Immobilization of Cytochrome C by Benzoic Acid (BA)-Functional UiO-66-NO2 and the Enzyme Activity Assay

Recently, metal–organic frameworks (MOFs) are considered to be the moderate hosts for the bio-enzymes owing to their unique 3D pores and controllable surface affinity to the target molecules. In this work, the benzoic acid (BA)–modulated UiO-66-NO2 was introduced, and cytochrome c (Cyt C) was chosen as the target enzyme to evaluate the immobilization efficiency of the resulting UiO-66-NO2-BA. The immobilization conditions including pH, adsorption time, and temperature and the initial concentrations of BA were optimized. The adsorption kinetics and thermodynamics were analyzed to further explore the enhanced adsorption mechanism. It is worth noted that all the UiO-66-NO2-BA exhibited evidently enhanced adsorption capacities in comparison with the unmodified UiO-66-NO2 due to the formation of the chemical bonds between the UiO-66-NO2-BA and cytochrome C, indicating the positive roles of BA modification. Finally, the activities of the immobilized cytochrome C were assessed by using the catalytic oxidation of ABTS in the presence of H2O2, which reactions were also conducted over the free cytochrome C for comparison. The evidently improved stability under definite pH range, prolonged durability against the organic solvents, and the good reusability of the immobilized cytochrome C highlight the prospect applications of functional MOF immobilized enzymes in the practical catalytic reactions.