A question of flexibility in cytochrome c oxidase models

Abstract

The structure-property relationships were compared for the iron and iron-copper complexes of two functional cytochrome c oxidase models, 1 and 2, both constructed upon a phenanthroline-strapped porphyrin bearing respectively pyridyl or picolinyl built-in proximal and distal ligands. The behavior of these heme models in the absence and in the presence of copper was studied by 1 H NMR, UV-visible absorption, EPR, Raman and FTIR spectroscopies, electrochemistry in solution and deposited on a rotating ring-disk graphite electrode. The distal binding site within the phenanthroline pocket of both 1 and 2 is available for the coordination of exogenic ligands, yet the oxygen binding affinity is higher for all complexes of 2 than for 1.Despite this difference, [1Fe II Cu I ] more efficiently reproduced the electrocatalyzed reduction of 2 oxygen to water than [2Fe II Cu I ]. The oxygenated complexes of both iron(II)-copper(I) species mimic the ability of cytochrome c oxidase to reversibly bind O2, as shown by competitive binding studies in the presence of CO. Differences in the binding and electrocatalytic properties of these models stem from difference in rigidity of scaffolds upon binding of both the proximal and distal ligands, as well as from the bulkiness of the distal ligand. KEYWORDS Cytochrome c oxidase, heme protein models, porphyrin, phenanthroline, oxygen binding, carbon monoxide binding.

Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function

“…Complex (E) is also less efficient as an O2-reduction catalyst in terms of the overpotential required for catalysis but yields fewer PROS overall. 1020 These systems provide insight into how drastically the catalytic activity of CcO model systems can change as a result of minor changes in axial ligand basicity and pendant arm flexibility.…”

ORR activity of metalated phenanthroline-strapped porphyrin adsorbed on carbon nanotubes

“…The complex shape of this redox couple associated with this process is attributable to the presence and exchange of an axial ligand (residual H 2 O, a solvent molecule, Cl − or no ligand) on the iron(III) center. As previously observed, when copper is present in the phenanthroline strap (Cu/Fe-P), the apical ligand exchange is slow or hindered and can result in an irreversible reduction wave [43,46]. Finally, in the Cu/Fe-P derivative, an additional reversible signal (III) is observed at 0.09 V and corresponds to the oxidation of Cu(I) to Cu(II).…”

“…In these ditopic ligands, the phenanthroline binds and stabilizes a copper(I) ion at a distance of approximately 4.7 Å from an iron porphyrin, mimicking a heme. In previous studies, these structures, decorated with pendant pyridine or imidazole ligands were evaluated as models of cytochrome c oxidase in physiological media [43] (phosphate buffer) but were never studied under the working conditions of a proton exchange membrane fuel-cell (PEMFC). The absorption of phenanthroline-strapped iron (Fe-P) and iron(III)/copper(I) porphyrins (Cu/Fe-P) on multiwalled carbon nanotubes (MWNTs) and their electrocatalytic properties are reported hereafter.…”

Hydrogen bond directed molecular recognition in water in a strapped-porphyrin-cyclodextrin assembly

“…A tremendous advantage of the phenanthroline-strapped structure is its synthetic availability on a gram scale within a few weeks. Over the last decade, the selective imidazole recognition [14,15] within the phenanthroline strap was used to construct a family of supramolecular complexes that mimic the hetero-binuclear site of cytochrome c oxidase [12,16]. Very simple derivatives of this strapped porphyrin can be sulfonated (Scheme 1) to favor their inclusion within b-CD hosts.…”