Unusual Dynamics of Concentration Fluctuations in Solutions of Weakly Attractive Globular Proteins

The globular proteinγB-crystallin exhibits a complex phase behavior, whereliquid−liquid phase separation characterized by a critical volume fractionφc= 0.154 and acritical temperatureTc= 291.8 K coexists with dynamical arrest on all length scales at volumefractions aroundφ≈0.3−0.35, and an arrest line that extends well into the unstable regionbelow the spinodal. However, although the static properties such as the osmoticcompressibility and the static correlation length are in quantitative agreement withpredictions for binary liquid mixtures, this is not the case for the dynamics of concentrationfluctuations described by the dynamic structure factorS(q,t). Using a combination ofdynamic light scattering and neutron spin echo measurements, we demonstrate that thecompetition between critical slowing down and dynamical arrest results in a much more complex wave vector dependence ofS(q,t) than previously anticipated