Development and Characterization of a Tunable Metal-Organic Framework (MOF) for the Synthesis of a Rare Sugar D-Tagatose.

D-tagatose is a valuable rare sugar with potential health benefits such as antiobesity, low-calorie, prebiotic, and anticancer. However, its production is mainly depending on chemical or enzymatic catalysis. Herein, a cobalt-based metal-organic framework (MOF) was developed at room temperature in an aqueous system using a self-assembly method. The L-arabinose isomerase (L-AI) was immobilized into this unique MOF by an in situ encapsulation process. The morphology and structural aspects of the MOF preparations were characterized by different analytical techniques such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), confocal laser scanning microscopy (CLSM), Fourier transform infrared spectroscopy (FT-IR), and X-Ray diffraction (XRD). Moreover, thermogravimetric analysis (TGA) suggested the high thermal stability of the L-AI@MOF. Significantly, the immobilized catalyst exhibited enhanced catalytic efficiency (k_cat/K_m) of 3.22 mM^-1 s^-1 and improved turnover number (k_cat) of 57.32 s^-1. The L-AI@MOF efficiently catalyzes the synthesis of D-tagatose from D-galactose up to the equilibrium level (~ 50%) of isomerization in heterogeneous catalysis. Interestingly, L-AI@MOF was found stable and reusable for more than five cycles without the requirement of additional metal ions during catalysis. Thus, L-AI stabilized in the MOF system demonstrated a higher catalytic activity and potential guidance for the sustainable synthesis of rare sugar D-tagatose.