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  • 1980-1984  (28)
  • Chemistry  (28)
  • Physical Chemistry  (2)
  • Biochemistry and Biotechnology
  • 1
    Electronic Resource
    Electronic Resource
    A critical evaluation of models for complex molecular dynamics: Application to NMR studies of double- and single-stranded DNA (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 2703-2726 
    Details
    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
    URL: http://dx.doi.org/10.1002/bip.360221214
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  • 2
    Electronic Resource
    Electronic Resource
    Micellar Solubilization of Biopolymers in Hydrocarbon Solvents III. Empirical Definition of an Acidity Scale in Reverse Micelles (1980)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 63 (1980), S. 2302-2311 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper deals with the problem of defining, and measuring, the pH inside the water pool (which we define as pHwp) of reverse micelles, i.e. micelles formed by surfactants dissolved in apolar solvents in the presence of minimal amounts of water. The conceptual and experimental difficulties are discussed, and it is argued that no absolute determination of pHwp is possible, mostly because water in the water pools of reverse micelles is a new solvent, for which no standardization of acidity is available. The problem can be approached only on the basis of an empirical acidity scale.An empirical acidity scale for water pools in reverse micelles of bis (2-ethyl-hexyl) sodium sulfosuccinate (AOT) in isooctane has been defined by measuring the 31P-chemical shifts of phosphate buffers. The chemical shifts in bulk water were compared to those found in reverse micelles under the assumption that the pK of phosphate ion is the same in the two systems. It was found that in most cases there was little difference (less than 0.4 pH units) between pHwp and the pH of the starting buffer in bulk water (which we define as pHst). However, this difference between pHwp and pHst may become much larger in certain cases.The difference (pHwp-pHst) is measured under a variety of conditions, and this permits the determination of an operational acidity in the micelle water pools as a function of the pHst with which the aqueous micelles are prepared. The significance of such data for interpreting the behaviour of enzymes confined in the micelles water pool is discussed. Based on the pHwp scale, the apparent pKa of phenol-red and 4-nitrophenol were determined in reverse micelles containing different buffers and different water content. The pKa values obtained were rather sensitive to changes of both these factors, which was taken to signify that organic dies have only a very limited applicability to measure the acidity of the water pools of reverse micelles.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19800630820
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  • 3
    Electronic Resource
    Electronic Resource
    Propriétés viscoélastiques de la poly(α,α-diéthyl-β-propiolactone) (1980)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 181 (1980), S. 857-867 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The viscoelastic properties of poly(α,α-diethyl-β-propiolactone) were investigated in the linear range using stress relaxation and dynamic mechanical methods. Using Ferry's reduction method, a horizontal shift factor was determined at each temperature, that satisfactorily agreed with the WLF equation in the transition zone. No vertical shift was required to superimpose different relaxation curves. The apparent activation energy was temperature dependent and passed through a maximum near Tg whose value is (311 ± 2)K. The relaxation spectrum has been calculated according to the first method of approximation of Schwarzl and Staverman. It consists of a high intensity plateau at shorter times, a wedge type portion with a slope of -0,15 and a low intensity plateau at longer times. Dynamical mechanical measurements revealed a β relaxation peak at 333 K and yielded the evidence of a γ peak around 120 K.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1980.021810408
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  • 4
    Electronic Resource
    Electronic Resource
    Miscibility of poly(caprolactone)/chlorinated polypropylene and poly(caprolactone)/poly(chlorostyrene) blends (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 27 (1982), S. 559-568 
    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: Poly(caprolactone) (PCL) was blended with poly(chlorostyrene) (PSCI) and chlorinated polypropylene (PPCl). A single glass transition temperature Tg was found for these mixtures, indicating their miscibility. PCL crystallizes in these blends when the chlorinated polymer content is not too high. Otherwise, Tg becomes higher than the melting point of PCL and the high viscosity of the medium hinders the crystallization. The miscibility of PCL/PPCI blends cannot be due to hydrogen bonding between the α-hydrogens of the chlorinated polymer and the carbonyl group of the polyester since PPCI does not have available a large number of α-hydrogens. It is suggested that a dipoledipole —C=O…Cl—C— interaction is responsible for the observed miscibility phenomenon and that this interaction is probably also responsible for the miscibility between all other polyesterchlorinated polymer mixtures. Finally, it was observed that poly(α-methyl-α-n-propyl-β-propiolactone), poly(α-methyl-α-ethyl-β-propiolactone) and poly(valerolactone) are not miscible with PSCI or PPCl, despite the fact that they are miscible with poly(vinyl chloride).
