Charge transfer in DNA.: Sensitivity of electronic couplings to conformational changes

Electronic matrix elements for hole transfer between adjacent Watson-Crick pairs in DNA have been calculated at the Hartree-Fock SCF level for various conformations of the dimer duplexes [(AT),(AT)], [(AT),(TA)], [(TA),(AT)]. Example configurations of [(TA),(TA)] have also been extracted from molecular dynamics simulations of a decamer duplex. The calculated electronic coupling is very sensitive to variations of the mutual position of the Watson-Crick pairs. The intra-strand A-A interaction is more susceptible to conformational changes titan the corresponding inter-strand interaction. The rate of charge migration as measured by the square of the electronic coupling matrix element may vary several hundred-fold in magnitude due to moderate changes of the duplex conformation. Thus, thermal fluctuations of the DNA structure have to be taken into account when one aims at a realistic description of the electron hole transfer in DNA.