Long-distance charge transport through DNA. An extended hopping model*

Abstract: Long-distance transfer of a positive charge through DNA can be described by a hopping model. In double strands where the (A:T)n bridges between the guanines are short (n ≥ 3), the charge hops only between guanines, and each hopping step depends strongly upon the guanine to guanine distances. In strands where the (A:T)n sequences between the guanines are rather long (n ≥ 4), also the adenines act as charge carriers. To predict the yields of the H2O-trapping products one has to take into account not only the charge-transfer rates but also the rates of H2O-trapping reactions. In the 1990s, the question of long-distance electron transfer through DNA raised a controversial dis-cussion [1]. We entered this area three years ago by studying radical-induced DNA strand cleavage reac-tions. Our experiments showed that photolysis of a 4'-acylated nucleoside in the DNA double strand 1 yields radical cation 2 that selectively oxidizes guanine (G) and forms a guanine radical cation (G•+) in 3 (Fig. 1) [2]. This reaction sequence led to an assay that made it possible to follow the charge migration through DNA by trapping of the positive charge at the heterocyclic base [3]. In order to understand the experimental results, we suggested in 1998 a hopping mechanism [3] for long-distance charge transport through DNA, which is based on the theoretical model of Jortner [4]. A similar hopping mechanism, which is slightly different in the details, was also suggested by Schuster [5], and today there is a con