Film‐formation property of vinylidene chloride‐methyl methacrylate copolymer latex. I. Effect of emulsion‐polymerization process

Changes in minimum film‐formation temperature (MFFT) during storage of latexes prepared from 91:9 wt % vinylidene chloride (VDC)‐methyl methacrylate (MMA) monomer mixture by seeded batch and seeded semicontinuous emulsion polymerization were investigated, with attention centered on polymer‐crystallization behavior during storage in the dispersed state. MFFT of latex prepared by the seeded batch process rose to 47 °C, whereas that of latex prepared by seeded semicontinuous process remained below 14 °C with storage at 20 °C for 12 weeks. Infrared absorption of latexes in the dispersed state and wide‐angle X‐ray diffraction of powder polymers obtained by lyophilization of fresh and stored latexes both indicated a much greater increase in polymer crystallinity during storage with latex prepared by the seeded batch process than with that prepared by the seeded semicontinuous process. Analysis of the copolymer composition drift calculated from reactivity ratios and ¹H NMR analysis indicated a wider sequence distribution and longer VDC sequences in polymer prepared by the seeded batch process than in polymer prepared by the seeded semicontinuous process. This explained the higher rate of crystallization during storage with latex prepared by the seeded batch process than with that prepared by the seeded semicontinuous process. Rising crystallinity during storage in the dispersed state is believed to have caused the MFFT rise. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 939–947, 2002     

Microwave-assisted polyol synthesis of copper nanocrystals without using additional protective agents

We report the synthesis of 2 nm copper nanocrystals (Cu NCs) via a microwave-assisted polyol method without using additional protective and reducing agents. The Cu NCs are oxidation resistant and exhibit photoluminescence and highly stable properties in a colloidal dispersion.     

Simultaneous determination of histamine and prostaglandin D<Subscript>2</Subscript> using an LC-ESI-MS/MS method with positive/negative ion-switching ionization modes: application to the study of anti-allergic flavonoids on the degranulation of KU812 cells

A new method for simultaneous determination of histamine and prostaglandin D₂ (PGD₂) by liquid chromatography–electrospray ionization tandem mass spectrometry operated in positive and negative ionization switching modes was developed and validated without a previous derivatization step. This method was used to measure histamine and PGD₂ release following degranulation of KU812 human basophilic cells, using pyrazol and d₄-PGD₂ as internal standards. Analyses were performed on a liquid chromatography system employing a Cosmosil 5C₁₈ PAQ column and an isocratic elution with mixed solution of methanol–water (7:3, v/v) with 0.0015% trifluoroacetic acid at a flow rate of 0.2 mL/min. A triple-quadrupole mass spectrometer operating in selected reaction monitoring mode simultaneously monitored using the following transitions: positive m/z 112/95 for histamine and negative m/z 351/271 for PGD₂. The retention times of histamine and pyrazol were 4.2 and 5.0 min, respectively. PGD₂ and d₄-PGD₂ had retention times of 8.5 min. The limits of detection were 0.3 and 0.5 ng/mL for histamine and PGD₂, respectively. The relative standard deviations of the retention time and peak area for histamine were between 1.6% and 7.7%, and were 1.2% and 7.8% for PGD₂. This method was used to evaluate the anti-allergic effects of 26 flavonoids and sodium cromoglicate which are first-line anti-allergic drugs. Of these compounds, baicalein and morin were the most potent inhibitors.     

Direct measurement of the out-of-plane spin texture in the Dirac-cone surface state of a topological insulator

We have performed spin- and angle-resolved photoemission spectroscopy of Bi(2)Te(3) and present the first direct evidence for the existence of the out-of-plane spin component on the surface state of a topological insulator. We found that the magnitude of the out-of-plane spin polarization on a hexagonally deformed Fermi surface of Bi(2)Te(3) reaches maximally 25% of the in-plane counterpart, while such a sizable out-of-plane spin component does not exist in the more circular Fermi surface of TlBiSe(2), indicating that the hexagonal deformation of the Fermi surface is responsible for the deviation from the ideal helical spin texture. The observed out-of-plane polarization is much smaller than that expected from the existing theory, suggesting that an additional ingredient is necessary for correctly understanding the surface spin polarization in Bi(2)Te(3).     

The topological types of hypersurface simple K3 singularities

We give a result that relates the diffeomorphism type of the link of a non-degenerate semi-quasi-homogeneous hypersurface simple K3 singularity with the singularities of the normal K  3 surface that appears as the exceptional divisor of the resolution of the singularity. As a result, we show that the links are diffeomorphic to the connected sum of copies of S²×S³$S^2\times S^3$. Moreover, we also show that the topological types of hypersurface simple K3 singularities defined by non-degenerate semi-quasi-homogeneous polynomials are all different.     

