A novel two-dimensional metal imidazolate sulphate framework as a versatile platform for enzyme immobilization

The encapsulation of enzymes in ZIF-8 (enzyme@ZIF-8 composites) via co-precipitation has attracted considerable attention. However, enzyme@ZIF-8 composites often exhibit low activity due to the three-dimensional (3D) structural characteristics of ZIF-8 and the protonation of the precursor, 2-methylimidazole (2-MeIm). In this study, a novel 2D catalase@ZIFs(SO4) composite was synthesized as an alternative to the conventional 3D catalase@ZIF-8 composites. The 2D catalase@ZIFs(SO4) composites demonstrated a nine-fold increase in activity and three-fold higher enzyme loading compared to their 3D counterparts. The enhanced catalytic performance is attributed to the 2D structure of the composites and the partial replacement of 2-MeIm with sulfate during enzyme immobilization, which reduces the protonation of 2-MeIm, enhances the hydrophilic microenvironment, and facilitates substrate transfer. Furthermore, compared to free enzymes, the 2D catalase@ZIFs(SO4) composites exhibited an expanded pH tolerance range, superior thermal stability, enhanced resistance to denaturants, and improved storage stability. To validate the concept, glucose oxidase, glutamate oxidase, and phenylalanine ammonia lyase were immobilized using the same approach. All immobilized enzymes demonstrated increased activity relative to the traditional CAT@ZIF-8 composites. This study offers a versatile platform for enzyme encapsulation within ZIF-8 through co-precipitation.