Affinity enrichment of plasma membrane for proteomics analysis

Proteomics analysis of plasma membranes from cells exposed to different extracellular environments is potentially a powerful approach for the identification of membrane-associated proteins responding to these environments. Preparation of high concentration plasma membrane fractions with low contamination from cellular organelles is essential for such studies. Here, we describe an affinity enrichment method, which combines cell surface biotinylation with affinity enrichment by immobilized streptavidin beads, for the isolation of plasma membranes. This method results in a 400-fold enrichment of plasma membrane relative to endoplasmic reticulum, a major contaminant in standard plasma membrane preparations, and dramatically reduces contamination from other cellular organelles. The biotinylation reaction did not interfere with ligand-dependent activation of receptor tyrosine kinases or G-protein coupled receptors, suggesting cell-surface signal transduction machinery remains functional. Membrane fractions prepared by this method should provide excellent starting materials for membrane proteomics analysis such as studies of dynamic trafficking and regulation of signaling molecules or identification of disease-specific membrane markers.     

Thermal degradation and flame retardancy of flexible polyvinyl chloride containing solid superacid

The objective of the present article was to study the thermal degradation behavior and flame retardancy of flexible polyvinyl chloride (PVC) composites containing TiO₂/SO ^2?₄ solid superacid because of its strong catalytic ability for esterification and dehydration. The TiO₂/SO ^2?₄ solid superacid was synthesized by using precipitation immersion method, and its structure was investigated by X-ray diffraction. As expected, the value of limiting oxygen index for PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) composite was 32.5% and the char yield of PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) composite was significantly improved compared to neat PVC in thermogravimetry tests. In addition, the peak heat release rate and smoke production rate of PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) decreased by 14% and 42%, respectively, compared with neat PVC. Moreover, the results of cone calorimetry tests and electron micrograph of char residue showed that the char yield of TiO₂/SO ^2?₄ was enhanced, resulting in a strong char layer structure with outstanding fire retardance cone. In conclusion, the results of this work showed that the addition of solid superacid promoted the decomposition and dehydration of PVC, which formed a compact and continuous char layer on the surface of the material. Hence, the study provides a new perspective for producing composites with excellent flame retardancy and smoke suppression properties of PVC.

     

反相液相色谱中固定相和流动相对柱相比的贡献

依据柱相比的热力学定义和反相液相色谱中溶质的计量置换保留理论(the stoichiometric dispheement heory of solute for retention，SDT-R)，对反相液相色谱中固定相和流动相性质、温度对柱相比的影响进行了研究。结果表明：固定相的种类和配基的疏水性对柱相比影响较大，而流动相中有机溶剂的种类，特别是脂肪酸作为置换剂时，对柱相比的影响更大，而柱相比受温度的影响较小。此外，通过用27种小分子溶质对柱相比的测定，其logI和Z良好的线性关系，进一步证明柱相比是一个与溶质性质无关的常数。     

Balancing kinetic and thermodynamic control: the mechanism of carbocation cyclization by squalene cyclase

Molecular dynamics simulations with a combined quantum mechanical and molecular mechanical (QM/MM) potential have been carried out to investigate the squalene-to-hopene carbocation cyclization mechanism in squalene-hopene cyclase (SHC). The present study is based on free energy simulations by constructing the free energy surface for the cyclization steps along the reaction pathway. The picture that emerges for the carbocation cyclization cascade is a delicate balance of thermodynamic and kinetic control that ultimately favors the formation of the final hopanoids carbon skeleton. A key finding is that the five- to six-membered ring expansion process is not a viable reaction pathway for either C- or D-ring formation in the cyclization reaction. The only significant intermediate is the A/B-bicyclic cyclohexyl cation (III), from which two asynchronous concerted reaction pathways lead to, respectively, the 6,6,6,5-tetracyclic carbon skeleton and the 6,6,6,6,5-pentacyclic hopanoids. Experimentally, these two products are observed to have 1% and 99% yields, respectively, in the wild-type enzyme. We conclude that the product distribution in the wild-type enzyme is dictated by kinetic control of these two reaction pathways.     

