Protein adsorbers from surface-grafted copolymers with selective binding sites

Abstract

A novel protein-selective copolymer with “vertical architecture” has been prepared via photo-initiated graft copolymerization from poly(ethylene terephthalate) track-etched membranes with a pore diameter of 700 nm. The “synergist immobilization” method for increasing the surface selectivity of photo-grafting using the photoinitiator benzophenone was successfully used to graft linear poly(acryl amide)s with layer thicknesses of up to 250 nm in their swollen state to the entire membrane pore surface. The molecular recognition properties of the arginine-selective functional monomer bisphosphonato-m-xylylene methacrylamide (M2) were employed in copolymers with the hydrophilic methacryloylamino-2-hydroxypropane (M1); reference materials were prepared with grafted polyM1. Characterization of the novel materials was conducted using gravimetry (for degree of grafting), contact angle measurements, hydraulic permeability (for effective grafted layer thickness) and 31P solid-state NMR spectroscopy. Protein binding was evaluated with six proteins of different size and pI value. Membranes with grafted poly(M1-co-M2) showed the highest binding capacities for lysozyme, and adsorption isotherms revealed a 15-fold higher association constant for the arginine-rich lysozyme compared to the lysine-rich cytochrome C, both having similar size and pI value. With these adsorbers, lysozyme was also selectively bound from a 1 : 1 mixture with cytochrome C. Specific π–cation interactions between arginines and the binding sites in the M2 segments along with the special grafted architecture are the basis for the function of these promising new materials, which can clearly distinguish between basic proteins of very similar pI and size.