Flexible taper-shaped liquid crystal trimer exhibiting a modulated smectic phase

We prepared some taper-shaped liquid-crystalline trimers in which two phenylpyrimidine units and a 1,4-diphenyl-2,3-difluorobenzene unit are connected to 2,4-dihdroxy benzoic acid via flexible spacers. We then investigated their liquid-crystalline properties using polarised optical microscopy, differential scanning microscopy and X-ray diffraction. 6-[4–(5-Octylpyrimidin-2-yl)phenyloxy]hexyl 2-{7-{4-[4–(4-hexylphenyl)-2,3-difluorophenyl]phenyloxy}heptanoyloxy}-4-{6-[4–(5-octylpyrimidin-2-yl)phenyloxy]hexyloxy}benzoate (1) was found to exhibit a phase sequence of isotropic liquid – nematic – intercalated smectic A – intercalated anticlinic smectic C – modulated smectic C. The structure–property relation in the taper-shaped trimers reveals that the modulated phase is induced by competition between an intercalated structure stabilised by dipole–dipole interaction and a monolayer structure by packing entropy effects. Conformational change of compound 1 induced by intermolecular interactions plays an important role in the phase transition behaviour.     

Weak interactions at the photoexcited states of partially oriented aromatic chromophores in man-made bilayer membranes

Monoalkyl and dialkyl quarternary ammonium salt-type cationic surfactants containing a phenoxy group as aromatic chromophores at different positions of alkyl chains were synthesized. Monoalkyl-type surfactants formed micelles in aqueous solutions. The bilayer structure similar to that found in phospholipid liposomes was obtained in the aqueous dispersions of dialkyl-type surfactants. The phenoxy groups were partially oriented and aligned in these molecular assemblies. The interactions of aligned phenoxy groups in micelles or bilayers resulted in luminescence with lower energy than that of the monomer fluorescence or in a radiationless deactivation of excited states. Such interactions could be effectively prevented in bilayer structures composed of surfactant molecules containing a “spacer chain” between aligned chromophores. Evidence was obtained supporting energy migrations between aligned chromophores that were separated by a dodecyl chain in the bilayer structure.     

二棕榈酰磷脂酰胆碱/豆固醇脂质体液态有序相的结构性质:同步辐射X光衍射研究

用同步辐射小角和宽角X光衍射实验技术研究了由二棕榈酰磷脂酰胆碱(DPPC)和豆固醇所形成的脂质体的液态有序相的结构性质. 结果表明液态有序相的小角X光衍射d值(d-spacing)随着固醇温度和浓度的变化仅有微小的改变. 与凝胶相及液晶相的宽角X光衍射d值相比, 液态有序相的宽角X光衍射d值有更宽的变化范围, 在30到52 °C的温度范围内, 液态有序相的宽角X光衍射d值从0.422 nm变化到0.460 nm. 电子云密度计算表明液态有序相的脂双层厚度和水层厚度都要大于与之平衡共存的液晶相的脂双层厚度和水层厚度. 电子云密度计算结果还表明液态有序相的脂双层厚度随温度升高而降低. 本研究结果对于从定量的角度认识 生物膜的相态及深入认识生物膜中的有序结构具有重要意义.     

On the interaction of the anthraquinone barbaloin with negatively charged DMPG bilayers

Barbaloin is a bioactive glycosilated 1,8-dihydroxyanthraquinone present in several exudates from plants, such as Aloe vera, which are used for cosmetic or food purposes. It has been shown that barbaloin interacts with DMPG (dimyristoylphosphatidylglycerol) model membranes, altering the bilayer structure (Alves, D. S.; Pérez-Fons, L.; Estepa, A.; Micol, V. Biochem. Pharm. 2004, 68, 549). Considering that ESR (electron spin resonance) of spin labels is one of the best techniques to monitor structural properties at the molecular level, the alterations caused by the anthraquinone barbaloin on phospholipid bilayers will be discussed here via the ESR signal of phospholipid spin probes intercalated into the membranes. In DMPG at high ionic strength (10 mM Hepes pH 7.4 + 100 mM NaCl), a system that presents a gel-fluid transition around 23 degrees C, 20 mol % barbaloin turns the gel phase more rigid, does not alter much the fluid phase packing, but makes the lipid thermal transition less sharp. However, in a low-salt DMPG dispersion (10 mM Hepes pH 7.4 + 2 mM NaCl), which presents a rather complex gel-fluid thermal transition (Lamy-Freund, M. T.; Riske, K. A. Chem. Phys. Lipids 2003, 122, 19), barbaloin strongly affects bilayer structural properties, both in the gel and fluid phases, extending the transition region to much higher temperature values. The position of barbaloin in DMPG bilayers will be discussed on the basis of ESR results, in parallel with data from sample viscosity, DSC (differential scanning calorimetry), and SAXS (small-angle X-ray scattering).     

