Magnetic MOF derivatives from Tunable MIL-88A for enhanced lipase immobilization and phosphatidyl EPA/DHA synthesis

Metal-organic frameworks (MOFs) with tunable porosity are promising carriers for enzyme immobilization, but their practical application is limited by structural instability and difficult recovery. We previously developed an oxidation-reduction (O-R) pyrolysis strategy for mesoporous MIL-88 A, yielding a magnetic carrier (O-R-Meso) with excellent lipase immobilization and recyclable catalysis. Herein, we verify the applicability of this O-R pathway for Fe-based MIL-88 A with tailored pore structures (micro-, meso-, macroporous) by extending it to microporous C-MIL-88 A and macroporous SOM-MIL-88 A. The O-R derivatives (O-R C, O-R-Meso and O-R-SOM) retained the original morphology and pore channel integrity, with improved specific surface area and sufficient magnetization (13–23 emu/g) for magnetic separation. Notably, after O-R pyrolysis, MIL-88 A with various pore sizes essentially maintained or even enhanced the specific activity of immobilized lipase ( Candida antarctica lipase B, CalB), successfully deriving into magnetic carriers with enhanced catalytic efficiency and recyclability. This superiority originates from the preserved pore structure and biocompatible γ-Fe 2 O 3 surface of the O-R derivatives, which effectively retain the native conformation of CalB. Besides, this work systematically compares the secondary structure of free and immobilized CalB on MOF-derived carriers with distinct pore architectures, providing direct structural evidence for the superior enzyme-carrier compatibility of mesoporous materials. In the transesterification synthesis of phosphatidyl EPA/DHA, CalB@O-R-Meso showed the highest EPA/DHA total incorporation, prominent sn -1 positional selectivity, and optimal reusability, outperforming CalB@O-R-C and CalB@O-R-SOM. Furthermore, kinetic studies on the CalB@O-R-Meso-catalyzed system confirmed a Ping-Pong Bi Bi mechanism and revealed competitive product inhibition by phosphatidyl EPA/DHA ( K i  = 29.8 mM) with negligible internal mass transfer resistance (η ≈ 1). This work establishes a O-R pyrolysis strategy for tunable porosity Fe-MOFs, clarifies pore size-dependent enzyme -carrier compatibility, and provides a fundamental kinetic basis for phosphatidyl EPA/DHA synthesis.