Comparison Between Antigen-Antibody Binding Energies and Interfacial Free Energies

Abstract

Antigen-antibody binding energies derived from equilibrium data are compared with the binding energies resulting from the interfacial free energies obtained from contact angle measurements of antigens and antibodies. From these interfacial free energies two sorts of theoretical antigen-antibody binding energies can be derived, as well as the Hamaker constants for most antigen-antibody systems. For interactions in vacuo the Hamaker constants obtained are between 4 and 6x 10^-13 ergs, while these constants for hydrated antigen antibody interactions are < 10^-14 ergs. For interactions in vacuo, interfacial free energies yield binding energies (δF^a)that lie between -120 and -140 ergs/cm². For interactions in the aqueous phase (with interstitial water still present), much lower binding energies (δF^b) are derived, of the order of -0.01 and -1 ergs/cm². In comparison, dextran-anti-dextran interactions show a binding energy derived from equilibrium data (δF^eq) of the order of -10 ergs/cm². In general the equilibrium binding energies δF^eq of-most antigen-antibody systems would vary between -1 and -20 ergs/cm². The implications of this comparison are discussed in the light of the influence of residual water between antigenic determinant and antibody-active site, as well as in the light of the degree of perfection of fit between these sites.