Controlling the viscosity of concentrated protein solutions – salt type and ionic strength

Protein solubility is highly dependent on the salt type and ionic strength in the buffer formulation.  This is due to the impact of the ions on the interaction between protein molecules.  These protein-protein interactions also control the viscosity directly and indirectly through their influence on the spatial arrangement of molecules (i.e. microstructure).  Viscosity data is presented for concentrated Bovine γ-Globulin solutions with various salt types and levels to illustrate this effect.  The results can be interpreted with respect to the position of the salt along the Hofmeister series which ranks the strength of hydration.