Keywords: star-shaped polyesters ; nematic phase ; phloritic acid ; spirobis indane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Star-shaped polyesters were prepared by polycondensation of tetraacetoxyspirobis(indane) and a 1 : 1 mixture of silylated β-(4-acetoxyphenyl)propionic acid and silylated 4-acetoxybenzoic acid. The lengths of the star arms were systematically varied, and the influence of the star center on the stability of the nematic phase was studied. It was found that on the average more than 10 monomer units per star arm are required to stabilize a homogeneous LC-phase. Furthermore, a second class of star-shaped polyesters consisting of β-(4-hydroxyphenyl)propionic acid (HPPA), 4-hydroxybenzoic acid (HBA), and 6-hydroxy-2-naphthoic acid (HNA) was prepared. This ternary copolyester proved to reduce the crystallinity but to stabilize the LC-character. A homogeneous nematic melt was obtained with 6 monomer units per star arm. This interpretation is based on optical microscopy which provides a static picture of the biphasic situation. Therefore, a preliminary study of the melt rheology was included, which proved that the typical LC-character of the melt was detectable ateven shorter star arms due to the shear orientation. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1387-1395, 1998
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  • 193
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    Structural effect of polymeric acid dopants on the characteristics of doped polyaniline composites: Effect of hydrogen bonding (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1431-1439 
    Details
    ISSN: 0887-624X
    Keywords: polyaniline ; polymeric acid dopant ; conducting polymer ; doping level ; chain alignment ; conductivity ; hydrogen bonding ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conductivities of polyaniline (PANi) composites doped with the copolymeric acids such as poly(methyl methacrylate-co-p-styrenesulfonic acid) (PMMA-co-SSA), poly(styrene-co-p-styrenesulfonic acid) (PS-co-SSA), and poly(methyl methacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (PMMA-co-AMPS) were investigated as a function of the acid content in the copolymeric acid dopants. With the fixed ratio of acid to aniline (1/1) in the PANi composites, the conductivities of the copolymeric acid-doped PANis decreased as the acid content in the copolymeric acids decreased. This could be attributed to the nonacidic units in the copolymeric acids which seemed to prevent adjacent acid groups from doping the PANi. Among the three kinds of copolymeric acid dopants, the PMMA-co-SSA series doped the PANi most effectively, and consequently, the PMMA-co-SSA-doped PANi composites showed the highest conductivities. The lack of conductivities of the PMMA-co-AMPS-doped PANi composites seems to be due to the doping ability of the AMPS groups. The higher conductivities of the PMMA-co-SSA-doped PANi composites rather than the PS-co-SSA-doped ones were attributed to the hydrogen bonding formed between the carbonyl groups in MMA and the amine groups in aniline which may hinder the phase separation and induce more homogeneous mixing and efficient doping. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1431-1439, 1998
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  • 194
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    Acid-catalyzed deprotection mechanism of tert-butyloxycarbonyloxy polymers in chemically amplified resists (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1035-1042 
    Details
    ISSN: 0887-624X
    Keywords: acid-catalyzed deprotection mechanism ; chemically amplified resist ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A mechanism of acid-catalyzed deprotection of poly(4-tert-butyloxycarbonyloxy-styrene), PBOCST, in chemically amplified resists has been elucidated in terms of elementary processes by means of semiempirical molecular orbital calculations. It is concluded that the overall deprotection of tert-butyloxycarbonyl (t-BOC) group proceeds stepwise; i.e., (a) the first products are an acid carbonate and a tert-butyl cation; (b) a phenolic compound is the secondary and final product from the acid carbonate, which is realized by assistance with a counter anion accompanied by acid; (c) the counter anion also assists acid regeneration from the tert-butyl cation to produce isobutylene. The yield rate of the phenol is proportional to the product of concentrations of the polymer, the catalytic acid, and the counter anion. The activation energy (21 kcal/mol) calculated for the rate-determining step (a) is in good agreement with an experiment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1035-1042, 1998
