Vibrational Circular Dichroism Study of Isotropic and Liquid Crystalline Phases Formed by Guanine Quadruplexes

V. Andrushchenko¹, D. Tsankov², M. Krasteva³, H Wieser³ and P. Bouř¹

¹Institute of Organic Chemistry and Biochemistry, Academy of Sciences, Flemingovo nam. 2, Prague, 16610, Czech Republic

²Institute of Organic Chemistry, Bulgarian Academy of Sciences, BG-1113 Sofia, Bulgaria

³University of Calgary, Calgary, T2N 1N4, Canada

andrushchenko@uochb.cas.cz

One of the preferred conformations of guanine-rich nucleic acids in aqueous solutions is a four-stranded G-motif. Both oligonucleotides and monomeric guanosine monophosphates can form G-quadruplex structure at certain experimental conditions. At lower concentrations they represent an isotropic solution of four-stranded systems. However, above certain concentration these structures can self-associate and form liquid crystalline phases. Depending on the concentration two types of assemblies can be distinguished, cholesteric and hexagonal. The optical behaviour of these supramolecular systems can be most conveniently monitored in the infrared region by vibrational circular dichroism (VCD) spectroscopy. An abnormally high VCD intensity was observed for both liquid crystalline phases compared to the isotropic solution. The direction of the helical twist was obtained for guadruplexes as well as for their supramolecular aggregates.

Support from the Grant Agency of the Czech Republic (grant P208/10/0559 (VA), P208/11/0105 (PB)) and Academy of Sciences (grant M200550902 (PB)) is gratefully acknowledged.