Light-driven oxygen atom transfer

Nature uses molybdenum-containing enzymes to catalyse reactions that involve the transfer of oxygen atoms from water. The electrons that are released during the oxidation are transported from the molybdenum centre to the other side of the enzymes, where they are handed over to a terminal electron acceptor. Light absorption can cause electron transfer from one part of a molecule to another or between molecules. Indeed such processes are crucial in photosynthesis. Within this project, we aim to mimic the electron transfer processes of molybdenum enzymes by connecting Mo-centre mimics to electron transfer units, which can be activated by light. This will allow us to trigger the oxygenation reaction with a light flash and help us to learn more about the function of the enzymes. By using a variety of different molybdenum centres and photoactive units, we will identify the best combinations of components. Once the model systems are optimised, photoactivation may allow us to improve the energy and atom efficiency of industrially relevant oxidation processes and to oxygenate molecules related to DNA bases that are similar to the substrates of the molybdoenzyme xanthine oxidase.

In addition to the immediate benefit of advancing our understanding of fundamental photo-induced electron transfer processes in biomimetic catalysts, the proposed work may lead to the development of new photo-catalysts with the potential to improve the energy and atom efficiency of industrially relevant oxidation processes. Such oxidations represent a key step in the conversion of petroleum-based feedstocks to higher-value compounds of a higher oxidation state. Relevant reactions range from large-scale processes, such as the oxidation of aldehydes obtained by hydroformylation to carboxylic acids and the production of adipic acid required for the production of nylon-6.6 from cyclohexene to smaller-scale processes, such as the epoxidation of terpenes, e.g. limonene, for the production of fragrances. The fact that the proposed biomimetic photocatalysts use hydrogen peroxide (produced in situ from dioxygen) or water as clean oxidants is advantageous not only on environmental and economic grounds but also for safety reasons. In addition, catalysts with photonuclease activity may be identified, with potential applications in biochemical assays or photodynamic cancer therapy. The proposal is thus relevant to several areas identified as of strategic importance by the research councils, including green technology, sustainability, self-assembly and the priority theme energy. Hence, the work could have considerable economic and societal impact in the long-term. In order to ensure the commercial potential of promising catalysts, we will seek both intellectual property (IP) protection and industrial expertise. Help will be provided by the University of York Enterprise and Innovation Office

Since the move towards greener chemical technology and energy efficiency is of much current interest and importance, the proposed work provides an opportunity to engage with the public and to raise awareness of environmental and sustainability issues.

In addition, the work will result in the training of a highly skilled PDRA, who will be well prepared for employment in either the academic and industrial sector. In addition, new graduates and final year undergraduates working on related projects will benefit from the training provided.