Study On Enzyme-catalyzed Reaction In Switchable Pickering Emulsions

As powerful biocatalysts,enzymes have important application value in the synthesis of fine chemicals.In general,enzymes are highly active in water while the majority of substrates are poorly soluble in water.Therefore,enzyme-catalyzed reactions are often carried out in organic-aqueous biphasic systems.However,conventional biphasic systems often suffer from low reaction efficiency due to the high mass transport resistance and the limited reaction interfacial area between reactants and enzymes.Recently,Pickering emulsions which are stabilized by surface-active nanoparticles have proven to be an efficient and versatile alternative to address the above problems.On the one hand,the problem of incompatibility between reactants and enzymes can be effectively solved in Pickering emulsions.On the other hand,Pickering emulsions exhibit high reaction efficiency due to large reaction interfacial area.At present,particle emulsifiers used to stabilize Pickering emulsions loaded with enzymes were mainly synthesized by surface grafting modification,which were performed through complicated chemical reaction routes with high cost.Fortunately,these severe problems in the process of preparing surface-active nanoparticles can be avoided by in-situ hydrophobization modification,a physical modification method,which has the advantages of simple operation,easy regulation,and low cost.Therefore,stimuli-responsive Pickering emulsions can be stabilized by commercial nanoparticles hydrophobized in-situ with a switchable surfactant.With these multifunctional Pickering emulsions,the catalytic performance of a biocatalytic active lipase from Candida rugose?CRL?was assessed by loading it in the aqueous phase.The main results are summarized as follows:1.A ferrocene-based redox-responsive surfactant,FcCOC₁₀N,was synthesized from ferrocene and 11-bromoundecanoic acid.Hydrophilic silica nanoparticles without surface activity could be converted into surface-active nanoparticles via in-situ hydrophobization with FcCOC₁₀N by the electrostatic interaction.In addition,the catalytic performance of CRL in the redox-responsive Pickering emulsions was further investigated by utilizing the hydrolysis of olive oil as a model reaction.It was found that CRL loaded in the Pickering emulsions exhibited higher catalytic performance than that in the organic-aqueous biphasic system.Under the same reaction conditions,the conversion of olive oil in the emulsion system was as high as 90%following reaction for 30 minutes.At the end of the reaction,the separation of the product and the recycling of CRL could be easily realized based on the redox-responsive property of the Pickering emulsions.Actually,FcCOC₁₀N was transformed into FcCOC₁₀N⁺after suffering from the oxidation by electrochemical stimuli.Thus,the surface-active nanoparticles hydrophobized in-situ with FcCOC₁₀N became hydrophilic again,leading to the demulsification of the Pickering emulsions.According to the research results,the conversion of olive oil was still about 50%after three reaction cycles.2.CO₂/N₂-switchable Pickering emulsions at ambient temperature could be prepared by silica nanoparticles hydrophobized in-situ with convenient compound N,N-dimethyl-dodecylamine?12DMA?.Similarly,the catalytic performance of CRL in the Pickering emulsions was also investigated by utilizing the hydrolysis of olive oil as a model reaction.It was found that CRL loaded in the CO₂/N₂-switchable Pickering emulsions exhibited higher catalytic performance than that in the organic-aqueous biphasic system.At the end of the reaction,the separation of the products and the recycling of CRL could be easily realized by bubbling N₂ at room temperature.Cheap,environmentally friendly,safe,and sensitive,N₂/CO₂ showed less influence on the catalytic activity of CRL.And the conversion of olive oil in CO₂/N₂-switchable Pickering emulsions was still up to 65%after three reaction cycles.3.Based on the above studies,magnetic Pickering emulsions stabilized by Fe₃O₄nanoparticles and CRL could be directly prepared.The interaction between Fe₃O₄nanoparticles and CRL was analyzed using Sodium dodecyl sulfate polyacrylamide gel chromatography?SDS-PAGE?,Fourier transform infrared spectroscopy?FT-IR?,and thermogravimetric analysis?TGA?.The catalytic performance of CRL in the magnetic Pickering emulsions was also investigated by utilizing the hydrolysis of olive oil as a model reaction.The research results indicated that the stability of the emulsions significantly increased by the addition of nanoparticles.Moreover,CRL loaded in the magnetic Pickering emulsions exhibited highest catalytic performance in all reaction systems.Under a magnetic field,the demulsification of the Pickering emulsions stabilized by Fe₃O₄ nanoparticles and CRL could be rapidly achieved with only five minutes.Notably,CRL loaded in the Pickering emulsion also exhibited excellent cyclic catalytic performance,which was attributed to the fact that Fe₃O₄ nanoparticles had least impact on the catalytic activity of CRL.After three reaction cycles,CRL still retained 80%of catalytic activity.