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 x 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.