Design of successive ion conduction paths in DNA films with ionic liquids

Abstract

Ion conductive DNA films were prepared by two methods. A DNA with salt containing PEO mixture gave a flexible film, and that showed ionic conductivity of about 10⁻⁶ S cm⁻¹ at room temperature. The second method gave successive ion conduction paths in DNA films with ionic liquids. When cytosine and adenine, as low molecular weight model compounds, were neutralized with acids, their melting points (T_m) were considerably decreased. These results encouraged us to prepare ionic liquid domains in DNA by the neutralization of the bases. However, the neutralization of DNA with fluoroboric acid gave a powder and it showed a low ionic conductivity. Although all adenine and cytosine moieties, about 50% of total bases in the DNA, were expected to yield ionic liquids, this was not sufficient to form a continuous ion conductive domain in the film. When ethylimidazolium tetrafluoroborate (EtImBF₄) was added to the DNA neutralized with HBF₄, a film was obtained even after adding 93 wt% of EtImBF₄ and, correlatively, very high ionic conductivity of 5.05 × 10⁻³ S cm⁻¹ was observed at 50 °C.