Nonionic diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains: thermotropic and lyotropic liquid crystalline phase behaviour

The thermotropic and lyotropic liquid crystalline phase behaviour of a series of diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains (geranoyl, H-farnesoyl, and phytanoyl) has been investigated. When neat, both H-farnesoyl and phytanoyl diethanolamide form a smectic liquid crystalline structure at sub-zero temperatures. In addition, all three diethanolamides exhibit a glass transition temperature at around -73 °C. Geranoyl diethanolamide forms a lamellar crystalline phase with a lattice parameter of 17.4 ? following long term storage accompanied by the loss of the glass transition. In the presence of water, H-farnesoyl and phytanoyl diethanolamide form lyotropic liquid crystalline phases, whilst geranoyl diethanolamide forms an L(2) phase. H-farnesoyl diethanolamide forms a fluid lamellar phase (L(α)) at room temperature and up to ～ 40 °C. Phytanoyl diethanolamide displays a rich mesomorphism forming the inverse diamond (Q(II)(D)) and gyroid (Q(II)(G)) bicontinuous cubic phases in addition to an L(α) phase.     

Nonionic diethanolamide amphiphiles with unsaturated C18 hydrocarbon chains: thermotropic and lyotropic liquid crystalline phase behavior

The neat and lyotropic liquid crystalline phase behavior of three nonionic diethanolamide amphiphiles with C18 hydrocarbon chains containing one, two or three unsaturated bonds has been examined. This has allowed the effect of degree of unsaturation on the phase behavior of diethanolamide amphiphiles to be investigated. Neat linoleoyl and linolenoyl diethanolamide undergo a transition from a glassy liquid crystal to a liquid crystal at ～-85 °C, while neat oleoyl diethanolamide undergoes a transition at ～-60 °C to a liquid crystalline material before re-crystallizing at -34 °C. Oleoyl diethanolamide then undergoes a third transition from a crystalline phase to a smectic liquid crystalline phase at ～5 °C. In the absence of water, the transition temperature from a smectic liquid crystal to an isotropic liquid decreases with increasing unsaturation. The addition of water results in the formation of a lamellar phase (L(α)) for all three amphiphiles. The lamellar phase is stable under excess water conditions up to temperatures of at least 70 °C. Approximate partial binary amphiphile-water phase diagrams generated for the three unsaturated C18 amphiphiles indicate that the excess water point for each amphiphile occurs at ～60% (w/w) amphiphile.     

Chelating DTPA amphiphiles: ion-tunable self-assembly structures and gadolinium complexes

A series of chelating amphiphiles and their gadolinium (Gd(iii)) metal complexes have been synthesized and studied with respect to their neat and lyotropic liquid crystalline phase behavior. These amphiphiles have the ability to form ion-tunable self-assembly nanostructures and their associated Gd(III) complexes have potential as magnetic resonance imaging (MRI) contrast enhancement agents. The amphiphiles are composed of diethylenetriaminepentaacetic acid (DTPA) chelates conjugated to one or two oleyl chain(s) (DTPA-MO and DTPA-BO), or isoprenoid-type chain(s) of phytanyl (DTPA-MP and DTPA-BP). The thermal phase behavior of the neat amphiphiles was examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cross polarizing optical microscopy (POM). Self-assembly of neat amphiphiles and their associated Gd complexes, as well as their lyotropic phase behavior in water and sodium acetate solutions of different ionic strengths, were examined by POM and small and wide angle X-ray scattering (SWAXS). All neat amphiphiles exhibited lamellar structures. The non-complexed amphiphiles showed a variety of lyotropic phases depending on the number and nature of the hydrophobic chain in addition to the ionic state of the hydration. Upon hydration with increased Na-acetate concentration and the subtle changes in the effective headgroup size, the interfacial curvature of the amphiphile increased, altering the lyotropic liquid crystalline structures towards higher order mesophases such as the gyroid (Ia3d) bicontinuous cubic phase. The chelation of Gd with the DTPA amphiphiles resulted in lamellar crystalline structures for all the neat amphiphiles. Upon hydration with water, the Gd-complexed mono-conjugates formed micellar or vesicular self-assemblies, whilst the bis-conjugates transformed only partially into lyotropic liquid crystalline mesophases.     

