Semiempirical calculation of electronic spectra of organic compounds by using the improved method of new-γ electron repulsion integral. Part 2. Polycyclic aromatic hydrocarbons (PAHs)

Excitation energies of 123 polycyclic aromatic hydrocarbons were calculated by incorporating the improved method of new-γ for the two-center electron repulsion integral into two semiempirical molecular orbital methods (CNDO/S and INDO/S). This variable method well reproduced experimental excitation energies of them. The average error of the improvement is about 0.162 (CNDO/S) or 0.237 eV (INDO/S) though the average error without the improvement is about 0.541 (CNDO/S) or 0.536 eV (INDO/S). The improvement was useful for the calculations of other organic compounds including hetero atoms, such as organic dye.     

Palladium-catalyzed cycloheptatriene formation by [3+2+2] cocyclization of 2-substituted allylic alcohols and alkynes

Cycloheptatrienes were obtained by the reaction of 2-substituted allylic alcohols with alkynes in the presence of catalytic amounts of palladium complexes and p-toluenesulfonic acid.     

Significant differences in site of protonation and extent of fragmentations in chemical ionization and fast atom bombardment mass spectrometry of simple bifunctional compounds. A mechanistic implication for formation of protonated molecules

Chemical ionization (CI) and fast atom bombardment (FAB) mass spectra of simple bifunctional aromatic compounds were compared. Some significant differences were revealed with respect to the site of protonation and extent of fragmentations. Unlike conventional CI ionization, the protonated molecule formation by FAB could not be accounted for by ordinary proton transfer reactions in the gas phase. The observed ions under FAB conditions appear to be regulated by proton exchange reactions through frequent collisions in some particular region between the matrix and the gas phase.     

Low temperature synthesis and characterization of porous anatase TiO2 nanoparticles

An ethanol solution of Ti-peroxy compounds was prepared from the ethanol solution of titanium isopropoxide (Ti(O-iPr)4) and H2O2. Heating of the ethanol solution of the Ti-peroxy compounds at 348 K formed a Ti-peroxy gel, and heat treatment of the gel at 348 K for more than 6 h formed gels that consisted of anatase nanoparticles. The diameter of the anatase nanoparticles increased from 9 to 15 nm as the heating time increased from 6 to 48 h. According to the results of the N2 adsorption measurement, the anatase nanoparticles had micropores, and the specific surface area (SBET) was in the range of 254 to 438 m2/g. The particle size, lattice strain, specific surface area, and photocatalytic activity of the anatase nanoparticles can be regulated by the heating time of the Ti-peroxy gel at 348 K.     

Regioselective synthesis and biological activity of oxidized chitosan derivatives

Oxidized chitosan derivatives with various degrees of oxidation (DS, 0.1–1.0) were prepared by the treatment of chitosan with CrO₃/aq HClO₄ or by the oxidation of ­3‐O‐ and N‐protected chitosan with 30% aq H₂O₂/Na₂WO₄ followed by 3‐O‐ and N‐deprotection. The oxidized products were then N‐acetylated with Ac₂O in order to improve their water‐solubility. Although the oxidized chitosan derivative of DS 0.28 and the degree of N‐acetylation of chitosan (DA) 38% was insoluble in the pH 3–8 region, that of DS 0.26 and DA 76% was soluble in the neutral pH range. The newly‐prepared acetylated and oxidized chitosan derivatives were found to suppress the chemiluminescence response of inflammatory cells such as canine polymorphonuclear cells (PMNs). Analysis by the surface plasmon resonance method revealed that the bind and release behavior of PMNs to acetylated oxidized chitosan derivatives was similar to that against carboxymethylated chitosan derivatives. The amount of water‐soluble chitosan derivative bound to cytokine IL‐8 was found to be affected by the structural and electronic features of the chitosan substituents in the chitosan chain. Copyright © 2003 John Wiley & Sons, Ltd.     

Photoswitchable organocatalysis in acylation of alcohol using dithienylethene-linked azoles

Three novel dithienylethenes bearing azole derivatives were synthesized and found to undergo reversible photocyclization of the dithienylethene units upon alternate irradiation with UV and visible light. Among them, the dithienylethene-linked imidazole and N-phenylimidazole exhibited a relatively high organocatalytic activity for the acylation of 2-decanol with acetic anhydride, and the catalytic activity of the dithienylethene-linked imidazole could be switched by reversible photoinduced cyclization/cycloreversion of the dithienylethene unit.     

