Role of conformational entropy in force-induced bio-polymer unfolding

TL;DR

This paper develops a statistical mechanical model for bio-polymer unfolding under force, revealing intermediate states, crossover behaviors, and unique force-extension patterns, enhancing understanding of polymer mechanics in poor solvents.

Contribution

It introduces a unified model for polymer response to force, including novel predictions of intermediate states and saw-tooth force-extension behavior for stiff chains.

Findings

Existence of multiple intermediate states at low temperatures.

Identification of a crossover length proportional to chain length.

Observation of saw-tooth force-extension curves in stiff chains.

Abstract

A statistical mechanical description of flexible and semi-flexible polymer chains in a poor solvent is developed in the constant force and constant distance ensembles. We predict the existence of many intermediate states at low temperatures stabilized by the force. A unified response to pulling and compressing forces has been obtained in the constant distance ensemble. We show the signature of a cross-over length which increases linearly with the chain length. Below this cross-over length, the critical force of unfolding decreases with temperature, while above, it increases with temperature. For stiff chains, we report for the first time "saw-tooth" like behavior in the force-extension curves which has been seen earlier in the case of protein unfolding.