Charge migration in DNA: Ion-gated transport

Electron hole (radical cation) migration in DNA, where the quantum transpor t of an injected charge is gated in a correlated manner by the thermal moti ons of the hydrated counterions, is described here. Classical molecular dyn amics simulations in conjunction with large-scale first-principles electron ic structure calculations reveal that different counterion configurations L ead to formation of states characterized by varying spatial distributions a nd degrees of charge localization. Stochastic dynamic fluctuations between such ionic configurations can induce correlated changes in the spatial dist ribution of the hole, with concomitant transport along the DNA double helix . Comparative ultraviolet tight-induced cleavage experiments on native B DN A oligomers and on ones modified to contain counterion (Na+)-starved bridge s between damage-susceptible hole-trapping sites called GG steps show in th e Latter a reduction in damage at the distal step. This reduction indicates a reduced mobility of the hole across the modified bridge as predicted the oretically.