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61.
Maaloum M Muller P Krafft MP 《Langmuir : the ACS journal of surfaces and colloids》2004,20(6):2261-2264
It has recently been found that monodisperse surface micelles (hemimicelles) were formed in Langmuir monolayers of the semifluorinated alkane C8F17C16H33 (F8H16) after transfer onto silicon wafers. Grazing incidence X-ray diffraction studies have demonstrated that compression of mixed Langmuir monolayers made from combinations of dipalmitoyl phosphatidylethanolamine (DPPE) and diblock F8H16 in various molar ratios resulted in the complete expulsion of the diblock molecule at high surface pressure. F8H16 then formed a second layer on top of a DPPE-only monolayer, demonstrating a novel type of reversible, pressure-induced, vertical phase separation. Using atomic force microscopy and X-ray reflectivity, we show now that mixed DPPE/F8H16 (1:1.3) Langmuir-Blodgett films transferred onto silicon wafers below 10 mN m(-1) are laterally phase separated and consist of domains of F8H16 surface micelles in coexistence with a monolayer of DPPE. The density of the network of F8H16 surface micelles increases when the surface pressure of transfer increases. Around 10 mN m(-1), the F8H16 surface micelles start to glide on the DPPE monolayer, progressively overlying it, until total coverage is achieved. 相似文献
62.
Synthesis and properties of 7-formyl-8-hydroxyquinoline and its transition metal complexes 总被引:4,自引:0,他引:4
Ahmed A. El-Asmy Adel Z. El-Sonbati Abdulla A. Ba-Issa Mohamed Mounir 《Transition Metal Chemistry》1990,15(3):222-225
Summary CoII, NiII, CuII, CdII and HgII complexes of 7-formyl-8-hydroxyquinoline (HFHQ) have been prepared, and characterized by elemental analysis, molar conductivities, electronic and i.r. spectra, and magnetic measurements. It was found that the ligand acts as a neutral monodentate or a monobasic bidentate donor. The CoII, NiII and CuII complexes possess, respectively, tetrahedral, octahedral and square-planar structures based on their magnetic and electronic spectral data. The electrical conductivities of HFHQ and its metal complexes were measured at different temperatures and their activation energies were calculated. The values obtained for the CoII, NiII, CdII and HgII complexes agree fairly well with those reported for semiconductors. The ligand was tested as a corrosion inhibitor for aluminium; the limiting concentration of HFHQ to give maximum efficiency (99.2%) is 10–3 mole dm–3 at 22°C. The metal-ligand ratios and apparent formation constants for the species generated in ethanol solution were determined spectrophotometrically. 相似文献
63.
Mounir Afilal Tarek Merabtene Karim Rhofir Abdelaziz Soufyane 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2016,67(5):119
We consider two Cauchy problems for the one-dimensional thermoelastic Bresse model. Using the energy method in the Fourier space, we show that for the first model, the \({L^{2}}\)-norm of the solution decays with the rate \({(1+t)^{-1/12}}\). In addition, the same decay rate has been obtained for the second model. 相似文献
64.
Dr. Emilie Moulin Dr. Gad Fuks Prof. Dr. Mounir Maaloum Prof. Dr. Eric Buhler Prof. Dr. Nicolas Giuseppone 《Angewandte Chemie (International ed. in English)》2016,55(2):703-707
An acid–base switchable [c2]daisy chain rotaxane terminated with two 2,6‐diacetylamino pyridine units has been self‐assembled with a bis(uracil) linker. The complementary hydrogen‐bond recognition patterns, together with lateral van der Waals aggregations, result in the hierarchical formation of unidimensional supramolecular polymers associated in bundles of muscle‐like fibers. Microscopic and scattering techniques reveal that the mesoscopic structure of these bundles depends on the extended or contracted states that the rotaxanes show within individual polymer chains. The observed local dynamics span over several length scales because of a combination of supramolecular and mechanical bonds. This work illustrates the possibility to modify the hierarchical mesoscopic structuring of large polymeric systems by the integrated actuation of individual molecular machines. 相似文献
65.
Blanco P Polyakov P Bou-Ali MM Wiegand S 《The journal of physical chemistry. B》2008,112(28):8340-8345
In the present work we studied the thermal diffusion behavior of n-decane in various alkanes by thermogravitational column (TC) technique and the thermal diffusion forced Rayleigh scattering (TDFRS) method. The investigated lighter alkanes compared to n-decane are n-pentane, n-hexane, n-heptane, n-octane, and the heavier ones are n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, and n-eicosane. The binary mixture n-decane/ n-pentane we investigated at several different concentrations; all other mixtures were only investigated at a mass fraction of 50%. Even for the volatile n-pentane/ n-decane mixture the deviations between the thermal diffusion coefficients determined by the different methods agreed within the error bars. Typically the agreement between the two methods was in the order of 5%. In comparison to recently published TC and TDFRS data we found deviations in the order of 30% up to 40%. We analyze and discuss the possible reasons for the discrepancies for the present and the past publications. 相似文献
66.