Scattering studies of hydrophobic monomers in liposomal bilayers: an expanding shell model of monomer distribution

Hydrophobic monomers partially phase separate from saturated lipids when loaded into lipid bilayers in amounts exceeding a 1:1 monomer/lipid molar ratio. This conclusion is based on the agreement between two independent methods of examining the structure of monomer-loaded bilayers. Complete phase separation of monomers from lipids would result in an increase in bilayer thickness and a slight increase in the diameter of liposomes. A homogeneous distribution of monomers within the bilayer would not change the bilayer thickness and would lead to an increase in the liposome diameter. The increase in bilayer thickness, measured by the combination of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS), was approximately half of what was predicted for complete phase separation. The increase in liposome diameter, measured by dynamic light scattering (DLS), was intermediate between values predicted for a homogeneous distribution and complete phase separation. Combined SANS, SAXS, and DLS data suggest that at a 1.2 monomer/lipid ratio approximately half of the monomers are located in an interstitial layer sandwiched between lipid sheets. These results expand our understanding of using self-assembled bilayers as scaffolds for the directed covalent assembly of organic nanomaterials. In particular, the partial phase separation of monomers from lipids corroborates the successful creation of nanothin polymer materials with uniform imprinted nanopores. Pore-forming templates do not need to span the lipid bilayer to create a pore in the bilayer-templated films.     

Coexistence of two different side chain packing structures in a smectic phase of liquid-crystalline side chain polymers

Ten varieties of liquid-crystalline side chain polymers, poly(cholesteryl-ω-(methacryloyloxy)alkanoates) (pChMO-n, n = 1, 2, 3, 4, 5, 7, 9, 10, 11 and 15; the carbon number of the alkyl chain), were studied by differential scanning calorimetry and small angle X-ray scattering. On and after the first cooling run from the isotropic state, these polymethacrylates gave the same smectic phase. X-ray investigations showed that pChMO-n with short spacers (n = 1-7) has a two layer (bilayer) S_A packing structure, and pChMO-n with a longer spacer (n= 15) has a single layer (monolayer) S_A packing structure. However, these two types of packing structure appear simultaneously in pChMO-n (n = 9s-11) below their phase transition temperature. To clarify the manner of the coexistence of the two different structures the smectic layer spacing and X-ray diffraction patterns were examined by small angle X-ray scattering at various temperatures.     

Intercalation of a nonionic surfactant (C10E3) bilayer into a Na-montmorillonite clay

A nonionic surfactant, triethylene glycol mono-n-decyl ether (C(10)E(3)), characterized by its lamellar phase state, was introduced in the interlayer of a Na-montmorillonite clay at several concentrations. The synthesized organoclays were characterized by small-angle X-ray scattering in conjunction with Fourier transform infrared spectroscopy and adsorption isotherms. Experiments showed that a bilayer of C(10)E(3) was intercalated into the interlayer space of the naturally exchanged Na-montmorillonite, resulting in the aggregation of the lyotropic liquid crystal state in the lamellar phase. This behavior strongly differs from previous observations of confinement of nonionic surfactants in clays where the expansion of the interlayer space was limited to two monolayers parallel to the silicate surface and cationic surfactants in clays where the intercalation of organic compounds is introduced into the clay galleries through ion exchange. The confinement of a bilayer of C(10)E(3) nonionic surfactant in clays offers new perspectives for the realization of hybrid nanomaterials, since the synthesized organoclays preserve the electrostatic characteristics of the clays, thus allowing further ion exchange while presenting at the same time a hydrophobic surface and a maximum opening of the interlayer space for the adsorption of neutral organic molecules of important size with functional properties.     

