Practical synthesis of 4,4,4-trifluorocrotonaldehyde: a versatile precursor for the enantioselective formation of trifluoromethylated stereogenic centers via organocatalytic 1,4-additions

The practical synthesis of 4,4,4-trifluorocrotonaldehyde (1) and its application to enantioselective 1,4-additions are described. The organocatalytic 1,4-addition of 1 with several nucleophiles such as heteroaromatics, alkylthiols and aldoximes afforded the corresponding products, each bearing a trifluoromethylated stereogenic center with high optical purity. A resulting product was converted into an MAO-A inhibitor, befloxatone.     

Post-synthesis dispersion of metal nanoparticles by poly(amidoamine) dendrimers: size-selective inclusion, water solubilization, and improved catalytic performance

Intermetallic Pt(3)Ti nanoparticles are solubilized in water by using a generation-five, hydroxyl-terminated, poly(amidoamine) dendrimer, G5OH, as a post-synthesis surfactant. Pt(3)Ti nanoparticles, encapsulated in G5OH and dispersed over the electrode surface, exhibited a superior catalytic activity toward the electro-reduction reaction of oxygen compared to as-prepared, highly agglomerated nanoparticles.     

Magnetism and structure of graphene nanodots with interiors modified by boron, nitrogen, and charge

The properties (geometry, spin, and charge distribution) of a series of flat hexagonal zigzag edged graphene nanodots (GNDs), with interiors modified by centrally located substituent atoms boron and nitrogen and by positive and negative charge, have been calculated using ab initio density functional theory. The doped series X-GND has the stoichiometry C(6m(2)-1)XH(6m), zigzag size index m = 2, 4, 6, 8, 10 and substituent X = B or N. The undoped parents C(6m(2) )H(6m) with m ≤ 8 have spin paired ground states and the parent m = 10 has a spin polarized singlet ground state with edges that alternate α- and β-spin. The spin on the substituent atom decreases to zero with size index m and magnetization builds on the edges of all the X-GND. This demonstrates translocation of substituent spin and a proximity or directional effect for small m as the edges show different degrees of magnetization. For the largest X-GND (m = 10) the magnetization on edges resembles the calculated triplet S = 1(a) configuration of the parent (four edge spins up and two down) and has a higher apparent symmetry than the C(2v) point group of X-GND. For charged (m = 10) GNDs the edge magnetization has strength comparable to the parent on two parallel edges and weak on the other four in a perimeter pattern that resembles the triplet S = 1(b) configuration of the undoped parent and not the ground configuration of the isoelectronic X-GND molecule. Many of the results can be interpreted by simple Kekule? valence bond structures for an unpaired spin on a network where the substituent site group symmetry is not compatible with the perimeter. A deeper understanding is provided by the properties of the Kohn-Sham orbitals. The calculations of the X-doped GNDs reveal limitations in the use of the hex-radical hypothesis of the parent ground state to systems where foreign atoms lower symmetry and perturb the π- and σ-bond manifolds.     

Phase conversion from graphite toward a simple monoclinic sp3-carbon allotrope

We identify by ab initio calculations a simple monoclinic carbon in P2/m (C(2h)(1)) symmetry with an alternating zigzag and armchair buckling of the carbon sheets in AA stacking, which is formed via a distinct one-layer by one-layer conversion mechanism along the [210] direction assisted by a large lattice distortion. It is dynamically stable and energetically favorable as well as recently identified orthorhombic W- and monoclinic M-carbon. Moreover, this new phase has a wider band gap than diamond's, and is compatible with the experimental x-ray diffraction data. These results broaden our understanding of the direct graphite-to-diamond phase transition.     

