Polaron Motion in DNA

We have shown that, for reasonable values of the parameters, stationary polarons, i.e., radical anions or cations extended over 5−7 base pairs, depending on base sequence, can exist in DNA. Here we report the results of an investigation of the drift motion of the polarons aimed at determining whether their formation can lead to rapid motion of charges introduced on DNA stacks. Starting from the same tight-binding Hamiltonian, we have used two different techniques for giving the polarons the kinetic energy required to make them move. We have applied these to the cases of DNA duplexes made up of (i) a single base pair repeated and (ii) a random sequence of base pairs, although we avoided sequences in which two guanines are next to each other. We find that the time required to deform the stack to produce a polaron after a hole or an extra electron is inserted into a DNA stack with uniformly spaced bases is ∼4 ps. For a DNA duplex made from the repetition of a single base pair, both theoretical techniques sho...