Gating motions in voltage-gated potassium channels revealed by coarse-grained molecular dynamics simulations 总被引:1,自引:0,他引:1
Voltage-gated potassium (Kv) channels are ubiquitous transmembrane proteins involved in electric signaling of excitable tissues. A fundamental property of these channels is the ability to open or close in response to changes in the membrane potential. To date, their structure-based activation mechanism remains unclear, and there is a large controversy on how these gates function at the molecular level, in particular, how movements of the voltage sensor domain are coupled to channel gating. So far, all mechanisms proposed for this coupling are based on the crystal structure of the open voltage-gated Kv1.2 channel and structural models of the closed form based on electrophysiology experiments. Here, we use coarse-grain (CG) molecular dynamics simulations that allow conformational changes from the open to the closed form of the channel (embedded in its membrane environment) to be followed. Despite the low specificity of the CG force field, the obtained closed structure satisfies several experimental constraints. The overall results suggest a gating mechanism in which a lateral displacement the S4-S5 linker leads to a closing of the gate. Only a small up-down movement of the S4 helices is noticed. Additionally, the study suggests a peculiar upward motion of the intracellular tetramerization domain of the channel, hence providing a molecular view on how this domain may further regulate conduction in Kv channels. 相似文献
67.
A new TEMPO-mediated catalytic oxidation method in combination with Py·HBr3 (stoichiometric) is developed for oxidation of secondary alcohols to the corresponding ketones. The performance of this oxidizing system is better compared with that of TEMPO method combined with R4NBr3. Poly(4-vinylpyridine)·HBr3 can be used in place of Py·HBr3. The electron-withdrawing substituent at the C-4 position of TEMPO increases the reactivity of TEMPO significantly in the oxidation of electron-deficient alcohols such as polyhaloalkylmethanols. Inductive effect of the substituent of TEMPO is discussed through the characterization of the redox potential of N-O radical by cyclic voltammetry. 相似文献
68.
Relative humidities have been measured for mixed aqueous electrolyte system of ammonium and potassium chlorides by the hygrometric method at total molalities from 0.3 to 6 mol-kg–1for ionic-strength fractions yof NH4Cl of 1/3, 1/2, and 2/3 at 25°C. The data allow the calculation of new water activities and osmotic coefficients. The proposed ECA (extended composed additivity) rule of calculation of water activity in mixed aqueous electrolyte solutions from the water activities of a single component is extended to this system. The experimental results and the predictions of the ECA rule are compared with the Robinson–Stokes, Reilly–Wood–Robinson, the Pitzer, and the Lietzke–Stoughton II models. Predictions made using these models are, in general, consistent with our results. From these measurements, the Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture for different ionic-strength fractions. 相似文献
69.
We study a second-order parabolic equation with divergence form elliptic operator,having a piecewise constant diffusion coefficient with two points of discontinuity.Such partial differential equations appear in the modelization of diffusion phenomena in medium consisting of three kinds of materials.Using probabilistic methods,we present an explicit expression of the fundamental solution under certain conditions.We also derive small-time asymptotic expansion of the PDE’s solutions in the general case.The obtained results are directly usable in applications. 相似文献
70.
A new spectrokinetic method is described that determines the absolute values of all five unknown parameters (εA, εB, ?AB, kAB, kBA) of AB(2k,1?) thermophotoreactive chromic systems. For the first time, solely kinetic data are used to perform complete analytical elucidations. Also, the method addresses realistic situations by considering that both absorption spectra of the reactive species are unknown and partially or totally overlap, solving the identifiability problem, and using a single set of experimental data (for the thermal and photochemical reactions). The absolute values for the five unknown parameters that make up the true kinetic solution are readily obtained by the application of five analytically defined algebraic equations. The method is independent of experimental conditions relating to initial concentration, temperature, threshold of incident light intensity, and the wavelength at which the kinetic traces are measured. The detailed mathematical algorithm also allows the determination of the reaction quantum yield at any (isosbestic and nonisosbestic) irradiation wavelength and proposes a new colorability expression for these systems. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 255–264, 2009 相似文献