Effect of solvent composition on free release static coating of capillary columns

Summary Three aspects with respect to the selection of solvents for static coating of capillary columns, i.e. coating speed, occurrence of bumping and solubility of stationary phases are discussed. Hypotheses are proposed in an attempt to explain the observed facts that mixed solvents result in much higher coating speeds than those obtained from pure solvents, that a proper choice of solvents together with a good and uniform deactivitation of the column inner wall is needed to prevent bumping. Stationary phase solubility vs. solvent composition is also briefly discussed.     

C2-symmetric bis(oxazolinato)lanthanide catalysts for enantioselective intramolecular hydroamination/cyclization

C(2)-symmetric bis(oxazolinato)lanthanide complexes of the type [(4R,5S)-Ph(2)Box]La[N(TMS)(2)](2), [(4S,5R)-Ar(2)Box]La[N(TMS)(2)](2), and [(4S)-Ph-5,5-Me(2)Box]La[N(TMS)(2)](2) (Box = 2,2'-bis(2-oxazoline)methylenyl; Ar = 4-tert-butylphenyl, 1-naphthyl; TMS = SiMe(3)) serve as precatalysts for the efficient enantioselective intramolecular hydroamination/cyclization of aminoalkenes and aminodienes. These new catalyst systems are conveniently generated in situ from the known metal precursors Ln[N(TMS)(2)](3) or Ln[CH(TMS)(2)](3) (Ln = La, Nd, Sm, Y, Lu) and 1.2 equiv of commercially available or readily prepared bis(oxazoline) ligands such as (4R,5S)-Ph(2)BoxH, (4S,5R)-Ar(2)BoxH, and (4S)-Ph-5,5-Me(2)BoxH. The X-ray crystal structure of [(4S)-(t)BuBox]Lu[CH(TMS)(2)](2) provides insight into the structure of the in situ generated precatalyst species. Lanthanides having the largest ionic radii exhibit the highest turnover frequencies as well as enantioselectivities. Reaction rates maximize near 1:1 BoxH:Ln ratio (ligand acceleration); however, increasing the ratio to 2:1 BoxH:Ln decreases the reaction rate, while affording enantiomeric excesses similar to the 1:1 BoxH:Ln case. A screening study of bis(oxazoline) ligands reveals that aryl stereodirecting groups at the oxazoline ring 4 position and additional substitution (geminal dimethyl or aryl) at the 5 position are crucial for high turnover frequencies and good enantioselectivities. The optimized precatalyst, in situ generated [(4R,5S)-Ph(2)Box]La[N(TMS)(2)](2), exhibits good rates and enantioselectivities, comparable to or greater than those achieved with chiral C(1)-symmetric organolanthanocene catalysts, even for poorly responsive substrates (up to 67% ee at 23 degrees C). Kinetic studies reveal that hydroamination rates are zero order in [amine substrate] and first order in [catalyst], implicating the same general mechanism for organolanthanide-catalyzed hydroamination/cyclizations (intramolecular turnover-limiting olefin insertion followed by the rapid protonolysis of an Ln-C bond by amine substrate) and implying that the active catalytic species is monomeric.     

Synthesis and magnetic properties of the one-dimensional linear chain structure cyano-bridged complex [Cu(teta)(H2O)2][Cu(teta) Fe(CN)6]ClO4·2H2O (teta=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacylotetradecane)

Reaction of either K₃[Fe(CN)₆] or K₄[Fe(CN)₆] with a macrocyclic Cu^II complex, [Cu(teta)](ClO₄)₂ (teta = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacylotetradecane), in aqueous solution gave the same product as shown by spectroscopic and physicochemical characterisation. The crystal structure of the complex shows that it is a one-dimensional linear chain type heterobinuclear Fe^III–Cu^II polymer. The unit is composed of a [Cu(teta)(H₂O)₂]²⁺ cationic complex, a Fe^III–Cu^II alternate linear chain unit, a ClO ₄ ^– ion and four water molecules. The Cu atom is coordinated in a distorted octahedral arrangement by four nitrogen atoms from one teta ligand and two nitrogen atoms of the bridging cyanide groups. The Cu—N bond distances involving the cyanide bridges, 2.522(7) and 2.608(7)Å, respectively, indicate weak antiferromagnetic interactions between the Fe^III and Cu^II atoms.     

Comparison of conventional and enhanced mass resolution triple-quadrupole mass spectrometers for discovery bioanalytical applications

A new triple-quadrupole mass spectrometry (MS) system with enhanced resolution capabilities has recently become available. In order to evaluate the performance of this new instrument for drug discovery assays, both the linearity and the limit of detection were compared in the positive electrospray ionization (ESI) mode with those of a conventional triple-quadrupole instrument supplied by the same manufacturer. For these studies, spiked mouse plasma standard samples were split and assayed by each instrument, which allowed for a direct comparison of the two systems. In the unit mass resolution mode, the new mass spectrometer was found to be at least ten-fold more sensitive than the conventional instrument. The sensitivity of the new mass spectrometer under the enhanced mass resolution mode was found to be even better by another factor of two. For the test compound, the linear dynamic range was found to be 0.05-5000 ng/mL for the new instrument as compared with 2.5-5000 ng/mL for the conventional mass spectrometer.     

