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  • 1
    Electronic Resource
    Electronic Resource
    Makromolekulare schalter für doppelschichtmembranen (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 166 (1989), S. 257-272 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Controlled polyelectrolyte adsorption can be used to render phospholipid bilayer membranes sensitive to physical and chemical signals. We describe in this paper the design and construction of macromolecular switches for bilayer membranes, which can be used to create lipid vesicles that release their contents rapidly and quantitatively in response to changes in pH, temperature, light intensity or glucose concentration. The kinetics and mechanisms of the molecular switching processes observed in such systems are also discussed.
    Notes: Kontrollierte Adsorption von Polyelektrolyten kann ein wirksames Werkzeug im Design von dünnen molekularen Filmen sein. Man kann erwarten, daß die Adsorption von Polyelektrolytketten das empfindliche Kräftegleichgewicht erheblich beeinflußt, das die strukturellen und funktionellen Eigenschaften von geordneten Strukturen wie Einzel-, Doppel- und Mehrfachschichten bestimmt. Andererseits ist die Adsorption von Polyelektrolyten außerordentlich sensitiv auf Umgebungsparameter, z.B. pH, Temperatur oder lonenstärke. Kontrollierte Adsorption kann daher zu Sensitivität auf bestimmte chemische oder physikalische Stimuli führen, sodaß auf diese Weise ein molekularer Schaltmechanismus entworfen werden kann. Durch Umsetzen dieser ldee in reale Systeme gelang es uns, molekulares Schalten in Mischungen von Poly(2-ethylacrylsäre) mit natürlichen oder synthetischen Phosphatidylcholinen zu bewirken. Insbesondere haben wir Phosphatidylcholinvesikel hergestellt, die ihren lnhalt nach einer Änderung von pH, Temperatur, Glukosekonzentration oder nach Bestrahlung mit Licht schnell und quantitativ freisetzen. Die Entwicklung und die Herstellung von Doppelschichtmembranen, die auf solche Änderungen reagieren, sowie die Kinetik und der Mechanismus des damit verbundenen molekularen Schaltprozesses werden im vorliegenden Artikel diskutiert.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1989.051660118
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  • 2
    Electronic Resource
    Electronic Resource
    Numerical solutions of the Lamm equation. III. Velocity centrifugation (1967)
    New York : Wiley-Blackwell
    Biopolymers 5 (1967), S. 697-713 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have generated solutions to the Lamm equation to examine the effects of concentration dependence on velocity experiments. Two forms of c dependence are considered: s/s0 = 1 - kc and s/s0 = (1 + kc)-1. Features of these solutions are discussed. The magnitude of the errors resulting from the usual procedure of measuring the rate of movement of schlieren maxima or of the position at which the concentration is one half the plateau value have been examined. These errors are usually negligible after sufficient centrifugation time. The errors in using the half-plateau concentration are less than those using the movement of the peak. We have also examined a technique due to Fujita for determining D from boundary spreading when s/s0 = (1+kc)-1. This method is satisfactory when s/s0 is actually of this form, or under certain limitations when s/s0 = (1 + kc)-1. Creeth has shown that under certain conditions the concentration gradient, curve remains virtually unchanged in shape after separating from the meniscus. When this occurs it is possible to estimate s/D from the data. The condition for such a steady state is that kc0 be sufficiently large. Numerical confirmation of this method is presented in the final section.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1967.360050804
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  • 3
    Electronic Resource
    Electronic Resource
    Measurement of preferential solvation of some glucans in mixed solvent systems by gel-permeation chromatography (1980)
    New York : Wiley-Blackwell
    Biopolymers 19 (1980), S. 639-653 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preferential solvation of the glucans amylose, pullulan, and dextran in binary dimethyl-sulfoxide/water (DMSO/H2O) solvent mixtures has been measured using gel-permeation chromatography. The preferential solvation behavior of the three glucans in DMSO/H2O solvent mixtures is indistinguishable in the experiments reported. In solvent mixtures with mol ratio DMSO/H2O less than 1:2, all three glucans are solvated preferentially by H2O. The maximum extent of preferential solvation by H2O is about 2.5 mol H2O/mol of glucose residues. When the DMSO/H2O mol ratio exceeds 1:2, DMSO solvates the glucans preferentially to a maximum extent of about 1 mol DMSO/mol of glucose residues. An interpretation of the change in preferential solvation with mixed solvent composition is suggested in terms of the known characteristics of the binary solvent system, and the relationship of preferential solvation, reported here, to the absolute solvation of the glucan chains is discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1980.360190313
