Buffer Effects in Zirconium-Based UiO Metal-Organic Frameworks (MOFs) That Influence Enzyme Immobilization and Catalytic Activity in Enzyme/MOF Biocatalysts

Novel biocatalyststhat feature enzymes immobilized onto solidsupports have recently become a major research focus in an effortto create more sustainable and greener chemistries in catalysis. Manyof these novel biocatalyst systems feature enzymes immobilized ontometal-organic frameworks (MOFs), which have been shown to increaseenzyme activity, stability, and recyclability in industrial processes.While the strategies used for immobilizing enzymes onto MOFs can vary,the conditions always require a buffer to maintain the functionalityof the enzymes during immobilization. This report brings attentionto critical buffer effects important to consider when developing enzyme/MOFbiocatalysts, specifically for buffering systems containing phosphateions. A comparative analysis of different enzyme/MOF biocatalystsfeaturing horseradish peroxidase and/or glucose oxidase immobilizedonto the MOFs UiO-66, UiO-66-NH2, and UiO-67 using a noncoordinatebuffering system (MOPSO buffer) and a phosphate buffering system (PBS)show that phosphate ions can have an inhibitory effect. Previous studiesutilizing phosphate buffers for enzyme immobilization onto MOFs haveshown Fourier transform infrared (FT-IR) spectra that have been assignedstretching frequencies associated with enzymes after immobilization.Analyses and characterizations using zeta potential measurements,scanning electron microscopy, Brunauer-Emmett-Tellersurface area, powder X-ray diffraction, Energy Dispersive X-ray Spectroscopy,and FT-IR show concerning differences in enzyme loading and activitybased on the buffering system used during immobilization.