Takahiro Kaneda

Synthetic macrocyclic ligands. IV. Lithium ion-characteristic coloration of a “crowned” dinitrophenylazophenol☆

Abstract A “crowned” dinitrophenylazophenol shows a characteristic coloration only with lithium ion of alkali metal ions, as if an indicator.

Preparation of chiral and meso-crown ethers incorporating cyclohexane-1,2-diol derivatives as a steric barrier and their complexation with chiral and achiral amines

Abstract The design and synthesis of chiral crown ethers possessing a chiral recognition ability which carry great potential for separation of enantiomers and analytical purpose has become an important and rapidly growing field of host-guest chemistry. One of the advantages of crown ethers constructed using a synthetic chiral building block is that it is rather easy to modify the chiral cavity resulting in the improvement in enantiomer selectivity. Cyclohexane-1,2-diol derivatives such as cis -1-phenylcyclohexane-1,2-diol, trans -1-phenylcyclohexane-1,2-diol and trans - 1,2-diphenylcyclohexane-1,2-diol are of interest as chiral building blocks of crown ethers, because incorporation of these subunits into the 18-crown-6 framework causes a reduction in conformational flexibility of the chiral cavity and fixes the phenyl chiral barrier perpendicularly above the face of crown ring to modify enantiomer recognition ability. Chiral crown ethers of the 18-crown-6 type were synthesized using these building blocks and their chiral recognition behaviour in differential enantiomer transport through bulk liquid membranes were examined. Chiral azophenolic crown ethers containing cis -1-phenylcyclohexane-1,2-diol or cis -cyclohexane-1,2-diol which can bind neutral amines to form a stable complex and exhibit enantiorecognitive coloration in complexation with chiral amines were prepared and the association constants for their complexes with chiral ethylamine and ethanolamine derivatives were determined on the basis of UV-visible absorbance. The observed enantioselectivity is rationalized in terms of complementarity between a host and a guest as indicated by CPK molecular model examination. The alternation of the position of chiral barriers resulted in a reversal of the enantioselectivity. Crown ethers with diastereotopic faces can bind a guest to each side of the diastereotopic faces to form diastereoisomeric complexes which occasionally cause troublesome “sidedness” problems. In order to avoid the problems, most crown ethers previously prepared contained at least one C 2 axis of symmetry. However, diastereotopic face selectivity in complexation does provide helpful information on the complexing behaviour of crown ethers to assist in the design of more elaborate and structured host molecules. meso -Crown ethers having cis-1-phenylcyclohexane-1,2-diol were prepared and the diastereotopic face selectivity by their diastereotopic faces in complexation with achiral amines was examined by temperature-dependent 1H nuclear magnetic resonance. Ethanolamine is attached stereoselectively to one of the faces to give one of diastereoisomeric complexes and the alternation of the position of steric barriers led to reversal of the diastereotopic face selectivity. A prediction of which diastereoisomeric complex is formed is made on the basis of CPK molecular model.

Photoswitching of the association of a permethylated α-cyclodextrin-azobenzene dyad forming a Janus [2]pseudorotaxane☆

For achieving the on–off operation of the superstructure formation of hermaphrodite cyclodextrin derivatives, we synthesized azobenzene-modified permethylated α-cyclodextrins, 1 and 2. These compounds formed Janus [2]pseudorotaxanes in CD3OD–D2O mixtures. The E-Z photoisomerization of 1 by UV light irradiation resulted in the dissociation of the superstructure, but, by boiling the solution, the superstructure was recovered through the thermal isomerization of (Z)-1 to (E)-1. These processes could be repeated many times without any side reactions. This is the first example of the dynamic control of the [2]pseudorotaxane formation of modified cyclodextrins by external stimuli.

Synthetic macrocyclic ligands. III. Synthesis of a quinone-hydroquinone redox system incorporated with complexing ability toward cations

Abstract Two quinones bridged with a polyether chain and the corresponding hydroquinones were synthesized, and their redox reaction and complexations with sodium and potassium ions were observed.

Chiral recognition in molecular complexation for the crown ether–amino ester system. A facile FAB mass spectrometric approach

Various degrees of chiral recognition properties of chiral crown ether hosts toward amino acid ester guests are directly, easily and reliably evaluated by the enantiomer deuterium-labelled racemic guest method using conventional FAB mass spectrometry.

Synthetic macrocyclic ligands. VI. Lithium ion-selectivefluorescent emission with crowned benzo- and naphtho-thiazolylphenols

Abstract Synthesis of fluorescent crowned benzo- and naphtho-thiazolylphenols are described and lithium ion-selective fluorescent emission is observed under the restricted conditions.

The first Janus [2]rotaxane

The first Janus [2]rotaxane 3 has been synthesized by bis-azo coupling of 2-naphthol-3,6-disulfonic acid with a Janus [2]pseudorotaxane 2 prepared by dimerization of 6-O-[(4-aminophenylazo)phenyl]-permethylated α-cyclodextrin 1 and characterized by MALDI-TOF-MS and 1H NMR methods.

A sensitive method for the fluorometric determination of lithium with a “crowned” benzothiazolylphenol

On mesure la fluorescence du phenolate du complexe Li/compose crown, obtenu par traitement a la methylamine

Identification of Face-to-Face Inclusion Complex Formation of Cyclodextrin Bearing an Azobenzene Group by Electrospray Ionization Mass Spectrometry

The solution-based self-assembly of native and permethylated cyclodextrins (CD) bearing an azobenzene substituent has been studied by electrospray ionization mass spectrometry (ESI-MS). The results revealed that the CD molecules form either a contact or a face-to-face inclusion complex depending on the interaction of their substituents. The mass spectrometric study further demonstrated that the inclusion complex is formed through the interaction between the host CD cavity and the guest-substituent and that a contact complex is formed by hydrogen-bonding of the hydroxyl functions at the rims of the CD molecule. We also found that in order to detect the face-to-face inclusion complex by ESI-MS, the following conditions have to be met: (1) The CD moieties must be permethylated to avoid formation of the contact complex, (2) they must possess a guest-substituent of suitable length, such as an azobenzene moiety, and (3) they must possess an NH2 or OH group at the substituent terminals for protonation and for detection as cations by ESI-MS. Formation of the inclusion complexes was further confirmed by the synthesis of a capped inclusion dimer and a capped monomer. Collision-induced dissociation (CID) experiments have been carried out for the contact, the host-guest inclusion, and the capped inclusion dimers, and the contact complexes are found to be the most stable among them.

Cation Selective Complexation-Coloration with Chromophoric Crowns

Amine selective complexation-coloration of some azophenol-dyed crowns and X-ray structures of two secondary amine complexes are reported as well as lithium ion specific coloration with an azophenol spherand.