A Quick Peek at X-ray Crystallography at the Diamond Light Source

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This is a short video recorded on a trip to the Diamond Light Source by a group of Imperial College crystallographers. The video attempts to give a flavor of the strange things that they do to protein crystals when trying figure out the structures of the molecules within them. Music, "Wavelength", is by Van Morrison.

X-ray crystallography is a technique for determining the precise arrangement of atoms within a crystal. To do this, a beam of X-rays strikes a pure crystal created from the molecule being studied, and the structure of that molecule diffracts the X-ray into many specific directions. This picture, which resembles a Rorschach inkblot test to the untrained eye, provides crystallographers (and their computers) with three-dimensional information about the density of electrons within the crystal. The electron density information provides valuable information about the nature of the chemical bonds, their disorder and various other information. Because atoms are surrounded by electrons, the angles and intensities of the diffracted X-ray beams also describe the "average" positions of atoms in the crystal.

Many materials form crystals, both inorganic and organic molecules, so X-ray crystallography has been fundamental in the development of many scientific fields. For example, crystallographer Rosalind Franklin's pictures provided Watson and Crick with critical information that allowed them to solve the structure of DNA and to then go on to win the Nobel Prize in Physiology or Medicine in 1962.

X-ray crystallography is still the primary technique used to characterize the atomic structure of new materials and in distinguishing molecules that provide similar experimental data, and for designing pharmaceuticals targeted against specific diseases.

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Rosalind was working on quasi-crystalline fibers of DNA, rather than bona fide crystals. Watson and Crick didn't so much "solve" the structure, at least not in the way a modern crystallographer would use that term, as construct a model that was consistent with a few characteristic distances that turned up in Rosalind's diffraction patterns. They used, what, less than 10 data points ? A crystal structure solved with experimental data uses multiple data sets each of which might have 10,000-100,000 data points (sometimes more, rarely less).

Watson and Crick's model was of course visionary in that it was subsequently amply validated by actual crystal structures. It was of an era where people used their brain more than their computer ;)