Advances in X-ray scattering: from solution SAXS to achievements with coherent beams.

Small-angle X-ray scattering (SAXS) of macromolecular systems in solution has become an obvious complement to high resolution structural studies. Using SAXS, structural hypotheses can be directly tested against experimental data in solution. Conformational changes or complex formation can be monitored, and help understanding structure-function relationships. Additionally, the reliability of the data has been much strengthened by on-line purification approaches. Moreover, when coherent X-rays are used for sample illumination, SAXS patterns become speckled and can provide electron-density maps directly by computational phase-retrieval methods. Furthermore, X-ray free-electron laser with femtosecond pulse duration will enable us to take time-frozen images of biomolecules in solution free from radiation damage. In this paper, recent experimental and methodological advances in both classical and coherent SAXS are reviewed.