Abstract
The charge transport properties of DNA have made this molecule very important for use in nanoscale electronics, molecular computing, and biosensoric devices. Early findings have suggested that DNA can behave as a conductor, semiconductor, or an insulator. This variation in electrical behavior is attributed to many factors such as environmental conditions, base sequence, DNA chain length, orientation, temperature, electrode contacts, and fluctuations. To better understand the charge transport characteristics of a DNA molecule, a more thorough understanding of the electronic coupling between base pairs is required. To achieve this goal, two mathematical methods for calculating the electronic interactions between base pairs of a DNA molecule have been developed, which utilize the concepts from Molecular Orbital Theory (MOT) and Electronic Band Structure Theory (EBST). The electronic coupling characteristics of a B-DNA molecule consisting of two Guanine-Cytosine base pairs have been examined for variation in the twist angle between the base pairs, the separation between base pairs, and the separation between base molecules in a given base pair, for both the HOMO and LUMO states. Comparison of results to published literature reveals similar outcomes. The electronic properties (metallic, semi-conducting, insulating) of a B-DNA molecule are also determined.
Highlights
The B-DNA molecule is considered to be a potential building block for molecular electronics due to its self-assembly and self-recognition properties
The electronic coupling t is very dependent on the motion of the base pairs with respect to each other (Figure 2), where t varies significantly for twist angle φ = 0° to 72 °
The following parameter values are used: the separation distance between the two base pairs of z = 3.375Å, a typical bond length of the B-DNA bases of d0 = 1.36 Å, η ppσ = 5.27 η ppπ = −2.26, an average of the van der Waals radii for C, N, and O atoms of D = 2.85 Å, and adjustment parameter values C of 0.025x10−40 eVÅ4 for HOMO and 3.4x10−40 eVÅ4 for LUMO
Summary
The B-DNA molecule is considered to be a potential building block for molecular electronics due to its self-assembly and self-recognition properties. The first method utilizes Molecular Orbital Theory, Linear Combination of Atomic Orbitals (LCAO) overlap integrals to calculate the bond integral parameter k values, which are used in a highly modified version of the extended Hückel method to determine the molecular orbital wave function coefficients. This more generalized form of the extended Hückel method was developed by essentially eliminating most of its assumptions and some of its limitations, resulting in more accurate values for the coefficients. The second method utilizes an amended version of the Slater-Koster relations from Electronic Structure Theory to acquire the necessary interatomic matrix elements This amendment was required due to the non-covalent interactions involved between the B-DNA base pairs. The reasons for discrepancies between the values presented in this paper and those of published literature [32] are discussed
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