Electrocatalytic
O<sub>2</sub>‑Reduction by
Synthetic Cytochrome <i>c</i> Oxidase Mimics: Identification
of a “Bridging Peroxo” Intermediate Involved in Facile
4e<sup>–</sup>/4H<sup>+</sup> O<sub>2</sub>‑Reduction
Sudipta Chatterjee
Kushal Sengupta
Shabnam Hematian
Kenneth D. Karlin
Abhishek Dey
10.1021/jacs.5b06513.s001
https://acs.figshare.com/articles/journal_contribution/Electrocatalytic_O_sub_2_sub_Reduction_by_Synthetic_Cytochrome_i_c_i_Oxidase_Mimics_Identification_of_a_Bridging_Peroxo_Intermediate_Involved_in_Facile_4e_sup_sup_4H_sup_sup_O_sub_2_sub_Reduction/2121838
A synthetic
heme–Cu C<i>c</i>O model complex shows
selective and highly efficient electrocatalytic 4e<sup>–</sup>/4H<sup>+</sup> O<sub>2</sub>-reduction to H<sub>2</sub>O with a
large catalytic rate (>10<sup>5</sup> M<sup>–1</sup> s<sup>–1</sup>). While the heme-Cu model (FeCu) shows almost exclusive
4e<sup>–</sup>/4H<sup>+</sup> reduction of O<sub>2</sub> to
H<sub>2</sub>O (detected using ring disk electrochemistry and rotating
ring disk electrochemistry), when imidazole is bound to the heme (Fe(Im)Cu),
this same selective O<sub>2</sub>-reduction to water occurs only under
slow electron fluxes. Surface enhanced resonance Raman spectroscopy
coupled to dynamic electrochemistry data suggests the formation of
a bridging peroxide intermediate during O<sub>2</sub>-reduction by
both complexes under steady state reaction conditions, indicating
that O–O bond heterolysis is likely to be the rate-determining
step (RDS) at the mass transfer limited region. The O–O vibrational
frequencies at 819 cm<sup>–1</sup> in <sup>16</sup>O<sub>2</sub> (759 cm<sup>–1</sup> in <sup>18</sup>O<sub>2</sub>) for the
FeCu complex and at 847 cm<sup>–1</sup> (786 cm<sup>–1</sup>) for the Fe(Im)Cu complex, indicate the formation of <i>side-on</i> and <i>end-on</i> bridging Fe-peroxo-Cu intermediates,
respectively, during O<sub>2</sub>-reduction in an aqueous environment.
These data suggest that <i>side-on</i> bridging peroxide
intermediates are involved in fast and selective O<sub>2</sub>-reduction
in these synthetic complexes. The greater amount of H<sub>2</sub>O<sub>2</sub> production by the imidazole bound complex under fast electron
transfer is due to 1e<sup>–</sup>/1H<sup>+</sup> O<sub>2</sub>-reduction by the distal Cu where O<sub>2</sub> binding to the water
bound low spin Fe<sup>II</sup> complex is inhibited.
2015-10-14 00:00:00
heme
electron
resonance Raman spectroscopy
peroxide
O 2 binding
FeCu
imidazole
state reaction conditions
formation
intermediate
cm
Synthetic Cytochrome c Oxidase Mimics
transfer
Fe
H 2O
RDS
ring disk electrochemistry
H 2O production
complex
data
model