Semi-flexible chain condensation by neutral depleting agents: role of correlations between depletants

TL;DR

This paper investigates how correlations among neutral depleting agents influence semi-flexible chain condensation, revealing conditions for effective condensation and comparing colloids and polymers as condensing agents.

Contribution

It introduces a formalism that captures the role of agent correlations in chain condensation, challenging recent claims about colloid efficiency.

Findings

Correlations cause chain reswelling at high agent volume fractions.

Spherical colloids have restrictive conditions for chain condensation.

The formalism compares efficiency of colloids versus polymers as condensing agents.

Abstract

We revisit the problem of semi-flexible chain condensation by neutral depleting agents (e.g. colloidal spheres or flexible polymers) by using a simple formalism that allows us to address its main features without specifying the kind of depleting agents. Correlations between depleting agents are shown to produce a reswelling of the chain at high enough volume fraction, consistent with an earlier analysis by Grosberg et al. (Biopolymers, 21:2413, 1982) in the context of DNA condensation induced by neutral polymers. It is also shown that the conditions under which spherical colloids can condense a semi-flexible chain are strongly restrictive, unlike what has been recently claimed. The formalism allows us to compare the efficiency of colloids vs polymers as condensing agents.