Influence of Solvent Quality on Conformations of Crowded Polymers

TL;DR

This study models how solvent quality influences polymer conformations in crowded environments, revealing that excluded-volume interactions significantly affect polymer shape and size, especially with small crowders, with implications for biological and medical applications.

Contribution

It introduces a coarse-grained simulation model combining polymer shape fluctuations and crowding effects, providing new insights into solvent-dependent polymer conformations in crowded environments.

Findings

Excluded-volume interactions are crucial in good solvents.

Crowders smaller than polymers greatly influence conformations.

Free-volume theory accurately predicts simulation results.

Abstract

The structure and function of polymers in confined environments, e.g., biopolymers in the cytoplasm of a cell, are strongly affected by macromolecular crowding. To explore the influence of solvent quality on conformations of crowded polymers, we model polymers as penetrable ellipsoids, whose shape fluctuations are governed by the statistics of self-avoiding walks, appropriate for a polymer in a good solvent. Within this coarse-grained model, we perform Monte Carlo simulations of mixtures of polymers and hard-nanosphere crowders, including trial changes in polymer size and shape. Penetration of polymers by crowders is incorporated via a free energy cost predicted by polymer field theory. To analyze the impact of crowding on polymer conformations in different solvents, we compute average polymer shape distributions, radius of gyration, volume, and asphericity over ranges of polymer-to-crowder size ratio and crowder volume fraction. The simulation results are accurately predicted by a free-volume theory of polymer crowding. Comparison of results for polymers in good and theta solvents indicates that excluded-volume interactions between polymer segments significantly affect crowding, especially in the limit of crowders much smaller than polymers. Our approach may help to motivate future experimental studies of polymers in crowded environments, with possible relevance for drug delivery and gene therapy.