Proton Coupled Electron Transfer as Explored by the Tryptophan Cation Radical Formation in Biomimetic Peptides

Abstract

Proton coupled electron transfer (PCET) is a mechanism exploited by many biological processes including the oxygen evolving complex (OEC) of photosystem II. PCET functions largely by the formation of a stable radical species. One amino acid with the ability to form such a stable cation radical is tryptophan. In this study, biomimetic beta-hairpin peptides have been synthesized with a cross-strand interacting tryptohan residue. The peptides have been characterized by circular dichroism spectroscopy, to be further explored by electrochemistry and electron paramagnetic resonance (EPR) spectroscopy. These techniques will provide insight into the formation of the tryptophan radical, the factors influencing its stabilization, the effect of the local amino acid environment, and, ultimately, the fundamentals of proton coupled electron transfer.