Bioactive Properties of Chitin/Chitosan—Calcium Phosphate Composite Materials

Calcium phosphate coating over phosphorylated derivatives of chitin/chitosan material was produced by a process based on phosphorylation, Ca(OH)₂ treatment and SBF (simulated body fluid solution) immersion. Chitin/chitosan phosphorylated using urea and H₃PO₄ and then soaked in saturated Ca(OH)₂ solution at ambient temperature, which lead to the formation of thin coatings formed by partial hydrolysis of the PO₄ functionalities, were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5 × SBF solution for as little as one day. The Ca(OH)₂ treatment facilitates the formation of a calcium phosphate precursor over the phosphorylated chitin/chitosan, which in turn encourages the growth of a calcium deficient apatite coating over the surface upon immersion in SBF solution. The bio-compatibility of calcium phosphate compound—chitin/chitosan composite materials was evaluated by cell culture test using L-929 cells. The initial anchoring ratio and the adhesive strength of L-929 cells for composites was higher than that for the polystyrene disk (LUX, control). The results of in-vitro evaluation suggested that the calcium phosphate—chitin/chitosan composite materials were suitable for cell carrier materials.     

Application of single-walled carbon nanotube body to unique emitter: a first-principles study

The field emission characteristics of the body for single-walled carbon nanotubes (SWNTs) are investigated by use of the first-principles calculations. We find that field emission property, chemical stability and binding energy of the tube body with the practical diameter are less sensitive to the tube diameter, morphology, and conductive characteristic, and conclude the emission features of the body film: consistence in emission sites, uniformity in emission energy distribution, predictability in emission effects and high emission stability, which are similar to those of graphite sheet or diamond film. These unique features guarantee the tube body to be applicable to flat panel displays with the same picture quality, cylindrical cathode and linear emitter.     

Redetermination of bis{[(2‐hydroxy­phenyl­methyl)­bis(2‐pyridyl­methyl)­aminato]copper(II)} diperchlorate

The structure of the title compound, [Cu₂(C₁₉H₁₈N₃O)₂](ClO₄)₂, was reported with insufficient accuracy because of a twinning problem by Adams, Bailey, Campbell, Fenton & He [J. Chem. Soc. DaltonTrans. (1996), pp. 2233–2237]. The dinuclear phenolate‐bridged Cu^II complex has an inversion centre.     

Chloro­[N′,N′‐diethyl‐N,N‐bis(2‐pyri­dyl­methyl)­ethyl­enedi­amine‐κ4N]copper(II) perchlorate

The title mononuclear copper(II) complex, [CuCl(C₁₈H₂₆N₄)]ClO₄, shows a square‐pyramidal coordination with the diethyl­amino N atom at the apical position. Large anisotropies in the displacement parameters of the non‐H atoms of the ligand seem to be due to rotational disorder of the ClO₄^? anion.     

Tetra‐μ‐acetato‐O:O′‐bis­[(7‐aza­indole‐N)­copper(II)]

The title complex, [Cu₂(C₂H₃O₂)₄(C₇H₆N₂)₂], shows a binuclear cage structure having an inversion centre. There are intramolecular N—H?O hydrogen bonds between the 7‐aza­indole ligands and the bridging acetate O atoms.     

Aerobic Dehydrogenation of N-Heterocycles with Grubbs Catalyst: Its Application to Assisted-Tandem Catalysis to Construct N-Containing Fused Heteroarenes

An aerobic dehydrogenation of nitrogen-containing heterocycles catalyzed by Grubbs catalyst is developed. The reaction is applicable to various nitrogen-containing heterocycles. The exceptionally high functional group compatibility of this method was confirmed by the oxidation of an unprotected dihydroindolactam V to indolactam V. Furthermore, by taking advantage of the oxygen-mediated structural change of the Grubbs catalyst, we integrated ring-closing metathesis and subsequent aerobic dehydrogenation to develop the novel assisted-tandem catalysis using molecular oxygen as a chemical trigger. The utility of the assisted-tandem catalysis was demonstrated by the concise synthesis of N-containing fused heteroarenes including a natural antibiotic, pyocyanine.