Regensburg 2004 – scientific programme

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AKB: Biologische Physik

AKB 50: Poster Session "Biological Physics"

AKB 50.23: Poster

Friday, March 12, 2004, 10:30–13:00, B

Probing molecular free energy landscapes by periodic loading — •Oliver Braun¹, Andreas Hanke^1,2, and Udo Seifert¹ — ¹Institute for Theoretical Physics II, University of Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany — ²Theoretical Physics Department, University of Oxford, 1 Keble Road, OX1 3NP Oxford, United Kingdom

Recent experimental developments of highly sensitive force probes such as atomic force microscopy, optical or magnetic tweezers and biomembrane force probes allow one to manipulate a single biological macromolecule. The free energy landscape along its end-to-end distance, which is governed by molecular forces and self-interactions, may be recovered by applying time-dependent forces. Previous experiments have mostly used a linear force ramp.

Using periodically modulated forces we show how to reconstruct this free energy landscape more efficiently. A central tool is Jarzynski’s identity, which allows us to recover equilibrium quantities from the statistics of non-equilibrium experimental data. As a main advantage, our method also yields the convex unstable part of the free energy surface, where the linear ramp protocol provides poor results. The quality of the reconstruction depends crucially on the frequency of the periodic forcing. Best results were obtained at frequencies of the order of the transition rates between adjacent meta-stable configurations.