Mechanisms of Electron Transfer in DNA

It is generally believed that the bases in the centre of the double helix molecule form the pathway for electron transfer. The delocalized p-orbitals in consecutive bases overlap to form a channel for the movement of electrons [7]. The works of Ladik et al. [40] and Bakhshi et al. [41] have led to the assumption that the transmission channels are along the long axis of the DNA molecule [101, 107-109]. Several mechanisms have been given for charge transport in DNA, but the dominant ones are the coherent transport via extended molecular orbitals, and the thermal hopping mechanism. 

In this case, there is a single step electron tunnehng through the potential barrier formed by certain base pairs [110]. This leads to an exponential decay of transmission with distance between the donor and the acceptor. The process is said to be coherent because the electron does not exchange any energy with the molecule during the transfer and the electron is never localized. 

For long distance electron transfer, thermal hopping or the incoherent mechanism dominates. In this case, the electron is localized on the molecule and moves in a series of steps. Evidence for this mechanism in DNA duplexes comes from the experiments of Nakatani et al. [111]. 

---