Effect of the reflectional symmetry on the coherent hole transport across DNA hairpins.

The coherent hole transfer in three types of DNA hairpins containing strands with adenine (A) and guanine (G) nucleobases has been studied. The investigated hairpins involve AGGAn, AGAGA, or (AG)A strands that connect the hole donor and hole acceptor located on opposite ends of hairpins. The positive charge transfer from the photo-excited donor to the acceptor is shown to be slower for AGGAn in comparison with AGAGA and (AG)A sequences. We have revealed that this is due to the reflectional symmetry of the last two sequences with respect to the axis passing through the middle base. As has been demonstrated, the symmetry of the sequence structure manifests itself in the reflectional symmetry of the energy eigenstates. In addition, it has been shown that (AG)A is the only symmetric sequence with a zero energy state in the middle of the LUMO tight-binding energy band. Based on our theoretical findings, we predict that the hairpin with this sequence should have the fastest coherent hole transfer rate among the class of base sequences studied.