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  • ASTROPHYSICS  (24)
  • Polymer and Materials Science  (20)
  • 1995-1999  (6)
  • 1990-1994  (26)
  • 1980-1984  (12)
  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The variable-temperature proton nmr spectra of the oligoribonucleotides in the series CpApX and the series ApGpX, X = A, G, C, U, together with the parent dimers CpA and ApG have been measured. A complete analysis of all the nonexchangeable base proton resonances and ribose H-1′ proton resonances was made. The presence of trends in the shielding abilities of the various bases at both the nearest-neighbor and next-nearest-neighbor positions were identified. The observed shieldings could be used to predict the chemical shifts of protons in related systems. Based on the empirical results from ribodinucleoside monophosphates, the temperature-dependent behavior of the J1′2′ coupling constants of the triribonucleotides suggested that the compounds in the CpApX series stacked from the 5′-end to the 3′-end, while those in the ApGpX series stacked from the 3′-end to the 5′-end.
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 169-179 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthetic cyclic octapeptides of general structure cyclo[Glu(γOBzl)-Sar-Gly-(N-R)Gly]2 (R = n-hexyl and cyclohexyl) transport calcium ions selectively across organic phases and phospholipid membranes. We have now used proton nmr spectroscopy (360 MHz) to study the solution conformation(s) of their calcium complexes. When Ca(ClO4)2 was added to solutions of these peptides in CDCl3, nmr spectra of the resulting calcium complexes were characteristic of a single C2-symmetric conformer. From a Karplus-Bystrov analysis of vicinal coupling constants in both the peptide backbone and Glu side chain (treated as an ABCC′MX spin system), in conjuction with model-building studies, a structure was proposed in which the calcium ion is bound in an octahedral-type complex by the four (coplanar) carbonyl groups of the (all-trans) Glu-Sar and Gly-(N-R)Gly peptide bonds. Occurrence of preferred rotamers about Glu side chain Cα-Cβ bonds indicated that restricted rotation in peptide side chains arises upon calcium binding.
    Additional Material: 5 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 183 (1982), S. 781-788 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Copolymerization of acrylamide with allyl glycidyl ether yielded water soluble polymers containing an epoxy group; addition of a crosslinking agent, N,N′-methylenebis(acrylamide), to the copolymerization mixtures resulted in the formation of similar though water insoluble polymers. Condensation of a potent beta-adrenergic antagonist Alm—H, which contains a reactive amino group, with a polymer containing an epoxy group yeilded a pharmacologically active polymer. The polymer containing the epoxy group was also converted, by reaction with sodium thiosulfate and subsequent reduction, into a mecapto groups containing polymer which was also water soluble. The latter polymer was converted by condensation with a beta-adrenergic antagonist Alm—COCH2Br, which contains a reactive bromoacetamido group, into a pharmacologically active polymer.
    Additional Material: 1 Ill.
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  • 4
    ISSN: 0887-624X
    Keywords: oligocyclosiloxanes ; hydrosilation ; heptamethylcyclotetrasiloxane ; siloxane redistribution ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of oligocyclosiloxanes via hydrosilation reactions has been investigated. Hydrosilation reactions employing heptamethylcyclotetrasiloxane and vinyl-containing silanes and siloxanes yielded a variety of oligocyclosiloxanes with various numbers of cyclosiloxane rings connected through tri-, tetra-, penta-, hexa-, hepta-, or octafunctional junctions. The oligocyclosiloxanes were characterized by gas chromatography, IR spectroscopy, 29Si-, 1H-, and 13C-NMR spectroscopy, elemental analysis, and vapor phase osmometry. The polycyclics were redistributed with hexamethyldisiloxane and the resulting fragments analyzed by gas chromatography. All results were consistent with the formation of isomeric oligocyclosiloxanes due to a lack of absolute regioselectivity of the hydrosilation reaction. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 5
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton nmr spectra of the oligoribonucleotides in the series CpXpG, ApXpG, CpApXpUpG, and ApGpXpC (X = A, G, C, and U), together with the reference compounds CpG, ApG, CpApUpG, and ApGpC, have been measured. A complete analysis of all the nonexchangeable base protons and the ribose H-1′ protons was made. The insertion of a nucleotide X into a oligoribonucleotide led to shift changes at both nearest-neighbor and next-nearest-neighbor positions, which were rationalized in terms of the shielding abilities of the various bases. The derived shielding trends in the ApGpXpC series of compounds were successfully used to predict the chemical shifts of resonances in the related ApGpXpCpU series.
    Additional Material: 13 Tab.
