Sequence-Specific Electron Transfer Mediated by DNA Duplexes Attached to Gold through the Alkanethiol Linker.

Ability of the DNA double helix to transport electrons is its critical feature, underlying a number of important biological and biotechnological processes. Here, we show that electron transfer (ET) from the gold electrode to the DNA-bound methylene blue (MB) mediated by the DNA base-pair π-stack is less efficient in (dGdC)-rich duplexes compared to pure (dAdT) DNA. The ET rate constant k _s extrapolated to the DNA surface coverage Γ _DNA → 0 is 121 ± 8 s ^-1 for (dAdT) ₂₅ , being almost twofold higher than 67 ± 3 s ^-1 shown for (dGdC) ₂₀ , consistent with the electric-field-disturbed submolecular structure of the (dGdC) ₂₀ duplex earlier shown at electrified interfaces. DNA-mediated ET occurs both to MB intercalated and thus perfectly π-stacked into the (dGdC) ₂₀ duplex and to MB solely groove-bound to (dAdT) ₂₅ . For both (dGdC) ₂₀ and (dAdT) ₂₅ , ET is less efficient than ET in DNA duplexes of a mixed dA, dT, dG, dC composition. The results suggest new interpretations of the biological ET processes that may occur in dsDNA of different compositions at polarized interfaces.