Ordered 2-D and 3-D nanostructured amphiphile self-assembly materials stable in excess solvent

Amphiphile lyotropic liquid crystalline self-assembly materials are being used for a diverse range of applications. Historically, the most studied lyotropic liquid crystalline phase is probably the one-dimensional (1-D) lamellar phase, which has been employed as a model system for biomembranes and for drug delivery applications. In recent years, the structurally more complex 2-D and 3-D ordered lyotropic liquid crystalline phases, of which reversed hexagonal (H(2)) and reversed cubic phases (v(2)) are two prominent examples, have received growing interest. As is the case for the lamellar phase, these phases are frequently stable in excess water, which facilitates the preparation of nanoparticle dispersions and makes them suitable candidates for the encapsulation and controlled release of drugs. Integral membrane protein crystallization media and templates for the synthesis of inorganic nanostructured materials are other applications for 2-D and 3-D amphiphile self-assembly materials. The number of amphiphiles identified as forming nanostructured reversed phases stable in excess solvent is rapidly growing. In this article, different classes of amphiphiles that form reversed phases in excess solvent are reviewed, with an emphasis on linking phase behavior to amphiphile structure. The different amphiphile classes include: ethylene oxide-, monoacylglycerol-, glycolipid-, phosphatidylethanolamine-, and urea-based amphiphiles.     

Diversifying the solid state and lyotropic phase behavior of nonionic urea-based surfactants

The solid state and lyotropic phase behavior of 10 new nonionic urea-based surfactants has been characterized. The strong homo-urea interaction, which can prevent urea surfactants from forming lyotropic liquid crystalline phases, has been ameliorated through the use of isoprenoid hydrocarbon tails such as phytanyl (3,7,11,15-tetramethyl-hexadecyl) and hexahydrofarnesyl (3,7,11-trimethyl-dodecyl) or the oleyl chain (cis-octadec-9-enyl). Additionally, the urea head group was modified by attaching either a hydroxy alkyl (short chain alcohol) moiety to one of the nitrogens of the urea or by effectively "doubling" the urea head group by replacing it with a biuret head group. The solid state phase behavior, including the liquid crystal-isotropic liquid, polymorphic, and glass transitions, is interpreted in terms of molecular geometries and probable hydrogen-bonding interactions. Four of the modified urea surfactants displayed ordered lyotropic liquid crystalline phases that were stable in excess water at both room and physiological temperatures, namely, 1-(2-hydroxyethyl)-1-oleyl urea (oleyl 1,1-HEU) with a 1D lamellar phase (Lalpha), 1-(2-hydroxyethyl)-3-phytanyl urea (Phyt 1,3-HEU) with a 2D inverse hexagonal phase (HII), and 1-(2-hydroxyethyl)-1-phytanyl urea (Phyt 1,1-HEU) and 1-(2-hydroxyethyl)-3-hexahydrofarnesyl urea (Hfarn 1,3-HEU) with a 3D bicontinuous cubic phase (QII). Phyt 1,1-HEU exhibited rich mesomorphism (QII1, QII2, Lalpha, LU, and HII), as did one other surfactant, oleyl 1,3-HEU (QII1, QII2, Lalpha, LU, and HII), in the study group. LU is an unusual phase which is mobile and isotropic but possesses shear birefringence, and has been very tentatively assigned as an inverse sponge phase. Three other surfactants exhibited a single lyotropic liquid crystalline phase, either Lalpha or HII, at temperatures >50 degrees C. The 10 new surfactants are compared with other recently reported nonionic urea surfactants. Structure-property correlations are examined for this novel group of self-assembling amphiphiles.     

