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991.
Dr. Hui Liu Dr. Yonggang Zhao Zhijuan Zhang Nour Nijem Prof. Dr. Yves J. Chabal Prof. Dr. Xiangfang Peng Prof. Dr. Heping Zeng Prof. Dr. Jing Li 《化学:亚洲杂志》2013,8(4):778-785
We report two new 3D structures, [Zn3(bpdc)3(2,2′‐dmbpy)] (DMF)x(H2O)y ( 1 ) and [Zn3(bpdc)3(3,3′‐dmbpy)]?(DMF)4(H2O)0.5 ( 2 ), by methyl functionalization of the pillar ligand in [Zn3(bpdc)3(bpy)] (DMF)4?(H2O) ( 3 ) (bpdc=biphenyl‐4,4′‐dicarboxylic acid; z,z′‐dmbpy=z,z′‐dimethyl‐4,4′‐bipyridine; bpy=4,4′‐bipyridine). Single‐crystal X‐ray diffraction analysis indicates that 2 is isostructural to 3 , and the power X‐ray diffraction (PXRD) study shows a very similar framework of 1 to 2 and 3 . Both 1 and 2 are 3D porous structures made of Zn3(COO)6 secondary building units (SBUs) and 2,2′‐ or 3,3′‐dmbpy as pillar ligand. Thermogravimetric analysis (TGA) and PXRD studies reveal high thermal and water stability for both compounds. Gas‐adsorption studies show that the reduction of surface area and pore volume by introducing a methyl group to the bpy ligand leads to a decrease in H2 uptake for both compounds. However, CO2 adsorption experiments with 1′ (guest‐free 1 ) indicate significant enhancement in CO2 uptake, whereas for 2′ (guest‐free 2 ) the adsorbed amount is decreased. These results suggest that there are two opposing and competitive effects brought on by methyl functionalization: the enhancement due to increased isosteric heats of CO2 adsorption (Qst), and the detraction due to the reduction of surface area and pore volume. For 1′ , the enhancement effect dominates, which leads to a significantly higher uptake of CO2 than its parent compound 3′ (guest‐free 3 ). For 2′ , the detraction effect predominates, thereby resulting in reduced CO2 uptake relative to its parent structure 3′ . IR and Raman spectroscopic studies also present evidence for strong interaction between CO2 and methyl‐functionalized π moieties. Furthermore, all compounds exhibit high separation capability for CO2 over other small gases including CH4, CO, N2, and O2. 相似文献
992.
Yu‐Long Wang Meng Feng Xian Tao Qing‐Yun Tang Ying‐Zhong Shen 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(1):25-28
The lanthanum(III) complexes tris(3,5‐diphenylpyrazolato‐κ2N,N′)tris(tetrahydrofuran‐κO)lanthanum(III) tetrahydrofuran monosolvate, [La(C15H11N2)3(C4H8O)3]·C4H8O, (I), and tris(3,5‐diphenyl‐1,2,4‐triazolato‐κ2N1,N2)tris(tetrahydrofuran‐κO)lanthanum(III), [La(C14H10N3)3(C4H8O)3], (II), both contain LaIII atoms coordinated by three heterocyclic ligands and three tetrahydrofuran ligands, but their coordination geometries differ. Complex (I) has a mer‐distorted octahedral geometry, while complex (II) has a fac‐distorted configuration. The difference in the coordination geometries and the existence of asymmetric La—N bonding in the two complexes is associated with intramolecular C—H...N/O interactions between the ligands. 相似文献
993.
