Liquid Crystal Ordering and Isotropic Gelation in Solutions of Four-Base-Long DNA Oligomers

Liquid crystal ordering is reported in aqueous solutions of the oligomer 5′-ATTAp-3′ and of the oligomer 5′-GCCGp-3′. In both systems, we quantitatively interpret ordering as stemming from the chaining of molecules via a "running-bond" type of pairing, a self-assembly process distinct from the duplex aggregation previously reported for longer oligonucleotides. While concentrated solutions of 5′-ATTAp-3′ show only a columnar liquid crystal phase, solutions of 5′-GCCGp-3′ display a rich phase diagram, featuring a chiral nematic phase analogous to those observed in solutions of longer oligonucleotides and two unconventional phases, a columnar crystal and, at high concentration, an isotropic amorphous gel. The appearance of these phases, which can be interpreted on the basis of features of 5′-GCCGp-3′molecular structure, suggests distinctive assembly motifs specific to ultrashort oligonucleotides.