Anionic [4+3] heteroannulation of 2-azidoacrylates: a modular synthesis of 2-benzazepin-1-ones

2-Azidoacrylates undergo [4+3] annulation with phthalides under anionic conditions at low temperatures to furnish 5-hydroxy-2-benzazepinones, the formation of which represents a new concept for the construction of azepines as well as a new reactivity of 2-azidoacrylates.     

A new type of migrating zone boundary in electrophoresis: 2. Transient sample zone shapes

A new type of migrating zone boundary in electrophoresis is presented theoretically and evidenced experimentally. This type of the boundary (called hybrid boundary) shows simultaneously a steady-state part with self-sharpening properties and an unsteady-state part with time-dependent electromigration dispersion. It is shown that a sample zone may possess a hybrid boundary both as its front and rear one simultaneously. In such a case, the evolution of a sample zone injected originally as a rectangular pulse exhibits very complex transient shapes before it reaches the well-known fronting or tailing triangular shape. Depending on the stage at which detection of such a sample zone occurs, variable and peculiar-shape peaks may appear in the electropherogram. Based on theoretical predictions, experimental examples of the above-mentioned phenomena are presented in this contribution for direct and indirect UV absorbance detection of sample zones. Excellent agreement of theoretical predictions with the experiments has been found. The knowledge of hybrid boundaries is of key significance for correct interpretation of records of CE analyses in practice.     

Heterogeneous Wheel‐Shaped Cu20‐Polyoxotungstate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25− Catalyst for Solvent‐Free Aerobic Oxidation of n‐Hexadecane

The selective oxidation of alkanes as a green process remains a challenging task because partial oxidation is easier to achieve with sacrificial oxidants, such as hydrogen peroxide, alkyl hydroperoxides or iodosylbenzene, than with molecular oxygen or air. Here, we report on a heterogeneous catalyst for n‐hexadecane oxidation comprised of the wheel shaped Cu₂₀‐polyoxotungstate [Cu₂₀Cl(OH)₂₄(H₂O)₁₂(P₈W₄₈O₁₈₄)]^25? anchored on 3‐aminopropyltriethoxysilane (apts)‐modified SBA‐15. The catalysts were characterized by powder X‐ray diffraction (XRD), N₂‐adsorption measurements and Fourier transform infrared reflectance (FT‐IR) spectroscopy. The heterogeneous Cu₂₀‐polyanion system catalyzed the solvent‐free aerobic oxidation of n‐hexadecane to alcohols and ketones by using air as the oxidant under ambient conditions. The catalyst exhibits an exceptionally high turn over frequency (TOF) of 20 000 h^?1 at 150 °C and is resistant to poisoning by CS₂. Moreover, it can be easily recovered and reused by filtration without loss of its catalytic activity. Possible homogeneous contributions also have been examined and eliminated. Thus, this system can use air as oxidant, which, in combination with its good overall performance and poison tolerance, raises the prospect of this type of heterogeneous catalyst for practical applications.     

Large prolongation of free-exciton photoluminescence decay in diamond by two-photon excitation

We report on time-resolved photoluminescence of a free-exciton in IIa chemical vapor deposition diamond crystal. Large difference between decay times for one- and two-photon excitation processes was observed. The longest room-temperature exciton photoluminescence lifetime τ(FE)=220 ns was obtained under two-photon excitation with a photon energy of 4.7 eV. The role of diffusion and surface recombination velocity in exciton photoluminescence dynamics was studied using a new optical method based on two-photon excited time-resolved photoluminescence. The measured room-temperature value of diffusion coefficient in diamond was D=40 cm(2)/s.     

Temperature effect on structural transformations in nanocrystalline cobalt films

The effect of annealing temperature on the structure and magnetic properties of nanocrystalline cobalt films has been studied by nuclear magnetic resonance (NMR) and magnetometric (vibrational magnetometer) techniques. Interpretation of the experimental data demonstrates that the initial films have an amorphous-like structure due to the high degree of disordering in the intergranular regions and nanoparticles. This structure transforms into the equilibrium polycrystalline state through the formation of a number of intermediate phases.     

Lattice Mismatch Guided Nickel-Indium Heterogeneous Alloy Electrocatalysts for Promoting the Alkaline Hydrogen Evolution

The immiscibility of crystallographic facets in multi-metallic catalysts plays a key role in driving the green H₂ production by water electrolysis. The lattice mismatch between tetragonal In and face-centered cubic (fcc) Ni is 14.9 % but the mismatch with hexagonal close-packed (hcp) Ni is 49.8 %. Hence, in a series of Ni−In heterogeneous alloys, In is selectively incorporated in the fcc Ni. The 18–20 nm Ni particles have 36 wt % fcc phase, which increases to 86 % after In incorporation. The charge transfer from In to Ni, stabilizes the Ni⁰ state and In develops a fractional positive charge that favors *OH adsorption. With only 5 at% In, 153 mL h⁻¹ H₂ is evolved at −385 mV with mass activity of 57.5 A g⁻¹ at—400 mV, 200 h stability at −0.18 V versus reversible hydrogen electrode (RHE), and Pt-like activity at high current densities, due to the spontaneous water dissociation, lower activation energy barrier, optimal adsorption energy of OH⁻ ions and the prevention of catalyst poisoning.     

On the gelation rate of thermoreversible poly(vinylidene fluoride) gels in glyceryl tributyrate

The gelation rate of poly(vinylidene fluoride) (PVF₂)/glyceryl tributyrate (GTB) system has been measured. It has been analysed with the help of an equation which contains φⁿ and f(T) term where φ is a reduced overlapping concentration and n is analogous to the percolation exponent β in a three-dimensional lattice. f(T) is related to the temperature function of the coil-to-helix transition. Analysis of the gelation rates supports that the three-dimensional percolation is a suitable mechanism in this gelation process and it also indicates that the gelation is caused by coil-to-helix transition followed by their association.