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  • 6
    ISSN: 0006-3525
    Keywords: AIDS ; DNA structure ; polymerase structure ; protein - DNA interaction ; x-ray crystallography ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of the DNA and the interactions of the nucleic acid with the protein in a complex of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) and a 19-mer/18-mer double-stranded DNA template-primer (dsDNA) are described. The structure of this HIV-1 RT complex with dsDNA serves as a useful paradigm for studying aspects of nucleotide polymerases such as catalysis, fidelity, drug inhibition, and drug resistance. The bound dsDNA has a bend of approximately 41° at the junction of an A-form region (first five base pairs near the polymerase active site) and a B-form region (the last nine base pairs toward the RNase H active site). The 41° bend occurs smoothly over the four base pairs between the A-form portion and the B-form portion in the vicinity of helices αH and αI of the p66 thumb subdomain. The interactions between the dsDNA and protein primarily involve the sugar - phosphate backbone of the nucleic acid and structural elements of the palm, thumb, and RNase H of p66, and are not sequence specific. Amino acid residues from the polymerase active site region, including amino acid residues of the conserved Tyr-Met-Asp-Asp (YMDD) motif and the “primer grip,” interact with 3′-terminal nucleotides of the primer strand and are involved in positioning the primer terminal nucleotide and its 3′-OH group at the polymerase active site. Amino acid residues of the “template grip” have close contacts with the template strand and aid in positioning the template strand near the polymerase active site. Helix αH of the p66 thumb is partly inserted into the minor groove of the dsDNA and helix αI is directly adjacent to the backbone of the template strand. Amino acid residues of Β1′, αA′, αB′, and the loop containing His539 of the RNase H domain interact with the primer strand of the dsDNA. © 1997 John Wiley & Sons, Inc. Biopoly 44: 125-138, 1997
    Additional Material: 8 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 999-1004 
    ISSN: 0887-6266
    Keywords: latex ; polystyrene ; luminescence ; particle ; micron-diameter ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A technique for rapid determination of the presence of polystyrene in individual micron-diameter polymer particles of mixed composition is presented. This technique is based upon observation of visible emission from conjugated regions of the polymer backbone, generated photochemically, while the particle is held in an optical trap. Particle emission characteristics are dependent upon particle size and suspending solvent. Emission spectra are provided for single component polystyrene particles and mixed polymer particles containing poly(methyl methacrylate), poly(N-vinyl pyrrolidone), and polystyrene. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 999-1004, 1998
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 485-496 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new route (“direct forming”) was developed for forming dense PBI shapes from PBI powder. The new process affords the possibility of automated PBI powder shaping (“cold compaction”) and densification in batches of multiple parts by a “powder-assisted hot isostatic pressing” process. Direct forming is a more productive alternative to hot compression molding. Two developments enable PBI direct forming: (1) the discovery that PBI powders that are porous and plasticized with moisture can be shaped by compaction at ambient temperatures (cold-compacted), and (2) a finding that cold-compacted shapes can be densified in large batches by a powder-assisted hot isostatic pressing. The porous PBI powder is formed from PBI in solution by a spray-precipitation process. When plasticized with moisture, this powder is cold-compactible to PBI shapes with densities up to 94% of that of ultimate density of PBI. These shapes, which have sufficient strength to be handled, are then further consolidated via powder-assisted hot isostatic pressing to shapes with excellent thermal and mechanical properties and densities of about 99% of the ultimate. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 9
    ISSN: 1045-4861
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The need for alternatives to autogenous bone grafts is widely recognized. This study compared the torsional strength of canine femora 1 year after grafting with one of three forms of a collagen/hydroxyapatite/tricalcium phosphate bone grafting material (COLLAGRAFT15), autogenous bone, or no graft. The groups were compared to each other and to the unoperated contralateral femora. Results of torsional testing were evaluated for torsional strength, torsional displacement, total energy to fracture and White fracture mode. Data analysis showed lower torsional strength of the operated vs. unoperated femora with the exception of morsellized COLLAGRAFT15 material, which had higher strength. However, the only difference in the operated groups was that the morsellized COLLAGRAFT15 had greater strength than several groups including the autogenous bone group. There was no difference found in angular displacement between any of the groups. However, there was a difference in the energy to fracture in both strip forms of the COLLAGRAFT15. The final conclusion is that in this model, grafting with COLLAGRAFT15 provided torsional properties at one year postoperatively at least equivalent to autogenous bone. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 26 (1981), S. 3467-3473 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Binary blends of poly(vinyl chloride) and a poly(ether urethane) containing 20 and 40 weight percent, respectively, of poly(vinyl chloride) have been prepared by solution blending from tetrahydrofuran and their degree of mixing investigated using dynamic mechanical analysis. In the polyurethane, transitions were found at -19°C and -119°C. The former was attributed to the glass transition and the latter to a Schatzki type of motion of the polyether sequences. This latter transition occurred at a temperature which is higher than the literature value for the low temperature transition in poly(tetrahydrofuran), which is equivalent to the polyether sequence in the polyurethane. This discrepancy is attributed to the influence of neighboring hard segments present because of incomplete segmental phase separation of the polyurethane. For the blends only one very broad transition was observed, indicating that there was substantial mixing of these two polymers. Three ternary blends were prepared, also by solution blending, containing poly(vinyl chloride), Hytrel, and the polyurethane in the ratios 1:1:1, 1:2:1, and 2:1:1, respectively. In the first two blends there was clear evidence of phase separation. It was only in the 2:1:1 blend that an apparently significantly compatible material resulted.
    Additional Material: 6 Ill.
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