Tetrazole-functionalized cation-exchange membrane adsorbers with high binding capacity and unique separation feature for protein

The modification with high-density functional groups is a widely used method to enhance the binding capacity of membrane adsorbers, where the types of the attached groups are crucial to achieve good selectivity for protein separation. In this work, a novel tetrazole-functionalized weak cation-exchange membrane with high-capacity was prepared by constructing tetrazole-containing polymer brushes on the surface of regenerated cellulose membrane via the combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and “click chemistry” between cyano and azide. Densities of tetrazolyl groups on the membranes can be easily controlled by manipulating the polymerization time. The binding capacity of lysozyme increased with the polymerization time but eventually reached maximum due to the reduction of the utilization percentage of ion-exchange sites. The adsorption of newly designed membrane conforms to the feature of weak cation exchanger in terms of pH and salt effects, whereas the effect of pH exhibits a large difference from that on the carboxylic-functionalized ion-exchange membranes. Most importantly, the membranes possess higher dynamic binding capacity independent of the flow rate of mobile phase compared with the previously reported cation-exchange membranes. Featured with the unique properties, the modified membrane could simultaneously purify lysozyme and ovotransferrin from hen egg white at higher productivity. The present work provides a new alternative for membrane chromatography of biomacromolecules.