Palladium-catalyzed hydrosilylation of ynones to access silicon-stereogenic silylenones by stereospecific aromatic interaction-assisted Si–H activation

Hydrosilylation is one of the most important reactions in synthetic chemistry and ranks as a fundamental method to access organosilicon compounds in industrial and academic processes. However, the enantioselective construction of chiral-at-silicon compounds via catalytic asymmetric hydrosilylation remained limited and difficult. Here we report a highly enantioselective hydrosilylation of ynones, a type of carbonyl-activated alkynes, using a palladium catalyst with a chiral binaphthyl phosphoramidite ligand. The stereospecific hydrosilylation of ynones affords a series of silicon-stereogenic silylenones with up to 94% yield, 20:1 regioselectivity and 98:2 enantioselectivity. The density functional theory(DFT) calculations were conducted to elucidate the reaction mechanism and origin of high degree of stereoselectivity, in which the powerful potential of aromatic interaction in this reaction is highlighted by the multiple C–H-π interaction and aromatic cavity-oriented enantioselectivitydetermining step during desymmetric functionalization of Si–H bond.     

Promising Chemotherapy for Malignant Pediatric Brain Tumor in Recent Biological Insights

Brain tumors are the most widespread malignancies in children around the world. Chemotherapy plays a critical role in the treatment of these tumors. Although the current chemotherapy process has a remarkable outcome for a certain subtype of brain tumor, improving patient survival is still a major challenge. Further intensive treatment with conventional non-specific chemotherapy could cause additional adverse reactions without significant advancement in survival. Recently, patient derived brain tumor, xenograft, and whole genome analysis using deep sequencing technology has made a significant contribution to our understanding of cancer treatment. This realization has changed the focus to new agents, targeting the molecular pathways that are critical to tumor survival or proliferation. Thus, many novel drugs targeting epigenetic regulators or tyrosine kinase have been developed. These selective drugs may have less toxicity in normal cells and are expected to be more effective than non-specific chemotherapeutics. This review will summarize the latest novel targets and corresponding candidate drugs, which are promising chemotherapy for brain tumors according to the biological insights.     

Improvement of amine-modification with piperazine for the adsorption of CO2

Both selectivity and capacity of CO₂ adsorption were considerably increased when PZ (piperazine) was added in MDEA (methyldiethylamine) that used to modify the surface of silica gels. The adsorbent saturated with CO₂ was regenerated at ambient temperature through nitrogen purge. A set of PSA (pressure swing adsorption) operation with 200 cycles was carried out and applicability of the modified adsorbent was thus illustrated. The CO₂ content in the column-top stream decreased from 13% to below 0.05% at steady state.     

CeO_2和Y_2Ba_1Cu_1O_(5-δ)共同掺杂对Y_1Ba_2Cu_3O_(7-δ)的超导电性及其晶格结构的影响

采用固相反应法成功制备出一批Y123与Y211的摩尔比为1∶0.47的混合物,并在此混合物的基础上掺入CeO2,掺入的比例x分别为0.5wt%、1.0wt%、2.0wt%、3.0wt%、4.0wt%。采用了X-射线衍射仪对样品的晶格结构进行了分析,测量结果表明:x=1.0wt%时掺杂效果最好,同时也充分说明Y123的晶格结构与其超导电性之间存在着一种内在的必然关联。并通过对其测试临界转变温度以及转变宽度,测量结果也充分验证了上述结论。     

一种电流引线的热力学计算方法

从超导磁体气冷电流引线的热平衡方程出发,对电流引线进行分段,提出了一种较为精确计算电流引线长横比及由电流引线末端流入低温容器热量的计算方法;电流引线中氦气流阻是设计电流引线时一个很重要的参数,由于电流引线片形状很复杂,计算其中氦气流阻比较好的方法是采用CFD软件Fluent。氦气模型单元数很庞大,因此对氦气模型进行了简化和分段,相邻两段模型间采用流量和压力边界条件进行耦合。     

The complex-mode vibration of ultrasonic vibration systems

The longitudinal-flexural and torsional-flexural vibrations are studied for the ultrasonic solid horn and the ultrasonic vibration system comprised of a sandwich transducer and a solid horn. The discussed solid horn is of arbitrary non-uniform cross-section. The analysis on flexural-mode vibration is based on Timoshenko theory. The theoretical results are verified by experiment.     

