排序方式: 共有130条查询结果,搜索用时 15 毫秒
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122.
Bernard AL Guedeau-Boudeville MA Marchi-Artzner V Gulik-Krzywicki T di Meglio JM Jullien L 《Journal of colloid and interface science》2005,287(1):298-306
This paper introduces a novel approach to controlling membrane permeability in free unilamellar vesicles using shearing in the presence of a detergent with a large head-group to tune pore formation. Such shear-induced permeation could offer a simple means of postencapsulating bioactive molecules to prepare vesicle vectors for drug delivery. Using UV absorption, fluorescence emission, dynamic light scattering, and electron microscopy, we investigated the membrane permeability and the morphology of unilamellar lipid vesicles (diameter in the range 50-400 nm) subjected to a shear stress in the presence of a small amount of nonionic surfactant (Brij 76). Shear-induced leakage and fusion events were observed. We analyzed the significance of the vesicle size, the shear rate, and the surfactant-to-lipid ratio for the observed phenomena. The present approach is evaluated for postloading of preformed vesicles. 相似文献
123.
The positive axial zero-field splitting parameter D relevant for the S = 2 ground state of [Mn(cyclam)I2]I (cyclam = 1,4,8,11-tetraazacyclotetradecane) is interpreted using the valence bond configuration interaction model which explicitly considers the covalency of the manganese-iodide bond. 相似文献
124.
The structure of a sulfonated polyimide (sPI) ionomer membranes was investigated via the transport properties of various confined cations (7Li+, 23Na+, 87Rb+, 133Cs+). Their NMR spectra show large residual quadrupolar splitting depending on the orientation of the film in the static magnetic field B0. This behavior is the fingerprint of a macroscopic nematic ordering of charged interfaces. This is also confirmed by the anisotropy of the self-diffusion tensor measured by 1H and 7Li PGSE experiments on N(CH3)4+ and Li+ cations, respectively. 相似文献
125.
Boskovic C Bircher R Tregenna-Piggott PL Güdel HU Paulsen C Wernsdorfer W Barra AL Khatsko E Neels A Stoeckli-Evans H 《Journal of the American Chemical Society》2003,125(46):14046-14058
A new family of tetranuclear Mn complexes [Mn4X4L4] (H2L = salicylidene-2-ethanolamine; X = Cl (1) or Br (2)) and [Mn4Cl4(L')4] (H2L' = 4-tert-butyl-salicylidene-2-ethanolamine, (3)) has been synthesized and studied. Complexes 1-3 possess a square-shaped core with ferromagnetic exchange interactions between the four Mn(III) centers resulting in an S = 8 spin ground state. Magnetochemical studies and high-frequency EPR spectroscopy reveal an axial magnetoanisotropy with D values in the range -0.10 to -0.20 cm(-1) for complexes 2 and 3 and for differently solvated forms of 1. As a result, these species possess an anisotropy-induced energy barrier to magnetization reversal and display slow relaxation of the magnetization, which is observed as hysteresis for 1 and 3 and frequency-dependent peaks in out-of-phase AC susceptibility measurements for 3. The effective energy barrier was determined to be 7.7 and 7.9 K for 1 and 3, respectively, and evidence for quantum tunneling of the magnetization was observed. Detailed magnetochemical studies, including measurements at ultralow temperatures, have revealed that complexes 1 and 2 possess solvation-dependent antiferromagnetic intermolecular interactions. Complex 3 displays ferromagnetic intermolecular interactions and approaches a ferromagnetic phase transition with a critical temperature of approximately 1 K, which is coincident with the onset of slow relaxation of the magnetization due to the molecular anisotropy barrier to magnetization reversal. It was found that the intermolecular interactions have a significant effect on the manifestation of slow relaxation of the magnetization, and thereby, these complexes represent a new family of "exchange-biased single-molecule magnets", where the exchange bias is controlled by chemical and structural modifications. 相似文献
126.
