Absolute configuration of (-)-biflora-4,10(19),15-triene,a diterpene from a termite soldier,as determined by the synthesis of its (1R, 6S, 7S, 11R)-(+)-isomer

(1R, 6S, 7S, 11R)-(+)-Biflora-4, 10(19),15-triene was synthesized starting from (r)-(+)-citronellic acid. This enabled us to assign (1S), 6R, 7R, (11S)-stereochemistry to the naturally occurring (-)-enantiomer isolated from soldiers of the termite species Cubitermes umbratus.     

pH-responsive aqueous foams stabilized by hairy latex particles

Polystyrene (PS) latex particles carrying pH-responsive poly[2-(diethylamino)ethyl methacrylate] (PDEA) hair (PDEA-PS particles) were synthesized by dispersion polymerization and characterized in terms of diameter, diameter distribution, morphology, chemical composition, surface chemistry, and pH-response using scanning electron microscopy (SEM), elemental microanalysis, (1)H nuclear magnetic resonance spectroscopy, the laser diffraction method, and zeta potential measurements. The hairy particles can act as pH-responsive stabilizers of aqueous foams by adsorption at the air-water surface. Above pH 8.0, where particles have nonprotonated PDEA hair, which is relatively hydrophobic, particle-stabilized foams are stable for at least 1 month. Optical microscopy and SEM confirmed that flocculated PDEA-PS latex particles were adsorbed at the air-water interface and stabilized the aqueous foams. At pH 6.1 and 7.1, relatively stable foams can be prepared that remain stable for at least 24 h. SEM studies indicated that the PDEA-PS particles were adsorbed at the air-water interface as a monolayer at pH 6.1. At pH 5.1 and 3.1, where the particles have cationic water-soluble PDEA hairs with hydrophilic character, no foam was formed. Rapid defoamation can be induced by lowering the solution pH; the addition of acid caused the in situ protonation of 2-(diethylamino)ethyl methacrylate residues, which impart water-soluble hydrophilic character to the PDEA hair, and the PDEA-PS particles desorbed from the air-water interface. The foaming and defoaming cycles could be repeated at least five times.     

Liquid phase formation of alkyl- and perfluoro-phosphonic acid derived monolayers on magnesium alloy AZ31 and their chemical properties

Alkyl- and perfluoro-phosphonic acid derived SAMs were successfully formed on Mg alloy by liquid phase method for the first time. The chemical and anticorrosive properties of the prepared SAMs on magnesium alloys were characterized using contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrochemical measurements. Water contact angle measurements revealed that the maximum advancing/receding water contact angles of n-octyl (OP: CH(3)(CH(2))(7)PO(OH)(2)), n-dodecyl (DP: CH(3)(CH(2))(11)PO(OH)(2)), n-octadecyl (ODP: CH(3)(CH(2))(17)PO(OH)(2)) phosphonic acid, and 2-(perfluorohexyl)ethyl (PFEP: CF(3)(CF(2))(5)CH(2)CH(2)PO(OH)(2)) phosphonic acid were 105.1/64.7°, 108.3/69.6°, 111.9/75.2°, and 115.2/67.4° respectively. In the case of alkylphosphonic acid SAMs (OP, DP, and ODP), the advancing and receding water contact angles increased with an increase in the preparation time. The angle-resolved XPS (AR-XPS) data revealed that the film thicknesses of the OP, DP, ODP, PFEP on Mg alloy were estimated to be 0.8, 1.2, 1.7, and 1.1 nm, respectively. The XPS O 1s data support that the phosphonic acid derived SAM is covalently bound to the oxide or hydroxide surface of the Mg alloy in a monodenate or bidenate manner. Chemical stability of the alkyl- and perfluoro-phosphonic acid modified Mg alloy surfaces was investigated using aqueous solutions at pH=4.0, 7.0, and 10.0. The contact angles of OP, DP, and PFEP modified Mg surface decreased rapidly within the first 5 min after immersion in all the aqueous solutions and were less than 20°. On the other hand, the contact angles of the ODP modified Mg alloy after immersion in aqueous solutions at pH 4, 7 and 10 for 5 min were 45.1°, 89.3,° and 85.5°, respectively. The ODP modified Mg alloy had highest chemical stability in four types of the phosphonic acid derived SAMs used in this study, indicating that the molecular density of ODP on Mg alloy would be higher than those of OP, DP, PFEP on Mg alloy. The corrosion resistance of ODP modified Mg alloy was investigated by potentiodynamic polarization curve measurements. The ODP modified Mg alloy exhibits protective properties in a solution containing Cl(-) ions compared to unmodified Mg alloy.     

Sub-Doppler high-resolution excitation spectroscopy of the S1 ← S0 transition of dibenzofuran

Rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the S₁ ← S₀ transition of dibenzofuran have been observed using the technique of crossing a collimated molecular beam and the single-mode UV laser beam. 3291 rotational lines of the band and 3047 rotational lines of the band have been assigned. The band has been found to be a b-type transition, in which the transition moment is along the twofold symmetry axis of this molecule, and only the ΔK_a = ± 1 transitions were observed. The excited state is identified to be the S₁¹A₁(ππ^∗) state. In contrast with this, the band has been found to be an a-type transition in which the transition moment is along the long axis in plane. It indicates that the intensity of this vibronic band arises from vibronic coupling with the S₂¹B₂(ππ^∗) state. We determined the accurate rotational constants and the molecule have been shown to be planar both in the ground and excited states.     

