Vol.1, No.2, 77-85 (2010) doi:10.4236/jbpc.2010.12010 Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/JBPC/ Journal of Biophysical Chemistry Distance-dependent coherent charge transport in DNA: crossover from tunneling to free propagation Natallia V. Grib 1* , Dmitry A. Ryndyk 2 , Rafael Gutiérrez 3 , Gianaurelio Cuniberti 3 1 Department of Micro- and Nanoelectronics, Belarusian State University of Informatics and Radioelectronics, Minsk, Belarus; *Corresponding Author: ngrib@uvic.ca 2 Institute for Theoretical Physics, University of Regensburg, Regensburg, Germany 3 Institute for Material Science and Max Bergmann Center for Biomaterials, Dresden University of Technology, Dresden, Germany Received 8 June 2010; revised 4 July 2010; accepted 10 July 2010. ABSTRACT Using a tight-binding model, we investigate the influence of intra- and interstand coupling pa- rameters on the charge transport properties in a G-(T) j -GGG DNA sequence and its (G:C)-(T:A) j - (G:C) 3 duplex attached to four electrodes. De- pendences of the transmission function and of the corresponding conductance of the system on the number of bridging sites were obtained. Simulation results of a recently proposed two- strand superexchange (tunneling) model were reproduced and extended. It is demonstrated that the crossover from strong to weak dis- tance-dependent charge transport is elucidated by a transition from under-barrier tunneling mechanism to free over-barrier propagation in the coherent regime, controlled by temperature and coupling parameters. The role of DNA- electrode coupling has been also considered. It was found that an asymmetry in the DNA-elec- trode coupling has a drastic effect on the con- ductance leading to an increase in delocaliza- tion of the electronic states in the DNA duplex. Keywords: DNA; Electron Transport; Modeling of DNA; Electronic Structure of DNA 1. INTRODUCTION The discovery of charge migration in deoxyribonucleic acid (DNA) stimulated intensive investigations of the electronic properties of DNA due to their significance in biosynthesis and radiation-induced damage and repair processes [1-3]. Furthermore, considerable interest in nanodimensional structures of DNA possessing unique self-assembling and self-recognition properties has in- creased the last decade in connection with the possibility of the development of molecular nanoelectronic devices which are expected to provide high storage of informa- tion and high-speed signal processing within a wide temperature range [4-6]. In fact, DNA molecules can be well combined with silicon technology transcending the potential of the present quantum wires and are supposed to be used in modern computer technology as a binary data structure by applying a programmable linear self- assembly of the sequence of complementary nucleic base pairs of DNA [7,8]. Until now numerous experimental and theoretical data on charge migration through DNA molecules show an apparently contradictory behavior which can be eluci- dated by supposing two primary mechanisms. They in- clude the single-step superexchange (tunneling) charge transfer that is strongly dependent on length of a mo- lecular chain, and the multi-step hopping mechanism that is characterized by a weak change in the charge transfer efficiency (CTE) with increasing of the donor- acceptor distance in the double helix [9-11]. However, experimental measurements of DNA molecule do not give any unequivocal evidence in favor of one or other mechanism of charge transfer in DNA. Many of them demonstrate a combined hopping-superexchange mech- anism with a transition from the coherent superexchange to the thermally induced incoherent hopping process. Beside electron transfer experiments, also transport experiments became an important field of modern re- search. In transport measurements a molecule is placed between metallic leads and steady-state current can be produced by finite voltage. A direct measurement of electrical transport through single biological molecules, such as DNA and peptides [12,13], is a very appealing, although challenging, issue in molecular electronics be- cause of the potential peculiar capabilities of forming self- assembled nanodevices at the molecular scale. Quantum transport experiments through single DNA oligomers This work was funded by the Deutsche Forschungsgemeinschaft (SPP 1243) and Collaborative Research Center SFB 689.