Research Director: Dr. Seiji Shinkai
(Professor, Faculty of Engineering, Kyushu University)
Research Term: 1990-1995

This project studied calixarenes and other compounds while aiming to establish ‘artificial’ high-precision chemirecognition systems comparable to those found in living systems. The establishment of a methodology for artificial recognition systems will make a substantial contribution to the creation of superior molecular sensors, artificial enzymes, new types of separation systems, and a variety of intelligent elements with high precision and selectivity, environmental resistance and wide utility.

Research Results

Sodium sensor with extraordinary selectivity: A synthesis of calixarenes that are highly selective for the sodium ion was achieved. Particularly noteworthy is a calix[4]crown derivative which shows sodium-ion selectivity of 10⁵ against the potassium ion, i.e., two orders of magnitude higher than the previous world record (10³), thus providing valuable information for designing highly selective ion sensors.

Novel lanthanide-based luminescence-emitting system: Calixarene derivatives were designed as ligands to form complexes with lanthanide ions. Several complexes with Tb or Eu were successfully synthesized which emit luminescence with extremely high quantum yields, representing a great contribution to designing organic luminescent elements with high quantum yields.

Saccharide-sensing system: A novel saccharide system has been established in which boronic acid moieties are utilized to recognize saccharide molecules and to read-out the recognition in the form of a physical signal: 1) Liquid crystal: The stability of the helical structure of a cholesteric liquid crystal is differently affected by the difference in the structure of an added saccharide/cholesterol boronic acid complex, thus producing a different color change which depends upon the type of saccharide in the complex. 2) Fluorescence: Novel compounds were synthesized which emit fluorescence upon binding to saccharides under neutral pH conditions. Even chiral discrimination of saccharides was achieved with a specific fluorescent diboronic compound, a world first. 3) Gelation: The gelation behaviors of saccharide/cholesterol phenylboronic acid complexes differ depending upon the type of the saccharide, a phenomenon which can be applied to the detection of saccharides.

Purification of fullerenes: It was found that the C₆₀ fullerene can be separated from other fullerenes using a specific calixarene. Calix[8]arene forms a complex selectively with C₆₀, resulting in a aggregated larger molecule that is easily precipitated, thus greatly reducing the separation costs and make the standard chromatographic method obsolete.

Molecular assemblies: The π-A isotherms of calixarene- or cholesterol-based amphiphilic compounds have demonstrated the selective recognition of metal ions and saccharide molecules, where the cholesterol-based amphiphilic compounds are of particular interest, because of the chiral discrimination of saccharides.

·An intelligent liquid crystal to read out saccharide structure as color-change

·A top view of C₆₀inclued in calix[8]arene