Optical and electronic properties of siloxane-bridged cyclic dimers with naphthylene or pyrenylene moieties

The optical and electronic properties of novel siloxane-bridged cyclic dimers with naphthylene (CD1) or pyrenylene (CD2) moieties are described. CD1 and CD2 were obtained by the cyclic dimerization of 1,4-bis(dimethylhydroxysilyl)naphthalene (M1) and 1,6-bis(dimethylhydroxysilyl)pyrene (M2), respectively. CD1 and CD2 mainly exhibited the emission from their excimers owing to their short distances between aryl moieties in CD1 and CD2, which were determined to be 3.44 Å and 3.41 Å by the X-ray crystallographic analysis, respectively. The absorption spectra of CD2 in the presence of 7,7,8,8-tetracyanoquinodimethane (TCNQ) revealed that CD2 has the ability to form 1:1 charge-transfer complex with TCNQ, indicating the existence of the transannular π-π interaction between closely located pyrene components in CD2.     

Coexistence properties of phase separation and CuPt-ordering in InGaAsP grown on GaAs substrates by organometallic vapor phase epitaxy

CuPt-ordering and phase separation were directly investigated in In_1-xGa_xAs_yP_1-y with a low arsenic content grown by organometallic vapor phase epitaxy on GaAs substrates. CuPt-ordering and phase separation in samples grown at the substrate temperatures of 630 and 690 °C were characterized by transmission electron diffraction and transmission electron microscopy. Although the immiscibility of InGaAsP was enhanced at the lower substrate temperature, the sample grown at 630 °C showed less phase separation than the 690 °C-grown sample. The degree of CuPt-ordering was significantly enhanced in the sample grown at 630 °C. The results demonstrated that the CuPt-ordering originating from surface reconstruction of P(2×4) suppressed the phase separation even in the miscibility gap. The detailed characterization of the phase separation clearly revealed a vertical composition modulation (VCM) in InGaAsP for the first time. The mechanism of the VCM formation is discussed based on the modulated-strain field on the surface.     

Effect of poly(ethylene oxide) on the rheological behavior of silica suspensions

The steady-shear viscosity, dynamic viscoelasticity, and sedimentation behavior were measured for silica suspensions dispersed in aqueous solutions of poly(ethylene oxide) (PEO). For suspensions prepared with polymer solutions in which the transient network is developed by entanglements, the viscosity at a given shear rate decreases, shows a minimum, and then increases with increasing particle concentration. Because the suspensions are sterically stabilized under the conditions where the particle surfaces are fully covered with by a thick layer of adsorbed polymer, the viscosity decrease can be attributed to the reduction of network density in solution. But under the low coverage conditions, the particles are flocculated by bridging and this leads to a viscosity increase with shear-thinning profiles. The polymer chains with high molecular weights form flexible bridges between particles. The stress-dependent curve of storage modulus measured by a stress amplitude sweep shows an increase prior to a drastic drop due to structural breakdown. The increase in elastic responses may arise from the restoring forces of extended bridges with high deformability. The effect of PEO on the rheological behavior of silica suspensions can be explained by a combination of concentration reduction of polymer in solution and flocculation by bridging.     

Antianoxic action and active constituents of atractylodis lanceae rhizoma

The screening test was carried out to identify new drugs from natural products for the KCN-induced anoxia model in mice. Acetone extract of Atractylodis Lanceae Rhizoma (Atractylodes lancea DC. var. Chinensis Kitamura) had a significant effect in the KCN-induced anoxia model and therefore the extract was selected for further study in order to identify the active principles. The result showed that beta-eudesmol was the active component in Atractylodis Lanceae Rhizoma.     

Simultaneous determination of cationic surfactants and nonionic surfactants by ion-association titration.

