Predicting the electrophoretic mobility of charged particles in an aqueous medium

Abstract

Electrophoresis of charged particles has important applications in biochemical separation processes. The mobility of these particles depends on the surrounding electric double layer (EDL), which is impacted by solvent restructuring because of hydration interactions. Nevertheless, most theoretical estimates ignore such interactions during computation of the electrophoretic mobility. Here, we employ a complementary blend of mean-field analysis and molecular dynamics simulations performed for a peptide–G-quadruplex complex to assess how hydration interactions alter the mobility of a charged particle in an aqueous medium. These interactions are seen to stabilize the EDL, resulting in more significant localized counterion concentrations while strengthening the ensuing electrokinetic flow. The ordering of ions near the particle surface is obtained only upon including hydration interaction, revealing that the hydration water molecules act as a glue for forming a stable EDL, a key finding of this work. Conversely, the observed microstructure of ions near the charged surface as obtained from our theory establishes a bridge link between the micro and continuum model. The presence of larger counter ions enhances the drag on the particle, thus restricting its mobility. The mobility also becomes dependent on size, which may be useful for isolating a wide array of biomolecules. The impact of hydration interactions intensifies with increases in particle size, surface charge density, and bulk ion concentration.