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
