Chiral imides as potential chiroptical switches: synthesis and optical properties

A series of chiral aromatic imides and diimides were synthesized and their electrochemical, absorption, fluorescent, and chiroptical properties were examined for their potential application as molecular chiroptical switches. These compounds exhibit strong UV-vis absorptions, and can be electrochemically reduced to radical anions that absorb in the near infrared (NIR) region. Further reduction to the dianionic states results in new absorptions in the visible region. The changes in circular dichroism upon redox switching were apparent in the UV-vis region but were absent in the NIR region.     

Three new lanthanide coordination polymers containing isophthalate and 1,10-phenanthroline

Three lanthanide coordination polymers were prepared by hydrothermal synthesis and characterized by single-crystal X-ray diffraction. [Pr₂(mBDC)₃(phen)(H₂O)]_n·0.5nH₂O (1) (mBDC=isophthalate, phen=1,10-phenanthroline) exhibits two kinds of metal environments (coordination numbers 7 and 8). In complex 1, mBDC ligands adopt the tetradentate (bridging and bridging) coordination mode and connect Pr ions into an undulating layer, and a 3D supramolecular structure is formed via hydrogen bonds between adjacent layers. [Tb₄(mBDC)₆(phen)]_n (2) has three types of metal environments (coordination numbers 6, 7 and 8) and is composed of a 3D network formed by mBDC linking Tb ions via tetradentate (bridging and bridging) and pentadentate (bridging/chelating and bridging) coordination modes. There are two kinds of small quadrilateral channels along the a-axis. [Er₄(mBDC)₆(phen)]_n (3) is isostructural to complex 2.     

Self-assembling of helical poly(phenylacetylene) carrying L-valine pendants in solution, on mica substrate, and on water surface

In the present work, we investigated self-assembling of a poly(phenylacetylene) carrying L-valine pendants (PPA-Val) in a water/methanol solution, upon evaporation of the solution on mica, and on the water surface. With intercalation of a fluorescence probe of Ru(phen)2(dppx)2+ (phen = 1,10-phenanthroline, dppx=7,8-dimethyldipyridophenazine) into the hydrophobic cavities associated by the PPA-Val chains, their helical structures were directly detected in solution with an in situ fluorescence microscope. Helical aggregates were observed with AFM upon evaporation of the solvents, suggesting that the helical structures in the solution are the building blocks of the helical aggregates. Self-assembling structures of PPA-Val on the water surface were, however, very different from that formed upon evaporation of its THF solution on the mica surface. The polymer chains associated into a monolayer of extended fibers on the water surface, whereas superhelical fibers formed on the mica surface. Water molecules play a critical role in inducing the polymer to form diverse morphological structures in its bulk solution and on its surface. In solution, the isotropic hydrophobic effect drove the polymer chains to form superhelical aggregates, while on the water surface, the hydrophobic effect concentrated mainly on the lateral part of the polymer, thus giving a monolayer of extended fibers.     

Determination of silicon by an indirect atomic-absorption method using carbon-rod electrothermal atomization

An indirect procedure has been developed for the determination of trace amounts of silicon by atomic-absorption with carbon-rod electrothermal atomization. After dissolution, the silicon is extracted as silicomolybdic acid into a mixture of diethyl ether and pentan-1-ol (5 + 1). The co-extraction of excess of molybdate reagent is prevented by the addition of citrate, which also destroys phosphomolybdic and arsenomolybdic acids. The organic layer is washed with hydrochloric acid, mul quantities are transferred to the electrothermal atomizer and the molybdenum is measured. The method has been applied to analysis of several steels.     

某些含二维液晶基元的热致液晶高分子的向列态纹影响构

发现某些含二维液晶基元的热致液晶高分子容易产生反向壁织构与含有高强度有错点（│Ｓ│大于１）的向列态纹影织构。这类液晶高分子的织构与形态学特点与含一维棒状液晶基元的其他液晶高分子不同。     

Design,Synthesis, and Characterization of Photolabeling Probes for the Study of the Mechanisms of the Antiviral Effects of Ribavirin

Ribavirin, the only small molecule available so far for treating hepatitis‐C‐virus infection, was recently used in an emergency context to treat patients with severe acute respiratory syndrome (SARS) in the early stages of the disease. To study the mechanisms responsible for the antiviral effects of ribavirin by using a photolabeling approach, we designed, synthesized, and characterized the azidotriazole nucleosides 1 and 2 as photolabeling probes of ribavirin. These probes were synthesized either by performing nucleophilic substitution of the corresponding bromotriazole nucleoside with NaN₃ (Scheme 2) or by directly coupling the azidotriazole with the protected ribose sugar (Scheme 4). The azidotriazole nucleosides 1 and 2 showed a fast, clear‐cut photochemical reaction, which suggests that they are promising candidates for use in photolabeling studies.     

Synthesis, Characterization and Catalysis of New Pillared Anionic Clays by [GaW_(11)O_(39)M(H_2O)]~(7-)(M=Mn~(2 ),Co~(2 ) or Ni~(2 ))

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Nickel-promoted ligand-free palladium-catalyzed Suzuki coupling reaction

Summary A Ni-promoted ligand free palladium catalyst system for Suzuki coupling of aryl bromides has been developed in high efficiency under mild reaction conditions. It was obtained in situ by introducing NiCl₂ to PdCl₂/PVP using a parallel high-throughput screening technique. A wide range of aryl bromides bearing a variety of functional groups was evaluated.     

The grain-boundary-related optical and electrical properties in polycrystalline p-type ZnO films

Cathodoluminescence spectra and electrical properties of the N doped and N–Al codoped p-type ZnO films and the dependence of these two properties on the post-annealing were investigated. Spectral analyses show that the intensity of the green emission strongly depends on the annealing ambient and closely relates with the width of the electron depletion region at the particle boundary. The conducting type and electrical properties of N doped and N–Al codoped ZnO films are greatly affected by the annealing process. The grain boundary effect was proposed to explain the green emission behavior and the p-type conduction in polycrystalline ZnO based films.     

Ru-Catalyzed asymmetric hydrogenation of alpha-ketoesters with CeCl3.7H2O as additive

[reaction: see text] An efficient asymmetric hydrogenation of alpha-ketoesters is reported with use of a catalyst prepared from [Ru((S)-3)(benzene)Cl]Cl and CeCl(3).7H(2)O. Alpha-hydroxy esters are obtained in up to 96% ee. The addition of CeCl(3).7H(2)O not only improves the enantioselectivity, but also enhances the stability of the catalyst. As a result, the hydrogenation of methyl benzoylformate affords the product with 92% ee with a substrate/catalyst ratio of 10 000. Hydrolysis of 2 provides the final compound with 83% yield at 99% ee after a single recrystallization from 1,2-dichloroethylene.