Experimental Free Energy Surface Reconstruction From Single-Molecule Force Spectroscopy Using Jarzynski's Equality

TL;DR

This paper demonstrates how Jarzynski's equality can be applied to single-molecule force spectroscopy data to accurately reconstruct free energy surfaces and determine activation energies, advancing the analysis of nonequilibrium molecular experiments.

Contribution

It introduces a method to reconstruct free energy surfaces from single-molecule experiments using Jarzynski's equality, including direct measurement of energy barriers.

Findings

Reconstructed free energy surfaces for titin I27 domain

First direct experimental determination of unfolding energy barrier

Validated Jarzynski's equality for analyzing nonequilibrium data

Abstract

We used the atomic force microscope to manipulate and unfold individual molecules of the titin I27 domain and reconstructed its free energy surface using Jarzynski's equality. The free energy surface for both stretching and unfolding was reconstructed using an exact formula that relates the nonequilibrium work fluctuations to the molecular free energy. In addition, the unfolding free energy barrier, i.e. the activation energy, was directly obtained from experimental data for the first time. This work demonstrates that Jarzynski's equality can be used to analyze nonequilibrium single-molecule experiments, and to obtain the free energy surfaces for molecular systems, including interactions for which only nonequilibrium work can be measured.