DFT Investigations of Aun Nano-Clusters Supported on TiO2 Nanotubes: Structures and Electronic Properties

TiO₂ nanotubes (TiO₂NTs) are beneficial for photogenerated electron separation in photocatalysis. In order to improve the utilization rate of TiO₂NTs in the visible light region, an effective method is to use Au_n cluster deposition-modified TiO₂NTs. It is of great significance to investigate the mechanism of Au_n clusters supported on TiO₂NTs to strengthen its visible-light response. In this work, the structures, electronic properties, Mulliken atomic charge, density of states, band structure, and deformation density of Au_n (n = 1, 8, 13) clusters supported on TiO₂NTs were investigated by DMOL3. Based on published research results, the most stable adsorption configurations of Au_n (n = 1, 8, 13) clusters supported with TiO₂NTs were obtained. The adsorption energy increased as the number of Au adatoms increased linearly. The Au_n clusters supported on TiO₂NTs carry a negative charge. The band gaps of the three most stable structures of each adsorption system decreased compared to TiO₂NTs; the valence top and the conduction bottom of the Fermi level come mainly from the contribution of 5d and 6s-Au. The electronic properties of the 5d and 6s impurity orbitals cause valence widening and band gap narrowing.     

Determination of protoapigenone in rat plasma by high‐performance liquid chromatography with UV detection and its application in pharmacokinetic studies

A simple and sensitive HPLC method using UV detection was developed to determine the concentration of protoapigenone in rat plasma. Chromatographic separation was conducted on a C₁₈ column with a mobile phase consisting of an acetonitrile–methanol–aqueous phase (containing 0.2% acetic acid, pH 3.0) system at a flow rate of 1.0 mL/min. The UV detector was set at 248 nm. The calibration curve was linear over the range of 0.031–10.0 µg/mL. The lower limit of quantification was 31 ng/mL. The recoveries for plasma samples ranged from 70.3 to 82.5%. The intra‐ and inter‐day accuracy and precision fulfilled the international standards. This method was successfully applied to a pharmacokinetic study of protoapigenone in rats after oral administration of protoapigenone. It was shown that protoapigenone could be absorbed rapidly after oral administration and could reach the maximum concentration within 1 h. Copyright © 2013 John Wiley & Sons, Ltd.     

A family of single‐isomer,dicationic cyclodextrin chiral selectors for capillary electrophoresis: Mono‐6A‐ammonium‐6C‐butylimidazolium‐β‐cyclodextrin chlorides

The first member of the single‐isomer, dicationic cyclodextrin (CD) family, 6^A‐ammonium‐6^C‐butylimidazolium‐β‐cyclodextrin chlorides (AMBIMCD), has been synthesized, analytically characterized, and used to separate a variety of acidic enantiomers and amino acids by CE. Starting from mono‐6^A‐azido‐β‐cyclodextrin, the cationic imidazolium and ammonium moieties were subsequently introduced onto primary ring of β‐cyclodextrin via nucleophilic addition and Staudinger reaction. The analytically pure AC regio‐isomer CD was further obtained via column chromatography. This dicationic CD exhibited excellent enantioselectivities for selected analytes at concentration as low as 0.5 mM, which were even better than those of its mono‐imidazolium or ammonium‐substitued counterpart CDs at 10 equivalent concentrations. The effective mobilities of all studied analytes were found to decrease with the concentration of AMBIMCD. Inclusion complexation in combination with eletrostatic interactions seemed to account for the enhanced chiral discrimination process.     

Study on the flow resistance of the dispersion system of deformable preformed particle gel in porous media using LBM-DEM-IMB method

After being injected into the porous media, the dispersion system of preformed particle gel (PPG) tends to enter high permeability regions and block water channeling passages, which forces the subsequent water to turn to the low permeability regions and thus increases sweep efficiency and enhances oil recovery. However, it is still unclear about the influence factors and the mechanisms how PPG increases water flow resistance, which limits the application of PPG in more oilfields. Therefore, the paper combines the lattice Boltzmann method (LBM), the discrete element method (DEM) and the improved immersed moving boundary (IMB) method to simulate the migration of deformable PPG in porous media. On the basis, the paper quantitatively analyzes the variation law of displacement pressure across the porous media and discusses the influence factors such as the PPG diameter, elasticity modulus and the number concentration. Results indicate that, because of the friction and retention of PPG in pore-throat, the displacement pressure across the porous media during PPG flooding is much higher than that during water flooding. In other words, the existence of PPG increases the flow resistance of injected water. Besides, the displacement pressure is always fluctuant resulting from the continuous process of PPG migration, retention, deformation and remigration. Influence factor analysis shows that the incremental value and fluctuation degree of flow resistance increase with the PPG diameter, elasticity modulus and the number concentration. The study not only provides useful reference for future PPG flooding, but also benefits the development of deformable particle flow theory.