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  • 195
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    Macrocycles IV. Macrocyclic polylactones as bifunctional monomers for polycondensations (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1373-1378 
    Details
    ISSN: 0887-624X
    Keywords: macrocyclic polymerization ; polycondensation ; 2-stanna-1,3-dioxacycloalkanes ; poly(ε-caprolactone) ; poly(δ-valerolactone) ; poly(β-D,L-butyrolactone) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tin containing macrocyclic polylactones were prepared by di-n-butyl-2-stanna-1,3-dioxepane-initiated polymerizations of ε-caprolactone in bulk. The average ring size was varied from 10 to 100 monomer units via the monomer/initiator (M/I) ratio. Addition of terephthaloyl or sebacoyl chloride to the in situ prepared macrocycles yielded polycondensates under elimination of di-n-butyl tin dichloride. The molecular weights increased with the reaction temperature (e.g., 80-140°C) and with the size of the macrocycles. Number-average molecular weights (Mns) up to 90,000 and polydispersities between 1.65 and 2.0 were obtained. Further polycondensations were conducted with isophthaloyl chloride, 4,4′-biphenyldicarbonylchloride and 4,4′-phenylenebisacryloylchloride. Several polycondensations were performed with macrocyclic poly (δ-valerolactone) and poly (β-D,L-butyrolactone). In those cases the increase of the molecular weight was lower. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1373-1378, 1998
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  • 196
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    Synthesis and characterization of poly(benzobisthiazole) with tetramethylbiphenyl moiety in the main chain (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1407-1416 
    Details
    ISSN: 0887-624X
    Keywords: PBZT ; polycondensation ; tetramethylbiphenyl substituted ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(benzobisthiazole)s containing an ortho-tetramethyl substituted biphenyl moiety were synthesized via the polycondensation of 2,5-diamino-1,4-benzenedithiol dihydrochloride with 2,2′,6,6′-tetramethylbiphenyl-4,4′-dicarboxylic acid in poly(phosphoric acid) (PPA). The intrinsic viscosities of the tetramethylbiphenyl poly-(benzobisthiazole)s in chlorosulfonic acid at 30°C were in the range of 6.9-13.4 dL/g. Copolycondensation of 2,5-diamino-1,4-benzenedithiol dihydrochloride with terephthalic acid and 2,2′,6,6′-tetramethylbiphenyl-4,4′-dicarboxylic acid was carried out as well by varying the ratio of the two dicarboxylic acid monomers in the reactant mixture. The homopolymers and copolymers were characterized by Fourier transform infrared spectroscopy (FTIR) and 13C solid-state nuclear magnetic resonance spectroscopy (NMR). Thermal stability of the polymers was evaluated by thermogravimetric analysis (TGA) and thermogravimetric mass spectrum analysis (TG-MS). The tetramethylbiphenyl poly(benzobisthiazole)s were found to be more stable at elevated temperatures than the parent poly(p-phenylene benzobisthiazole) (PBZT). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1407-1416, 1998
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  • 197
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    Anomalous viscosity behavior of rodlike polyelectrolytes: Partially sulfonated poly(2-benzoyl-1,4-phenylene)s in aqueous solution (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1425-1429 
    Details
    ISSN: 0887-624X
    Keywords: anomalous viscosity ; rodlike polyelectrolytes ; sulfonated poly(2-benzoyl-1,4-phenylene) ; aqueous solution ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two stereoisomeric poly(2-benzoyl-1,4-phenylene)s were synthesized. Polymer I has exclusively a head-to-tail structure; however, polymer II contains both head-to-head and head-to-tail units. The sulfonation reaction of polymers I and II was found to occur mainly on the meta position of the benzoyl group on the phenylene backbone. The viscosities of polymers Ia (27% sulfonated) and Ic (51% sulfonated) in aqueous solutions at 25°C were measured with and without NaBr addition. Upon the addition of NaBr (0.05 and 0.1M), the reduced viscosities were found to increase gradually and reach a constant value in each case after standing at room temperature for 30-40 h. Without NaBr, the time effect was not found. The reduced viscosities of solutions with NaBr were also higher than those without the salt. These results are quite different from the typical “polyelectrolyte” behavior. A possible explanation of the salt effect of rigid rodlike polymers such as sulfonated poly(2-benzoyl-1,4-phenylene) is discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1425-1429, 1998
