Isolation and stereostructures of neocitreoviridinol and epineocitreoviridinol

Both neocitreoviridinol and epineocitreoviridinol with a 2,5-dioxabicyclo[2.2.1]-heptane ring have been isolated as new metabolises of $\text{Penicillium citreo-viride}$ B., and their stereostructures have also been elucidated on the basis of their spectral data coupled with molecular mechanics calculations. In addition, a promising synthetic intermediate for neocitreoviridinol has been made.     

Preparation and physical properties of amorphous V2O5 containing TiO2, Na2O or Li2O

V₂O₅ gels containing up to 18 mol% of TiO₂ were obtained through the simultaneous hydrolysis of alkoxides in ethanol solution. V₂O₅ gels containing Na₂O or Li₂O were obtained through the ion exchange method. The crystallization temperature, T_cr, of the gels increased and the H₂O content of the gels decreased by the addition of TiO₂ or Na₂O. These additives seem to stabilize the amorphous state of the gels. On the other hand, T_cr and the H₂O-content slightly varied with the addition of Li₂O. No ionic polarization was observed in coating films of the gels dried at temperatures below T_cr. The dc conductivity of the films was anisotropic, and increased with the addition of Li₂O or Na₂O. However, it decreased with increasing TiO₂ content. The fiber-like structure of gels was observed by TEM. The gels obtained from alkoxides were thin and short in comparison with the gels obtained through the ion exchange method.     

Epitaxial growth of GaAs and GaN by gas source molecular beam epitaxy using organic group V compounds

GaAs and GaN epilayers were grown on GaAs substrates by gas source molecular beam epitaxy technique using triethylarsine (TEAs) and diethylarsine (DEAsH) as As sources, and dimethylhydrazine (DMHy) as an N source. It was found that GaAs grows layer by layer even when organic arsine molecular sources are used. Cubic GaN was found to grow epitaxially on sufficiently nitrided surfaces of GaAs (001) substrates, in contrast with the growth of hexagonal GaN on GaAs (111) surfaces. It was also found that nitridation of GaAs surfaces does not occur when DEAsH and DMHy beams are supplied onto the GaAs substrates, simultaneously. Thus, GaN/GaAs multilayers were obtained only by intermittent supply of a DEAsH beam.     

An EXAFS study of Ag3AsS3 glass

The local structures of Ag₃AsS₃ glass at 80 and 300 K have been investigated by extended X-ray absorption fine structure analysis. By comparing the glass structure with that of Ag₃AsS₃ crystal (proustite), the possibility of ionic conduction by this glass is discussed. The local structure around an As atom in the glass is similar to that in the crystal. This fact suggest that, even in the glass structure, the As atoms from AsS₃ trigonal pyramids of shape similar to that in the crystal. The Ag---S distance (2.449 Å at 300 K) and the large root mean square displacement, σ, for the Ag---S atomic pairs in the glass, groups with a by the parameter fitting method, show that the Ag atoms are quite randomly distributed around the AsS₃ groups with a similar Ag---S distance to that in the crystal. Further, it is possible that the large thermal contribution to σ_Ag---S² for the glass may indicate the involvement of the Ag atoms in ionic conduction.     

Theoretical investigation of ethylene/1-butene copolymerization process using constrained geometry catalyst (CpSiH2NH)-Ti-Cl2

The ethylene/1-butene copolymerization using constrained geometry catalyst CpSiH₂-NH-TiCl₂ (CGC) was investigated by the density functional theory and molecular dynamics. Structures and energetics of reactants, π-complexes, transition states, and products during insertion of ethylene and 1-butene monomers into the catalytic reactive site of the CGC were investigated by the density functional theory (DFT) using the software Dmol³, while dynamics of atoms during copolymerization process was investigated by classical molecular dynamics (MD) using the New-Ryudo-CR program. The calculated results were compared with the available experimental and theoretical ones. It was found that the ethylene insertion into Ti-Me active species is energetically more favorable than the butene one and the 2,1-butene insertion is more favorable than 1,2-butene one. Once the initial ethylene insertion has taken place, the further ethylene insertion occurring with a less energy barrier, in good agreement with experimental findings.     

Selective determination of tryptophan-containing peptides through precolumn derivatization and liquid chromatography using intramolecular fluorescence resonance energy transfer detection.

A selective and sensitive fluorometric determination method for native fluorescent peptides has been developed. This method is based on intramolecular fluorescence resonance energy transfer (FRET) detection in a liquid chromatography (LC) system following precolumn derivatization of the amino groups of tryptophan (Trp)-containing peptides. In this detection process, we monitored the FRET from the native fluorescent Trp moieties (donor) to the derivatized fluorophore (acceptor). From a screening study involving 10 fluorescent reagents, we found that o-phthalaldehyde (OPA) generated FRET most effectively. The OPA derivatives of the native fluorescent peptides emitted OPA fluorescence (445 nm) through an intramolecular FRET process when they were excited at the excitation maximum wavelength of the Trp-containing peptides (280 nm). The generation of FRET was confirmed through comparison with the analysis of a non-fluorescent peptide (C-reactive protein fragment (77 - 82)) performed using LC and a three-dimensional fluorescence detection system. We were able to separate the OPA derivatives of the Trp-containing peptides when performing LC on a reversed-phase column. The detection limits (signal-to-noise ratio = 3) for the Trp-containing peptides, at a 20-microL injection volume, were 41 - 180 fmol. The sensitivity of the intramolecular FRET-forming derivatization method is higher than that of the system that takes advantage of the conventional detection of OPA derivatives. Moreover, native non-fluorescent amines and peptides in the sample monitored at FRET detection are weaker than those of conventional fluorescence detection.