Proton-Coupled Electron Transfer Drives Long-Range Proton Translocation in Bioinspired Systems

ODELLA, EMMANUEL; WADSWORTH, BRIAN L.; MORA, S. JIMENA; GOINGS, JOSHUA J.; HUYNH, MIOY T.; GUST, DEVENS; MOORE, THOMAS A.; MOORE, GARY F.; HAMMES-SCHIFFER, SHARON; MOORE, ANA L.

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

AMER CHEMICAL SOC

Año: 2019 vol. 141 p. 14057 - 14061

0002-7863

Proton-coupled electron transfer (PCET) combines the movement of fundamental charged species to form an essential link between electron- and proton- transport reactions in bioenergetics and catalysis in general. The length scale over which proton transport may occur within PCET processes and the thermody- namic consequences of the resulting proton chemical potential to the oxidation reaction driving these PCET processes have not been generally established. Here we report the design of bioinspired molecules that employ oxidation−reduction processes to move reversibly two, three, and four protons via a Grotthuss-type mechanism along hydrogen-bonded networks up to ∼16 Å in length. These molecules are composed of benzimidazole moieties linking a phenol to the final proton acceptor, a cyclohexylimine. Following electrochemical oxidation of the phenol, the appearance of an infrared band at 1660 cm−1 signals proton arrival at the terminal basic site. Switching the electrode potential to reducing conditions reverses the proton translocation and resets the structure to the initial species. In addition to mimicking the first step of the iconic PCET process used by the Tyrz-His190 redox relay in photosystem II to oxidize water, this work specifically addresses theoretically and experimentally the length scale over which PCET processes may occur. The thermodynamic findings from these redox-driven, bio- inspired ?proton wires? have implications for under- standing and rationally designing pumps for the generation of proton-motive force in artificial and reengineered photosynthesis, as well as for management of proton activity around catalytic sites, including those for water oxidation and oxygen reduction.