Role of protons in superoxide reduction by a superoxide reductase analogue

Inorg Chem. 2005 Mar 7;44(5):1169-71. doi: 10.1021/ic048818z.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Hydrogen Peroxide / chemistry
  • Models, Chemical
  • Molecular Structure
  • Oxidation-Reduction
  • Oxidoreductases / chemistry*
  • Oxidoreductases / metabolism
  • Protons*
  • Reactive Oxygen Species / chemistry
  • Superoxides / chemistry*
  • Thermodynamics

Substances

  • Protons
  • Reactive Oxygen Species
  • Superoxides
  • Hydrogen Peroxide
  • Oxidoreductases
  • superoxide reductase