Enzymatic Cascade Reactions Mediated by Highly Efficient Biomimetic Quasi Metal-Organic Frameworks

The integration of chemo- and enzymatic catalysis for effective multistep cascades has presented critical challenges for decades. In this work, the biomimetic quasi NH₂-MIL-101 (qNM) with highly efficient peroxidase-like activity was synthesized via a palmitic acid-induced strategy followed by pyrolysis. The effects of the amount of palmitic acid and calcination temperature on the synthesis of qNM were optimized. It was found that qNM was an excellent catalyst for oxidations of various peroxidase substrates, and a possible mechanism was proposed, i.e., the presence of Fe^II species in qNM was responsible for its excellent activity, which facilitated the transition between Fe^II and Fe^III species to produce more hydroxyl radicals by H₂O₂ decomposition. The qNM served as the potential matrix for enzyme immobilization through a cross-linking method, and kinetic studies revealed that the catalytic efficiency (k_cat/K_m) for the immobilized GOx (23.7 mM^-1 s^-1) is comparable to that of free GOx (26.9 mM^-1 s^-1). The immobilized GOx also showed improved stability against high temperatures and organic solvents compared to free GOx, and analysis of the secondary structure of GOx indicated that the improved stability resulted from enzyme rigidity by the intense covalent linkage with qNM. Furthermore, qNM contributed its biomimetic activity to cooperate with a single enzyme (GOx) or two enzymes (β-Gal and GOx) for the enzymatic cascade reactions. Compared with the mixture of each component in the solution, the combination of the single-enzyme system (GOx) or the two-enzyme system (β-Gal and GOx) in qNM achieved 2.67-fold and 1.83-fold enhancements in the activity of catalytic cascades, respectively. This study provides new insights into the construction of effective and synergistic cascade reactions by integrating biomimetic MOF with natural enzyme, which holds potential for applications in biotechnology and ecofriendly and biomimetic catalysis.