也论化学元素周期表的形成和发展

In the time order, the author proposes that the discovery and development of the periodic table of chemical elements are divided into four stages:point→1D→2D→3D. This article cites the main historical facts and documents available to unscramble the above four stages, which will facilitate the teaching and scientific research of the periodic table.     

Bifunctional Iminophosphorane-Catalyzed Enantioselective Nitroalkane Addition to Unactivated α,β-Unsaturated Esters**

Herein we describe the enantioselective intermolecular conjugate addition of nitroalkanes to unactivated α,β-unsaturated esters, catalyzed by a bifunctional iminophosphorane (BIMP) superbase. The transformation provides the most direct access to pharmaceutically relevant enantioenriched γ-nitroesters, utilizing feedstock chemicals, with unprecedented selectivity. The methodology exhibits a broad substrate scope, including β-(fluoro)alkyl, aryl and heteroaryl substituted electrophiles, and was successfully applied on a gram scale with reduced catalyst loading, and, additionally, catalyst recovery was carried out. The formal synthesis of a range of drug molecules, and an enantioselective synthesis of (S)-rolipram were achieved. Additionally, computational studies revealed key reaction intermediates and transition state structures, and provided rationale for high enantioselectivities, in good agreement with experimental results.     

Tracking an FeV(O) Intermediate for Water Oxidation in Water

High-valent iron-oxo species are appealing for conducting O−O bond formation for water oxidation reactions. However, their high reactivity poses a great challenge to the dissection of their chemical transformations. Herein, we introduce an electron-rich and oxidation-resistant ligand, 2-[(2,2′-bipyridin)-6-yl]propan-2-ol to stabilize such fleeting intermediates. Advanced spectroscopies and electrochemical studies demonstrate a high-valent Fe^V(O) species formation in water. Combining kinetic and oxygen isotope labelling experiments and organic reactions indicates that the Fe^V(O) species is responsible for O−O bond formation via water nucleophilic attack under the real catalytic water oxidation conditions.     

Balancing the Crystallinity and Film Formation of Metal–Organic Framework Membranes through In Situ Modulation for Efficient Gas Separation

Polycrystalline metal–organic framework (MOF) layers hold great promise as molecular sieve membranes for efficient gas separation. Nevertheless, the high crystallinity tends to cause inter-crystalline defects/cracks in the nearby crystals, which makes crystalline porous materials face a great challenge in the fabrication of defect-free membranes. Herein, for the first time, we demonstrate the balance between crystallinity and film formation of MOF membrane through a facile in situ modulation strategy. Monocarboxylic acid was introduced as a modulator to regulate the crystallinity via competitive complexation and thus concomitantly control the film-forming state during membrane growth. Through adjusting the ratio of modulator acid/linker acid, an appropriate balance between this structural “trade-off” was achieved. The resulting MOF membrane with moderate crystallinity and coherent morphology exhibits molecular sieving for H₂/CO₂ separation with selectivity up to 82.5.     

Effect of particulate filler on cell size in membranes formed via liquid–liquid thermally induced phase separation

This paper discusses the effects of adding particulate filler to a system undergoing liquid–liquid thermally induced phase separation (L–L TIPS). While much is known about the growth of droplets in L–L TIPS, little is known about the effect particular fillers have on droplet growth and the final cell size in the resulting microporous membranes. In this work, zeolite particles are shown to have a significant effect on the final cell size of these microporous membranes, the extent of which depends on the particle loading and processing conditions used to form the membrane. Two polymer–diluent–zeolite systems are reported: isotactic polypropylene–diphenyl ether and poly(methyl methacrylate)–cyclohexanol, both with zeolite 4A particles.     

硅基超薄多孔氧化铝膜的制备

将二次阳极氧化法应用于硅基铝膜的制备, 在草酸溶液中得到了厚度可控的硅基超薄多孔氧化铝膜(PAM), 厚度小于100 nm. 实验中记录了氧化电流随时间的实时变化曲线, 发现硅衬底的氧化电流在大幅下降前有一小幅波动. 对应于Al/Si界面的氧化过程中, 孔洞底部之间的残留铝岛被优先氧化, 可将此作为终止铝氧化的标志. 扫描电镜(SEM)观察表明, 二次氧化提高了孔洞分布的均匀性, 使得孔在一定的区域内呈现有序六角分布.这种模板可进一步用于硅基纳米器件和纳米结构的制备.     

Spectrophotometric study of the supramolecular complexes of [60]- and [70]Fullerenes with biscalix[6]arene and crown[4]calix[6]arene

[60]- and [70]Fullerenes have been shown to form 1:1 supramolecular complexes with bis[2-(5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41-pentahydroxycalix[6]arenyl-oxy ethyl ether) (1) and 5,11,17,23,29,35-hexa-tert-butyl-37,38,40,41-tetra hydroxyl-39,42-(crown-4)calix[6]arene (2) in CHCl3 medium by electronic absorption spectroscopy. Formation constants (K) of the complexes of [60]- and [70]fullerenes with 1 and 2 have been determined at room temperature from which free energy of formation values of the complexes have been estimated. The very high formation constant value of [60]fullerene/1 complex (5900 dm3 mol-1) in indicative of formation of inclusion complex. Moreover, PM3 calculations reveal that intermolecular interaction between [60]fullerene and 1 proceeds through quite deep energy molecular orbital.     

气敏半导体材料Cd2Sb2O6.8的制备及其性能研究

采用化学共沉淀法,在较低温度(750℃)下制备了具有缺陷烧绿石结构的复合氧化物Cd₂Sb₂O_6.8的纯相超微粉;研究了制备条件对物相、结构和气敏性能的影响,并对其反应过程机理进行了探讨,气敏性能测试结果表明,纯相Cd₂Sb₂O_6.8气敏元件对乙炔气体有较高的灵敏度和较好的选择性.     

R(-)四氢噻唑-2-硫酮-4-羧酸对D,L-氨基酸酯拆分的研究

以新手性拆分试剂R(-)四氢噻唑-2-硫酮-4-羧酸[简称R(-)TTCA]对D,L-氨基酸酯进行手性拆分,分别得到(R)TTCA氨基酸酯盐1a_1f([α]_D²⁰＝-30.40°～-42.70°)及光学活性氨基酸酯2a-2f,其光学纯度为35.4%～75.8%.由1a_1f在碱存在下分解出2a-2f的对映体3a-3f,光学纯度为39.50%～69.10%.用半经验的量子化学PM3方法研究了氨基的碱性、中间产物铵盐生成热和稳定性.