Delocalization and electron transfer in polypeptides with different secondary structures

The polypeptide-mediated electron transfers (ET) in opposite directions are studied by analyzing the electronic structures. The electron delocalizations in polypeptides are mainly occurring from carboxyl end to amino end (direction A). The lowest unoccupied molecular orbital (LUMO) energies of the peptide subgroups decrease obviously along this direction. Accordingly, the ET in direction A would occur by the superexchange mechanism. The formation of intramolecular hydrogen bond may provide new tunneling pathway with lower energy barrier, and promotes the ET in direction A markedly. As to the ET in opposite direction, the thermally activated hopping mechanism should be adopted.