Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 10: Poster: Charged Soft Matter

CPP 10.1: Poster

Montag, 14. März 2011, 17:30–19:30, P2

Crystallization of β-Lactoglobulin in Solution in the Presence of YCl₃ — •Andrea Sauter, Fajun Zhang, and Frank Schreiber — Institut für Angewandte Physik, Universität Tübingen, Germany.

In order to understand the vitally important tasks of proteins in living organisms, knowledge of their interactions is needed. The determination of the structure of a protein by x-ray diffraction requires high quality single crystals which are not always easy to obtain. During the last years simulations, theories and experiments suggested a two-step process of protein crystal nucleation, differing from classical nucleation theory (CNT). The system we are engaged in consists of an aqueous solution of the globular protein β-Lg with YCl₃. A reentrant phase behavior was observed [1]: The samples show aggregation between two critical YCl₃ concentrations c* and c** while a uniform solution exists for concentrations below c* or above c**. Near c* crystals grow directly from solution, following CNT. Near to c** a critical temperature T_c exists, above which the supernatant of a sample is clear. Below T_c it becomes reversible turbid due the forming of dense liquid drops. At lower initial protein concentrations c_p these are caused by critical concentration fluctuations. The formation of aggregates precedes crystal growth. At higher c_p a metastable liquid-liquid phase separation occurs. Crystallization is observed afterwards in the dense phase or starting from its interface as well as in the dilute phase. This cannot be explained by CNT, instead a two-step mechanism is assumed.

[1] F. Zhang et al. Phys Rev Lett 2008, 101, 148101.