Formation and stability of polyelectrolyte/polypeptide monolayers determined by electrokinetic measurements

Abstract

Physicochemical characteristics of cationic macroions: poly(allylamine hydrochloride) (PAH), poly(diallyldimethylammonium chloride) (PDDA) and poly-L-lysine (PLL) of molar mass equal to 70, 150, and 300kD, respectively were acquired at various pHs stabilized by Tris and PBS buffers. They comprised the diffusion coefficient, hydrodynamic diameter and the electrophoretic mobility of the macromolecules for various ionic strengths. Afterward, formation of polyelectrolyte monolayers on mica and their electrokinetic properties were investigated using the in situ streaming potential method. In this way macromolecule adsorption mechanism was evaluated. Additionally, unique desorption measurements were carried out that allowed to determine macromolecule monolayer stability. The results were interpreted in terms of the general electrokinetic model expressing the macromolecule coverage in terms of the zeta potential of the monolayers. This allowed to determine the adsorption constant and the binding energy of macromolecules at different ionic strengths and pHs. It was shown that PLL and PDDA formed the most stable monolayers on mica characterized by the binding energy equal to −21 and − 20 kT, for pH 7.4 and 9.0, respectively. Therefore, both these macroions can be exploited for creating convenient substrates for efficient immobilization of protein molecules.