Amphiphilic Carbonaceous Microsphere‐Stabilized Oil‐in‐Water Pickering Emulsions and Their Applications in Enzyme Catalysis

Abstract

An oil‐in‐water Pickering emulsion system stabilized by amphiphilic porous carbonaceous microspheres was prepared and successfully used in enzyme‐catalyzed hydrolysis. The control of the emulsion droplet size and size distribution were investigated by adjusting the particle content and the dispersed phase volume fraction. More than 99 % of the lipase was adsorbed at the interface of the emulsion droplets and showed excellent stability and activity. The size of the emulsion droplets exerted two opposite influences on the catalytic efficiency of the enzyme: increasing the rate of the process by providing a large interfacial area, thereby overcoming mass transfer limitations, and reducing the rate of the process by decreasing the interfacial enzyme concentration. A high hydrolysis yield (up to 100 %) was obtained after 2 h. This study shows the great potential and advantages of using an oil‐in‐water Pickering emulsion system for enzyme‐catalyzed reactions.

Recent developments in catalysis with Pickering Emulsions

“…93 One example being the heterogenization of biocatalysts, in which enzymes were immobilized on or in the stabilizing materials. [94][95][96] These are often lipases, such as the one from Candida rugosa (CRL), which in combination with the metal-organic framework (MOF) ZIF-8 was shown to form an o/w PE with an aqueous buffer phase and heptane. Two different examples of incorporating the enzyme in the MOF were reported, one being the immobilization of CRL on the outer surface of ZIF-8 crystals after synthesis (Table 1, entry 6) 94 and the other being encapsulation of CRL inside the ZIF-8 crystals by addition during MOF synthesis (Table 1, entry 7).…”

Enzyme-Loaded Mesoporous Silica Particles with Tuning Wettability as a Pickering Catalyst for Enhancing Biocatalysis

“…One includes free enzymes located in the inner aqueous phase [12][13][14][15][16][17]. The other includes enzyme-immobilized particles anchored around droplet interfaces [18][19][20][21][22][23][24][25][26], by contrast, it enables enzymes to be recycled, maximizes the contact area between enzymes and substrates, reduces diffusion distance of substrate molecules and improves the stability of enzymes. In the above two kinds of Pickering catalysis system, the changing of the organic-aqueous phases ratio or increasing particulate emulsifiers concentration is applied to improve interfacial area to enhance the enzymatic reaction.…”

Submicron Inverse Pickering Emulsions for Highly Efficient and Recyclable Enzymatic Catalysis

“…Pioneering work on the immobilization of enzymes by using Pickering emulsions was accomplished by the groups of Wang and van Hest, who used hydrophobic SiO 2 nanoparticles and polymersomes, respectively, to emulsify aqueous solutions of enzymes in organic medium . Since then, various colloidal particles, such as polymer nanoparticles, carbonaceous microspheres, enzyme‐conjugated ZIF‐8 (ZIF=zeolitic imidazolate framework) particles, and even microorganisms, have been exploited for the preparation of enzyme‐loaded Pickering emulsion systems for various biocatalytic reactions . However, it is well‐known that the droplets in most Pickering emulsions are micron‐sized, ranging from several microns to tens of microns.…”

“…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.…”

“…[7,9] Since then, various colloidal particles, such as polymern anoparticles, carbonaceous microspheres, enzyme-conjugated ZIF-8 (ZIF = zeolitic imidazolate framework) particles, and even microorganisms, have been exploitedf or the preparation of enzyme-loaded Pickering emulsion systems for variousb iocatalytic reactions. [4,10,18,19] However,i ti sw ellknownt hat the droplets in most Pickering emulsions are micron-sized, ranging from several microns to tens of microns. There are af ew reports of the preparation of submicron emulsions that are stabilized by nanoparticles.…”