Molecular Interaction of Imidazolium-based Ionic Liquids with a DNA-Oligonucleotide

Abstract

A self-complimentary 14-mer (7-TA) double stranded DNA oligonucleotide and a representative set of ILs from the imidazolium family were selected to determine the degree to which the ILs intercalate within the DNA. Steady-state and time-resolved fluorescence measurements were made using the dye 4,6-diamidino-2-phenylindole (DAPI) in buffer solutions with varying IL concentrations. DAPI was selected because it is known to bind to the minor groove of AT-rich sections of DNA. Various control experiments were made against which we compared the results from DNA/IL solutions. Steady-state excitation and emission spectral maxima shift for DAPI/DNA in the presence of the C16mim and C10mim ILs. This shows that both of these ILs bind to the minor groove of the DNA and displace the DAPI. The observed thresholds for IL concentration were ~5µM and ~40µM, respectively. The C4mim had no significant effect on the DAPI/DNA complex. Time-resolved measurements also support the conclusion that ILs displace DAPI from the minor groove, though apparently at a lower IL concentration threshold than the steady-state measurements suggest. The lifetime and anisotropy time constants suggest that the IL threshold concentrations are ~3µM and ~10 µM. Differences between the threshold concentrations will be discussed.