X-ray tomography on MX samples

The anomalous scattering properties of innate sulphur can be used to solve the phase problem in macromolecular crystallography (MX) via the SAD method. However, this method, which is used at longer X-ray wavelengths (1.5 – 2.5 Å), is still not a routine tool in MX. One of the difficulties associated with the longer wavelengths, is the increased absorption from both air and sample. So far, only empirical absorption algorithms exist, because of the difficulties of routinely and precisely measuring the shape of the absorbing objects. In this report [1], we present the use of X-ray microtomography to reconstruct the 3D shape of crystal, surrounding solvent and sample holder. The setup can be integrated within a general MX environment. The dose needed for the tomographic measurements could be low enough to allow the technique to be used for crystal integrity characterization and alignment.