Liquid crystallinity of newly synthesized glucose derivatives with mesogenic side chains

Synthesis of glucose derivatives by direct esterification of the five available sites on D-(+)-glucose with side chains containing a biphenyl mesogenic moiety, a pentyl spacer and an alkyl tail is reported for the first time. Liquid crystalline phase behaviour of these glucose derivatives was studied by optical microscopy, thermal and X-ray diffraction methods. A layered arrangement of the smectic A (SmA) type was commonly observed in the above materials. An increase in the length of the alkyl tail results in a change of the phase structure from smectic Ai(SmAi), intercalated layer phase, to smectic As(SmAs), segregated bilayer phase. From the transition temperature and enthalpy observations, the SmAs phase has higher order than the SmAi phase. Cholesteric and chiral smectic C phases were also observed in addition to the SmA for some of the glucose derivatives, demonstrating a potential for preparing chiral liquid crystals.     

Stereochemistry of heterocycles

2-Methyl-and 2,5-dialkyl-5-phenoxy-1,3-dioxanes were synthesized and separated into their geometrical isomers by precision rectification. The configuration and conformations of these isomers were determined by PMR spectroscopy. It is shown that the low-boiling trans isomers exist primarily in the chair conformation with an equatorial phenoxy group, whereas the high-boiling cis isomers exist primarily in the chair conformation with an axial phenoxy group.     

Liquid crystalline properties of asymmetric molecules: II. Smectic properties of 4-alkoxyphenyl 4-(4-trifluoromethylbenzoyloxy)benzoates

The thermal properties of a homologous series of 4-alkoxy-phenyl 4-(4-trifluoromethylbenzoyloxy)benzoates were examined. The homologues show remarkable smectic properties involving a smectic A and a higher order smectic phase characterized by microscopic and X-ray experiments, indicating that the molecules have a partially bilayer arrangement in both smectic phases. Based on these results, molecular arrangements of the two smectic phases are proposed. The effects of the trifluoromethyl group on the thermal properties of the smectic and crystalline phases are discussed in terms of the fluorophilic interaction around the boundary of the smectic layer.     

Variable interlayer distance of intercalates of naphthalenedisulfonate isomers in hydrotalcite-like Zn and Al layered double-hydroxides

Three isomers of naphthalenedisulfonates (naphthalene-2,6-,-1,5- and -2,7-disulfonates; abbreviated as N26DS, N15DS and N27DS, respectively, and collectively abbreviated as NijDS) are intercalated in the interlayer region of Zn and Al layered double-hydroxides (Zn/Al-LDH). The intercalated products are obtained under weak alkaline conditions as precipitates from reaction mixtures containing one of the isomers and calcined powder prepared by using carbonate-intercalated Zn/Al-LDH. When N26DS or N15DS is intercalated, two solid phases are observed which have different values of basal spacing in powder X-ray diffraction (XRD) patterns, whereas only one phase appears when N27DS is intercalated. The different basal spacing results from one of two alternate orientations taken by the interlayer NijDS. One of the two phases appears exclusively in XRD patterns, although the other is produced together with a by-product. A more closely packed orientation is suggested for the interlayer guest molecules in the latter phase. The solid state chemistry has been investigated using UV visible diffuse reflection (DR) spectroscopy, differential thermal analysis/thermogravimetry (DTA/TG) and X-ray photoelectron spectroscopy (XPS).     

无机-有机杂化树枝状香蕉形液晶化合物的合成与表征

利用硅氢加成反应制备得到8个香蕉形液晶基元尾接于六面体倍半硅氧烷的8个顶点之上的杂化树枝状香蕉形液晶化合物.此化合物的化学结构通过核磁、红外、元素分析和GPC表征.一维和二维X-射线衍射研究表明,该化合物具有两个双层近晶C相;对样品施加三角波电压后显示该化合物具有反铁电性.     

