A NONPERTURBATIVE RELATION BETWEEN THE MUTUAL DIFFUSION-COEFFICIENT, SUSPENSION VISCOSITY, AND OSMOTIC COMPRESSIBILITY - APPLICATION TO CONCENTRATED PROTEIN SOLUTIONS

We test a proposed relation between mutual diffusion coefficient and v iscosity in suspensions which is essentially identical to a dynamic mo de-coupling theory of diffusion in binary fluid mixtures near a critic al mixing point. In contrast to conventional treatments of suspension hydrodynamics, this relation is non-perturbative in the sense that it is not necessary to assume that the volume fraction of suspended parti cles is a small parameter. In order to apply this theory to protein so lutions, we measured the mutual diffusion coefficient of several globu lar proteins in aqueous solutions containing 2% ampholyte and protein up to 40% by weight. The viscosity was also measured in aqueous soluti ons of up to 30% protein by weight. The mutual diffusion coefficient w as then related to the viscosity and osmotic compressibility of the co ncentrated suspension relative to the infinite dilution limit. We conc lude that this non-perturbative relation provides a convenient estimat e of protein diffusion coefficients as a function of protein concentra tion.