Fei Ye Dr. Zhan‐Jiang Zheng Wen‐Hui Deng Long‐Sheng Zheng Dr. Yuan Deng Prof. Chun‐Gu Xia Prof. Dr. Li‐Wen Xu 《化学:亚洲杂志》2013,8(9):2242-2253
In this work, we have successfully synthesized a new family of chiral Schiff base–phosphine ligands derived from chiral binaphthol (BINOL) and chiral primary amine. The controllable synthesis of a novel hexadentate and tetradentate N,O,P ligand that contains both axial and sp3‐central chirality from axial BINOL and sp3‐central primary amine led to the establishment of an efficient multifunctional N,O,P ligand for copper‐catalyzed conjugate addition of an organozinc reagent. In the asymmetric conjugate reaction of organozinc reagents to enones, the polymer‐like bimetallic multinuclear Cu? Zn complex constructed in situ was found to be substrate‐selective and a highly excellent catalyst for diethylzinc reagents in terms of enantioselectivity (up to >99 % ee). More importantly, the chirality matching between different chiral sources, C2‐axial binaphthol and sp3‐central chiral phosphine, was crucial to the enantioselective induction in this reaction. The experimental results indicated that our chiral ligand (R,S,S)‐ L1 ‐ and (R,S)‐ L4 ‐based bimetallic complex catalyst system exhibited the highest catalytic performance to date in terms of enantioselectivity and conversion even in the presence of 0.005 mol % of catalyst (S/C=20 000, turnover number (TON)=17 600). We also studied the tandem silylation or acylation of enantiomerically enriched zinc enolates that formed in situ from copper‐ L4 ‐complex‐catalyzed conjugate addition, which resulted in the high‐yield synthesis of chiral silyl enol ethers and enoacetates, respectively. Furthermore, the specialized structure of the present multifunctional N,O,P ligand L1 or L4 , and the corresponding mechanistic study of the copper catalyst system were investigated by 31P NMR spectroscopy, circular dichroism (CD), and UV/Vis absorption. 相似文献
994.
The introduction of sulfur atoms onto target molecules is an important area in organic synthesis, in particular in the synthesis of pharmaceutical compounds, and a wide variety of sulfuration agents have been developed for thionation reactions over the past few decades. In this Focus Review, we collect and summarize the C? S bond‐formation reactions that have been used to construct C? S bonds in natural products and pharmaceutical compounds. 相似文献
995.
Bi‐Qin Wang Hai‐Biao Yan Zheng‐Qing Huang Zhi Zhang 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(6):616-619
A new metal–formate framework, poly[1H‐imidazol‐3‐ium [tri‐μ2‐formato‐manganese(II)]], {(C3H5N2)[Mn(HCOO)3]}n, was synthesized and its structural phase transition was studied by thermal analysis and variable‐temperature X‐ray diffraction analysis. The transition temperature is around 435 K. The high‐temperature phase is tetragonal and the low‐temperature phase is monoclinic, with a β angle close to 90°. The relationship of the unit cells between the two phases can be described as: aHT = 0.5aLT + 0.5bLT; bHT = −0.5aLT + 0.5bLT; cHT = 0.5cLT. In the high‐temperature phase, both the framework and the guest 1H‐imidazol‐3‐ium (HIm) cations are disordered; the HIm cations are located about 2mm sites and were modelled as fourfold disordered. The Mn and a formate C atom are located on fourfold rotary inversion axes, while another formate C atom is on a mirror plane. The low‐temperature structure is ordered and consists of two crystallographically independent HIm cations and two crystallographically independent Mn2+ ions. The phase transition is attributable to the order–disorder transition of the HIm cations. 相似文献
996.
A direct synthesis of methyl levulinate from cellulose alcoholysis in methanol medium under mild condition (180–210 °C) catalyzed by extremely low concentration sulfuric acid (≤0.01 mol/L) and the product isolation were developed in this study. Effects of different process variables towards the catalytic performance were performed as a function of reaction time. The results indicated that sulfuric acid concentration, temperature and initial cellulose concentration had significant effects on the synthesis of methyl levulinate. An optimized yield of around 50% was achieved at 210 °C for 120 min with sulfuric acid concentration of 0.01 mol/L and initial cellulose concentration below 100 g/L. The resulting product mixture was isolated by a distillation technique that combines an atmospheric distillation with a vacuum distillation where n-dodecane was added to help distill the heavy fraction. The light fraction including mainly methanol could be reused as the reaction medium without any substantial change in the yield of methyl levulinate. The chemical composition and structural of lower heavy fraction were characterized by GC/MS, FTIR, 1H-NMR and 13C-NMR techniques. Methyl levulinate was found to be a major ingredient of lower heavy fraction with the content over 96%. This pathway is efficient, environmentally benign and economical for the production of pure levulinate esters from cellulose. 相似文献
997.
