Hideyo Matsuzawa

Conformational transition of gellan gum of sodium, lithium, and potassium types in aqueous solutions

Abstract The effects of cationic ions on the conformational properties of gellan gum in aqueous solutions with and without salts are studied using highly purified lithium, sodium, and potassium-type gellan gum samples by measuring the osmotic pressure, intrinsic viscosity, and circular dichroism (CD). The M n values of Li, Na, and K-gellan obtained at 45°C were nearly the same. The M n values of Na-gellan or Li-gellan obtained at 45°C in aqueous solutions with added salts were almost half or slightly less than half the value of that obtained at 28°C, respectively. The temperature dependence of θ 201 and ( η sp / c p )for Li, Na, and K-gellan solutions with and without added salts showed drastic changes at the transition temperatures. These results could be interpreted as the occurrence of the coil to double-helix transition and partial aggregation of helices at the transition temperatures on lowering temperature. In the aqueous solutions without added salts, the transition temperatures for Li, Na, and K-gellans determined by CD are almost coincident with those obtained from viscometry. The transition temperatures for Li, Na, and K-gellan solutions increased with increasing polymer concentration but almost independent of the chemical species of countercations. In the aqueous solutions with added salts, the transition temperature of Li, Na, and K-gellan depends not only on polymer concentration but also the concentration of added salt and the chemical species of countercations. The observed transition temperature for K-gellan solution with KCl is higher than that for the solutions of Li-gellan with LiCl and Na-gellan with NaCl.

Self-association of octan-1-ol in the pure liquid state and in decane solutions as observed by viscosity, self-diffusion, nuclear magnetic resonance and near-infrared spectroscopy measurements

The self-association of octan-1-ol in the pure liquid state and in decane solutions has been studied by near-infrared spectroscopic observation over the temperature range 298.1–348.1 K and also by viscosity, self-diffusion and NMR measurements. The absorption bands assigned to the hydroxy group are superimposed on several bands attributed to the methylene groups belonging to both the alcohol and decane molecules. A superior technique using a computer was adopted for the cancellation of the absorption bands due to the methylene groups so as to obtain the net OH absorption bands. The analysis of the sharp band at 1410 nm (the first overtone band of the OH-stretching vibration attributed to the free OH-monomer and partly to the OH-polymer) leads to the conclusion that the mean degree of association n(i.e. the average size of the multimer in monomeric units) in the polymer of octan-1-ol is ca. four, both in the liquid and in decane solutions under the temperature conditions given above. From the arguments about the aggregated species, a cyclic tetramer was proposed as the associated alcohol species in the liquid and in decane solutions. The association equilibrium constant and other thermodynamic properties such as changes in enthalpy, entropy and Gibbs energy for tetramer formation were also determined.

Tetrathiafulvalenylallene: a new class of donor molecules having strong chiroptical properties in neutral and doped states.

A chiral tetrathiafulvalene (TTF) dimer bridged by an allene framework (1) was synthesized. An X-ray analysis of 1 revealed an effective conjugation between TTF and the allene backbone. Allene 1 was resolved into both enantiomers, which showed strong chiroptical electrochromic properties. Absolute configuration of the allene was validated by theoretical study of the electronic circular dichroism (ECD) spectrum. ECD spectra of cationic species 1(2+) and 1(4+) exhibited intense Cotton Effects over the visible region.

Molecular Self-Assembling of Butan-1-ol, Butan-2-ol, and 2-Methylpropan-2-ol in Carbon Tetrachloride Solutions as Observed by Near-Infrared Spectroscopic Measurements:

The self-associations of butan-1-ol, butan-2-ol, and 2-methylpropan-2-ol (tert-butanol) in the pure liquid state and in carbon tetrachloride solutions have been studied mainly through near-infrared spectroscopic observation at various temperatures. A new analysis assuming a successive association process for the alcohol molecules was applied to the sharp band around 1410 nm (the first-overtone band of the OH stretching vibration mode attributed to free OH monomer and partly to OH polymer); it became clear that the mean association number for each alcohol increases with increasing concentration and decreases with increasing temperature. Comparisons of the association numbers at various constant temperatures for the three kinds of alcohols show that the association abilities are on the order butan-1-ol > butan-2-ol > 2-methylpropan-2-ol.