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1982.070270219
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  • 5
    Electronic Resource
    Electronic Resource
    The effects of thermooxidative aging on the fatigue behavior of a structural adhesiveCorrected proofs received September 19, 1984 (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 29 (1984), S. 3499-3511 
    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 kinetics of autoxidation of FM-73U, a rubber-modified epoxy adhesive, were investigated by Fourier transform infrared analysis. Absorbance spectra for thin samples aged in hot, moist, oxygen-rich environments were used to assess a plausible reaction mechanism; rate constants, Arrhenius plots, and oxidation rates were determined. Concurrently, crack growth rates were measured on specimens which had been exposed to similar environments for periods of up to 8 months. Paris parameters measured in these tests were correlated with the results of the oxidation studies. These correlations were used to predict the crack growth rate of the adhesive after 10 years of aging in ambient conditions. Although the prediction indicates that the adhesive becomes more brittle with age, the changes are not severe.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1984.070291125
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  • 6
    Electronic Resource
    Electronic Resource
    Equilibrium acid concentrations in hydrolyzed polyesters and polyester-polyurethane elastomersPresented in part at the 184th meeting of the American Chemical Society, Kansas City, MO, September 12-17, 1982, Ref. 1. (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 28 (1983), S. 3779-3792 
    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: Equilibrium acid concentrations, [Ae], were determined in butylene adipate and caprolactone polyesters, of low molecular weight, and in thermoplastic polyurethane elastomers based on these polyesters. Values of [Ae] of the polyesters at 85°C were 0.7, 1.3, and 3-4 × 10-3 mol/g at relative humidities (RH) of 25%, 50%, and 93%, respectively. [Ae] of the thermoplastic elastomers at 85°C were about 3 and 7 × 10-4 mol/g at 10% and 25% RH, respectively. Values of [Ae] were not very dependent on temperature at constant RH. Equilibrated thermoplastic elastomers had low molecular weights and poor physical properties. Consequently, equilibration does not set a practical limit on hydrolytic degradation, even at low RH. Equations were developed that described the variation in acid content with time. Rate constants for hydrolysis and esterification increased as RH decreased. Reesterification in the elastomers in the absence of water is too slow to be a useful method of decreasing hydrolytic damage.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1983.070281218
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  • 7
    Electronic Resource
    Electronic Resource
    Antifreeze glycoproteins: Influence of polymer length and ice crystal habit on activityPortions of this work have been published in a preliminary letter (Ref. 1) and have been presented at the American Chemical Society National Meeting, 1982, St. Louis, Mo. Parts of this material were taken from the theses of M.J.K. and T.S.B. submitted to the Graduate Division, University of California, Davis in partial fulfillment of the requirements for an M.S. degree. (1984)
    New York : Wiley-Blackwell
    Biopolymers 23 (1984), S. 1379-1395 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of the ice crystalline habit and the length of the polymer on the ability of the antifreeze glycoproteins (AFGP) from polar fish to depress the freezing temperature of water was investigated. The low-molecular-weight components of the glycoproteins, AFGP- 6-8, are inactive when a solution of such a sample is nucleated at -6°C. A solution of large AFGP (1-4) is fully functional under the same conditions. The low-molecular-weight components differ from the height-molecular-weight components in that they contain some proline replacing the alanine in the Ala-Ala-Thr · disaccharide polymer unit. In the present experiments, antifreeze activity was examined in the presence of two different forms of ice crystal growth habits, and homodimders of AFGP 6 and 8 were prepared to investigate the function of polymer length and the on antifreeze activity at different degrees of supercooling. The results indicate that the ice crystal growth habit and the introduction of proline into the polymer unit may be responsible for the loss of activity at deep supercooling (-6°C) of AFGP 6-8. The loss in the ability of AFGP to depress the freezing temperature of water at deep supercooling is not solely due to polymer length, as carbodiimide-linked dimers of AFGP 6 do not function under these freezing conditions. A Model of antifreezing action based on Langmuirian adsorption of AFGP on the ice surface and direct competition between water and AFGP molecules for the incorporation sites in the ice crystal lattice is presented.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360230720
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  • 8
    Electronic Resource
    Electronic Resource
    A study of aromatic polyester/chlorinated polymer blends (1984)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 350-354 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 large number of studies have been devoted in recent years to the miscibility behavior of linear polyesters with chlorinated polymers, including poly(vinyl chloride) (PVC), chlorinated PVC, chlorinated poly(ethylenes), and copolymers of vinylidene chloride (Saran). However, similar studies with aromatic polyesters are lacking. It is the purpose of this paper to compare the properties of blends made of poly(ethylene terephthalate), poly(butylene terephthalate) or poly(hexamethylene terephthalate) and of various chlorinated polymers. It is shown that a high concentration of chlorine atoms is required to achieve miscibility. Moreover, there is a “miscibility window” in terms of the carbonyl concentration of polyesters, immiscibility being found for carbonyl concentrations outside this window, A similar behavior was observed before for linear polyester/chlorinated polymer blends and for polyester/polycarbonate blends. Solid state small-angle light scattering experiments were also conducted to follow the morphology of the blends as a function of composition. Spherulites were found but their size vary with composition.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760240509
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  • 9
    Electronic Resource
    Electronic Resource
    Miscibility phenomena in polyester/chlorinated polymer blends (1982)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 22 (1982), S. 90-95 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: Poly(caprolactone) (PCL)/poly(vinyl chloride) (PVC) blends are known to be miscible in the solid state. Recents measurements however indicate that a large number of polyesters are also miscible with PVC if the ratio CH2/C=O of the polyester is between 4 and 10. At low CH2/C=O ratios, polyesters are too rigid to interact specifically with PVC. At high CH2/C=O ratios, the number of interacting groups becomes too small to give miscibility. Similarly, a large number of chlorinated polymers are shown to be miscible with PCL if their chlorine content is high enough. Surprisingly, polyesters are not in general miscible with chlorinated polymers if the mixture does not contain either PCL or PVC. The results presented in this paper suggest that a dipole-dipole interaction, between the carbonyl groups and the C-Cl groups, is responsible for the miscibility phenomena observed in polyester/chlorinated polymer blends.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760220210
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  • 10
    Electronic Resource
    Electronic Resource
    The determination of the thermodynamic interaction parameter χ in polymer blends (1984)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 1291-1299 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 miscibility of polymer blends is related to the polymer-polymer interaction parameter χ23, Several methods can be used to evaluate this parameter and five of the most important ones are reviewed: two equilibrium methods (melting-point depression and vapor sorption), a transport method (inverse-phase gas chromatography) and two scattering methods (neutron scattering and small-angle x-ray scattering). Examples are cited where χ23 values for a given blend were determined by several of these methods. This comparison leads to the conclusion that a reasonable agreement is often reached despite conceptual differences between the methods involved.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760241705
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