The Persistence Length of a Strongly Charged, Rod-like, Polyelectrolyte in the Presence of Salt

TL;DR

This paper theoretically investigates how salt and counterion correlations affect the stiffness and stability of strongly charged, rod-like polyelectrolytes, revealing potential chain collapse and DNA condensation phenomena.

Contribution

It extends mean-field theory by including correlations and fluctuations, providing new insights into polyelectrolyte stiffness and collapse mechanisms.

Findings

Counterion correlations reduce chain stiffness

Potential for chain collapse and DNA condensation

More counterions condense on bent conformations

Abstract

The persistence length of a single, intrinsically rigid polyelectrolyte chain, above the Manning condensation threshold is investigated theoretically in presence of added salt. Using a loop expansion method, the partition function is consistently calculated, taking into account corrections to mean-field theory. Within a mean-field approximation, the well-known results of Odijk, Skolnick and Fixman are reproduced. Beyond mean-field, it is found that density correlations between counterions and thermal fluctuations reduce the stiffness of the chain, indicating an effective attraction between monomers for highly charged chains and multivalent counterions. This attraction results in a possible mechanical instability (collapse), alluding to the phenomenon of DNA condensation. In addition, we find that more counterions condense on slightly bent conformations of the chain than predicted by the Manning model for the case of an infinite cylinder. Finally, our results are compared with previous models and experiments.