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Stochastic dynamics of single molecules across phase boundaries

Stefano Bo, Lars Hubatsch, Jonathan Bauermann, Christoph A. Weber, and Frank Jülicher
Phys. Rev. Research 3, 043150 – Published 2 December 2021
Physics logo See synopsis: The Microscopic Dynamics of Biomolecular Condensates

Abstract

We discuss the stochastic trajectories of single molecules in a phase-separated liquid, when a dense and a dilute phase coexist. Starting from a continuum theory of macroscopic phase separation we derive a stochastic Langevin equation for molecular trajectories that takes into account thermal fluctuations. We find that molecular trajectories can be described as diffusion with drift in an effective potential, which has a steep gradient at phase boundaries. We discuss how the physics of phase coexistence affects the statistics of molecular trajectories and in particular the statistics of displacements of molecules crossing a phase boundary. At thermodynamic equilibrium detailed balance imposes that the distributions of displacements crossing the phase boundary from the dense or from the dilute phase are the same. Our theory can be used to infer key phase separation parameters from the statistics of single-molecule trajectories. For simple Brownian motion, there is no drift in the presence of a concentration gradient. We show that interactions in the fluid give rise to an average drift velocity in concentration gradients. Interestingly, under non-equilibrium conditions, single molecules tend to drift uphill the concentration gradient. Thus, our work bridges between single-molecule dynamics and collective dynamics at macroscopic scales and provides a framework to study single-molecule dynamics in phase-separating systems.

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  • Received 16 July 2021
  • Accepted 19 October 2021

DOI:https://doi.org/10.1103/PhysRevResearch.3.043150

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Polymers & Soft MatterStatistical Physics & ThermodynamicsPhysics of Living Systems

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The Microscopic Dynamics of Biomolecular Condensates

Published 2 December 2021

A physical description of the trajectories of single molecules suggests a new way to study a biologically important subcellular environment.

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Authors & Affiliations

Stefano Bo1,*, Lars Hubatsch1,*, Jonathan Bauermann1, Christoph A. Weber1, and Frank Jülicher1,2,†

  • 1Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, DE-01187 Dresden, Germany
  • 2Cluster of Excellence Physics of Life, TU Dresden, 01062 Dresden, Germany

  • *These authors contributed equally to this work.
  • julicher@pks.mpg.de

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Vol. 3, Iss. 4 — December - December 2021

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