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  • ASTROPHYSICS  (14)
  • Polymer and Materials Science  (13)
  • GEOPHYSICS  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Structure-activity studies on magainins and other host defense peptides (1995)
    New York : Wiley-Blackwell
    Biopolymers 37 (1995), S. 105-122 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Host defense peptides are widely distributed in nature, being found in species from bacteria to humans. The structures of these peptides from insects, horseshoe crabs, frogs, and mammals are known to have the common features of a net cationic charge due to the presence of multiple Arg and Lys residues and in most cases the ability to form amphipathic structures. These properties are important for the mechanism of action that is thougln to be a nonreceptor-mediated interaction with the anionic phospholipids of the target cell followed by incorporation into the membrane and disruption of the membrane structure. Host defense peptides have been shown to have broad spectrum antimicrobial activity, able to kill most strains of bacteria as well as some fungi, protozoa, and in addition, many types of tumor cells. Specificity for pathogenic cells over host cells is thought to be due to the composition of the cell membranes, with an increased proportion of anionic phospholipids making the pathogen more susceptible and the presence of cholesterol making the host membranes more resistant. Structure-activity relationship studies have been performed on insect cecropins and apidaecins. horseshoe crab tachyplesins and polyphemusins. and the frog magainins. CPFs (caerulein precursor fragments) and PGLa. In general, changes that increased the basicity and stabilized the amphipathic structure have increased the antimicrobial activity: however, as the peptides become more hydrophobic the degree of specificity decreases. One magainin-2 analogue. MSI-78. has been developed by Magainin Pharmaceuticals as a topical antiinefective and is presently in clinical trials for the treatment of infected diabetic foot ulcers. © 1994 John Wiley & Sons, Inc.
    Additional Material: 16 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360370206
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of cohesive forces on the glass transition temperatures of polymers (1968)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 12 (1968), S. 1397-1409 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The relationship between cohesive energy (c.e.) or cohesive energy density (c.e.d.) and the glass transition tenperature (Tg) of polymers has been re-examined on the basis of literature data. For polymers with Tg above 25°C., there is no correlation between published or calculated values of c.e. or c.e.d. and Tg. However, for the rest of the polymers there is a linear relationship between c.e.d. and Tg, and a broad relationship between c.e. and Tg. These results imply that c.e.d. is the regulating, though not the only, factor in determining Tg's up to values of approximately 25°C.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1968.070120612
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  • 3
    Electronic Resource
    Electronic Resource
    The preparation and characterization of new polyether ketone-tetraethylorthosilicate hybrid glasses by the sol-gel method (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 40 (1990), S. 1177-1194 
    Details
    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: In recent years, tetraethyl orthosilicate (TEOS) has been used as a precursor in preparing inorganic glasses. The technique, known as the sol-gel process involves a two step poly(hydrolysis-condensation)reaction sequence. The work presented here is concerned with the utilization of a suitably functionalized oligomeric “glassy” organic polymeric component in this two step sequence. In particular, an amine terminated amorphous poly(arylene ether) ketone, (PEK), end capped with isocyantonropyl triethoxy silane was used to synthesize a hybrid network with TEOS. Low incorporation of the PEK oligomers into the network caused by early vitrification can be eliminated by carrying out reactions at elevated temperatures. A systematic change in mechanical and physical properties of the hybrid glass has been found with TEOS content and the annealing temperatures. A model for the network has been proposed based on structural and morphological evidence.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1990.070400709
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  • 4
    Electronic Resource
    Electronic Resource
    Calibration of the gel permeation chromatography polyester resins (1978)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 22 (1978), S. 3343-3344 
    Details
    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
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1978.070221128
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  • 5
    Electronic Resource
    Electronic Resource
    Chromatogram broadening of proteins and dextrans in size exclusion chromatography (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 29 (1984), S. 3533-3546 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The mechanisms governing the broadening of experimental chromatograms for proteins and paucidisperse dextrans were studied on TSK-G2000SW and TSK-G3000SW columns. Within the conditions studied, the chromatogram variance for all solutes increased linearly with increasing effluent flow rate. As predicted by current theories of the kinetics of size exclusion chromatography, this flow rate dependence is caused mainly by slow mass transport of the solute within the stationary phase of the column. Restricted diffusion within the stationary phase was dependent upon the ratio of solute molecular size to column pore radius and was similar for both proteins and dextrans. In comparison with results for monodisperse proteins, the broader chromatograms produced by dextrans were due to sample polydispersity and not to differences in solute column spreading. Corrections for column spreading on these columns are small for the determination of integral properties of polymers but may be significant when molecular weight distributions are of interest.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1984.070291127
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  • 6
    Electronic Resource
    Electronic Resource
