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Description
Salt-induced charges in aqueous suspensions of proteins can give rise to complex phase diagrams including homogeneous solutions, large aggregates, and reentrant dissolution regimes. Moreover, depending on the temperature, a liquid-liquid phase separation may occur within the aggregation regime. Here, we systematically explore the phase diagram of the globular protein BSA via its dynamics as a function of temperature $T$ and protein concentration $c_p$ as well as of the concentrations $c_s$ of trivalent salts YCl$_3$ and LaCl$_3$. By employing incoherent neutron backscattering spectroscopy at BASIS (SNS) with energy transfers up to 100 $\mu$eV, we unambiguously access the global and internal short-time self-diffusion of the protein clusters depending on $c_p,c_s$ and $T$. We determine the cluster size in terms of effective hydrodynamic radii as manifested by the cluster center-of-mass diffusion coefficients $D$. For both salts, we find a simple functional form $D(c_p,c_s,T)$ in the parameter range explored. The master-curve observed previously [1] can be confirmed also for different temperatures and different salts. The salt- specific calculated binding probabilities and inter-particle attraction strengths, based on the short-time microscopic diffusive properties, increase with salt concentration and temperature in the regimes investigated and can be linked to the macroscopic behavior and to microscopy data.
[1] M. Grimaldo et al. J. Phys. Chem. Lett. 6 (2015)
