Tunneling Energy Effects on GC Oxidation in DNA

Abstract

Hole-mediated electronic couplings, reorganization energies, and electron transfer (ET) rates are examined theoretically for hole-transfer reactions in DNA. Electron transfer rates are found to depend critically on the energy gap between the donor/acceptor states and the intervening basesthe tunneling energy gap. The calculated distance decay exponent for the square of the electronic coupling, β, for hole transfer between GC base pairs (and pi-electron D/A pairs) ranges from 0.95 to 1.5 A-1 in the model structures as the tunneling energy gap varies from 0.3 to 0.8 eV (which we argue is the range of energy gaps for GC oxidation probed in recent experiments). We show that the tunneling energy gap depends on the ET reorganization energy, which itself grows rapidly with distance for ET over 1−5 base pairs. Inclusion of the distance dependence of reorganization energies for these hole transfer reactions gives the tunneling rates an apparent decay exponent of ∼1.5−2.5 A-1. We show that ET rates observed in DNA ...