AUC in the High Concentration of Salts/Cosolvent
Résumé
Macromolecule stability, conformations, and equilibrium are modulated by solvent composition. This chapter presents the formalism allowing to study in analytical ultracentrifugation (AUC) the sedimentation of macromolecules in a solvent with a high salt or other cosolvent concentration. It allows to relate the buoyant molar mass, measured in AUC at low concentration of macromolecule, to the macromolecule molar mass, through thermodynamic preferential binding parameters. These parameters allow to derive values for the numbers of water and cosolvent interacting with the macromolecule, in the framework of models. When modifying the solvent composition, i.e., cosolvent activity, equilibrium constants characterizing conversion between macromolecular species changes are directly related to the differences in the preferential binding parameters, which can be interpreted, in the framework of models, in terms of differences in bound water and cosolvent.