5-Aminoindole, a new ligand for hydrophobic charge induction chromatography

Hydrophobic charge induction chromatography (HCIC) is a mixed-mode chromatography that achieves high adsorption capacity by hydrophobic interaction and facile elution by pH-induced charge repulsion between the solute and ligand. This article reports a new medium, 5-aminoindole-modified Sepharose (AI-Sepharose) for HCIC. The adsorption equilibrium and kinetics of lysozyme and bovine serum albumin (BSA) to AI-Sepharose were determined by batch adsorption experiments at different conditions to provide insight into the adsorption properties of the medium. The influence of salt type on protein adsorption to AI-Sepharose corresponded with the trend for other hydrophobicity-related properties in literature. Both ligand density and salt concentration had positive influences on the adsorption of the two proteins investigated. The adsorption capacity of lysozyme, a basic protein, decreased rapidly when pH decreased from 7 to 3 due to the increase of electrostatic repulsion, while BSA, an acidic protein, achieved maximum adsorption capacity around its isoelectric point. Dynamic adsorption experiments showed that the effective pore diffusion coefficient of lysozyme remained constant at different salt concentrations, while that of BSA decreased with increased salt concentration due to its greater steric hindrance in pore diffusion. High protein recovery by adsorption at pH 7.10 elution at pH 3.0 was obtained at a number of NaCl concentrations, indicating that the adsorbent has typical characteristics of HCIC and potentials for applications in protein purification.