Pickering Emulsion as an Efficient Platform for Enzymatic Reactions without Stirring

Abstract

To address the current limitations of enzymatic reactions, we develop a novel strategy to conduct stirring-free biphasic enzymatic reactions. This strategy involves translation of a conventional biphasic enzymatic reaction to a water-in-oil (W/O) Pickering emulsion system by adding a small amount of solid particle emulsifier. In such a system, enzymes, for example, a Candida Antarctica lipase B (CALB), are compartmentalized within millions of micron-sized water droplets, while organic substrates are dissolved in the oil phase (outside the droplets). It was demonstrated that CALB-catalyzed hydrolysis kinetic resolution of racemic esters in the stirring-free Pickering emulsion system gave favorable reaction efficiency and enantioselectivity as compared to those for the conventional biphasic system under stirring conditions, which was due to the large reaction interfacial area and the short molecule distances created by the Pickering emulsion droplets. The specific activity was found to depend on the water droplet size, highlighting the importance of the presence of droplets in the reaction system. Moreover, the convenient and effective recycling of CALB could be achieved through simple demulsification by centrifugation. After 27 reaction cycles, the ee values of ester and alcohol were still as high as 87.5% and 99%, respectively, which significantly exceed those of the conventional biphasic reaction. The high recyclability may be attributed to avoiding stirring that often causes damage to the three-dimensional structure of enzymes. This study compellingly demonstrates that a Pickering emulsion is an innovative platform to efficiently process enzymatic reactions without need for stirring and immobilization.

Submicron Inverse Pickering Emulsions for Highly Efficient and Recyclable Enzymatic Catalysis

“…Thus, to demonstrate the significance of submicron Pickering emulsions for biphasic enzymatic catalysis, we performed two control experiments with micron Pickering emulsions. Synchronously, considering the tremendous interfacial area of the two phases and the extremely short diffusion distance for the enzyme or substrates in our reaction system, the biocatalytic reaction was performed under stirring‐free conditions, to effectively avoid the destruction of the enzyme structure . Thus, we used hydrophobic silica nanoparticles with diameters of about 230 and 120 nm (see the Supporting Information, Figure S3 and S4) to emulsify aqueous solutions of lipase in toluene.…”

“…Pickering emulsions, a type of emulsion that are stabilized by colloidal particles, have attracted tremendous interest for biphasic enzyme catalysis . Compared to conventional surfactant‐stabilized emulsions, Pickering emulsions offer many unique advantages, such as enhanced enzyme stability, simplified product separation, and facile enzyme recycling.…”

“…Therefore, although micron‐sized Pickering emulsions have been extensively studied over the past decade, there have been no reports of submicron Pickering emulsions that are solely stabilized by colloidal particles in biphasic enzyme catalysis. The increase in interfacial area between the organic and aqueous phases is a crucial reason for increasing the reaction efficiency in biphasic enzymatic transformations based on Pickering emulsions . The smaller size of the dispersion phase typically leads to a larger interfacial area between the two phases for increasing mass transfer in biphasic enzymatic reactions and, thus, the catalytic efficiency.…”

“…[8] Pickering emulsions, at ype of emulsion that are stabilized by colloidal particles, have attracted tremendousi nterest for biphasic enzymec atalysis. [9][10][11][12][13][14][15][16][17] Compared to conventional surfactant-stabilized emulsions, Pickering emulsions offer many unique advantages,s uch as enhanced enzyme stability, simplified product separation, and facile enzyme recycling. Pioneering work on the immobilization of enzymesb yu sing Pickering emulsions was accomplished by the groups of Wang and van Hest, who used hydrophobic SiO 2 nanoparticles and polymersomes, respectively,t oe mulsify aqueous solutionso fe nzymes in organic medium.…”

Flow Pickering Emulsion Interfaces Enhance Catalysis Efficiency and Selectivity for Cyclization of Citronellal

“…Stirring (900 rpm) could dramatically improve the CE up to 0.5 mol mol À1 h À1 (Figure 3B,b )o wing to the enhanced mass transport. [28][29][30][31] The large reaction interface area and short molecule diffusion distance createdb yt he Pickering emulsion account for the high reaction efficiency without need for stirring. If the conventional biphasic system was changed to aP icking emulsion system, the cyclization reaction proceeded faster,a nd the conversion reacheda bove 80 %a fter 10 ha nd above 93 %a fter 15 h ( Figure 3A,c ), much highert han those of the conventionalb iphasic systems.…”