Present status and future directions of research in electron-transfer mediated by DNA

This commentary article presents an overview of recent experimental results on DNA-mediated electron transfer (ET) from the perspective of semiclassical ET theory. The question concerning whether or not DNA can act as a wire is addressed, Much of the article focuses on a discussion of the decay of electronic coupling (beta) between electron donors and accepters with increasing donor/acceptor separation in DNA and in protein systems. In particular, the dependence of the electronic coupling itself (H-AB) on the energy gap between the tunneling energy of the reactants and the virtual ionic states of the DNA bridge is highlighted. The article concludes by suggesting that future experimental and theoretical work in this field should focus on the tunneling gap energies of the systems studied and that special attention should be paid to systems that are likely to be in the "small tunneling gap" regime. It is these systems that are expected to exhibit enhanced electronic couplings and consequently enhanced rates of long-distance ET.