A. Yu. Grosberg

Screening of a charged particle by multivalent counterions in salty water: Strong charge inversion

Screening of a macroion such as a charged solid particle, a charged membrane, double helix DNA, or actin by multivalent counterions is considered. Small colloidal particles, charged micelles, short or long polyelectrolytes can play the role of multivalent counterions. Due to strong lateral repulsion at the surface of the macroion such multivalent counterions form a strongly-correlated liquid, with the short-range order resembling that of a Wigner crystal. These correlations create additional binding of multivalent counterions to the macroion surface with binding energy larger than kBT. As a result even for a moderate concentration of multivalent counterions in the solution, their total charge at the surface of the macroion exceeds the bare macroion charge in absolute value. Therefore, the net charge of the macroion inverts its sign. In the presence of a high concentration of monovalent salt the absolute value of inverted charge can be larger than the bare one. This strong inversion of charge can be observ...

Chain length dependence of the state diagram of a single stiff-chain macromolecule: Theory and Monte Carlo simulation

We present a Monte Carlo computer simulation and theoretical results for the dependence of the state diagram of a single semiflexible chain on the chain length. The calculated transition lines between different structures in the state diagrams for both studied chain lengths N=40 and N=80 can be described by theoretical predictions which include chain length dependence explicitly. The stability criteria of different structures are discussed. The theoretically predicted exponent in the dependence of the toroid size on the chain length is compatible with computer simulation results.

Giant charge inversion of a macroion due to multivalent counterions and monovalent coions: Molecular dynamics study

We report molecular dynamics simulation of the (overall neutral) system consisting of an immobile macroion surrounded by the electrolyte of multivalent counterions and monovalent coions. In a short time ( 1, where ζ=(A0/rs)2, rs is the Debye screening length in the electrolyte and A0 is the distance ...

Electrophoresis of a charge-inverted macroion complex: Molecular-dynamics study

Abstract:We have performed molecular-dynamics simulations to study the effect of an external electric field on a macroion in the solution of multivalent Z : 1 salt. To obtain plausible hydrodynamics of the medium, we explicitly make the simulation of many neutral particles along with ions. In a weak electric field, the macroion drifts together with the strongly adsorbed multivalent counterions along the electric field, in the direction proving inversion of the charge sign. The reversed mobility of the macroion is insensitive to the external field, and increases with salt ionic strength. The reversed mobility takes a maximal value at intermediate counterion valence. The motion of the macroion complex does not induce any flow of the neutral solvent away from the macroion, which reveals screening of hydrodynamic interactions at short distances in electrolyte solutions. A very large electric field, comparable to the macroion unscreened field, disrupts charge inversion by stripping the adsorbed counterions off the macroion.

Conductivity of a suspension of nanowires in a weakly conducting medium

We study the macroscopic electrical conductivity of a composite made of straight or coiled nanowires suspended in a poorly conducting medium. We assume that the volume fraction of the wires is so large that spaces occupied by them overlap, but there is still enough room to distribute the wires isotropically. We found a wealth of scaling regimes at different ratios of conductivities of the wire, 1, and of the medium, 2, lengths of wires, and their persistent lengths and volume fractions. There are large ranges of parameters where macroscopic conductivity is proportional to 12 1/2 . These results are directly applicable to the calculation of the macroscopic diffusion constant of nonspecific DNA-binding proteins in semidilute DNA solution.

LOW TEMPERATURE PHYSICS AT ROOM TEMPERATURE IN WATER: CHARGE INVERSION IN CHEMICAL AND BIOLOGICAL SYSTEMS*

We review recent advances in the physics of strongly interacting charged systems functioning in water at room temperature. We concentrate on the phenomena which go beyond the framework of mean field theories, whether linear Debye-Huckel or non-linear Poisson-Boltzmann. We place major emphasis on charge inversion - a counterintuitive phenomenon in which a strongly charged particle, called macroion, binds so many counterions that its net charge changes sign. We discuss the universal theory of charge inversion based on the idea of a strongly correlated liquid of adsorbed counterions, similar to a Wigner crystal. This theory has a vast array of applications, particularly in biology and chemistry; for example, the DNA double helix in the presence of positive multivalent ions (e.g., polycations) acquires a net positive charge and drifts as a positive particle in electric field. This simplifies DNA uptake by the cell as needed for gene therapy, because the cell membrane is negatively charged. We discuss also the analogies of charge inversion in other fields of physics.

Worm-like polymer loops and Fourier knots

Every smooth closed curve can be represented by a suitable Fourier sum as a function of an arbitrary parameter τ . We show that the ensemble of curves generated by randomly chosen Fourier coefficients with amplitudes inversely proportional to spatial frequency (with a smooth exponential cutoff) can be accurately mapped on the physical ensemble of inextensible worm-like polymer loops. The τ → s mapping of the curve parameter τ on the arc length s of the inextensible polymer is achieved at the expense of coupling all Fourier harmonics in a non-trivial fashion. We characterize the obtained ensemble of conformations by looking at tangent–tangent and position–position correlations. Measures of correlation on the scale of the entire loop yield a larger persistence length than that calculated from the tangent–tangent correlation function at small length scales. The topological properties of the ensemble, randomly generated worm-like loops, are shown to be similar to those of other polymer models.

LOW TEMPERATURE PHYSICS AT ROOM TEMPERATURE IN WATER: CHARGE INVERSION IN CHEMICAL AND BIOLOGICAL SYSTEMS

We review recent advances in the physics of strongly interacting charged systems functioning in water at room temperature. We concentrate on the phenomena which go beyond the framework of mean field theories, whether linear Debye-Huckel or non-linear Poisson-Boltzmann. We place major emphasis on charge inversion - a counterintuitive phenomenon in which a strongly charged particle, called macroion, binds so many counterions that its net charge changes sign. We discuss the universal theory of charge inversion based on the idea of a strongly correlated liquid of adsorbed counterions, similar to a Wigner crystal. This theory has a vast array of applications, particularly in biology and chemistry; for example, the DNA double helix in the presence of positive multivalent ions (e.g., polycations) acquires a net positive charge and drifts as a positive particle in electric field. This simplifies DNA uptake by the cell as needed for gene therapy, because the cell membrane is negatively charged. We discuss also the analogies of charge inversion in other fields of physics.