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Crystallography: A Core Science?

Crystallography is the science underpinning crystallisation, as well as a basic understanding of atomic arrangement within solids and their resulting structures. The United Nations announced that 2014 would be the International Year of Crystallography (IYCr2014). IYCr2014 commemorates the 100th anniversary of X-ray diffraction according to Bragg’s Law (celebrated by the 1915 Nobel Prize for Physics), and the 400th anniversary of ice crystal symmetry by Johannes Kepler, who identified the critical role of symmetry in the solid state.

Since its inception in 1901, the Nobel Prize has been awarded 29 times to research groups using, or involving the use of, crystallographic methodologies and techniques1; including 18 Chemistry awards, 10 Physics awards and 1 Physiology/Medicine award (DNA helical structure; Watson, Crick and Wilkins, 1962). Nowadays, there is no branch of the natural sciences, structural or material sciences that does not heavily rely on crystallography. Gautam Desiraju (President, International Union of Crystallography) indicated that, ‘The benefits to mankind have been enormous and range from the discovery of medicines and drugs, to materials that make the quality of life better for all’ (IUCr, 2014).

Just over a century ago, von Laue (Nobel Prize in Physics, 1914) recognised that highly energetic photons (i.e. X-rays) would be required to observe compounds at the molecular level, i.e. 0.1 nanometres. Unfortunately, there is currently no equivalent to the ubiquitous ‘visible light’ microscope (390-700nm), when using X-ray crystallography. To overcome this problem, a crystal lattice is irradiated with an X-ray beam and the resulting diffraction pattern is used to re-construct the image of the original structure using mathematical modelling2. Karle and Hauptman were awarded the 1985 Nobel Prize in Chemistry for their work in using X-ray scattering techniques to determine the structure of crystals (the so called Direct Methods).

The last 100 years have seen structures of increasing complexity determined by X-ray crystallography. In 1923, the first organic molecular structure (hexamethylene tetramine) was solved, showing that molecules, and not just atoms, can make up the repeating unit of a crystal lattice. By the early 1950s, the first X-ray picture of a biological macromolecule, DNA, helped researchers to develop their understanding of the genetic code used in the development and functioning of most organisms (including many viruses). The first protein structure (myoglobin) was published soon afterwards and a decade later, the first enzyme (lysozyme) was solved2.

Synchrotron-generated X-rays, which produce highly energetic X-rays, were first used in 1970 to image muscle cells and eight years later the first atomic-scale image of a complete virus was produced. This structure demonstrated that viruses were surprisingly complex entities. Following on from this, ribosomes, the sub-cellular organelles that assemble proteins using encoded DNA, were imaged in 20002.

Recently, XFEL (X-ray free electron lasers) have been used to try to elucidate the structures of macromolecules that are difficult to crystallise3. Due to the very high energies utilised (many orders of magnitude greater than synchrotron-generated X-rays), even very small nanocrystals can be used. These X-ray pulses completely destroy the crystal, but as the X-ray pulse is generated over a very small time period (1 x 10-15 seconds or 1 femtosecond), a diffraction pattern can be readily generated in this timeframe4. Eventually, it is hoped that this approach could be used to produce ‘time-resolved’ images, i.e. every femtosecond, of biomolecules in a natural setting, including imaging molecular interactions.

However, despite these achievements, crystallography is still a relatively poorly understood science. IYCr2014 is intent on increasing public awareness of crystallography, its broad based applicability and how it is an essential science underpinning most recent technological advances. IYCr2014 will promote both basic learning and fundamental research into crystallography particularly in countries without large crystallography communities (IUCr, 2014). This will be achieved via collaborative interactions through the ‘OpenLab’ projects. This involves a series of world-wide lectures and practical initiatives for researchers, teachers and students from neighbouring and less developed countries. IYCr2014 will seek to embed crystallographic understanding into Africa, as well as Asia and Latin America and foster ‘North-South’ collaborations. The 2014 programme will also target young people via a worldwide educational initiative including conferences, exhibitions and a schools agenda with programmes such as a crystal growing competition. Finally, IYCr2014 will involve interactions with the large synchrotron and neutron radiation facilities across the world1.

References

  1. IUCr (International Union of Crystallography), 2014. http://www.iucr.org/people/nobel-prize. Accessed on 17th February 2014.
  2. Jones, N. Crystallography: Atomic secrets. Nature 505 (2014) 602-603.
  3. Waldrop M. M. X-Ray science: The big guns. Nature 505 (2014) 604-606.
  4. McSweeney S., Fromme, P. Crystallography: Sources of inspiration. Nature 505 (2014) 620-621.

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