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Updated: Jan 4, 2026

Structural Studies of Macromolecules in Solution using Small Angle X-Ray Scattering
Published on: November 5, 2018
Experimental determination of second virial coefficients by small-angle X-ray scattering: a problem revisited
Tyler Mrozowich1, Donald J Winzor2, David J Scott3,4
1Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, 4401 University Drive, Lethbridge, AB, T1K 3M4, Canada.
Abstract:
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 [Formula: see text] still establishes the existence of slightly associative interactions between protein molecules, irrespective of the molecular source-protein self-interactions and/or protein-cosolute contributions.
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