Reentrant Condensation of DNA induced by Multivalent Counterions

TL;DR

This paper presents a new theoretical model explaining DNA reentrant condensation driven by multivalent cations, predicting charge sign reversal and matching experimental thresholds for DNA condensation and resolubilization.

Contribution

It introduces a novel theory of macroion screening that accounts for charge reversal and reentrant condensation in DNA with multivalent counterions, supported by experimental data.

Findings

Charge sign of DNA changes at a small cation concentration N_0

DNA condenses near N_0 due to correlation-induced attraction

Condensation energy per nucleotide is approximately 0.07 k_B T

Abstract

A theory of condensation and resolubilization of a dilute DNA solution with growing concentration of multivalent cations, N is suggested. It is based on a new theory of screening of a macroion by multivalent cations, which shows that due to strong cation correlations at the surface of DNA the net charge of DNA changes sign at some small concentration of cations N_0. DNA condensation takes place in the vicinity of N_0, where absolute value of the DNA net charge is small and the correlation induced short range attraction dominates the Coulomb repulsion. At N > N_0 positive DNA should move in the oppisite direction in an electrophoresis experiment. From comparison of our theory with experimental values of condensation and resolubilization thresholds for DNA solution containing Spe$^{4+}$, we obtain that N_0 = 3.2 mM and that the energy of DNA condensation per nucleotide is $0.07 k_B T$.