Chiral Sc-catalyzed asymmetric Michael reactions of thiols with enones in water

Asymmetric Michael reactions of thiols with enones were catalyzed by a Sc(OTf)(3)-chiral bipyridine complex at room temperature in water without using any organic solvents, to afford the desired sulfides in high yields with high enantioselectivities.     

Synthesis, structures and ab initio studies of selenium and tellurium bis(carbodithioates and carbothioates)

A series of selenium and tellurium bis(carbodithioates and carbothioates) were synthesized. X-Ray structure analysis revealed that Se(SSCC(6)H(4)OMe-2)(2), Te(SSCC(6)H(4)OMe-2)(2) and Te(SSCC(6)H(4)Me-4)(2) have trapezoidal-planar configuration of ES(4) (E = Se, Te) and despite the larger atomic radii, the C=S···Te distances in Te(SSCC(6)H(4)OMe-2)(2) are comparable to those in the corresponding selenium derivatives Se(SSCC(6)H(4)OMe-2)(2). Molecular-orbital calculations performed on compounds E(E'SCR)(2) (E = S, Se, Te; E' = O, S; R = Me, Ph, C(6)H(4)OMe-2) showed that the syn-conformers of Se(SSCR)(2) and Te(SSCR)(2) are more stable than the corresponding anti-ones, while, in the case of carbothioic acid derivatives, E(SOCR)(2) showed that their anti-conformers are all more stable than the corresponding syn-ones. Natural bond orbital (NBO) analyses of these dithio-compounds revealed that two types of orbital interactions, n(S(1))→σ*(E-S(2)) and n(O)→σ*(E-S(2)), play a role in the bonding of E[S(2)S(1)CC(6)H(4)OMe-2](2) (E = Se, Te) and the former play a particularly predominant role.     

Thermoreversible gelation of isotactic-rich poly(N-isopropylacrylamide) in water

We report the experimentally determined phase diagram for an aqueous solution of isotactic-rich poly(N-isopropylacrylamide) (PNiPAM) composed of the sol-gel transition curve and the cloud-point curve. The meso diad content of isotactic-rich PNiPAM is 64%, and it is soluble in water at low temperatures, but undergoes a sol-to-gel transition with increasing temperature in the investigated concentration range of 1.8 wt. %-6.0 wt. %. With a further increase in temperature, the system becomes turbid. The gel formation and clouding behavior are thermally reversible. This is the first observation of thermoreversible gelation under the cloud-point temperature for an aqueous solution of PNiPAM. On the basis of the determined phase diagram, we carried out light scattering experiments to characterize the sol-gel transition behavior as a function of temperature.     

Surface segregation of poly(2-methoxyethyl acrylate) in a mixture with poly(methyl methacrylate)

Poly(2-methoxyethyl acrylate) (PMEA) exhibits excellent blood compatibility. To understand why such a surface functionality exists, the surface of PMEA should be characterized in detail, structurally and dynamically, under not only ambient conditions, but also in water. However, a thin film of PMEA supported on a solid substrate can be easily broken, namely it is dewetted. Our strategy to overcome this difficulty is to mix PMEA with poly(methyl methacrylate) (PMMA). Differential scanning calorimetry and cloud point measurements revealed that the PMEA/PMMA blend has a phase diagram with a lower critical solution temperature. The blend surface was also characterized by X-ray photoelectron spectroscopy in conjunction with microscopic observations. Although PMEA is preferentially segregated over PMMA at the blend surface due to its lower surface free energy, the extent of segregation in the as-prepared films was not sufficient to cover the surface. Annealing the blend film at an appropriate temperature, higher than the glass transition temperature and lower than the phase-separation temperature of the blend, enabled us to prepare a stable and flat surface that was perfectly covered with PMEA.     

Synthesis and Photocatalytic Property of Hectorite/(Pt,TiO2) and H4Nb6O17/(Pt,TiO2) Nanocomposites

Abstract

TiO₂ and Pt have been intercalated in hectorite and H₄Nb₆O₁₇. The height of TiO₂ and Pt pillars was less than 0.8 nm and the band gap energy of TiO₂ pillars was ca. 3.3 eV. Both hectorite/TiO₂ and H₄Nb₆O₁₇(Pt, TiO₂) were capable of hydrogen evolution following irradiation from a high pressure mercury are (λ > 290 nm) in the presence of methanol as a sacrificial hole acceptor and the hydrogen evolution was enhanced by co-incorporation of Pt, although hectorite and hectorite/Pt did not show photocatalytic activity. Incorporation of Pt or Pt and TiO₂ in the interlayer of H₄Nb₆O₁₇ has resulted in enhanced photo evolution of hydrogen, however, TiO₂ alone in the interlayer of H₄Nb₆O₁₇ showed adverse photocatalytic activity.     

Ultrafast Encapsulation of Metal Nanoclusters into MFI Zeolite in the Course of Its Crystallization: Catalytic Application for Propane Dehydrogenation

Encapsulating metal nanoclusters into zeolites combines the superior catalytic activity of the nanoclusters with high stability and unique shape selectivity of the crystalline microporous materials. The preparation of such bifunctional catalysts, however, is often restricted by the mismatching in time scale between the fast formation of nanoclusters and the slow crystallization of zeolites. We herein demonstrate a novel strategy to overcome the mismatching issue, in which the crystallization of zeolites is expedited so as to synchronize it with the rapid formation of nanoclusters. The concept was demonstrated by confining Pt and Sn nanoclusters into a ZSM-5 (MFI) zeolite in the course of its crystallization, leading to an ultrafast, in situ encapsulation within just 5 min. The Pt/Sn-ZSM-5 exhibited exceptional activity and selectivity with stability in the dehydrogenation of propane to propene. This method of ultrafast encapsulation opens up a new avenue for designing and synthesizing composite zeolitic materials with structural and compositional complexity.     

Capacitance-conductance detector for high-pressure liquid chromatography. Application to alkaloids and fatty acids

Summary A new type of detector for high-pressure liquid chromatography has been designed. This detector is equipped with a RC resonance circuit, and is similar to the capacitance detector previously reported. It is operated as a capacitance detector with nonpolar eluents; while with polar solvents, it behaves as a conductance detector. Electrolytes such as salts, acids and bases are sensitively detected. The detector was successfully used for the detection of fatty acids and alkaloids.

---

Zusammenfassung Ein neuartiger Detektor für die Hochdruck-Flüssigchromatographie wurde entwickelt. Dieser ist mit einem Resonanzstromkreis ausgestattet und ähnelt dem kürzlich beschriebenen Kapazitanz-Detektor. Als solcher funktioniert er mit nichtpolaren Eluenten, während er sich mit polaren Lösungsmitteln wie ein Leitfähigkeitsdetektor verhält. Salze, Säuren und Basen werden empfindlich nachgewiesen. Das Gerät wurde zum Nachweis von Fettsäuren und Alkaloiden verwendet.

     

A quantitative analysis of the through-space and the through-bond interactions between lone-pairs in azines: pyridazine,pyrimidine and pyrazine

The INDO calculations were performed on the three azines: pyridazine, pyrimidine, and pyrazine. The cannonical molecular orbitais obtained by these calculations were then transformed into the localized molecular orbitals. With the use of the localized molecular orbitals, the variation in the lone-pair orbital energies of these molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized molecular orbitals in a molecule selectively. The interactions were expressed by the summation of several terms: through-space, through-bond, through-virtuals and coupling terms.