Lyotropic smectic layering of side-on polysoaps in water

 The synthesis and characterization of lyotropic smectic amphiphilic side-on polymers are described. The amphiphile consists of a rigid, aromatic core with two terminal ethyleneoxide chains of various lengths and is laterally attached to a polysiloxane backbone; the length of the spacer has also been varied. The phase behavior of the monomeric amphiphiles and side-on polymers are determined by polarizing microscopy and ²H-NMR measurements. In water, most of the low molecular weight surfactants show restricted lyotropic properties, namely lyotropic smectic phases. The packing restriction of the amphiphiles is due to their geometric anisometry. All side-on polymers exhibit only lyotropic smectic phases. The phase regime of the polymer mesophase with respect to the monomers depends on the spacer length. In contrast to surfactants having a flexible hydrophobic group, these amphiphiles align spontaneously parallel to an external magnetic field, leading to perfect lyotropic smectic monodomains. Received: 21 May 2001 Accepted: 27 August 2001     

Nonionic urea surfactants: formation of inverse hexagonal lyotropic liquid crystalline phases by introducing hydrocarbon chain unsaturation

The homo-interaction between urea moieties residing in close proximity to each other generally results in very strong intermolecular hydrogen bonding. The bifurcated hydrogen bonding exhibited by n-alkyl substituted ureas means that for those urea surfactants possessing medium and long hydrocarbon chain substituents the crystal to isotropic liquid melting point is high and the solubility in water is very low, compared to other similar chain length nonionic surfactants. In addition, saturated n-alkyl urea surfactants do not form lyotropic liquid crystalline phases in water. In this work the strong intermolecular hydrogen bonding of the urea headgroup has been ameliorated through the introduction of unsaturated hydrocarbon chains, viz., oleyl (cis-octadec-9-enyl), linoleyl (cis, cis-octadec-9,12-dienyl), and linolenyl (cis, cis, cis-octadec-9,12,15-trienyl) with one, two, and three carbon double bonds, respectively. Unsaturation in the C18 urea surfactants lowers the melting point and promotes an inverse hexagonal phase, in oleyl urea-water and linoleyl urea-water systems, which is thermodynamically stable in excess water. As the degree of unsaturation is increased to three in linolenyl urea, there is a tendency for autoxidation/polymerization. The occurrence of an inverse hexagonal phase in the nonionic urea surfactant-water systems has been rationalized in terms of both local molecular and global self-assembled aggregate packing constraints.     

Substitution effects on the liquid crystalline properties of D,L-xylitol amphiphiles

In this article we describe the self-assembling properties of alkyl substituted xylitols in relation to both thermotropic and lyotropic liquid crystalline mesophases. Three series of substituted xylitols were prepared where aliphatic chains of varying length were attached to a xylitol moiety via ether, thioether and ester linking groups. The thermotropic properties were investigated by thermal polarized light microscopy and differential scanning calorimetry, and evaluated as a function of chain length and linking group. The lyotropic phase behaviour was investigated via the addition of water to each material at room temperature. The efficiency for forming thermotropic phases was found to be reversed for the lyotropic phases in respect of the three series, i.e. as a function of the linking unit.     

Hydrostatic pressure effects on the lamellar to gyroid cubic phase transition of monolinolein at limited hydration

Monoacylglycerol based lipids are highly important model membrane components and attractive candidates for drug encapsulation and as delivery agents. However, optimizing the properties of these lipids for applications requires a detailed understanding of the thermodynamic factors governing the self-assembled structures that they form. Here, we report on the effects of hydrostatic pressure, temperature, and water composition on the structural behavior and stability of inverse lyotropic liquid crystalline phases adopted by monolinolein (an unsaturated monoacylglycerol having cis-double bonds at carbon positions 9 and 12) under limited hydration conditions. Six pressure-temperature phase diagrams have been determined using small-angle X-ray diffraction at water contents between 15 wt % and 27 wt % water, in the range 10-40 °C and 1-3000 bar. The gyroid bicontinuous cubic (Q(II)(G)) phase is formed at low pressure and high temperatures, transforming to a fluid lamellar (L(α)) phase at high pressures and low temperature via a region of Q(II)(G)/L(α) coexistence. Pressure stabilizes the lamellar phase over the Q(II)(G) phase; at fixed pressure, increasing the water content causes the coexistence region to move to lower temperature. These trends are consistent throughout the hydration range studied. Moreover, at fixed temperature, increasing the water composition increases the pressure at which the Q(II)(G) to L(α) transition takes place. We discuss the qualitative effect of pressure, temperature, and water content on the stability of the Q(II)(G) phase.     

