A Bioinspired NiII Superoxide Dismutase Catalyst Designed on an ATCUN-like Binding Motif

Nickel superoxide dismutase (NiSOD) is an enzyme that protects cells against O2 · –. While the structure of its active site is known, the mechanism of the catalytic cycle is still not elucidated. Its active site displays a square planar NiII center with two thiolates, the terminal amine and an amidate. We report here a bioinspired NiII complex built on an ATCUN-like binding motif modulated with one cysteine, which demonstrates catalytic SOD activity in water (k cat = 8.4(2) × 105 M–1 s–1 at pH = 8.1). Its reactivity with O2 · – was also studied in acetonitrile allowing trapping two different short-lived species that were characterized by electron paramagnetic resonance or spectroelectrochemistry and a combination of density functional theory (DFT) and time-dependent DFT calculations. Based on these observations, we propose that O2 · – interacts first with the complex outer sphere through a H-bond with the peptide scaffold in a [NiIIO2 · –] species. This first species could then evolve into a NiIII hydroperoxo inner sphere species through a reaction driven by protonation that is thermodynamically highly favored according to DFT calculations.