Kazuaki Nakashima

ORGANIC GELS ARE USEFUL AS A TEMPLATE FOR THE PREPARATION OF HOLLOW FIBER SILICA

A novel mesoporous silica with a tubular structure has been prepared using organic gel fibers as a template.

Influence of para-substituents and solvents on selective precipitation of fullerenes by inclusion in calix[8]arenes

Abstract Twelve calix[8]arene derivatives ( 1 8 R) with different para -substituents (R) were synthesized and applied to selective precipitation of C 60 and C 70 from benzene and toluene. 1 8 Pr i and 1 8 Bu t precipitates from benzene and toluene, forming a 1:1 complex with C 60 whereas only 1 8 Bu t precipitates from benzene, forming a 1:2 1 8 Bu t /C 70 complex. The spectroscopic studies of the precipitate complexes are also reported.

Specific recognition of disaccharides by trans-3,3′-stilbenediboronic acid: rigidification and fluoresecence enhancement of the stilbene skeleton upon formation of a sugar–stilbene macrocycle

The molecular sensor trans-3,3′-stilbenediboronic acid 3 gave enhanced fluorescence in the presence of disaccharides whereas no response was found for monosaccharides.

Fluorescent calix[4]arene which responds to solvent polarity and metal ions

A calix[4]arene having two pyrene moieties on the lower rim has been synthesized; the ratio of the monomer vs. excimer emission was sensitively affected by solvent polarity and added metal ions.

The unexalted resonance scale of substituent effect in the benzylic solvolysis

Abstract The substituent effect on the solvolysis of 4-methylbenzobicyclo[2,2,2]octen-1-yl triflates where no through-conjugative aryl-cation center interaction is possible, can be described in terms of resonance-unexalted σo parameters of the aryl substituents.

STRUCTURE DETERMINATION OF A 1:2 THREITOL-BORONIC ACID COMPLEX : COMMENTS ON THE STRUCTURAL CONTROVERSY BETWEEN 5,5- AND 6,6-MEMBERED RINGS

Abstract The complexation between d -threitol (1) and 2,4,6-[3,4-bis(bromomethyl)phenyl]boroxin (2) selectively afforded d -threitol-1,3:2,4-bis[-3,4-(bisbromomethyl)phenylboronate] (4) including two six-membered rings, whose structure was identified by means of NMR and IR spectroscopy and X-ray crystallographic analysis. The superior stability of 4 over 3 including two five-membered rings was discussed.

Induction of chirality into metal complexes by boronic acidsugar interactions

Abstract By sonication in MeOH N-m -(phenylboronic acid)-2,2′-bipyridine-5-carboxylamide easily formed its bidentate boronate sugar ligands. Solutions of the corresponding Cu(I) and Fe(II) complexes showed opposite CD effects for the D and the L form of the sugar. The stoichiometry of the metal complexes was determined by Job plots and by mass spectrometry. A macrocyclic structure, that includes ten cycles, is proposed as the most probable CD-active species.

Molecular design and characterizations of new calixarene-based gelators of organic fluids

We have found that certain calix[n]arenes having long acyl groups at the p-positions (e.g., 5,11,17,23,29,35,41,47-octadodecanoylcalix[8]arene-49,50,51,52,53,54,55,56-octol: 28C12) act as excellent and unique gelators of various organic solvents (e.g., toluene, carbon tetrachloride, carbon disulfide, hexane, isopropanol, etc.). The sol–gel phase transition temperatures (Tgel) could be determined by the inverted test-tube method or by the DSC method. The change in the aggregation mode at the phase transition temperature was directly observable by an optical microscope: below Tgel., the fibrillar network (diameter ca. 1 µm) appeared whereas above Tgel, it ‘melted’ down. It was shown on the basis of these measurements that the sol-gel phase transition occurs reversibly. The spectroscopic studies using 1H NMR and IR spectroscopy and the comparative experiments using the analogues of 28C12(nine cyclic and six non-cyclic) established that the prerequisites for the formation of the stable organic gels are (i) the intermolecular CO ⋯ HO hygrogen-bonding interaction to form the three-dimensional network and (ii) the moderate affinity of gelators with solvent molecules. The results offer important strategies useful for the molecular design of new gelators of organic fluids.

Sugars intensify the inhibitory effect of phenylboronic acid on the hydrolytic activity of α-chymotrypsin

The inhibitory effect of phenylboronic acid which acts as a transition state analogue for certain peptidases is efficiently intensified by added saccharides: this finding enables us to control the enzyme activity with sugars.

Preparation of novel silica structures using a library of carbohydrate gel assemblies as templates for sol–gel transcription

Four sugar-based organogelators (1–4) were synthesized, and their gelation ability was evaluated in organic solvents and water. It was shown that they act as versatile gelators of various organic fluids, forming various superstructural aggregates. The xerogels showed a single- and lotus-type fiber structure or a spherical structure. The difference in these organogel supramolecular structures has successfully been transcribed into silica structures by sol–gel polycondensation of tetraethoxysilane (TEOS), resulting in single or multiple (lotus-shaped) hollow fiber structures with 5–10 nm inner diameters or a spherical structure with 700–1300 nm outer diameters. These results indicate that novel silica structures can be created by transcription of various superstructures formed in organogels through the hydrogen-bonding interaction. Nitrogen adsorption–desorption isotherms were measured by a BET method. The silica obtained from the α-glucose-based organogel 1, β-glucose-based organogel 2, α-galactose-based organogel 3 and α-mannose-based organogel 4 had BET surface areas of 450, 475, 650 and 670 m2 g−1, respectively. The Q4/Q3 ratios of these silicas were estimated by 29Si MAS NMR spectroscopy. The Q4/Q3 ratios for the silica materials obtained from 1, 2, 3 and 4 were 3.00, 3.05, 4.87 and 5.25, respectively. This is a novel and successful example showing that a variety of new silica structures are created using a library of carbohydrate gel fibers as their templates.