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 ks extrapolated to the DNA surface coverage ΓDNA → 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.