Highly diastereo- and enantioselective direct aldol reactions promoted by water-compatible organocatalysts bearing a pyrrolidinyl-camphor structural scaffold

Efficient synthetic routes have been developed for the synthesis of a series of pyrrolidinyl-camphor containing organocatalysts (1-10). Structural modifications were made by varying the stereo- and electronic properties of the camphor scaffold and the aromatic substituents. These readily tunable and amphiphilic organocatalysts were evaluated for the direct asymmetric aldol reaction of various aromatic aldehydes and cyclohexanone either in organic solvents or in the presence of water. The aldol reaction proceeded smoothly with excellent chemical yields (up to 99%), enantioselectivities (up to 99% ee), and anti-diastereoselectivities (up to 99:1) with a catalytical amount of the bifunctional organocatalysts (20 mol %) under optimal reaction conditions. Mechanistic transition models are proposed and the stereochemical bias of the asymmetric aldol reaction is presented.     

Growth characteristics of ultra long double-ended acicular ZnO synthesized by a hydrothermal process

Double-ended acicular ZnO structure can be synthesized via a hydrothermal process with tetramethylammonium hydroxide and zinc acetate as precursors and polyvinyl alcohol (PVA) as a structure-directing agent. The as-prepared ZnO products show the well crystalline wurtzite structure with growth direction along [0 0 0 1]. For the first time, PVA is found to be employed as a reservoir of Zn²⁺ ions in the present study, and can control the concentration of Zn²⁺ in reaction solution, and the acicular morphology can be formed at the two ends of the 1-D ZnO structure, due to the effect of secondary growth that occurs as the sufficient concentration of Zn²⁺ ions chelated by PVA releasing to the reaction solution. Furthermore, the size of the 1-D ZnO structure can be tuned by different amounts of PVA addition.     

制备MoS2修饰的秸秆碳点纳米酶及对人尿液中尿酸含量的检测

采用水热合成法制备了MoS2修饰的秸秆碳点纳米酶(Mo,S-CDs)用于人尿液中尿酸含量的检测,发挥了秸秆自身的结构优势,并实现了生物质废弃物的回收利用.对Mo,S-CDs的表征结果表明,Mo元素和S元素成功地修饰在秸秆碳点结构中,Mo,S-CDs为球形,表面有丰富的官能团,保障了其可较好地分散于水介质中,晶体层面为无...     

Thermal characteristics in the annulus with an inner rotating rib-roughness cylinder

This work experimentally investigates the heat transfer characteristics in the annulus with an inner rotating rib-roughness cylinder, whose flow and thermal behaviors are associated with Taylor number (Ta) and centrifugal buoyancy parameter (Gr _Ω/Ta). The operating range of Ta is from 4.90 × 10² to 5.80 × 10⁵, while the surface of the inner cylinder is heated up with several constant heat fluxes (279, 425 and 597 W/m²) to obtain various values of Gr _Ω/Ta. Besides, three modes of the inner cylinder without/with longitudinal ribs are considered. The end of the annular channel is connected to a side chamber to fit practical applications (such as in the rotary blade coupling of a four-wheel-drive vehicle). The experimental results show that the average Nusselt number was almost constant at low Ta, but increased rapidly with Ta when Ta exceeded some critical value (3,000–5,200 for present study). Additionally, the Gr _Ω/Ta effect on the heat transfer was negligible herein. Furthermore, by comparing with the inner cylinder without longitudinal ribs, stalling ribs on the inner cylinder increases the transport of heat by a factor of 1.22 at 10⁵ < Ta < 10⁶, and embedding cavities into the ribs increases the transport of heat by a factor of 1.16 at 10⁵ < Ta < 10⁶. Finally, the relationships between the and the Ta for various modes of test sections were proposed.     

Synthesis and Cytotoxicity Evaluation of Certain α‐Methylidene‐ γ‐butyrolactones Bearing Coumarin,Flavone, Xanthone,Carbazole, and Dibenzofuran Moieties

The cytotoxicities of α‐methylidene‐γ‐butyrolactones, which are linked to coumarins (see 15 and 16 ) and to potential DNA‐intercalating carriers such as flavones, xanthones, carbazole, and dibenzofuran (see 9a – e , 10a – e , 11 , and 12 ), were studied. These compounds were synthesized via alkylation of their hydroxy precursors followed by a Reformatsky‐type condensation (Scheme). These α‐methylidene‐γ‐butyralactones were evaluated in vitro against 60 human tumor cell lines derived from nine cancer cell types and demonstrated a strong growth‐inhibitory activity against leukemia cancer cells (Tables 1 and 2). For flavone‐ and xanthone‐containing α‐methylidene‐γ‐butyrolactones 9a – e and 10a – e , respectively, the overall potency (mean value) decreased on introduction of an electron‐withdrawing substituent at the γ‐phenyl substituent and increased with an electron‐donating substituent. Comparing the different chromophores established the following order of decreasing potency (log GI₅₀): dibenzofuran ( 12 , −6.17) > flavone ( 9a , −5.96) > carbazole ( 11 , −5.80) and xanthone ( 10a , −5.77) > coumarin ( 15 , −5.60; 16 , −5.65). Among them, the dibenzofuran derivative 12 showed not only strong inhibitory activities against leukemia cancer cell lines with an average log GI₅₀ value of −7.22, but also good inhibitory activities against colon, melanoma, and breast cancer cells with average log GI₅₀ values of −6.23, −6.31, and −6.39, respectively.     

