DNA strands robed with ionic liquid moiety

An ionic liquid domain was successfully prepared outside double-stranded DNA by fixing 1-alkyl-3-methyl-imidazolium (CnMI) cations on the phosphate groups of DNA. First, four species of ionic liquid were made using phosphoric acid di-n-butyl ester and CnMI (n=2,4,8, and 12) as a low molecular weight model. They were obtained as liquid salts, and their ionic conductivity ranged up to 10−5 S cm−1 at 50 °C. Based on this model study, counter cations of the phosphate groups of DNA were exchanged for four kinds of imidazolium cations. The resulting ionic liquid-robed DNA (IL-robed DNA) was soluble in ordinary organic solvents such as methanol or ethanol. Ionic conductivity was low, because the ion density was insufficient to form a continuous ionic liquid domain around the DNA strands. When 11 mol% 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), which is a typical ionic liquid, was mixed with the IL-robed DNA, an ionic conductivity of 5.4×10−5 S cm−1 at 30 °C was observed because a continuous ionic liquid domain was successfully formed.