Liquid Crystalline Phases of DNA

The DNA molecule is the support of the genetic information. It is a right-handed double helix, 22 angstrom in diameter, and 50 nm in the persistence length. The two strands of the helix are complementary in their nucleotide sequence with about 10 nucleotide pairs per helical turn. DNA is a long and strongly charged heteropolymer. It bears on average one elementary negative charge per each 0.17 nm of the double helix. In the late 1940s, the ability of duplex DNA to form liquid crystal (LC) phases when hydrated was known. Since that time, the LC phases of solutions of duplex B-form DNA (B-DNA) have been extensively characterized. The chain length N of DNA ranges from mega-base pair (bp) semiflexible polymers down to approximately 100 bp rigid rodlike segments. These studies of long DNA (lDNA) have revealed cholesteric, columnar hexagonal and blue liquid crystalline phases. In 2007, Michi Nakata and his collaborators found nematic and columnar liquid crystal phases in the short complementary B-form DNA oligomers with 6 to 20 base pairs in length. Structural study shows that these phases are produced by the end-to-end adhesion and consequent stacking of the duplex oligomers into polydisperse anisotropic rod-shaped aggregates, which order into liquid crystals.