A simultaneous determination of cationic and nonionic surfactants has been developed using ion-association titration. Tetrabromophenolphthalein ethyl ester (TBPE) was used as an indicator. Benzalkonium reacted with TBPE to form a blue ion-associate in the organic phase. When tetrakis(4-fluorophenyl)borate was added dropwise to the solution, the color of the organic phase turned to yellow at the equivalence point. In addition, when a large amount of potassium ion was added to a solution including Triton X-100, Triton X-100 could be determined by the same technique as described above because of formation of the K+-Triton X-100 cation. The proposed method is available for the stepwise determination of cationic and nonionic surfactants in mixtures.     

Three‐component negative‐type photosensitive polyimide precursor based on poly(amic acid), a crosslinker,and a photoacid generator

A new negative‐working and alkaline‐developable photosensitive polyimide precursor based on poly(amic acid) (PAA), 4,4′‐methylenebis[2,6‐bis(hydroxymethyl)]phenol (MBHP) as a crosslinker, and a photoacid generator (5‐propylsulfonyloxyimino‐5H‐thiophen‐2‐ylidene)‐2‐(methylphenyl)acetonitrile (PTMA) has been developed. PAA was prepared by ring‐opening polymerization of pyromellitic dianhydride with 4,4′‐oxydianiline. The photosensitive polyimide precursor containing PAA (65 wt %), MBHP (25 wt %), and PTMA (10 wt %) showed a clear negative image featuring 10 μm line and space patterns when it was exposed to 436 nm light at 100 mJ·cm^?2, post‐exposure baked at 130 °C for 3 min, followed by developing with a 2.38 wt % aqueous tetramethylammonium hydroxide solution at 25 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 593–599, 2005     

Stereoselective anti-SN2′ Mitsunobu reaction of α-hydroxy-α-alkenylsilanes

A novel silyl group-directed anti-S_N2′ reaction of allylic alcohols under Mitsunobu reaction conditions is described. The Mitsunobu reaction of α-hydroxy-α-alkenylsilanes with a TBS or TIPS group gave the anti-S_N2′ product, in which regio- and stereochemical outcomes of the reaction depended on the steric bulkiness of the silyl group.     

The synthetic and biological studies of discorhabdins and related compounds

Various analogues of the marine alkaloids, discorhabdins, have been synthesized. The strategy contains spirocyclization with phenyliodine(III) bis(trifluoroacetate) (PIFA), oxidative fragmentation of the β-amino alcohols with the hypervalent iodine reagent C(6)F(5)I(OCOCF(3))(2), the detosylation and dehydrogenation reaction of the pyrroloiminoquinone unit in the presence of a catalytic amount of NaN(3) and the bridged ether synthesis with HBr-AcOH as the key reactions. All the synthesized compounds were evaluated by in vitro MTT assay for cytotoxic activity against the human colon cancer cell line HCT-116. Furthermore, the discorhabdin A oxa analogues were also evaluated against four kinds of tumor model cells, a human colon cancer cell line (WiDr), a human prostate cancer cell line (DU-145) and murine leukemia cell lines (P388 and L1210). For the identification of the target, discorhabdin A and the discorhabdin A oxa analogue were evaluated by an HCC panel assay. In the test, discorhabdins could have a novel mode of action with the tumor cells.     

Ultrafast spectroscopy and coherent acoustic phonons of Au-Ag core-shell nanorods

We performed the first investigations of coherent acoustic phonons in Au-Ag core-shell nanorods, which were compared with the results of parental Au nanorods. Both breathing and extensional modes were observed in Au-Ag core-shell nanorods with ~11 nm Ag shell while only extensional modes were detected in other core-shell nanorods with 4-7 nm Ag shell. Young's modulus estimated from the oscillation period of extensional modes was found to be larger for Au-Ag core-shell nanorods with ~4 nm Ag shell, as compared with that of Au nanorods. The value of Young's modulus decreases with the increase of the Ag shell thickness and finally becomes smaller than that of Au nanorods. This phenomenon is interpreted in terms of the surface effects and the existence of grain boundaries in the lattice structure of Ag shell.