Magnetic ordering of DNA liquid crystals

Sonicated calf thymus DNA with an average length of approximately 100 base pairs has been found to form a cholesteric liquid crystal at a concentration of approximately 250 mg of DNA/mL of solution. Immediately after preparation, small ordered domains of a few micrometers are formed, resulting in an opaque solution. This liquid crystal can readily be oriented in the magnetic field of an NMR magnet, resulting in a clear birefringent phase. The DNA molecules align with their helix axes perpendicular to the field so that the cholesteric pitch axis was parallel with the field. A pitch length of approximately 2.5 microns for the cholesteric phase was determined both from optical measurements (optical light rotation) and from NMR measurements (solvent diffusion). The observation that DNA molecules can be magnetically oriented opens up new possibilities for studying the structure and dynamics of the aligned DNA molecules.