Modified chitosan-based, pH-responsive membrane for protein separation

Abstract

N-Carboxymethyl chitosan (N-CMCS) and O-carboxymethyl chitosan (O-CMCS)-based amphoteric or pH-responsive charged membranes were prepared for protein separation. Both membranes (O-CMCS and N-CMCS) exhibited different charged natures and acidic/alkaline ion-exchange capacities along with 16–19 kDa molecular weight cut-off (MWCO), corresponding to 0.53 nm and 0.48 nm pore radius at pH 7.0 for O-CMCS and N-CMCS, respectively. Water permeability for O-CMCS and N-CMCS membranes varied between 5.0–6.0 × 10⁻⁸ Pa⁻¹ m h⁻¹ (ultra-filter range) and increased with equilibrating medium pH. The dual-charged nature of these membranes (presence of –COOH and –N⁺H₃ groups) was advantageously used to achieve antifouling properties in biomolecule separation. The N-CMCS membrane exhibited a positively charged nature in the 2.0–12.0 pH range. Thus, Donnan exclusion due to mutual electrostatic attraction between the membrane and protein was insignificant in accelerating the mobility of a protein molecule, thus achieving its separation. Meanwhile, the O-CMCS membrane showed pH-tunable charged nature and suitable separation performance for β-casein (β-Cas) and lysozyme (Lys) across alkaline media, as a representative case. Furthermore, no membrane fouling was detected after 50 days of operation in a protein environment.