Probing hydration and the stability of protein solutions--a colloid science approach.

The stability of protein solutions is a topic of much theoretical and practical interest. The theory of Derjaguin, Landau, Verweey and Overbeek (DLVO theory) has long been used by colloid scientists and chemical engineers to define conditions leading to stability of dispersion, but has found very little application by protein chemists. We apply DLVO theory to demonstrate that protein solution stability appears to be closely related to the presence of the hydration layer, rather than to significant inter-molecular net repulsive force. A novel but simple formalism is then developed which indicates, via computation of a newly defined parameter ('site relaxation time'), that estimated 'dwell times' for water molecules on a protein surface are of a magnitude adequate to account for such a role.