Electronic coupling for charge transfer and transport in DNA

We calculated electronic matrix elements for hole transfer between adjacent nucleobases in DNA. Calculations of the matrix elements for intrastrand an d interstrand transfer were performed at the Hartree-Fock level employing t he 6-31G* and 6-311G** basis sets. The matrix elements for intrastrand hole transfer, for which a wealth of experimental solution data is available, a re almost independent of the basis set and exhibit an exponential interbase distance dependence, sensitivity to the donor-acceptor geometry, and depen dence on 5' --> 3' direction base sequence. The calculated intrastrand hole transfer matrix elements between adjacent thymines, v(+)(T,T) = 0.16 eV, i s in good agreement with the experimental estimate, v(+)(T,T) = 0.18 eV, in ferred from hole hopping in G(+)(T)(m)GGG (m = 1-3). The features of the nu cleobase bridge specificity for superexchange-induced hole hopping between guanines in G(+)XY...G (X,Y = T or A) were elucidated, with the prediction of enhanced efficiency of thymine relative to adenine as mediator. Informat ion on superexchange-mediated intrastrand and direct interstrand hole hoppi ng between guanine bases was also inferred. Our results for interstrand. ad jacent G(+)G coupling predict the existence of zigzagging pathways for hole hopping, in line with experiment.