Origin of translocation barriers for polyelectrolyte chains

TL;DR

This paper investigates the free energy barriers in the initial stage of polyelectrolyte translocation through narrow pores, highlighting the dominant entropic contribution and effects of electrostatics, salt, and solvent quality.

Contribution

It provides a self-consistent field theory analysis of translocation barriers, incorporating electrostatic interactions and conformational entropy without assuming radial symmetry.

Findings

Barrier is mainly entropic due to conformational changes.

Electrostatic effects slightly increase the barrier.

Lower salt concentration and poorer solvent quality raise the barrier.

Abstract

For single-file translocations of a charged macromolecule through a narrow pore, the crucial step of arrival of an end at the pore suffers from free energy barriers, arising from changes in intrachain electrostatic interaction, distribution of ionic clouds and solvent molecules, and conformational entropy of the chain. All contributing factors to the barrier in the initial stage of translocation are evaluated by using the self-consistent field theory for the polyelectrolyte and the coupled Poisson-Boltzmann description for ions, without radial symmetry. The barrier is found to be essentially entropic, due to conformational changes. For moderate and high salt concentrations, the barriers for the polyelectrolyte chain are quantitatively equivalent to that of uncharged self-avoiding walks. Electrostatic effects are shown to increase the free energy barriers, but only slightly. The degree of ionization, electrostatic interaction strength, decreasing salt concentration and the solvent quality all result in increases in the barrier.