Molecular chains under tension: Thermal and mechanical activation of statistically interacting extension and contraction particles

TL;DR

This paper presents a statistical mechanical framework to analyze polymer chains under tension, capturing thermal and mechanical responses, including structural transformations, with applications to DNA stretching that align well with experimental data.

Contribution

Introduces a novel methodology for analyzing polymer chain mechanics using statistically interacting particles, applicable to various elastic and structural behaviors including DNA overstretching.

Findings

Accurately models force-extension behavior of DNA under tension.

Describes thermal unbending and nonlinear elasticity of polymer chains.

Matches empirical force-extension data across different regimes.

Abstract

This work introduces a methodology for the statistical mechanical analysis of polymeric chains under tension controlled by optical or magnetic tweezers at thermal equilibrium with an embedding fluid medium. The response of single bonds between monomers or of entire groups of monomers to tension is governed by the activation of statistically interacting particles representing quanta of extension or contraction. This method of analysis is capable of describing thermal unbending of the freely jointed or wormlike chain kind, linear or nonlinear contour elasticity, and structural transformations including effects of cooperativity. The versatility of this approach is demonstrated in an application to double-stranded DNA undergoing torsionally unconstrained stretching across three regimes of mechanical response including an overstretching transition. The three-regime force-extension characteristic, derived from a single free-energy expression, accurately matches empirical evidence.