Enantioselective desymmetrization of meso-N-(heteroarenesulfonyl)aziridines with TMSN3 catalyzed by chiral Lewis acids

A catalytic enantioselective desymmetrization of meso-N-(heteroarenesulfonyl)aziridines with TMSN₃ using chiral Lewis acids afforded products with high enantioselectivity. As proof of the utility of this procedure, the precursor of selective κ-opioid agonist (1S,2S)-(−)-U-50,488 was synthesized.     

Coordination-induced branched self-assembly of porphyrins bearing two redox-active phenylenediamine chains

The porphyrins bearing two three-dimensionally regulated oligoaniline chains with terminal pyridyl groups were synthesized. The self-assembled branched polymer complex by introducing Zn(II) to the porphyrin was achieved in solution, which underwent dropcasting on the surface of mica to result in dome-like nanostructures.     

Pulsed EPR Analysis of the Photo-Induced Triplet Radical Pair in the BLUF Protein SyPixD: Determination of the Protein–Protein Distance and Orientation in the Oligomeric Protein

A photo-induced radical pair of FADH^· and Y8^· and in BLUF protein SyPixD was studied by pulsed electron paramagnetic resonance (EPR) spectroscopy. Blue light illumination at 150 K for 30 min followed by cooling to 50 K during illumination induced the stable radical pair. The EPR signal has been characterized by a Pake doublet signal with complete S = 1 spin state. The radical pair was utilized as a probe to analyze the oligomer of SyPixD. The relative arrangement of PixD proteins in the complex was investigated by pulsed electron–electron double resonance (PELDOR) with the orientation selection. Based on the decameric structure in the crystal, the possible structure for the PELDOR results was discussed.     

Investigation of void formation beneath thin AlN layers by decomposition of sapphire substrates for self-separation of thick AlN layers grown by HVPE

Void formation at the interface between thick AlN layers and (0 0 0 1) sapphire substrates was investigated to form a predefined separation point of the thick AlN layers for the preparation of freestanding AlN substrates by hydride vapor phase epitaxy (HVPE). By heating 50–200 nm thick intermediate AlN layers above 1400 °C in a gas flow containing H₂ and NH₃, voids were formed beneath the AlN layers by the decomposition reaction of sapphire with hydrogen diffusing to the interface. The volume of the sapphire decomposed at the interface increased as the temperature and time of the heat treatment was increased and as the thickness of the AlN layer decreased. Thick AlN layers subsequently grown at 1450 °C after the formation of voids beneath the intermediate AlN layer with a thickness of 100 nm or above self-separated from the sapphire substrates during post-growth cooling with the aid of voids. The 79 μm thick freestanding AlN substrate obtained using a 200 nm thick intermediate AlN layer had a flat surface with no pits, high optical transparency at wavelengths above 208.1 nm, and a dislocation density of 1.5×10⁸ cm⁻².     

An ab initio-based approach to the stability of GaN(0 0 0 1) surfaces under Ga-rich conditions

Structural stability of GaN(0 0 0 1) under Ga-rich conditions is systematically investigated by using our ab initio-based approach. The surface phase diagram for GaN(0 0 0 1) including (2×2) and pseudo-(1×1) is obtained as functions of temperature and Ga beam equivalent pressure by comparing chemical potentials of Ga atom in the gas phase with that on the surface. The calculated results reveal that the pseudo-(1×1) appearing below 684–973 K changes its structure to the (2×2) with Ga adatom at higher temperatures beyond 767–1078 K via the newly found (1×1) with two adlayers of Ga. These results are consistent with the stable temperature range of both the pseudo-(1×1) and (2×2) with Ga adatom obtained experimentally. Furthermore, it should be noted that the structure with another coverage of Ga adatoms between the (1×1) and (2×2)-Ga does not appear as a stable structure of GaN(0 0 0 1). Furthermore, ghost island formation observed by scanning tunneling microscopy is discussed on the basis of the phase diagram.     

A numerical study of 3D natural convection in a cube: effects of the horizontal thermal boundary conditions

A high-resolution, three-dimensional finite-difference numerical study of natural convection flows of a viscous fluid in a differentially heated cubical box is reported. The vertical sidewalls of the enclosure are maintained at constant temperatures of different values. The other vertical walls (the end walls) are thermally insulated. For the horizontal walls, two kinds of thermal boundary conditions are specified: adiabatic and perfectly conducting. Computations have been performed for an air-filled cavity for Rayleigh numbers of 10⁵ and 10⁶. The specific effects of the horizontal thermal boundary conditions on the flow structure are examined in detail. In the case of conducting walls, heat transfer through the horizontal walls enhances the convective flow activities. The numerically predicted velocity and temperature profiles in the symmetry planes are consistent with previous experimental measurements and computations.     

Electronic structures of the highest occupied molecular orbital bands of a pentacene ultrathin film

We report the energy dispersions of the highest occupied molecular orbitals (HOMO)-derived bands of a pentacene (Pn) thin film, whose in-plane structure resembles closely that of the ab plane of a low-density bulk Pn phase. Our present photoemission result indicates that the overlap of the pi-orbitals of adjacent Pn molecules is larger than what was expected from theoretical calculations. Further, of the two HOMO-derived bands, the large dispersion width of the band with higher binding energy suggests that this one mainly contributes to the bandlike charge transport in a Pn crystal.     

Polyaniline‐Induced CH Arylation of Arenes with Arenediazonium Salts

A reduced form of polyaniline has been shown to induce direct arylation of an arenediazonium salt with an arene (Gomberg–Bachmann reaction) to give the cross‐coupling product in moderate to good yields under mild conditions. Various arenediazonium salts and arenes, including heteroarenes such as furans, thiophenes, and pyrroles, are employed for the reaction. The most favorable combination of substrates is an electron‐poor arenediazonium salt with an electron‐rich heteroarene. Investigation of the mechanism by reactions with radical scavengers and experiments on kinetic isotope effects indicated the occurrence of a radical chain reaction initiated by one‐electron reduction of an arenediazonium salt by the polyaniline. Only 1 mol % (based on aniline tetramer) of the polyaniline is required for the cross‐coupling reaction to occur. This reaction proceeds under metal‐free conditions and with no need for photonic activation.