Lyotropic liquid crystalline phase behaviour of a monomeric and a polymeric monosaccharide amphiphile in aqueous solution

Monomeric and polymeric amphiphiles were synthesized which exhibit lyotropic liquid crystalline phases in aqueous solution. The hydrophobic group of the monomeric surfactant is a dodecane-group esterified with acrylic acid. The hydrophilic unit is a monosaccharide derivative. By radical polymerization the monomer (N-D(-)-gluco-N-methyl-(12-acryloyloxy)-dodecane-l-amide) is converted into the corresponding polymeric surfactant. The monomer as well as the polymer exhibit a lyotropic 1.c. phase of lamellar structure. Owing to the polymerization the regime of the lamellar phase is greatly enlarged for the polymer, compared to the monomeric sufactant. These results confirm earlier investigations on non-ionic ethylene-glycol surfactants.     

LYOTROPIC LIQUID CRYSTALS IN BINARY SYSTEMS N-ALKYL GLYCOSIDES/WATER*

The formation of lyotropic mesophases (liquid crystals) in four binary systems n-alkyl glycosides/water was examined in dependence on surfactant concentration, temperature and the chain lengths (alkyl = heptyl, octyl, nonyl, decyl). The binary phase diagrams were established and the enthalpies of phase transitions were measured. The following phase transitions were detected by texture observation and calorimetry: hexagonal phase H, lamellar phase L, cubic phase Q, gel phase G and crystalline phase C. The positions of the corresponding regions of these phases in the phase diagram were determined. Sequence of phases and the localization of the phase regions were depended on the chain length of the alkyl group. So in the binary system n-decyl-β-D-glucoside/water the H-phase was not observed.     

Effect of pharmaceutically acceptable glycols on the stability of the liquid crystalline gels formed by Poloxamer 407 in water

The ability of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (Poloxamers) to form "gels" (lyotropic liquid crystalline structures) in water is of interest to pharmaceutical applications. In such applications the presence of polar organic solvents is often desirable or required. The effect of such solvents on the stability of lyotropic liquid crystalline gels formed by PEO-PPO-PEO block copolymers was assessed by studying the phase behavior and structure in ternary isothermal (25 degrees C) systems of pharmaceutical interest consisting of Poloxamer 407 (EO(100)PO(70)EO(100)), water, and one of the following solvents (referred to here collectively as "glycols"): glycerol, propylene glycol, ethanol, polyethylene glycol 400, and glucose. Small-angle X-ray scattering was employed to establish the structure of the liquid crystals obtained and to determine their characteristic length scales. The stability range of the liquid crystalline gel phases in the systems studied was found to vary with the glycol type. For example, the micellar cubic structure can accommodate about 0.85:1 parts glucose per part water (in terms of weight) and up to as much as 5.5:1 parts propylene glycol per part water. A correlation between the glycol effects on the stability of the liquid crystalline phases and glycol physiochemical characteristics such as octanol/water partition coefficient or solubility parameter is proposed.     

Penetration by water of polyhydroxy amphiphiles in the crystalline versus the liquid crystalline states

The penetration of water in contact preparations with polyhydroxy amphiphiles in different aggregation states is compared. The onset of penetration is found at much higher temperatures when the samples are in the solid state than when they are in a super-cooled liquid-crystalline state in the case of the smectic A_d and smectic B₂phases, but not the columnar hexagonal (D_hd) mesophase. The enhanced accessibility of the bilayer smectic phases can be explained by assuming that the molecular arrangement in the layers is similar to that found in the lamellar lyotropic phase, where the polar groups are on the outside and the (partially intercalated) alkyl chains are in the core of the layers.     

