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  • 1
    Electronic Resource
    Electronic Resource
    Role of Surface Effects in the Inelastic Background of X-ray Photoelectron Spectroscopy (1996)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 24 (1996), S. 490-496 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: We have derived a new deconvolution formula to obtain the original no-loss XPS spectra, the so-called source function, by taking surface effects into account. With this formula the primary XPS spectra of Au 4d and Au 4f are carried out from the experimental data. The primary excitation spectra are compared to the results derived by Tougaard’s method in which surface effects were neglected. The present result is markedly different from Tougaard’s result, which consists of a tail extending ∽50 eV below the peak. The result reveals that the influence of surface effects on the background removal of the spectra is considerably significant for the energy range ∽50 eV below the peak energy. It is also found that the large tail in Tougaard’s results can be essentially removed when surface effects are considered.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Premelting thermal fluctuational base pair opening probability of poly(dA) · poly(dT) as predicted by the modified self-consistent phonon theory (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 139-148 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We employ a mean field, modified, self-consistent phonon theory to evaluate the single base-pair opening rate and the probability of a base pair in the amino proton exchangeable state for the homopolymer poly(dA) · poly(dT) at temperatures below the helix-coil transition region. Our calculated premelting single base-pair opening probabilities are in general agreement with several available experimental estimates from imino proton exchange and formaldehyde-induced DNA melting measurements. These calculated opening probabilities, however, are in disagreement with the prediction of the helix-coil transition theory. Possible reasons for the differences are discussed, especially the possible different definition of a meaningful open state in the premelting region. The premelting open state of the modified self-consistent phonon approximation theory seems to be appropriate to describe a solvent-accessible open configuration that is sufficient to facilitate important chemical reactions such as imino proton exchange and formaldehyde reaction with the bases. This can be compared with the completely unstacked open state of the helix-coil transition theory originally defined in the helix-coil transition region. We propose that the amino proton exchangeable state is different from the open state associated with melting and only involves the breaking of the amino interbase H bond. The agreement between the calculated and experimentally estimated probability of a base pair in the amino proton exchangeable state seems to support this hypothesis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360310202
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  • 3
    Electronic Resource
    Electronic Resource
    Sequence and temperature dependence of the interbase hydrogen-bond breathing modes in B-DNA polymers: Comparison with low-frequency Raman peaks and their role in helix melting (1995)
    New York : Wiley-Blackwell
    Biopolymers 35 (1995), S. 573-582 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We carry out temperature-dependent lattice dynamics calculations to determine the vibrational normal modes associated with the interbase H-bond breathing motion in several B-DNA copolymers at temperatures from room temperature to the melting temperatures. We take into consideration Raman selection rules and incorporate a simple empirical model of Raman susceptibility in the interbase H bonds in our calculation and compare them to Raman measurements. Our calculations are carried out using empirical force constants that are not further refined to low-frequency spectra. Our calculations show the existence of strong interbase H-bond breathing modes at frequencies and with relative oscillator strengths close to the observed Raman peaks in the range of 60-140 cm-1 for the DNA sequences considered except for one helix. The correlation between the calculated and observed frequencies and oscillator strengths indicates that the observed Raman peaks in the frequency range are likely interbase H-bond breathing modes. We find that these modes exhibit sizable temperature as well as sequence dependence. We show the softening of these modes on approaching thermal denaturation that is also in agreement with the observed behavior in Raman and melting measurements. The sensitivity of the calculation on the empirical model of Raman susceptibility and the possible reasons for the discrepancy between a few calculated values and observations are discussed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360350603
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  • 4
    Electronic Resource
    Electronic Resource
    Normal mode calculation of a netropsin-DNA complex: Effect of structural deformation on vibrational spectrum (1995)
    New York : Wiley-Blackwell
    Biopolymers 35 (1995), S. 657-666 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calculations of the normal mode spectrum of a netropsin-DNA complex, an isolated DNA helix of the same sequence, and a free netropsin molecule were carried out and compared with observations. We find that the frequency of modes of the complex that are primarily vibrations localized to the helix are relatively unchanged from the frequencies found for similar modes of the isolated helix. On the other hand, the frequencies of those modes of the complex that are found to be primarily in the netropsin are found to change significantly in the complex from that of the free netropsin. Further analysis indicates that the changes in the “netropsin modes” are primarily due to the conformational deformation induced in the netropsin by formation of the complex. All the frequencies and shifts in frequency are in good agreement with recent Raman measurements. © 1995 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360350611
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  • 5
    Electronic Resource
    Electronic Resource
    Hybrid Monte Carlo simulations theory and initial comparison with molecular dynamics (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 1307-1315 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A formal partially dynamical approach to ergodic sampling, hybrid Monte Carlo, has been adapted for the first time from its proven application in quantum chromodynamics to realistic molecular systems. A series of simulations of pancreatic trypsin inhibitor were run using temperature-rescaled molecular dynamics and hybrid Monte Carlo. It was found that simulations run using hybrid Monte Carlo equilibrated an order of magnitude faster than those run using temperature-rescaled molecular dynamics. Certain aspects of improved performance obtained using hybrid Monte Carlo are probably due to the increased efficiency with which this algorithm explores phase space. To discuss this we introduce the notion of “trajectory stiffness”. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330815
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  • 6
    Electronic Resource
    Electronic Resource