Application of simplified desorption method to study on sorption of americium(III) on bentonite

To elucidate the sorption behavior of americium(III) on bentonite, which is a mixture of montmorillonite clay, quartz and other minerals, simplified desorption experiments were applied to the solid phases collected after the sorption experiments. The sorption–desorption behavior was examined in the final pH range from 2 to 8. The desorption experiments revealed that most of the Am was sorbed on the montmorillonite moiety of the bentonite. The sorption of Am on montmorillonite was divided into two types: one was the “exchangeable” sorption, in which the sorbed Am was desorbed with a 1 M KCl aqueous solution, and the rest was the “unexchangeable” sorption. The exchangeable sorption was ion exchange of mostly Am³⁺. The unexchangeable sorption was the strong sorption of Am hydroxides. An accessory iron mineral, pyrite, might be involved in the Am sorption on bentonite at neutral pH.     

Silk‐Pectin Hydrogel with Superior Mechanical Properties,Biodegradability, and Biocompatibility

A new method is developed to prepare silk hydrogels and silk‐pectin hydrogels via dialysis against methanol to obtain hydrogels with high concentrations of silk fibroin. The relationship between the mechanical and biological properties and the structure of the silk‐pectin hydrogels is subsequently evaluated. The present results suggest that pectin associates with silk molecules when the silk concentration exceeds 15 wt%, suggesting that a silk concentration of over 15 wt% is critical to construct interacting silk‐pectin networks. The silk‐pectin hydrogel reported here is composed of a heterogeneous network, which is different from fiber‐reinforced, interpenetrated networks and double‐network hydrogels, as well as high‐stiffness hydrogels (elastic modulus of 4.7 ± 0.9 MPa, elastic stress limit of 3.9 ± 0.1 MPa, and elastic strain limit of 48.4 ± 0.5%) with regard to biocompatibility and biodegradability.     

Spectral analysis of Sr 3d XPS spectrum in Sr-containing hydroxyapatite

The Sr 3d X-ray photoelectron spectroscopy (XPS) spectrum of Sr-containing hydroxyapatite (SHAp) overlaps completely with the P 2p spectrum. Thus, the chemical state identification of Sr in SHAp is a challenging task. In this work, the Sr 3d spectrum was isolated from the overlapping spectra for analyzing the chemical state of Sr using a generic peak-fitting method. The SHAp layers containing various Sr concentrations were produced on a Ti substrate using a chemical treatment process with a calcium phosphate slurry that included Sr (NO₃)₂. The distribution of the constituent elements changed according to the Sr concentration, implying that the chemical state of Sr varied with concentration. The isolation of the Sr 3d XPS spectrum was conducted via spectral deconvolution using the P 2p spectrum corresponding to HAp. The isolated Sr 3d spectrum revealed that the chemical state of Sr was in SrO and Sr-substituted HAp states, and their ratio varied with the Sr concentration in the layer. The SrO to Sr-substituted HAp ratios affected the Sr ion releasing behavior from the SHAp layer, supporting the validity of the obtained analytical results.     

Profiles of ethylene polymerization with zirconocene–trialkylaluminum/borane compound

Ethylene polymerization was conducted with bis(cyclopentadienyl)zirconium dichloride (1) and rac-dimethylsilylenebis(indenyl)zirconium dichloride (2) combined with trialkylaluminum (AlR₃; R=methyl (Me), ethyl (Et), isobutyl (iBu))/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph₃CB(C₆F₅)₄) or tris(pentafluorophenyl)borane (B(C₆F₅)₃) to study the effect of cocatalysts on polymerization rate (R_p). When AlMe₃ was used, no activity or very low activity was observed with both zirconocenes regardless of the borane compounds used. The replacement of AlMe₃ to AlEt₃ or AliBu₃ with 1–AlR₃/Ph₃CB(C₆F₅)₄ caused polymerization and induction time was observed to reach the maximum R_p. Especially in the case of using AlEt₃, it took about 30 min to show the activity. When B(C₆F₅)₃ was used, AlEt₃ was not effective but AliBu₃ gave the highest activity among all the combinations of AlR₃ and the borane compounds. In the case of polymerization with 2 using Ph₃CB(C₆F₅)₄, high activity was observed with both AlEt₃ and AliBu₃ without any induction period. When B(C₆F₅)₃ was used instead of Ph₃CB(C₆F₅)₄, very low activity was observed with AlEt₃. On the other hand, high activity was observed with AliBu₃, and the maximum R_p was found at the beginning of the polymerization. The effect of AlR₃ on the formation of active species was discussed based on these results.