Introduction to X-ray crystallography

Haemoglobin crystals, 1960s

By studying X-ray diffraction photographs of crystals, scientists could calculate the arrangement of atoms within molecules. Some of the materials analysed occur naturally as crystals. Others, such as haemoglobin, have to be crystallised first. Crystallising a substance orders the arrangement of its atoms into a repetitive pattern, which makes it possible to interpret accurately the diffraction patterns it produces. Making a crystal of adequate quality to study is a complex process and can take considerable time.

Crystallographer: Max Perutz
Image: MRC Laboratory of Molecular Biology, Cambridge

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Introduction to X-ray crystallography

X-ray diffraction pattern from a haemoglobin crystal, 1962

When X-rays hit a crystal they scatter, producing a regular pattern of spots, which are recorded on a photographic plate. The crystal is rotated and a diffraction pattern is made from each angle. These images provide the information required to solve the structure of the crystal substance. Arriving at this solution involves the application of sophisticated mathematics and a repetitive process of refinement.

Crystallographer: Max Perutz
Image: MRC Laboratory of Molecular Biology, Cambridge

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Introduction to X-ray crystallography

Fourier drawing, 1957

This shows the process of mapping contours on an electron density map. The data from all the spots in a diffraction pattern can be combined to represent molecules in the structure of a crystal by applying a mathematical procedure known as a Fourier synthesis.

Image: MRC Laboratory of Molecular Biology, Cambridge

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Introduction to X-ray crystallography

W H Bragg and his spectrometer, c.1915

Father and son William Henry and William Lawrence Bragg shared the Nobel Prize in 1915 for their services in the analysis of crystal structure by means of X-rays. This image shows the elder Bragg with his spectrometer, a crucial piece of equipment that he had constructed while teaching at the University of Leeds.

Image: Royal Institution of Great Britain

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Introduction to X-ray crystallography

Reproduction of a page from W L Bragg’s notebook, c.1913

At the top of this page from one of W L Bragg’s early notebooks is a diffraction pattern. The dark spot at the centre is made by the X-ray beam; the diffraction of the beam by the crystal creates the surrounding dots.

Image: Royal Institution of Great Britain

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