Synthesis of silicon nitride based ceramic nanoparticles by the pyrolysis of silazane block copolymer micelles

Diblock copolymer poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane)‐block‐polystyrene (polyVSA‐b‐polySt) and triblock copolymer poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane)‐block‐polystyrene‐block‐poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane) (polyVSA‐b‐polySt‐b‐polyVSA), consisting of silazane and nonsilazane segments, were prepared by the living anionic polymerization of 1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane and styrene. PolyVSA‐b‐polySt formed micelles having a poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane) (polyVSA) core in N,N‐dimethylformamide, whereas polyVSA‐b‐polySt and polyVSA‐b‐polySt‐b‐polyVSA formed micelles having a polyVSA shell in n‐heptane. The micelles with a polyVSA core were core‐crosslinked by UV irradiation in the presence of diethoxyacetophenone as a photosensitizer, and the micelles with a polyVSA shell were shell‐crosslinked by UV irradiation in the presence of diethoxyacetophenone and 1,6‐hexanedithiol. These crosslinked micelles were pyrolyzed at 600 °C in N₂ to give spherical ceramic particles. The pyrolysis process was examined by thermogravimetry and thermogravimetry/mass spectrometry. The morphologies of the particles were analyzed by atomic force microscopy and transmission electron microscopy. The chemical composition of the pyrolysis products was analyzed by X‐ray fluorescence spectroscopy and Raman scattering spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4696–4707, 2006     

Fluorescence spectra,fluorescence quantum yields and fluorescence lifetimes of polymers having trans-1,2-dicarbazolylyclobutane or carbazolyl group

Quantum yields, lifetimes and shapes of fluorescence from polymers containing the trans-1,2-dicarbazolylcyclobutane (DCZB) or carbazolyl structures were studied in N,N-dimethylformamide. No sandwich-type excimer formation was observed for DCZB polymers. The so-called second excimer observed in poly(9-vinylcarbazole) might also be produced in poly(9-ethyl-3-vinylcarbazole).     

Effective Hamiltonian method for environmental effects

Some novel physical ideas and mathematical techniques are described, useful in the development of effective Hamiltonian methods for studying molecular environmental effects.     

Development of dynamic compartment model for prediction of behavior of radioiodine in rice paddy field

For the assessment of a public impact caused by radionuclides released from nuclear facilities, a dynamic compartment model was developed for prediction of behavior of radioiodine in air, paddy field and rice plant system. The transfer coefficients among compartments were determined by some experimental data and assumptions for each chemical form of iodine. A verification of the model was carried out by some case studies.     

Structure of Sol-Gel-Derived Sodium Dititanate Glass

The sodium dititanate, Na₂O·2TiO₂ glass was prepared by the sol-gel method. The structure of the glass, especially local environment of Ti⁴⁺ ions was examined using X-ray diffraction and X-ray absorption fine structure (XAFS) analyses, and was compared with that of the melt-derived glass with the same composition. It was found that Ti⁴⁺ ions are rather in five-fold coordination state, forming TiO₅ pyramids with one doubly bonded Ti=O in the gel-glass, while they were in lower coordination state or four-fold coordination in the melt-derived glass.     

Microdetermination of fluorine in organic compounds by oxygen flask combustion and conductometric titration

For the conductometric titration of fluoride with calcium acetate, solvent system in sample solution and titrant, concentration, and acidity of sample solution were examined to establish the titration conditions. Results of these examinations were transferred to the microdetermination of fluorine in organic compounds using oxygen flask combustion method.Comparative examination between quartz and Pyrex flasks for the combustion of fluorine samples indicated that good results were obtained by the use of the former flask, whereas the use of the latter one gave negative values of 1.0–1.6% due to the formation of boron fluoride during the combustion.     

Property of TS-16N solid state nuclear track detectors as an imaging medium for macroautoradiography of alpha-emitters in biological specimens

Feasibility of TS-16N solid state nuclear track detectors for an imaging medium of rapid autoradiography of alpha-emitters is described. Though a little longer etching time was required, the contrast of autoradiographic image on this detector proved to be superior to CR-39 detectors whose property for macroautoradiography was previously reported by the authors. The resolutions of these two different type detectors were almost equivalent to each other. The autoradiography taken by way of trial proved that this detector could be used to study metabolism and dosimetry of internally deposited alpha-emitters. With further study, the inherent properties of this detector such as low background or high sensitivity should extend the field of track etch imaging technique such as fast neutron radiography.     

Amphotericin B covalent dimers forming sterol-dependent ion-permeable membrane channels

Polyenemacrolides such as amphotericin B (AmB) were thought to assemble together and form an ion channel across plasma membranes. Their antimicrobial activity has been accounted for by this assemblage, whose stability and activity are dependent on sterol constituents of lipid bilayer membranes. The structure of this channel-like assemblage formed in biomembranes has been a target of extensive investigations for a long time. For the first step to this goal, we prepared several AmB dimers with various linkers and tested for their channel-forming activity. Among these, AmB dimers that bore an aminoalkyl-dicarboxylate tether covalently linked between amino groups of AmB showed potent hemolytic activity. Furthermore, K+ influx actions monitored by measuring the pH of the liposome lumen by 31P NMR revealed that the dimers formed the molecular assemblage similar to that of AmB in phospholipid membrane. Judging from changes in 31P NMR spectra, the dimers appeared to induce "all-or-none"-type ion flux across the liposome membrane in the presence of ergosterol, which suggested that the ion channel formed by ergosterol/dimer is similar to that of AmB. With these data in hand, we are now trying to elucidate the structure of the ion-channel complex by making the labeled conjugates of AmB for NMR measurements.     

Protonation-induced structural change of lyotropic liquid crystals in oley- and alkyldimethylamine oxides/water systems

Lyotropic phase behavior of the nonionic and the half-ionized oleyldimethylamine oxide (OlDMAO)/water systems was investigated using polarized light microscopy, small-angle X-ray diffraction, and differential scanning calorimetry. Nonionic OlDMAO formed isotropic micellar solution, nematic, hexagonal, cubic, and lamellar liquid crystalline phases as the surfactant concentration increased. In contrast, half-ionized OlDMAO (i.e., 1:1 mixture of the nonionic and the protonated species) had a greater tendency to form bilayer structures, and the phase diagram became quite similar to those of double-chained ionic surfactants rather than single-chained ones, despite the introduction of positive charges to the nonionic one. The preference of the bilayer structures in the half-ionized OlDMAO was interpreted in terms of the dimers stabilized by the hydrogen bond between the nonionic and protonated species. For alkyldimethylamine oxides with a saturated hydrocarbon chain (CnDMAO, chain length: n = 14, 16, and 18), the phase sequence of lyotropic liquid crystals was hardly affected by the protonation, but an elongation of the cylinders of the hexagonal phase was observed for the half-ionized C14DMAO. Consequently, it can be considered that the dominant bilayer formation of the half-ionized OlDMAO is attributed to the combined effect of the hydrogen-bonded dimer formation and the cis-double-bond configuration of the alkyl chain.