Takeshi Nagasaki

Novel conformational isomerism of water-soluble calix[4]arenes

Abstract The conformer distribution of 5, 11, 17, 23-tetrasulfonato-25, 26, 27, 28-tetramethoxycalix[4]arene (1) and 5, 11, 17, 23-tetrakis (trimethylammoniomethyl)-25, 26, 27, 28-tetramethoxycalix[4]arene (2) was estimated in an aqueous system. Surprisingly, these calix[4]arenes adopt a 1, 3-alternate conformation which has never been found as a major species in organic solvents but has been predicted to be most stable on the basis of computational studies.

Sugar sensing utilizing aggregation properties of a boronic-acid-appended porphyrin

Abstract It was shown that monosaccharides can be sensitively detected utilizing aggregation properties of a boronic-acid-appended porphyrin. Since the magnitude of the spectral change is correlated with the association tendency between sugars and boronic acids, the origin of the spectral change is related to the increase in the hydrophilicity in the sugar-binding site.

Calixarene-based molecular capsule

Abstract A molecular capsule was synthesized by the equimolar reaction of 5,11,17,23,29,35-hexakis(chloromethyl)-37,38,39,40,41,42-hexamethoxycalix[6]arene and 5,11,17,23,29,35-hexakis(mercaptomethyl)-37,38,39,40,41,42-hexamethoxy-calix[6]arene. The capsule is capable of “constrictive binding” of a guest molecule (N-methylformanilide).

Calixarene-Tetracyanoethylene Complexes. On the Selective Complexation with Calix[4]arene Conformers

Abstract The complexation behaviors of O-alkylated p-t-butylcalix[n]arenes (1nR), calix[n]arenes (2nR), and their noncyclic analogs were investigated in dichloromethane. All compounds formed a 1:1 complex with TCNE, indicating that complexation with the first TCNE suppresses further complexation with the second TCNE. The λmax values for the CT complexes with 16R and 18R (496-498 nm) were comparable with those for the noncyclic analogs, whereas the λmax values for the CT complexes with 14R shifted to longer wavelengths (525-567 nm): the order (from longer to shorter wavelength) for 14Prn is 1,3-alternate > partial cone > 1,2-alternate > cone. The association constants (K) for 14R were small in comparion to the λmax. It was shown on the basis of 1H NMR measurements that “out” - 14R (four alkyl groups are turned outward) is sterically-stable but cannot accept TCNE because of steric crowding on the benzene ring whereas “in” -14R 14R (one alkyl group is turned inward) is sterically-unstable but can provide a room to accept TCNE. In 14R, therefore, the complex formation occurs in conjugation with “out”-to-“in” displacement. This is the first example for the selective CT complexation with calix[4]arene conformers.

Attempts to change the color of dye molecules by saccharides

Abstract Azobenzene derivatives bearing a phenylboronic acid moiety changed their colors in response to added saccharides. On the basis of detailed spectral studies the color change was ascribed to deaggregation of dye molecules induced by complexation with these saccharides.

Sugar-induced color and orientation changes in a cyanine dye bound to boronic -acid-appended poly(L-lysine)

Abstract A cyanine dye (2) can be orientated on boronic-acid-modified poly(L- and D-lysine)s (L- and D-1, respectively) in the presence of saccharides. The main driving-force for the association is the electrostatic attraction between cationic 2 and the anionic center developed by complexation of the boronic acid residue with saccharides. The chiral orientation can be monitored by a CD spectroscopic method: it is mainly governed by the chirality of 1 but not by the chirality of saccharides. This is a novel system to control the dye orientation which occurs owing to the cooperative action of both naturally-originated α-amino acids and saccharides.

Molecular design of hard-soft ditopic metal-binding sites on a calix[4]arene platform

Abstract Ditopic “hard”-“soft” metal binding-sites composed of four EtS(CH2)nNHCOCH2O-groups were designed for the first time on a calix[4]arene platform. N = 2 is too short to form a bimetallic complex whereas n = 6 is long enough to accept two metal ions. 1H NMR spectral studies established that although Cd2+ bound to the “soft” binding-site excludes Na+ out of the “hard” binding-site, Ag+ can be co-existent with Na+ in the ionophoric cavity.

Thiadiphosphetane disulfide as a metal extractant which shows high Ag+ selectivity

It was shown that cis-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,2,4-thiadiphosphetane 2,4-disulfide (1) acts as an excellent Ag+-selective extractant. Two-phase solvent-extraction and spectral examination with 1H and 31P NMR established that 1 forms a 1:1 complex with Ag+ using the P(=S)-S-P(=S) linkage designed in the rigid four-membered ring.