Bridging the Catalytic Turnover Gap Between Single-Atom Iron Nanozymes and Natural Enzymes by Engineering the First and Second Shell Coordination

Single-atom nanozymes (SAzymes) constitute a promising category of enzyme-mimicking materials with outstanding catalytic performance. The performance of SAzymes improves through modification of the coordination environments around the metal center. However, the catalytic turnover rates of SAzymes, which are key measures of the effectiveness of active site modifications, remain lower than those of natural enzymes, especially in peroxidase-reactions. Here, the first and second shell coordination tuning strategy that yields SAzymes with structures and activities analogous to those of natural enzymes is reported. The optimized SAzyme exhibits a turnover rate of 52.7 s⁻¹ and a catalytic efficiency of 6.97 × 10⁵ M⁻¹ s⁻¹. A computational study reveals that axial S-ligands induce an alternative reaction mechanism, and SO₂− functional groups provide hydrogen bonds to reduce the activation energy. In addition, SAzyme shows superior anti-tumor ability in vitro and in vivo. These results demonstrate the validity of coordination engineering strategies and the carcinostatic potential of SAzymes.