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 molecules 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 states with different molar interfacial area. The model calculations show the particular features common to protein adsorption kinetics: induction period for low bulk concentrations, steep interfacial tension changes, significant effect of the transition kinetics on the overall adsorption process. A comparison with dynamic surface tension data for β-lactoglobulin at the water/air interface shows good agreement. In full agreement with the generally excepted physical picture, it turns out that the adsorption kinetics is significantly influenced by the transfer kinetics between the different adsorption states of the protein molecule. The estimation of the transfer rate constant yields values of the order of k=10−3 s−1.