Construction And Application Of Hydrophobic Ionic Liquids-Based Microemulsions Stabilized By C_nE_m

The enzyme is a protein which has catalytic activity. Usually, enzyme-catalyzed reaction happens under mild conditions. The reactions have good catalytic activity and selectivity (including chemo-, region-and stereo-selectivity). Ionic liquid is composed of a bulky organic cation and an inorganic/organic anion, and it is liquid under room-temperature. Compared with traditional molecular organic solvent, ionic liquid of low volatility used as enzyme-catalyzed reaction medium has characteristic of green chemistry. And the physical and chemical properties of ionic liquid could be tuned. Nowadays, enzyme-catalyzed reaction in ionic liquid medium is a hot topic. In pure hydrophilic ionic liquids, enzymes could be dispersed at a single molecular level, but they are usually deactivated. By contrast, in hydrophobic ionic liquids, enzymes are catalytically active, but they could not be dispersed at a single molecular level. So, it is still a challenging problem to reconcile the contradiction between the solubility of an enzyme in ionic liquids and the retention of its activity in the ionic liquids. To construct microenvironment that is suit for the expression of enzyme activity is significant for the design of ionic liquid system in which enzymes have high catalytic activity. Microemulsication of hydrophobic ionic liquid is an effective strategy. So, some attempts have been made:1. Investigation of the fish diagrams of CnEm(n-alcohol)/H2O/hydrophobic ionic liquid systemSince bicontinuous microemulsion has a very large oil-water interface, it is a good choice as the medium of enzyme-catalyzed reactions. The reported bicontinuous microemulsion systems are formed under high temperature, however, the high temperature usually leads to the inactivation of enzymes. So it is significant to reduce the temperature under which bicontinuous microemulsions form. Besides, the increasement of the effectiveness of the surfactant always is of great significance. Fish diagram is a common method to investigate the bicontinuous microemulsions; however, few researches of the bicontinuous microemulsion based on hydrophobic ionic liquid have been reported. To develop bicontinuous microemulsions that is effective medium for enzyme-catalyzed reactions, we investigate the effect of surfactant and alcohol on the fish diagram of H2O/[Omim][PF6]/CnEm(n-alcohol) systems. We found that the amphipathy of surfactant have an influence on the phase inversion temperature, the size of fish and the effectiveness of the surfactant. The addition of short chain alcohol makes the phase inversion temperature increase. By contrast, the addition of long chain alcohol makes the phase inversion temperature decrease.2. Effect of the alkyl chain length of a hydrophobic ionic liquid on the phase behavior and microstructure of microemulsions stabilized by CnEm and the activity of solubilized emzymeThe use of hydrophobic ionic liquid as oil phase to formulate a H2O-in-ionic liquid microemulsion is of great significance to enzyme catalysis. In this report, we present the essential influence of the alkyl chain length of ionic liquids on the phase behavior and the microstructure of H2O/ionic liquid/CnEm (polyoxyethylene alkyl ether) ternary systems. The ILs are [Bmim][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate) and [Omim][PF6] (1-octyl-3-methylimidazolium hexafluorophosphate). For a given nonionic surfactant, the alkyl chain length of ionic liquids has an influence on the water solubilization capacity. The difference in the capacity, however, narrows and even disappears upon significant increase of the hydrophilic chain length of CnEm. The FTIR spectroscopy and UV-Vis spectroscopy confirm the existence of bulk water in both [Bmim][PF6] and [Omim][PF6] based C12E23 stabilized H2O-in-ionic liquid microemulsions. The catalytic activity of laccase hosted in the H2O-in-ionic liquid microemulsion and the dynamic light scattering measurement reveal that under the same conditions, the water droplet size dispersed in [Bmim][PF6] is larger than that in [Omim][PF6]. To establish the newly developed H2O-in-ionic liquid microemulsion as an effective medium for laccase, a control study is presented, demonstrating that the H2O-in-ionic liquid microemulsion is superior to the pure ionic liquids for the expression of the catalytic activity of laccase.