Right- and left-handed liquid crystal assemblies of oligonucleotides: phase chirality as a reporter of a change in non-chiral interactions?

Using molecular theory and coarse grained modelling, based on sequence dependent structural data, we have investigated the relationship between the sequence of oligonucleotides and their organization in the cholesteric phase. Despite the significantly different structure of the double helix, the same result has been found for all the investigated sequences: hard-core interactions would promote a right-handed cholesteric twist, whereas a change to a left-handed twist would be produced by electrostatic interactions. On the other hand, the structural differences between oligomers have been found to strongly influence the concentration at which the cholesteric phase appears. We propose that the sequence dependence of the cholesteric handedness, revealed by recent experiments (G. Zanchetta et al., Proc. Natl. Acad. Sci. U. S. A., 2010, 107, 17497), reflects a change in non-chiral interactions in DNA and RNA solutions under conditions of molecular crowding.