Bio-inspired electron-delivering system for reductive activation of dioxygen at metal centres towards artificial flavoenzymes.

Yoann Roux,Jean-Pierre Mahy,Frédéric Avenier,Rémy Ricoux

doi:10.1038/ncomms9509

Abstract

Development of artificial systems, capable of delivering electrons to metal-based catalysts for the reductive activation of dioxygen, has been proven very difficult for decades, constituting a major scientific lock for the elaboration of environmentally friendly oxidation processes. Here we demonstrate that the incorporation of a flavin mononucleotide (FMN) in a water-soluble polymer, bearing a locally hydrophobic microenvironment, allows the efficient reduction of the FMN by NADH. This supramolecular entity is then capable of catalysing a very fast single-electron reduction of manganese(III) porphyrin by splitting the electron pair issued from NADH. This is fully reminiscent of the activity of natural reductases such as the cytochrome P450 reductases with kinetic parameters, which are three orders of magnitude faster compared with other artificial systems. Finally, we show as a proof of concept that the reduced manganese porphyrin activates dioxygen and catalyses the oxidation of organic substrates in water.

Highlights

Development of artificial systems, capable of delivering electrons to metal-based catalysts for the reductive activation of dioxygen, has been proven very difficult for decades, constituting a major scientific lock for the elaboration of environmentally friendly oxidation processes
Other metallic monooxygenases activate dioxygen to perform oxidation reactions, and in all cases the two electrons needed at each catalytic cycle are provided to the metal centres by reductase proteins capable of harvesting electrons from NAD(P)H owing to their flavin cofactors flavin mononucleotide (FMN) or FAD3,4
Since the flavin mononucleotide (FMN) cofactor (Fig. 2) usually binds to proteins by simple electrostatic interactions[26], we decided to design bio-inspired artificial systems based on the same concept

Summary

Introduction

Development of artificial systems, capable of delivering electrons to metal-based catalysts for the reductive activation of dioxygen, has been proven very difficult for decades, constituting a major scientific lock for the elaboration of environmentally friendly oxidation processes. It provides a binding site for NAD(P)H and it finely tunes the redox potential of flavin cofactors by creating a local specific microenvironment[5,6] These selective electron transfers constitute the main scientific lock in the perspective of performing a bio-inspired oxidation catalysis using dioxygen with metal-based catalysts. Despite the few examples cited above, efficient water-soluble systems capable of selectively driving electrons to metallic centres for the reductive activation of dioxygen are still highly needed In this perspective, multibranched polyethyleneimine (PEI), which are water-soluble polymers, can be modified with various chemical groups and they generate supramolecular entities bearing a specific local microenvironment, reminiscent to the active site of enzymes. In terms of oxidation catalysis, the incorporation of polyoxometalate allowed, for example, the epoxidation of styrene in good yield in the presence of hydrogen peroxide[25]

Methods

Results

Conclusion