Sialylation is essential for a variety of cellular functions. Herein, we used bovine fetuin with three potential N-linked glycosylation sites containing complex-type glycan structures, four potential O-linked glycosylation sites and six potential phosphorylation sites as a model compound to develop a highly-efficient digestion strategy for sialylated glycoproteins and efficient enrichment strategy for sialylated glycopeptides using titanium dioxide. The former according to the process of alkaline phosphatase digestion followed by tryptic digestion and then proteinase K digestion could greatly improve the enzymatic efficiency on fetuin, and the latter could obviously enhance the enrichment efficiency for multisialylated glycopeptides using phosphoric acid solution as elution buffer. The mass spectra of the enriched glycopeptides derived from fetuin reveal that several series of the ion clusters with mass difference of 291 Da correspond to the presence of multisialylated glycopeptides. In addition, the approach was applied to characterize the sialylated status of α2-macroglobulin and transferrin, respectively, from the sera of healthy subjects and sex- and age-matched patients with thyroid cancer, and their spectra indicate that the change in the amount of the glycoforms containing different number of sialic acid (SA) residues from one glycosylation site may be used to differentiate between healthy subjects and cancer cases. 相似文献
998.
A simple approach to fabricate hybrid monolithic column within the confines of fused-silica capillaries (75 μm i.d.) was introduced. A polyhedral oligomeric silsesquioxanes (POSS) reagent containing a methacrylate group was selected as functional monomer, and copolymerized with bisphenol A dimethacrylate (BPADMA) or ethylene dimethacrylate (EDMA) in the presence of porogenic solvents via thermally initiated free radical polymerization. After optimization of the preparation conditions, two POSS-containing hybrid monoliths were successfully prepared and exhibited good permeability and stability. By comparison of the separation efficiencies of the resulting poly(POSS-co-BPADMA) and poly(POSS-co-EDMA) monoliths in capillary electrochromatography (CEC) and capillary liquid chromatography (cLC), it was indicated the former has better column efficiencies for alkylbenzenes, phenols, anilines and PAHs in CEC and cLC than the latter. Particularly, the hybrid poly(POSS-co-BPADMA) monolith is more suitable for separation of PAHs due to π–π interaction between the analytes and aromatic rings in the surface of monolithic stationary phase. 相似文献
999.
Paper-based microfluidic devices have been widely investigated in recent years. Among various detection techniques, colorimetric method plays a very important role in paper-based microfluidic devices. The limitation, however, is also clear: they generally require highly sensitive indicators. In this work, we have developed a novel enrichment-based paper test for the discrimination of heavy-metal ions. Comparing to regular paper-based microfluidic devices, enrichment-based technique showed largely improved sensitivity. Combining with eight pyridylazo compounds and array technologies-based pattern-recognition, we have obtained the discrimination capability of eight different heavy-metal ions at same concentration as low as 50 μM using our enrichment-based pyridylazo compounds array paper. Identification of the heavy-metal ions was readily achieved using a standard chemometric approach. This method can be, of course, used for other analytes as well. 相似文献
1000.
A novel technique utilizing the adsorptive potential of immobilized multi‐walled carbon nanotubes (I‐MWCNT) in hollow fiber liquid‐phase microextraction (HF‐LPME) was developed for the determination of diuretics in urine. In this study, the potential of carbon nanotubes as a sorbent for three‐phase liquid‐phase microextraction of diuretics from urine samples was evaluated. Analysis was performed using liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). A novel method was applied to detect acetazolamide (AAA), chlorothiazide (CTA), hydrochlorothiazide (HCT), hydroflumethiazide (HFT), clopamide (CA), trichlormethiazide (TCM), althiazide (AT) and bendroflumethiazide (BFT) in urine. Two‐step extractions using different times and temperatures for each step were adopted. Parameters influencing the extraction efficiency, including the extraction solvent, sample pH, salt concentration, extraction time and extraction temperature were systematically optimized. Under the resulting optimal extraction conditions, this method showed good linearity over an analytes concentration range of 1 to 1000 ng/mL, high extraction repeatability with relative standard deviations of less than 6%, and low detection limits (0.09 to 0.51 ng/mL). The application of the methods to the determination of diuretics in real samples was tested by analyzing urine samples of patient. 相似文献