Axial Chlorination Engineering of Single-Atom Nanozyme: Fe-N₄Cl Catalytic Sites for Efficient Peroxidase-Mimicking

Developing axial coordination engineering of single-atom nanozymes (SAzymes), directly regulating the axial coordination environment of the catalytic site, and optimizing the axial adsorption are meaningful and challenging for boosting the enzyme-like activities. Herein, the axial chlorination engineering of SAzyme with the Fe-N₄Cl catalytic site (Fe-N₄Cl/CNCl) was first proposed, exhibiting superior peroxidase-like activity compared to the traditional Fe-N₄/CN SAzyme with Fe-N₄ site. The maximal reaction velocity (4.73 × 10^-5 M min^-1), the catalytic constant (246.4 min^-1), and the specific activity (81 U/mg) catalyzed by the Fe-N₄Cl/CNCl SAzyme were 4.9 times, 3.9 times, and 2.7 times those of the Fe-N₄/CN SAzyme, revealing the enormous advantages of axial chlorination engineering of SAzymes for remarkably improving enzyme-like activities. Moreover, the Fe-N₄Cl/CNCl SAzyme also exhibited an enhanced inhibition effect of tumor cell growth in vitro and in vivo. The density functional theory calculation revealed that the Fe-N₄Cl site was more favorable for releasing ^•OH radical, lowering the energy barrier of rate-determining step, and accelerating the reaction rate compared to the Fe-N₄ site. This work demonstrated the outstanding potential of axial chlorination engineering of SAzymes for improving enzyme-like activities and practical application in tumor therapy.