Preparation of Proline-Modified UIO−66 Nanomaterials and Investigation of Their Potential in Lipase Immobilization

Abstract

Metal–organic frameworks (MOFs) are regarded as excellent carriers for immobilized enzymes due to their substantial specific surface area, high porosity, and easily tunable pore size. Nevertheless, the use of UIO−66 material is significantly limited in immobilized enzymes due to the absence of active functional groups on its surface. This study comprised the synthesis of UIO−66 and subsequent modification of the proline (Pro) on UIO−66 through post-synthetic modification. UIO−66 and UIO−66/Pro crystals were employed as matrices to immobilize Rhizopus oryzae lipase (ROL). The contact angle demonstrated that the introduction of Pro onto UIO−66 resulted in favorable conformational changes in the structure of ROL. The immobilized enzyme ROL@UIO−66/Pro, produced via the covalent-bonding method, exhibited greater activity (0.064715 U/mg (about 1.73 times that of the free enzyme)) and stability in the ester hydrolysis reaction. The immobilized enzymes ROL@UIO−66 (131.193 mM) and ROL@UIO−66/Pro (121.367 mM), which were synthesized using the covalent-bonding approach, exhibited a lower Km and higher substrate affinity compared to the immobilized enzyme ROL@UIO−66/Pro (24.033 mM) produced via the adsorption method. This lays a solid foundation for the industrialization of immobilized enzymes.