International year of crystallography

Present year is being celebrated as International year of crystallography to commemorate the centennial of X-ray diffraction and the award of Nobel Prize to Laue and Bragg. It also marks the 400 th anniversary of Keplar's observation in 1611 of the symmetrical form of ice crystals. Many countries throughout world have released commemorative postage stamps and coins on this occasion. The commemorative postage stamp issued by India post (Fig 1) depicts a diamond crystal and the structure of curcumin, the active constituent of turmeric, as determined by X-ray crystallography. The diamond is known for its exceptional hardness and the flashes of light given off by its natural crystal structure. Curcumin is the compound responsible for the bright orange colour of turmeric. lt is known to exhibit biological, pharmaceutical and wide-ranging pharmacological activities such as antioxidant, anti-inflammatory, antimicrobial and anti carcinogenic. The stamp was released on 30 January 2014, in the Indian Institute of Science.

The study of crystals inner structure and properties gives us our deepest insight into the arrangement of atoms in the solid state. In the early 20th century, it was realized that X-rays could be used to ‘see’ the structure of matter in a non-intrusive manner. This marks the dawn of modern crystallography. When X-rays hit an object, the object’s atoms scatter the beams. Scientists discovered that crystals, because of their regular arrangement of atoms, scattered the rays in just a few specific directions. By measuring these directions and the intensity of the scattered beams, scientists are able to produce a three-dimensional picture of the crystal’s atomic structure. Thanks to X-ray crystallography, scientists can study the chemical bonds which draw one atom to another. Graphite and diamonds are composed of carbon but have different crystalline structure hence exhibit different properties. Graphite is opaque and soft whereas diamond is transparent and hard.

Crystallographers discovered that they could study biological materials, such as proteins or DNA, by making crystals of them. This extended the scope of crystallography to biology and medicine. Crystallography is now a truly interdisciplinary field   encompassing Physics, Chemistry, Biology, Medicine, Engineering and Maths. Rosalind Franklin took X ray image of DNA fiber that proved instrumental to Watson and Krick’s Nobel prize discovery of the double helix. She also studied structure of Carbon in coal and graphite and TMV.

Two thousand years ago, Roman naturalist Pliny the Elder admired ‘the regularity of the six-sided prisms of rock crystals.’ At the time, the process of crystallizing sugar and salt was already known to the ancient Indian and Chinese civilizations. Cane sugar crystals were manufactured from sugar cane juice in India. In China, brine was boiled down into pure salt crystals. Modern crystallography started with an attempt by Kepler in 1611 to understand the formation of ice crystals in terms of compact packing of six units around a seventh one. In 1771 Hauy showed that the shapes of crystals could be obtained by an appropriate 3D packing of identical parallelopipeds. During the 19th century modern geometrical crystallography developed with formal mathematical descriptions of crystals based on symmetry. A

complete theoretical geometrical background had been developed by the time X-rays were discovered by Rontgen in 1895. In 1912, Laue and his co workers carried out a revolutionary experiment which

demonstrated how X-rays travelling into a crystal interact with it and diffracted in particular directions depending on the nature of crystals. Laue's experiment marks the birth of radio-crystallography. Next year father and son team of WH Bragg and WL Bragg related the directions and intensities of the diffracted beams to the atomic structure of the crystals. They showed that X-rays can be used to determine accurately the positions of atoms within a crystal and thus unravel its 3D structure. Synchrotrons  (sources of intense X ray) enable archaeologists to pinpoint the composition and age of artefacts dating back tens of thousands of years, for instance, and geologists to analyse and date meteorites and lunar rocks. Crystallography allows us to understand and fabricate computer memories, showing us how proteins are created in cells and helping us to design powerful new materials and drugs. The Curiosity rover used X-ray crystallography in October 2012 to analyse soil samples on the planet Mars. NASA had equipped the rover with a diffractometer. The results suggested that the Martian soil sample was similar to the weathered basaltic soils of Hawaiian volcanoes. Crystallography is used to control the quality of processed drugs, including antiviral drugs, at the stage of mass production, in order to ensure that strict health and safety guidelines are met. Cocoa butter, the most important ingredient of chocolate, crystallizes in six different forms but only one melts pleasantly in the mouth and has the surface sheen and crisp hardness that make it so tasty.

Fig. 1: Commemorative postage stamp issued by India post on International year of crystallography