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  • Polymer and Materials Science  (152)
  • Cell & Developmental Biology  (92)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 2811-2817 
    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: When hexaphenylcyclotrisilazane was heated above 450°C. at atmospheric pressure, it formed an infusible polymer of exceptional thermal and chemical stability. The polymerization, which was accompanied by elimination of benzene, is represented approximately by the equation: \documentclass{article}\pagestyle{empty}\begin{document}$\eta [({\rm C}_6 {\rm H}_5)_2 {\rm SiNH}]_3\,\, \to \,\,({\rm C}_6 {\rm H}_5 {\rm SiN})_{3n} + 3n{\rm C}_6 {\rm H}_6$\end{document} The infusible polymer was a foamed, vitreous, pale yellow solid with a high degree of stability to heat, acids, alkali, and organic solvents. A similar reaction occured with a resein that was obtained as a by-product in the preparation of hexaphenylcyclotrisilazane and with a mixture of silylamines that was obtained from the reaction of methylphenyldichlorosilane with ammonia. Coatings on aluminum and steel prepared by heating the silylamine polymers had good thermal stability and adhesion. Inclusion of a polymeric dimethylsilyl derivative of ethylenediamine improved the flexibility of the coatings.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization of γ-benzyl-L-glutamate NCA initiated by n-hexylamine in DMF proceeds with two successive propagation rates whose ratio is about 1.5. The onset of the increase in rate of propagation occurred at a DPn of 7-14, which was independent of initiator to anhydride ratio and anhydride concentration and not a result of anhydride impurities. The increase in rate is likely a result of a conformational change in the polymer at a DPn of 7-14.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1573-1605 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dependence of Förster long-range resonance energy transfer efficiency on the orientational freedom of donor D and acceptor A molecules attached to a macromolecular substrate is examined. The usefulness of polarized emission measurements in determining the mutual orientation as well as the degree of orientational freedom of D and A and thereby deriving maximum and minimum values for the D-A separation from the transfer efficieny is demonstrated.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A thermal perturbation curve (TPC) is defined to be the derivative of the fractional degree of saturation, f, with respect to temperature, considered as a function of the natural logarithm of free ligand concentration, y. The theoretical framework for the use of such curves in the thermodynamic analysis of ligand binding to macromolecules is presented. The thermal perturbation curve either provides or complements the information obtained from the derivative binding isotherm ∂f/∂y. For a single set of identical and independent sites the TPC is identical to the derivative binding isotherm. Analysis of such a curve directly yield ΔH0 and ΔG0 for the binding reaction. In actual experimental work, however, the TPC can only be approximated because of “self-buffering” effects relations between the parameter of the approximate curve and the thermodynamic quantities have been developed. This technique is applied to the proflavin-α-chymotryspin system to demonstrate its usefulness. The general features of thermal perturbation curves for cases of multiple sets of independent sites and cooperatively interacting sites have also been developed. The analysis of thermal perturbation curves in combination with other methods should provide a more powerful approach to the characterization of ligand-macromolecule interactions.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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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: Stoichiometric mixtures of acridine orange with dermatan sulfate at total dye concentrations ≤ 1 × 10-5 M show fluorescence maxima at 540 nm and 660 nm on excitation at 436 nm. By means of membrane filtration, it is directly demonstrated that the species emitting at 540 nm is due only to unbound dye whereas the 660-nm emitting species is due to bound dye. It is, therefore, possible to differentiate unbound acridine orange from its dermatan sulfate complex solely by spectroscopic methods. Thermodynamic binding parameters can be calculated from rapid spectroscopic measurements without disturbing the system.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nature of internal and overall motions in native (double-stranded) and denatured (single-stranded) DNA fragments 120-160 base pairs (bp) long is examined by molecular-dynamics modeling using 13C-nmr spin-relaxation data obtained over the frequency range of 37-125 MHz. The broad range of 13C frequencies is required to differentiate among various models. Relatively narrow linewidths, large nuclear Overhauser enhancements (NOEs), and short T1 values all vary significantly with frequency and indicate the presence of rapid, restricted internal motions on the nanosecond time scale. For double-stranded DNA monomer fragments (147 bp, 24 Å diam at 32°C), the overall motion is that of an axially symmetric cylinder (τx = ∼10-6 s;τZ = ∼1.8 × 10-8s), which is in good agreement with values calculated from hydrodynamic theory (τx = ∼1.8 × 10-6 s; τZ = ∼2.7 × 10-8 s). The DNA internal motion can be modeled as restricted amplitude internal diffusion of individual C—H vectors of deoxyribose methine carbons