# Orientational transition and complexation of DNA with anionic membranes: weak and intermediate electrostatic coupling

## TL;DR

This paper develops a theoretical framework to understand how charge correlations influence the adsorption and orientation of negatively charged polyelectrolytes on similarly charged membranes, revealing mechanisms like salt-induced forces and charge inversion.

## Contribution

It introduces a new theory elucidating the roles of charge correlations and salt effects in like-charge polyelectrolyte-membrane complexation, highlighting orientational transitions and charge inversion phenomena.

## Key findings

- Weakly charged membranes cause polyelectrolyte depletion and parallel orientation.
- Intermediate charges induce salt-mediated attraction and orientation change.
- High charges lead to charge inversion and extended complexation.

## Abstract

We characterize the role of charge correlations in the adsorption of a short, rod-like anionic polyelectrolyte onto a similarly charged membrane. Our theory reveals two different mechanisms driving the like-charge polyelectrolyte-membrane complexation: in weakly charged membranes, repulsive polyelectrolyte-membrane interactions lead to the interfacial depletion and a parallel orientation of the polyelectrolyte with respect to the membrane; while in the intermediate membrane charge regime, the interfacial counterion excess gives rise to an attractive "salt-induced" image force. This furthermore results in an orientational transition from a parallel to a perpendicular configuration and a subsequent short-ranged like-charge adsorption of the polyelectrolyte to the substrate. A further increase of the membrane charge engenders a charge inversion, originating from surface-induced ionic correlations, that act as a separate mechanism capable of triggering the like-charge polyelectrolyte-membrane complexation over an extended distance interval from the membrane surface. The emerging picture of this complexation phenomenon identifies the interfacial "salt-induced" image forces as a powerful control mechanism in polyelectrolyte-membrane complexation.