Reorganization energy, activation energy, and mechanism of hole transfer process in DNA: A theoretical study

The density functional calculations with aug-cc-pVDZ basis sets on cationic guanine-cytosine (GC+) and adenine-thymine (AT+) base pairs suggest that the cationic charge is almost entirely localized on the G and A units with significant changes in the N-H and NO distances around the H-bonded area. While the calculated intramolecular reorganization energy (λv) for a GC base pair (0.75 eV) is remarkably larger than that for an isolated G base (0.49 eV), for the AT base pairs these values (0.44 and 0.40 eV) are almost the same. The gas phase activation energies (Ea) for GC+ GC→ GCGC+, AT+ AT→ ATAT+, and GC+ AT→ GCAT+ hole transfer processes are 0.19, 0.11, and 0.73 eV with rate constants of 1.69× 1011, 3.15× 1011, and 4.61 (0.168) s-1, respectively, at 298 K. An alternative mechanism of hole transfer has been proposed on the basis of energy barriers.