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981.
Membrane fusion is very important for the formation of many complex organs in metazoans throughout evolution, such as muscles, bones, and placentae. Lipid vesicles (liposomes) are frequently used as model membranes to study the fusion process. This work demonstrates for the first time the real-time membrane fusion of giant polymer vesicles by directly displaying a series of high-resolution and real-time transformation images of individual vesicles. The fusion process includes the sequential steps of membrane contact, forming the center wall, symmetric expansion of fusion pore and complete fusion, undergoing the intermediates of "8" shape with a protruding rim at the contact site, peanut (pear) shape, and oblate sphere. The vesicle swells during fusion, and the fusing vesicle only deforms in the neck domain around the fusion pore in the lateral direction, which verifies the importance of the lateral tension on the fusion pore at the vesicle deformation level. The successful fusion of the synthetic and protein-free polymer vesicles reported here also supports that vesicle proximity combined with membrane perturbation suffices to induce membrane fusion, and that the protein is not necessary for the fusion process. 相似文献
982.
Efforts to develop a database of quadratic force fields for organic molecules are described. The database is based on systematic ab initio calculations, scaled to reproduce the experimentally observed frequencies. The choice of the theoretical method, the basis sets, geometries, internal coordinates and the scaling procedure are discussed. A key point in the procedure is the automatic generation of the internal valence coordinates. This is also very advantageous for geometry optimization. The database should permit the prediction of vibrational frequencies for most organic molecules to 10–20 cm−1, together with semiquantitative intensities. The accuracy is sufficient to identify unknown compounds from a list of reasonable candidates. 相似文献
983.
Electrocatalytic oxidation of thiosulfate on a modified nickel hexacyanoferrate film electrode 总被引:1,自引:0,他引:1
Xingyao Zhou Shengfu Wang Zhengpin Wang Mian Jiang 《Fresenius' Journal of Analytical Chemistry》1993,345(6):424-427
Summary A modified nickel hexacyanoferrate film glassy carbon electrode is prepared by the electrochemical deposition technique. The film is very stable upon voltammetric scanning in the potential range of 1.0 to –0.5 V (vs. SCE) and an oxidation peak occurs at 0.35 V (vs. SCE) (1 mol/l NaNO3). The effects of electrolyte, solvent, coexisting ions and other variables on the voltammetric behaviour of the modified film have been studied. The thickness of the resulting film can be controlled by changing the number of voltammetric cycles and the concentrations of nickel(II) and hexacyanoferrate(III) ions. The film shows catalytic activity towards electrooxidation of thiosulfate with a peak potential +0.5 V (K–-containing media). This oxidation potential of thiosulfate on the modified electrode is shifted negatively by about 550 mV as compared to the naked glassy carbon electrode. For practical application, the modified electrode can be used for the determination of thiosulfate in concentrations from 5.0×10–5 to 1.0×10–1 mol/l. This method has been successfully applied to the determination of thiosulfate in photographic waste effluents. 相似文献
984.
Micellar shape change and internal segregation induced by chemical modification of a tryptych block copolymer surfactant 总被引:1,自引:0,他引:1
Zhou Z Li Z Ren Y Hillmyer MA Lodge TP 《Journal of the American Chemical Society》2003,125(34):10182-10183
We report the detailed characterization of micelles formed by two nonionic, amphiphilic ABC triblock copolymers. Poly(ethylene oxide)-b-poly(styrene)-b-1,2-poly(butadiene) (PEO-b-PS-b-PB) triblock copolymer "OSB" forms core-corona spherical micelles in aqueous solution, and the two hydrophobic blocks S and B are mixed homogeneously within the micelle core. PEO-b-PS-b-PB:C6F13I triblock copolymer "OSF" was prepared by selective fluorination of the B block in OSB with n-perfluorohexyl iodide. Fluorination of the B block induces internal segregation into an inner F core and an intermediate S shell. Furthermore, the strong incompatibility that results from fluorination drives a shape change into an oblate ellipsoid. These micellar morphologies are confirmed by combined light, neutron, and X-ray scattering measurements, as well as TEM imaging. 相似文献
985.
A novel hypoxanthine (Hx) microsensor was constructed. In this work, Nafion xanthine oxidase (XOD) and Au colloid were immobilized onto the surface of a Pt microelectrode. The enzyme biosensor displayed a quick and sensitive response to Hx. Under physiological conditions, a low detection limit, with high selectivity and sensitivity for Hx determination were obtained. The oxidation current [investigated using current-time (I-t) plots] was linear with Hx concentration ranging from 2.0 x 10(-7) to 2.0 x 10(-5) mol L(-1) with a calculated detection limit of 1.0 x 10(-7) mol L(-1) (S/N of 3). The biosensor should be promising for in vivo measurement of Hx without interferences and fouling. The change of Hx concentration in cardiac myocytes stimulated by L-arginine (L-Arg) and acetylcholine (Ach) was also studied. 相似文献
986.
