Microscopic Dynamics of Liquid-Liquid Phase Separation and Domain Coarsening in a Protein Solution Revealed by X-Ray Photon Correlation Spectroscopy

Anita Girelli, Hendrik Rahmann, Nafisa Begam, Anastasia Ragulskaya, Mario Reiser, Sivasurender Chandran, Fabian Westermeier, Michael Sprung, Fajun Zhang, Christian Gutt, and Frank Schreiber
Phys. Rev. Lett. 126, 138004 – Published 2 April 2021
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Abstract

While the interplay between liquid-liquid phase separation (LLPS) and glass formation in biological systems is highly relevant for their structure formation and thus function, the exact underlying mechanisms are not well known. The kinetic arrest originates from the slowdown at the molecular level, but how this propagates to the dynamics of microscopic phase domains is not clear. Since with diffusion, viscoelasticity, and hydrodynamics, distinctly different mechanisms are at play, the dynamics needs to be monitored on the relevant time and length scales and compared to theories of phase separation. Using x-ray photon correlation spectroscopy, we determine the LLPS dynamics of a model protein solution upon low temperature quenches and find distinctly different dynamical regimes. We observe that the early stage LLPS is driven by the curvature of the free energy and speeds up upon increasing quench depth. In contrast, the late stage dynamics slows down with increasing quench depth, fingerprinting a nearby glass transition. The dynamics observed shows a ballistic type of motion, implying that viscoelasticity plays an important role during LLPS. We explore possible explanations based on the Cahn-Hilliard theory with nontrivial mobility parameters and find that these can only partially explain our findings.

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  • Received 19 October 2020
  • Accepted 23 February 2021

DOI:https://doi.org/10.1103/PhysRevLett.126.138004

© 2021 American Physical Society

Physics Subject Headings (PhySH)

Physics of Living SystemsPolymers & Soft Matter

Authors & Affiliations

Anita Girelli1, Hendrik Rahmann2, Nafisa Begam1, Anastasia Ragulskaya1, Mario Reiser2,3, Sivasurender Chandran1,4, Fabian Westermeier5, Michael Sprung5, Fajun Zhang1,*, Christian Gutt2,†, and Frank Schreiber1,‡

  • 1Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
  • 2Department Physik, Universität Siegen, Walter-Flex-Strasse 3, 57072 Siegen, Germany
  • 3European X-Ray Free-Electron Laser XFEL, Holzkoppel 4,22869 Schenefeld, Germany
  • 4Department of Physics, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India
  • 5Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany

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Issue

Vol. 126, Iss. 13 — 2 April 2021

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