Effects of sodium chloride addition on immunoglobulin G partitioning and solubility in polyethylene glycol/hydroxypropyl starch aqueous two-phase system

The effect mechanisms of sodium chloride (NaCl) addition on the partitioning and solubility of immunoglobulin G (IgG) in polyethylene glycol (PEG)/hydroxypropyl starch (HPS) aqueous two-phase system (ATPS) were studied. The influences of NaCl on PEG/HPS phase diagram and the hydrophobicity of IgG were investigated. The results indicated that the hydrophobicity difference between two phases and the IgG hydrophobicity were both enhanced with NaCl addition, so IgG preferred to partition into the top phase with more hydrophobicity. The solubilities of IgG in PEG and HPS solutions with or without NaCl were measured. It was found that NaCl addition could significantly reduce IgG precipitation in PEG solution. The effects of NaCl on the interaction between IgG and PEG was studied by Isothermal Titration Calorimetry (ITC). It was found that the main interactions between IgG and PEG changed from electrostatic force to hydrophobic interaction with NaCl addition. IgG would be wrapped by PEG molecules due to hydrophobic interaction so that the solubility of IgG in PEG solution was enhanced. The results reveal the mechanisms of NaCl addition on the partitioning and solubility of IgG in PEG/HPS systems, and PEG/HPS ATPS might be a promising alternative for IgG separation with good purity and yield.