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At least 1,225 records · Page 68Linked to original sources
PubMed1999

Attractive interactions between rodlike polyelectrolytes: polarization, crystallization, and packing.

We study the attractive interactions between rodlike charged polymers in solution that appear in the presence of multivalence counterions. The counterions condensed to the rods exhibit both a strong transversal polarization and a longitudinal crystalline arrangement. At short distances between the rods, the fraction of condensed counterions increases, and the majority of these occupy the region between the rods, where they minimize their repulsive interactions by arranging themselves into packing structures. The attractive interaction is strongest for multivalent counterions. Our model takes into account the hard-core volume of the condensed counterions, and their angular distribution around the rods. The hard-core constraint strongly suppresses longitudinal charge fluctuations.

Journal Article↗
PubMed2002

Complexes of semiflexible polyelectrolytes and charged spheres as models for salt-modulated nucleosomal structures.

We investigate the complexation behavior between a semiflexible charged polymer and an oppositely charged sphere with parameters appropriate for the DNA-histone system. We determine the ground state of a simple free energy expression (which includes electrostatic interactions on a linear level) numerically and use symmetry arguments to divide the obtained DNA configuration into broad classes, thereby obtaining global phase diagrams. We pay specific attention to the effects of salt concentration, DNA length variation, DNA charge renormalization, and externally applied force on the obtained complex structures.

Biophysical Phenomena↗
PubMed2002

Complex formation in systems of oppositely charged polyelectrolytes: a molecular dynamics simulation study.

Results of molecular dynamics simulations for systems with two flexible, oppositely charged polymer chains are presented. The lengths N and interaction strength lambda of the chains are varied. We find that the chains remain separated for small values of lambda. For large interaction strengths, i.e., large Bjerrum lengths, we find glasslike structures and order on the length scale of a few monomer diameters. Between these two limits of the interaction strengths, the chains of various lengths collapse into compact complexes that exhibit self-similar structures. The scaling behavior of the radius of gyration is discussed as a function of chain length and interaction strength. In addition, the local structure of the collapsed systems is analyzed and the dependence of the density of the aggregate on the interaction strength is discussed.

Journal Article↗
PubMed2003

Nanostructures of polyelectrolyte gel-surfactant complexes in uniaxially stretched networks.

Nanostructures of poly(acrylate) gel and dodecylpyridinium complexes equlibrated with the NaCl aqueous solution (from 5 to 100mM) and their time evolution after stretching uniaxially were investigated by means of time-resolved small-angle x-ray scattering. The scattering profile revealed the existence of the cubic nanostructure belonging to Pm3n space group in the gel before and long after the stretch. Each of the three intensive peaks was found to be resolved into two, which suggested the existence of two cubic structures with the slightly different lattice spacings. On the other hand, the splits of scattering peaks were not observed for the linear poly(acrylate) and dodecylpyridinium complexes. This indicates that the existence of the cross-linked chain is concerned in the formation of the double structure in the complex system. A series of time-resolved experiments demonstrated that the peaks corresponding to the longer lattice constant disappeared once just after stretching and regenerated to grow up, whereas the peaks corresponding to the shorter lattice constant were continuously observed. The growing rates of the peaks increased with the NaCl concentration. It was also found that a two-dimensional scattering pattern changed from the Debye-Scherrer ring type into the Laue spot type with stretching at the lower NaCl concentrations. This indicates that the single-crystal-like domains align in the stretched network due to the strong electrostatic interaction between the dodecylpyridinium cation and poly(acrylate) anion.

Journal Article↗
PubMed2005

Orientational ordering and dynamics of rodlike polyelectrolytes.

The interplay between electrostatic interactions and orientational correlations is studied for a model system of charged rods positioned on a chain, using Monte Carlo simulation techniques. It is shown that the coupling brings about the notion of electrostatic frustration, which in turn results in: (i) a rich variety of orientational orderings such as chiral phases, and (ii) an inherently slow dynamics characterized by stretched-exponential behavior in the relaxation functions of the system.

Journal Article↗
PubMed2005

Effect of low-molecular-weight salt on the nematic ordering in solutions of rodlike polyelectrolytes.

Nematic ordering is studied in solutions of rodlike macroions in the presence of monovalent salt ions. The correlation free energy of electrostatic interactions is calculated within the framework of the Debye-Hückel approach. The phase diagram of the system is obtained. We have shown that the addition of salt destroys the weakly ordered nematic phase which is stable at small polymer concentrations. On the other hand, the salt widens the region of the phase separation between the isotropic (or weakly ordered nematic) and the highly ordered nematic phases at high polymer concentrations. An explanation of these effects is proposed.

Journal Article↗
PubMed2001

Elastically driven linker aggregation between two semiflexible polyelectrolytes.

The behavior of mobile linkers connecting two semiflexible charged polymers, such as polyvalent counterions connecting DNA or F-actin chains, is studied theoretically. The chain bending rigidity induces an effective repulsion between linkers at large distances while the interchain electrostatic repulsion leads to an effective short-range interlinker attraction. We find a rounded phase transition from a dilute linker gas where the chains form large loops between linkers to a dense disordered linker fluid connecting parallel chains. The onset of chain pairing occurs within the rounded transition.

Actins↗
PubMed1977

Plant Cuticles Are Polyelectrolytes with Isoelectric Points around Three.

The isoelectric points of isolated cuticles from Citrus aurantium L. (3.15), Prunus armeniaca L. (3.45), and Pyrus communis L. (2.90) leaves were determined from membrane potentials. At pH values below the isoelectric point, cuticular membranes carry a net positive charge and are permselective to anions (determined using (82)Br(-)). Above the isoelectric point, they carry a net negative charge and are permselective to cations (determined using (24)Na(+)). There are no gradients of fixed charges across the cuticular membranes as indicated by the absence of asymmetry potentials. Positive charges in the membranes originate from residues of basic amino acids of proteins or polypeptides contained in a nonextractable form within the cuticle. The exchange capacity of basic fixed groups in the cuticles of six species (Lycopersicon esculentum Mill., Capsicum annuum L. fruit cuticles, and Brassaia spec. leaf cuticles in addition to the above species) varied between 0.010 and 0.025 meq g(-1) cuticle. Fixed acidic groups were donated by residues of acidic amino acids, polygalacturonic acid, and nonesterified -COOH groups of the cutin polymer. At pH 8, total cation exchange capacity as determined using (45)Ca(2+) varied between 0.26 (Citrus) and 0.30 (apricot) meq g(-1).

Journal Article↗