Ionic liquid–polyvinyl chloride ionomer for highly selective isolation of basic proteins

Hydrophilic ionic liquid–polyvinyl chloride (PVC) hybrids were prepared by immobilizing N-methylimidazole (N-mim) to PVC chains in toluene. The NmimCl–PVC hybrids were characterized by FT-IR, 1H NMR, surface charge analysis and elemental analysis. The immobilization ratio, i.e., the percentage of chloride on PVC chain reacting with N-mim to form the hybrid, varies from 4.3% to 15.1% by increasing the N-mim/PVC molar ratio. The most distinct feature of the hybrid is its excellent selectivity for adsorbing basic proteins by effective suppression of the non-specific protein adsorption by pure PVC, and a higher immobilization ratio facilitates better selectivity. In Tris–HCl buffer, 100 μg mL−1 of basic proteins, i.e., lysozyme (Lys), cytochrome c (cyt-c) and hemoglobin (Hb), were favorably adsorbed with efficiencies of 97%, 98% and 94% by the hybrid with an immobilization ratio of 15.1%, while the adsorption of acidic proteins, i.e., bovine albumin serum (BSA), transferring (Trf) and immunoglobulin G (IgG) were negligible. The retained Lys, cyt-c and Hb could be readily recovered by elution with phosphate buffer, carbonate buffer and SDS solution with efficiencies of 89%, 87% and 84%, respectively. Another feature of the hybrid is the significant improvement of the biocompatibility characterized by the maintenance of the activity of hemoglobin after adsorption and elution process. The practical usefulness of the hybrid was demonstrated by selective isolation of hemoglobin from human whole blood.