SPring-8, the large synchrotron radiation facility

A joint research group comprising RIKEN (President, Ryoji Noyori), the University of Tokyo (President, Junichi Hamada), Aoyama Gakuin University (President, Ken-ichi Semba), and JASRI (President, Yoshiharu Doi) developed a technique for visualizing chirality domains in crystalline substances with micron resolution using synchrotron radiation X-rays. The group was led by Hiroyuki Ohsumi (senior research scientist) and Masaki Takata (Group Director) from the Spin Order Research Team, Quantum Order Research Group, RIKEN SPring-8 Center (Director, Tetsuya Ishikawa); Taka-hisa Arima (professor) from the Graduate School of Frontier Sciences, the University of Tokyo (also the leader of the Spin Order Research Team); and Yusuke Kousaka (postdoctoral researcher) and Jun Akimitsu (professor) from College of Science and Engineering, Aoyama Gakuin University.

“Chiral” originates from the Greek word for “hand”, and chiral substances refer to substances that are not identical to their mirror image, similarly to human hands. Various sugars and amino acids that constitute human bodies are chiral substances and require strict matching of handedness in normal metabolism. For example, monosodium glutamate naturally found in kelp is a left-handed substance responsible for umami (i.e. fifth taste). In artificial synthesis, however, bitter right-handed monosodium glutamate is also produced. Therefore, only the substances with the desired handedness must be separated and purified for use in medicines, pharmaceuticals, and food additives. However, reagents and filters used for separation and purification are also made of chiral substances, that is, purification for purifiers is recursively required, which takes enormous labor and cost. The labor and cost of separation and purification can be greatly reduced if high-quality crystals of chiral substances with the same handedness can be grown. Thus, the development of a technique that enables such crystal growth is much needed. The conventional method described in Fig. 1 can be used to determine the fraction of left- and right-handed substances in aqueous solution but cannot tell which part of crystal is left- or right-handed. The understanding of the mechanisms behind such crystal growth is also limited.

To solve this problem, the joint research group has worked on the development of an X-ray microscope system at SPring-8^[1] for visualizing the difference in the handedness of substances. In this research, the group succeeded in three-dimensionally observing the distribution of left- and right-handed domains in the chiral substance cesium copper chloride (CsCuCl₃).

The achievements of this research will contribute to the understanding of the mechanism behind the crystal growth of chiral substances, leading to markedly improved technologies for producing medicines, pharmaceuticals, food additives, and even spintronics materials. In addition, new knowledge may be gained on the origin of the homochirality of life^[2], which has long been a mystery of living organisms.

The results of this research were published online in the German scientific journal Angewandte Chemie International Edition on 1 July 2013 prior to the paper version.

Publication:
"Three-Dimensional Near-Surface Imaging of Chirality Domains with Circularly Polarized X-rays"
H. Ohsumi, A. Tokuda, S. Takeshita, M. Takata, M. Suzuki, N. Kawamura, Y. Kousaka,J.Akimitsu, and T. Arima
Angewandte Chemie International Edition, 2013