Effects Of Interfacial Couplings And Configuration Disorder On The Charge Transport Properties Of DNA

Desoxyribo-Nucleic-Acid(DNA)is a complicated biomolecular,which encodes the fundamental nature of living species.In recent years,the charge migration along the duplex DNA stack is attracting considerable interest for the biochemical reasons in life science,as well as for the possible applications in molecular electronics.A number of experiments have showed that,the product of electron transfer will lead to DNA mutation;light-induced electron transfer will damage DNA,or repair it to cure tumors.However,at present the mechanism of charge transport in DNA molecular is controversial.The experiments of charge transport in DNA molecular have shown that DNA molecular may be conductor,semiconductor or insulator.So how to interpret these controversial experiment phenomena and ravel the mechanism of charge transport in DNA molecular has important significance for using DNA as a molecular device and understanding of DNA mutation and repairing of the damaged DNA.The density of itinerant electrons is variable,not fixed.The electric channel of DNA is composed of theπ-electrons system.Because the component and structure of DNA molecular and the environment condition are of complexity and variety and have an effect on the the itinerant electrons of DNA,the number ofπ-electrons in principal chain is a changeable unknown one.DNA is a soft biomolecular.The charge transport in DNA is affected by many factors,such as the molecular configuration,the sequence of base pair,temperature, humidity,solution and impurity in the molecular.For the complicated structure of DNA molecule,people look for the appropriatest model at all times in order to study it.Up to now,several models like one-dimensional tight binding model,fishbone model,ladder model,three-dimensional tight binding model have been suggested to study the charge transport phenomenon of DNA.The effect of these factors on the electronic structure and the charge transport of DNA has been extensively studied. These theory works partly explain the diversity of charge transport in DNA.One dimensional tight binding model ignores the double helix structure of DNA,however, experiments have proved that the helix structure of DNA has important effects on the charge transport in DNA.Referencing D.Hennig's work,we suggest a three dimensionals tight binding model to describe DNA molecule.We have studied the effects of several factors on the charge transport in DNA with three dimensionals tight binding model in the paper.The primary content and results are given as follows:1.Effects of the itinerant electrons density on the electronic structure of DNA and the charge transport in it1.1 Due to the softness of DNA,the itinerant electrons of DNA have an important effect on its electronic structure and they may induce the conductivity of the DNA to change.A three dimensional tight binding model with electron-phonon interaction is adopted to study the effect of the density of itinerant electrons on the lattice configuration,electronic structure of poly(dG)-poly(dC)and both change with different density of itinerant electrons.It is found that the energy gap(the difference between the lowest unoccupied molecular orbit(LUMO)and the highest occupied molecular orbit(HOMO))changes with the density of itinerant electrons.DNA may show the behavior of conductor,semiconductor,or insulator with different density of itinerant electrons.1.2 The ground states,dopping states,configurations,electric charge distribution and the types of excitations were studied.It is found that the polaron is the main excitation when the DNA molecule was doped.It's consistent with the experimental conclusion.2.Effects of interfacial couplings between metallic electrode and DNA on charge transport in DNAUsing the three-dimensional tight-binding model and the matrix transfer method, effects of interfacial couplings on the charge transport properties of DNA molecule have been studied.The results indicate,when the interfacial couplings are ideal,both transmission coefficient and localization length of electrons are larger,molecule takes on better conductivity,while the case is contrary when the interfacial couplings are unideal.When molecule and metallic electrodes couple ideally,through voltage-current characteristic,it is found that the onset voltage of Poly(dG)-Poly(dC) is less than Poly(dA)-Poly(dT)counterpart,and the former's current is larger than the latter's in the same bias voltage,so the conductivity of Poly(dG)-Poly(dC)is better than Poly(dA)-Poly(dT)counterpart.3.Effects of configuration disorder effects on charge transport of DNA moleculeUsing the three-dimensional tight-binding model and the matrix transfer method, effects of disorder about the DNA sequence and helix structure on the charge transport of DNA molecule have been studied.Poly(dG)-Poly(dC)which is consisted of single G/C base pairs has better transmission coefficient and voltage-current characteristic; with the concentration of A/T base pairs increasing,the conductivity of DNA is obviously weakened.These indicate that the conductivity of DNA depends on its sequence intensively.Effects of helix structure disorder about the hydrogen bond length and helix angle on charge transport of Poly(dG)-Poly(dC)have been studied. The results indicate that the hydrogen bond length disorder has a significant effect on charge transport,while the case is contrary in the situation of helix angle disorder.