Surface Properties of Protein–Polyelectrolyte Solutions. Impact of Polyelectrolyte Hydrophobicity

The strong influence of an amphiphilic polyelectrolyte, poly(N,N-diallyl-N-hexyl-N-methylammonium chloride), on the surface properties of solutions of globular proteins (lysozyme, β-lactoglobulin, bovine serum albumin, and green fluorescent protein) depends on the protein structure and allows elucidation of the contribution of hydrophobic interactions in the protein–polyelectrolyte complex formation at the liquid–gas interface. At the beginning of adsorption, the surface properties are determined by the unbound amphiphilic component, but the influence of the protein–polyelectrolyte complexes of high surface activity increases at the approach to equilibrium. The kinetic dependencies of the dilational dynamic surface elasticity with one or two local maxima give a possibility to distinguish clearly between different steps of the adsorption process and to trace the formation of the distal region of the adsorption layer. The conclusions from the surface rheological data are corroborated by ellipsometric and tensiometric results.