A Ce-MOF as an alkaline phosphatase mimic: Ce-OH2 sites in catalytic dephosphorylation?

Inorganic Chemistry Frontiers Pub Date: 2022-09-01 DOI: 10.1039/D2QI01443B

Abstract

The field of biomimetic catalysis poses several challenges, including selective dephosphorylation of enzymes. Lanthanide-based metal–organic frameworks (Ln-MOFs) are widely used as hydrolytic enzymes due to their well-controlled structural motifs and having comparable enzyme cofactors, making them ideal for biomimetic catalysis. In this work, we have synthesized and structurally characterized a Ce–OH2–Ce motif-containing MOF (Ce-MOF) to mimic the active sites of alkaline phosphatase. Single crystal X-ray diffraction (SXRD) analysis illustrates that the Ce-MOF has a robust ladder-like supramolecular network that is stable in a wide range of solvents and basic aqueous solutions, which is confirmed through independent powder XRD (PXRD) analysis. The catalytic activity of the Ce-MOF was investigated by UV-visible spectroscopy by hydrolyzing the model substrate, the disodium salt of 4-nitrophenyl phosphate (4-NPP), taken in an N-methylmorpholine buffer aqueous solution. Experimental studies reveal that the Ce-MOF has the highest catalytic activity for the hydrolysis of the P–O bond of 4-NPP at pH 9.0. To the best of our knowledge, this is the first time a cerium-MOF has been used as a catalyst in an alkaline medium to mimic phosphatase enzymes. Importantly, the high catalytic activity of the Ce-MOF towards 4-NPP hydrolysis was found owing to the synergistic effect of the Ce(III) ion, which reinforces the P[double bond, length as m-dash]O bond with the metal, and metal hydroxide activation under basic circumstances. The calculated turnover number (kcat) for 4-nitrophenyl phosphate (4-NPP) hydrolysis was 7.42 × 10?3 min?1. The formation of phosphate ions during the hydrolytic reaction has been monitored through time-dependent 31P-NMR spectroscopy and this provides very crucial information on the possible mechanistic pathway.

Graphical abstract: A Ce-MOF as an alkaline phosphatase mimic: Ce-OH2 sites in catalytic dephosphorylation
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