Proton coupled electron transfer (PCET) was studied in a Photosystem II mimic [Ru(bpy)2(phen-imidazole-Ph(OH)(tBu)2)]2+, in which Ru(III) generated by a flash-quench experiment with methyl viologen oxidizes the phenol and the proton is transferred to the hydrogen-bonded imidazole base. In contrast to related systems, the donor and acceptor are strongly coupled and the PCET reaction occurs by a stepwise electron transfer/proton transfer mechanism. The bimolecular recombination reaction, reduction of the phenoxyl radical by the viologen radical cation, was also examined as the analogy to reduction of the PSII tyrosyl radical by the oxygen evolving complex. In our mimetic system, the recombination reaction is concerted, nonadiabatic with respect to proton and electron movement, and exhibits an unexpected inverse kinetic isotope effect.

Tyrosine-histidine mimic with stepwise oxidation and concerted reduction by proton coupled electron transfer

251st National Meeting (2016)

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