Effect Of The Microstructure Of Surfactant Aggregates On The Catalytic Properties Of Solubilized Or Immobilized Enzymes

Enzymes are biological catalysts. They have good catalytic activity and selectivity (including chemo-, region-, and stereo-selectivity) under mild reaction conditions. Enzyme-catalyzed biosynthesis and biotransformation are hot topics in both biology and chemistry. Ionic liquids are widely used as solvents in enzyme-catalyzed reactions due to their unique physical and chemical properties. 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. Despite the designability of ionic liquids, 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. It follows that it is of significance to construct different microemulsion and investigate the effect of the microstructure of surfactant aggregates on the catalytic properties of solubilized or immobilized enzymes. To this end, some attempts have been made:1. Construction, characterization and application of water-in-hydrophobic ionic liquid microemulsion formulated by mixed cationic/nonionic surfactantsOver the past decades, a W/O microemulsion has become the preferred medium for hydrophobic substrate involved enzyme catalysis. An ionic liquid-based microemulsion formulated with hydrophobic ionic liquid instead of volatile organic solvent has the merits of both ionic liquid and microemulsion. Some attempts on the construction, characterization and implication of the medium in biocatalysis have been made at home and abroad in recent years. The microemulsions stabilized by anionic or nonionic surfactants have been reported, but those W/IL microemulsion stabilized by cationic surfactant have not. In this thesis, a surfactant mixture of1-tetradecyl-3-methylimidazolium bromide ([C14mim]Br) and Triton X-100was tried to formulate a W/IL microemulsion with positively charged interfacial membrane. The pseudo ternary phase diagrams of [C14mim]Br/Triton X-100/H2O/[Bmim]PF6were constructed at different molar ratios of [C14min]Br to Triton X-100. The formed monophasic region was divided via electrical conductivity measurement into W/IL microemulsion, bicontinuous, IL/W microemulsion. The existence of bulk water in the W/IL microemulsion was demonstrated based on the change of the normalized O-D vibration frequency with the content of D2O added and confirmed using UV-Vis technique with CoCI2as probe. Laccase could be solubilized in the W/IL microemulsion and exhibited a catalytic activity. The interfacial membrane formed by the [C14mim]Br/Triton X-100mixed surfactants had an inhibitory effect on the expression of the laccase activity. The inhibition of the three surfactants with different electrical property decreases in order of [C14min]Br> Triton X-100> AOT.2. A low molecular weight gel formed by cationic surfactant1-dodecylpyridinium bromide in acetone/water:its characterization and implication for enzyme immobilizationAlthough microemulsions formulated by amphiphilic molecules are considered as effective media for enzymatic reactions, but the recycle of an enzyme needs to be solved. The microemulsion gelation brings us an opportunity to solve the problem. It has been shown that an enzyme in the matrix of the gel could maintain its catalytic activity and its stability; the micro-channels in the gel also facilitate mass transfer of substrates. Till now, there are many reports on the use of macromolecules-based organogels for enzyme immobilization, but few reports on the use of the low molecular weight gel as a carrier for the immobilization of an enzyme.A new cationic surfactant1-dodecylpyridinium bromide (DPB)-based gelling system was reported. The DPB could form a gel in the mixture of acetone/water without additives and the gel structure varied with the gelator concentration, the gelation mechanism were studied using techniques of rheology, microscopy and spectroscopy and demonstrated that the DPBs, driven by hydrogen bonding, van der Waals force and other non-covalent interactions, self-assembled into rod-like fibers. The fibrous structures intertwined into a three-dimensional network. In this gel, both laccase and horseradish peroxidase were catalytically active, indicating the present gel can be used as a carrier for the immobilization of biologically active macromolecules. Moreover, the present gel did not swell in hydrophobic ionic liquid [Bmim]PF6, showing its great promise in green biocatalysis and biotransformation.