July 10, 2014 12:00 am JST

X-ray diffraction marks 100 years by being more important than ever

TAKURO KUSASHIO, Nikkei staff writer

TOKYO -- The United Nations has proclaimed 2014 the International Year of Crystallography to commemorate 100 years since the discovery of the diffraction of X-rays by crystals.

     That discovery led directly to the development of crystallography to study matter at the molecular and atomic levels.

     X-ray diffraction has helped produce some of the great discoveries of modern science, including that of the double-helix structure of DNA.

Developments from developments

The technique is still an essential tool for cutting-edge science today. And now private companies are even using it for product development.

     In 1912, German physicist Max von Laue shot X-rays at a crystal to measure the rays' trajectories. The points he observed in concentric circles on the developed photographic plates were the diffraction patterns for the crystals involved. He had discovered X-ray diffraction.

     The following year, the British father-son team of William Henry Bragg and William Lawrence Bragg studied these diffraction patterns and proposed the fundamental law of X-ray diffraction, which has come to be known as Bragg's law.

     The Nobel Prize in physics was awarded to von Laue in 1914, and to the Braggs in 1915. Japanese physicist Torahiko Terada was also a pioneer in X-ray diffraction studies, but he missed his chance for a Nobel as he published his findings in 1913, in the British scientific journal Nature, after the Braggs did.

     "With the advent of X-ray diffraction, light has been shed on the structure of a variety of materials," said Tetsuya Ishikawa, director of the SPring-8 Center at Riken, a Japanese government-backed research institute. The center is now one of the premier facilities in the world for powerful X-ray research.

     The technique is based on the diffraction that occurs as X-rays travel through a crystal. When the short-wavelength electromagnetic waves knock into the atoms of the crystal, their trajectories are scattered. Depending on the spacing between atoms, the peaks and troughs of the waves can become more pronounced or can cancel each other out, resulting in a flecked X-ray diffraction pattern with telltale signs of the structure of the crystal under study.

     During the 1920s and '30s, scientists used X-ray diffraction to study the structure of common substances like benzene. After World War II, the tool also began being applied in biology. In 1953, Francis Crick and James Watson used the technique to clarify the molecular structure of DNA -- at the Cavendish Laboratory in England headed by Lawrence Bragg.

     It has been used for other Nobel Prize-winning work, including the analysis of the structure of hemoglobin, which transports oxygen in the blood, and the structure of penicillin, the world's first antibiotic.

New business tool

Most substances take on a crystal structure comprising an orderly arrangement of atoms and molecules. Compounds can be made of the same elements, but when their atomic arrangements differ, so too do their crystal structures. Even these small differences can be detected using X-ray diffraction.

     With the advances in analysis techniques and high-performance computers, now even researchers who are not crystallography experts can use the tool to determine the structure of unknown compounds.

     While it remains an important tool of cutting-edge science, it is now also finding greater use by industry. Japan's large synchrotron radiation facility, the SPring-8, which boasts one of the highest resolutions of its kind, has been in service since 1997. For many years, use by industry accounted for just 5% of the total, but today that ratio is up to around 20%.

     Some interesting products have resulted based on these studies from SPring-8. One prime example is the fuel-saving tires developed by Sumitomo Rubber Industries.

     One way to improve the fuel performance of a vehicle is to reduce tire resistance due to deformation as the tires roll over the road. But if tire resistance is reduced too much, the car will have trouble stopping on wet pavement.

     Sumitomo Rubber solved this problem by studying the internal structure of tire rubber through X-ray diffraction. Those studies revealed that friction resistance increased due to the clumping together of silica particles mixed into the rubber to improve grip. Based on the findings, the company devised a material that prevented this clumping, yielding a tire with both improved grip and better fuel performance.

     "We succeeded because we could analyze the structure of the material with submicron precision," said section chief Hiroyuki Kishimoto.

     Another example is the cavity-fighting chewing gum developed by candy and gum maker Ezaki Glico.

     In the early stage of cavity formation, acids produced by bacteria dissolve crystals of phosphorus and calcium, causing demineralization of the tooth down to a depth of several hundred microns. Dental caries, or tooth decay, will result if this process continues.
     With the help of X-ray diffraction, Ezaki Glico determined that teeth can be remineralized by gum containing a proprietary synthetic compound the company calls phosphoryl oligosaccharides of calcium. "We could see that this made beautiful crystals and were able to verify the effect," said Tomoko Tanaka of the Glico Institute of Health Sciences.

     Other products developed with the help of this technique include lightweight concrete, highly durable artificial joints and a shampoo that adds luster to hair.
     More companies that once looked at X-ray diffraction as a technology for future investment are now realizing that it is an essential tool for product development.

     Japan Synchrotron Radiation Research Institute, which operates the SPring-8 facility, is now making a greater effort to encourage companies to use its machines. Groundbreaking new products should result from companies using SPring-8 and the neighboring Sacla X-ray free electron laser facility.

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