Role of protons in superoxide reduction by a superoxide reductase analogue.
Superoxide reduction by thiolate-ligated [FeII(SMe2N4(tren))]+ (1) involves two proton-dependent steps and a single peroxide intermediate, [FeIII(SMe2N4(tren))(OOH)]+ (2). An external proton donor is required, ruling out mechanisms involving H+ or H-atom abstraction from the ligand N-H. The initial protonation step affording 2 occurs with fairly basic proton donors (EtOH, MeOH, NH4+) in THF. More acidic proton donors are required to cleave the Fe-O(peroxide) bond in MeOH, and this occurs via a dissociative mechanism. Reaction rates are dependent on the pKa of the proton donor, and a common [FeIII(SMe2N4(tren))(MeOH)]2+ (3) intermediate is involved. Acetic acid releases H2O2 from 2 under pseudo-first-order conditions ([HOAc] = 138 mM, [2] = 0.49 mM) with a rate constant of 8.2 x 10(-4) s(-1) at -78 degrees C in MeOH. Reduction of 3 with Cp2Co regenerates the active catalyst 1.
Theisen
Roslyn M
RM
Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98105-1700, USA.
Kovacs
Julie A
JA
D006861:Hydrogen Peroxide / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D011522:Protons; D017382:Reactive Oxygen Species / Q000737:chemistry; D013481:Superoxides / Q000737:chemistry*; D013816:Thermodynamics
D011522:Protons; D017382:Reactive Oxygen Species; D013481:Superoxides; D006861:Hydrogen Peroxide; D010088:Oxidoreductases; C121849:superoxide reductase
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