Refusing to twist: Demonstration of a line hexatic phase in DNA liquid crystals

We report conclusive high resolution small angle x-ray scattering evidence that long DNA fragments form an untwisted line hexatic phase between the ch olesteric and the crystalline phases. The line hexatic phase is a liquid-cr ystalline phase with long-range hexagonal bond-orientational order, long-ra nge nematic order, but liquidlike, i.e., short-range, positional order. So far, it has not been seen in any other three dimensional system. By line-sh ape analysis of x-ray scattering data we found that positional order decrea ses when the line hexatic phase is compressed. We suggest that such anomalo us behavior is a result of the chiral nature of DNA molecules.