A Bio‐inspired Cu4O4 Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution

Inspired by the cubic Mn₄CaO₅ cluster of natural oxygen‐evolving complex in Photosystem II, tetrametallic molecular water oxidation catalysts, especially M₄O₄ cubane‐like clusters (M=transition metals), have aroused great interest in developing highly active and robust catalysts for water oxidation. Among these M₄O₄ clusters, however, copper‐based molecular catalysts are poorly understood. Now, bio‐inspired Cu₄O₄ cubanes are presented as effective molecular catalysts for electrocatalytic water oxidation in aqueous solution (pH 12). The exceptional catalytic activity is manifested with a turnover frequency (TOF) of 267 s^?1 for [(L_Gly‐Cu)₄] at 1.70 V and 105 s^?1 for [(L_Glu‐Cu)₄] at 1.56 V. Electrochemical and spectroscopic study revealed a successive two‐electron transfer process in the Cu₄O₄ cubanes to form high‐valent Cu^III and Cu^IIIO^. intermediates during the catalysis.     

Solid‐State NMR Study on Relationships between Miscibility and Chain Mobility in Poly(4‐Methylstyrene)/Poly(Cyclohexyl Methacrylate) Blend

The phase behavior and motional mobility in binary blends of poly(4‐methylstyrene) (P4MS) and poly(cyclohexyl methacrylate) (PCHMA) have been examined by ¹³C solid state NMR techniques. The blend miscibility was studied by measuring the ¹H spin‐relaxation times in the laboratory frame (T₁^H) and in the rotating frame (T_1ρ^H), respectively. Although intermolecular spin diffusion contributes to the proton relaxations in accordance with homogeneity, T_1ρ^H data shows signs of in complete averaging. The T_1ρ^H relaxation behavior indicates the existence of heterogeneous do mains with shortest dimensions in the nanometer range, which is also sup ported by the intermolecular cross polarization experiments with variable contact times. In addition, according to the resuits of carbon T_1ρ relaxation time measurements, it is concluded that mixing is intimate some what enough to cause a reduction in local chain mobility for P4MS and vice versa for PCHMA.     

Polarographic Studies of Dithiodiacetic Acid and the Uranyl-Dithiodiacetic Acid Complex

The polarographic behaviour of dithiodiacetic acid and that of U(VI) in a solution containing dithiodiacetic acid as complexing agent have been investigated. For the dithiodiacetic acid system, two waves appear over the pH range studied. The prewave is kinetic in nature and the mainwave is diffusion-controlled. However, as U(VI) is added into the dithiodiacetic acid system, the polarogram changes due to the existence of a complex. The current-potential curve of the first wave is not the normal S shape. This is due to the superposition of the first wave of the ligand and the wave due to the reduction of the U(VI) in the complex to U(V). The second wave is due to the reduction of the complex The first wave is an adsorption-controlled current and the second wave is partly diffusion-controlled and partly adsorption-controlled. We propose an electrode reaction mechanism for both systems and the complex species. The dissociation constant of the complex HASSAUO⁺₂ is found to be of the order of 10^?4.     

tert-BuOK-mediated carbanion-yne intramolecular cyclization: synthesis of 2-substituted 3-benzylbenzofurans

A mild, efficient, and regioselective carbanion-yne intramolecular cyclization mediated by t-BuOK for the synthesis of 2-substituted 3-benzylbenzofurans is developed. It was started from o-iodophenol (1), based on O-alkylation, and the Sonogashira reaction in sequence to produce 2-(2-phenylethynylphenoxy)-1-arylalkanones (5). An intramolecular carbanion-yne 5-exo-dig cyclization reaction of 5, which was mediated by t-BuOK, yielded title benzofurans in good yields.     

Scalar-tensor theory and the anisotropic perturbations of the inflationary universe

Inflationary higher derivative scalar-tensor theory is analyzed in this paper in a de Sitter background space. A useful model-independent formula of the Friedmann equation is derived and used to study the stability problem associated with the anisotropic perturbations of the inflationary solution. The stability conditions of the de Sitter solution are derived for a general class of models. For a simple demonstration, an induced gravity model is considered in this paper for the effects of the higher derivative interactions including a cubic term.     