Thermotropic behavior of asymmetric chain length catanionic surfactants: the influence of the polar head group

Catanionic surfactants formed by the pairing of two ionic amphiphilic chains of opposite charge are now recognized as an important class of amphiphiles. Many aspects of their phase behavior have yet to be explored. In this work, two homologous series of catanionic surfactants were synthesized, based on the cationic headgroups trimethylammonium and pyridinium. Within each series, the headgroup and chain length of the cationic counterpart remains constant while for the anionic counterpart the headgroup is varied, while its alkyl chain length is also kept constant. Thus, one can directly monitor the influence of headgroup chemistry on the thermal behavior of these compounds. Differential scanning calorimetry (DSC) and polarizing light microscopy show that these compounds bear a rich and often complex thermotropic behavior, with the headgroup chemistry in some instances having a rather dramatic influence on phase behavior. Several liquid crystalline phases appear between the solid crystalline phase and the isotropic liquid phase. A qualitative correlation between the observed thermotropic behavior and the chemical nature of headgroup is presented.     

Phase behavior and polymerization of lyotropic phases. II. A series of polymerizable amphiphiles with systematically varied critical packing parameters

A group of polymerizable amphiphiles, with their critical packing parameters systematically varied, were studied with respect to the phase behavior and immobilization of their lyotropic liquid‐crystalline phase structures. Small‐angle X‐ray scattering and polarized light microscopy were used to study their liquid‐crystalline phases before and after photopolymerization. The liquid crystallinity of the amphiphiles depended on the contents of both oil and water in the ternary systems. Through photopolymerization, hexagonal phases could generally be immobilized, with the structural order reduced to various degrees. However, the cubic phases evolved with polymerization into another structural pattern, which was possibly related to the lamellar structure. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5887–5897, 2006     

Aqueous phase behavior of polyelectrolytes with amphiphilic counterions modulated by cyclodextrin: the role of polyion flexibility

Polyelectrolytes with amphiphilic counterions, PEACs, are water insoluble because the amphiphiles self-assemble into highly charged micelles that strongly associate with the equally highly charged polyions. However, in the presence of water soluble cyclodextrins (CDs) that form inclusion complexes with the amphiphiles and prevent micellization, PEACs become soluble as the dispersed amphiphiles behave essentially as simple monovalent counterions. In this paper, we illustrate, by example, how strongly the ternary phase behavior of PEAC:CD:water depends on the polyion flexibility; for a highly flexible polyion (polyacrylate) the amphiphilic aggregates dictate the phase behavior, whereas a much stiffer polyion (DNA) itself dictates liquid crystalline ordering.     

Lyotropic liquid crystalline phases formed in ternary mixtures of 1-cetyl-3-methylimidazolium bromide/p-xylene/water: a SAXS, POM, and rheology study

The phase behavior of ternary mixtures of 1-cetyl-3-methylimidazolium bromide (C(16)mim-Br)/p-xylene/water is studied by small-angle X-ray scattering (SAXS), polarized optical microscopy (POM), and rheology measurements. Two types of lyotropic liquid crystalline phases are formed in the mixtures: hexagonal and lamellar. The structural parameters of the lyotropic liquid crystalline phases are calculated. Greater surfactant content in the sample leads to denser aggregation of the cylindrical units in the hexagonal liquid crystalline phase. The increase in lattice parameter and thickness of the water layer in lamellar phase are attributed to the increase of water content, and the area per surfactant molecule at the hydrophobic/hydrophilic interface for lamellar phase is found to be larger than that for hexagonal phase. The structural parameters of the liquid crystalline phases formed from the cetyltrimethylammonium bromide (CTAB) system are larger than those for the C(16)mim-Br system. The rheological properties of the samples are also found to be related to the structure of the liquid crystalline phases.     