Highly selective multilayer polymer thin films for CO2/N2 separation

Multilayer thin films of poly(ethylene oxide) (PEO) and poly(methacrylic acid) (PMAA), deposited via layer‐by‐layer (LbL) assembly from aqueous solutions, are investigated for CO₂/N₂ separation. Eight and ten bilayer (217 and 389 nm thick, respectively) PEO/PMAA thin films deposited on a 25 μm polystyrene substrate exhibit CO₂/N₂ selectivities of 142 and 136, respectively. These are the highest reported to‐date for this gas pair separation using a homogeneous polymer film. While further work remains to improve CO₂ permeability, these results indicate the potential of LbL assemblies as standalone CO₂ separation membranes for low‐flux/high‐purity applications, or as part of a composite and/or mixed‐matrix membrane for high‐flux applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1730–1737     

Anion‐ and Solvent‐Induced Assembly and Reversible Structural Transformation of d10‐Metal Coordination Architectures Containing N‐(4‐(4‐Aminophenyloxy)phenyl)isonicotinamide

We set out studies on anion‐ and solvent‐induced assembly based on the ligand N‐(4‐(4‐aminophenyloxy)phenyl)isonicotinamide (papoa), which is synthesized to show a bent and flexible backbone. Reactions of papoa with ZnX₂ (X=Cl, Br, and I) gave the dinuclear macrocycles ([ZnX₂(papoa)]₂; X=Cl ( 1 a ), Br ( 2 a ), I ( 3 )), the structure of which was determined by X‐ray diffraction. Notably, the less bulky Cl and Br compounds afforded the coordinated imine in acetone (i.e., [ZnX₂(papoi)]₂, papoi=N‐(4‐(4‐(propan‐2‐ylideneamino)phenoxy)phenyl)isonicotinamide; X=Cl ( 1 b ), Br ( 2 b )), whereas the iodine one only gave the coordinated amine compound 3 under the same reaction condition. In fact, the coordinated imine can return to the amine analogue upon exposure to air or in DMSO, which has been monitored by ¹H NMR spectroscopy and powder X‐ray diffraction. Both the dinuclear [Zn(papoa)(NO₃)₂]₂ ( 4 a ) and the 1D [Zn(papoa)₂(NO₃)₂]_n ( 4 b ) were formed from the reaction of Zn(NO₃)₂ and papoa in mixed solvents with acetone and acetonitrile, respectively. In addition, Cd(ClO₄)₂ can react with papoa to give the 1D framework {[Cd(papoa)₂(CH₃CN)₂](ClO₄)₂}_n ( 5 a ) and the 2D framework [Cd(papoa)₂(ClO₄)₂]_n ( 5 b ), depending on the solvent used, that is, MeOH and CH₃CN, respectively. Importantly, the 1D framework with axially coordinated CH₃CN molecules and the 2D framework with axially coordinated ClO₄^? ions can be interconverted by heating and grinding in the presence of CH₃CN, respectively. Such a reversible structural transformation process was proven by PXRD studies.     

广义Goppa码最小距离下限的扩张及其译码

本文建立了由Lagrange插值公式决定的广义Goppa码最小距离下限扩张的一般定理,它包括了BCH码、广义BCH码和修改RS码的子域子码最小距离下限扩张结果,并对这些结果进行了改进,使其适用性更强.另外,本文还建立了用解线性方程组的方法实现最小距离下限扩张了的广义Goppa码的译码.广义Goppa码是目前较大的一种分组纠错码.因而,本文的结果可应用于现有的所有分组纠错码.     

Pulsed microwave plasma etching of polymers in oxygen and nitrogenfor microelectronic applications

Gaseous plasma generated by a half-wave rectified power supply are characterized and applied to the etching of photoresist and polymide in oxygen, dry air, or air. Activation energies of 8.6 kcal/mole and 10.9 kcal/mole are calculated for oxygen plasma etching of photoresist and polyimide, respectively. An average power of 625 W at 2.45 GHz is supplied by a magnetron through a rectangular waveguide to a 51-mm diameter quartz tube generating pulsed plasmas in oxygen and nitrogen at pressures between 0.1 torr and 10 torr with a repetitive rate of 60 Hz. The plasmas are studied by a double Langmuir probe and an optical emission spectrometer. Polymers placed in the downstream of the plasma are etched at high rates, especially when external heating is applied to raise the sample temperature. The characteristics of the plasmas and the application to the fast etching of polymers are discussed