Spin‐State Rationale for the Peroxo‐Stabilizing Role of the Thiolate Ligand in Superoxide Reductase

Anti-push: The axial thiolate ligand stabilizes high-spin FeIII-OOR species (see picture) such as those found in superoxide reductase. This situation is in contrast to the “push effect” observed in structurally similar low-spin FeIII-OOR systems, including cytochrome P450, which promote OO bond cleavage. These results show how very similar enzyme-active sites can carry out two very different functions.