Repulsive van der Waals Forces. II. Mechanism of Hydrophobic Chromatography

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Abstract
When two materials with different interfacial free energies are immersed in a liquid with an interfacial free energy intermediate between those of the two materials, the net van der Waals forces between these two materials are repulsive. Thus by lowering the interfacial free energy of the liquid medium, solutes or particles previously adsorbed onto low energy surfaces can be readily eluted from such surfaces. This is demonstrated by the coupling to and subsequent elution from Octyl Sepharose and Phenyl Sepharose of serum and other proteins. The elution of all proteins commenced when the surface tension of the eluting liquid was decreased to a point just below that of the protein in question. The eluted serum proteins successively emerged from the column in the exact decreasing order of their own interfacial free energies. In hydrophobic chromatography, coupling is favored when the van der Waals forces between solutes (or particles) and ligand are attractive (and maximum, frequently through the admixture of salts); elution is brought about by causing the van der Waals interaction between each solute (or particle) and ligand successively to become repulsive (by gradually lowering the surface tension of the eluting liquid).