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    Living polymers. Their discovery, characterization, and properties (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. IX 
    Details
    ISSN: 0887-624X
    Keywords: living polymerization ; discovery ; significance ; revised definition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The story of the discovery of living polymers is presented. Living polymers are polymers that retain their ability to propagate and grow to a desired size while their degree of termination or chain transfer is still negligible. Theoretical and mechanistic considerations are discussed. The living polymerization technique provides access to uniform polymers (Poisson molecular weight distribution) of controllable size, block copolymers, functional polymers, and star and comb-shaped polymers. The quantitative aspects of electron transfer are fully discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: ix-xv, 1998
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    Controlling surfaces and interfaces with functional polymers: Preparation and functionalization of dendritic-linear block copolymers via metal catalyzed “living” free radical polymerization (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1-10 
    Details
    ISSN: 0887-624X
    Keywords: living free-radical polymerization ; dendrimer ; polystyrene ; block copolymer ; chemical modification ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and chemical modification of dendritic-linear block copolymers with surface functionalized dendritic components are presented. Isophthalate ester-functionalized dendrons featuring benzylic halide groups at their focal points have been used for the metal catalyzed “living” radical polymerization of styrene. The molecular weight of the dendritic-linear block copolymers determined by MALDI-TOF and Size Exclusion Chromatography was found to be accurately controlled up to molecular weights of ca. 30,000 a.m.u., with polydispersities less than 1.2. Subsequent functional group modifications of the peripheral ethyl ester groups of the dendritic block have been successfully carried out leading to carboxylic acids, butyl amides, benzyl alcohols, benzyl halides, and also accelerated generation growth via transesterification with a first generation dendritic alcohol. Several of these new dendritic-linear block copolymers exhibit interesting aggregation characteristics as evidenced by 1H-NMR spectroscopic studies. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1-10, 1998
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    Effects of complex formation and cyclization in radical copolymerization of allyl(metha)acrylates with maleic anhydride (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1501-1508 
    Details
    ISSN: 0887-624X
    Keywords: copolymerization ; charge transfer complex ; cyclization ; allyl acrylate ; allyl methacrylate ; maleic anhydride ; chain growth reactions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical copolymerization of allyl acrylate (AA) and allyl methacrylate (AMA) as bifunctional monomers of donor (allyl)-acceptor (acryl) type with maleic anhydride (MA) as an acceptor monomer were carried out in metrhyl ethyl ketone (MEK) at 50-70°C in the presence of 2,2′-azoisobutyronitrile (AIBN) as initiator. Constants of complex formation (Kc), cyclization (kcl), and copolymerization (r1, r2, r1c, r1c1, and r1c2) as well as energies of activation for cyclization (Eac) and copolymerization reactions (Ea), and orders for the monomer (m) and initiator (n) concentrations were determined. The following values were found, for AA and AMA, respectively: Kc = 0.038 and 0.11 L/mol in deutered acetone at 35 ± 0.1°C, kcl = 6.45 and 6.53, r1 = 0.083 ± 0.005 and 0.028 ± 0.002, r2 = 0.027 ± 0.002 and 0.063 ± 0.003 (by the Kelen-Tüdös method), r1c = 0.04 and 0.025, r1c1 = 0.128 and 0.176, r1c2 = 0.127 and 0.177 (by the Seiner-Litt equation), Eac = 28.9 and 28.7 kJ/mol, Ea = 67.0 and 87.9 kJ/mol, m = 1.53 and 1.45, and n = 0.50 and 0.52. The presence of cyclic, unsaturated, and anhydride fragments in the macromolecules was confirmed with FTIR data and chemical (iodometrical and potentiometric titrations) analysis. It was established that complex formation in the monomer systems studied is the main factor for alternating cyclocopolymerization leading to formation of copolymers containing lactone and linear-unsaturated fragments in the macromolecular chain. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1501-1508, 1998
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