Theoretical mechanisms of the superoxide radical anion catalyzed by the nickel superoxide dismutase

The disproportionation of superoxide radical anions catalyzed by nickel superoxide dismutase was investigated in detail using density functional theory. The structures of each stationary point and the transition states were located so that the reaction pathways were determined. The results indicated that the reactions proceeded by two steps both for the oxidized process of superoxide radical anion and the reduced one. The Gibbs free energy of the reactions in gas-phase was obtained. The hydrogen bond was considered in the reactive processes. Electron transfer was explained by natural bond orbital (NBO) analysis. In addition, the singlet–triplet energy gap was also discussed and the triplet states were more stable than the singlet states for state 1–3 involved in the first half-reaction.