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  • 1
    Electronic Resource
    Electronic Resource
    Electrostatic properties of zwitterionic micelles (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 6442-6449 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100194a063
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  • 2
    Electronic Resource
    Electronic Resource
    A conformational interpretation for the peak of reduced viscosity for polyelectrolytes at low ionic strength (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2515-2521 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Several articles over the past decades have reported a peak in the curve of reduced viscosity ηr vs polyelectrolyte concentration Cp when diluted with pure water or a fixed, low ionic strength solution. The current article shows that the large changes in conformation which accompany changes in ionic strength Cs, for long, linear, semiflexible polyelectrolytes, and which enter in the first, quadratic interaction term of the solution viscosity, are sufficient to account for the existence, relative magnitudes, and positions of peaks in such viscosity profiles. This is illustrated for hyaluronic acid (HA), for which the variations of radius of gyration with ionic strength have been previously determined experimentally. The conformational interpretation predicts that in the coil limit, the position of the viscosity vs Cp peak is independent of mass, but that its height should be roughly proportional to M at fixed Cs, and to roughly CpCs−1.5 for a fixed M. The explanation is meant as a limiting case for long, linear polyelectrolytes and posits that steric, or hard, interactions between separate polymers dominate over electrostatic interactions when the polyelectrolyte dimensions are much larger than κ−1 the electrostatic screening length. The other extreme, short, chain polyelectrolytes and other inextensible objects, such as spheres, are mentioned in light of previously elaborated theories based on interacting electrostatic atmospheres when the dimensions of such objects are smaller than κ−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468473
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  • 3
    Electronic Resource
    Electronic Resource
    Dependence of polyelectrolyte apparent persistence lengths, viscosity, and diffusion on ionic strength and linear charge density (1991)
    s.l. : American Chemical Society
    Macromolecules 24 (1991), S. 6189-6198 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00023a021
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  • 4
    Electronic Resource
    Electronic Resource
    Monte Carlo study of light scattering by linear polyelectrolytes (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7766-7776 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The light scattering function P(aitch-theta) of charged isolated threefold rotational isomeric state model polymers was simulated by Metropolis Monte Carlo in the Debye–Hückel approximation. Number of chain units N (up to 250), and ratio (from 0.5 to 64) of Debye screening length κ−1 to bond length D were varied at a bond angle θ of 90°; θs of 70° and 45° were also investigated. Charge was fixed by setting the "Manning parameter'' to 1. Because the properties of linear polyelectrolytes have been interpreted in terms of electrostatic excluded volume and electrostatic persistence lengths, similar chains with hard sphere repulsion were simulated, up to N=400, as were nearly wormlike chains with no repulsion. Overall, a function suggested by Noda et al. described the P(aitch-theta) of both hard sphere chains and electrostatic repulsion chains with κ−1/D of 0.5 moderately well. However, first order renormalization group (RG) calculations correctly predict an intersection between this P(aitch-theta) and that for Gaussian random coils, while the Noda et al. function does not. Requirements for experimental observation of excluded volume effects in polyelectrolytes are discussed. The P(aitch-theta) of chains with large κ−1/D was not fit well by that of nonexcluded volume wormlike chains with the persistence lengths predicted by theory, possibly because excluded volume effects were not small. Linear fits to a log–log plot of 1/P(aitch-theta) vs the square of the scattering vector times the radius of gyration gave the expected slopes, but not intercepts, as predicted by first order RG, probably because u was not large enough.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463496
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  • 5
    Electronic Resource
    Electronic Resource
    Monte Carlo study of titration of linear polyelectrolytes (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1609-1620 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An off-lattice Metropolis Monte Carlo algorithm with reptation is used to find the average fractional ionization α¯ as a function of pH for a generic ionizable linear polyelectrolyte in a salt solution. The polyelectrolyte is treated as a threefold rotational isomeric state model polymer; each unit can bear a negative charge or not with intrinsic ionization constant pKa. Debye–Hückel screening is assumed between the charges. For computational convenience, the dielectric constant of the polymer is taken to be that of the solvent. The number of units N was either 50 or 100. Monte Carlo results were collected for various Debye screening lengths at six combinations of number of chain units N, bond angle θ, and Manning parameter when fully charged, ξ0. For four of the combinations, ξ0 was 1 to take partial account of counterion condensation. These runs had N and θ of 50 and 1°, 50 and 70°, 100 and 1°, and 100 and 70°. The fifth combination had N=50, θ=70°, and ξ0=2.85. The sixth had N=50, θ=27.34°, and ξ0=0.72, for comparison with data for hyaluronate. The Monte Carlo results are compared to third nearest-neighbor linear Ising type calculations and to simple mean field theories in α. Mean field theory in α worked very well in the (nearly rodlike) θ=1° cases using the known distance between units. Mean field theory in α using an estimate for the distance between units based on the ideas of electrostatic persistence length and excluded volume worked equally well for the θ=1° cases and moderately well for the θ=70° cases. The free energy and entropy per simulated chain were calculated by thermodynamic integration of the Monte Carlo results for α¯ as a function of pH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462145
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  • 6
    Electronic Resource
    Electronic Resource
