The development of a bidirectional catalyst for oxygen reduction and water oxidation is the key to establishing sustainable energy transduction from renewable resources. We report a stable homogeneous molecular copper complex, comprising of a labile diimine-dioxime ligand framework, that enables rapid and complete 4e − /4H + electrocatalysis for both oxygen reduction (2.1(±0.01) × 10 5 s −1 ) and water oxidation (3.2(±0.01) × 10 5 s −1 ) in aqueous solution presumably via in situ formation of binuclear intermediates. Computational investigations unravel the pivotal role of the interactive flexible ligand scaffold in accommodating the copper-core in variable oxidation states and influencing the O−O bond cleavage/formation dynamics during the catalysis. This study sets up a template for designing molecular catalysts for mediating energyrelevant multielectron/multiproton reactions in both oxidizing and reducing environments.
Copper-containing metalloenzymes constitute a major class of proteins that catalyze a myriad of reactions in nature. Inspired by the structural and functional characteristics of this unique class of metalloenzymes, we report the conception, design, characterization, and functional studies of a de novo artificial copper peptide (ArCuP) within a trimeric self-assembled polypeptide scaffold that activates and reduces peroxide. Using a first-principles approach, the ArCuP was designed to coordinate one Cu via three His residues introduced at an a site of the peptide scaffold. X-ray crystallography, UV–vis, and electron paramagnetic resonance data demonstrate that Cu binds via the Nε atoms of His forming a T2Cu environment. When reacted with hydrogen peroxide, the putative copper-hydroperoxo species is formed where a reductive priming step accelerates the rate of its formation and reduction. Mass spectrometry was used to identify specific residues undergoing oxidative modification, which showed His oxidation only in the reduced state. The redox behavior of the ArCuP was elucidated by protein film voltammetry. Detailed characterization of the electrocatalytic behavior of the ArCuP led us to determine the catalytic parameters (K M and k cat), which established the peroxidase activity of the ArCuP. Combined spectroscopic and electrochemical data showed a pH dependence on the reactivity, which was optimum at pH 7.5.
We report a series of de novo designed Artificial Cu Peptides (ArCuPs) that oxidize and peroxygenate C-H bonds of model abiotic substrates via electrochemically generated Cu-oxygen species using H2O2 as the terminal oxidant, akin to native Cu enzymes. Detailed assessment of kinetic parameters established the catalytic nature of the ArCuPs. Selective alteration of outer sphere steric at the d layers above and below the Cu site allows facilitated access of substrates, where a more pronounced effect on catalysis is observed when space is created at the d layer below the Cu site via Ile to Ala mutation producing a kcat of 6.2 s-1, TONmax of 14800 and catalytic proficiency (kcat/KM/kuncat) of 340 M-1 for the oxidation of benzyl alcohol. Independent spectroscopic studied revealed that the rate of formation of the Cu-oxygen species and the spectroscopic feature of the most active variant is distinct compared to the other ArCuPs. Systematic alteration of outer sphere hydrophobicity led to a correlated tuning of the T2 Cu site redox potentials by ~80 mV. The enhanced activity of the ArCuP variant is attributed to a combination of steric effect that allows easy access of substrates, the nature of Cu-oxygen species, and stability of this construct compared to others, where Ile to Ala mutation unexpectedly leads to a higher thermostability which is further augmented by Cu binding.
We report the construction of de novo designed artificial Cu peptides (ArCuPs) that support the oxidation and peroxygenation of C–H bonds of abiotic substrates via electrochemically generated Cu–oxygen species. Selective alteration of outer sphere steric at the d layers above and below the Cu site allows facilitated access of substrates, where a more pronounced effect on catalysis is observed when space is created at the d layer below the Cu site via Ile to Ala mutation. Independent spectroscopic studies revealed that the rate of formation of the Cu–oxygen species and the spectroscopic feature of the most active variant is distinct compared to the other ArCuPs. Systematic alteration of outer sphere hydrophobicity led to a correlated tuning of the T2 Cu site redox potentials by ∼80 mV. The enhanced activity of the ArCuP variant is attributed to a combination of steric effect that allows easy access of substrates, the nature of Cu–oxygen species, and stability of this construct compared to others, where Ile to Ala mutation unexpectedly leads to a higher thermostability that is further augmented by Cu binding.
We report a series of de novo designed Artificial Cu Peptides (ArCuPs) that oxidize and peroxygenate C-H bonds of model abiotic substrates via electrochemically generated Cu-oxygen species using H2O2 as the terminal oxidant, akin to native Cu enzymes. Detailed assessment of kinetic parameters established the catalytic nature of the ArCuPs. Selective alteration of outer sphere steric at the d layers above and below the Cu site allows facilitated access of substrates, where a more pronounced effect on catalysis is observed when space is created at the d layer below the Cu site via Ile to Ala mutation producing a kcat of 6.2 s-1, TONmax of 14800 and catalytic proficiency (kcat/KM/kuncat) of 340 M-1 for the oxidation of benzyl alcohol. Independent spectroscopic studied revealed that the rate of formation of the Cu-oxygen species and the spectroscopic feature of the most active variant is distinct compared to the other ArCuPs. Systematic alteration of outer sphere hydrophobicity led to a correlated tuning of the T2 Cu site redox potentials by ~80 mV. The enhanced activity of the ArCuP variant is attributed to a combination of steric effect that allows easy access of substrates, the nature of Cu-oxygen species, and stability of this construct compared to others, where Ile to Ala mutation unexpectedly leads to a higher thermostability which is further augmented by Cu binding.
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