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  • 4
    Electronic Resource
    Electronic Resource
    On the CD helix band for long helical polymers (1987)
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 109-119 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The CD helix bands for infinitely long helical polymers are shown tobe composed of two parts: a derivative-shaped band plus an ordinary Gaussian-like band. The derivative-shaped band results from the zero-order term of an expansion while the Gaussian-like band results from the first-order expansion term. However, the intensities of the two bands are shown to be of the same order of magnitude. They are both linear in the coulombic coupling of transition charge densities for polymer transitions. The sum yields a skewed derivative-shaped band. The shapes of net CD helix bands are shown to not depend on the approximations used for averaging over orientations if the usual systems, such as polypeptides and polynucleotides, are considered in their long-wave-length spectral regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360260112
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  • 5
    Electronic Resource
    Electronic Resource
    Conformational studies of nucleic acids. V. Sequence specificities in the conformational energetics of oligonucleotides: The homo-tetramers (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 59-77 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational energetics of the tetranucleoside triphosphates d(ApApApA), d(GpGpGpG), d(CpCpCpC), d(TpTpTpT), ApApApA, GpGpGpG, CpCpCpC, and UpUpUpU are thoroughly examined using a classical potential energy function. The sugar modeling method and multiple correlation functions derived in previous papers of this series are utilized in these examinations. The data are analyzed and compared in terms of the energy profiles for rotation about the conformation-determining torsion angles in the tetramers. Overall, the predictions are in reasonable qualitative agreement with the existing experimental data. It is found that the base type does not greatly affect the locations of the important minima in these profiles, but rather exerts a large influence on the relative depths of the minima and the barriers to conversion between them. Conformational sequence dependence is manifest to a greater extent by the DNA tetramers than the RNA tetramers. Of the DNA tetramers, d(CpCpCpC) appears, from the results presented herein, to have the greatest potential for polymorphism. This and other findings are analyzed in terms of the preferences of particular DNA sequences for either the A-, B-, or Z-conformation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270105
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of nucleotide bromination on the stabilities of Z-RNA and Z-DNA: A molecular mechanics/thermodynamic perturbation study (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 1939-1957 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of ZI- and ZII- form RNA and DNA oligonucleotides were energy minimized in vacuum using the AMBER molecular mechanics force field. Alternating C-G sequences were studied containing either unmodified nucleotides, 8-bromoguanosine in place of all guanosine residues, 5-bromocytidine in place of all cytidine residues, or all modified residues. Some molecules were also energy minimized in the presence of H2O and cations. Free energy perturbation calculations were done in which G8 and C5 hydrogen atoms in one or two residues of Z-form RNAs and DNAs were replaced in a stepwise manner by bromines. Bromination had little effect on the structures of the energy-minimized molecules. Both the minimized molecular energies and the results of the perturbation calculations indicate that bromination of guanosine at C8 will stabilize the Z forms of RNA and DNA relative to the nonbrominated Z form, while bromination of cytidine at C5 stabilizes Z-DNA and destabilizes Z-RNA. These results are in agreement with experimental data. The destabilizing effect of br5C in Z-RNAs is apparently due to an unfavorable interaction between the negatively charged C5 bromine atom and the guanosine hydroxyl group. The vacuum-minimized energies of the ZII- form oligonucleotides are lower than those of the corresponding ZI- form molecules for both RNA and DNA. Previous x-ray diffraction, nmr, and molecular mechanics studies indicate that hydration effects may favor the ZI- conformation over the ZII- form in DNA. Molecular mechanics calculations show that the ZII-ZI energy differences for the RNAs are greater than three times those obtained for the DNAs. This is due to structurally reinforcing hydrogen-bonding interactions