High Resolution NMR Studies of Lithium and Sodium lons at the Membrane Interface

High resolution NMR spectra of lithium-6, lithium-7 and sodium-23 in a liquid crystalline mesophase consisting of sodium decylsulfate, lithium sulfate, decanol and water have been recorded. From the quadrupole splittings of the two lithium isotopes, a ratio of the quadrupole moment (Q) of ⁷Li/⁶Li equal to 49 ± 1 was obtained. By comparing the temperature dependence of the quadrupole splittings of ⁶Li, ⁷Li and ²³Na in the same mesophase, it is apparent that lithium and sodium ions interact differently with the polar head group of the mesophase. The implication of this difference is discussed.     

Liquid Crystalline and Luminescent Behavior of Lanthanide Complexes Composed of Terbium or Europium and Dendritic Amphiphile

Luminescent lanthanide (Tb³⁺, Eu³⁺) complexes were prepared by reaction of Tb³⁺ or Eu³⁺ with dendritic amphiphile (3,4,5-tris(dodecyloxy)benzoate), then their liquid crystalline and luminescent behavior were studied. The complexes exhibited thermotropic liquid crystalline mesophases with columnar hexagonal structure. The complexes emitted the characteristic luminescence of the core metals. Additionally, in the Eu³⁺ complex, the ratio of the intensity of 614 nm to the intensity of 585 nm (I₆₁₄/I₅₈₅) remarkably decreased around the transition temperature from crystal to mesophase, suggesting that the coordination environment of Eu³⁺ gets more symmetrical due to the phase transition.     

The Effect of Sequence Incorporation of Sodium Ions on Structural and Thermal Properties of CoMo/Al2O3

The alumina supported cobalt-molybdena catalysts containing sodium ions were subjected to X-ray diffraction studies, IR spctroscopy and thermal analysis. Sodium ions were introduced onto Al₂O₃ either simultaneously with the other components, or prior to them or after them. Di- and polymolybdates phases were found to be formed on the support in all samples. In samples obtained in a two-stage process the interaction of Na⁺ ions with the support ions was detected which did not occur in samples obtained in a single-stage process. Nitrate ions introduced simultaneously with the other components undergo a relatively strong thermal decomposition while in the samples synthesised in two stages they are strongly bounded. The greatest number of strongly bound nitrates was found in the sample into which sodium ions were introduced in the second stage of the preparation procedure.     

Control of the Discotic to Isotropic Transition in Alkoxy-Substituted Silicondihydroxo-Phthalocyanines by Axial Substituents

The synthesis of a homologous series of octaalkoxy-substituted silicondihydroxo-phthalocyanines is described. The mesomorphic properties of these new materials were studied by DSC, optical microscopy and X-ray investigations. Compounds with n ≤ 4 (n is the number of carbon atoms in a single alkoxy side chain) show a discotic mesophase transition. A transition to the isotropic state is only observed when n ≤ 8. X-ray diffraction patterns of the mesophases confirm that all compounds form a hexagonal columnar mesophase of the type D_hd.     

Amphotropic Properties of Cyclic Scyllitol Hexaesters [1]

Abstract

The new Scyllitol hexaesters with cyclic fragments in lateral substituents of series 1 were synthesized and their thermo- and lyotropic properties (with various organic linear or cyclic solvents) have been studied. It was established that the presence of benzene fragments in the substituents of the scyllitol hexaesters (1a-e) reduces the ability of the mesophase formation. The cyclohexane unit instead (sf. 1f) increases the thermostability of mesophase. While using above mentioned solvents a lot of cases of the induction of mesomorphic properties for non-mesogenic compounds of series 1 have been described. With cyclic solvents lyotropic mesophases were induced in binary mixtures of the hexaester 1a which showed mesomorphic properties neither under thermotropic conditions nor in binary mixtures with linear alkanes.     

Hydrogen–sodium interdiffusion in borosilicate glasses investigated from first principles

Density functional calculations are performed to investigate the effect of hydronium–sodium interdiffusion in a sodium borosilicate glass. It is found that the substitution of the Na⁺ network modifiers does not alter the glass covalent network, whereas a bridging bond is systematically broken when the substitution involves Na⁺ ions bonded to BO₄ tetrahedra. The systematic dissociation of hydronium into water and proton suggests that this chemical species probably has a short lifetime in the glass, due to the capability of anionic sites to trap the protons very strongly. The relative basicities of the sites involved are compared, and a nice correlation is found between hydroxyl bond lengths and hydrogen bond strengths present in the hydrated glass.     

