European Biophysics Journal

, Volume 48, Issue 8, pp 781–787 | Cite as

Experimental determination of second virial coefficients by small-angle X-ray scattering: a problem revisited

  • Tyler Mrozowich
  • Donald J. Winzor
  • David J. ScottEmail author
  • Trushar R. PatelEmail author
Original Article


This investigation examines the validity of employing single-solute theory to interpret SAXS measurements on buffered protein solutions—the current practice despite the necessity to regard the buffer components as additional non-scattering solutes rather than as part of the solvent. The present study of bovine serum albumin in phosphate-buffered saline supplemented with 20–100 g/L sucrose as small cosolute has certainly verified the prediction that the experimentally obtained second virial coefficient should contain protein–cosolute contributions. Nevertheless, the second virial coefficient determined for protein solutions supplemented with high cosolute concentrations on the basis of single-solute theory remains a valid means for identifying conditions conducive to protein crystallization, because the return of a slightly negative second virial coefficient based on single-solute theory \(A_{2}^{\text{app}}\) still establishes the existence of slightly associative interactions between protein molecules, irrespective of the molecular source–protein self-interactions and/or protein–cosolute contributions.


Small-angle X-ray scattering Thermodynamic nonideality Second virial coefficients Bovine serum albumin Small cosolute effects 



TM is supported by the NSERC Discovery Grant to TRP (RGPIN-2017-04003). TRP is a Canada Research Chair in RNA & Protein Biophysics.


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Copyright information

© European Biophysical Societies' Association 2019

Authors and Affiliations

  1. 1.Department of Chemistry and Biochemistry, Alberta RNA Research and Training InstituteUniversity of LethbridgeLethbridgeCanada
  2. 2.School of Chemistry and Molecular BiosciencesUniversity of QueenslandBrisbaneAustralia
  3. 3.National Centre for Macromolecular Hydrodynamics, School of BiosciencesUniversity of NottinghamNottinghamUK
  4. 4.ISIS Spallation Neutron and Muon Source, Rutherton Appleton Research Complex at HarwellHarwellUK
  5. 5.Department of Microbiology, Immunology and Infectious Disease, Cumming School of MedicineUniversity of CalgaryCalgaryCanada
  6. 6.Li Ka Shing Institute of Virology and Discovery LabUniversity of AlbertaEdmontonCanada

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