Kinetics of adsorption of globular proteins at liquid/fluid interfaces

A model for the adsorption kinetics of globular proteins at a liquid/fluid interface is described which takes into consideration the transport of mole cules in the bulk by diffusion and a process accounting for the transition between the adsorption states of the protein molecules. The model is based on a recently published thermodynamic model for the adsorption isotherm of proteins at a liquid/fluid interface, which considers various adsorption st ates with different molar interfacial area. The model calculations show the particular features common to protein adsorption kinetics: induction perio d for low bulk concentrations, steep interfacial tension changes, significa nt effect of the transition kinetics on the overall adsorption process. A c omparison with dynamic surface tension data for P-lactoglobulin at the wate r/air interface shows good agreement. In full agreement with the generally excepted physical picture, it turns out that the adsorption kinetics is sig nificantly influenced by the transfer kinetics between the different adsorp tion states of the protein molecule. The estimation of the transfer rate co nstant yields values of the order of k = 10(-3) s(-1). (C) 2001 Elsevier Sc ience B.V. All rights reserved.