Melting and swelling behaviors of UV-irradiated gelatin gel microcapsules

Gelatin gel microcapsules with a narrow size distribution have been prepared for the use of regenerative therapy by means of SPG (Shirasu porous glass) emulsification and UV-induced cross linking, and the melting and swelling behaviors of the gel membrane of the microcapsules were observed. The gel melting temperature was proportional to the 2/3 power of UV irradiation time t for tor=1 h. The average cross-sectional area of the microcapsules that remains insoluble normalized by that at 25 degrees C monotonically increased with temperature for tor=1 h. Repeated quenching of the gel microcapsules between two temperatures (25 and 40 degrees C) induced a reversible size change, which was attributed to the helix-coil transition of collagen molecules locally. From a theoretical consideration of gel particles, the observed gel melting behavior was explained well, and the scaled volume of the microcapsules was expressed as a function of scaled temperature with four fitting parameters for t相似文献   

Palladium-catalyzed addition of nitrogen pronucleophiles to alkylidenecyclopropanes

The inter- and intramolecular additions of cyclic amides (nitrogen pronucleophiles) to methylenecyclopropanes proceeded smoothly in the presence of catalytic amounts of Pd(PPh(3))(4), affording the corresponding hydroamination products in good to high yields with high regioselectivities. The ring opening of methylenecyclopropanes occurred at the distal position of the cyclopropane ring.     

Stability of two-dimensional crystalline aggregates of a protein studied by molecular dynamics

Two-dimensional protein (ferritin) aggregates with a square lattice symmetry, which were formed within a thin liquid layer on a mercury surface, were studied by molecular dynamics (MD) simulation. For the simulation, the ferritin molecule was modeled by an assembly of 49 spheres, and the intermolecular interactions were given by simple formulae. During the simulation, molecules were confined within a layer, which corresponds to the thin liquid layer. An annealing MD simulation was done starting from a random molecular configuration within the layer, and aggregates with the square lattice symmetry were also obtained. To study the stability of aggregates, dissociation processes of the aggregates were analyzed using MD simulations at room temperature. Interactions between the nearest-neighbor molecules were regarded as bonds. Mean bond energies and correlation coefficients between the bond energies were calculated from the MD trajectories. A decay profile according to the dissociation was obtained, yielding a dissociation rate constant. Buried bonds were stronger than peripheral bonds. The larger the aggregate size, the stronger the bond for each of the buried and peripheral bonds. A simple theoretical account, which is applicable to a general bonded network, was introduced to analyze the dynamics of the aggregates. © 1994 by John Wiley & Sons, Inc.     

Ultrahigh Electron Emissive Carbon Nanotubes with Nano-sized RuO2 Particles Deposition

Multi-wall carbon nanotubes (MWNTs) have a great commercial potential as electron field emitters, but suffer from fundamental problems such as stability and brightness. By depositing the MWNTs with nano-sized ruthenium dioxide (RuO₂) particles, a new high performance emitter has been developed. When compared to MWNTs, the MWNTs impregnated with 1–2 nm sized RuO₂ have superior and more efficient electrical characteristics. MWNTs supported by a silicon substrate showed a reduction in the onset voltage from 5.4 to 4 V/μm after RuO₂ impregnation. The long-term stability of the impregnated MWNTs is also demonstrated with only a 20% increase in applied voltage required after 700 h operation at 40 mA/cm².     

Liquid crystalline gel beads of curdlan

Curdlan beads consisting of liquid crystalline gel (LCG) and amorphous gel (AG) in alternating layers in a wide range of diameters were newly prepared by interfacial insolubilization reactions using calcium chloride as the setting reagent. The thickness of the liquid crystalline layer was proportional to the diameter of the gel bead, and the proportional constant agreed with that determined for the cylindrical gel prepared by a dialysis method. The proportional constant initially increased with increasing calcium concentration of the dispersing medium and saturated at a high concentration limit. These results suggest that the mechanisms for forming the alternating LCG/AG structures prepared with different boundary conditions are the same. The LCG/AG structure could be controlled by calcium concentration.     

(NH4)3[VO2(SO4)2(H2O)2]·1.5H2O

The title compound, tri­ammonium cis‐di­aqua‐cis‐dioxo‐trans‐disulfatovanadate 1.5‐hydrate, was obtained by oxidizing V^IV to V^V in a 2 M sulfuric acid solution of vanadyl­ sulfate and adding ammonium sulfate. Here, the V atom is sandwiched by two sulfate groups by corner‐sharing to form a discrete [VO₂(SO₄)₂(OH₂)₂]^3? anion. The water mol­ecules occupy cis positions in the equatorial plane of the vanadium octahedron.