Hydration of DNA: A neutron scattering study of oriented NaDNA

A preliminary neutron‐scattering study of wet‐spun oriented NaDNA samples with various contents of H2O or D2O has been performed to obtain information about the hydration of NaDNA. The preferred orientation was in the direction of the crystallographic c axis. Perpendicular to this direction the samples could be regarded as poly‐crystalline. It has been found that the preferred crystallite orientation was also reflected in the water structure. This fact, taken together with the small energy widths of the measured near‐elastic peaks indicates that water molecules in the sample are relatively strongly bound to the DNA helix either directly or via other water molecules. Angular distribution measurements of elastically scattered neutrons were performed with the momentum transfer vector directed along and perpendicular to the DNA helix axis. Different Debye‐Waller factors were obtained, indicating different water dynamics in the two directions. Comparison between the H2O and D2O measurements suggests that the difference is caused by motions of rotational nature. The shape of the frequency distribution function for the H2O molecules in the NaDNA sample was somewhat similar to that which has been measured in ice.