Electron momentum spectroscopy of CF2Cl2: experimental and theoretical momentum profiles for outer valence orbitals

Electron momentum distributions for outer valence orbitals of CF2Cl2 have been obtained by (e,2e) electron momentum spectroscopy at an incident energy of 1200 eV + binding energy. The experimental electron momentum profiles are compared with Hartree-Fock and density functional theory (DFT) calculations using B3LYP hybrid functional with the 6-31G and 6-311+G* basis sets. Generally, the shapes of the experimental momentum profiles are well reproduced by DFT calculations using larger basis sets 6-311 + G*. An attempt has been made to clarify the ordering of the outer valence orbitals, which have been in controversy, by comparing experimental results with B3LYP/6-311 + G* calculations.     

Direct STM investigation of cinchona alkaloid adsorption on Cu(III)

Scanning tunneling microscopy (STM) combined with cyclic voltammetry has been employed to investigate the adsorption of cinchonine on Cu(111). Similar to cinchonidine, cinchonine forms a long-range ordered adlayer with (4 x 4) symmetry on the substrate. The structural details on molecular adsorption were obtained by high-resolution STM images. On the basis of the previous results and obtained STM images, the quinoline ring is proposed to lie parallel to Cu(111) and serve as an anchoring group. The chiral quinuclidine moiety extends out of the surface to facilitate the interaction with the prochiral reactants.     

高压下制备的累托石/酚醛树脂复合材料微结构和热性能研究

 采用物理方法在高压下制备了酚醛树脂（PF）/累托石（REC）纳米复合材料,用X射线衍射（XRD）、透射电子显微镜（TEM）及热分析（DSC/TGA）等方法,研究了复合材料的物相、显微结构以及热学性能。结果表明,不通过层间高分子聚合反应,不预先对累托石进行有机化处理,在高压下,由聚合物分子插入粘土层间,可以形成剥离型树脂/粘土纳米复合材料,并且其热学性能发生了较大的改变。     

聚苯乙烯型离子交换树脂的研究进展

介绍了聚苯乙烯型离子交换树脂的合成方法;综述了近年来在氯甲基化反应、Mannich反应以及磺化反应上的新进展、新理论：从结构上对聚苯乙烯型离子交换树脂的强度和热稳定性进行了分析。聚苯乙烯型离子交换树脂具有稳定的物理化学性质、吸附选择独特、再生容易、操作简便、使用周期长等优良性能,大大促进了化工企业、制药工业、环保、医疗、分析等行业的发展,具有广阔的发展前景。     

无机元素与计量学模型结合的半夏产地溯源研究

目的:建立不同产地半夏无机元素的分析方法和溯源体系,为半夏药材的质量控制和道地性评价提供技术支持。方法:采用电感耦合等离子体质谱法(ICP-MS)和电感耦合等离子体原子发射光谱法(ICP-AES)对我国6个主产区72份半夏样品中K、Ca、Na、Mg、Al等37种无机元素的含量进行测定,并采用方差分析、主成分分析、因子分析等计量学方法进行统计与评价。通过对比BP-神经网络算法、K-最近邻算法、最小二乘支持向量机等多种模式识别方法,探索适合半夏产地溯源的最佳模型。结果:不同产地半夏中无机元素的构成各具特征,各无机元素含量在产地间差异显著(P＜0.05),其中La、Pb、As、Na、Bi、Hg、Sn、Cd、Ag 9种元素在不同产区间的差异最为明显;3D-plots图显示不同产地半夏样品分布相对集中,具备产地分类的可行性;KNN分类模型(曼哈顿距离)是半夏产地溯源的最佳方法,测试集的正确率达到100%。结论:无机元素分析技术结合适当的计量学模型可以实现半夏的产地溯源。     

Enhancing cell membrane phase separation for inhibiting cancer metastasis with a stimuli-responsive DNA nanodevice

Phase separation in cell membranes promotes the assembly of transmembrane receptors to initiate signal transduction in response to environmental cues. Many cellular behaviors are manipulated by promoting membrane phase separation through binding to multivalent extracellular ligands. However, available extracellular molecule tools that enable manipulating the clustering of transmembrane receptors in a controllable manner are rare. In the present study, we report a DNA nanodevice that enhances membrane phase separation through the clustering of dynamic lipid rafts. This DNA nanodevice is anchored in the lipid raft region of the cell membrane and initiated by ATP. In a tumor microenvironment, this device could be activated to form a long DNA duplex on the cell membrane, which not only enhances membrane phase separation, but also blocks the interaction between the transmembrane surface adhesion receptor and extracellular matrix, leading to reduced migration. We demonstrate that the ATP-activated DNA nanodevice could inhibit cancer cell migration both in vitro and in vivo. The concept of using DNA to regulate membrane phase separation provides new possibilities for manipulating versatile cell functions through rational design of functional DNA structures.

A DNA nanodevice is developed to enhance the cell membrane phase separation in a tumor microenvironment to weaken the formation of focal adhesion. As a result, the migration of cancer cells is inhibited both in vitro and in vivo.