Chimeric Liquid Crystallinity:  Noncovalent Association of DNA and Bacterial Levan

Abstract

The liquid-crystalline phase of cell-free and nominally pure bacterial levan in water is shown to depend on the presence of DNA. The necessary concentrations of DNA are 2 orders of magnitude lower than those needed to stabilize a mesophase in aqueous solutions of DNA on its own and are similarly small in comparison to the number concentration of the globular levan molecules. A partial phase diagram for liquid crystallinity in the ternary system water/levan/DNA is mapped out. A model is proposed in which the levan and DNA associate noncovalently, to produce supramolecular, rodlike aggregates. The term “chimeric liquid crystal” is coined to denote a mesophase based on such rods assembled from otherwise unrelated molecular species. The model can account for several characteristics of the liquid-crystalline phase of bacterial levan, including the unexpected observation that liquid crystal phase formation is accompanied by a continuous increase in viscosity.

Supramolecular Liquid Crystallinity: Spherical Coils of Levan Surrounding Cylindrical Rods of DNA

“…column was used to remove both DNA and RNA, with purity being monitored by a combination of absorbance measurements, agarose gel electrophoresis, fluorescent molecular probes, and dynamic light scattering [16,17]. TPLM and turbidimetry showed that aqueous solutions of the purified levan had lost the ability to develop liquid crystalline order.…”

“…TPLM revealed a nematic liquid crystalline texture (of undetermined chirality), indistinguishable from that exhibited by solutions of as-received levan. Turbidity characterization enabled us to determine the ternary phase diagram for water/levan/ctDNA [16,17]. The concentra-tion of ctDNA needed to restore liquid crystallinity is 2 to 3 orders of magnitude smaller (by weight) than that of the levan.…”

“…The necessary DNA concentrations are also approximately 3 orders of magnitude lower than the critical concentration [18] for lyotropic behavior in solutions of pure DNA of comparable molecular weight. In terms of relative numbers of molecules, there are approximately 180 molecules of averaged sized levan present per average length DNA in the liquid crystalline phase [16,17]. This ratio is necessarily approximate because solutions are prepared by weight and both solutes are significantly polydisperse [16].…”