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Celebrating 100 years of X-ray crystallography

  • A commemorative stamp released by India Post
    A commemorative stamp released by India Post

A commemorative stamp released by India Post.

A little over hundred years ago, in 1912, German scientists Max von Laue, Sommerfield and others were out skiing in the mountains, when von Laue discussed an idea that he was nurturing for sometime: to know how atoms are arranged in table salt, all you have to do is to let X-rays pass through the grains of salt and do some analysis. Of course, this does need some advanced training, but it is a simple way to know the inner structure of materials. What von Laue probably didn’t expect that his insight would revolutionise the way humans look at materials, ranging from table salt to complex biological molecules like the DNA. In 1914, Max von Laue was awarded the Nobel Prize in physics for this great discovery. British scientists W.H. Bragg and W.L Bragg continued von Laue’s work, and in 1915 became the first father and son team to win a Nobel Prize in physics. Thus began the era of X-ray crystallography, now a time-tested and hugely successful tool to explore the inner structure of matter. So far, as many as 26 Nobel Prizes have been won for discoveries involving X-ray crystallography, including the celebrated discovery of the braid structure of the DNA. Today X-ray crystallography plays a major role in man’s fight against deadly diseases including cancer and the HIV. The Mars Rover launched by NASA to Mars, has an X-ray crystallography unit to study minerals on the red planet. To celebrate the 100th anniversary of the recognition of von Laue’s pioneering work, and to increase public awareness about X-ray crystallography, the United Nations has declared 2014 the International Year of Crystallography.

Most of the solid materials (and a few liquids as well) we come across in our daily lives, have their atoms or molecules (group of atoms) arranged in a highly orderly fashion. Such materials are said to be crystalline. Examples vary from table salt to materials used in making aeroplanes and rockets. The most popular exception is glass. The arrangement of atoms (or molecules) in a crystalline solid is unique to each material. This means that no other material has its atoms arranged in the way they are arranged in table salt, for example. Moreover, table salt manufactured anywhere in the world will have the same arrangement of atoms, barring a few discrepancies which crop up randomly. The DNA has the same double helical structure in all human beings, though we carry different genetic information. What is common to all these is that the distance between the individual atoms (or molecules) is in terms of few nanometers. That is extremely small; smaller than you can imagine. If you divide a centimeter into one crore equal parts, each part will measure one nanometer. For example, a sheet of paper is one lakh nanometer thick; our nails grow one nanometer in length in one second, and the width of the human hair is 80,000-1,00,000 nanometer. Interestingly, the wavelength of X-rays is also a few nanometers. When a wave of such a small wavelength enters a region between the atoms in the crystal, it gets deflected. The deflected waves produce a pattern when exposed to a photographic film. The pattern on the film is the signature of the material; no two materials produce the same pattern on the film. Scientists analyse this pattern and find information about the crystal structure that produced it. Of course, it’s a detective work: all a scientist has is the ‘signature’ of the material, and her job is to find out which material’s signature is that. This is the way humans have discovered the structure of table salt; this is what James Watson and Francis Crick did to find out the double helical structure of DNA. 

X-ray crystallography today is quite different from its humble beginnings a hundred years ago. Advances in the production of X-rays coupled with the advent of powerful computers has allowed X-ray crystallography to grow leaps and bounds in the last few decades.  According to the ‘Worldwide Protein Data Bank’, structures of almost one lakh proteins have been found out so far, and the list is only expected to grow more. Today, X-rays are produced by accelerating electrons to very high speeds in huge circular machines called synchrotrons. UK’s Diamond Light Source, is one such machine, which can produce X-rays that are 100 billion times more energetic than a those produced by machines to check for fractures in bones. Recently, a group of scientists from the University of Oxford, University of Reading and Pirbright Institute used the Diamond Light Source to design better vaccines to foot-and-mouth disease which claimed thousands of heads of cattle in Karnataka in 2013.

In the Indian context, X-ray crystallography has played a fundamental role in some of the recent technological strides like the development of Light Combat Aircraft, Tejas. As a nation we must be proud of G N Ramachandran (1922 - 2001) of Indian Institute of Science, whose work on biological structures is considered to be of Nobel calibre. The ‘Ramachandran Plot’ is used by protein crystallographers all over the world. The Indian Institute of Science, the IITs, and the Universities in India use X-ray crystallography to peek into the inner structure of different materials and biological molecules. Indian scientists are also using X-ray crystallography to design cheap drugs for some of the deadliest diseases. If they become successful, then that would be a fitting tribute to Laue and his colleagues who heralded the era of X-ray crystallography on a skiing holiday, about a hundred years ago.