The mechanism of long-distance radical cation transport in duplex DNA: Ion-gated hopping of polaron-like distortions

The irradiation of an anthraquinone derivative that is covalently attached to duplex DNA injects a radical cation into the bases of the DNA. This radical cation can migrate hundreds of Angstroms before it is trapped at GG steps by reaction with water. These damaged guanines result in DNA strand scissions when they are treated with piperidine. Investigation of several such DNA constructs reveals that the efficiency of radical cation migration is strongly dependent on the sequence of bases in the DNA. This observation led to the formulation of the phonon-assisted polaron hopping model for the mechanism of radical cation migration. In this model, DNA and its ionic and solvent environment are assumed to undergo motions on the timescale of the radical cation hopping. These motions lead to a distortion of the local environment around the radical cation that causes it to gain stability (the polaron). Thermal motions of the DNA and its environment (phonons) cause the radical cation to migrate adiabatically from one polaronic site to another.