On the Possibility of Superfast Charge Transfer in DNA

Numerous experiments on charge transfer in DNA yield a contradictory picture of the transfer: on the one hand they suggest that it is a very slow process and the charge is almost completely localized on one Watson-Crick pair, but on the other hand they demonstrate that the charge can travel a very large distance. To explain this contradiction we propose that superfast charge transitions are possible between base pairs on individual DNA fragments resulting in the establishment of a quasi-equilibrium charge distribution during the time less than that of charge solvation. In other words, we hypothesize these states irrespective of the nature of a mechanism responsible for their establishment, whether it be a hopping mechanism, or a band mechanism, or superexchange, or polaron transport, etc., leaving aside the debates of which one is more advantageous. We discuss qualitative differences between the charge transfer in a dry DNA and that in a solution. In a solution, of great importance is the charge solvation which decreases the transfer rate $10^7 - 10^8$ times as compared with a dry DNA. We consider the conditions under which the superfast charge transfer in a DNA leading to quasi-equilibrium distributions of polarons in a duplex is possible. Comparison of calculated quasi-equilibrium distributions with the experiment testifies to the possibility of superfast tunnel transitions of a hole in a DNA duplex in a solution.