Energetics of Protein−Interface Interactions and Its Effect on Protein Adsorption

The kinetics of adsorption of several positively and negatively charged proteins at the air/water and triolein/water interfaces have been studied. It is shown that adsorption of proteins at these interfaces is not simply diffusion-controlled but is strongly influenced by the energetics of interaction of proteins with the interfaces. Generally, positively charged proteins experience an energy barrier for adsorption at the air−water interface and therefore exhibit adsorption rates an order of magnitude slower than their respective bulk diffusivities. In contrast, the negatively charged proteins exhibit an attraction toward the air/water interface and therefore their adsorption rates are either slightly higher or 1.5−2 times lower than their bulk diffusivities. At the triolein−water interface however, all proteins, except phosvitin, adsorbed at rates 1−2 orders of magnitude faster than their bulk diffusivities. The differences between adsorptivities of positively and negatively charged proteins at the air−water interface, and the differences between adsorptivities of all proteins at the air/water and triolein/water interfaces can be explained convincingly in terms of the energetics of interaction of proteins with the interfaces.