Tin Porphyrin-Based Nanozymes with Unprecedented Superoxide Dismutase-Mimicking Activities

As the oxidative stress is related to human aging and many diseases, a diversity of antioxidant biomimetic enzymes to eliminate reactive oxygen species in vivo and maintain the redox balance has attracted intensive attention. Of particular interest are superoxide dismutase (SOD)-mimicking artificial enzymes that bear inherent characteristics of natural counterparts but overcome their deficiencies in thermal and acidic stability. Inspired by the metallized active center of natural SODs, here, we engineered different groups of metalloporphyrins and found that Sn-metallized porphyrins can act as novel SOD mimics, in which Sn-metallized meso-tetra­(4-carboxyphenyl) porphine (Sn-TCPP) can more effectively catalyze the disproportionation of superoxide radical anions (•O₂^–) into hydrogen peroxide and oxygen. Especially, Sn-TCPP-based metal–organic frame nanozyme (Sn-PCN222) displays an unusually high catalytic activity that remarkably exceeds those of commonly used counterparts. Such unprecedented catalytic behaviors are proposed to depend on the Sn­(IV)/Sn­(II) transition at the center of Sn-TCPP. In addition, the metal–organic framework (MOF) nanozymes also display higher thermal and acidic stability than natural SODs. Interestingly, we find that Sn-complexed methylated tetra-(4-aminophenyl) porphyrin shows an aggregation-induced SOD activity in an acidic environment, whereas conventional SOD mimics do not function well in this case. Given these unique features, our reported Sn-porphyrin-based nanozymes would be potent alternatives for natural SODs to be widely used in clinical treatments of oxidative stress-related diseases.