Keijiro Taga

Diffuse reflectance infrared Fourier transform spectral study of the thermal and adsorbed-water effects of a 3-aminopropyltriethoxysilane layer modified onto the surface of silica gel

Abstract Infrared absorption spectra of some polyaminopropylsiloxane (poly-APS) samples with different degrees of polymerization have been examined. The results show that this difference results in a marked variation in the environment of the NH 2 groups. The thermal and adsorbed-water effects on the silane-coated layer of silica gel samples, modified with 3-aminopropyltriethoxysilane (APTS), have also been investigated using a diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic method. The results are summarized as follows. For the silica gel samples, the DRIFT spectral features in the CH stretch and NH 2 bend modes are almost independent of temperature within the range 303–373 K, indicating stable environments for the aminopropylsilyl segments of the silane-coated layer. For a sample which was treated with a higher APTS concentration, the spectral features were little affected by adsorption of water, while the effect of adsorbed water on a sample treated with a small APTS concentration led to observation of pronounced spectral features. These results have been ascribed to the difference in the degree of polymerization of the silane-coated layer between the samples.

Synthesis and properties of BF2 complexes to dihydroxydiones of tetracene and perylene: novel electron acceptors showing n-type semiconducting behavior.

BF(2) complexes containing tetracene and perylene moieties were synthesized as new types of electron-deficient arene compounds. These compounds exhibit long wavelength absorption and high electron affinities, as revealed through spectral and electrochemical studies, due to their quadrupolar structures represented by resonance contributors. The BF(2) complex containing tetracene exhibits an n-type semiconducting behavior. These compounds are new types of electron acceptors functionalized by BF(2) chelation.

A linear chain of water molecules accommodated in a macrocyclic nanotube channel.

A macrocyclic tetramer of 2-phenyl-1,3,4-oxadiazole was synthesized, and its self-assembly was investigated. The macrocycle was stacked to form a one-dimensional (1D) columnar structure containing water molecules. The nanotube self-assembled into a bundle, which grew into a molecular wire. The association of the water molecules in the tubular cavity resulted in shielding of the 1D chain of water molecules by the nanotube; these macrocyclic nanotube channels are promising candidates for nanotechnological applications.

Raman scattering study of the interaction of 3-aminopropyltriethoxy silane on silica gel. Time-dependent conformational change of aminopropylsilyl segments

Abstract Silica gel samples, modified with 3-aminopropyltriethoxy silane (APTS), have been prepared by sequentially sampling the substrate from the reaction vessel at various time intervals, and the Raman spectra of these samples have been measured. The CH stretch Raman bands at 2938 and 2981 cm −1 became more intense as the reaction proceeded. Kinetic analyses were then carried out, after making the assumption that the time dependence of relative Raman peak heights ( I 2938 / I 800 and I 2981 / I 800 ) is a pseudo-first order. The rate constants obtained are k =8.05×10 −4 s −1 for the 2938 cm −1 band and k =9.45×10 −4 s −1 for the 2981 cm −1 band. We may assume that the dependence of the change in intensity of the CH stretch Raman bands on time is a reflection of the change in conformation of the APS moieties.

Aggregation of polyene antibiotics as studied by electronic absorption and circular dichroism spectroscopies

Abstract The self-association of amphotericin B and hamycin, the heptaene polyene antibiotics, was observed in alcoholic solutions on addition of increasing amounts of water at a studied antibiotics concentration of 1 × 10 −5 M. An increase in the aggregation was noticed in methanolic solutions at and above 65–70% (vol. %) water content. The antibiotics were found to be aggregated at and above 85% water content in propanol. The increased water content required to initiate the aggregation in propanol was related to the more hydrophobic nature of the latter. The aggregation of antibiotics was hindered by the addition of Triton X-100, a non-ionic detergent, at a concentration of 0.5%. The self-association of amphotericin B and hamycin was observed at concentrations of 5 × 10 −7 and 1 × 10 −7 M respectively, in phosphate-buffered saline as detected by the presence of an excitonic doublet in their circular dichroism (CD) spectra. The aggregation was found to be enhanced while the concentration increased up to the studied concentration of 5 × 10 −5 M. The polyene antibiotics existed as monomers in dimethyl sulfoxide(DMSO) at concentrations of 1 × 10 −7 −4.3 × 10 −2 M and 1 × 10 −7 −1 × 10 −2 M for amphotericin B and hamycin respectively, as revealed by their concentration-independent CD spectra.

