Sodium sensor with extraordinary selectivity: A synthesis of calixarenes that are highly selective for the sodium ion was achieved. Particularly noteworthy is a calixcrown 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. Calixarene 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.