The stability of foam is investigated experimentally through coalescence events. Instability (coalescence) occurs when the system is submitted to external perturbations (T1) and when the liquid amount in the film network is below a critical value. Microscopically, transient thick films are observed during film rearrangements. Film rupture, with coalescence and eventual collapse of the foam, occurs when the available local liquid amount is too small for transient films to be formed. Similar experiments and results are shown in the two-bubble case. 相似文献
127.
We consider the homogenization of the Navier-Stokes equation, set in a channel with a rough boundary, of small amplitude and wavelength ?. It was shown recently that, for any non-degenerate roughness pattern, and for any reasonable condition imposed at the rough boundary, the homogenized boundary condition in the limit ε=0 is always no-slip. We give in this paper error estimates for this homogenized no-slip condition, and provide a more accurate effective boundary condition, of Navier type. Our result extends those obtained in Basson and Gérard-Varet (2008) [6] and Gerard-Varet and Masmoudi (2010) [13], in which the special case of a Dirichlet condition at the rough boundary was examined. 相似文献
128.
Stoyanova R Barra AL Yoncheva M Kuzmanova E Zhecheva E 《Dalton transactions (Cambridge, England : 2003)》2011,40(36):9106-9115
The zero-field splitting parameters (ZFS) of Mn(4+) and Fe(3+) ions in LiAlO(2) with a layered structure are analyzed experimentally and theoretically by using high-frequency electron paramagnetic resonance spectroscopy, Neuman superposition model (NSM), DFT and multiconfigurational calculations. The interpretation of ZFS is based on the comparison of the experimentally determined values with the calculated ones. This approach allows assessing the performance of different methods for computation of ZFS of Fe(3+) and Mn(4+) in layered oxide matrices. DFT and multiconfigurational calculations are used to analyze the effect of oxygen, aluminium, and lithium neighbours on ZFS of Fe(3+) and Mn(4+). These calculations are based on a cluster comprising Fe(3+) or Mn(4+) ions in a trigonally compressed octahedron with 6 metal ions (Al(3+) or Co(3+)) as first metal neighbours and 6 O(2-) and 2 Li(+) (above and below the layer) as second neighbours. A satisfactory agreement with the experimental data is achieved when the local structure of Mn(4+) and Fe(3+) deviates from the trigonal host-site geometry. The local structure of Fe(3+) comprises an axial distortion, while trigonal environment with reduced extent of distortion appears around Mn(4+). 相似文献
129.
Rodriguez-Douton MJ Mannini M Armelao L Barra AL Tancini E Sessoli R Cornia A 《Chemical communications (Cambridge, England)》2011,47(5):1467-1469
Iron(III)-based single-molecule magnets have been covalently grafted on Au(111) in one step using 1,2-dithiolan-3-yl side groups. Reaction with the substrate quantitatively affords a monolayer of electronically intact clusters doubly linked to the surface via Au-S bonds, as demonstrated by a combination of STM, XAS/XMCD and XPS studies. 相似文献
130.
Fameau AL Douliez JP Boué F Ott F Cousin F 《Journal of colloid and interface science》2011,362(2):397-405
The ethanolamine salt of 12-hydroxy stearic acid is known to form tubes having a temperature tunable diameter. Here, we study the behavior of those tubes at the air/water interface by using Neutron Reflectivity. We observed that tubes indeed adsorbed at this interface below a fatty acid monolayer and exhibit the same temperature behavior as in bulk. There is however a peculiar behavior at around 50 °C for which the increase of the diameter of the tubes at the interface yields an unfolding of those tubes into a multilamellar layer. Upon further heating, the tubes re-fold and their diameter re-decreases after which they melt into micelles as observed in the bulk. All structural transitions at the interface are nevertheless reversible. This provides to the system a high interest for its interfacial properties because the structure at the air/water interface can be tuned easily by the temperature. 相似文献