Synthesis and study of mesomorphic properties in rod-like chalconyl compounds

In order to investigate the influence of the central linking group and effect on flexibility on mesophase behavior of liquid crystal we have synthesized newly homologous series viz. 3-(4-Octyloxyphenyl)-1-(4′-n-alkoxy phenyl) prop-2-en-1-one (Series-l) consists of thirteen homologues (C₁ to C₈, C₁₀, C₁₂, C₁₄, C₁₆, C₁₈). Textures of a nematic phases are threaded or Schlieren type. The textures of smectic and nematic phase are directly judged from the heating and cooling condition. Group efficiency order for mesophases is derived on the basis of thermal stabilities from the comparative study of thermometric data determined from structurally analogous series. A transition curve as depicted in a phase diagram behaves in normal manner. Structural and conformational characterization of these new compounds had achieved by ¹H NMR, ¹³C NMR, IR, and elemental analysis.     

K8Gd3Si12O32Cl · 2H2O,a new member of the family of porous silicates with K and RE elements

Crystals of K₈Gd₃Si₁₂O₃₂Cl · 2H₂O (space group $P\bar 1$ ), a new member of the family of porous silicates containing rare earths, are obtained under hydrothermal conditions. The structure retains the main features of the family in which original one-story layers of Si-tetrahedra formed by 6-membered rings of two types and large-in-diameter 8-membered and 12-membered rings are bound by Gd-octahedra to form a framework. Large pores in the interlayer space of the mixed framework are filled with K⁺ ions. The penetration of Cl^? ions from a concentrated mineralizing solution into the centers of the eight-membered rings of the layer corroborates the ion-exchanging properties of the crystals of this structural type. The filling of rings and pores of different types in different members of the family by K⁺ and Cl^? ions, hydroxyl groups, and water molecules is analyzed.     

Preparation of three‐dimensional symmetric dendrites of BaWO4 microcrystals

Three‐dimensional symmetric dendrites of BaWO₄ were prepared by performing solvothermal reactions in water‐hexane bilayer solutions that contained a barium‐oleate complex in the hexane layer and sodium tungstate in the water layer. The barium‐oleate complex in hexane was obtained via a phase transfer reaction in which aqueous Ba²⁺ ions pass into the hexane phase with the assistance of sodium oleate, oleic acid, and oleylamine. Each of the BaWO₄ dendrites has a three‐dimensional structure with one trunk along the c‐axis and a series of four branches perpendicular to the trunk. As the reaction temperature or the amount of oleylamine increases, BaWO₄ dendrites with sharper branches and higher order hierarchical structures are formed. The presence of oleylamine plays an important role in the formation of the hierarchical superstructures of BaWO₄ dendrites.     

Imidazolium based ionic liquid crystals: structure,photophysical and thermal behaviour of [Cnmim]Br·xH2O (n = 12, 14; x=0, 1)

The long chain imidazolium halides [C_nmim]Br·xH₂O (n = 10, 12; x = 0, 1) have been synthesized and their structural and thermal behaviour together with their photophysical properties characterized. X‐ray structure analyses of the monohydrates ([C₁₂mim]Br·H₂O: triclinic, P1, no. 2, Z = 2, Pearson code aP112, a = 550.0(5) pm, b = 779.4(5) pm, c = 2296.1(5) pm, α = 81.89(5)°, β = 83.76(5)°, γ = 78.102(5)°, 3523 unique reflections with I_o > 2σ(I_o), R₁ = 0.0263, wR₂ = 0.0652, GooF = 1.037, T = 263(2) K; [C₁₄mim]Br•H₂O: triclinic, P1, no. 2, Z = 12, Pearson code aP11, a = 549.86(8) pm, 782.09(13) pm, c = 2511.3(4) pm, α = 94.86(2)°, β = 94.39(2)°, γ = 101.83(2)°, 2063 unique reflections with I_o > 2σ(I_o), R₁ = 0.0429, wR₂ = 0.0690, GooF = 0.770, T = 293(2) K) show for both compounds similar bilayered structures. Sheets composed of hydrophilic structure regions constituted by positively charged imidazolium head groups, bromide anions and hydrogen bonded water alternate with hydrophobic areas formed by interdigitated long alkyl chains belonging to imidazolium cations with different orientation. Combined differential scanning calorimetry and polarizing optical microscopy shows that the monohydrates as well as the anhydrous imidazolium salts are thermotropic liquid crystals which adopt smectic mesophases. The mesophase region is larger in case of the monohydrates when compared to the anhydrous compounds indicating that water obviously stabilizes the mesophase. All compounds show an intense whitish photoluminescence with short lived (¹π←¹π*) and long lived (¹π←³π*) transitions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Novel Azoester Compounds with a Lateral Methyl Substituent