    Premelting thermal fluctuational interbase hydrogen-bond disrupted states of a B-DNA guanine-cytosine base pair: Significance for amino and imino proton exchange (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1273-1281 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modified self-consistent phonon theory when applied to the DNA double helix indicates the existence of fairly long-lived states in which single interbase H bonds are disrupted. One can then postulate a number of situations in which particular disrupted H bonds can enhance particular proton exchange. In this paper we postulate a number of such partially open states for a B-conformation GC base pair and calculate the probability of each of these states for a B-conformation poly(dG) · poly(dC). We compare these probabilities to those probabilities needed to explain various observed proton exchange rates. We propose that, for a GC base pair in B conformation, there are two amino proton exchangeable states - a cytosine amino proton exchangeable state and a guanine amino proton exchangeable state; both require the disruption of only the corresponding inter base H bond. The imino proton exchange, however, requires the disruption of all three inter base H bonds and this defines a third open state. Our calculated probabilities for a GC base pair in these three states are in fair agreement with available experimental estimates from measurements of amino and imino proton exchange.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311105
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  • 7
    Electronic Resource
    Electronic Resource
    The influence of molecular weight on the large deformation behavior of SBS triblock copolymer elastomers (1977)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 21 (1977), S. 629-643 
    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: Engineering stress-strain properties were determined for two polystyrene-polybutadiene-polystyrene (SBS) triblock copolymer elastomers, one consisting of blocks of molecular weight 7000/43000/7000 and the other, 16000/85000/17000. In addition, various blends of these two materials were prepared in order to vary the number-average molecular weight of the blocks in a systematic way while maintaining polystyrene content in the range of 25-28 wt %. Samples were solvent cast from benzene or benzene/heptane mixtures and annealed before testing. Ring specimens were extended to rupture at varying strain rates on an Instron tensile tester. Results indicate that number-average molecular weight has a marked influence on stress-strain behavior over the range of molecular weights and testing conditions employed. The observed behavior is consistent with a systematic increase in the proportion of a mixed interfacial region between the pure polystyrene and polybutadiene domain as molecular weight decreases. The interfacial region contributes to mechanical hystersis, rate sensitivity, and toughness in the SBS materials. Scanning electron photomicrographs of fracture surfaces also showed systematic changes with molecular weight.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1977.070210305
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of azo-containing polydimethylsiloxanes and their copolymers with methyl methacrylate (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 2613-2620 
    Details
    ISSN: 0887-624X
    Keywords: polydimethylsiloxane ; poly(methyl methacrylate) ; block copolymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azo group-containing polydimethylsiloxanes (PDMS-ACP), macroazoinitiators, were prepared by polycondensation reaction of 4,4′-azobis-4-cyanopentanoyl chloride (ACPC) with hydroxybutyl-terminated polydimethylsiloxane (PDMS) of varying molecular weights. The activation energy (Ea), activation enthalpy (ΔH
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Differences in melting behavior between homopolymers and copolymers of DNA: Role of nonbonded forces for GC and the role of the hydration spine and premelting transition for AT (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 797-812 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Melting measurements of the mono-base-pair DNA polymers showed that the melting temperature Tm of the B-DNA homopolymer poly (dA ) · poly (dT) is higher than that of the copolymer poly [d(A-T)]. On the other hand, the Tmof the B-DNA homopolymer poly (dG) · poly (dC) is lower than that of the copolymer poly [d (G-C)]. From a structural point of view, the cross-strand base-stacking interaction in a DNA homopolymer is weaker than that in a DNA copolymer with the same base pair. One would then expect that all the DNA homopolymers are less stable than the copolymer with the same base pair. We find that the inversion of the melting order seen in the AT mono-base-pair DNA polymers is caused by the enhanced thermal stability of poly (dA) · poly (dT) from a well-defined spine of hydration attached to its minor groove. In this paper we employ the modified self-consistent phonon theory to calculate base-pair opening probabilities of four B-DNA polymers: poly(dA)-poly(dT), poly(dG) · poly(dC), poly[d(A-T)], and poly[d(G-C)] at temperatures from room temperature through the melting regions. Our calculations show that the spine of hydration can give the inverted melting order of the AT polymers as compared to the GC polymers in fair agreement with experimental measurements. Our calculated hydration spine disruption behavior in poly(dA) · poly(dT) at premelting temperatures is also in agreement with experimentally observed premelting transitions in poly (dA) · poly (dT). The work is in a sense a test of the validity of our models of nonbonded interactions and spine of hydration interactions. We find we have to develop the concept of a strained bond to fit observations in poly (dA) · poly(dT). The strained-bond concept also explains the otherwise anomalous stability of the hydration chain. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330508
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  • 10
    Electronic Resource
    Electronic Resource
    A cooperative self-consistent microscopic theory of thermally induced melting of a repeat sequence DNA polymer (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 351-362 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We attempt to extend the modified self-consistent phonon theory to describe thermal fluctuational base-pair opening of repeat sequence DNA polymers in the helix-coil transition region as well as in the premelting region. A microscopic base-pair open state is introduced and the effect of this open state is taken into account self-consistently in a mean field system that models the DNA polymer. Our analysis indicates the structure of this open state changes with temperature in such a manner that on average a base pair opens and unstacks with its neighbors more completely as temperature increases. We apply this theory to a homopolymer - poly(dG) · poly(dC) to evaluate the base-pair opening probability in a temperature range from 273 to 366.5 K. At 366.5 K the system undergoes cooperative melting. Our calculated base-pair opening probabilities are in general agreement with several experimental estimates at room temperature. The calculated probabilities show typical melting curve behavior at temperatures close to the observed melting temperature. The cooperative modified self-consistent phonon approximation approach becomes a viable microscopic theory of melting. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330304
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