A three-component theory of sedimentation equilibrium in a density gradient

In the original analysis (1) of the behavior of macromolecules and viruses in a density gradient at equilibrium in the ultracentrifuge, only two incompressible components were considered to be present. These were the polymer and the solvent which forms the density gradient. The pressure-dependent terms and the cross terms in the chemical potential which describe the chemical reactions between the polymer and the solute were neglected. It has been pointed out from theoretical considerations (2-4) that these terms are important. In experimental studies of the buoyant behavior of bovine mercaptalbumin in aqueous cesium chloride,(5) it was observed that both solvation and pressure effects are large.