Electronic coupling between Watson-Crick pairs for hole transfer and transport in desoxyribonucleic acid

Electronic matrix elements for hole transfer between Watson-Crick pairs in desoxyribonucleic acid (DNA) of regular structure, calculated at the Hartre e-Fock level, are compared with the corresponding intrastrand and interstra nd matrix elements estimated for models comprised of just two nucleobases. The hole transfer matrix element of the GAG trimer duplex is calculated to be larger than that of the GTG duplex. "Through-space" interaction between two guanines in the trimer duplexes is comparable with the coupling through an intervening Watson-Crick pair. The gross features of bridge specificity and directional asymmetry of the electronic matrix elements for hole trans fer between purine nucleobases in superstructures of dimer and trimer duple xes have been discussed on the basis of the quantum chemical calculations. These results have also been analyzed with a semiempirical superexchange mo del for the electronic coupling in DNA duplexes of donor (nuclobases)-accep tor, which incorporates adjacent base-base electronic couplings and empiric al energy gaps corrected for solvation effects; this perturbation-theory-ba sed model interpretation allows a theoretical evaluation of experimental ob servables, i.e., the absolute values of donor-acceptor electronic couplings , their distance dependence, and the reduction factors for the intrastrand hole hopping or trapping rates upon increasing the size of the nucleobases bridge. The quantum chemical results point towards some limitations of the perturbation-theory-based modeling. (C) 2001 American Institute of Physics.