Long-range electron transfer in rigid 3(10)-helical oligopeptides containing redox cyclic alpha-amino acids

Intrahelical photoinduced electron transfer processes (ET) in conformationa lly restricted oligopeptides have been studied by nanosecond time-resolved transient spectroscopy. The helical peptides were constructed from sterical ly hindered a-aminoisobutyric acid (Aib) and two cyclic cu-amino acids (Bib class) bearing electron acceptor and donor side chains (DMNap, ThQx), This helical backbone design pro,ides high conformation stability, as previousl y demonstrated, and yields reliable 3(10)-helical architectures in solution . The forward ET between ThQx and (3)DKNap is followed by a slow back ET th us giving rise to an accumulation of the charge-separated ion pairs for hun dreds of nanoseconds. We demonstrate the modulation of electronic interacti ons by the number of intervening Aib residues separating acceptor-donor sid e chains and propose modifications of the peptide framework by inclusion of a non-Aib amino acid residue. These well-defined and sterically stable fra meworks are suited for the precise evaluation of intrahelical electron tran sfer processes mediated by peptides.