Analysis of amino acids and biogenic amines in breast cancer cells by capillary electrophoresis using polymer solutions containing sodium dodecyl sulfate

We describe simultaneous analysis of naphthalene-2,3-dicarboxaldehyde (NDA)-amino acid and NDA-biogenic amine derivatives by CE in conjunction with light-emitting diode-induced fluorescence detection using poly(ethylene oxide) (PEO) solutions containing sodium dodecyl sulfate (SDS). After sample injection, via EOF 0.1% PEO prepared in 100 mM TB solution (pH 9.0) containing 30 mM SDS entered a capillary filled with 0.5 M TB solution (pH 10.2) containing 40 mM SDS. Under this condition, 14 NDA-amino acid and NDA-amine derivatives were separated within 16 min, with high efficiency ((1.0–3.2) × 10⁵ theoretical plates) and sensitivity (LODs at S/N = 3 ranging from 2.06 to 19.17 nM). In the presence of SDS and PEO, analytes adsorption on the capillary wall was suppressed, leading to high efficiency and reproducibility. The intraday analysis RSD values (n = 3) of the mobilities for the analytes are less than 0.52%. We have validated the practicality of this approach by quantitative determination of 9 amino acids in breast cancer cells (MCF-7) and 10 amino acids in normal epithelial cells (H184B5F5/M10). The concentrations of Tau and Gln in the MCF-7 cells were different than those in the H184B5F5/M10 cells, respectively. Our results show the potential of this approach for cancer study.     

Synthesis and electrogenerated chemiluminescence of donor-substituted phenylquinolinylethynes and phenylisoquinolinylethynes: effect of positional isomerism

In furtherance of our research on the design, synthesis and study of electrogenerated chemiluminescence (ECL) of new donor substituted phenylquinolinylethynes, we report here more new series with the aim of studying the effect of positional isomerism on their overall photophysical properties with a special focus on ECL. For this study we have chosen 2-, 3-, and 4-(p-substituted phenyl)ethynylquinolines, and 1- and 4-(p-substituted phenyl)ethynylisoquinolines. These ethynes were synthesized in good yields by modified Sonogashira coupling of the corresponding terminal alkyne with the respective haloquinolines. The photophysical properties and ECL were studied in acetonitrile solvent and the various results are discussed.     

Anomalous structural phase transition properties in ReSe2 and Au-doped ReSe2

The high pressure induced phase transition in rhenium diselenides (ReSe(2)) and gold-doped rhenium diselenides (Au-ReSe(2)) at ambient temperature have been investigated using angular-dispersive x-ray diffraction (ADXRD) under high pressure up to around 10.50 and 9.98 GPa, respectively. In situ ADXRD measurements found that the phase transition pressures of ReSe(2) and Au-ReSe(2) began at 9.98 and 8.52 GPa, respectively. Compressibilities analysis shows the relationship of along c-axis > along a-axis > along b-axis. The linear compressibility of the pressure dependence of α, β, and γ of ReSe(2) shows that a phase transition can be related to a counterclockwise rotational trend of the selenium atoms around the chain of Re(4) atoms during the decrease of the c-axis distance by a combination of stresses due to the bending effect of α and stretching effect of β. The cause of the reduction of the phase transition pressure of Au-ReSe(2) is attributed mainly to a structural distortion as evidenced by the observation of a weak clockwise rotational trend of Se atoms around the chain of Re(4) atoms in the pressure range 3.99-4.99 GPa which subsequently reversed to counterclockwise rotation under higher pressure.     

Particle size effects of carbon sources on electrochemical properties of LiFePO<Subscript>4</Subscript>/C composites

Carbon-coated LiFePO₄ cathode materials were prepared by a solid-state method incorporating different sizes of polystyrene (PS) spheres as carbon sources. In scanning electron microscope images, small PS spheres appear more effective at preventing aggregation of LiFePO₄ particles. From transmission electron microscopy images, it was found that the LiFePO₄ particles were completely uniformly coated with 5-nm carbon layer when the carbon source was 0.22 μm PS spheres. When the size of PS sphere was increased to 2.75 μm, a network of carbon was formed and wrapped around the LiFePO₄ to create a conductive web. Raman spectroscopy and four-point probe conductivity measurement showed that using larger sizes of PS spheres as carbon sources leads to greater conductivity of LiFePO₄/C. The LiFePO₄ precursor sintered with 0.22 μm PS spheres delivered an initial discharge capacity of 145 mAh g^?1 at a 0.2 C rate, but it only sustained 289 cycles at 80% capacity. When the diameter of PS spheres was increased to 2.75 μm, the discharge capacity of LiFePO₄/C decreased, but the cycle life reached 755 cycles, the highest number in this work probably due to the network formation of carbon wrapping around LiFePO₄ particles.     

Synthetic Transformations of Sulfur‐Substituted 4‐Quinolizidinones

Sulfur‐substituted 4‐quinolizidinones, previously prepared by aza‐Diels‐Alder reactions and ring‐closing metathesis, are now subjected to further synthetic transformations. Formal synthesis of cermizine C and 5‐epi‐cermizine C, and some other useful reactions have been achieved.