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

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.