Polymer Crowding and Shape Distributions in Polymer-Nanoparticle Mixtures

TL;DR

This study investigates how nanoparticle crowding affects polymer shapes using simulations and theory, revealing that increased crowding makes polymers more compact and spherical, with implications for biopolymer behavior.

Contribution

It introduces a coarse-grained model combining Monte Carlo simulations and free-volume theory to quantify shape changes of polymers under nanoparticle crowding.

Findings

Polymers become more compact with increased nanoparticle crowding.

Polymer shape distributions shift towards more spherical conformations.

The model aligns with free-volume theory predictions.

Abstract

Macromolecular crowding can influence polymer shapes, which is important for understanding the thermodynamic stability of polymer solutions and the structure and function of biopolymers (proteins, RNA, DNA) under confinement. We explore the influence of nanoparticle crowding on polymer shapes via Monte Carlo simulations and free-volume theory of a coarse-grained model of polymer-nanoparticle mixtures. Exploiting the geometry of random walks, we model polymer coils as effective penetrable ellipsoids, whose shapes fluctuate according to the probability distributions of the eigenvalues of the gyration tensor. Accounting for the entropic cost of a nanoparticle penetrating a larger polymer coil, we compute the crowding-induced shift in the shape distributions, radius of gyration, and asphericity of ideal polymers in a theta solvent. With increased nanoparticle crowding, we find that polymers become more compact (smaller, more spherical), in agreement with predictions of free-volume theory. Our approach can be easily extended to nonideal polymers in good solvents and used to model conformations of biopolymers in crowded environments.