A pyrrole-containing surfactant as a tecton for nanocomposite SiO2 films

A surfactant featuring a polymerizable pyrrole head group (dodecyl-dimethyl-(2-pyrrol-1-yl-ethyl)-ammonium bromide, DDPABr) was synthesized. The thermotropic behavior of the surfactant was investigated by differential scanning calorimetry (DSC) and X-ray scattering techniques, with small-angle X-ray scattering (SAXS) analysis revealing a highly ordered lamellar bilayer structure. After full characterization, DDPABr was used in the preparation of mesostructured SiO2 nanocomposite thin films via evaporation-induced self-assembly (EISA). Resulting thin SiO2-DDPABr films were studied by 1D and 2D small-angle X-ray scattering (SAXS) techniques, indicating a lamellar nanocomposite structure. Suitable theoretical SAXS models were applied to fit the experimental 1D SAXS data. The surfactant could be chemically polymerized within the lamellar domains.     

Phase transitions in novel disulphide-bridged alkoxycyanobiphenyl dimers

The synthesis, characterization and mesomorphic properties of the first examples of novel disulphide-bridged alkoxycyanobiphenyl dimers are reported. The thermal behaviour of these mesogens was investigated by polarizing optical microscopy, differential scanning calorimetry and X-ray diffractometry. The dimers with a shorter spacer exhibit only the nematic phase while dimers with a longer spacer display nematic as well as smectic phases. X-ray diffraction experiments reveal the intercalated structure of the SmA phase of these dimers and the presence of short range SmA-like order in the N phase (cybotactic nematic) of all the compounds, except the one with the shortest spacer.     

Synthesis of poly(methyl methacrylate) nanocomposites via emulsion polymerization using a zwitterionic surfactant

The synthesis of nanocomposites via emulsion polymerization was investigated using methyl methacrylate (MMA) monomer, 10 wt % montmorillonite (MMT) clay, and a zwitterionic surfactant octadecyl dimethyl betaine (C18DMB). The particle size of the diluted polymer emulsion was about 550 nm, as determined by light scattering, while the sample without clay had a diameter of about 350 nm. The increase in the droplet size suggests that clay was present in the emulsion droplets. X-ray diffraction indicated no peak in the nanocomposites. Transmission electron microscopy showed that emulsion polymerization of MMA in the presence of C18DMB and MMT formed partially exfoliated nanocomposites. Differential scanning calorimetry showed an increase of 18 degrees C in the glass transition temperature (Tg) of the nanocomposites. A dynamic mechanical thermal analyzer also verified a similar Tg increase, 16 degrees C, for the partially exfoliated nanocomposites over poly(methyl methacrylate) (PMMA). Thermogravimetric analysis indicated a 37 degrees C increase in the decomposition temperature for a 20 wt % loss. A PMMA nanocomposite with 10 wt % C18DMB-MMT was also synthesized via in situ polymerization. This nanocomposite was intercalated and had a Tg 10 degrees lower than the emulsion nanocomposite. The storage modulus of the partially exfoliated emulsion nanocomposite was superior to the intercalated structure at higher temperatures and to the pure polymer. The rubbery plateau modulus was over 30 times higher for the emulsion product versus pure PMMA. The emulsion technique produced nanocomposites of the highest molecular weight with a bimodal distribution. This reinstates that exfoliated structures have enhanced thermal and mechanical properties over intercalated hybrids.     

染料敏化太阳电池中双层结构TiO2薄膜空间的电子分布与接触界面转移过程

采用电化学阻抗谱(EIS)研究了双层结构TiO2薄膜的电子积累和与电解液接触界面的电子转移过程. 通过制备纳米颗粒单层和纳米颗粒/亚微米颗粒双层2种不同微结构的TiO2薄膜电极, 对其电容分布、 局域态密度、 薄膜内部电子传输和固/液界面电子转移过程进行了研究. 分析了纳米颗粒/亚微米颗粒双层结构电极对染料敏化太阳电池(DSC)性能的影响. 结果表明, 一定数量的电子会积累在亚微米颗粒层中引起薄膜电极化学电容的增加. 在纳米颗粒层上端覆盖亚微米颗粒后降低了界面复合电阻, 但对薄膜电极的传输性能影响较小. 因此在筛选和制备DSC散射层材料时除应具有良好的光散射性能外, 还应考虑材料的化学电容和界面转移电阻等因素.     

