Attraction between DNA molecules mediated by multivalent ions

TL;DR

This study uses computer simulations to explore how multivalent ions influence the attractive forces between DNA molecules, revealing tunable attraction and complex salt effects.

Contribution

It provides detailed insights into the electrostatic and entropic mechanisms of DNA attraction mediated by multivalent ions, with implications for understanding DNA behavior in ionic solutions.

Findings

Multivalent ions induce significant DNA attraction.

Salt concentration can switch the force from attractive to repulsive.

Attraction does not necessarily correlate with DNA overcharging.

Abstract

The effective force between two parallel DNA molecules is calculated as a function of their mutual separation for different valencies of counter- and salt ions and different salt concentrations. Computer simulations of the primitive model are used and the shape of the DNA molecules is accurately modelled using different geometrical shapes. We find that multivalent ions induce a significant attraction between the DNA molecules whose strength can be tuned by the averaged valency of the ions. The physical origin of the attraction is traced back either to electrostatics or to entropic contributions. For multivalent counter- and monovalent salt ions, we find a salt-induced stabilization effect: the force is first attractive but gets repulsive for increasing salt concentration. Furthermore, we show that the multivalent-ion-induced attraction does not necessarily correlate with DNA overcharging.