Encapsulating β-Glucosidase within Nanoporous ZIF-8-Cu Nanoparticles Enables High-Temperature Activity

Abstract

Recently, metal–organic frameworks (MOFs) have become a promising carrier for immobilized enzymes. However, the long transmission distance and microporous nature of traditional 3D ZIF-8 materials not only reduce the accessibility of the enzyme and the substrate, but also the enzymes “encapsulated” by microporous ZIF-8 suffer compromising enzyme activity (<10% of the original enzyme activity). In this article, a method is proposed to construct one kind of new-type mesoporous 3D ZIF-8-Cu composed of 2D nanostructures that utilize a metal competitive coordination-induced defect structure by adjusting a metal guide agent copper chloride (CuCl). In addition, the feasibility of in situ encapsulating β-G within the developed mesoporous 3D ZIF-8-Cu endows that the enzyme complex (β-G@ZIF-8-Cu) possessed remarkably enhanced synergistic catalysis ability. The enzyme activity of mesoporous β-G@ZIF-8-Cu (with respect to cellobiose) was up to 50.1%, while that of 3D microporous β-G@ZIF-8 was only 5.1% at 50 °C. Significantly, with the increase of temperature, the enzyme activity of mesoporous β-G@ZIF-8-Cu increased as high as approximately 178.3%, almost 34.2 times that of β-G@ZIF-8 (5.2%) at 90 °C. This improvement results from the expansion of pores (significantly increased at 10∼50 nm), promoting substrate diffusion, and the thinner 2D structure shortened the mass transfer distance, accelerating the transport rate of reactants. In addition, 3D mesoporous β-G@ZIF-8-Cu composed of multilayer 2D nanostructures with better high-temperature resistance.

A Hydrophilic Metal Azolate Coordination Polymer for In Situ Encapsulation of Haloalkane Dehalogenase with Enhanced Enzymatic Performance

“…Most MOF-encapsulated enzymes exhibited favorable catalytic performance under harsh conditions, , and ZIF-8 is one of the most widely explored MOF materials constituted with 2-MI and Zn 2+ , so the possibility of using ZIF-8 for in situ encapsulation was investigated. It can be seen in Figure a that the DhaA activity after encapsulation significantly decreased to only 1.3% of the free enzyme.…”

“…However, the fragile nature of enzymes (low stability at high temperature, poor tolerance to organic solvents, and difficulty in separation and reusability) increases cost and impairs catalytic effects, consequently limiting broader applications of the biocatalysts . A variety of approaches including chemical modification, cross-linking, and immobilization have been used to improve the catalytic performance of enzymes under harsh conditions. , In the past decade, metal–organic frameworks (MOFs), a class of materials that are synthesized via coordination between metal ions and organic ligands, have become a valuable platform for enzyme immobilization, − and some of the MOF-immobilized enzymes exhibited extraordinary stability as well as maintained the initial activity for multiple cycles. − …”