Membrane absorbers are attractive for protein purification due to rapid mass transport in micron-sized pores, but the binding capacity of membranes is modest compared to nanoporous resins. Layer-by-layer (LBL) polyelectrolyte adsorption provides a simple way to modify membranes with highly swollen, functional polymer films that increase protein-binding capacity.  Additionally, careful selection of synthetic schemes can reduce ligand costs.  For example, the synthesis of poly(N,N-dicarboxymethylallyl amine) (PDCMAA) occurs in 85% yield, and this relatively inexpensive polymer forms iminodiacetate-metal-ion complexes that should capture His-tagged proteins.  LBL adsorption of protonated poly(allylamine) (PAH) and PDCMAA yields micron-thick films upon deposition of only 10 bilayers. Although these films show a high Cu2+ binding capacity (~2.5 mmol/cm3 of film), binding of a metal ion is a necessary but not sufficient condition for creating membranes that selectively capture large amounts of polyhistidine-tagged protein.  The adsorbed polymer must also swell in water to provide space for protein-ligand interactions. Unfortunately, PAH/PDCMAA films do not swell sufficiently for extensive protein capture.  LBL adsorption of star-shaped polyelectrolytes may lead to increased film swelling due to a high concentration of unpaired ionic groups. Synthesis of cationic (poly(dimethylaminoethyl methacrylate)) and anionic (poly(acrylic acid)) polymers with 3, 4 and 6 arms occurred with ~80-90% yields. In LBL adsorption, preliminary results show that an increase in the number of arms on the cationic polymer increases the amount of anionic polymer adsorbed on the surface. Films with fewer than 5 bilayers can swell more that 200-500% in water, but swelling decreases with additional bilayers or an increase in the number of arms on the polymers. Highly swollen films exhibit lysozyme-binding capacities as high as 10-20 multilayers of protein. Future studies will examine the protein and Ni2+ binding in membranes modified with these films.

Swellable polyelectrolyte multilayer films for inexpensive, rapid protein purification

248th National Meeting (2014)

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