Electrochemical synthesis of dendritic diarylcarbenium ion pools

Dendritic diarylcarbenium ion pools were synthesized by the low temperature electrochemical oxidation of the corresponding dendritic (diarylmethyl)trimethylsilanes, which were prepared by use of the iterative method consisting of electrochemical activation and Friedel-Crafts type coupling. Time-course NMR studies revealed that thermal stability of dendritic diarylcarbenium ions depends both on the generation of the dendritic structure and on the para-substituents of the terminal phenyl groups. Dendritic diarylcarbenium ions up to the third generation exhibited high reactivity as a carbon electrophile.     

Adsorption of Zn(II) and Cd(II) ions onto magnesium and activated carbon composite in aqueous solution

Magnesium and coconuts shell activated carbon composite was prepared to selectively remove heavy metals ions in aqueous solution. Zinc(II) and cadmium(II) ions were used to clarify the adsorption capacity of the composite in comparison with no magnesium containing activated carbon. Influence of the initial heavy metal concentration, time course and solution temperature on the adsorption amounts were examined for the two adsorbents, and surface chemistry of the adsorbents was also characterized using Boehm titration. The magnesium composite adsorbed greater amount of Zn(II) and Cd(II) ions than the no magnesium counterpart. The adsorption amount of Cd(II) was not influenced with rise in solution temperature for the composite, whereas decrease in adsorption was observed for the counterpart. The loaded magnesium was estimated to be combined with carbon surface via oxygen bridge. Cadmium(II) was adsorbed onto the composite surface by ion exchange process with releasing equivalent amount of Mg(II) from the carbon surface, while Zn(II) would adsorb onto the composite by not only the ion exchange, but also the electrostatic interaction with the Cπ electrons on the graphite surface from the experimental results.     

A Lipschitz semigroup approach to two-dimensional Navier–Stokes equations

Motivated by the notion of integral solutions in the sense of Bénilan, a dissipative condition combined with a tangential condition is introduced. A generation problem of semigroups of Lipschitz operators is discussed under such a dissipative condition and the result is applied to the initial–boundary value problem for the Navier–Stokes equation in two-dimensional space.     

Chirality and ferromagnetism in NiBPO4(OH)2 containing helix edge-sharing NiO6 chains

Two isotypic borophosphates MBPO₄(OH)₂ (M=Mg, Ni) have been hydrothermally synthesized and structurally characterized by powder X-ray diffraction in the space group P3₁21. Nickel (or magnesium) atoms are octahedrally coordinated. The octahedra share edges to form helix chains around the three-fold screw-axis. Boron and phosphorus atoms are both tetrahedrally coordinated. The BO₄ and PO₄ tetrahedra are alternately connected, forming vierer-single chains. These two kinds of chains are intersected in the three-dimensional framework structure. NiBPO₄(OH)₂ can be considered as a quasi-one-dimensional magnet because the shortest Ni²⁺-Ni²⁺ distance within the helix chain is about 3.187(1) Å, while the shortest inter-chain connection of the nickel ions is through a BO₄ group (5.650(1) Å). Both dc and alternating current (ac) susceptibilities and isothermal magnetization have been measured on powder sample. The intra- and inter-chain interactions are proved to be both ferromagnetic, and a long-range ordering is established below 2.2 K in NiBPO₄(OH)₂.     

Diastereodifferentiating the [2+2] Photocycloaddition of Ethylene to Arylmenthyl Cyclohexenonecarboxylates: Stacking‐Driven Enhancement of the Product Diastereoselectivity That Is Correlated with the Reactant Ellipticity

Upon diastereodifferentiating the [2+2] photocycloaddition of ethylene to a series of p‐substituted (?)‐8‐phenylmenthyl cyclohexenonecarboxylates, the diastereoselectivity was critically controlled by the nature of the substituent introduced to the chiral auxiliary, and the p‐nitro‐substituted substrate afforded the cycloadducts in 90 % diastereomeric excess (de) and with 97 % isolated yield. Detailed experimental and theoretical conformation analyses revealed that the stacking interaction of the aromatic auxiliary with the cyclohexenone moiety plays the decisive role in determining the substrate conformation and is, therefore, responsible for the dramatic enhancement of the de. Of particular interest, the product de was directly related to the ellipticity of the substrate, enabling us to “predict” the de prior to photoirradiation.     

Polymer-Protected Bimetallic Clusters. Preparation and Application to Catalysis

Colloidal dispersions of polymer-protected Pd/Pt and Pd/Au bimetallic clusters were prepared by reduction of an alcoholic solution of PdCl₂ and H₂PtCl₆ or HAuCl₄ in the presence of poly(N-vinyl-2-pyrrolidone). The reduction can be carried out by refluxing in alcohol or by irradiation with visible light. The dispersions of the bimetallic clusters obtained are stable for months at room temperature and have from dark brown to brownish red color. Transmission electron micrographs show that the bimetallic clusters are composed of well-dispersed ultrafine particles of uniform size, about 1.5 nm for Pd-Pd and 3.4 nm for Pd-Au in diameter. The catalytic activity of the bimetallic clusters depends on the metal composition. In the case of the partial hydrogenation of 1, 3-cyclooctadiene, the activity went through a maximum when the alloy composition reached about 80% Pd and 20% Pt, or 60% Pd and 40% Au.     

Magnetic tuning of all-organic binary alloys between two stable radicals

Mixtures of 2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) and 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (BImNN) crystallize as solid solutions (alloys) across a wide range of binary compositions. (F4BImNN)(x)(BImNN)((1-x)) with x < 0.8 gives orthorhombic unit cells, while x ≥ 0.9 gives monoclinic unit cells. In all crystalline samples, the dominant intermolecular packing is controlled by one-dimensional (1D) hydrogen-bonded chains that lead to quasi-1D ferromagnetic behavior. Magnetic analysis over 0.4-300 K indicates ordering with strong 1D ferromagnetic exchange along the chains (J/k = 12-22 K). Interchain exchange is estimated to be 33- to 150-fold weaker, based on antiferromagnetic ordered phase formation below Néel temperatures in the 0.4-1.2 K range for the various compositions. The ordering temperatures of the orthorhombic samples increase linearly as (1 - x) increases from 0.25 to 1.00. The variation is attributed to increased interchain distance corresponding to decreased interchain exchange, when more F4BImNN is added into the orthorhombic lattice. The monoclinic samples are not part of the same trend, due to the different interchain arrangement associated with the phase change.