Pickering Emulsion-Based Microreactors for Size-Selective Interfacial Enzymatic Catalysis

Abstract

In this study, we have developed a mild and effective method to prepare a metal-organic framework (MOF)-based microcapsule by the self-assembly of pre-synthesized zeolite imidazolate framework-8 (ZIF-8) nanoparticles at the oil-water interface combined with deposition of a dense ZIF-8 coating outside the capsule. By introducing the enzyme Candida antarctica lipase B (CalB) directly into the stabilizer ZIF-8 or the water phase of Pickering emulsion during the preparation process, we achieved that the enzyme was immobilized within the shell (CalB@ZIF-8@cap) or in the cavity (ZIF-8@cap-CalB) of the microcapsules, respectively. The resulting CalB-loaded microcapsules were robust and had a core-shell structure proved by scanning electron microscopy. Meanwhile, Fourier transform infrared spectroscopy was conducted to confirm the encapsulation of enzymes in the microcapsules and their position in the microcapsules was confirmed by fluorescence microscopy. Furthermore, through the comparison of transesterification reactions between a pair of small substrates and a pair of larger ones, the two types of CalB-loaded microcapsules showed great catalytic activity, stability and size selectivity, and the catalytic activity of CalB@ZIF-8@cap was slightly higher than that of ZIF-8@cap-CalB. Importantly, due to the large size of the microcapsules, the catalyst could be separated from the reaction system by sedimentation, thereby reducing the energy consumption for separation. These kinds of multifunctional MOF-enzyme composites may open up new opportunities for the biocatalysis and microreactor.

Current Status and Future Perspectives of Supports and Protocols for Enzyme Immobilization

“…successfully in hybrid inorganic nanoflowers based on Cu3(PO4)2 through biomimetic mineralization. The catalytic derivative showed high thermal stability, maintaining catalytic activity above 70% after eight reaction cycles at temperatures between 65 °C and 70 °C [260]. In Figure 7.…”

“…successfully in hybrid inorganic nanoflowers based on Cu 3 (PO 4 ) 2 through biomimetic mineralization. The catalytic derivative showed high thermal stability, maintaining catalytic activity above 70% after eight reaction cycles at temperatures between 65 • C and 70 • C [260]. In these examples, the efficiency of this new immobilization strategy is noticeable, primarily when researchers aim mainly to maintain the catalytic activity at high temperatures.…”

“…Furthermore, it is noteworthy that the HNF-lipase exhibited increased stability against high temperature and denaturants, obtaining good storage stability and reusability [259]. Liu et al (2020) [260] immobilized the thermophilic lipase QLM from Alcaligenes sp. successfully in hybrid inorganic nanoflowers based on Cu 3 (PO 4 ) 2 through biomimetic mineralization.…”

Pickering-Droplet-Derived MOF Microreactors for Continuous-Flow Biocatalysis with Size Selectivity

“…Nevertheless, this system suffers from some intrinsic obstacles in the precise regulation of mass transportation at a molecular level, due to the loose linkage and irregular interstitial pores between solid particles, resulting in uncontrollable permeability and insufficient encapsulation performance. − We envisage that if such a Pickering system could be significantly upgraded with an MOF structure, a closer platform capable of mimicking a living cell microfactory, particularly in terms of size-selective permeability and industrial productivity, might be realized. To achieve this upgrade, significant efforts have been made in assembling preformed MOF-nanoparticles at the droplet interface or cross-linking those nano-objects together via polymerization processes. − However, these developed MOF-based Pickering systems in fact still face severe difficulty in precisely regulating the permeability, because of the intrinsic shortfalls existing in the interfacial nanoparticle assembly method. Moreover, the usually harsh polymerization conditions are not favorable for the preservation of enzyme activity.…”

Molecular Decoration of Ceramic Supports for Highly Effective Enzyme Immobilization—Material Approach

“…The feature of the supporting material (e.g., surface property, size, and morphology) have a substantial influence on the performance of the immobilized enzymes and amid various supporting materials, nanostructured ones have received growing interest since (i) providing a higher specific surface area for enzyme anchoring, and (ii) a high physical curvature allowing for a greater degree of freedom for the enzyme active sites location, thus minimizing lateral interactions between enzymes and self-digestion. The usage of nanostructured materials therefore supports greater enzyme activity and interactions with contaminants in solution [11,[17][18][19][20][21][22]. A challenge of discrete nanoparticles for immobilization however lies with the dynamic nature of such slurries, leading over time to self-digestion through particle-particle contacts, using functionalized microporous supports such as membranes was found to limit losses in enzymic activity and thus long-term performance [23,24].…”