Long-range charge hopping in DNA

The fundamental mechanisms of charge migration in DNA are pertinent for cur rent developments in molecular electronics and electrochemistry-based chip technology. The energetic control of hole (positive ion) multistep hopping transport in DNA proceeds via the guanine, the nucleobase with the lowest o xidation potential. Chemical yield data for the relative reactivity of the guanine cations and of charge trapping by a triple guanine unit in one of t he strands quantify the hopping, trapping, and chemical kinetic parameters. The hole-hopping rate for superexchange-mediated interactions via two inte rvening AT base pairs is estimated to be 10(9) s(-1) at 300 K. We infer tha t the maximal distance for hole hopping in the duplex with the guanine sepa rated by a single AT base pair is 300 +/- 70 Angstrom. Although we encounte r constraints for hole transport in DNA emerging from the number of the med iating AT base pairs, electron transport is expected to be nearly sequence independent because of the similarity of the reduction potentials of the th ymine and of the cytosine.