Ramoplanin is a cyclicdepsipeptide antibiotic that inhibits peptidoglycan biosynthesis. It was proposed in 1990 to block the MurG step of peptidoglycan synthesis by binding to the substrate of MurG, Lipid I. The proposed mechanism of MurG inhibition has become widely accepted even though it was never directly tested. In this paper, we disprove the accepted mechanism for how ramoplanin functions, and we present an alternative mechanism. This work has implications for the design of ramoplanin derivatives and may influence how other proposed substrate binding antibiotics are studied. 相似文献
987.
Heterotrimetallic 4f-3d coordination polymers: synthesis, crystal structure, and magnetic properties
A series of cyano-bridged heterotrimetallic complexes [CuL](2)Ln(H(2)O)(2)M(CN)(6).7H(2)O have been synthesized by the reactions of CuL (L(2)(-) = dianion of 1,4,8,11-tetraazacyclotradecane-2,3-dione), Ln(3+) (Ln = Gd or La), and [M(CN)(6)](3)(-) (M = Co, Fe, or Cr). X-ray diffraction analysis reveals that these complexes are isostructural and have a novel chain structure. The Ln(3+) ion is eight-coordinated by six oxygen atoms of two CuL and two water molecules and two nitrogen atoms of the bridging cyano ligands of two [M(CN)(6)](3)(-), while the [M(CN)(6)](3)(-) anion connects two Ln(3+) using two trans-CN(-) ligands giving rise to a chainlike structure. In the chain, every CuL group tilts toward the CN(-) ligand of adjacent [M(CN)(6)](3)(-) with the Cu-N(cyano) contacts ranging from 2.864(6) to 2.930(6) A. Magnetic studies on the CuGdCo complex (1) indicate the presence of ferromagnetic coupling between Cu(II) and Gd(III). The CuLaCr (5) and CuLaFe (2) complexes exhibit ferromagnetic interaction between paramagnetic Cu(II) and Cr(III)/Fe(III) ions through the weak cyano bridges (Cu-N(cyano) = 2.930(6) A for 2). A global ferromagnetic interaction is operative in the CuGdFe complex (3) with the concurrence of dominant ferromagnetic Cu(II)-Gd(III) and minor antiferromagnetic Gd(III)-Fe(III) as well as the ferromagnetic Cu(II)-Fe(III) interaction. For the CuGdCr complex (4), an overall antiferromagnetic behavior was observed, which is attributed to the presence of dominant antiferromagnetic Cr(III)-Gd(III) coupling and the minor ferromagnetic Cu(II)-Gd(III) and Cu(II)-Cr(III) interaction. Moreover, a spin frustration phenomenon was found in complex 4, which results from the ferro-ferro-antiferromagnetic exchanges in the trigonal Cu-Gd-Cr units. The magnetic susceptibilities of these complexes were simulated using suitable models. The magneto-structural correlation was investigated. These complexes did not show a magnetic phase transition down to 1.8 K. 相似文献
988.
Yizhao Ouyang Miao Zhan Jing Zhou Jiao Jiao Hao Hu Yoichi M. A. Yamada Pengfei Li 《中国化学》2019,37(8):807-810
A rigid C2‐symmetric chiral bipyridine ligand Z‐bpy with a triptycene‐like backbone was designed and synthesized from simple chemicals in a scalable route. Using this new ligand, copper(I) catalyzed cyclopropanation of styrenes with commercial ethyl diazoacetate produced various corresponding cyclopropanes in high yields, diastereoselectivity and enantioselectivity up to 97% ee. 相似文献
989.
Li Xiuzhen Zhou Guimin Bao Miansheng Zhang Yukui Lu Peichang 《Journal of separation science》1981,4(11):569-576
Using a specially designed column system, we have systematically investigated the effect of mobile phase velocity on column efficiency. The performance of small bore columns operated at different linear velocities of mobile phase was examined for three different types of injection system. Using the value of H∞/u or n∞/t as a criterion of a high speed separation, we calculated values of n/t for different solutes according to the equation \documentclass{article}\pagestyle{empty}\begin{document}$ {{\rm n}\mathord{\left/ {\vphantom {{\rm n} {{\rm t}_{\rm r}^ \circ }}}\right. \kern-\nulldelimiterspace} {{\rm t}_{\rm r}^ \circ }} = {{{\rm n}^\infty } \mathord{\left/ {\vphantom {{{\rm n}^\infty } {{\rm t}_{\rm r}^ \circ }}} \right. \kern-\nulldelimiterspace} {{\rm t}_{\rm r}^ \circ }}\left({\frac{{1 + {\rm k'}}}{{{\rm k' + }\beta }}} \right)^2 $\end{document}; the results obtained are in agreement with the experimentally determined values. These systematic investigations culminated in the separation of seven compounds in less than 10 s; the respective chromatogram is shown. 相似文献
990.
Solid phase microextraction (SPME) then capillary gas chromatography with mass spectrometric detection have been used for determination of nine phenyl compounds in snow water in Beijing City. Headspace extraction with a fiber coated with 100 µm PDMS was used to extract the compounds. Extraction and desorption times were optimized at 8 and 2 min, respectively. Relative standard deviation (RSD) of the analytical method was found to be less than 5%. The linear range was wide and limits of detection were less than 5 ng mL−1 for the nine target analytes. Several phenyl compounds at ng mL−1 levels were detected in snow samples in Beijing, indicating the corresponding air pollution. 相似文献