Structures of americanol A and isoamericanol A having a neurotrophic property from the seeds of Phytolacca americana.

The structures of new neo-lignans, isoamericanol A (1) and americanol A (2) isolated from the seeds of Phytolacca americana have been elucidated on the basis of spectroscopic data and then confirmed by chemical correlation with the previously known isoamericanin A (3) and americanin A (4). Isoamericanol A, americanol A, and americanin A have been found to enhance choline acetyltransferase activity at 10(-5) M in a cultured neuronal cell system derived from fetal rat hemisphere.     

Growth Mechanism of Large Monodispersed Silica Particles Prepared from Tetraethoxysilane in the Presence of Sodium Dodecyl Sulfate

Monodispersed silica particles up to ca. 1.2 μm in diameter were prepared by hydrolysis of tetraethoxysilane in the presence of sodium dodecyl sulfate (SDS). The particle size was increased with an increase of SDS added. The geometrical standard deviation of the particles was decreased with an increase of SDS. In the earlier reaction stage, double spherical particles by the coalescence of the particles were frequently observed when large amounts of SDS were added. Particle size was gradually increased after the coalescence occurred and spherical particles were finally obtained. The results of Nielsen’s chronomal analysis suggest that the polynuclear layer growth took place after the coalescence of the particles in the presence of larger amount of SDS.     

Evaluation of Photocatalytic Activity of Transparent Anatase Nanocrystals-Dispersed Silica Films Prepared by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals were precipitated mainly at the surface of the silica-titania gel films with hot water treatment, whereas the addition of poly(ethylene glycol) (PEG) in the films led to the dispersion of anatase nanocrystals in the whole of the films after the treatment. Both films with and without PEG showed high photocatalytic activities for acetaldehyde, NO _x and stearic acid in the gas-solid system, and for methylene blue and potassium iodide in the liquid-solid system. The addition of PEG improved the photocatalytic activities of the resultant films due to the smaller anatase crystallites and the porous film structure. The residual silica under-layer of the superficially anatase-precipitated films is expected to act as a protective one for an organic polymer substrate against the photocatalytic degradation.     

Mechanistic approaches to asymmetric synthesis of aziridines from guanidinium ylides and aryl aldehydes

To approach more realistic mechanisms for asymmetric aziridine synthesis from guanidinium ylides and aryl aldehydes, reactions were systematically carried out by using a variety of p-substituted benzaldehydes under modified conditions. Two kinds of reaction mechanisms controlled by the nature of the p-substituents of aryl aldehydes is proposed for the two-steps aziridine synthesis composed of a C-C bond formation by nucleophilic addition of guanidinium ylides to aryl aldehydes (step 1) and the fragmentation of intermediate adducts to aziridine products by intramolecular nucleophilic substitution (step 2). A S_Ni-like mechanism via cationic-like transition state is proposed for step 2 in the asymmetric synthesis using EDG-substituted benzaldehydes, whereas with EWG-substituted benzaldehydes, a S_N2-like mechanism is proposed. Hammett analysis, based on the diastereomeric ratio in the aziridine products, is consistent with the proposed rate-determining steps in these two mechanisms. A second Hammett analysis, based on the enantiomeric ratio of the aziridine products, clearly reveals the difference in the susceptibilities to the electronic substituents effect between step 1 and step 2.     

Preparation of Titania Nanosheet-Precipitated Coatings on Glass Substrates by Treating SiO2-TiO2 Gel Films with Hot Water Under Vibrations

Titania nanosheet-precipitated coatings have been prepared by treating SiO₂-TiO₂ gel films on glass substrates with hot water at 90°C under vibration. Longitudinal vibrations at about 6 Hz during the treatment enhanced the formation of titania nanosheet. The titania nanosheet consisted of several layers with a spacing of about 0.6 nm and was identified as hydrated titania with a lepidocrocite-type structure. The morphology of the titania nanosheet-precipitated coatings is probably achieved by lowering of the concentration of hydrolyzed titania species at the surface due to rapid water flow driven by the vibrations. The coatings were transparent in the visible range and showed high photocatalytic activity and antifogging property.     

Structure of an anti-plasmin inhibitor, eckol, isolated from the brown alga Ecklonia kurome Okamura and inhibitory activities of its derivatives on plasma plasmin inhibitors

Eckol (1), a novel phlorotannin with a dibenzo-1,4-dioxin skeleton, has been isolated from the brown alga Ecklonia kurome Okamura as a potent and specific anti-plasmin inhibitor. Its structure has been elucidated based on the spectral data, in particular, by means of negative nuclear Overhauser effect (NOE), and finally established as 1-(3,5-dihydroxyphenoxy)-2,4,7,9-tetrahydroxydibenzo-1,4-dio xin by X-ray analysis. Some partially methoxylated derivatives of eckol were prepared by methylation with diazomethane and also by selective dimethylation of eckol permethylate (1b) to establish the structural requirements for inhibitory activities on alpha 2-macroglobulin and alpha 2-plasmin inhibitor, the main plasmin inhibitors in plasma.     

Alternative copolymerization of aziridines and carbon monoxide by γ-ray irradiation

The copolymerization of carbon monoxide and aziridines such as ethylenimine and propylenimine was carried out by γ-ray irradiation. Aziridines and carbon monoxide were allowed to copolymerize under γ-ray irradiation from a Co⁶⁰ source and gave a crystalline solid copolymer. The yield of the copolymer increased with reaction temperature. The composition of copolymers obtained did not depend on the feed ratio of monomers and was found to be almost equimolar. The copolymer of ethylenimine and carbon monoxide melted at about 322–335°C. with decomposition and has an infrared spectrum identical with that of poly-β-alanine obtained by the hydrogen-migration polymerization of acrylamide. The hydrolyzed product of the ethylenimine–carbon monoxide copolymer was confirmed to be β-alanine by paper chromatography. These results lead to the conclusion that the copolymerization of aziridines and carbon monoxide took place alternatively by γ-ray irradiation, and produced crystalline poly-β-alanines.     

Synthesis and polymerization of N-[N′-(α-methylbenzyl)aminocarbonyl-n-alkyl]maleimide

Two types of optically active N-[N′-(α-methylbenzyl)amino/carbonyl-n-alkyl]maleimides (MBAC) were synthesized from maleic anhydride, 6-amino-n-caproic acid (or 12-amino-n-dodecanoic acid), and (R)-(+)-α-methylbenzylamine. Radical homopolymerizations of MBAC were performed in several solvents at 60 and 110°C for 24 h to give optically active polymers. Radical copolymerizations of MBAC were performed with styrene (ST) and methyl methacrylate (MMA) in dioxane at 60°C. The monomer reactivity ratios and the Alfrey-Price Q-e values were determined. Chiroptical properties of the polymers and copolymers were investigated. © 1995 John Wiley & Sons, Inc.     

Efficient photochemical oxetane formation from 1-methyl-2,4,5-triphenylimidazole and benzophenones

In contrast to simple imidazoles, 1-methy1–2,4,5-triphenylimidazole ($\text{1}$) produced stable oxetane photoadducts $\text{3b}$ - $\text{e}$ with good efficiency upon irradiation in the presence of benzophenone derivatives $\text{2b}$ - $\text{e}$ in acetonitrile solution. Irradiation in the solid-phase was also studied. The oxetanes $\text{3b}$ - $\text{e}$ readily underwent cycloreversion by acid catalysis or by heating.