Molecular Simulation On The Adsorption And Displacement Process In Hydrophobic Charge Induction Displacement Chromatography

Hydrophobic charge induction displacement chromatography (HCIDC) has been successfully used in antibody separation and purification. However, little is understood about the microscopic process and molecular mechanism within adsorbent pores. This paper focused on the microscopic dynamic process of HCIDC using coarse-grained molecular dynamics (MD) simulation, and studied the factors influencing adsorption and displacement properties.First, a pore model was established to represent the realistic adsorbent pore composed of matrix and immobilized 5-aminoindole (AI) ligands. Lysozyme was chosen as a model protein. Three displacers, tributyltetradecylphosphonium chloride (TC), cetyldimethylbenzylammonium chloride (CC), and benzethonium chloride (BC) were investigated.Then a coarse-grained model for the whole system was established according to Martini forcefield. Protein adsorption, displacement and conformational transition in the pore were examined by MD simulation. Meanwhile, the effect of ligand density and displacers on separation performance was investigated.The simulation results indicated that before adsorption, lysozyme constantly adjusted its conformation and orientation to form stable contact with ligands. During adsorption, lysozyme was in a dynamic equilibrium between its native state and partially unfolding state. The interaction between lysozyme and ligands was mainly hydrophobic, where residue 129 LEU was the key residue for adsorption. Under higher ligand density, the adsorption was stronger but lysozyme also suffered larger extent of unfolding. In displacement process, displacers had stronger interaction with ligands than lysozyme. So lysozyme was displaced from the original adsorption site and then adsorbed again at a new site, indicated by its center-of-mass motion. In the simulation, TC was a better displacer than CC, while BC exhibited some characteristics of chemically selective displacers. Higher-concentration displacers performed better in displacing lysozyme. However, they might cause elution difficulties in the chromatographic column regeneration.This paper provides molecular insight into HCIDC and examines the protein behavior in adsorbent pores. It also points out some factors that may have impact on the separation performance. Therefore, the research would be beneficial to the process optimization of HCIDC, and the rational design of both ligands and displacers.