Using anomalous small angle X-ray scattering to probe the ion atmosphere around nucleic acids.

Anomalous small angle X-ray scattering (ASAXS) exploits contrast variation methods to highlight the scattering from one elemental component in a multielement sample, such as one ion species in an ion-DNA system. The ASAXS method has been applied to measure ions condensed around short nucleic acid duplexes. This chapter, which briefly describes the origin of the ASAXS signal, focuses on the experimental methods required to carry out these measurements and the interpretation of the anomalous signals.