Peptide interfacial adsorption is kinetically limited by the thermodynamicstability of self association

We present a study of the adsorption of two peptides at the octane-water in terface. The first peptide, Lac21, exists in mixed monomer-tetramer equilib rium in bulk solution with an appreciable monomer concentration. The second peptide, Lac28, exists as a tetramer in solution, with minimal exposed hyd rophobic surface. A kinetic limitation to interfacial adsorption exists for Lac28 at moderate to high surface coverage that is not observed for Lac21. We estimate the potential energy barrier for Lac28 adsorption to be 42 kJ/ mol and show that this is comparable to the expected free energy barrier fo r tetramer dissociation. This finding suggests that, at moderate to high su rface coverage, adsorption is kinetically limited by the availability of in terfacially active monomeric "domains" in the subinterfacial region. We als o show how the commonly used empirical equation for protein adsorption dyna mics can be used to estimate the potential energy barrier for adsorption. S uch an approach is shown to be consistent with a formal description of diff usion-adsorption, provided a large potential energy barrier exists. This wo rk demonstrates that the dynamics of interfacial adsorption depend on prote in thermodynamic stability, and hence structure, in a quantifiable way.