Single Crystal Diffraction

Single crystal X-ray diffraction is the use of X-rays to examine a sample in which the constituent atoms or molecules are well ordered such that all crystal planes of the same type are aligned. Often it is only possible to see whether the sample is a single crystal by looking at its diffraction pattern. The high brightness of synchrotron radiation allows investigation of small single crystals, e.g. less than 0.15 mm3 for protein crystallography and typically 0.0001 mm3 for small molecule crystallography. The diffraction measurements are generally carried out to enable the internal three-dimensional structure to be deduced at atomic resolution. Much larger crystals are sometimes studied (by X-ray Diffraction Topography) to investigate such things as growth history, growth defects, and the physical properties of highly perfect material.

On the SRS, the technique is most widely employed in the structure solution and refinement of small molecules, macromolecules and even protein systems (such as viruses) although the apparatus used and limits to the structural information gained change according to the system under investigation. Likewise the size of the single crystal under investigation can vary depending upon its “quality”, the atom types (elements) present and the intensity of the incident X-ray source. Parameters such as: atom type, bond lengths, bond angles, non-bonded interactions, structural geometry, and the absolute structural confirmation of chiral moieties can be readily extracted from the processed data.

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