Electrophoresis of a rod macroion under polyelectrolyte salt: Is mobility reversed for DNA?

TL;DR

This study uses molecular dynamics simulations to investigate charge inversion and mobility reversal of a rod macroion, like DNA, in the presence of polyelectrolyte salt, revealing conditions under which mobility reversal occurs.

Contribution

It demonstrates how charge inversion and mobility reversal of a macroion occur with polyelectrolyte counterions, highlighting the roles of line charge density and adsorption mechanisms.

Findings

Charge inversion occurs when counterions have higher line charge density than coions.

Mobility reversal is achieved through polyelectrolyte adsorption or combined electrostatic and short-range interactions.

Reversal is observed for macroions with surface charge density similar to DNA.

Abstract

By molecular dynamics simulation, we study the charge inversion phenomenon of a rod macroion in the presence of polyelectrolyte counterions. We simulate electrophoresis of the macroion under an applied electric field. When both counterions and coions are polyelectrolytes, charge inversion occurs if the line charge density of the counterions is larger than that of the coions. For the macroion of surface charge density equal to that of the DNA, the reversed mobility is realized either with adsorption of the multivalent counterion polyelectrolyte or the combination of electrostatics and other mechanisms including the short-range attraction potential or the mechanical twining of polyelectrolyte around the rod axis.