Conformational dynamics and internal friction in homo-polymer globules: equilibrium vs. non-equilibrium simulations

TL;DR

This study investigates the internal conformational dynamics and friction in homo-polymer globules using equilibrium and non-equilibrium simulations, revealing a transition from liquid-like to solid-like behavior depending on cohesion strength and globule size.

Contribution

It provides a detailed analysis of how cohesion strength and globule size influence internal dynamics and friction, identifying a phase transition between liquid-like and solid-like regimes.

Findings

Internal friction increases with cohesion strength {} and scales with globule size.

Two dynamical regimes identified: liquid-like with fast dynamics, solid-like with slow dynamics.

Comparison of equilibrium and non-equilibrium simulations reveals consistent internal viscosity behavior.

Abstract

We study the conformational dynamics within homo-polymer globules by solvent-implicit Brownian dynamics simulations. A strong dependence of the internal chain dynamics on the Lennard-Jones cohesion strength {\epsilon} and the globule size NG is observed. We find two distinct dynamical regimes: a liquid- like regime (for {\epsilon} < {\epsilon}s) with fast internal dynamics and a solid-like regime (for {\epsilon} > {\epsilon}s) with slow internal dynamics. The cohesion strength {\epsilon}s of this freezing transition depends on NG. Equilibrium simulations, where we investigate the diffusional chain dynamics within the globule, are compared with non-equilibrium simulations, where we unfold the globule by pulling the chain ends with prescribed velocity (encompassing low enough velocities so that the linear-response, viscous regime is reached). From both simulation protocols we derive the internal viscosity within the globule. In the liquid-like regime the internal friction increases continuously with {\epsilon} and scales extensive in NG. This suggests an internal friction scenario where the entire chain (or an extensive fraction thereof) takes part in conformational reorganization of the globular structure.