C1′, C3′, and C4′, either with conic boundary conditions (τw = ∼4 × 10-9 s, θcone = ∼21°) or as a bistable jump (τA = τB = ∼2 × 10-9 s, θ = ∼15°). We discuss the critical role in molecular-dynamics modeling played by the angle (β) that individual C—H vectors make with the long axis of the DNA helix. Heat denaturation brings about increases in both the rate and amplitude of the internal motion (described by the wobble model with τW = ∼0.2 × 10-9 s, θcone = ∼50°), and overall motion is affected by becoming essentially isotropic (τx = τZ = ∼5 × 10-8 s) for the single-stranded molecules. Since 13C-nmr data obtained at various DNA concentrations for C2′ of the deoxyribose ring is not described well by the above models, a new model incorporating an additional internal motion is proposed to take into account the rapid, extensive, and weakly coupled motion of C2′.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hinge-bending mode of hen egg white lysozyme is studied by a constrained minimization technique. Results with and without a bound inhibitor, tri-N-acetyl-glucosamine, are obtained. The frequency of the mode with the inhibitor is found to be 4.3 cm-1, in contrast to 3.0 cm-1 for the free enzyme. Also, the hinge-bending angle with the lowest energy is shifted 10° towards a more closed cleft in the bound species. The main contribution to these differences arise from interactions with the residues lining the cleft and those on the back side of it. Structural details that account for the energetics are presented. The method of calculation is somewhat different from a previous study [J. A. McCammon, B. R. Gelin, M. Karplus & P. G. Wolynes, (1976) Nature 262, 325-326] to reduce the likelihood of artifacts in the results.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 137-168 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A procedure, CONGEN, for uniformly sampling the conformational spaceof short polypeptide segments in proteins has been implemented. Because thetime required for this sampling grows exponentially with the number of residues, parameters are introduced to limit the conformational space that has to be explored. This is done by the use of the empirical energy function ofCHARMM [B. R. Brooks, R. E. Bruccoleri, B. D. Olafson, D. J. States, S. Swaminathan and M. Karplus (1983) J. Comput. Chem. 4, 187-217] and truncating the search when conformations of grossly unfavorable energy are sampled. Tests are made to determine control parameters that optimize the search without excluding important configurations. When applied to known protein structures, the resulting procedure is generally capable of generating conformations where the lowest energy conformation matches the known structure within a rms deviation of 1 Å.
    Additional Material: 9 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1847-1862 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-temperature molecular dynamics as a method for conformational search was explored on the antigen combining site of McPC 603, a phosphorylcholine binding immunoglobulin. Simulations at temperatures of 500, 800, and 1500 K were run for 111.5, 101.7, and 76.3 ps, respectively. The effectiveness of the search was assessed using a variety of methods. For the shorter hypervariable loops, molecular dynamics explored an appreciable fraction of the conformational space as evidenced by a comparison to a simple theoretical model of the size of the conformational space. However, for the longer loops and the antigen combining site as a whole, the simulation times were too short for a complete search. The simulations at 500 and 800 K both generated conformations that minimized to energies 200 kcal/mole lower than the crystal structure. However, the 1500 K simulation produced higher energy structures, even after minimization; in addition, this highest temperature run had many cis-trans peptide isomerizations. This suggests that 1500 K is too high a temperature for unconstrained conformational sampling. Comparison of the results of high temperature molecular dynamics with a direct conformational search method, [R. E. Bruccoleri & M. Karplus (1987) Biopolymers 26, 137-168]. showed that the two methods did not overlap much in conformational space. Simple geometric measures of the conformational space indicated that the direct method covered more space than molecular dynamics at the lower temperature, but not at 1500 K. The results suggest that high-temperature molecular dynamics can aid in conformational searches.
    Additional Material: 6 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 61-72 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: UV stabilization of polymer systems containing brominated flame retardants has proven to be a difficult technical challenge. Generation of acidic products during processing or exposure can cause a catastrophic deactivation of the Hindered Amine Light Stabilizer (HALS). An understanding of the mechanism for bromine generation from aliphatic and aromatic based flame retardants has lead to formulation approaches based on flame retardant structure. In formulations containing aromatic brominated flame retardants, combinations of UV absorbèrs and a new class of siloxane HALS provide the highest level of UV stabilization to date. Alternatively, bicomponent fiber spinning technology can also provide outstanding UV resistance at significantly lower levels of stabilizers than that used in the monocomponent formulation approach.
    Additional Material: 11 Ill.
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