Viscosity and diffusion: Crowding and salt effects in protein solutions

Research output: Contribution to journalArticle


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.


  • Marco Heinen
  • Fabio Zanini
  • Felix Roosen-Runge
  • Diana Fedunová
  • Fajun Zhang
  • Marcus Hennig
  • Tilo Seydel
  • Ralf Schweins
  • Michael Sztucki
  • Marián Antalík
  • Frank Schreiber
  • Gerhard Nägele
External organisations
  • Jülich Research Centre
  • University of Tübingen
  • Institute of Experimental Physics SAS
  • Institut Laue Langevin
  • European Synchrotron Radiation Facility
  • Pavol Jozef Safarik University in Kosice
Original languageEnglish
Pages (from-to)1404-1419
Number of pages16
JournalSoft Matter
Issue number5
Publication statusPublished - 2012 Feb 7
Publication categoryResearch
Externally publishedYes