Protein–Ligand interactions for hydrophobic charge-induction chromatography: A QCM-D study

Hydrophobic charge-induction chromatography (HCIC) is a novel technology for antibody purification. The interaction between immunoglobulin G (IgG) and HCIC ligands was investigated by dissipative quartz crystal microbalance (QCM-D). HCIC ligands 2-mercapto-1-methylimidazole (MMI), 2-mercaptobenzimidazole (MBI) and 2-mercapto-4-methylpyrimidine hydrochloride (MMp) were coupled to the surface of a self-assembled monolayer (SAM) terminated by epoxy groups. The ellipsometric ligand densities of MMI, MBI and MMp on the SAMs were 1.54, 1.64 and 1.47 chain/nm2, respectively. QCM results indicated the Au–MBI sensor to exhibit excellent performance in IgG adsorption compared with other sensors, with a maximum adsorption capacity of 1601 ng/nm2 and a dissociation constant of 2.84 × 10−6 M. The structure of the adsorbed IgG layer changed as a result of changes in the pH of the protein buffer and the addition of free and stable salts, probably due to changes in IgG conformation. According to Au–MBI surface regeneration experiments, the degree of regeneration afforded by NaOH 0.1 M was 99.7%. The QCM-D platform based on SAMs proved to be a powerful tool for studying ligand–protein interactions and the structures of protein adsorption layers. This study provides accurate theoretical guidance for the practical application of protein adsorption and antibody purification procedures.