Random-Sequence DNA Oligomers Make Liquid Crystals: A Case of Collective Ordering in a Superdiverse Environment

The availability of synthetic, analytical, and predictive tools makes DNA an ideal platform, not yet considered, to investigate statistical and soft matter physics. Here we report and interpret the equilibrium collective ordering in solutions of random-sequence DNA (rsDNA) oligomers of lengths L = 8 and L = 12. Despite the extreme molecular diversity inherent in rsDNA solutions, which for L = 12 are composed of 20 million distinct molecular species, these systems develop long-range columnar liquid crystal (LC) ordering when equilibrated at high osmotic pressure. By a combination of experimental models and computed statistics, we demonstrate that the residual end-to-end attraction between rsDNA duplexes, which typically terminate with various forms of pairing errors, is indeed sufficient to drive LC ordering. The resulting narrow range of isotropic-LC phase coexistence, in seeming contrast with the variety of phase behaviors of the species composing rsDNA, demonstrates that the (nearly) continuum distribution of molecular interaction strengths effectively reduces the tendency for demixing instead of enhancing it, in line with theoretical modeling.