Second-order concentration correction to the mutual diffusion coefficient of a suspension of hard Brownian spheres

Translational Diffusion Coefficients of Bovine Serum Albumin in Aqueous Solution at High Ionic Strength

“…Theories that predict the concentration dependence of the diffusion coefficient of spherical particles have been given by Batchelor (13), by Felderhoff (15), and by Phillies (18). Batchelor (13) was the first to obtain a theoretical expression for the mutual diffusion coefficient which incorporates exact numerical knowledge of the two-body hydrodynamic interaction between particles.…”

“…The authors point out (18), in Eq. [19], that the difference between their value of the first-order correction coefficient, k ϭ 0.56, and that obtained by Felderhoff (15), k ϭ 1.56, Eq.…”

“…The predictions embodied in Eqs. [9], [11], [18], and [19] are distinctly different, which suggests that the effect of the reference frame and divergence terms should be large enough to be observed by appropriate experiments. Here, a relevant point is that the divergence terms are most sensitive to the hydrodynamic interactions at short interparticle distances and hence are more important when long-range repulsions are absent (33).…”

“…Here, concentration is expressed as particle hydrodynamic volume fraction, ϭ (4/3) R 3 . The coefficient k d is determined by integration of the radial distribution function of the particles, which depends on the form of the interaction potential between particles; k h is generally evaluated from the Smoluchowski equation describing particle motions and depends on both potential and hydrodynamic interactions (13)(14)(15)(16)(17)(18).…”

“…Since the scattering power of globular proteins is weak, static and dynamic light scattering experiments can be carried out to relatively high concentrations without problems from multiple scattering artifacts, as confirmed directly by experiment (5). As a framework for the discussion of the effects of ionic strength and pH on the diffusion coefficient of BSA, we utilize the theoretical calculations of Batchelor (13), Felderhoff (15), and Phillies (18), which assume an impermeable hard-sphere model. We compare data on D m and d/dc at the isoelectric pH ϭ 4.7 and I ϭ 0.1, where BSA has a net charge of zero (19), with results at pH ϭ 7.4 and I ϭ 0.15, pH ϭ 7.4 and I ϭ 1.5, and pH ϭ 7.4 and I ϭ 3.3.…”