Planning, executing and assessing the validity of SANS contrast variation experiments.

Small angle neutron scattering (SANS) along with contrast variation (CV) can provide key information that is used to determine the shape and structure of biological complexes in solution. The successful SANS CV experiment is usually a result of judicious planning, careful execution and meticulous scrutiny of the resultant SANS data. A workflow for planning, executing and, importantly, assessing the validity of SANS CV data is presented here, along with tips to follow in order to perform a successful SANS CV experiment. Some knowledge of the basics of small angle scattering is assumed, including data reduction and standard analysis to obtain model independent parameters such as the radius of gyration and forward scattering intensity, and SANS CV theory is not covered in detail. Rather, the focus is on the SANS CV workflow from in silico experiment planning and execution to obtaining the SANS CV data, assessing its validity, and determining a model structure or ensemble of structures using the SANS CV data as constraints.