Study On Molecular Mechanism Of ATP Hydrolase Activity Simulated By UiO-66(Zr/Ce) Metal-Organic Framework

Metal-organic framework（MOFs）is a new kind of porous nanomaterial,which has become a star material in the field of heterogeneous catalysis due to its excellent properties such as rich structure,high frequency of particle utilization,large surface area,multiple active sites and strong binding with substrates.Recently,various MOFs materials,such as UiO-66（Ce）and MIL-53（Fe）,have been reported to have activities mimicking natural oxidases,peroxidases and phosphate hydrolases,and are called MOFs nanozymes.Nanozymes are nanomaterials that catalyze the conversion of enzyme substrates into products and follow enzyme-like kinetics under relevant physiological conditions.Since the first reported in 2007,more than 1200 nanozymes have been identified that can mimic enzymatic activities such as peroxidase,catalase,superoxide dismutase,oxidase,glucose oxidase,glutathione peroxidase,protease,esterase,nuclease,and dozens of others.Together with the excellent optical,electrical and magnetic properties of nanomaterials themselves,nanozymes show great potential for application in many fields such as catalytic medicine,sensing and detection,green synthesis,new energy and environmental management.Phosphatases is one kind of hydrolases which belong to the seven main enzyme classes.Phosphatases can catalyze the dephosphorylation of substrates by hydrolyzing the phosphate monoester bond.The phosphate group on the substrate molecule is thus removed to produce phosphate ions.Phosphate groups are widely found in nucleic acids,proteins,membranes,lipids,and many biomolecules including adenosine triphosphate（ATP）,and are important for maintaining their biological functions.Therefore,the study of the pervasive molecular mechanism of nanomaterials mimicking phosphate hydrolases and the establishment of conformational relationships for precise regulation of activity are not only beneficial for basic chemical theory research,but also important for new technologies such as gene editing,disease treatment,and environmental restoration.UiO-66 based MOFs containing Lewis acidic metal ions Ce（IV）and Zr（IV）have excellent catalytic properties and their enzyme-like activities has attracted wide attention from scientists.UiO-66-X（Zr/Ce）containing different substituents（X = F,Cl,Br,CH₃,NH₂,NO₂）provides an excellent model system for systematic studies of phosphate hydrolysis mechanisms and conformational relationships.First-principles calculations can profoundly portray the structural and electronic structure dynamics of molecules and materials during chemical reactions at the molecular level,and have become the most effective and irreplaceable theoretical tool for studying the mechanism of chemical reactions by experimental means.In view of this,current work systematically investigates the hydrolysis mechanism and the effect of substituents on the catalytic activity of UiO-66-X（Zr/Ce）（X = F,Cl,Br,CH₃,NH₂,NO₂）taking ATP hydrolysis producing phosphoric acid and ADP as a model reaction.The hydrolysis activity was firstly predicted at the theoretical level and was then experimentally verified.The following results were obtained:（1）The geometric and electronic structures of the UiO-66-X（Zr/Ce）material system were systematically studied,and the effects of different substituents on the water adsorption strength were investigated.It was found that the order of adsorption strength of water on UiO-66（Zr）-X material was-NO₂ >-CH₃ >-H >-NH₂ >-F >-Cl >-Br.The adsorption order of water on UiO-66（Ce）-X is as follows:-NO₂ >-Br >-Cl >-NH₂ >-F >-H >-CH₃;（2）The molecular mechanism of catalytic hydrolysis of ATP by UiO-66-X（Zr/Ce）was systematically investigated,and the predicted order of activity was: UiO-66-X（X=electron-absorbing group）> UiO-66-H > UiO-66-X（X= electron-donating group）was predicted.;（3）The catalytic activity was experimentally verified to be consistent with the theoretically predicted order.The-NO₂,which has a strong electron-absorbing effect,can enhance the efficiency of UiO-66-NO₂（Zr/Ce）in hydrolyzing ATP,while-NH₂,which has strong electron-giving ability,decreases its catalytic efficiency instead;（4）The structure-effect relationship of the substituent-regulated hydrolysis activity was summarized,and it was found that the catalytic activity of UiO-66-X（Zr/Ce）hydrolysis of ATP was proportional to the empirical constant of Hammett σ of the substituent,which is usually used to measure the electron-absorbing ability of the substituent in the π-conjugated system.This is because the acquisition of electrons from the reaction substrate is a key step in the catalytic process of MOFs materials,and a substituent with strong electron absorption can pull down the LUMO energy level of the material,making it easier for the material to acquire electrons in the decisive step and thus have strong catalytic activity.The above results not only deepen the understanding of the ATP hydrolysis mechanism of UiO-66-X（Zr/Ce）materials,but also provide theoretical tools for the prediction and precise regulation of the subsequent efficient phosphate hydrolase activity.