Happy hour for time-resolved crystallography

Researchers from the Department of Atomically Resolved Dynamics of the Max Planck institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Hamburg ...

New structure for human flu virus protein

Researchers from Oxford University have worked out the molecular structure of a protein that is vital for survival of the flu virus. Recently published in Nature, they used several different techniques to look at the arrangement ...

How to trick electrons to see the hidden face of crystals

The 3-D analysis of crystal structures requires a full 3-D view of the crystals. Crystals as small as powder, with edges less than one micrometer, can only be analysed with electron radiation. With electron crystallography, ...

X-ray laser sight reveals drug targets

Researchers from the Moscow Institute of Physics and Technology have published a review on serial femtosecond crystallography, one of the most promising methods for analyzing the tertiary structure of proteins. This technique ...

Molecular energy machine as a movie star

Researchers at the Paul Scherrer Institute PSI have used the Swiss Light Source SLS to record a molecular energy machine in action and thus to reveal how energy production at cell membranes works. For this purpose they developed ...

Plant discovery opens frontiers

University of Adelaide researchers have discovered a biochemical mechanism fundamental to plant life that could have far-reaching implications for the multibillion dollar biomedical, pharmaceutical, chemical and biotechnology ...

Virulence factor of the influenza A virus mapped in real-time

The influenza A viruses, which are responsible for deadly pandemics in the past, still remain a major global public health problem today. Molecules known as virulence factors are produced by bacteria, viruses, and fungi to ...

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Crystallography

Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.

Before the development of X-ray diffraction crystallography (see below), the study of crystals was based on their geometry. This involves measuring the angles of crystal faces relative to theoretical reference axes (crystallographic axes), and establishing the symmetry of the crystal in question. The former is carried out using a goniometer. The position in 3D space of each crystal face is plotted on a stereographic net, e.g. Wulff net or Lambert net. In fact, the pole to each face is plotted on the net. Each point is labelled with its Miller index. The final plot allows the symmetry of the crystal to be established.

Crystallographic methods now depend on the analysis of the diffraction patterns of a sample targeted by a beam of some type. Although X-rays are most commonly used, the beam is not always electromagnetic radiation. For some purposes electrons or neutrons are used. This is facilitated by the wave properties of the particles. Crystallographers often explicitly state the type of illumination used when referring to a method, as with the terms X-ray diffraction, neutron diffraction and electron diffraction.

These three types of radiation interact with the specimen in different ways. X-rays interact with the spatial distribution of the valence electrons, while electrons are charged particles and therefore feel the total charge distribution of both the atomic nuclei and the surrounding electrons. Neutrons are scattered by the atomic nuclei through the strong nuclear forces, but in addition, the magnetic moment of neutrons is non-zero. They are therefore also scattered by magnetic fields. When neutrons are scattered from hydrogen-containing materials, they produce diffraction patterns with high noise levels. However, the material can sometimes be treated to substitute hydrogen for deuterium. Because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies.

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