Fabrication of high-capacity cation-exchangers for protein chromatography by atom transfer radical polymerization

• We synthesized a novel poly(SPM)-grafted cation-exchanger by ATRP.
• The gels provided three-dimensional ligand arrangement by virtue of ATRP.
• Poly(SPM)-grafted cation-exchanger had a higher ionic capacity than the commercial gels.
• The gels show high binding capacity and great salt tolerance.
• The result demonstrates the mechanism of protein adsorption in the cation-exchangers.

This work reports the synthesis of novel cation-exchanger with controllable charge density and polymer chain length of poly(3-sulfopropyl methacrylate) (poly(SPM)) grafted via atom transfer radical polymerization onto Sepharose FF matrix. Polymer grafting provided a three-dimensional regular arrangement of the ligand and increased ionic capacity of the poly(SPM)-grafted cation-exchangers. The result showed that adsorption capacity for lysozyme enhanced greatly in poly(SPM)-grafted cation-exchangers whereas adsorption capacity for γ-globulin decreased dramatically. It can be attributed to the consequence of the competition between electrostatic interaction and repulsive excluded volume interaction of grafted polymer and protein. For lysozyme, protein adsorption on poly(SPM)-grafted cation exchangers was driven dominantly by electrostatic interaction. By constrast, the repulsive excluded volume interaction between grafted polymer and protein was remarkable in adsorption of γ-globulin on poly(SPM)-grafted cation exchangers. Moreover, the poly(SPM)-grafted cation exchangers exhibited great salt tolerance in protein adsorption and distinct intraparticle mass transfer properties. Finally, the results of dynamic binding capacity (DBC) for lysozyme showed that the poly(SPM)-grafted cation-exchangers had higher binding capacities than did the commercial SP Sepharose FF, and the maximal DBCs reached 192 mg/mL at 50 mmol/L NaCl. These results demonstrate great potential of poly(SPM)-grafted cation-exchangers for the large-scale purification of proteins.