Chwen-Yang Shew

Structure of Polyelectrolyte Solutions.

Structure of Polyelectrolyte Solutions (Commemoration Issue Dedicated to Professor Hiroshi Ibagaki, Professor Michio Kurata, Professor Ryozo Kitamura, On the Occasion of Their Retirments) Author(s) Kaji, Keisuke; Kanaya, Toshiji; Urakawa, Hiroshi; Nishida, Koji; Kitamaru, Ryozo; Higgins, Julia S.; Gabry�, Barbara Citation Bulletin of the Institute for Chemical Research, Kyoto University (1989), 66(3): 352-367 Issue Date 1989-02-15

INTEGRAL EQUATION THEORY OF SOLUTIONS OF RIGID POLYELECTROLYTES

The properties of dilute and semidilute solutions of rigid polyelectrolytes are investigated using integral equation theory. The theory predicts liquidlike structure on length scales of the order of the length of the molecules in dilute solution. This structure appears at concentrations much lower than the overlap threshold concentration, and disappears when the concentration is sufficiently high. Liquidlike order reappears at higher concentrations on a lengthscale of the order of the thickness of the rods. The predictions of the theory for the static structure factor in tobacco mosaic virus solutions are in good agreement with light scattering experiments in both dilute and semidilute solutions. The theory predicts that kmax∼ρν, where kmax is the position of the maximum in the structure factor and ρ is the concentration, with ν≈1/3 and 1/2 in the dilute and semidilute regimes, respectively. These values are consistent with experimental results. Predictions are also presented for rigid starlike polymers.

Monte Carlo simulations and self-consistent integral equation theory for polyelectrolyte solutions

The static structure and conformational properties of salt-free polyelectrolyte solutions are studied using many-chain Monte Carlo simulations and integral equations. The polymer molecules are modeled as freely jointed tangent sphere chains with a hard sphere plus screened Coulomb potential between the beads. Monte Carlo simulations are for the most part in agreement with previous molecular dynamics simulations of a related model of polymers but the present work facilitates an unambiguous comparison between theory and simulation. An integral equation theory is implemented where the properties of the polymer are obtained from a single chain simulation where the beads interact via the bare potential plus a self-consistently determined solvation potential. The theory overestimates the degree of liquidlike order and underestimates the size of the chains (when compared to many chain simulations) especially for long chains and high densities. A more approximate theory that employs a thread model for the polymer...

Computer simulations and integral equation theory for the structure of salt-free rigid rod polyelectrolyte solutions: Explicit incorporation of counterions

The static structure of salt-free solutions of rod-like polyelectrolyte solutions is studied using Monte Carlo simulations and integral equations. The polymer reference interaction site model theory with the reference Laria–Wu–Chandler closure is found to be in good agreement with the simulations for the polyion–polyion and counterion–counterion correlation functions, and in qualitative agreement with the simulations for the counterion–polyion correlation functions. The effect on the polyion concentration on the counterion distribution is found to be important at low concentrations and becomes more significant when the Bjerrum length or degree of polymerization are increased. The theory is in almost quantitative agreement with the simulations for the static structure factor. The theory predicts that all three partial structure factors display low angle peaks at roughly the same wave vectors. The position and intensity of the peak in the polyion structure factor is insensitive to the Bjerrum length. These ...

Loosening of DNA/Polycation Complexes by Synthetic Polyampholyte to Improve the Transcription Efficiency: Effect of Charge Balance in the Polyampholyte

High mobililty group proteins are amphoteric nuclear proteins that are known to unfold chromatin to stimulate transcription. To mimic their structures, we synthesized the novel polyethylene glycol (PEG) derivatives, PEG-ACs, consisting of both amino- and carboxyl-pendants in various ratios, and their loosening and transcription-improving activity on the DNA complex was examined. Fluorescence anisotropy measurement revealed that anionic PEG-ACs with more carboxyls than amines could efficiently loosen the DNA/polyethyleneimine complex. Those anionic PEG-ACs showing a loosening effect on the DNA complex evidently increased the transcription rate to >20 times higher than that of the original complex, probably owing to the facilitated approach of transcriptional factors to the DNA segments in the loosened complexes. The complexes with anionic PEG-ACs also showed improved transgene expression level on the cultured cells, indicating the effectiveness of improving transcriptional activity to attain a high extragene expression by the plasmid complex. The loosening mechanism of DNA/polycation complexes was investigated with a simplified model via Monte Carlo simulation to discern the difference in the presence of cationic polyampholytes, anionic polyampholytes, and polyanions.

Density functional theory for pair correlation functions in polymeric liquids

A density functional theory is presented for the pair correlation functions in polymeric liquids. The theory uses the Yethiraj–Woodward free-energy functional for the polymeric liquid, where the ideal gas free-energy functional is treated exactly and the excess free-energy functional is obtained using a weighted density approximation with the simplest choice of the weighting function. Pair correlation functions are obtained using the Percus trick, where the external field is taken to be a single polymer molecule. The minimization of the free energy in the theory requires a two molecule simulation at each iteration. The theory is very accurate for the pair correlation functions in freely jointed tangent-hard-sphere chains and freely rotating fused-hard-sphere chains, especially at low densities and for long chains. In addition, the theory allows the calculation of the virial pressure in these systems and shows a remarkable degree of consistency between the virial and compressibility pressure.

Phase behavior of the Widom–Rowlinson mixture

The Widom–Rowlinson mixture is a two component fluid where like species do not interact and unlike species interact via a hard core repulsion. As the density is increased this fluid phase separates. Using semigrand ensemble simulations and finite size scaling we accurately locate the critical density at ρσ3=0.762±0.016 where ρ is the total number density and σ is the hard sphere diameter. This density is much higher than previous estimates for this model. We implement several integral equation theories, none of which are accurate for the critical point or coexistence curve.

Self-consistent integral equation theory for semiflexible chain polyelectrolyte solutions

A self-consistent integral equation theory is presented for the conformational behavior and static structure of polyelectrolyte solutions composed of semiflexible chain molecules. The free energy of the solution is expressed as the sum of an elastic, a Coulombic, and a medium-induced contribution, and is minimized with respect to the single chain structure factor. In the flexible limit, the theory is accurate for the chain conformations and static structure factor when compared to Monte Carlo simulations of flexible chains. For semiflexible chains near the flexible limit, the chain conformations are sensitive to the bare persistence length in dilute solutions but not in the semidilute regime. In contrast, the effect of the bare persistence length on the static structure factor is not as significant. The theory predicts that charged flexible chains exhibit more pronounced liquidlike order in solution than their rigid-rod counterparts, and the length scale of these liquidlike correlations is also shorter in...

Ion binding in tobacco mosaic virus solutions

The structure of salt-free solutions of tobacco mosaic virus particles is investigated using integral equations with the counterions incorporated explicitly. The results for the structure factor are identical to previous studies which used a Debye–Huckel approximation. The results are explained using a model of the particles as polyacids.

Conformational properties of isolated polyelectrolytes in poor solvents

The conformational behavior of isolated polyelectrolytes in poor solvents is investigated using theory and computer simulation. DiMarzio’s approach for the collapse transition in neutral polymers is extended to uniformly charged polymers [E. A. diMarzio, Macromolecules 17, 969 (1984)]. The theory predicts a discontinuous collapse transition with decreasing solvent quality in highly charged polymers. A discontinuous collapse transition is also observed when the charge fraction is decreased in very poor solvents. Monte Carlo simulations are reported for the collapse transition in a lattice model of polyelectrolytes. Under some conditions the distribution of polymer size is bimodal, consistent with the theory.