MULTIPLET

Perhaps the most important fundamental question in chemical research resides in how we can convert abundant stable molecules such as H2O, CO2, O2 and N2 into an energy carrier and provide valuable chemical synthons for industrial usage so as to mitigate the environmental and industrial constraints from extensive use of fossil resources. Nature provides us with main clues on how to do so through the process of photosynthesis where energy from sunlight is used to drive multielectron catalysis, first oxidising water in a four-electron and four-proton process and then reducing CO2 to sugars or protons to H2. The coupling of different catalytic modules performing on one side an oxidation process and on the other a reductive one is a source of inspiration for chemists. Performing light driven multielectronic catalytic chemical transformations are targeted objectives for chemists. For instance, Oxygen Atom Transfer Reactions (OATR) can be achieved through the photo generation of metal-oxo species with water as the sole source of oxygen atom. However, these systems are intrinsically limited by the requirement of a sacrificial electron acceptor. If we want to deploy controlled light driven multielectron chemical transformation in viable applications it is urgent to exclude sacrificial electron acceptors in OATR. With MULTIPLET our objective is to build a self-sufficient system for OATR by grafting a synthetic sensitizer-catalyst (Mn or Fe complexes "clicked" to a chromophore) able to photoactivate H2O (2e-+2H+, eq. 1) to the surface of an active robust multi-copper oxidase (laccase) that performs O2 reduction (4e-+4H+, eq. 3). The resulting hybrids should then couple the substrate oxygenation reaction (eq. 2) to dioxygen reduction. Mn+-OH2 ? [M(n+2)+-O] + 2e- + 2H+ (1) [M(n+2)+-O] + Substrate ? Substrate(O) + Mn+ (2) 4e- + 4H+ + O2 ? 2H2O (3) The challenging and ambitious goal of this project is to couple the light triggered oxidative process to a photo-driven catalytic reduction of dioxygen at the enzyme laccase. This proposal is based on our continuing effort to investigate on alternative routes for solar energy conversion. Taking profit of a versatile synthetic route based on the Huisgen cycloaddition (click chemistry) we have established in our labs we will develop original molecular assemblies consisting of our designed molecular catalysts based on Mn or Fe complexes and a photoactive chromophore in order to drive the light activation of a metal bound H2O molecule. Targeting OATR from water to an organic substrate, we should recover two electrons and two protons per water molecule. On the other hand, we have recently published on the photocatalytic reduction of O2 into H2O by an active biological catalyst, a laccase. Now, in MULTIPLET, we will covalently link the OATR photocatalytic unit to a laccase to form a photocatalytic triad able to synergistically couple the two processes. Providing an unprecedented way to use light, water and O2 to oxidise organic substrates with water as sole by-product, this strategy will be beneficial on several grounds, i) circumventing the use of non-sustainable electron acceptors, and ii) with the help of a laccase to recover electrons and protons issued from a synthetic catalytic unit, providing a positive feedback to drive the initial energetically uphill oxidation process. Thus, successes in this research project would open new realms in the development of unique photocatalytic transformations of value-added compounds. With MULTIPLET, we seek to stimulate discussion on important phenomena that may be pertinent to multiple electron transfer processes. We believe that the goals of MULTIPLET are within reach in our consortium and the outcome of this project will contribute to set experimental as well as fundamental grounds to further development in photocatalysis using abundant renewable sources for the production of a fuel or for chemical conversion.