New lamellar structure formed by an adamantyl derivative of cholic acid

The self-aggregation of the sodium salt of a new adamantyl amide of the 3beta-amino derivative of cholic acid (Na-AdC) in aqueous solution has been investigated by surface tension, dynamic light scattering, fluorescence, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) measurements. These last two techniques suggest that a lamellar phase, consisting of charged bilayers of Na-AdC separated by solvent and periodically stacked, is formed in aqueous solution. The structure of the bilayer is inferred from the resolution of the crystal of the compound in its acid form. The adamantyl moieties, which are mutually interlocked, reside in the central region of the bilayer, and the carboxylic groups are directed toward the hydrophilic region. The structure is open enough to allow water molecules to interact with a fluorescence probe located at the central hydrophobic region.     

Self-cleaning resins

This paper introduces a fundamentally new concept in adsorbents, whereby the sorption of an aqueous solute by a cross-linked polymer is controlled by a gel to liquid-crystalline phase transition. To demonstrate proof of principle, a bilayer forming surfactant, N,N-dioctadecyl,N,N-dimethylammonium bromide (DODAB) has been immobilized onto a cation exchange resin, Dowex 50WX2, and its thermotropic phase behavior and solute-adsorption properties have been investigated. Examination by a combination of differential scanning calorimetry and X-ray scattering has confirmed the retention of a gel to liquid-crystalline phase transition of the surfactant, occurring between 296 and 318 K. Adsorption measurements that were made for 4-chlorotetrahydropyran, 1,2-dichloroethane, and benzyl alcohol have also confirmed uptake by the resin in the liquid-crystalline phase and release in the gel phase.     

Physicochemical investigation of a lipid with a new core structure for gene transfection: 2-amino-3-hexadecyloxy-2-(hexadecyloxymethyl)propan-1-ol

Cationic liposomes/DNA complexes can be used as nonviral vectors for direct delivery of DNA-based biopharmaceuticals to damaged cells and tissues. In order to obtain more effective and safer liposome-based gene transfection systems, the new cationic lipid 2-amino-3-hexadecyloxy-2-(hexadecyloxymethyl)propan-1-ol (AHHP) was synthesized. In this paper we report on the synthesis of AHHP and investigations of its physical-chemical properties. Langmuir monolayers of AHHP were studied at the air/buffer interface by film balance measurements, grazing incidence X-ray diffraction (GIXD), and infrared reflection absorption spectroscopy (IRRAS). Structure and thermotropic phase behavior of AHHP in aqueous dispersion were examined by small-angle and wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). The results show clear differences in structure and phase behavior of AHHP, both in the monolayer system and in aqueous dispersions, in dependence on the subphase pH due to protonation or deprotonation of the primary amine in the lipid head group. Thermodynamic data derived from pi-A isotherms provide information about the critical temperature (Tc), which is in rough agreement with the temperature of the lipid phase transition from gel to fluid state (Tm) found by X-ray and calorimetry studies of AHHP aqueous dispersions. The packing properties of the molecules in mono- and bilayer systems are very similar. DNA couples to the monolayer of the new lipid at low as well as at high pH but in different amounts. The DNA coupling leads to an alignment of adsorbed DNA strands indicated by the appearance of a Bragg peak. The distance between aligned DNA strands does not change much with increasing monolayer pressure.     

Physicochemical characterization of PEG1500-12-acyloxy-stearate micelles and liquid crystalline phases

PEG 12-acyloxy-stearates are used as drug delivery carriers that have low cell damage effects. The mechanical and physical properties surrounding these processes and surfactants are still however not known. In this study, the physicochemical micellar properties of PEG 12-acyloxy-stearates were characterized by optical microscopic, nuclear magnetic resonance, and small-angle X-ray scattering techniques. We determined the phase diagrams of the surfactants as a function of surfactant concentration and temperature, the micellar size and shape, and micellar dynamics. We found that each surfactant has a micellar, cubic Im3m, and hexagonal phase. The aggregation number in the discrete cubic phase, as determined by small-angle X-ray scattering, was approximately 150 for each surfactant, and showed no measurable chain-length dependence. The diffusion coefficients of the surfactant showed a discontinuity between the micellar and cubic phases, where the cubic phases gave very low values on the order of 10(-)(16) m(2) s(-)(1): this value indicates a non-bicontinuous cubic structure. In summary, these surfactants behave to a large extent as nonionic poly(ethylene glycol) surfactants with extended PEG headgroups.