The Rigakubu News

Disclaimer: machine translated by DeepL which may contain errors.


I have consistently been interested in artificially creating systems that behave like life through chemistry. Life is composed of chemical substances such as nucleic acids, amino acids, and lipids. While individual substances are "dead," the aggregate of these substances, life, is "alive. Why is this so? How can we achieve the same thing artificially?

My interest in artificial systems such as life was nurtured during my time in the Faculty of Science. As an undergraduate, I did my thesis research in Prof. Mitsuhiko Shiotani's laboratory and learned the basics of supramolecular chemistry. Supramolecular chemistry is a thematic study of interactions between molecules. A supramolecular viewpoint is essential to understand and reproduce biological phenomena that consist of complex and sophisticated interactions among a wide variety of molecules. In the beginning, it was difficult even to reproduce the results of existing experiments, and there were a series of failures. The fact that I was able to learn the basics of experimentation through such trial and error is a great asset for my later life in research. In addition, Dr. Yusuke Takezawa, who directly supervised me, gave me many clues to materialize my interests. One of them is nonequilibrium systems. A system in which there is no inflow of energy or matter from the outside settles down to an equilibrium state with no change in temperature or concentration. Life, however, takes in energy and matter from the outside in the form of light and food, and maintains a state of non-equilibrium. This non-equilibrium state gives rise to life-like behaviors such as perception, locomotion, self-propagation, and information processing. At that time, non-equilibrium systems were beginning to attract attention in the context of supramolecular chemistry, and I felt that I had found my path.

I was particularly intrigued by the study of molecular machines, i.e., machines of miniscule size. I decided to study under Dr. David Leigh at the University of Manchester, a world leader in this field. During my doctoral studies, I immersed myself in research on the Brownian ratchet, the fundamental mechanism of molecular machines. The working principles of molecular-sized machines are very different from those of ordinary macroscopic machines. At its core is the Brownian ratchet principle. This prevents the random motions of molecular machines caused by thermal fluctuations (Brownian motion), which dominate on the molecular scale, from reversing in undesirable directions, thus realizing unidirectional motion. Although there are still only a few examples of such a realization in artificial systems, we have succeeded in building a molecular pump based on this principle and have analyzed it theoretically (see figure). Recently, more and more attempts are being made to apply the Brownian ratchet principle to non-equilibrium systems other than molecular machines, and its deepening and generalization are urgently needed. It was an irreplaceable experience for me to freely launch the project while discussing with my colleagues from all over the world, and to overcome numerous difficulties to complete it.

Autonomous molecular pump. The long, thin molecule on the right is the pump, which pumps the crown ether into the catchmentregion by reacting with the fuel molecule (chemicalfuel) inside the ring molecule (crown ether). The Brownian ratchet mechanism, in which a portion of the chemical fuel binds to the pump and prevents the brown ether from falling back into the solution, allows multiple amounts of crown ether to be pumped in succession. It looks simple, but it took one year of conception and one year of experimentation to realize it (credit: Stuart Jantzen).

In recent years, the environment surrounding basic research has been harsh in both the East and the West. However, if applied research is to build "useful" houses and skyscrapers, basic research is to find and pioneer the continents that will serve as the foundation for such buildings. Genitsu Kita, the founder of the Kyoto School of Chemistry, is said to have advised Kenichi Fukui, "If you want to do applied research, do basic research," and these words will remain true. The possibilities of non-equilibrium chemistry are unknown, but I would like to continue my efforts to explore them, believing that they are part of a vast continent.


September 2023 issue

A Door to the Future