Untersuchungen an Polyhalogeniden. XXIII. Kristallstrukturen der N-Alkylurotropiniumtriiodide UrRI3 mit R = Methyl,Ethyl, n-Propyl und n-Butyl

Studies on Polyhalides. 23. Crystal Structures of N-Alkylurotropinium Triiodides UrRI₃ with R = Methyl, Ethyl, n-Propyl, and n-Butyl The salts UrRI₃ may be prepared by the reaction of N-alkylurotropinium iodides UrRI with iodine I₂ at room temperature from aqueous solution. N-methylurotropinium triiodide C₇H₁₅N₄I₃ crystallizes monoclinically in P2₁/c with a = 1300.8(2) pm, b = 1276.0(3) pm, c = 859.3(2) pm, β = 94.75(2)° and Z = 4. The crystal structure is built up from layers of cations UrMe⁺ and of linear symmetric triiodide ions I₃^? alternating along [100]. N-ethylurotropinium triiodide C₈H₁₇N₄I₃ crystallizes orthorhombically in Pnma with a = 1397.3(5) pm, b = 1221.3(2) pm, c = 886.2(2) pm and Z = 4. The cationic (UrEt⁺) and anionic (I₃^?) layers alternate along [0 10]. N-propylurotropinium triiodide C₉H₁₉N₄I₃ crystallizes monoclinically in P2₁/c with a = 1885.7(5) pm, b = 1657.1(5) pm, c = 1700.5(4) pm, β = 112.39(2)° and Z = 12. The three independent cations and anions are slightly, but differently distorted. N-butylurotropinium triiodide C₁₀H₂₁N₄I₃ crystallizes monoclinically in P2₁/m with a = 991.8(3) pm, b = 757.8(2) pm, c = 1128.2(2) pm, β = 90.73(2)° and Z = 2. The crystal structure is stacked by alternating cationic and anionic layers along [001]. The triiodide ion is asymmetric and linear.     

Optical <Emphasis Type="Italic">Gaussons</Emphasis> and dark solitons in directional couplers with spatiotemporal dispersion

This paper study the dynamics of optical solitons for nonlinear directional couplers. This coupler system is considered with the group velocity dispersion and the cross-phase modulation of two components along with the spatiotemporal dispersion coefficients. The constraint conditions for the existence of optical Gaussons and dark solitons are listed under the log law and Kerr law nonlinearities, repectively. Additionally, a couple of other solutions known as singular periodic and combined dark-singular solitons, fall out as a by-product of this scheme. This scheme however fails to retrieve bright soliton solution.     

Soft nanosystems based on hydroxypiperidinium surfactants as adjuvants and micellar catalysts

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Investigation of structural and magnetoelectronic properties of new half-metallic Heusler alloys Ru2VGexSb1−x (x = 0, 0.5 and 1): A density functional theory study

We performed an ab initio study using a method named linearized augmented plane wave with a full potential (FP-LAPW) based on the density functional theory. We predicted the physical properties of Ru₂VGe_xSb_1−x (x = 0, 0.5 and 1) Heusler alloys in L2₁ structure. We computed the magnetic and structural properties using the general gradient approximation. The modified Becke-Johnson scheme was used to study the electronic structure of these compounds. The obtained results show that the lattice constants and the spin magnetic moments are in favorable agreement compared with theoretical values and experimental data. The computed densities of state (DOSs) of these compounds indicate a half-metallic behavior with a real gap for the ternary materials, which gives perfect spin polarization, while for the quaternary one, the DOS indicate a nearly half-metallic character with a pseudogap in the minority spin close to the Fermi level E_F.     

Phase diagrams of poly(dimethylsiloxane) and 5CB blends

The phase diagrams of poly(dimethylsiloxane) (PDMS) and 4‐cyano‐4′‐n‐pentyl‐biphenyl (5CB) mixtures are studied for two systems of different molecular weights of the polymer. The experimental diagrams are established by polarized optical microscopy (POM), and analyzed using a combination of the Flory–Huggins theory of isotropic mixing and the Maier–Saupe theory of nematic order. The results are compared with those of polystyrene (PS) and 4‐cyano‐4′‐n‐octyl‐biphenyl (8CB) with analogous molecular weight of the polymer. This investigation could be useful for the choice of systems in electro‐optical devices. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 581–588, 2001     

