Rayleigh light scattering is often used to quantify protein-protein interactions in solution via experimental measurement of the osmotic second virial coefficient (OSVC), but analysis of measurements from such experiments requires identification of a scattering volume and the thermodynamic constraints imposed on that volume, i.e., the statistical mechanical ensemble in which light scattering occurs. Depending on the set of constraints imposed on the scattering volume, one can obtain either an apparent OSVC, A2,app, or the true thermodynamic OSVC, Bosm22, that is rigorously defined in solution theory [Blanco et al., J. Chem. Phys. 134, 225103 (2011)]. However, it is unclear to what extent A2,app and Bosm22 differ, which may have implications on the physical interpretation of OSVC measurements from light scattering experiments. In this paper we use the multicomponent hard-sphere model and a well-known equation of state to directly compute and compare A2,app and Bosm22. Our results for the hard-sphere fluid indicate that A2,app underestimates Bosm22, but in a systematic manner that may be explained using fundamental thermodynamic expressions for the two OSVCs. The difference between A2,app and Bosm22 may be quantitatively significant, but may also be obscured in experimental application by statistical uncertainty or non-steric interactions. Consequently, the two OSVCs that arise in the analysis of light scattering measurements do formally differ, but in a manner that may not be detectable in actual application.
Citation: Journal of Chemical Physics
Pub Type: Journals
light scattering, osmotic virial coefficient, hard-sphere fluid, protein interaction