Dithia-crown-annelated tetrathiafulvalene disulfides: synthesis, electrochemistry, self-assembled films, and metal ion recognition

The synthesis and electrochemistry of a series of tetrathiafulvalene (TTF) and dithia-crown-TTF derivatives attached with one or two disulfide group(s) 7a-f are reported. The self-assembled monolayers (SAMs) of these TTF disulfides on gold were prepared and characterized by reflection-absorption infrared spectroscopy. The SAMs are extremely stable under a wide variety of conditions and over extended periods of time and show remarkable electrochemical stability upon repeated potential scans. SAMs of the crown-TTF disulfides 7c,d,f can recognize alkali metal ions, and the process can be monitored following the electrochemical potential shift of the surface-confined TTF group.     

Single-sweep polarography of the copper(II)-3-hydroxy-1-p-sulphonatophenyl-3-phenyltriazene complex and its analytical applications

A polarographic investigation of the copper-3-hydroxy-1-p-sulphonatophenyl-3-phenyltriazene (HSPT) complex in 0.05 M sodium tetraborate medium is described and a simple and sensitive single-sweep polarographic method for the determination of trace amounts of copper in biological samples is proposed. The complex was shown to be Cu(HSPT)2 with log beta' = 11.38. The polarographic wave is caused by the reduction of copper(II) in the adsorbed complex to copper amalgam on the surface of a mercury electrode. The current peak is directly proportional to the concentration of copper in the range 8.0 x 10(-9)-4.0 x 10(-6) M and the detection limit is 5.0 x 10(-9) M.     

Capillary electrophoresis with amperometric detection of curcumin in Chinese herbal medicine pretreated by solid-phase extraction

In the present study, curcumin from Chinese herbal medicine turmeric was determined by capillary electrophoresis with amperometric detection (CE-AD) pretreated by a self-designed, simple, inexpensive solid-phase extraction (SPE) cartridge based on the material of tributyl phosphate resin. An average concentration factor of 9 with the recovery of > 80% was achieved when applied to the analysis of curcumin in extracts of tumeric. Under the optimized CE-AD conditions: a running buffer composed of 15 mM phosphate buffer at a pH 9.7, separation voltage at 16 kV, injection for 6 s at 9 kV and detection at 1.20 V, CE-AD with SPE exhibited low detection limit as 3 x 10(-8) mol/l (S/N = 3), high efficiency of 1.0 x 10(5) N, linear range of 7 x 10(-4) -3 x 10(-6) mol/l (r = 0.9986) for curcumin extracted from light petroleum. The method developed resulted in enhancement of the detection sensitivity and reduction of interference from sample matrix in complicated samples and exhibited the potential application for routine analysis, especially in food, because a relatively complete process of sample treatment and analysis was described.     

The intercalation of cetyltrimethylammonium cations into muscovite by a two-step process: II. The intercalation of cetyltrimethylammonium cations into Li-muscovite

The alkylammonium cations were successively intercalated into the interlayer of muscovite. It was achieved by inorganic-organic ion exchange in the hydrothermal reaction of the LiNO₃-treated muscovite with cetyltrimethylammonium bromide solution. One-dimensional Patterson plots and electron density calculations show that hydrated Li⁺ and CTA⁺ cations entered the interlayer of muscovite successively. The CTA⁺-intercalated muscovite was characterized by powder X-ray diffraction and elemental analysis, in conjunction with FTIR, nuclear magnetic resonance, X-ray photoelectron spectra, high-resolution transmission electron microscopy, etc. The experiments show that organo-muscovite composite with ordered structure has been obtained. The CTA⁺ headgroups are distributed in the interlayer uniformly. However, the arrangement and conformation of CTA⁺ chains are strongly dependent upon the reaction temperature. At lower reaction temperature, the chains of CTA⁺ ions adopt a little more disordered arrangement and have higher gauche/trans conformer ratio, resulting in the disturbance to the interlayer symmetry. Whereas at higher reaction temperature, the sample with paraffin-like arrangement of CTA⁺ chains could be obtained, in which the methylene chains of CTA⁺ adopt a fully stretched, all-trans conformation.     

利用压电频移法测定水中的痕量亚硝酸盐

提出了利用压电频移法测定亚硝酸盐的方法。方法以碘离子与亚硝酸根之间的氧化还原反应为依据，通过测定由反应生成的碘所引起的压电晶体频率的变化，在被萃取水相中亚硝酸盐浓度为０．００９￣２．３ｍｇ／Ｌ范围内，频移值与浓度成正比：ΔＦ＝５．８＋２．５×１０＾３Ｃ（ｍｇ／Ｌ），ｒ＝０．９９０１。方法简便，用于天然水中亚硝酸盐的测定，结果令人满意。