Repulsive van der Waals Forces. I. Complete Dissociation of Antigen-Antibody Complexes by Means of Negative van der Waals Forces

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Abstract
When two types of particles and/or macromolecules with different inter- facial free energies are immersed (or dissolved) in a liquid medium with an interfacial free energy intermediate between those of the particles or macro- molecules, the net van der Waals forces between these particles or molecules are repulsive. Thus by lowering the interfacial free energy (proportional to the surface tension) of their liquid medium, antigen-antibody (Ag-Ab) complexes of the van der Waals type can be readily dissociated, as could be demonstrated with the antigen 3-azopyridine (P3) coupled to rabbit serum albumin (P3A) and rabbit anti-P3 antiserum. As surface tension lowering agents, ethylene glycol (EG) and dimethyl sulfoxide (DMSO) were principally used. Prevention of the formation of P3A-anti-P3 complexes could be effected with the addition of less EG or DMSO than was needed for the dissociation of the precipitate, once formed. The reasons for this effect are discussed. P3A-anti-P3 complexes dissociated with EG, re-precipitated upon removal of the EG by dialysis. The mixed Coulombic-van der Waals system, bovine serum albumin (BSA)-goat anti-BSA antiserum, could be dissociated by lowering the pH (to pH 4.0) or raising it (to pH 9.5) while simultaneously lowering the surface tension.