Observation of the Formation of the Dynamic Clusters in Concentrated Lysozyme Protein Solutions

Neutron spin echo (NSE) and small angle neutron scattering (SANS) are used to investigate the structure and short-time dynamics of lysozyme protein solutions with the presence of the equilibrium clusters. The Q dependent collective diffusion coefficient indicates there are no significant inter-monomeric-protein dynamics at high Q. Upon increasing the concentration, the self diffusion coefficient at short-time limit is seen to decrease much faster than that of the hard-sphere and charge stabilized colloidal suspensions, further supporting the formation of clusters under the probed experimental conditions. These clusters are further argued to have finite life time instead of conglomerating permanently. Moreover, evidenced by the average hydrodynamic radius, at relatively low concentration, there are very few dynamical clusters, while at higher concentrations, the diffusion behavior at short-time limit is dominated by the dynamic clusters.