Fluorescence quenching mechanisms of aromatic hydrocarbon-dicyanobenzene and-n.n-dimethylaniline systems in aqueous micellar solutions

Fluorescence quenching of pyrene and several other aromatic hydrocarbons by dicyanobenzenes as well as N,N-dimethylaniline has been observed in aqueous micellar solutions. The experimental results have been explained by means of equations for fluorescence intensity and decay curve derived on the basis of a simplified model.     

Crystal and molecular structure of lycorine-chlorohydrin: Revision of the stereochemistry

Action of POCl₃ and HCl on 1-O-acetyllycorine gave, quantitatively, O-acetyllycorine-chlorodhydrin, which was convertible, in good yield, to lycorene-α-oxide and so-called lycorine-cis-chlorohydrin. The configuration of the latter compound was revised establishing as trans by a single crystal X-ray analysis.     

Synthesis of nanosized TiO2 particles in reverse micelle systems and their photocatalytic activity for degradation of toluene in gas phase

Nanosized pure TiO₂ particles with high crystallinity and large surface area were prepared by hydrolysis of tetrabutyl titanate in water/Triton X-100/isooctane reverse micelle solutions as reaction media followed by hydrothermal treatment to improve crystallinity. The prepared TiO₂ nanoparticles were characterized by XRD, BET, TGA, FT-IR and TEM. The size of ultrafine particles was controlled by changing the water content of the reverse micelle solution. The TiO₂ particles showed monodispersity, large surface area and high degrees of crystallinity and thermostability. The photocatalytic activity of the TiO₂ particles was evaluated by decomposition of toluene in the gas phase. The activity of the TiO₂ nanoparticles was higher than that of commercially available anatase fine particles, such as ST-01, which is one of the most active photocatalysts for degradation of organic compounds in the gas phase.     

Construction and structural characterization of versatile lactosaminoglycan-related compound library for the synthesis of complex glycopeptides and glycosphingolipids

We have established a facile and efficient protocol for the preparative-scale synthesis of various compound libraries related to lactosaminoglycans: cell surface oligosaccharides composed of N-acetyllactosamine as a repeating disaccharide unit, based on chemical and enzymatic approaches. Substrate specificity and feasibility of a bacterial glycosyltransferase, Neisseria meningitidis beta1,3-N-acetylglucosaminyltransferase (LgtA), were investigated in order to synthesize various key intermediates suited for the construction of mammalian O-glycopeptides and glycosphingolipids containing poly-N-acetyllactosamine structures. Recombinant LgtA exhibited the highest glycosyltransferase activity with strongly basic conditions (pH = 10, glycine-NaOH buffer) and a broad range of optimal temperatures from 20 to 30 degrees C. Interestingly, it was found that LgtA discriminates L-serine and L-threonine and functions both as a core-1 beta1,3-N-acetylglucosaminyltransferase and core-2 beta1,3-N-acetylglucosaminyltransferase toward Fmoc-Ser derivatives, while LgtA showed only core-2 beta1,3-N-acetylglucosaminyltransferase activity in the presence of Fmoc-Thr derivatives. Combined use of LgtA with human beta1,4-galactosyltransferase allowed for controlled sugar extension reactions from synthetic sugar amino acids and gave synthetic lactosaminoglycans, such as a decasaccharide derivative, Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Ser-OH (6), and a dodecasaccharide derivative, Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Ser-OH (9). A partially protected pentasaccharide intermediate, GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Thr-OH (11), was applied for the microwave-assisted solid-phase synthesis of a MUC1-related glycopeptide 19 (MW = 2610.1). The findings suggest that this sugar extension strategy can be employed for the modification of lactosyl ceramide mimetic polymers to afford convenient precursors for the synthesis of various glycosphingolipids.     

Evidence for second-phonon nuclear wobbling

The nucleus 163Lu has been populated through the reaction 139La(29Si,5n) with a beam energy of 157 MeV. Three triaxial, strongly deformed (TSD) bands have been observed with very similar rotational properties. The first excited TSD band has earlier been assigned as a one-phonon wobbling excitation built on the lowest-lying (yrast) TSD band. The large B(E2)(out)/B(E2)(in) value obtainable for one of four observed transitions between the second and first excited TSD bands is in good agreement with particle-rotor calculations for a two-phonon wobbling excitation.     

Pyrene-N,N-dimethylaniline heteroexcimer systems in aqueous micellar solutions

Strong quenching of fluoroscence of pyrene by N,N-dimethylaniline as well as N,N-dimethylaniline sulfonate has been observed in aqueous micellar solutions. Photoinduced electron transfer from the anilines to excited pyrene near the micelle-water interface has been demonstrated by means of laser photolysis studies.     

Thermal conductivity of mixed alkali silicate glasses at low temperature

Thermal conductivity of glass is one of the fundamental properties of it. However, that has not been studied enough. That of only less than 20 compositions has been measured below the room temperature. In this study, we measured the thermal conductivity of xNa₂O · (100 ? x)SiO₂ and (33 ? y)Na₂O · yCs₂O · 67SiO₂ glasses by a transient heating method in the temperature range from about 150 K to room temperature. The conductivity of xNa₂O · (100 ? x)SiO₂ is found to decrease with the increase in alkali content. The dominant factor of this behavior is the decrease in phonon mean free path, which is due to the increase of non-bridge oxygen. Thermal conductivity of (33 ? y)Cs₂O · yNa₂O · 67SiO₂ is decreased with the increase in Cs₂O/(Na₂O + Cs₂O) ratio. The dominant factor of this behavior is the decrease of sound velocity. However, composition dependence of the phonon mean free path also affects the thermal conductivity. Phonon mean free path of 33Cs₂O · 67SiO₂ glass is longer than that of 33Na₂O · 67SiO₂ glass, and should be related to the change in distribution of structural unit in glass. In addition, phonon mean free path of mixed alkali glasses are shorter than that of single alkali glasses.     

Solvent dependence of absorption intensities and wavenumbers of the fundamental and first overtone of NH stretching vibration of pyrrole studied by near-infrared/infrared spectroscopy and DFT calculations

Near-infrared (NIR) and IR spectra were measured for pyrrole in CCl(4), CHCl(3), and CH(2)Cl(2) to study solvent dependence of absorption intensities and wavenumbers of the fundamental and first overtone of NH stretching vibration. It was found that the wavenumbers of the NH fundamental and its first overtone decrease in the order of CCl(4), CHCl(3), and CH(2)Cl(2), which is the increasing order for of the dielectric constant of the solvents. Their absorption intensities increase in the same order, and the intensity increase is more significant for the fundamental than the overtone. These results for the solvent dependence of the wavenumbers and absorption intensities of NH stretching bands of pyrrole are quite different from those due to the formation of hydrogen bonds. Quantum chemical calculations of the wavenumbers and absorption intensities of NH stretching bands by using the 1D Schr?dinger equation based on the self-consistent reaction field (SCRF)/isodensity surface polarized continuum model (IPCM) suggest that the decreases in the wavenumbers of both the fundamental and the overtone of the NH stretching mode with the increase in the dielectric constant of the solvents arise from the anharmonicity of vibrational potential and their intensity increases come from the gradual increase in the slope of the dipole moment function.