Interstrand Charge Transport within Metallo-DNA: the Effect Due to Hg(II)- and Ag(I)-Mediated Base Pairs
Abstrakt
Metallo-DNA is considered promising in regard to functional molecular electronic elements. From this perspective, the longitudinal charge transport within metallo-DNA is usually studied.
By contrast, this work was aimed at the transversal conductance of metallo-DNA, particularly at the effect of Hg and Ag metals on the conductance of base pairs. The charge transport through metal-mediated base pairs involving Hg(II) and Ag(I) metals, deoxythymidine (T) and 4-deoxythiothymidine (Ts), was studied by means of density functional theory (DFT) calculations employing the non-equilibrium Green's function (NEGF) method and electronic coupling calculations.
The calculations showed that the conductance along the base-to-base charge transport pathway was significantly enhanced mainly due to the Hg(II)-mediated linkage. This work further showed that not only the metals within the metallo-base pair but also the substitution of the O4 atom in deoxythymidine by sulfur (the Ts nucleoside) enhanced molecular conductance as in the case of Ts-Ag(I)(2)-Ts.
The bias charge transport for T-Ag(I)(2)-T was less effective than the transport for a TT mismatched base pair. The Ag orbitals participated in the highest occupied molecular orbital (HOMO) of T-Ag(I)(2)-T and Ts-Ag(I)(2)-Ts in contrast to negligible participation of Hg orbitals in the HOMO of T-Hg(II)-T.
Therefore, a Coulomb blockade effect can be assumed particularly for Ag-mediated base pairs as was apparent from the plateau obtained for the calculated I/V dependencies. The Ag-mediated base pairs can, thus, be potentially utilized as molecular transistors.
In addition, the metallo-base pairs anchored to gold electrodes mediated by sulfur preferred hole transport against the electron transport mechanism. This work highlighted the importance of electronic compatibility between the organic DNA scaffold and a particular metal that is essential for effective charge transport through metallo-base pairs (M-base pairs).