  Wide-angle x-ray scattering (WAXS) is emerging as a powerful tool for
increasing the resolution of solution structure measurements of biomolecules.
Compared to its better known complement, small angle x-ray scattering (SAXS),
WAXS targets higher scattering angles and can enhance structural studies of
molecules by accessing finer details of solution structures. Although the
extension from SAXS to WAXS is easy to implement experimentally, the
computational tools required to fully harness the power of WAXS are still under
development. Currently, WAXS is employed to study structural changes and ligand
binding in proteins; however the methods are not as fully developed for nucleic
acids. Here, we show how WAXS can qualitatively characterize nucleic acid
structures as well as the small but significant structural changes driven by
the addition of multivalent ions. We show the potential of WAXS to test
all-atom molecular dynamics (MD) simulations and to provide insight in
understanding how the trivalent ion cobalt(III) hexammine (CoHex) affects the
structure of RNA and DNA helices. We find that MD simulations capture the RNA
structural change that occurs due to addition of CoHex.