    Polyelectrolyte properties of proteoglycan monomers (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4568-4580 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Light scattering measurements were made on proteoglycan monomers (PGM) over a wide range of ionic strengths Cs, and proteoglycan concentrations [PG]. At low Cs there were clear peaks in the angular scattering intensity curve I(q), which moved towards higher scattering wave numbers q, as [PG]1/3. This differs from the square root dependence of scattering peaks found by neutron scattering from more concentrated polyelectrolyte solutions. The peaks remained roughly fixed as Cs increased, but diminished in height, and superposed I(q) curves yielded a sort of isosbestic point. Under certain assumptions the static structure factor S(q) could be extracted from the measured I(q), and was found to retain a peak. A simple hypothesis concerning coexisting disordered and liquidlike correlated states is presented, which qualitatively accounts for the most salient features of the peaks. There was evidence of a double component scattering autocorrelation decay at low Cs, which, when resolved into two apparent diffusion coefficients, gave the appearance of simultaneous "ordinary'' and "extraordinary'' phases. The extraordinary phase was "removable,'' however, by filtering. At higher Cs the proteoglycans appear to behave as random nonfree draining polyelectrolyte coils, with a near constant ratio of 0.67 between hydrodynamic radius and radius of gyration. The apparent persistence length varied as roughly the −0.50 power of ionic strength, similar to various linear synthetic and biological polyelectrolytes. Electrostatic excluded volume theory accounted well for the dependence of A2 on Cs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460585
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  • 7
    Electronic Resource
    Electronic Resource
    Monte Carlo electrostatic persistence lengths compared with experiment and theory (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8479-8486 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An off-lattice rotational isomeric state model Monte Carlo algorithm for a polyelectrolyte with Debye–Hueckel screening and no hard core repulsion is used to generate short (up to 150 unit) chains at (1) different ionic strengths, (2) varying uniform charge densities, and (3) pH–pK0 governed ionization. The mean square radii of gyration are related to the apparent total persistence lengths of the polyelectrolytes via the wormlike chain model. Near the random coil limit the apparent electrostatic persistence length varies approximately as the inverse square root of the ionic strength and linearly with charge density. The persistence length behavior is very similar in cases (2) and (3). These approximate power laws agree well with those found experimentally for hyaluronate and variably ionized polyacrylic acid. The original electrostatic persistence length theory, which does not contain excluded volume effects, predicts power law exponents which are twice these. Corrections due to polyelectrolyte excluded volume theories do not consistently yield good fits to the data, but do give "pseudo-,'' or weakly changing power laws similar to those obtained from the Monte Carlo and experimental data. The similarity between the Monte Carlo and experimental results may indicate that the Debye–Hueckel approximation is reasonable, and that the neglect of hard core repulsion (e.g., zero chain diameter) is insignificant compared to electrostatic effects. This lends strength to the interpretations that electrostatic excluded volume effects explain much of the apparent deviation from the electrostatic persistence length theory and that the approximation of a smeared out line charge works fairly well, even when the actual charges are irregularly spaced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460081
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of polydispersity and second virial coefficient on light scattering by randomly cut random coils (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9069-9076 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The light scattering by an initially monodisperse population of Gaussian random coils in a theta solvent is described by the well known Debye function: P(θ)=D[u(θ)] =(2/u2)(e−u−1+u), where u=u0≡〈S2〉q2. S is the radius of gyration, and q=(4πñ/λ)sin(θ/2) is the magnitude of the scattering vector, λ being the vacuum wavelength of the incident light, ñ the index of refraction, and θ the scattering observation angle. If the molecules undergo random scission, P(θ)=D(u0+r), where r is the average number of scissions per original molecule. In a good solvent, one should include the effect of the second virial coefficient A2 on the light scattering. In the single contact approximation this can be done by using Kc/R=1/MP(θ)+2A2c for an originally monodisperse solution. K is a constant, R the absolute Rayleigh scattering ratio, and c the concentration. The above equation is generalized to originally polydisperse solutions and branched random coils without loops. We discuss its mathematical limits and range of validity, and how to apply it to experimental situations. It is speculated that it may work fairly well when the penetration function ψ is less than about 0.1. We also discuss possible methods of extending its range of validity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459198
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  • 9
    Electronic Resource
    Electronic Resource
    Light scattering power of randomly cut random coils with application to the determination of depolymerization rates (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7193-7199 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The scattering of light by a dilute monodisperse population of random-coil molecules is approximately described by the well-known function P(θ)=(2/u2)(e−u+u−1), where u=R2gq2, Rg is the radius of gyration of the random coils, and q=(4πn/λ)sin(θ/2) is the magnitude of the scattering vector. We show that if the molecules in this population undergo random scission, then P(θ) is still given by the above formula where, however, u is now equal to R2goq2+r, where r is the average number of scissions per molecule in the originally monodisperse population and Rgo is the original radius of gyration. It is suggested that this could be useful for determining depolymerization rate constants, and for investigating whether various forms of scission are actually random. Results from initial experiments which apply the theory to the acid hydrolysis of hyaluronic acid are presented. The rate constants found are in reasonable agreement with values in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457286
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  • 10
    Electronic Resource
    Electronic Resource
    Time-dependent light scattering from singly and multiply stranded linear polymers undergoing random and endwise scission (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7576-7584 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time-dependent light scattering signatures for singly and multiply stranded polymers of arbitrary shape undergoing random and endwise degradation are developed. For the case of random scission, useful generalizations at low scattering angle are found for linear polymers of arbitrary conformation and any initial polydispersity, which permit deductions to be made concerning the degree of association of the polymer (single, double, triple strand, mixtures, etc.), in addition to determination of absolute polydispersity-independent depolymerization rates. For the particular case of random scission of multiply stranded random coils the form factor is shown to be the Debye function whose usual argument is simply translated by a function dependent on the average number of cuts per original strand and on the number of strands and monomers per strand. The contrasting case of end-wise cleavage (e.g., "exocydic'' enzymatic cleavage) is also presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470275
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