Formulation And Application Of Biocompatible Bicontinuous Microemulsion Based On Functionalized Ionic Liquid

Bicontinuous microemulsion is a macroscopically homogeneous but microscopically heterogeneous system in which the irregularly interwoven water tubules and oil tubules are separated by surfactant interface layer.It has strong solubilization capacity,ultralow interfacial tension and large interfacial area with an average interfacial curvature of zero,and therefore is widely used in the field of the preparation of nanomaterials and the biocatalytic conversion of water-insoluble substrates.The formulation of a bicontinuous microemulsion depends on the phase behavior study on oil/water/surfactant/cosurfactant systems.The construction of biocompatible bicontinuous microemulsion usually requires the synergistic action of multiple components.Obviously,a complex microemulsion system is not favorable for the study of enzyme-catalyzed reactions.Therefore,it is essential to construct a biocompatible bicontinuous microemulsion system with simple composition.Good’s buffer ionic liquid(GB-IL)is a special functionalized organic salt with the self-buffering property and enzyme compatibility.As an electrolyte,it is supposed to have an effect on the phase behavior of the microemulsion system.Considering the multiple advantages of GB-IL,it is expected that the use of GB-IL as an electrolyte could result in a biocompatible bicontinuous microemulsion with simple composition.Based on the above background,the following studies have been tried in this thesis:1.Good’s buffer ionic liquid tunes the phase behavior of anionic surfactant SDBS-stabilized n-octane-water microemulsion and the stability of the solubilized horseradish peroxidaseGB-IL composed of quaternary ammonium cation and Good’s buffer anion is first introduced into a microemulsion system as a self-buffering and biocompatible electrolyte.The effects of the GB-IL on the phase behavior of anionic surfactant sodium dodecylbenzene sulfonate(SDBS)-stabilized n-octane-H2O microemulsion system were studied using the ε-βfish-like phase diagram method.The result indicates that the phase behavior of the above microemulsion system is greatly affected by GB-IL cations with a longer alkyl chain on the cation being more favorable for phase inversion.Compared with NaCl,GB-IL of the same concentration is more efficient for achieving phase inversion,due to the dual role of an electrolyte and a co-alcohol.In addition to the phase behavior,the research of the stability of horseradish peroxidase(HRP)solubilized in the SDBS stabilized bicontinuous microemulsion shows that the GB-IL composed of the quaternary ammonium cation with a longer alkyl chain is better for the stabilization of the HRP activity.For a given GB-IL,a higher level of the GB-IL results in a better HRP stability.More interestingly,the GB-IL-buffered bicontinuous microemulsion is more advantageous,at the same level of the buffering salt,than the phosphate-buffered one for the stabilization of the HRP activity.This advantage is more pronounced for higher concentrations of the buffering salt.To get insight into the mechanism of this difference in the HRP stability,the microstructure of bicontinuous microemulsion system was characterized by small angle X-ray scattering.The results indicate that the difference of HRP stability caused by different buffer salts should be ascribed to the microemulsion microstructure effect as well as the Hofmeister effect of electrolyte.The present study provides a guideline for the construction of a bicontinuous microemulsion with a simplified composition and stabilizing effect on the solubilized enzyme.2.Oxidative polymerization of aniline catalyzed by horseradish peroxidase in Good’s buffer ionic liquid-buffered H2O/AOT/isooctane bicontinuous microemulsionThe effect of GB-IL on the phase behavior of sodium bis(2-ethylhexyl)sulfosuccinate(AOT)stabilized H2O/isooctane microemulsion system was studied by the T-y fish-like phase diagram method.It was found that the phase inversion temperature of the above microemulsion system could be regulated by changing the alky chain length of quaternary ammonium cations of GB-IL in the absence of alcohol.Based on the study of phase behavior,the H2O(0.1 M[N1,1,1,1][MES])/AOT/isooctane bicontinuous microemulsion system with appropriate phase inversion temperature was constructed for the oxidative polymerization of aniline catalyzed by HRP.The polymerization process was monitored by UV-VIS-NIR and electron spin resonance techniques,and the morphology of the resulting polyaniline was characterized using scanning electron microscopy.Results indicate that the composition of microemulsion(the surfactant concentration and oil/water ratio)has great effect on the conductivity and morphology of product.The polyaniline with good conductivity could be obtained in low surfactant content and high oil/water ratio.This work provides an experimental support for the development of a simplified bicontinuous microemulsion suitable for biocatalytic conversion reaction.