Twelve novel homologues with an azo linkage of the series 4-carbethoxy-[3′methyl-4′ (4^″-n-alkoxy benzoyloxy)] azobenzenes have been synthesized. The methyl to n-hexyl homologues exhibit only nematic mesophases, while the n-heptyl to n-tetradecyl homologues exhibit both smectic and nematic mesophases. The n-hexadecyl homologue exhibits only a smectic mesophase. The plot of transition temperatures versus number of carbon atoms in alkoxy chain exhibits an odd-even effect for the nematic-isotropic transitions. The mesogenic behavior of present series is explained by comparing each homolog of the related mesogenic series. The synthesized compounds were characterized by a combination of elemental analysis and standard spectroscopic methods. For the exhibition of mesomorphic property the role of ester and azo linkages has been discussed. The impact of the lateral methyl group on mesomorphism is also discussed.     

The mixed alkali effect in the Na2OCs2OSiO2 glasses

As an approach to the mixed alkali effect in glass, the self-diffusion coefficients of sodium and cesium ions in Na₂OCs₂OSiO₂ glasses were measured at temperatures 350–550°C. Electrical conductivity of the glasses and the transport number for sodium ions were also measured. The substitution of the alkali ions in the glass by different alkali ions caused the mobility of each alkali ion to decrease pronouncedly and the activation energy for migration to increase rapidly. The increase of activation energy was attributed to an increase in alkali-oxygen bond strength resulting from the presence of two kinds of alkali ions. This is related to the expectation that the activity of the alkali ions decreases when two alkali ions are mixed.     

Sodium-hydrogen interdiffusion in sodium silicate glasses

The hydration of Na₂O · 3 SiO₂ glasses is studied using the sputter-induced photon spectrometry technique (SIPS) to measure the depth-profiles of hydrogen and sodium. The results clearly show a penetration of hydrogen and a leaching of sodium in the glass. The thicknesses of the hydrated layers are determined as functions of time and temperature. The thicknes dependence on the square root of time indicates that a diffusion process is in operation. The data are fitted to he Doremus model of interdiffusing ions and the diffusion coefficients for hydrogen and sodium are calculated.     

Transitions de Phase en Series Mesogenes:

The polymorphism of the di(4-alkylphenyl) and di(4-alkoxyphenyl) tetrathiafulvalene (TTF) is investigated by optical, crystallographic and calorimetric methods. All the studied derivatives are mesomorphic. The first mesophase is always a smectic G phase; the second one is a nematic N phase for short chains and a smectic C phase for long chains.

The entropies corresponding to the passage high-temperature crystalline phase C₁ → S_G and to the “melting” (C₁ → mesophases → isotropic phase I) increase with the length of the chain and with the presence of the oxygen atom in the radical.     

X-ray absorption near edge structure analysis of valence state and coordination geometry of Ti ions in borosilicate glasses

The effects of borosilicate glass composition and melting condition on valence state and coordination geometry of polyvalent Ti ions have been studied by X-ray absorption experiments. The results indicate that most of Ti³⁺ ions are oxidized into Ti⁴⁺ ions when Ti₂O₃ is doped into sodium borosilicate glasses. When TiO₂ is doped into sodium borosilicate glasses, almost all of titanium ions are in the form of Ti⁴⁺. Doping both graphite and titanium oxide simultaneously in borosilicate glasses favors the formation of small amounts of Ti³⁺ ions. Ti⁴⁺ ions occupy both fivefold and sixfold coordinated sites in borosilicate glasses with non-bridging oxygen (NBS1), mainly fivefold coordinated sites. For borosilicate glasses without non-bridging oxygen (NBS2), Ti⁴⁺ ions are in both fourfold and fivefold coordinated sites. Using reducing agents during melting procedure favors the formation of fourfold coordinated Ti⁴⁺ ions in NBS2.     

