X-rays and neutrons for the study of DNA structure, hydration, and transitions

X-ray fibre diffraction methods have provided a major contribution to our understanding of a wide variety of biological polymers. However they are less effective for study of location of water and hydrogen atoms in these systems. Here neutron methods can provide vital information. The ability to deuterate biopolymers either throughout the entire molecule or in a more specific way adds a powerful dimension to work aimed at investigating hydration patterns or hydrogen positions and changes that occur during water-driven transitions. The purpose of this paper is to demonstrate how X-ray and neutron fibre diffraction methods can provide powerful probes of polymer structure when used in a genuinely complementary way.Two examples illustrating these issues are described. The first describes an X-ray fibre diffraction study of the A–B structural transition in natural DNA. The second describes preliminary results from the first neutron fibre diffraction study of a selectively labelled DNA polymer carried out on the instrument D19 at ILL using samples prepared in the ILL-EMBL Deuteration Laboratory.