Liquid crystal phase behavior of a DNA dodecamer and the chromonic dye Sunset Yellow

摘要

Sunset Yellow (SSY) is an aromatic heterocycle nano-sheet functionalized by hydrophilic sulphanate groups. SSY forms chromonic stacks and liquid crystal (LC) phases in aqueous solution. The DNA oligomer 5'- GCGCTTAAGCGC-3' is a self-complementary strand which forms duplexed B-form helices in aqueous solution, which, similarly, aggregate into chromonic stacks and form LC phases. Binary aqueous solutions of these two molecules were investigated using polarized optical microscopy, x-ray diffraction, and spectroscopy. At lower solute concentrations and/or higher temperatures these solutions form uniformly mixed single phases, including isotropic, chiral nematic, and hexagonal columnar LCs. At higher solute concentrations and/or lower temperatures, the uniform columnar solution separates into two columnar phases, one containing SSY with trace DNA and the other containing both SSY and DNA aggregates. The study of these solutions indicates that the mixed and unmixed phases are composed of single component SSY or DNA chromonic stacks, with the DNA stacks containing a small fraction of intercalated SSY, evidenced by structurally induced circular dichroism in the SSY absorption band. In the columnar monophase, the hexagonal lattice sites are occupied randomly by either DNA or SSY columns, with the column spacing varying continuously with the SSY-DNA mass ratio. The results demonstrate significant selectivity in the chromonic stacking of both molecules. The binding mode of these chromonic LCs may have applications to adaptive optics and nucleic acid chemistry.