involving the hydroxyl groups in the ZII form, especially between the guanosine hydroxyl hydrogen atom and the 3′-adjacent phosphate oxygen. In addition, the cytidine hydroxyl oxygen forms a hydrogen bond with the 5′-adjacent guanosine amino group in the ZII- form molecule. Both of these interactions are less likely in the ZI- form molecule: the former due to the orientation of the GpC phosphate away from the guanosine ribose in the ZI form, and the latter apparently due to competitive hydrogen bonding of the cytidine 2′-hydroxyl hydrogen with the cytosine carbonyl oxygen in the ZI form. The hydrogen-bonding interaction between the cytidine hydroxyl oxygen and the 5′-adjacent guanosine amino group in Z-RNA twists the amino group out of the plane of the base. This may be responsible for differences in the CD and Raman spectra of Z-RNA and Z-DNA.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360281111
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  • 7
    Electronic Resource
    Electronic Resource
    Side-chain interactions in the C-peptide helix: Phe 8 ⃛ His 12+ (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1-11 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous studies have demonstrated that His 12 plays a major role in the pH-dependent stability of the helix formed by the isolated C-peptide (residues 1-13 of ribonuclease A). Here, amino acid replacement experiments show that His 12+ stabilizes the C-peptide helix chiefly by interacting with Phe 8. The Phe 8 ⃛ His 12+ ring interaction is specific for the protonated form of His 12 (His 12+) and the interaction is not screened significantly by NaCl, unlike the charged group ⃛ helix dipole interactions studied earlier in C-peptide. Analogs of C-peptide that are unable to form the Phe 8 ⃛ His 12+ interaction show large increases in helix content for Phe → Ala and His → Ala. Therefore, the helical tendencies of the individual residues Phe, His, and Ala are important in determining the result of a replacement experiment. Since the side chains of Phe 8 and His 12 probably interact within the N-terminal helix of ribonuclease A, the existence of the Phe 8 ⃛ His 12+ interaction in the isolated C-peptide helix adds to the evidence that the C-peptide helix is an autonomous folding unit.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290104
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  • 8
    Electronic Resource
    Electronic Resource
    Numerical solutions of the Lamm equation. II. Equilibrium sedimentationPresented, in part, at, the Ninth Annual Meeting of the Biophysical Society, San Francisco, 1965. (1966)
    New York : Wiley-Blackwell
    Biopolymers 4 (1966), S. 457-468 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Lamm equation has been solved numerically for conditions corresponding to equilibrium runs for a nonlinear concentration dependence of the form s/s0 = (1 + kc)-1. It is shown that the approach to equilibrium is very close to being exponential (in time) as in the case k = 0. We also compare results for the nonlinear case given above with results obtained for linear c-dependence of the form s/s0 = 1 - kc. For relatively high speeds the time required to attain equilibrium may be greatly underestimated by use of the latter approximation. Finally, we present analytic approximations for the concentration distribution at equilibrium and as a function of time.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1966.360040407
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  • 9
    Electronic Resource
    Electronic Resource
    Numerical solutions of the Lamm equation. I. Numerical procedurePresented, in part, at the Ninth Annual Meeting of the Biophysical Society, San Francisco, 1965. (1966)
    New York : Wiley-Blackwell
    Biopolymers 4 (1966), S. 449-455 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper gives an account, of the numerical technique used to derive results to he presented in future papers of this series.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1966.360040406
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  • 10
    Electronic Resource
    Electronic Resource
    Instability in pressure-dependent sedimentation of monomer - polymer systems (1973)
    New York : Wiley-Blackwell
    Biopolymers 12 (1973), S. 2477-2490 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The possibility of convection in velocity sedimentation studies on pressure dependent associating systems is known both experimentally and theoretically. We present accurate numerical solutions to the Lamm equation to illustrate this phenomenon for monomer-polymer systems. An approximate theory based on the absence of diffusion is then developed to predict the onset of convection. Comparison of the theory with the numerical solutions shows it to be quite accurate.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1973.360121104
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