Activation of dioxygen by copper metalloproteins and insights from model complexes

Abstract

Nature uses dioxygen as a key oxidant in the transformation of biomolecules. Among the enzymes that are utilized for these reactions are copper-containing met-alloenzymes, which are responsible for important biological functions such as the regulation of neurotransmitters, dioxygen transport, and cellular respiration. Enzymatic and model system studies work in tandem in order to gain an understanding of the fundamental reductive activation of dioxygen by copper complexes. This review covers the most recent advancements in the structures, spectroscopy, and reaction mechanisms for dioxygen-activating copper proteins and relevant synthetic models thereof. An emphasis has also been placed on cofactor biogenesis, a fundamentally important process whereby biomolecules are post-translationally modified by the pro-enzyme active site to generate cofactors which are essential for the catalytic enzymatic reaction. Significant questions remaining in copper-ion-mediated O2-activation in copper proteins are addressed.

Immobilization of Molecular Catalysts for Enhanced Redox Catalysis

“…Catalytic intermediates,s uch as metal-superoxo (M-O 2 C À ), metal-peroxo (M-O 2 2À ), metal-hydroperoxo (M-OOH) and metaloxo (M = O 2À )s pecies, in redox enzymes are prone to be deactivatedb yb imolecular reactions, [56][57][58][59][60] which can be avoided by immobilization of catalysts. This Reviewi si ntended to focus on immobilization of the photosynthetic reactionc enter model compounds as well as redox enzyme model metal complexes to develop molecular photonic devices such as photovoltaic devices as well as efficient heterogeneouscatalysts.…”

Mechanisms of Two‐Electron versus Four‐Electron Reduction of Dioxygen Catalyzed by Earth‐Abundant Metal Complexes

“…A variety of metal complexes in homogeneous solution as well as metal catalysts in the heterogeneous cathodes catalyze the two‐electron/two‐proton or/and four‐electron/four‐proton reduction of O 2 in aqueous solutions at various pH values, as well as in aprotic solvents with acids . The most important question is how the four‐electron/four‐proton reduction of O 2 to water occurs without releasing the two‐electron reduced species (H 2 O 2 ) or how the two‐electron reduction of O 2 to H 2 O 2 occurs without the further reduction of H 2 O 2 to H 2 O despite the more favorable energetics (vide supra).…”

“…Av ariety of metal complexes in homogeneous solution as well as metal catalysts in the heterogeneous cathodes catalyze the two-electron/two-proton or/and four-electron/four-proton reduction of O 2 in aqueous solutionsa tv arious pH values, as well as in aprotic solvents with acids. [2,[33][34][35][36][37][38][39][40][41][42][43] The most important question is how the four-electron/four-protonr eduction of O 2…”

Electrocatalytic Properties of Cuprous Delafossite Oxides for the Alkaline Oxygen Reduction Reaction

“…Looking to nature for inspiration, several biomolecules and their model complexes have mono‐, bi‐, or trinuclear copper sites that have been shown to bind and activate O 2 . For example, binuclear Cu I sites bind to O 2 to form a side‐on peroxo‐bridged structure with an interatomic copper distance near 3.6 Å .…”

“…Important to this structure is that the unoccupied peroxide σ* orbital interacts with occupied copper d orbitals, which significantly weakens the O−O bond (Figure ) . Multicopper oxidase enzymes containing a trinuclear copper site with a neighboring fourth copper can also directly catalyze the four‐electron reduction of O 2 to water . The catalytic activity of these biomolecular copper active sites has been extensively studied with several examples of their direct use or use of their model complexes as heterogeneous ORR catalysts.…”