Ionic liquids (ILs) have numerous applications in industrial processes as a benign alternative to conventional volatile organic solvents. However, many of them are toxic to organisms and are poorly biodegradable. In this work, a series of environmentally friendly cholinium ILs have been designed and synthesized. It was found that these ILs could form aqueous two-phase systems (ATPSs) with polypropylene glycol 400 (PPG400) which is thermo-sensitive, non-toxic and biodegradable. In order to understand the phase formation processes and possible application of these ATPSs for extraction/separation of proteins, the binodal curves and tie lines of these ATPSs were measured at 25 °C, and the effects of anionic structure of the ionic liquids, nature of the proteins and difference in the concentration of top- and bottom-phases on the partitioning behavior of some typical proteins were investigated systematically. It was shown that bovine serum albumin (BSA), trypsin, papain and lysozyme could be enriched effectively into the ionic liquid-rich phase of the ATPSs, and single-step extraction efficiency could be as high as 86.4–99.9% under the optimized conditions. Furthermore, enzyme activity of the native trypsin in water and in aqueous ionic liquid solutions was determined by using N-a-benzoyl-L-arginine ethyl ester as a substrate, and activity increases to about 127% was observed after 13 months storage. In addition, PPG400 has been recovered simply by heating and reused in the next extraction processes. This avoids the non-sustainable issue of highly salty water produced in the application of the polyethylene glycol (PEG) + salt and ionic liquid + salt ATPSs.

The high crystallization degree of chitosan and therefore its poor solubility in water and in most of the conventional organic solvents limits its extensive applications in practical processes. In this study, ionic liquids [C₄mim][HCOO], [C₄mim][CH₃COO], [C₄mim][CH₃CH₂COO], [C₄mim][CH₃CH₂CH₂COO], [C₄mim][HOCH₂COO], [C₄mim][C₆H₅COO], [C₄mim][CH₃CHOHCOO] and [C₄mim][N(CN)₂] have been used to study the effect of anionic structure on solubility of chitosan and the possible dissolution mechanism in ionic liquids. For this purpose, solubilities of chitosan in these ionic liquids have been determined as a function of temperature, and hydrogen bond accepting ability of the ionic liquids has been estimated by ¹H NMR and solvatochromic UV/vis measurements. At the same time, the interaction between [C₄mim][CH₃COO] and chitosan in the chitosan + [C₄mim][CH₃COO] solution is investigated by ¹³C NMR, and the regenerated chitosan from ionic liquids by addition of ethanol is characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). It is shown that in the ionic liquids investigated, [C₄mim][CH₃COO] is the most efficient ionic liquid for the dissolution of chitosan. Solubilities of chitosan increase almost linearly with increasing hydrogen bond accepting ability of the ILs. Both the anions and the [C₄mim]⁺ cation play important roles in the dissolution of chitosan, possibly by the disruption of native hydrogen bonds in chitosan. In addition, good thermal stability has been observed for the regenerated chitosan.

It was found for the first time that single tail ionic liquid (IL) surfactants, 1-alkyl-3-methylimidazolium bromides [C_nmim]Br (n = 10, 12, 14), form unilamellar vesicles in aqueous solutions without any additives. With the increase in IL concentrations, the self-assembly of these ILs can transfer from spherical micelles to rodlike micelles and then to vesicles.