(546d) Ionic Liquid-Based Aqueous Biphasic Systems for High-Performance Extraction

Aqueous biphasic systems (ABSs) offer a benign alternative process for conventional extraction systems with volatile organic solvents to separate biomasses, such as amino acids, antibiotics, alkaloids, and proteins et al. And the employment of ionic liquids (ILs) in ABSs vastly promotes the extraction efficiency of various solutes because when compared with traditional polymers, ILs are highly designable and have tunable polarity in dealing with specific tasks. However, it is still challenging to construct an IL-based ABS with fine phase splitting ability, excellent extraction efficiency and low IL loss. Herein we report a series of newly designed IL-based ABSs that contains long-chain carboxylate anions and a cholinium cation that are all derived from biomass. This strategy introduced long alkyl chains into the anions, which not only significantly increased the hydrogen bond (HB) acceptor ability of the carboxylate anions through remarkable electron-donating effect but also ensured good hydrophobicity for achieving better phase splitting. The developed IL-based ABSs demonstrated a relatively broad biphasic area and extraordinary extraction efficiency for amino acids and bioactive compounds with partition coefficients for tryptophan, phenylalanine and caffeine of 58.54, 120, and 120, respectively, which were remarkably higher than those obtained in ABSs with conventional ILs. In addition, liquid crystal structures were observed when the carbon number of the carboxylate anion of the ILs exceeded eight; thus, IL-based ABSs with liquid crystal structures were reported for the first time. Furthermore, we synthesized a family of polymeric ionic liquids (PILs) to explore IL-based ABSs further. Phase diagrams determined by cloud point method demonstrated that the PILs have far more powerful ability to construct ABSs than conventional ILs. And it was demonstrated that in the designed PIL-based ABSs, unprecedentedly high partition coefficients were obtained (K_Trp = 1127, K_Phe = 188). Prospectively, PIL-based ABSs successfully combine the unique properties of PILs and ABSs, and offer a new platform for the development of green and high-performance extraction methods.