Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 34: P6: Biomaterials and Biopolymers

CPP 34.10: Poster

Tuesday, March 17, 2015, 14:00–16:00, Poster C

Diffusion in protein solutions upon approaching a liquid-liquid phase transition and its critical point — •Michal Braun, Marcell Wolf, Fajun Zhang, and Frank Schreiber — Institut für Angewandte Physik, Universität Tübingen, 72076 Tübingen

We study aqueous solutions of globular proteins and multivalent salts ([1], [2], [3]). In the bovine serum albumin (BSA) system with YCl₃ liquid-liquid phase separation (LLPS) occurs in a certain region of the phase diagram. We performed temperature dependent dynamic light scattering measurements to monitor the diffusion behavior upon approaching the liquid-liquid phase transition. We found two contributions to the collective diffusion. The faster diffusion is ascribed to small clusters whereas the slower contribution is due to collective diffusion of larger clusters. Both the slow and fast collective diffusion coefficients first increase as expected according to the Stokes-Einstein equation. Upon approaching the phase transition they decrease linearly due to the formation of clusters. A new theoretical model is needed to explain these experimental observations. The Rayleigh ratio as well as the diffusion coefficients may be used to estimate the spinodal and binodal temperatures of the system. The classification of the critical behavior turns out to not be as straightforward as in the case of other binary systems. This is due to the formation of clusters before the onset of phase transition. [1] Zhang et al., PRL, 101, 148101, 2008, [2] Zhang et al., Soft Matter, 8, 1313, 2012, [3] Roosen-Runge et al., PNAS, 108, 11815, 2011