Abstract
Photosynthesis powers our planet and is a source of inspiration for developing artificial constructs mimicking many aspects of the natural energy transducing process. In the complex machinery of photosystem II (PSII), the redox activity of the tyrosine Z (Tyrz) hydrogen-bonded to histidine 190 (His190) is essential for its functions. For example, the Tyrz–His190 pair provides a proton-coupled electron transfer (PCET) pathway that effectively competes against the back-electron transfer reaction and tunes the redox potential of the phenoxyl radical/phenol redox couple ensuring a high net quantum yield of photoinduced charge separation in PSII. Herein, artificial assemblies mimicking both the structural and redox properties of the Tyrz–His190 pair are described. The bioinspired constructs contain a phenol (Tyrz model) covalently linked to a benzimidazole (His190 model) featuring an intramolecular hydrogen bond which closely emulates the one observed in the natural counterpart. Incorporation of electron-withdrawing groups in the benzimidazole moiety systematically changes the intramolecular hydrogen bond strength and modifies the potential of the phenoxyl radical/phenol redox couple over a range of ~ 250 mV. Infrared spectroelectrochemistry (IRSEC) demonstrates the associated one-electron, one-proton transfer (E1PT) process upon electrochemical oxidation of the phenol. The present contribution provides insight regarding the factors controlling the redox potential of the phenol and highlights strategies for the design of futures constructs capable of transporting protons across longer distances while maintaining a high potential of the phenoxyl radical/phenol redox couple.
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Acknowledgements
The research leading to these results received funding from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Grant DE-FG02-03ER15393.
Funding
The research leading to these results received funding from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Grant DE-FG02-03ER15393.
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All authors contributed to the conception and design of the systems. Preparation of the compounds and data collection were performed by EO. Analysis of the data was performed by EO, TAM, and ALM. The first draft of the manuscript was written by EO. All authors contributed to writing the final manuscript.
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Odella, E., Moore, T.A. & Moore, A.L. Tuning the redox potential of tyrosine-histidine bioinspired assemblies. Photosynth Res 151, 185–193 (2022). https://doi.org/10.1007/s11120-020-00815-x
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DOI: https://doi.org/10.1007/s11120-020-00815-x