Structural and Functional Models of the Dimanganese Catalase Enzymes. 2. Structure, Electrochemical, Redox, and EPR Properties

P. J. Pessiki, S. V. Khangulov, D. M. Ho, G. C. Dismukes

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Catalysts which functionally mimic the bacterial dimanganese catalase enzymes have been synthesized and their structure, electrochemical, redox, and EPR spectra have been compared to the enzyme. These compounds are formulated as [LMn2II, IIX] Y2, µ-X = CH3CO2, ClCH2CO2; Y = ClO4, BPh4, CH3CO2, possessing a bridging µ-alkoxide from the ligand, HL = N, N, Nʹ,Nʹ-tetrakis(2-methylenebenzimidazole)-1, 3-diaminopropan-2-ol. An X-ray diffraction structure of [LMn2(CH3CO2)(butanol)] (ClO4)2·H2O, in the monoclinic space group P2(1)/c, confirmed the anticipated N6O septadentate coordination of the HL ligand, the bridging μ-acetate, and revealed both five-and six-coordinate Mn ions; the latter arising from a butanol solvent molecule. This contrasts with the six-coordinate Mn ions observed for the µ-Cl and µ-OH derivatives, LMn2Cl3 and LMn2(OH)Br2 (Mathur et al. J. Am. Chem. Soc. 1987, 109, 52275232). Like the enzyme, three electrons can be removed from these complexes to form four oxidation states ranging from Mn2II, II to Mn2III, IV. Three of these have been characterized by EPR and found to possess electronic ground states, MnIII electron orbital configurations, 55Mn hyperfine parameters, and Heisenberg exchange interactions analogous to those observed in the enzyme. For the µ-carboxylate derivatives electrochemistry reveals the initial oxidation process involves loss of two electrons at 0.81-0.86 V, forming Mn2III, III, followed by dismutation to yield a Mn2II, III and Mn2III, IV species. By contrast, the µ-Cl and µ-OH derivatives oxidize by an initial one-electron process (0.49-0.54 V). For the μ-carboxylate derivatives chemical oxidation with Pb(OAc)4 also reveals an initial two-electron oxidation to a Mn2III, III species, which dismutates to form both Mn2II, III and Mn2III, IV species. The two Mn2II, III species formed by these methods exhibit 55Mn hyperfine fields differing in magnitude by 9% (150 G), implying different Mn coordination environments induced by the electrolyte. The different ligand coordination observed in the enzyme (predominantly oxo and carboxylato) appears to be responsible for stabilization of the MnCatIII, III oxidation state as the resting state.

Original languageEnglish (US)
Pages (from-to)891-897
Number of pages7
JournalJournal of the American Chemical Society
Issue number3
StatePublished - Feb 1 1994
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


  • EPR
  • X-ray synthesis
  • catalase
  • electrochemical
  • enzyme
  • hydrogen peroxide
  • manganese


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