β-Tosylethylazide: a useful synthon for preparation of N-protected 1,2,3-triazoles via click chemistry

β-Tosylethylazide (TSE-N₃), which can be prepared in one step from p-tolyl vinyl sulfone and sodium azide/H₂SO₄, undergoes metal-catalyzed 1,3-dipolar cycloadditions with alkynes to produce TSE-protected 1,2,3-triazoles. The protecting group can be removed using potassium tert-butoxide in THF at −78 to 0 °C.     

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) as ligand for atom transfer radical polymerization (ATRP)

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) has been used as a bidentate ligand of copper (I) bromide for the ATRP of (meth)acrylates and styrene. With methyl methacrylate, the polymerization reached high conversions producing polymers with a good control of Mn and low polydispersity indexes (PDI = 1.19). Higher PDI were obtained with polystyrenes and poly(methyl acrylate)s. These results have been correlated to the redox properties of the catalytic complex.     

Template free fabrication of hollow hematite spheres via a one-pot polyoxometalate-assisted hydrolysis process

Uniform hollow hematite (α-Fe₂O₃) spheres with diameter of about 600-700 nm and shell thickness lower than 100 nm are obtained by direct hydrothermal treatment of dilute FeCl₃ and tungstophosphoric acid H₃PW₁₂O₄₀ solution at 180 °C. The hollow spheres are composed of robust shells with small nanoparticles standing out of the surface and present a high-surface area and a weak ferromagnetic behavior at room temperature. The effect of concentration of H₃PW₁₂O₄₀, reaction time and temperature for the formation of the hollow spheres are investigated in series of experiments. The formation of the hollow spheres may be ascribed to a polyoxometalte-assisted forced hydrolysis and dissolution process.     

还原熔融法同时测定铜铬合金中的氧氮含量

样品经过表面预处理，选择合适的样品质量及仪器测试条件，应用TC-30还原熔融法同时测定铜铬合金中的氧氮。氧氮的回收率为97．2％～101．1%，相对标准偏差小于3．5%。     

油菜蜂花粉浸取液中黄酮含量的电导滴定测定

采用电导滴定法对芦丁标样及对花粉浸取液中黄酮进行了测定并与分光光度法进行比较,相对标准偏差小于5％,加标回收率94％～105％。     

Preparation and Properties of Enterosorbents Based on Carboxylated Microcrystalline Cellulose

Features of a non-traditional method of preparation of cellulose-based cation-exchange enterosorbents using nitrogen (IV) oxide are discussed. The proposed approach involves sequential use of oxidative and acid-hydrolyzing functions of nitrogen (IV) oxide to convert ordinary cellulose into carboxylated microcrystalline cellulose. X-ray phase analysis and transmission electron microscopy data show evidence of a topochemical character of cellulose microcrystal modification with carboxyl groups. Factors are indicated causing enhanced stability and whiteness of the samples thus obtained as compared with oxidized cellulose fibres, as well as the ease of stable tixotropic gel formation from the samples prepared in a salt form. Exemplified by methylene blue sorption, a comparative assessment of the sorptive ability of enterosorbent powders and hydrogels prepared in acid and salt forms. Results of clinical trials conducted with the gel enterosorbents in the areas of gastroenterology and detoxication therapy are presented. In view of compatibility of carboxylated microcrystalline cellulose in hydrogel form with many biologically active ingredients, prospective character of using the enterosorbents not only as such but also as a matrix for the development of new dosage forms of other medications is pointed out. Examples showing advantages of such combinations in specific sustained release drug forms (ointments and microgranules) are given.     

NO与Ag(110)表面的相互作用

采用Ｘ射线光电子能谱、紫外光电子能谱和原位Ｒａｍａｎ光谱研究了ＮＯ和Ｏ２在Ａｇ（１１０）表面的吸附和反应。结果表明，室温条件下，ＮＯ在银表面不发生明显的吸附和分解，氧的加入导致了ＮＯ在角表面的氧化反应生成吸附态的氮氧化物和原子态氧。     

Chiral Aziridines—Their Synthesis and Use in Stereoselective Transformations

The preparation of enantiomerically pure compounds is one of the major areas of organic chemistry. Much emphasis is placed on the elaboration of naturally occurring starting materials and on the development of techniques for enantio-selective transformations of achiral substrates. In this field, chiral aziridines form an attractive class of compounds, since they are available in enantiomerically pure (or highly enriched) form by a variety of procedures and can be used for asymmetric synthesis in a number of different ways. The chemistry of aziridines is dominated by ring-opening reactions, the driving force for which is relief of ring strain. By suitable choice of sub-stituents on the carbon and nitrogen atoms, excellent stereo- and regiocontrol can be attained in ring-opening reactions with a wide variety of nucleophiles, including organometallic reagents; this makes chiral aziridines useful as substrates for the synthesis of important biologically active species including alkaloids, amino acids, and /Mactam antibiotics. Substrate-controlled diastereo-selective synthesis is also possible by use of aziridines as removable chiral auxiliaries, while metalation at a ring carbon atom allows aziridines to be used as chiral reagents for asymmetric synthesis. Chiral bisaziridines can act as ligands for transition metals, and applications in the challenging field of enantioselective catalysis can be envisioned. Today, the exclusion of three-membered carbo- and heterocycles from the arsenal of the organic chemist is inconceivable.

1 H. Heimgartner, Angew. Chem. 1991 , 103, 271; Angew. Chem. Int. Ed. Engl. 1991 , 30, 238.

     

Recent advances of MXene as promising catalysts for electrochemical nitrogen reduction reaction

Electrochemical reduction of N_2,as an eco-friendly alternative,not only allows the use of protons in water as a source of hydrogen under mild conditions but also can be driven by renewable electric energy.The major challenge is to identify high-efficiency electrocatalysts.MXene is a new class of 2D transition metal carbides,nitrides,and carbonitrides that have received significant attention in electrocatalysis.The investigations on MXene in electrocatalytic nitrogen fixation are rapidly proceeding,and some breakthroughs have emerged ve ry recently due to MXenes' satisfacto ry catalytic activity.Here,the recent progress concerning the MXene-based catalysts for electrochemical N_2 reduction reaction(NRR) is highlighted.In regards to giving guidelines for exploring more efficient MXene-based catalysts for the NRR,the fabrication and surface modification of MXene are discussed.Besides,the shortcomings and challenges of current research are summarized and the future research directions are prospected.     

A molecular orbital study of nitrogen inversion in aniline with extensive geometry optimization

The geometry and energy of aniline have been calculated using the 6-31G and 6-31G^*(5D) basis sets for the planar structure and various pyramidal structures, assuming that the ring and the N-atom bonded to it lie in the same plane, but otherwise with full geometry optimization. With the 6-31G basis set the planar structure is predicated to be the most stable, whereas the inclusion of polarization functions in the 6-31G^*(5D) basis set finds a pyramidal structure with the out-of-plane angle =42.3° to be most stable and the energy barrier to inversion via the planar transition state to be 1.59±0.02 kcal mol^–1, in close agreement with experiment. Completing the optimization, allowing the N-atom and the C- and H-atoms of the ring to take up equilibrium out-of-plane positions increases the calculated energy carrier to inversion by less than 0.1 kcal mol^–1 to 1.66 kcal mol^–1. The ring adopts a very shallow inverted boat-type conformation with N₇-C₁C₄ = 2.0°.