Experimental support for reclassification of the light scattering second virial coefficient from macromolecular solutions as a hydrodynamic parameter

This investigation examines the source of the disparity between experimental values of the light scattering second virial coefficient A_2 (mL.mol/g 2 ) for proteins and those predicted on the statistical mechanical basis of excluded volume. A much better theoretical description of published results for lysozyme is obtained by considering the experimental parameters to monitor the difference between the thermodynamic excluded volume term and its hydrodynamic counterpart. This involves a combination of parameters quantifying concentration dependence of the translational diffusion coefficient obtained from dynamic light scattering measurements. That finding is shown to account for observations of a strong correlation between A_2M_2 (mL/g), where M 2 is the molar mass (molecular weight) of the macromolecule and the diffusion concentration parameter k_D (mL/g). On the grounds that k_D is regarded as a hydrodynamic parameter, the same status should be accorded the light scattering second virial coefficient rather than its current incorrect thermodynamic designation as B_2 (mL.mol/g 2 ), or just B , the osmotic second virial coefficient for protein self-interaction.