Base pair dynamic assisted charge transport in DNA

An 1d model with time-dependent random hopping is proposed to describe charge transport in DNA. It admits to investigate both diffusion of electrons and their tunneling between different sites in DNA. The tunneling appears to be strongly temperature-dependent. Observations of a strong (exponential) as well as a weak distance dependence of the charge transfer in DNA can be explained in the framework of our model. Electronic transport is a ground to a wide range of important biological processes in DNA. Besides, the phenomenon has a fundamental physical interest, since the transport properties of biomolecules are expected to differ considerably from those of macroscopic conductors. And at last, very recently material scientists also turned their attention to charge migration in DNA for the development of DNA-based molecular technologies. Although first attempts to measure DNA conductivity [1], and to give a theory of the phenomenon [2] have been made almost 40 years ago, the question concerning charge transport through DNA remains unsettled, and there is an impressive quantity of unexplained or partially explained data. Different publications report frequently contradictory results. Two kinds of techniques for getting information on charge transport in DNA are used. First, direct or indirect electrical conductivity measurements on micrometer-long DNA ropes are performed [3–7]. Experimental results obtained in this technique are ambiguous. DNA conductivity σ was reported as almost metallic of the order 10 4 Ω −1 cm −1 [3] (in a recent publication [4] the authors claim they observed even proximity induced superconductivity in DNA) or semiconducting with σ ≃ 0.1 Ω −1 cm −1 [6]. Very recently experimental techniques have progressed to the point where the conductivity on individual 10nm long double stranded molecules was measured [7] and the result implies that DNA is a good insulator. Clearly this frustrating situation with conductivity measurements means that there are many relevant factors which can influence the charge transport in DNA by different way and which are hardly controlled in real experiments. The second technique, related to fluorescence quenching measurements on DNA strands, doped with donor and acceptor molecules [8–23], seems more reliable, and it is our main concern here. In this technique photo-excitation of a donor associated with the stack of base pairs in some fashion, allows transfer of an electron to the stack. The migrating electron is trapped finally at the acceptor site, and charge transfer is monitoring by the yield of a chemical reaction accompanying …