Protein binding on polyelectrolyte-treated glass. Effect of structure of adsorbed polyelectrolyte.

Polyelectrolyte adsorption can be used to modify the surface of chromatographic packings in order to make them more suitable for protein separations. We studied the binding of proteins to controlled pore glass (CPG) on which the polycation poly(diallyldimethylammonium chloride) (PDADMAC) was noncovalently immobilized through electrostatic interaction. We found that the selectivity of PDADMAC for bovine serum albumin vs. beta-lactoglobulin, identified in previous selective coacervation studies, is conserved after its immobilization on the CPG surface. Protein binding results showed that the pH, ionic strength, and mixing time for polyelectrolyte adsorption all affect subsequent protein binding, presumably via the molecular properties of the adsorbed polyelectrolyte layer. The polyelectrolyte adsorption layer thickness, for polyelectrolyte adsorbed at pH 9.0, ionic strength I = 0.001, was measured with size-exclusion chromatography as delta H = 2.5 +/- 0.5 nm. Quasielastic light scattering measurement of the polyelectrolyte hydrodynamic layer thickness (HLT) with a model system of PDADMAC and silica, supported a correlation between the structure of the adsorbed polyelectrolyte layer (e.g., loops and tails) and subsequent protein binding, although differences in magnitude between delta H and HLT suggest that adsorption onto silica may not mimic adsorption on CPG.