Activation volumes and site relaxation in mixed alkali glasses

Evidence is presented for site relaxations occurring in mixed alkali (cation) glasses based on activation volumes, V_A(σ) = −RT[d ln σ/dp]_T, which are determined for sodium aluminoborate glasses of varying Na₂O content, and for mixed alkali glasses where Na⁺ is partially replaced by Li⁺, K⁺ or Cs⁺ ions. In accordance with the ‘updated’ dynamic structure model, activation volumes are identified here with local expansions that accompany the opening up of C′ sites to admit incoming ions. ‘Anomalous’ increases in activation volume in mixed cation glasses correlate with the size of minority (guest) cations. This anomaly is interpreted in terms of a ‘leader follower’ mechanism that involves dynamic coupling between the faster (majority) and slower (minority) cations. Because of mismatch effects in mixed cation glasses this coupling requires the opening up of additional cation sites by the slower follower cations. The resulting disturbances in the glass network are responsible for many characteristic features of the mixed alkali effect, including the appearance of high temperature internal friction peaks and observed minima in glass transition temperatures and melt viscosities.     

Lyotropic Mesophase Behaviour of n-C16H33EO3 - Evidence for Two “V2” Phases

Abstract

Nonionic surfactants of the alkyl polyoxyethylene ether variety commonly form hexagonal (H₁) or lamellar (L_α) lyotropic mesophases with water¹. Less well-known is the frequent occurrence of I₁ or V₁ cubic mesophases.? No reports exist to date of the occurrence of reversed phases with these materials. While the surfactants are known to form several solid complexes with water, their melting points are below those of the anhydrous surfactants². In an optical microscope study of the liquid crystals formed by water penetration into n-hexadecyl trioxyethylene glycol ether (C₁₆EO₃) we have observed a solid complex with a melting point above that of the pure surfactant. We also observe a cubic region which we classify as a reversed structure (V₂). Moreover, the occurrence of a refractive index discontinuity within this region strongly suggests that two different phases are present. The cubic region coexists with water for part of the temperature range over which it occurs. When water droplets form within the cubic region on heating, they adopt angular shapes which suggest that a single, long-range structure exists, rather than a “powder” orientation of domains.     

Sodium ion transport in high purity borosilicate glasses

²²Na diffusion coefficients and dc electrical conductivity were measured in 0.7 B₂O₃·0.3 SiO₂ (mole ratio) glasses containing small amounts of Na₂O (111 ppm to 2.6 mol%). Correlation factors near unity were obtained from the Nernst-Einstein equation for these glasses. These values are in agreement with a previously proposed free “interstitial” alkali ion diffusion mechanism in low alkali content glasses. It is concluded from the low values of the sodium diffusion coefficients and dc conductivity in these glasses (relative to similar silicate and germanate glasses) that the Na⁺ are bound strongly to the borate-rich glass network and that the number of dissociated Na⁺ at any given time is small.     

New Mesogenic Compounds Containing a Terminal-Substituted Benzoxazole Unit

A series of novel mesogenic 2-(4-alkoxyphenyl-1-yl)-benzoxazole derivatives bearing different substituents (H, NO₂, CH₃, Cl, coded as nPB-H, nPB-N, nPB-M, and nPB-C, respectively) at the 5-position were prepared and characterized. nPB-N, nPB-M, and nPB-C exhibited enantiotropic smectic mesophases with the mesophase ranges 3 °C–32 °C and 3 °C–82 °C on heating and cooling processes, whereas nPB-H showed no mesophases. The substituents with the stronger electron withdrawing effect let to the wider mesomorphic temperature domain. The nPB-M, nPB-C, and nPB-H displayed intense emission in CH₂Cl₂ solutions with λ_max peaks of the photoluminescence spectra at 350–355 nm when excited at their absorption maxima.     

Mesomorphic Properties of an Homologous Series of Alkoxy-Terminated Enamine-Ketone Containing Liquid Crystals

An homologous series of enamine-ketone compounds has been synthesized and their thermal properties investigated. The bis [3- p-n-alkoxyanilino)-2-butenoyl] benzenes exhibited nematic mesophases when the terminal alkoxy substituents were short and both nematic and smectic mesophases when the terminal alkoxy substituents contained twelve or more carbons. The thermal data indicate that although crystalline order is largely determined by the packing of the hydrocarbon tails, there is a low degree of interaction by the tails in the nematic mesophase.