Pathway analysis on DNA charge transfer through adenine and guanine bridges

Long-range DNA charge transfer dynamics of 5'-GA_nGA _mG₃-3' (n = 1, 2, m = 1-3) sequences have been explored on a quantitative basis. First, the degree of coherence was determined in terms of coherence length. Second, relative contribution of charge transfer mechanisms such as incoherent (nearest-neighbor) hopping, through-bridge, and superexchange as well as G-hopping mechanism was assessed by the density matrix decomposition based on the path integral formalism. Finally, time evolution of individual trajectory contribution was investigated through pathway analysis. Although G-hopping pathways were indeed found to be crucial, we have also shown that the initial transfer is driven by the nearest-neighbor hopping pathways through energetically less favored adenines followed by G-hopping pathways. Therefore, not only the G-hopping pathways but also the through-adenine pathways govern the overall long-range DNA charge transfer. By placing guanines no farther than two adenines apart, one can fully utilize efficient tunneling between guanines for long-range DNA charge transfer.