MOLECULAR SELF-ASSEMBLING OF CHIRAL AND RACEMIC BUTAN-2-OL IN CARBON TETRACHLORIDE SOLUTIONS

Abstract The self-association of (R)-, (S)- and (RS)-butan-2-ol in their carbon tetrachloride solutions was studied through the mid-infrared (mid-IR) and near-infrared (NIR) spectroscopic observations. The mid-IR and NIR spectra for each chiral butan-2-ol were compared with those for the racemic (RS)-butan-2-ol. Although it has been reported that the hydrogen bonding among the chiral butan-2-ol molecules was stronger than that among the racemic ones, any distinguishable differences between the chiral and the racemic butan-2-ol in CCl4 solution or even in their pure liquid state were not observed both in their mid-IR and NIR spectra. A superior analytical method, assuming a successive association process for the alcohol molecules, was applied to the analysis of the sharp band at 3630 cm−1 (the OH-stretching vibration mode attributed to free OH-monomer) for the (R)-, (S)- or (RS)-butan-2-ol in CCl4. The mean association number 〈N〉 for each alcohol increased with increasing in concentration until 0.12 mol dm−3 and then becomes constant (about four). On the other hand, Zankers plotting method, assuming an equilibrium between monomers and only one kind of polymer species, was also applied to the analysis of the above spectroscopic results; the association number n evaluated from the Zankers method fairly agreed with the 〈N〉 value in the concentration region of 0.12–0.60 mol dm−3.

Macrocyclic Oligothiophene with Stereogenic [2.2]Paracyclophane Scaffolds: Chiroptical Properties from π‐Transannular Interactions

The enantiomers of a new cyclic oligothiophene, bridged by two pseudo-ortho[2.2]paracyclophanes, were synthesized as a new class of the chiral π-conjugated system. Single-crystal X-ray diffraction analysis revealed a twisted structure for these oligothiophenes induced by a torsion of the cyclophane moieties. The embedding oligothiophenes into the inherent planar chirality provided a significant enhancement in circular dichroism (CD) spectra thanks to the large magnetic/electric transition dipole moments. In the dicationic state, an intramolecular π dimer was formed due to the strong interactions of the oligothiophenes. We further recorded unprecedented wide ranges of CD spectra in 250-1800 nm region. The transitions are reasonably described by the exciton coupling of the oligothiophenes.

Dimeric Tetrathiafulvalene Linked to pseudo-ortho-[2.2]Paracyclophane: Chiral Electrochromic Properties and Use as a Chiral Dopant

A dimeric tetrathiafulvalene installed into a chiral pseudo-ortho-[2.2]paracyclophane framework was synthesized as a novel chiral electrochromic material. This compound exhibited pronounced chiroptical properties in the UV-Vis-NIR range depending on its redox states without racemization. Each enantiomer was examined as a chiral dopant for nematic liquid crystals (LCs), and the induced helicity of the LC solvent was in accord with that of the tetrathiafulvalene compound.

Chiroptical Properties and the Racemization of Pyrene and Tetrathiafulvalene-Substituted Allene: Substitution and Solvent Effects on Racemization in Tetrathiafulvalenylallene

Dissymmetric 1,3-diphenylallene derivative 3 connected with 4,5-bis(methyl-thio)tetrathiafulvalenyl and 1-pyrenyl substituents was prepared and characterized. The molecular structure was determined by X-ray crystallographic analysis. Optical resolution was accomplished using a recycling chiral HPLC, and its chiroptical properties were examined with optical rotation and electronic circular dichroism (ECD) spectra. The title compound underwent photoracemization under daylight. This behavior was investigated in various solvents and compared with that of 1,3-bis(tetrathiafulvalenyl)allene (bis-TTF-allene) derivative 2. The first-order rate plot of the intensity of the ECD spectra at a given time interval gave the rate of racemization. Mild racemization was observed in polar solvents, whereas a relatively fast rate was obtained in less polar solvents. In addition, the TTF groups of the allene also accelerate the racemization rate. These results suggest that the racemization mechanism occurs via a non-polar diradical structure.

X-ray diffraction study on the aggregate structure of 5,10,15,20-tetra(4-sulfophenyl)porphinatopalladium(II)(4-) in aqueous solution

The aggregate structure of 5,10,15,20-tetra(4-sulfophenyl)porphinatopalladium(II) ion (PdTPPS4–) in aqueous solution has been investigated in terms of the distance between the porphyrin monomers, by use of absorption spectroscopy, paramagnetic relaxation of NMR signals, and an isomorphic substitution method for X-ray diffraction of the solution. From absorption spectroscopy results it was concluded that the aggregate was regarded as a dimer arising from hydrophobic attraction between the porphyrin rings. Paramagnetic effects on the longitudinal relaxation time (T1) for 13C NMR of PdTPPS4– by the addition of 5,10,15,20-tetra(4-sulfophenyl)porphinatocopper(II)(CuTPPS4–) suggested that the paramagnetic centre was located along a C4-axis of PdTPPS4– in a PdTPPS4––CuTPPS4– dimer. The dimer of PdTPPS4– was determined to have a twisted face-to-face stacked structure (D4d) at a distance of 4.1 A by the isomorphic substituted X-ray diffraction study on PdTPPS4– and CuTPPS4– solutions.