Photochemical tyrosine oxidation with a hydrogen-bonded proton acceptor by bidirectional proton-coupled electron transferElectronic supplementary information (ESI) available: Synthetic procedures, detailed experimental methods, kinetic analysis, fitting details, base concentration-dependent emission quenching data. See DOI: 10.1039/c2sc20113e

Amino acid radical generation and transport are fundamentally important to numerous essential biological processes to which small molecule models lend valuable mechanistic insights. Pyridyl-amino acid-methyl esters are appended to a rhenium( i ) tricarbonyl 1,10-phenanthroline core to yield rhenium-amino acid complexes with tyrosine ([Re]-Y-OH) and phenylalanine ([Re]-F). The emission from the [Re] center is more significantly quenched for [Re]-Y-OH upon addition of base. Time-resolved studies establish that excited-state quenching occurs by a combination of static and dynamic mechanisms. The degree of quenching depends on the strength of the base, consistent with a proton-coupled electron transfer (PCET) quenching mechanism. Comparative studies of [Re]-Y-OH and [Re]-F enable a detailed mechanistic analysis of a bidirectional PCET process. Photoinitiated tyrosine oxidation occurs by proton-coupled electron transfer (PCET) upon self-assembly of a modular scaffold incorporating a hydrogen-bonded proton acceptor.