Bio-inspired nanocatalysts for the oxygen reduction reaction

Electrochemical conversions at fuel cell electrodes are complex processes. In particular, the oxygen reduction reaction has substantial overpotential limiting the electrical power output efficiency. Effective and inexpensive catalytic interfaces are therefore essential for increased performance. Taking inspiration from enzymes, earth-abundant metal centres embedded in organic environments present remarkable catalytic active sites. Here we show that these enzyme-inspired centres can be effectively mimicked in two-dimensional metal-organic coordination networks self-assembled on electrode surfaces. Networks consisting of trimesic acid and bis-pyridyl-bispyrimidine coordinating to single iron and manganese atoms on Au(111) effectively catalyse the reduction and reveal distinctive catalytic activity in alkaline media. These results demonstrate the potential of surface-engineered metal-organic networks for electrocatalytic conversions. Specifically designed coordination complexes at surfaces inspired by enzyme cofactors represent a new class of nanocatalysts with promising applications in electrocatalysis.Fil: Grumelli, Doris Elda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Max Planck Institute for Solid State Research; AlemaniaFil: Wurtser, Benjamin. Max Planck Institute for Solid State Research; AlemaniaFil: Stepanow, Sabastian. Max Planck Institute for Solid State Research; AlemaniaFil: Kern, Klaus. Max Planck Institute for Solid State Research; Alemania. Ecole Polytechnique Federale de Lausanne; Suiz

Vibrational resonances and Cu B displacement controlled by proton motion in cytochrome c oxidase

Cytochrome c oxidase (CcO), found in the inner mitochondrial membranes or in many bacteria, catalyzes the four-electron reduction of molecular oxygen to water. Four protons are pumped across the inner mitochondrial membrane through CcO. In this study, quantum mechanics/molecular mechanics and molecular dynamics calculations are used to probe the spectroscopic characteristics of the ferryl intermediates in the aa 3 CcO/O 2 reaction. These highly elaborate calculations, supported by several calculations on smaller model systems, demonstrate the sensitivity of vibrational frequencies on the Coulombic field of heme a 3 and their dependence on the distance of the adjacent Cu B to the heme a 3-Fe atom. This distance seems to be associated with the protonation state of the heme a 3 propionate A, and we propose that it plays a crucial role on the mechanism of action of CcO. In detail, we link proton pumping activity in CcO enzyme (a) to a multiple (1:1:2) resonance among the frequencies of FeIV=O bond stretching, the breathing mode of Histidine 411, and a bending mode of the His411-FeIV=O species (aa 3 from Paracoccus denitrificans numbering) and (b) to Cu B displacement by electrostatic interactions toward the heme a 3 iron. We find that the vibrations of the His411-FeIV=O unit become highly coupled depending on the protonation state of the heme a 3 ring A propionate/Asp399 pair, and we propose a mechanism for the resonance Raman enhancement of the bending mode δ(His411-FeIV=O). Calculations on model systems demonstrate that the position of Cu B in relation to heme a 3 iron-oxo plays a crucial role in regulating that resonance. We also discuss the origin of the coupling between bending, δ(His411- FeIV=O) and v(Fe=O) stretching modes, and the role played by such vibrational coupling interactions or CuB position in controlling functional properties of the enzyme, including electron/proton coupling as well as experimental spectr