On the distance-independent hole transfer over long (A • T)n-sequences in DNA

Electron holes can travel through DNA double strands over long distances in a multistep 'hopping' process. But the influence of the DNA sequence on this process is still not understood in all details. We have carried out new experiments to understand the recent observation that the efficiency of the hole transport between guanines (G). which are separated from each other by long adenine - thymine (A (.) T) sequences, is nearly independent of the length of the (A (.) T)(n) sequence for n greater than or equal to 4. For this purpose, a new synthesis of the modified adenosine 16 and its incorporation into a DNA double strand was worked out. Subsequent experiments demonstrated that the hole transport between GGG units and the H2O trapping of the guanine radical cation display similar rates. We conclude that the charge must be already partially equilibrated before being trapped by Thus, the weak distance effect is caused not only by the rate of the hole transport, but also by its equilibration over the (A (.) T)(n) sequence.