Directional Preference of DNA-Mediated Electron Transfer in Gold-Tethered DNA Duplexes: Is DNA a Molecular Rectifier?

Electrical properties of self-assembling DNA nanostructures underlie the paradigm of nanoscale bioelectronics, and as such require clear understanding. DNA-mediated electron transfer (ET) from a gold electrode to DNA-bound Methylene Blue (MB) shows directional preference, and it is sequence-specific. During the electrocatalytic reduction of [Fe(CN)₆ ]^3- catalyzed by DNA-bound MB, the ET rate constant for DNA-mediated reduction of MB reaches (1.32±0.2)10³ and (7.09±0.4)10³ s^-1 for (dGdC)₂₀ and (dAdT)₂₅ duplexes. The backward oxidation process is less efficient, making the DNA duplex a molecular rectifier. Lower rates of ET via (dGdC)₂₀ agree well with its disturbed π-stacked sub-molecular structure. Such direction- and sequence-specific ET may be implicated in DNA oxidative damage and repair, and be relevant to other polarized surfaces, such as cell membranes and biomolecular interfaces.