Heme-copper/dioxygen adduct formation relevant to cytochrome c oxidase: Spectroscopic characterization of [(6L)FeIII-(O 22-)-CuII]+

Reza A. Ghiladi, Hong Wei Huang, Pierre Moënne-Loccoz, Jay Stasser, Ninian J. Blackburn, Amina S. Woods, Robert J. Cotter, Christopher D. Incarvito, Arnold L. Rheingold, Kenneth D. Karlin

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25 Scopus citations


In the further development and understanding of heme-copper dioxygen reactivity relevant to cytochrome c oxidase O2-reduction chemistry, we describe a high-spin, five-coordinate dioxygen (peroxo) adduct of an iron(II)-copper(I) complex, [(6L)FeIICu I](BArF20) (1), where 6L is a tetraarylporphyrinate with a tethered tris(2-pyridylmethyl)amine chelate for copper. Reaction of 1 with O2 in MeCN affords a remarkably stable [t1/2 (rt; MeCN)≈60 min] adduct, [(6L)Fe III-(O22-)-CuII]+ (2) [EPR silent; λmax = 418 (Soret), 561 nm], formulated as a peroxo complex based on manometry (1:O2 = 1:1; spectrophotometric titration, -40°C, MeCN), mass spectrometry {MALDI-TOF-MS: 16O2, m/z 1191 ([(6L)FeIII-( 16O22-)-CuII]+); 18O2, m/z 1195}, and resonance Raman spectroscopy (νv(O-O) = 788 cm-1; Δ16O 2/18O2 = 44 cm-1; Δ16O2/16/18O2 = 22 cm -1). 1H and 2H NMR spectroscopy (-40°C, MeCN) reveals that 2 is the first heme-copper peroxo complex which is high-spin, with downfield-shifted pyrrole resonances (δpyrrole = 75 ppm, s, br) and upfield shifted peaks at δ = -22, -35, and -40 ppm, similar to the pattern observed for the μ-oxo complex [(6L)Fe III-O-CuII](BArF) (3) (known S = 2 system, antiferromagnetically coupled high-spin FeIII and CuII). The corresponding magnetic moment measurement (Evans method, CD3CN, -40°C) also confirms the S = 2 spin state, with μB = 4.9. Structural insights were obtained from X-ray absorption spectroscopy, showing Fe-O (1.83 Å) and Cu-O (1.882 Å) bonds, and an Fe...Cu distance of 3.35(2) Å, suggestive of a μ-1,2-peroxo ligand present in 2. The reaction of 2 with cobaltocene gives 3, differing from the observed full reduction seen with other heme-Cu peroxo complexes. Finally, thermal decomposition of 2 yields 3, with concomitant release of 0.5 mol O2 per mol 2, as confirmed quantitatively by an alkaline pyrogallol dioxygen scavenging solution.

Original languageEnglish (US)
Pages (from-to)63-77
Number of pages15
JournalJournal of Biological Inorganic Chemistry
Issue number1
StatePublished - Jan 2005


  • Dioxygen adduct
  • Heme-copper
  • Iron(II)-copper(I) complex
  • Mass spectrometry
  • Model compound
  • Peroxo complex
  • Resonance Raman spectroscopy

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry


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