Poly (Ionic Liquid)S-Based Aqueous Biphasic System And Their Extraction Performance

Ionic liquids (ILs)-based aqueous biphasic systems (ABSs) refer to a special type of biphasic system composed of ILs and salting-out agents, which possesses the advantages of environmentally friendly technology, wide range of polarity, phase-spilt easily and hardly ever emulsifying. ILs-based ABSs showed considerable potential in separation and purification of biomolecules and natural products. Poly (ionic liquid)s (PILs) are a new kind of polymeric materials, which not only incorporate the advantages of ILs, such as the molecular recognition ability, but also have enhanced mechanical stability, safety and self-organization properties. Besides, PILs are more easily to be recycled and reused. Nowadays, the researches on ILs in aqueous biphasic systems (ABSs) have been studied by a lot of researches, but the ABSs incorporating PILs have rarely been reported. Herein, we synthesized a series of PILs with specific molecular weight by Reversible Addition Fragmentation chain Transfer polymerization (RAFT), explored the establishment of the ABSs composed of PILs and studied their application in extracting biomolecules.Six kinds of PILs with different molecular weight based on 1-vinyl-3-butylimidazolium bromide monomer were synthesized by RAFT. We successfully obtained PILs with fatty acidic anions for the first time by anion exchange. The physical and chemical properties of PILs were characterized by elemental analysis,1H NMR and gel permeation chromatography (GPC). The number-average molecular weights of PILs obtained by GPC were within the range of 4880-14848 g/mol and the low polydispersity index (PDI) were within the range of 1.10-1.26. The results indicated that the initial decomposition temperature of PILs (Tonset) rose with the increase of the molecular weight of PILs. Besides, the counter anions influence the thermal stability of PILs and the Tonset of PILs with bromide anion was higher than those with fatty acidic anions.ABSs composed of imidazolium-based PILs and K3PO4 aqueous solution were successfully established for the first time and the relationship among the structures and molecular weight of PILs and the salting-out agents was studied. The research showed that the ability of PILs which containing hydrophobic CTA segment owned stronger ability to form ABSs than IL monomer. Besides, the ability of PILs with different molecular weight to form ABSs with K3PO4 aqueous solution followed the rule:P[IL29]Br> P[IL38]Br> P[IL49]Br> P[IL53]Br. When the degree of polymerization was above 29, PILs with lower the molecular weight presented better phase-spilt ability. PILs with more hydrophobic fatty-acid counter anion were more easily to form ABSs. In addition, the length of the tie-lines can be increased by decreasing the temperature, or increasing the mass fraction of PILs and K3PO4.The extraction efficiency of PILs+K3PO4+H2O was investigated. The PILs-based ABSs presented excellent extraction efficiency and the distribution coefficients of the selected biomolecules were:Dtryptophan=922, Dtyrosine=318, Dphenylalanine=200, Dtheophylline=427, Dcaffeine=124, Dchlorogenic acid=289, Dcaffeic acid=111.The extraction fractions were all above 95%. The Dtryptophan was 900 times larger than traditional PEG-polysaccharide systems,130～900 times larger than PEG-inorganic salts systems and 12～18000 times larger than the water-soluble ILs reported in the literature. Dtyrosine was 80-636 times larger than the water-soluble ILs and potassium citrate/PPG 400 system. Besides, the influences of the molecular weight of PILs, the counter anions, the extraction temperature, the compositions of the systems and the concentration of the solutes were further discussed.The extraction experiments of phospholipids with PILs/methanol-hexane liquid-liquid biphasic systems were conducted. The distribution coefficient of phosphatidylcholine (Dpc) and the selectivity of PC to phosphatidyl ethanolamine (PE) (SPC/PE) with P[IL20]Br/methanol-hexane as the extractant were 2.57 and 2.98, respectively, which were much higher than the data reported in the previous literatures. DPC declined significantly and DPE and SPC/PE declined slowly with the increase of the molecular weight of PILs. DPE reached the maximum,3.87, when the mass fraction of P[IL2o]Br was 15%. Dpc decreased with the increase of the mass fraction of PILs in methanol. In addition, Dpc decreased while DPE increased with the increase of temperature. Besides, the extraction mechanism was also studied by ab initio calculations and the results showed that the hydrogen-bonding interactions between PC and IL were beneficial for the extraction process.