Photochemistry of Quinone-Bridged Amino Acids. Intramolecular Trapping of an Excited Charge-Transfer State

Abstract

Linkages to amino acids that feature a chlorinated p-benzoquinone as a bridging group have been prepared by reaction of 2,5-dichloro-p-benzoquinone or chloranil with the free amine groups of alanine and proline. Electron-transfer capabilities of these peptide conjugates have been assessed through cyclic voltammetry and laser flash photolysis measurements. Phototransients are observed (λmax = 410 nm) that cannot be assigned to either triplet or radical anion intermediates normally associated with quinones. These intermediates are associated with novel biradical zwitterions that result from intramolecular trapping of an aminoquinone excited charge-transfer (CT) state.