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Structure and dynamics

Web life: Crystallography365

08 Jan 2015
Taken from the January 2015 issue of Physics World

So what is the site about?

A little over a year ago, an eclectic group of (mostly) Australia-based researchers set themselves a challenge. On each day of 2014, they vowed, one of them would write a blog post about the crystal structure of an element, molecule or bulk material – one for every day of the United Nations International Year of Crystallography. As of early December 2014, they were tantalizingly close to completing their mission, with posts on more than 320 materials ranging from α-amylase (an enzyme in saliva that aids digestion of sugars) to zircon (a tough, diamond-like mineral found in some of the world’s oldest rocks).

Who is behind it?

The Crystallography365 website lists 33 authors, drawn from fields as diverse as chemistry, solid-state physics, structural biology and (of course) crystallography itself. Most are PhD students or early-career researchers, with a scattering of undergraduates and a few senior scientists who serve as “activators” in this scintillating mixture (see what we did there?). The project’s co-ordinator, Helen Maynard-Casely, works as an instrument scientist at the Bragg Institute in Sydney, Australia (named in honour of the pioneers of X-ray crystallography, William and Lawrence Bragg), and several other authors are likewise affiliated with its parent body, the Australian Nuclear Science and Technology Organisation (ANSTO).

What are some of the crystal structures that are covered?

The four crystals in the collection that begin with the letter “D” nicely illustrate its variety and, by extension, the importance of crystallography across many scientific fields. First up is diamond, one of three allotropes of carbon to get a blog entry of its own (buckminsterfullerene, graphite and tetrahedral amorphous carbon are the others). Next comes a mineral, diopside, whose structure was the first to be determined by studying how the intensity (rather than just the position) of peaks of diffracted light varies with the angle of incidence. The structure of the third “D” crystal, disulfide bond proteins, was discovered much more recently; these protein-folding enzymes help give structure to the walls of bacteria, and are thus a promising target for new antibacterial drugs. The final “D” in the collection is DNA, the subject of a blog post on 25 July – the birthday of Rosalind Franklin, whose X-ray crystallography images proved crucial to understanding the structure of this “molecule of life”.

Anything else of note?

The collection contains no fewer than 10 entries for water ice, from the hexagonal variety found in snowflakes (Ice Ih) to Ice XV. The latter substance, which was only discovered in 2009, is an ordered crystal that forms at low temperatures (below 150 K) and high pressures (around 1 GPa). There is also an entry for Ice IX – a real substance, but one that fortunately lacks the extraordinary properties attributed to it in Kurt Vonnegut’s science-fiction novel Cat’s Cradle (which was published 10 years before Ice IX’s real-life discovery). The emphasis on ice is partly Maynard-Casely’s doing: some of her previous research focused on the behaviour of ices under pressure, with particular applications to “ice giant” planets such as Uranus and Neptune.

Why should I visit?

Compared with some of its predecessors (particularly 2009’s International Year of Astronomy), the International Year of Crystallography received relatively little attention from the physics community – including, it must be said, in the pages of Physics World, which mentioned it only a handful of times. That’s a shame, because as Crystallography365 shows time and again, there is plenty of physics both in the techniques of crystallography and in what those techniques can reveal about the composition of the natural world. So, as physicists begin to celebrate the International Year of Light in 2015, it’s worth taking a moment to reflect on this one particular application of light and the riches of information it has yielded over the past century.

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