Outstanding Superoxide Dismutase Catalytic Activity Of Simple Peptide-Based Nickel(II) Complexes

We present here the most active synthetic Ni superoxide dismutase (NiSOD) mimic reported to date. Reactive oxygen species are aggressive compounds, which concentrations are tightly regulated in vivo. Among them, the superoxide anion, O₂⋅^-, is controlled by superoxide dismutases. Capitalizing on the versatility of the Amino-Terminal Cu^II- and Ni^II-binding (ATCUN) peptide motif, we introduced positive charges around the Ni^II center to favor the interaction with the superoxide radical anion. At physiological pH, the pentapeptide H-Cys-His-Cys-Arg-Arg-NH₂ coordinates Ni^II after the deprotonation of one thiol, two amides, and either the second thiol or the N-terminal ammonium, leading to an equilibrium between the two N₃S₁ and N₂S₂ coordination modes. Under catalytic conditions, a k_cat value of 8.6(4)×10⁶ L.mol^-1.s^-1 was measured. Within the first second, the catalyst remained undegraded with quantitative consumption of O₂⋅^- (completed up to 37 catalytic cycles). An extra arginine (Arg) was introduced at the peptide C-terminus to increase the global charge of the Ni^II complex from +1 to +2. This had no effect on the catalytic performance, highlighting the critical role of charge distribution in space as a determining factor influencing the reactivity.