On the phase behavior of blends of polymers and nematic liquid crystals

The phase behavior of mixtures of polymers and nematic liquid crystals (LC) is investigated. Two types of systems are examined. The first one deals with blends in which the polymer is made of linear chains. In this case, a systematic study of the effects of various parameters on the phase diagrams is performed. In particular, it is shown how increasing the polymer size and/or the LC molecule size increases the miscibility gap of the mixture. It also reduces the region where a single nematic phase is observed in the presence of a tiny amount of polymer. Likewise, the relative effects of the isotropic and the nematic interaction parameters on the phase diagrams are examined. The second part of this investigation deals with blends involving crosslinked polymers. Here, substantial differences are observed as compared to the case where the polymer components are made of linear chains. These differences are illustrated by showing the phase diagrams in similar conditions for both blends. Unlike the case of a linear polymer matrix, it is observed that the single nematic phase and the nematic-isotropic spinodal branches are absent from the phase diagram of crosslinked polymers. This results into significant distortions of the phase diagram. In order to highlight all these effects, examples representing hypothetical blends are considered. These examples are chosen for illustration of the results in which the choice of numerical parameters is made consistently with the existing values in the literature which makes comparison with published data possible.     

Structural Properties and Phase Behavior of Crosslinked Networks in Polymer Solutions

Structural properties and phase behavior of crosslinked networks embedded in polymer solutions are theoretically investigated. The partial structure factor of the network is calculated using a matrix formulation of the random phase approximation and the forward scattering limit is correlated with the phase behavior. Swelling and deswelling processes are analyzed in terms of the polymer concentration, the mismatch of solvent quality with respect to polymer and network, the polymers incompatibility and their characteristic sizes. Most studies reported so far in the literature have focussed on the swelling of crosslinked networks and gels in pure solvents but the correlation of the structural properties with the phase behavior in the presence of high molecular weight polymers in solution has not been given sufficient attention. The present work is intended to fill this gap in view of the current efforts to develop novel drug encapsulating and targeted delivery devices.     

Application of pulsed field gradient NMR with high gradient strength for studies of self-diffusion in lipid membranes on the nanoscale

This work demonstrates the feasibility of noninvasive studies of lipid self-diffusion in model lipid membranes on the nanoscale using proton pulsed field gradient (PFG) NMR spectroscopy with high (up to 35 T/m) gradient amplitudes. Application of high gradients affords for the use of sufficiently small diffusion times under the conditions when the width of the gradient pulses is much smaller than the diffusion time. As a result, PFG NMR studies of partially restricted or anomalous diffusion in lipid bilayers become possible over length scales as small as 100 nm. This length scale is important because it is comparable to the size of membrane domains, or lipid rafts, which are believed to exist in biomembranes. In this work, high-gradient PFG NMR has been applied to study lipid self-diffusion in three-component planar-supported multibilayers (1,2-dioleoyl- sn-glycerol-3-phosphocholine/sphingomyelin/cholesterol). The degree of lipid orientation in the bilayers was determined with (31)P NMR. A special insert was designed to mechanically align the multibilayer stack at the magic angle with respect to the direction of the constant magnetic field to address the detrimental effects of proton dipole-dipole interactions on the NMR signal. This insert is an alternative to the conventional method of magic angle orientation of lipid membranes, the goniometer probe, which is not compatible with commercial high-gradient coils because of the lack of space in the magnet bore. Macroscopic orientation of the multibilayer stacks using the insert was confirmed with (1)H NMR spectroscopic studies and the comparison of results obtained from identical experiments using a goniometer probe for orientation. Diffusion studies were carried out at three different constant magnetic field strengths ( B 0) over a range of temperatures and diffusion times. The measured diffusivities were found to be in agreement with the data obtained previously by techniques that are limited to much larger length scales of diffusion observation than high-gradient PFG NMR.     

Stereoselective synthesis of nonsymmetrical difructose dianhydrides from xylylene-tethered d-fructose precursors

Nonsymmetrical furanose-pyranose difructose dianhydrides (DFAs), a class of cyclic disaccharides present in foodstuffs, have been prepared in high yield by connecting the reacting monosaccharide moieties through a xylylene bridge prior to triflic acid-promoted bis-spiroketalization. The reaction can then proceed either intra- or intermolecularly, both the regio- and the stereoselectivity being strongly dependent on the spacer length. Noteworthy, the longer m- and p-xylylene positional isomers led to the thermodynamic α-d-fructofuranose β-d-fructopyranose 1,2′:2,1′-dyanhydride 1, the major DFA in commercial caramel, in a stereoselective manner. The shorter o-xylylene tether afforded preferentially the elusive contra-thermodynamic β-d-fructofuranose α-d-fructopyranose diastereomer 2, a trace constituent of caramel. The results have been rationalized in terms of stereoelectronic and conformational properties and offer new perspectives for the preparation of pure DFA standards for analytical and nutritional studies.