Conformational Effects on the Electron-Transfer Efficiency in Peptide Foldamers Based on α,α-Disubstituted Glycyl Residues



Peptide foldamers based on α,α-disubstituted glycyl residues were synthesized and chemically characterized to investigate the effects of the electric field generated by a 310-helix on the rate of intramolecular photoinduced electron-transfer reactions. To this end, two new octapeptides having identical sequences were suitably side-chain functionalized with the same electron-transfer donor–acceptor pair, but inverting the position of the pair along the main chain. The electron-transfer rate constants, measured by time-resolved spectroscopy techniques (nanosecond transient absorption and time-resolved fluorescence), indicated that, in the case of the 310-helix, the electrostatic effect is significant, but smaller than that obtained for α-helical peptides. This finding can be likely ascribed to the distortion of the H-bond network with respect to the helical axis taking place in the former secondary structure. Overall, these results could have implications on electron-transfer phenomena in model and biomembranes facilitated by peptaibiotics.