Study of Conformers of 6,6'-Dimethyl-2,2'-bipyridine in the Ground and Excited States

UV absorption, luminescence, and luminescence-excitation spectra of the trans and metal-free cis conformers of 6,6'-dimethyl-2,2'-bipyridine (6,6'-Me₂bpy) and its Zn²⁺ complex have been observed in 2-propanol and 2-propanol-water mixtures at 77 K. The stable conformation of 6,6'-Me₂bpy in the ground state depends on the composition of the mixture at 77 K and the conformation remains unchanged upon photoexcitation. The lowest excited sing let energy is sensitive to the coordination to Zn²⁺, while the fluorescence lifetime is sensitive to both the conformation change of 6,6'-Me₂bpy and to the coordination to Zn²⁺.     

Magnetic Correlation Engineering in Spin-Sandwiched Layered Magnetic Frameworks

The insertion of “sandwiched spins” between magnetic layers could efficiently affect the interlayer magnetic correlations, but doing so increases the complexity in the interlayer spin alignment because of competition between the inserted spin-layer interaction J_NNI and the interlayer through-space interaction J_NNNI if the magnitude of J_NNI is of the same order as J_NNNI with reciprocal signs of the respective interactions. Herein, systematic tuning of the magnetic phase variations by J_NNI and J_NNNI in two kinds of metal-variable isostructural series of supramolecular pillared layer magnets [MCp*₂][{Ru₂^II,II(2,3,5,6-F₄CO₂)₄}₂(TCNQ)] ⋅ 2 DCE (M=Co, Fe, Cr; 2,3,5,6-F₄PhCO₂⁻=2,3,5,6-tetrafluorobenzoate; TCNQ=7,7,8,8-tetracyano-p-quinodimethane; DCE=1,2-dichloroethane) and their DCE-free series, in which [MCp*₂]⁺ (Cp*=η⁵-C₅Me₅) species with S=0, 1/2, and 3/2 for M=Co, Fe, Cr, respectively, are sandwiched between ferrimagnetic layers of [{Ru₂}₂(TCNQ)]⁻, is demonstrated. The results showed that the flexible magnetic natures of these magnets are changeable in dependence on J_NNI and J_NNNI, as well as on interlayer inserted spins M.     

Hydrostatic Pressure on Toroidal Interaction and Propeller Chirality of Hexaarylbenzenes: Explicit Solvent Effects on Differential Volumes in Methylcyclohexane and Hexane

A unique and effective interaction between the peripheral aromatic blades makes hexaarylbenzenes (HABs) attractive in fundamental research as well as for various applications such as molecular wires, sensors, and supramolecular assemblies. The chiroptical responses of HABs are susceptible to environmental factors such as solvent and temperature owing to the dynamic conformational transitions between the conformers. In this study, pressure dependence on the propeller chiral HABs in two different solvents was studied in detail. The effective differential volumes for two different equilibria were determined by quantitative analyses of CD spectra, affording very large differential volumes from the propeller to toroidal conformer (ΔV_T-C) of +43 and +42 cm³ mol⁻¹, for H2 and H6 , respectively, in methylcyclohexane. The value of H6 was further enhanced to +72 cm³ mol⁻¹ in hexane, the largest value for the typical unimolecular conformational change. Such a response of propeller chirality in HABs is expedient in designing more advanced piezo-sensitive materials.     

Field methane tracking with a portable and real-time open-gas monitor based on a cw-driven Pb-salt diode laser

An atmospheric gas monitor with a PbSnTe diode laser has been developed. The open, 1 m optical path in a single-folded configuration enables local and non-contact measurement in a portable instrument. The accuracy is dependent on optical noise and a technique in diode-current modulation was effective in suppressing it. Analysis of the system noise based on the experimental data was made and a 10 ms interval was sufficient to attain an accuracy of 3 ppm for methane. Field measurements were made and a rapid fluctuation in the density of atmospheric methane density was recorded.     

Novel liquid crystalline compounds having an enyne unit

Novel series of liquid crystalline compounds having an enyne unit, 1-(4-alkylphenyl)-4-(trans-4-alkylcyclohexyl)-but-3-en-1-yne and 1-(4-alkoxyphenyl)-4-(trans-4-alkylcyclohexyl)-but-3-en-1-yne are presented. The synthetic methods, mesomorphic phases, and some physical properties of these series are reported.