The movement of protons and electrons in proteins drives many essential processes in biology, including photosynthesis and cellular respiration. In some cases, the most efficient mechanism for transfer of one proton and one electron is concerted rather than stepwise.  Surprisingly, such an energetic preference for concerted mechanisms can be observed even when the proton and electron move in different directions. For this reason, multiple-site concerted proton electron transfer (MS-CPET) is prevalent in biological systems, for instance in tyrosine oxidation in photosystem II and in hydroquinone oxidation as part of mitochondrial respiratory chains.We have designed and synthesized a single molecule substrate to serve as a mimic for MS-CPET from tyrosine, with the aim to develop a better understanding of how the rate and mechanism of MS-CPET are controlled. This substrate and its relatives contain a phenol to release the proton and electron, a photooxidant to receive the electron, and a base to receive the proton, all covalently tethered together. The synthetic model provides an opportunity to study MS-CPET under conditions not limited by diffusion, allowing rates to be measured by fluorescence quenching of the excited photooxidant moiety of the substrate. The synthesis of this substrate will be presented, together with preliminary photochemical studies.

Unimolecular model to probe multiple-site concerted proton electron transfer

248th National Meeting (2014)

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