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Issue 5, 2012
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Viscosity and diffusion: crowding and salt effects in protein solutions

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Abstract

We report on a joint experimental–theoretical study of collective diffusion in, and static shear viscosity of solutions of bovine serum albumin (BSA) proteins, focusing on the dependence on protein and salt concentration. Data obtained from dynamic light scattering and rheometric measurements are compared to theoretical calculations based on an analytically treatable spheroid model of BSA with isotropic screened Coulomb plus hard-sphere interactions. The only input to the dynamics calculations is the static structure factor obtained from a consistent theoretical fit to a concentration series of small-angle X-ray scattering (SAXS) data. This fit is based on an integral equation scheme that combines high accuracy with low computational cost. All experimentally probed dynamic and static properties are reproduced theoretically with an at least semi-quantitative accuracy. For lower protein concentration and low salinity, both theory and experiment show a maximum in the reduced viscosity, caused by the electrostatic repulsion of proteins. On employing our theoretical and experimental results, the applicability range of a generalized Stokes–Einstein (GSE) relation connecting viscosity, collective diffusion coefficient, and osmotic compressibility, proposed by Kholodenko and Douglas [Phys. Rev. E, 1995, 51, 1081] is examined. Significant violation of the GSE relation is found, both in experimental data and in theoretical models, in concentrated systems at physiological salinity, and under low-salt conditions for arbitrary protein concentrations.

Graphical abstract: Viscosity and diffusion: crowding and salt effects in protein solutions

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Publication details

The article was received on 01 Jul 2011, accepted on 08 Nov 2011 and first published on 29 Nov 2011


Article type: Paper
DOI: 10.1039/C1SM06242E
Citation: Soft Matter, 2012,8, 1404-1419
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    Viscosity and diffusion: crowding and salt effects in protein solutions

    M. Heinen, F. Zanini, F. Roosen-Runge, D. Fedunová, F. Zhang, M. Hennig, T. Seydel, R. Schweins, M. Sztucki, M. Antalík, F. Schreiber and G. Nägele, Soft Matter, 2012, 8, 1404
    DOI: 10.1039/C1SM06242E

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