Lyotropic phases reinforced by hydrogen bonding

Amphiphilic guanidinium alkylbenzenesulfonates (GCnBS; n = number of carbons in the alkyl chain) exhibited lyotropic behavior in aqueous and organic solvents. The GCnBS compounds formed gel-like phases in certain cyclic organic solvents (e.g. p-xylene, cyclohexane) through the formation of swollen interdigitated lamellar phases reinforced by hydrogen bonding between the guanidinium ions and sulfonate moieties. This behavior was not observed for the homologous sodium alkylbenzenesulfonates, indicating that hydrogen bonding, mediated by the guanidinium (G) ion, was required for gel formation. Infrared spectroscopy unambiguously demonstrated the existence of the quasi-hexagonal hydrogen-bonded sheet typically adopted by G ions and the sulfonate groups in layered, solvent-free crystalline phases of the compounds, supporting lamellar structures in the gels. Small-angle X-ray scattering analysis of these gels revealed GCnBS lamellar phases with interlayer spacings (d) that increased with increasing temperature, consistent with increased absorption of solvent by the nonpolar regions of the gelator. At the lower gelator concentrations, the increase in d-spacing achieved at the higher temperatures exceeded the sum of the alkylbenzene chain lengths, suggesting either long-range interactions between the GS sheets or undulation stabilized lamellae, which have been reported in aqueous lamellar gels. The GCnBS compounds also formed lyotropic phases in water, but the phase behavior was more complex than that of the organogels. The rheology suggested gel-like behavior associated with entangled worm-like micelles at these higher concentrations. These lyotropic phases were reminiscent of crystalline layered and tubular architectures exhibited by various guanidinium organomonosulfonate compounds. These lyotropic phases expand the liquid crystal behavior observed for GS compounds beyond recently observed thermotropic smectic phases, adding to the portfolio of phase behavior exhibited by these materials.     

Protonation-induced structural change of lyotropic liquid crystals in oley- and alkyldimethylamine oxides/water systems

Lyotropic phase behavior of the nonionic and the half-ionized oleyldimethylamine oxide (OlDMAO)/water systems was investigated using polarized light microscopy, small-angle X-ray diffraction, and differential scanning calorimetry. Nonionic OlDMAO formed isotropic micellar solution, nematic, hexagonal, cubic, and lamellar liquid crystalline phases as the surfactant concentration increased. In contrast, half-ionized OlDMAO (i.e., 1:1 mixture of the nonionic and the protonated species) had a greater tendency to form bilayer structures, and the phase diagram became quite similar to those of double-chained ionic surfactants rather than single-chained ones, despite the introduction of positive charges to the nonionic one. The preference of the bilayer structures in the half-ionized OlDMAO was interpreted in terms of the dimers stabilized by the hydrogen bond between the nonionic and protonated species. For alkyldimethylamine oxides with a saturated hydrocarbon chain (CnDMAO, chain length: n = 14, 16, and 18), the phase sequence of lyotropic liquid crystals was hardly affected by the protonation, but an elongation of the cylinders of the hexagonal phase was observed for the half-ionized C14DMAO. Consequently, it can be considered that the dominant bilayer formation of the half-ionized OlDMAO is attributed to the combined effect of the hydrogen-bonded dimer formation and the cis-double-bond configuration of the alkyl chain.     

甲壳素类液晶高分子的研究Ⅱ-侧基长度和取代度对羧酰化壳聚糖的液晶性的影响

五种羧酰化壳聚糖即乙酰化、丙酰化、丁酰化、己酰化和庚酰化壳聚糖在二氯乙酸溶液中均呈现胆甾型溶致液晶相．临界浓度随侧基长度的增加而增加,但取代度（ 从０－２１ 变化到０－９４） 对临界浓度没有影响．在两相共存浓度区内,均呈现典型的滴状织构．从两相共存到完全液晶相的转变浓度也随侧基长度的增加而增加．