Charge transfer via a two-strand superexchange bridge in DNA

TL;DR

This paper investigates charge transfer in DNA using a tight-binding model and transfer matrix method, explaining weak distance dependence via a two-strand superexchange mechanism without multi-step hopping.

Contribution

It introduces a unistep two-strand superexchange model to explain charge transfer in DNA, challenging previous multi-step or dephasing explanations.

Findings

Weak distance dependence in long DNA chains explained by superexchange.

Crossover point M_c reflects intra- and inter-strand coupling ratios.

Model aligns with experimental observations of charge transfer in DNA.

Abstract

Charge transfer in a DNA duplex chain is studied by constructing a system with virtual electrodes connected at the ends of each DNA strand. The systeym is described by the tight-binding model and its transport is analyzed by the transfer matrix method. The very weak distance dependence in long (G:C)(T:A)_M(G:C)_3 DNA chain observed in experiment [B. Giese, et al., Nature 412, 318 (2001)] is explained by a unistep two-strand superexchange bridge without the need for the multi-step thermally-induced hopping mechanism or the dephasing effect. The crossover number M_c of (T:A) base pairs, where crossover between strong and weak distance dependence occurs, reflects the ratio of intra- and inter-strand neighboring base-base couplings.