Energetic control and kinetics of hole migration in DNA

Two elements of energetic control of charge migration in DNA involve the donor-bridge and the intrabridge energetics. These were applied for hole (positive ion) hopping transport via the guanines (G) (i.e., the nucleobase with the lowest oxidation potential) along the strand G⁺(T)_mG(T)_mG...G(T)_pGGG (m = 1-3, p = 1-4) of the duplex (containing N G bases), where hole trapping occurs via the GGG triple unit. The individual hopping rates and the trapping rate are mediated by off-resonance superexchange coupling with the thymine (T) bases. The size dependence of the chemical yield ratios reveals a crossover from an algebraic to an exponential asymptotic N dependence. From the asymptotic relation for the yield we infer that maximal distances for hole hopping are 70, 175, and 380 Å for the TTT, TT, and T bridges, respectively, which specify the initiation of chemistry over a large distance of several hundreds of angstroms in DNA. Time-resolved data serve as fingerprints for the diffusive-reactive processes of hole hopping. Finally, we examine the parallel superexchange-thermally induced hopping in a system characterized by a positive donor-bridge energy gap.