Tuning the Mn II2/Mn III2 Redox Cycle of a Phenoxo-Bridged diMn Catalase Mimic With Terminal Carboxylate Donors

J Inorg Biochem. 2018 May;182:29-36. doi: 10.1016/j.jinorgbio.2018.01.013. Epub 2018 Feb 2.

Abstract

A new phenoxo-bridged diMnIII complex, Na[Mn2L(OH)2(H2O)2]·5H2O (1), obtained with the ligand L5- = 5‑methyl‑2‑hydroxo‑1,3‑xylene‑α,α‑diamine‑N,N,N',N'‑tetraacetato, has been prepared and characterized. Mass spectrometry, conductivity, UV-visible, EPR and 1H NMR spectroscopic studies showed that the complex exists in solution as a monoanionic diMnIII complex. Complex 1 catalyzes H2O2 disproportionation with second-order rate constant kcat = 305(9) M-1 min-1 and without a time-lag phase. Based on spectroscopic results, the catalase activity of complex 1 in methanol involves a MnIII2/MnII2 redox cycle, which distinguishes this catalyst from other phenoxo-bridged diMn complexes that cycle between MnIIMnIII/MnIIIMnIV species. Addition of base stabilizes the catalyst, restrains demetallation during catalysis and causes moderate enhancement of catalase activity. The terminal carboxylate donors of 1 not only contribute as internal bases to assist deprotonation of H2O2 but also favor the formation of active homovalent diMn species, just as observed for the enzyme.

Keywords: Catalase mimic; Kinetics; Manganese; Polycarboxylate ligand.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalase / chemistry
  • Catalase / metabolism*
  • Catalysis
  • Hydrogen Peroxide / chemistry
  • Hydrogen Peroxide / metabolism
  • Kinetics
  • Manganese / chemistry*
  • Manganese / metabolism*
  • Oxidation-Reduction

Substances

  • Manganese
  • Hydrogen Peroxide
  • Catalase