Abstract
In principle, DNAโmediated charge transfer processes can be categorized as either oxidative hole transfer or reductive electron transfer. In research on DNA damage, major efforts have focused on the investigation of oxidative hole transfer or transport, resulting in insights on the mechanisms. On the other hand, the transport or transfer of excess electrons has a large potential for biomedical applications, mainly for DNA chip technology. Yet the mechanistic details of this type of charge transfer chemistry were unclear. In the last two years this mechanism has been addressed in ฮณโpulse radiolysis studies with randomly DNAโbound electron acceptors or traps. The major disadvantage of this experimental setup is that the electron injection and trapping is not siteโselective. More recently, new photochemical assays for the chemical and spectroscopic investigation of reductive electron transfer and electron migration in DNA have been published which give new insights into these processes. Based on these results, an electronโhopping mechanism is proposed which involves pyrimidine radical anions as intermediate electron carriers.