ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 94 (1990), S. 3722-3725 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 1467-1471 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8479-8486 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9069-9076 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7193-7199 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7766-7776 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1609-1620 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4568-4580 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6916-6926 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Metropolis Monte Carlo program with reptation is used to generate sample configurations of short electrically charged polymers with thermally distributed Debye–Hückel electrostatic energies. The polymer is a three fold rotational isomeric state model with bond angle θ between 5° and 90° and number of units N between 10 and 225. To compare the resulting root-mean-square (rms) values for radius of gyration S, and end-to-end length R, to theory, we use a wormlike chain with contour length L equal to the stretched out length of the polymer, the same total charge, and an intrinsic persistence length set so that, for large N, for specified θ and L, S agrees with the rotational isomeric state model. The results are compared with the predictions for S, with correction for finite L, of Odijk [J. Polymer Sci., Polymer Phys. Ed. 15, 477 (1977)]. They are then compared with three attempted corrections for excluded volume: (1) Odijk and Houwaart [J. Polymer Sci., Polymer Phys. Ed. 16, 627 (1978)]; (2) correction (1) modified by using the electrostatic excluded volume of Fixman and Skolnick [Macromolecules 11, 863 (1978)]; (3) correction (2) modified by replacing the Yamakawa–Tanaka formula by an approximation due to Gupta and Forsman [Macromolecules 5, 779 (1972)]. Odijk's prediction with correction for finite length works fairly well under conditions of small excluded volume. The excluded volume corrections are often but not always of about the right size; the latter two work better.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 2914-2924 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Static and dynamic polarized and depolarized light scattering, static, and time-resolved dichroic anisotropy, as well as conventional magnetization versus applied magnetic field determinations have been carried out on aqueous commercial ferrofluids and on surfactant aggregate stabilized Fe3O4 in aqueous solution. Over a dilution range of more than three orders of magnitude there is no evidence for field-induced cooperative effects. The shape of the dichroic anisotropy versus applied field curve superimposes virtually exactly onto the magnetization curve. Rotational and translational diffusion coefficients indicate ellipsoidal magnetic aggregates with average minor to major axial ratios around 0.33 and major axis of 285 nm, which are insensitive to dilution, and far above the expected value of around 10 nm. Electron micrographs have revealed polydisperse clusters of around 150 nm composed of particles with sizes on the order of 10 nm. The scattered intensity autocorrelation curve shows no appreciable change upon application of a magnetic field to the ferrofluids. Evidence for the shape anisotropy of the presumed 140-nm clusters is apparent in the depolarized light scattering autocorrelation decay curves. In the absence of field-induced particle chaining, aggregation, or shape deformation, the origin of the field-induced dichroism was attributed to the permanent shape anisotropy of the clusters. Subtle field-induced alteration of the spatial arrangement of particles within the stable clusters or an unexpected anisotropic polarizability of the magnetite crystals do not seem to be likely origins of the dichroic effect.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...