Repulsion between oppositely charged rod-shaped macromolecules: Role of overcharging and ionic confinement

Abstract

The interaction between two oppositely charged rod-shaped macro-ions in a micro-ion solution is investigated via Monte Carlo simulations of the primitive model. The focus is on the asymmetry in rod and/or ion charge, i.e., conditions where oppositely charged objects can repel one another. For equally and oppositely charged rods with asymmetric z:1 micro-ions, repulsion may be induced by overcharging one of the rods with the z valent ions. For asymmetrically charged rods in a symmetric z:z micro-ion solution, a repulsive interaction-at separation of the order of one ion diameter-can arise via an unbalanced osmotic pressure contribution from the ionic atmosphere in the inter-rod space, and an attractive interaction-at a smaller separation-may occur due to a "squeezing out" of the micro-ions from the space between the rods (with a consequent gain in entropy). The thermodynamics of each mechanism is investigated in terms of rod charge and size and micro-ion valence, size, and concentration. Our findings contribute to the understanding of the complex role of charge asymmetry on the interaction of, for example, oppositely charged polyelectrolytes, functionalized nanotubes, and rod-like biomolecules, e.g., viruses.

Theoretical and Computational Insight into Solvent and Specific Ion Effects for Polyelectrolytes: The Importance of Local Molecular Interactions

“…In more detail, multivalent counterions are strongly attracted and thus screen the monomeric charge due to their valency more effectively [100]. In contrast, repulsion effects between polyelectrolytes were attributed to overcharging as well as ionic confinement mechanisms [101]. In contrast to bulk solutions, polyelectrolytes in confinement and in presence of dielectric mismatch conditions show a transitional behavior into various conformations.…”

Counterion of Chitosan Influences Thermodynamics of Association of siRNA with a Chitosan-Based siRNA Carrier

“…A lower influence was also observed investigating interactions of siRNA with siRNA carriers prepared with chitosan acetate, NP-CS Lab P and NP-CS Com -mod2P. Going further, it was recently pointed out that interactions between polyelectrolytes can be influenced when they take place in a confine environment [82]. Interactions of siRNA with our carrier occur in such conditions and the influence of the counterion on the thermodynamic aspects of interactions between siRNA and chitosan should also be considered regarding confinement found at the surface of nanoparticles.…”

Multivalent Ion-Mediated Attraction between Like-Charged Colloidal Particles: Nonmonotonic Dependence on the Particle Charge

“…The total mean force acting on colloidal particle i along the reaction coordinate (the X -axis) is composed of two terms Here, F ele i ( x ) is the electrostatic force between colloidal particle i and all other charged objects, and F hs i ( x ) is the depletion force (hard-sphere collision force) between colloidal particle i and the counterions in contact with it. The electrostatic force F ele i ( x ) is expressed as ,,, where θ is the polar angle formed with the reaction coordinate and the angular brackets···denote the ensemble average. x is the separation between two colloidal particles and r ij is the distance between colloidal particle i and ion j .…”

“…Counterions can bind to charged particles and consequently modulate effective interactions between charged particles. Beyond the mean-field descriptions, for oppositely charged particles, multivalent ions of a high concentration can modulate intrinsically Coulombic attractions into effective repulsions. − In parallel, for like-charged particles, multivalent ions can modulate intrinsically Coulombic repulsions into effective attractions, which could drive the condensation or aggregation of charged particles such as nucleic acids, − proteins, , and colloids. − The mechanisms for multivalent ion-mediated like-charge attractions are diverse and are attributed to counterion bridging, ,,− depletion force, , and charge fluctuations of condensed counterions. ,− Alternatively, condensed counterions could be modeled as one component plasma around oppositely charged particles (voids), and the effective like-charge attraction could be attributed to a competition among the ion–ion and void–void repulsions and the ion–void attraction . Recently, specific counterion configuration and depletion were reported to be able to cause the like-charge attractions at high monovalent salt concentrations.…”