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251.
Choucair A Soo PL Eisenberg A 《Langmuir : the ACS journal of surfaces and colloids》2005,21(20):9308-9313
Vesicles are spherical bilayers that offer a hydrophilic reservoir, suitable for the incorporation of water-soluble molecules, as well as a hydrophobic wall that protects the loaded molecules from the external solution. The permeability of a vesicle wall made from polystyrene can be enhanced by adding a plasticizer such as dioxane. Tuning the wall permeability allows loading and release of molecules from vesicles to be controlled. In this study, vesicles are prepared from polystyrene(310)-b-poly(acrylic acid)(36) and used as model carriers for doxorubicin (DXR), a weak amine and a widely used anticancer drug. To increase the wall permeability, different amounts of dioxane are added to the vesicle solution. A pH gradient is created across the vesicle wall (inside acidic) and used as an active loading method to concentrate the drug inside the vesicles. The results show that a pH gradient of ca. 3.8 units can enhance the loading level up to 10-fold relative to loading in the absence of the gradient. After loading, the release of DXR from vesicles is followed as a function of the wall permeability. The diffusion coefficient of doxorubicin through polystyrene (D) is evaluated from the initial slope of the release curves; the value of D ranges from 8 x 10(-17) to 6 x 10(-16) cm(2)/s, depending on the degree of plasticization of the vesicle wall. 相似文献
252.
Khalifa?Dabbek Fredj?ElkhadhraEmail author Hassine El?Mir 《Mathematische Zeitschrift》2003,245(3):455-481
Let A be a closed subset of an open subset of
n
and T be a negative current on \ A of bidimension (p,p). Assume that T is psh and A is complete pluripolar such that the Hausdorff measure
, then T extends to a negative psh current on . We also show that if T is psh or if dd
cT
extends to a current with locally finite mass on , then the trivial extension
of T by zero across A exists in both cases: A is the zero set of a k–convex function with kp–1 or
. Our basic tool is the following theorem [El3]: Let A be a closed complete pluripolar subset of an open subset of
n
and T be a positive current of bidimension (p,p) on \ A. Suppose that
and
exist (resp.
exists and dd
cT
0 on \ A), then there exists a positive (resp. closed positive) current S supported in A such that
. Furthermore, we give a generalization of some theorems done by Siu and Ben Messaoud-El Mir and Alessandrini-Bassanelli without requiring anything from dT. 相似文献
253.
254.
An efficient synthesis of bromomethyl-d2-benzene as reagent for protection of hydroxyl groups and its benefit in 1H- and 13C-NMR-spectroscopical analysis of benzylether blocked saccharides is described. 相似文献
255.
Synthesis of Some New Heterocycles Derived from Novel 2‐(1,3‐Dioxisoindolin‐2‐yl)Benzoyl Isothiocyanate
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Novel 2‐(1,3‐Dioxisoindolin‐2‐yl)benzoyl isothiocyanate was prepared and underwent addition–cyclization reactions with some nucleophilic reagents. Simultaneous or subsequent cyclization of the obtained adducts gave a diverse range of differently sized heterocycles and thioureas. The structures of the synthesized compounds were confirmed by microanalytical and spectral data. 相似文献
256.
Atmospheric pressure chemical ionization of explosives induced by soft X‐radiation in ion mobility spectrometry: mass spectrometric investigation of the ionization reactions of drift gasses,dopants and alkyl nitrates
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![点击此处可从《Journal of mass spectrometry : JMS》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Daniel Riebe Alexander Erler Thomas Ritschel Toralf Beitz Hans‐Gerd Löhmannsröben Andreas Beil Michael Blaschke Thomas Ludwig 《Journal of mass spectrometry : JMS》2016,51(8):566-577
A promising replacement for the radioactive sources commonly encountered in ion mobility spectrometers is a miniaturized, energy‐efficient photoionization source that produce the reactant ions via soft X‐radiation (2.8 keV). In order to successfully apply the photoionization source, it is imperative to know the spectrum of reactant ions and the subsequent ionization reactions leading to the detection of analytes. To that end, an ionization chamber based on the photoionization source that reproduces the ionization processes in the ion mobility spectrometer and facilitates efficient transfer of the product ions into a mass spectrometer was developed. Photoionization of pure gasses and gas mixtures containing air, N2, CO2 and N2O and the dopant CH2Cl2 is discussed. The main product ions of photoionization are identified and compared with the spectrum of reactant ions formed by radioactive and corona discharge sources on the basis of literature data. The results suggest that photoionization by soft X‐radiation in the negative mode is more selective than the other sources. In air, adduct ions of O2– with H2O and CO2 were exclusively detected. Traces of CO2 impact the formation of adduct ions of O2– and Cl– (upon addition of dopant) and are capable of suppressing them almost completely at high CO2 concentrations. Additionally, the ionization products of four alkyl nitrates (ethylene glycol dinitrate, nitroglycerin, erythritol tetranitrate and pentaerythritol tetranitrate) formed by atmospheric pressure chemical ionization induced by X‐ray photoionization in different gasses (air, N2 and N2O) and dopants (CH2Cl2, C2H5Br and CH3I) are investigated. The experimental studies are complemented by density functional theory calculations of the most important adduct ions of the alkyl nitrates (M) used for their spectrometric identification. In addition to the adduct ions [M + NO3]– and [M + Cl]–, adduct ions such as [M + N2O2]–, [M + Br]– and [M + I]– were detected, and their gas‐phase structures and energetics are investigated by density functional theory calculations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
257.
