ADSORPTION OF PROTEINS AT THE LIQUID AIR INTERFACE/

Thermodynamic equations for describing protein adsorption layers at li quid/fluid interfaces are derived as a generalization of a theory publ ished recently [J. Colloid Interface Sci. 1996, 183, 26]. In this new theory the nonideality of enthalpy (Flory-Huggins' parameter) and entr opy of mixing are taken into account, and also the effect of the elect ric charge of the protein molecules on surface pressure is considered. The model is verified by experimental dynamic and equilibrium surface tension data for HA solutions obtained from pendent drop experiments (ADSA), The derived isotherm is in good agreement with the experimenta l data. The values of the isotherm parameters surface area per molecul e, electric charge of the HSA molecule, and the adsorption layer thick ness are close to values obtained by other methods in literature. It f ollows that HSA molecules undergo almost no denaturation at the soluti on/air interface and occupy a surface area of about 50 nm(2), independ ent of the packing in the adsorption layer, which is in agreement with the concept of a triple-domain structure.