Quaternary Diffusion Coefficients in a Protein−Polymer−Salt−Water System Determined by Rayleigh Interferometry

Abstract

We have experimentally investigated multicomponent diffusion in a protein-polymer-salt-water quaternary system. Specifically, we have measured the nine multicomponent diffusion coefficients, D ij , for the lysozyme-poly(ethylene glycol)-NaCl-water system at pH 4.5 and 25°C using precision Rayleigh interferometry. Lysozyme is a model protein for protein-crystallization and enzymology studies. We find that the protein diffusion coefficient, D 11 , decreases as polymer concentration increases at a given salt concentration. This behavior can be quantitatively related to the corresponding increase in fluid viscosity only at low polymer concentration. However, at high polymer concentration (250 g/L), protein diffusion is enhanced compared to the corresponding viscosity prediction. We also find that a protein concentration gradient induces salt diffusion from high to low protein concentration. This effect increases in the presence of poly(ethylene glycol). Finally, we have evaluated systematic errors associated with measurements of protein diffusion coefficients by dynamic light scattering. This work overall helps characterize protein diffusion in crowded environments and may provide guidance for further theoretical developments in the field of protein crystallization and protein diffusion in such crowded systems, such as the cytoplasm of living cells.

Pentanary Cross‐Diffusion in Water‐in‐Oil Microemulsions Loaded with Two Components of the Belousov–Zhabotinsky Reaction

“…The values we have found for the cross-diffusion coefficients are sufficient to generate a shift in the onset of Turing instability comparable to the effect produced by increasing [BrO 3 À ] or decreasing [MA] by 5-10 %. The dependence of the cross-diffusion coefficients on the species concentrations makes the diffusive terms divA C H T U N G T R E N N U N G [D ij grad(u j )] nonlinear and may lead not only to a shift in the onset of bifurcation, but also to the emergence and stabilization of new forms of dissipative patterns.…”

“…There are several methods for obtaining cross-diffusion coefficients. The most commonly used are interferometry techniques [2,3] and the Taylor dispersion method. [4][5][6] Here we employ the latter approach.…”

Light scattering studies on Ficoll PM70 solutions reveal two distinct diffusive modes

“…Such cases may be difficult to properly account for and may falsify results and conclusions. Similar pitfalls may also hamper the more sensitive Rayleigh interferometric determinations of diffusivities in multicomponent systems [30,31].…”

Cross‐diffusion and viscoelastic effects on multidiffusive porous convection

“…The cross‐diffusion terms in the diffusivity matrix control the instability of the system considerably but they are commonly unnoticed on the basis of the often repeated slogan that these are of smaller magnitude compared with the main diagonal elements. But in some liquid mixtures, cross‐diffusion terms (off‐diagonal elements) are found to be much larger than the self‐diffusion (main diagonal elements) terms 6,7 …”

“…As envisaged, it is recognizable that the cross‐diffusion effects are bound to occur when more than one compositional gradient is present. In some liquid mixtures, cross‐diffusion terms are found to be much larger than self‐diffusion terms 6,7 . The inevitability of off‐diagonal elements (cross‐diffusion terms) in ternary/quaternary system was recommended by Onsager and Fuoss 3 .…”