    Physical characteristics of Ti-6Al-4V implants fabricated by electrodischarge compaction (1991)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 25 (1991), S. 1417-1429 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Physical characteristics of a Ti-6Al-4V implant were evaluated following fabrication using a new electrodischarge compaction technique. Ti-6Al-4V atomized powders were loaded into Pyrex tubes (3.3 mm ID) and subjected to a highvoltage, high-current-density pulse in air for a period of less than 300 μs. Single pulses (1.0, 1.5, 2.0 and 2.5 KJ/grampowder) were applied from a capacitor bank (240, 480 or 720 μF) to produce solid core implants with porous surface layers. Implants were evaluated microscopically for core size, neck size, pore size, grain structure, and incorporated oxide film. Hardness was also evaluated. Implants were compared with Ti-6Al-4V commercial powders. Core size increased and pore size decreased with increases in energy and capacitance. The cores were composed of equiaxed grains which were free of oxide at the grain boundary. Porous layers, consisting of particles connected in three dimensions by necks, were free of oxide films at the connecting interfaces. Neck size increased with increases in input energy and capacitance. Hardness readings of the core, necks, and porous particles resulted in readings higher than or similar to control materials. Electrodischarge compaction did not alter the physical characteristics during compaction.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820251202
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  • 7
    Electronic Resource
    Electronic Resource
    Structure of hydrated Na+ ions around a region of A- or B-DNA helix (1984)
    New York : Wiley-Blackwell
    Biopolymers 23 (1984), S. 257-270 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecular-dynamics simulation was used to carry out an introductory study of the hydration of a section of a rigid single A- or B-DNA helix with one Na+ counterion per nucleotide. Four Na+ ions and four nucleotides and periodic boundary conditions were used to mimic an infinite helix. The atoms of the helix and the Na+ ions were assumed to be Lennard-Jones spheres that also carried charges. Stillinger four-point charge model water molecules were used. We carried out five calculations, for 26 and 46 water molecules in B-DNA and 20, 32, and 46 in A-DNA fragments. The arrangements of the Na+ ions are found to have some similarities to those obtained by Clementi and Corongiu. In the calculations with 46 water molecules, we found that two Na+ ions can be bridged by about two water molecules and form a hydrated bound pair, which in turn forms a bridge between the guanine N7 and a near phosphate group. These bound pairs may be important in stabilizing the helix structure of DNA molecules.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360230207
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  • 8
    Electronic Resource
    Electronic Resource
    Calculation of the glass transition temperatures of polymers. Part I. Homopolymers and copolymers with alkyl side chains (1970)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 555-570 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Four equations, relating the glass transition temperatures Tg of homopolymers and copolymers to invariant additive temperature parameters (ATP) associated with their constituent groups, but weighted in different ways, have been applied to the calculation of the Tg of seven series of polymers having alkyl side chains. It is shown that the Tg of the 32 polymers considered may be calculated, within 7°K of the observed values, without the use of interaction coefficients from 15 independent variables, representing summations of the ATP's. The present calculations are confined to those structures which may be formed by a recombination of the structures corresponding to these independent variables. It is an essential feature of the approach that a distinction is made between groups with different nearest neighbors. Alternative methods of calculation are considered. The temperature parameter for a sequence of three or more methylene groups is estimated as 141°K, in conformity with the transition in polyethylene at 148°K. Nearest-neighbor interactions, stereoregularity, and crystallinity effects are discussed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1970.160080407
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  • 9
    Electronic Resource
    Electronic Resource
    Laser light scattering studies of poly(L-lysine HBr) in aqueous solutionsPartly presented at the 1974 March Meeting of the American Physical Society, Philadelphia, Pa. (1975)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 13 (1975), S. 873-888 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A simple theory for the relaxation of concentration fluctuations in polyelectrolyte solutions is presented, and particular results for the high-salt and no-salt limiting cases are discussed.Autocorrelation functions for the fluctuating intensity of scattered light from dilute aqueous solutions of poly(L-lysine HBr) (PLL-HBr) with and without added salt have been observed over a wide range of pH. The observed autocorrelation functions are in general very satisfactorily represented by single exponentials except at high pH (〉10.5), where considerable aggregation is manifested. Solutions of PLL HBr without added salt exhibit extraordinary behavior, evident at low pH, involving a species with a very slowly decaying autocorrelation function. Though this species is readily annealed to a more ordinary individual free-molecule form by cycling the pH to 9.5 or higher and back, the resulting molecules are found to require unusually long times to reach internal configuration equilibrium under low pH conditions. Solutions of PLL-HBr in 0.2M NaBr and 0.1M NaCl are apparently free of similar extraordinary effects and show the normal isothermal helix-coil transition accompanied by a 15-30% rise in the diffusion coefficient to a maximum at pH 10.5, which is interpreted in terms of a change in molecular dimension of an interrupted helix.The predicted K2 dependence of the reciprocal relaxation time and enhancement of the apparent diffusion coefficient of the polyelectrolyte in the absence of salt is confirmed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1975.180130501
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  • 10
    Electronic Resource
    Electronic Resource
    Heat capacity of fluoropolymers (1975)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 13 (1975), S. 619-635 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The heat capacities of poly(vinyl fluoride), poly(vinylidene fluoride), and polytrifluoroethylene have been measured between 80 and 340°K. The results can be expressed as the sum of two terms: the optical contribution calculated from the vibrational band assignments in the literature and the acoustical contribution calculated according to the Tarasov continuum model. Combining our data with those for polyethylene and polytetrafluoroethylene, it is concluded that the force constant for one-dimensional intrachain interaction is approximately constant for all polymers with carbon backbones. The force constant for three-dimensional interchain interaction is one order of magnitude smaller than the one-dimensional force constant, and decreases when the hydrogen atoms in polyethylene are replaced by fluorine atoms. The thermodynamic functions for the three polymers have been evaluated. Glass transitions at 228°K and 305°K have been found in poly(vinylidene fluoride) and polytrifluoroethylene, respectively.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1975.180130312
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