High‐performance liquid chromatography with electrospray ionization ion mobility spectrometry: Characterization,data management,and applications
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![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Martin Zühlke Daniel Riebe Toralf Beitz Hans‐Gerd Löhmannsröben Sandro Andreotti Knut Reinert Karl Zenichowski Marc Diener 《Journal of separation science》2016,39(24):4756-4764
The combination of high‐performance liquid chromatography and electrospray ionization ion mobility spectrometry facilitates the two‐dimensional separation of complex mixtures in the retention and drift time plane. The ion mobility spectrometer presented here was optimized for flow rates customarily used in high‐performance liquid chromatography between 100 and 1500 μL/min. The characterization of the system with respect to such parameters as the peak capacity of each time dimension and of the 2D spectrum was carried out based on a separation of a pesticide mixture containing 24 substances. While the total ion current chromatogram is coarsely resolved, exhibiting coelutions for a number of compounds, all substances can be separately detected in the 2D plane due to the orthogonality of the separations in retention and drift dimensions. Another major advantage of the ion mobility detector is the identification of substances based on their characteristic mobilities. Electrospray ionization allows the detection of substances lacking a chromophore. As an example, the separation of a mixture of 18 amino acids is presented. A software built upon the free mass spectrometry package OpenMS was developed for processing the extensive 2D data. The different processing steps are implemented as separate modules which can be arranged in a graphic workflow facilitating automated processing of data. 相似文献
258.
Rúben Maia Ricardo Branco F. V. Antunes M. C. Oliveira Andrei Kotousov 《Mathematics in Computer Science》2016,10(3):343-352
Stress state is a main parameter within fracture mechanics. It has a major influence on different phenomena, namely those involving diffusion, plastic deformation, and brittle fracture. As is well-known, in the near-surface regions of a crack front, the plane stress state dominates, while at interior positions the plane strain state prevails. The main objective here is to examine the extent of surface regions in through-cracked planar geometries subjected to cyclic loading. Two constitutive material models were developed to characterise the stress state along the crack front. A new criterion based on the h stress triaxiality parameter was proposed to define the transition between surface and near-surface regions. Finally, a linear relation between the stable value of the extent of surface region and the maximum stress intensity factor was established. 相似文献
259.
Shawky A. El-Shazly Abdalla A. S. Babaqi Mohamed T. Mohamed Amal A. Zaghlol Mohamed F. Amira 《Transition Metal Chemistry》1991,16(5):488-491
Summary The aquation kinetics of the chloropenta-aminecobalt(III) ion in H2O–EtOH mixtures have been determined. A new correlation is described for calculating the chemical potential from kinetic data and molar thermodynamic excess functions for binary mixtures. The rate constants correlate well with Grunwald-Winstein solvating power Y parameter and with the dielectric constant of the medium. The data supports the D mechanism. 相似文献
260.
聚合物基粘土纳米复合材料的流变行为研究 总被引:7,自引:0,他引:7
聚合物基粘土纳米复合材料具有与常规颗粒填充体系类似的流变特性 :在整个频率范围内 ,储能模量和损耗模量均随粘土含量的增加而变高 ,其频率依赖性会表现出非未端行为 :且当粘土含量超过临界值以后 ,储能模量会在低频区表现出似固体的平台发展。但与之不同的是前者在低粘土含量的条件下 (<10 % (wt) )就会表现出似固体行为或非末端行为。这些流变特性还会受到粘土的径厚比、化学特性、聚合物基体的分子结构参数和粘土与基体间的相互作用强度等因素的影响。聚合物基粘土纳米复合材料的流变行为是与其微观结构的形成和演化以及聚合物分子链在特定环境下的粘弹松弛过程紧密联系在一起的。本文综述了插层型、剥离型和聚合物分子链一端受限剥离型聚合物基粘土纳米复合材料在力场作用下的流变特性和粘弹松弛机理方面的研究进展。 相似文献