Dual enzyme-like activities of transition metal-doped MnO2 nanocoatings and their dependence on the electronic band structure and ionic dissolution

Abstract Doping is a valid strategy to tailor nanozyme activities benefited from the change of the electronic properties and/or nanoparticle dissolution. Here, we used the transition metal-doped MnO2 (Zn-MnO2 and Cu-MnO2) nanocoatings to distinguish the effects of electronic band structure by introducing oxygen vacancies from those of ionic dissolution on superoxide dismutase (SOD) and catalase (CAT) mimic activities, respectively. The enzymatic analysis showed that the CAT-like activity correlated with the increased content of surface oxygen vacancies, in contrast to the relationship between surface oxygen vacancies and SOD-like property. The released metal ions were required to conduct the SOD-like activity, which was promptly enhanced in the presence of phosphate or chloride ligand. The mechanisms for the CAT- and SOD-mimetic behavior were elucidated through comparing the electronic band structure of the nanocoatings with the redox potential of different redox couples in CAT and SOD catalytic reactions. Despite the higher SOD-like activity, the excessive Mn2+/Cu2+ release from MnO2 and Cu-MnO2 nanocoatings generated higher levels of hydroxyl radical from H2O2 through a Fenton-like reaction, which induced higher levels of apoptosis. This study may provide a prospective approach to engineer MnO2 enzyme-like activity and selectivity by regulation of the electronic band structure and nanomaterial dissolution.