Quantum chemical study of TiO₂/dopamine-DNA triads

Photoinduced charge separation in triads of DNA covalently linked to an anatase nanoparticle via a dopamine bridge was studied by ab initio calculations of the oxidation potentials of carboxyl-DNA trimers and the TiO₂/dopamine complex. Conjugation of dopamine to the TiO₂ surface results in a lower oxidation potential of the complex relative to the surface and in localization of photogenerated holes on dopamine, while photogenerated electrons are excited into the conduction band of TiO₂. Linking dopamine to the DNA trimers at the 5′ end of the oligonucleotide may lead to further hole migration to the DNA. Calculations show that for several different sequences hole migration is favorable in double stranded DNA and unfavorable in single-stranded DNA. This extended charge separation was shown to follow from the redox properties of DNA sequence rather than from the modification of DNA's electron donating properties by the dopamine linker, which explains experimental observations.