Professor, Department of Applied Chemistry, Graduate School of Engineering, Kyushu University
Creating artificial nanofossils
—Transcription of diversified shapes of organic molecules into inorganic materials—
Silica nanotubes and right- and left-handed nanohelices are various types of silica superstructures, which have been created by Prof. Shinkai. He developed a method to transcribe various shapes of aggregated organic molecules into inorganic silica. In his method, a cholesterol-based gelator is added to a solution containing tetraethoxysilane (TEOS), which is then transformed into silica through polycondensation in the gel phase. The cations introduced into the cholesterol-based gelator attract negatively charged silanol oligomers, an intermediate between TEOS and silica, to the surface of the organic gel. After calcinating the cholesterol-based organic gel and removing the organogel templates from the gel, silica nanotubes with the template's shape transcribed into them remain. This process, through which various structures of organic materials are transcribed into inorganic substances, is similar to how fossils are formed from traces of ancient organisms. Silica superstructures are “artificial fossils on a nanometer scale,” according to Prof. Shinkai.
Prof. Shinkai has already succeeded in making both right- and left-handed helical silica nanotubes. Right- and left-handed inorganic products cannot be fabricated easily without special treatment because inorganic materials have no chirality, and therefore, organogel templates with chirality have made it possible to fabricate right- and left-handed inorganic products. Silica nanotubes produced through this method can be used as catalysts for asymmetric synthesis. The silica nanotubes are highly expected to be useful in making durable and inexpensive columns for separating mixtures of right- and left-handed organic molecules.
With this method, the shape of any organic compound can be transcribed into silica in principle. However, it is still very difficult to form organic molecular aggregates for use as the template during the gelation process. Therefore, Prof. Shinkai adopted combinatorial chemistry -- a method to find chemical compounds that can form targeted shapes, from a large number of various organic molecular groups. He has made a wide range of superstructures based on a diversified set of organic molecules and has transcribed these superstructures into silica. He is spreading the diversity of the organic chemistry into inorganic chemistry.
Prof. Shinkai is the project leader of “Functional Innovation of Molecular Informatics,” the 21st century COE program of the Ministry of Education, Culture, Sports, Science and Technology (MEXT). This is a grand scheme designed to develop the field of molecular informatics by integrating molecular chemistry and informatics. He says, “Molecules have various shapes and functions, and their information can be read optically or magnetically. It may be possible to create a database of molecular functions that is as extensive as, or more extensive than, that of proteins. I think we will be able to create molecular informatics matching bioinformatics by combining the database of molecular functions with informatics.”
His grand idea can be attributed partially to the locality of Kyushu Island, in southwestern Japan. He says, “People in Tokyo can get new information faster than people in the rest of Japan, and I envy them. However, there is also a negative aspect to the researchers being in Tokyo. They tend to shorten the periods of their studies because new information reaches them continuously. Therefore, we outside Tokyo carry out comparatively longer-term research with aims at big things.” He hopes young researchers pursue big themes rather than produce many papers on smallish ideas. How can researchers find big ideas? He says, “Researchers need to find the ideas on their own by attending academic conferences and reading papers. They have to think and find their own themes themselves and should not be passive.”
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