Studies On The Separation Of Biomolecules By Ionic Liquids-Based Aqueous Two-Phase Systems

As a new green separation technology, ionic liquid-based aqueous two-phase systems (ATPSs) are attracting the attention of a growing number of scientists and engineers in recent years. These new ATPSs have many advantages shared by ionic liquids and traditional ATPSs, such as low viscosity, little emulsion formation, no need of using volatile organic solvent, and quick phase separation. At present, most of the researches on the ATPSs reported in literature focused on the ionic liquids based on imidazole and the inorganic salts. However, many of these ionic liquids may be harmful to organisms. Therefore, developing the non-toxic, harmless, biodegrable ionic liquids is the premise to achieve green separation by ionic liquids based ATPSs. As a part of the project supported by the National Natural Science Foundation of China (No. 20873036), in the present work, a series of choline-based ionic liquids have been synthesized and characterized. The phase equilibrium of ATPSs formed by these choline-based ionic liquids and temperature sensitive polymers was studied systermatically. The partition behavior of amino acids and proteins in these new ATPSs were also studied. The major content of the present work is as follows:1. A series of choline-based ionic liquids: choline formate, choline acetate, choline propionate, choline butyrate, choline glycollate, choline lactate, choline oxalate, choline benzoate, tri-choline citrate have been synthesized and purified in this work. These ionic liquids have also been characterized by NMR and DSC.2. The liquid-liquid equilibria were determined for ATPSs based on the ionic liquids (choline formate, choline acetate, choline propionate, choline butyrate, choline glycollate, choline lactate, choline oxalate, tri-choline citrate) and temperture sensitive polymer (PPG400,PPG1000,EO10PO90) at 298.15K. The effects of the structure of ionic liquids or polymers and temperature on the equilibrium of the ionic liquid-polymer ATPSs have been investigated systematically.3. The partition behaviors of L-Tryptophan and L-Tyrosine in the choline-based ionic liquids-PPG400 ATPS were determined. The effects of the concentrations of ionic liquids or polymer, structure of the amino acids on the partitioning of amino acids were examined. A green separation process based on ionic liquids-polymer ATPS was proposed.4. Extraction efficiencies of bovine serum albumin (BSA) and lysozyme were studied by using choline-based ionic liquids-PPG400 ATPSs. The effects of the structure of the ionic liquids and the size of the proteins on the partitioning of proteins were examined.5. The phase equilibrium of an ATPS based on the hydrophilic ionic liquid 1-butyl-3-methylimidazolium dicyanamide ([C4mim][N(CN)₂]) and K2HPO4 was studied, and the selective separation of BSA and saccharides (arabinose, glucose, sucrose, raffinose, dextran) from protein/saccharides mixed aqueous solutions was reported for the first time. The conductivities, dynamic light scattering, transmission electron microscopy were used to investigate the microscopic structure of the ionic liquids-rich top phase and the possible mechanism for the selective separation. Our findings suggest that [C4mim][N(CN)₂] + K2HPO4 ATPSs have the potential to offer new possibility in the selective separation of protein and saccharides.