Multivariate mesoporous MOFs with regulatable hydrophilic/hydrophobic surfaces as a versatile platform for enzyme immobilization

Zeolitic imidazole frameworks materials-8 (ZIF-8), a member of the metal-organic framework (MOFs) series, have been extensively used as a host matrix for enzyme immobilization. However, the microporous structure and hydrophobicity, as well as the protonation of the precursor 2-methylimidazole (2-MeIm) of ZIF-8, remain considerable challenges in maintaining the activity of immobilized enzymes. Here, novel multivariate mesoporous MOFs (mMOFs) with regulatable hydrophilic/hydrophobic surfaces were designed by the multivariate competitive strategy and pore modification engineering. 3-Methyl-1H-1,2,4-triazole (3-MTZ) and 5-methyltetrazole (5-MTA) were employed to partially replace 2-MeIm. These were then combined with zinc sulfate heptahydrate (soft templates) to yield mMOFs in a methanol solution. As a proof-of-concept application, we used mMOFs as carriers for enzyme immobilization and investigated the properties of the immobilized enzymes. Benefiting from their mesoporous structure, hydrophilic surface, and improved microenvironment, multivariate mMOFs exhibit a strong ability to stabilize enzyme conformation and increase enzyme activity compared with traditional ZIF-8. Our study offers an avenue for the controllable preparation of well-designed MOF structures, which will further broaden the application opportunities of MOF materials for enzyme immobilization.