Counterion binding to micelles measured by sodium-23 NMR relaxation times: Enhancement by anesthetics

Abstract Counterion (Na+) binding to anionic surfactant (monoalkylphosphate) micelles was monitored by 23Na nuclear magnetic resonance spectroscopy using spin-lattice (T1) and spin-spin (T2) relaxation times. The T1 and T2 values were almost identical at all surfactant concentrations within experimental error. At concentrations below the critical micelle concentration (CMC), T1 and T2 showed almost a constant value. A sudden decrease in relaxation times (increase in relaxation rates) occurred at the CMC, as expected. Above the CMC, the relaxation times decreased with the increase in surfactant concentrations. Double reciprocal plots between relaxation times and surfactant concentrations produced rectilinear curves. Extrapolation of the linear portions intersected each other at the CMC. When the surfactant concentration was below the CMC, inhalation anesthetics (chloroform, enflurane, and halothane) did not affect the apparent T2 value even with saturating concentrations. When the surfactant concentration exceeded the CMC, these inhalation anesthetics decreased apparent T2 value dose-dependently, indicating stronger binding of sodium ions. The anesthetics appear to be solubilized at the micelle-water interface and increase hydrophobicity of the interface by replacing water molecules. A decrease in the local dielectric constant by anesthetic molecules may account for the increase in the counterion binding to the micellar surface.

Proton flow along lipid bilayer surfaces: effect of halothane on the lateral surface conductance and membrane hydration

Impedance dispersion in liposomes measures the lateral charge transfer of lipid membrane surfaces. Depending on the choice of frequency between 1 kHz and 100 GHz, relaxation of the counterions at the interface, orientation of the head group, and relaxation of the bound and free water are revealed. This study measured the impedance dispersion in dipalmitoylphosphatidylcholine (DPPC) liposomes at 10 kHz. The surface conductance and capacitance showed breaks at pre- and main transition temperatures. Below the pre-transition temperature, the activation energy of the ion movement was 18.1 kJ.mol-1, which corresponded to that of the spin-lattice relaxation time of water (18.0 kJ.mol-1). At temperatures between pre- and main transition it increased to 51.3 kJ.mol-1, and agreed with 46.2-58.0 kJ.mol-1 of the activation energy of the dielectric relaxation of ice. Because the present system was salt-free, the ions were H3O+ and OH-, hence, their behavior represents that of water. The above results show that below the pre-transition temperature, the conductance is regulated by the mobility of free ions, or the number of free water molecules near the interface. On the other hand when the temperature exceeded pre-transition, melting of the surface-bound water crystals became the rate-limiting step for the proton flow. Halothane did not show any effect on the ion movement when the temperature was below pre-transition. When the temperature exceeded pre-transition, 0.35 mM halothane (equilibrium concentration) decreased the activation energy of the ion movement to 29.3 kJ.mol-1. This decrease indicates that halothane enhanced the release of the surface-bound water molecules at pre-transition. The surface-disordering effect of halothane was also shown by depression of the pre-transition temperature and decrease of the association energy among head groups from 9.7 kJ.mol-1 of the control to 5.2 kJ.mol-1 at 0.35 mM.

Raman spectra and rotational isomerism of dimethylphosphorochloridate and trimethyl phosphate

Abstract The Raman spectra of dimethylphosphorochloridate, (CH3O)2P(O)Cl, and trimethyl phosphate, (CH3O)3P(O), have been measured in the liquid and solid states. Rotational isomerism about the COP(O) bond was investigated on the basis of normal coordinate treatment. For (CH3O)2P(O)Cl, four rotational isomers of (T,G), (T,G′), (G′,G) and (G,G) are present in the liquid state. Two crystalline modifications have been obtained and the molecular conformation is the same as (T,G) form in both the solid phases. The wavenumbers of PCl stretching mode are correlated with the molecular conformation similar to the result for the wavenumbers of XCl (XC and Si) stretching mode. In the case of (CH3O)3P(O), three rotational isomers, C1, Cs and C3, have been found to coexist in the liquid state. Three crystalline modifications are obtained in this molecule and the conformer in these phases is the same as the C1 form.

Vibrational Spectroscopic Evidence for the Associated-Anion Promotion of the Helical Structure of N-Acylglycine Oligomers

Vibrational spectroscopic evidence for conformational change of the anions of N-acylglycine oligomers (trimers, tetramers, and pentamers) in aqueous solution is reported. The infrared absorption spectra of sample solutions diluted below the critical micelle concentration (cmc) can be explained by the coexistence of several conformations containing the polyglycine I-like extended form and the polyglycine II-like helix. However, above the cmc the infrared bands arising from the polyglycine II-like helix are intensified. This result is due to preferential stabilization of the helical structure, promoted by intermolecular association of the anions. The helical structure is also stable in the hydrophobic environment of micelles.

Vibrational spectra of N-acylglycine oligomers and the long N-acyl chain effect

Trimers, tetramers and pentamers of N-acylglycine oligomer acid types with various acyl chains, their potassium or sodium salts, and their N-deuterated salts have been prepared. The vibrational spectra of these molecules have been measured and compared with those of polyglycine I (PGI; extended β form) and polyglycine II (PGII; helical form). Only a conformation similar to PGII exists in the solid state for these compounds. The long acyl chains induce a further PGII-like structure in the NH⋯OC and peptide skeletons. This effect is reflected markedly in the NH and ND stretching, amide I and II and low-frequency regions.