Interaction of Natural and Modified β-Cyclodextrins with a Biological Membrane Model of Dipalmitoylphosphatidylcholine

Lipid vesicles made up of dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) were used as a biological membrane model to investigate the interaction between natural and modified β-cyclodextrins and these membrane bilayers. Differential scanning calorimetry was used to study the thermotropic behavior of the DPPC vesicles and any change caused by the presence of cyclodextrins. The presence of dimethyl-β-cyclodextrin (DM-β-CyD) triggered a reduction in the enthalpy values related to the main transition peak from gel state to liquid crystal phase of DPPC aqueous dispersions, as a function of the DM-β-CyD molar fraction: the larger the amount of DM-β-CyD, the greater the reduction in ΔHvalues. This effect was probably due to the ability of DM-β-CyD to extract and to complex the DPPC molecules forming the phospholipid vesicles. The presence of β-cyclodextrin (β-CyD) or hydroxypropyl-β-cyclodextrin (HP-β-CyD) caused no particular alteration in the thermotropic parameters of DPPC vesicles, whereas trimethyl-β-cyclodextrin (TM-β-CyD) at molar fractions higher than 0.12 caused broadening of the transition peak due to a possible interaction with the hydrophobic part of the bilayers. Experiments on DPPC–cholesterol (10 mol%) vesicles showed the capability of β-CyD and TM-β-CyD to extract cholesterol from the ordered bilayer structures, triggering an alteration in the lipid constituents of the membranes. HP-β-CyD caused no variation in the thermotropic parameters of the DPPC–cholesterol (10 mol%) vesicles. The findings show that HP-β-CyD seems the most suitable molecular drug carrier forin vivoadministration.     

Milk membrane lipid vesicle structures studied with Cryo-TEM

Milk fat globule membrane (MFGM) lipids have been studied in the presence and absence of proteins β-lactoglobulin and β-casein. The aim of this study was to relate the self-assembly structure, e.g. vesicles, formed in aqueous dispersions of MFGM lipids to the lipid composition, electrolyte composition as well as the effect of added milk proteins, i.e. β-lactoglobulin and β-casein. For this purpose, vesicles of phospholipid mixtures, containing dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM), dioleoylphosphatidylethanolamine (DOPE), phosphatidylinositol (PI) and dioleoylphosphatidylserine (DOPS) at composition corresponding to that of the MFGM, were prepared by extrusion. The morphology of the formed structures of different sample compositions was studied with cryogenic transmission electron microscopy (Cryo-TEM). Mixtures of membrane lipid with a composition (e.g. 80% DOPE, 12% DOPC and 8% SM) that at high lipid content give liquid crystalline phases at the boundary of lamellar to reversed hexagonal phase rather formed microtubular structures than vesicles at high water content. A large proportion of multilamellar vesicles is formed in buffer and divalent salts than in pure water. A small increase in the interlayer spacing of the multilamellar vesicle was observed in the presence of β-casein.     

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.     

Self-Organization and Formation of Liquid Crystal Phases by Molecular Templates Related to Membrane Components of Archaebacteria

Tubular supramolecular aggregates are formed from glycolipids 1 , which are closely related to natural components of membranes of archaebacteria. The glycolipids exhibit disordered columnar thermotropic and hexagonal lyotropic liquid crystal phases. Whereas formation of the mesophases is insensitive to stereochemical factors, formation of the tubules is dependent on the configuration of the stereocenters that are shown in the picture but not specified.     

Aqueous phase behavior and dispersed nanoparticles of diglycerol monooleate/glycerol dioleate mixtures

The first part of this study concerns the aqueous phase behavior of mixtures of diglycerol monooleate (DGMO) and glycerol dioleate (GDO) examined by X-ray diffraction (XRD). The ternary phase diagram displays a multitude of liquid crystalline phases (polymorphism). With increasing GDO content the following phase sequence was observed: lamellar (L(alpha)); two reversed bicontinuous cubic phases (Q(230) and Q(224)); reversed hexagonal (H(II)); the reversed micellar (L(2)) phase. The second part deals with the preparation and characterization of aqueous dispersions of the reversed hexagonal phase in the presence of the nonionic triblock copolymer Pluronic F127. Submicrometer-sized monocrystalline H(II) phase particles were obtained, as evidenced by cryo-transmission electron microscopy (cryo-TEM), laser diffraction, and XRD, by use of a simple and reproducible preparation method including a heat-treatment step. Moreover, the particle size distributions of the H(II) phase nanoparticle dispersions were narrow as determined by laser diffraction measurements. Using XRD, we show that the polymeric stabilizer is depleted from the core of the hexagonal particles and preferentially located at the surface. It is concluded that the preferential distribution of stabilizing agents at particle surfaces is a prerequisite for the formation of structurally well-defined and kinetically stable H(II) phase particles (Hexosome).     

Nanoorganization and Phase Behavior of Mixtures of Nicotinic Acid with Dodecylbenzenesulfonic Acid

Abstract

Mesomorphically ordered structures and phase behavior of the mixtures of nicotinic acid (NICA) and dodecylbenzenesulfonic acid (DBSA) were investigated by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and polarized optical microscopy (POM). The POM observations revealed that the NICA–DBSA mixtures spontaneously formed liquid crystalline phases, although both NICA and DBSA were not liquid crystalline molecules. The NICA–DBSA mixtures formed ordered lamellar structures in DBSA‐rich mixtures and hexagonal cylinder structure in NICA‐rich mixtures. The mesomorphically ordered structures and optical anisotropy were caused by hierarchical interactions in the NICA–DBSA mixtures. The phase diagram divided into five regions—optically isotropic disordered phase, optically isotropic lamellar phase, optically anisotropic lamellar phase, optically anisotropic cylinder phase, and crystalline solid phase—is drawn by summarizing the XRD and POM results.     

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.     

Understanding the interfacial properties of nanostructured liquid crystalline materials for surface-specific delivery applications

Nonlamellar liquid crystalline dispersions such as cubosomes and hexosomes have great potential as novel surface-targeted active delivery systems. In this study, the influence of internal nanostructure, chemical composition, and the presence of Pluronic F127 as a stabilizer, on the surface and interfacial properties of different liquid crystalline particles and surfaces, was investigated. The interfacial properties of the bulk liquid crystalline systems with coexisting excess water were dependent on the internal liquid crystalline nanostructure. In particular, the surfaces of the inverse cubic systems were more hydrophilic than that of the inverse hexagonal phase. The interaction between F127 and the bulk liquid crystalline systems depended on the internal liquid crystalline structure and chemical composition. For example, F127 adsorbed to the surface of the bulk phytantriol cubic phase, while for monoolein cubic phase, F127 was integrated into the liquid crystalline structure. Last, the interfacial adsorption behavior of the dispersed liquid crystalline particles also depended on both the internal nanostructure and the chemical composition, despite the dispersions all being stabilized using F127. The findings highlight the need to understand the specific surface characteristics and the nature of the interaction with colloidal stabilizer for understanding and optimizing the behavior of nonlamellar liquid crystalline systems in surface delivery applications.     

Liquid crystal polymers. XVIII. Comparison of the properties of aromatic polyesters with different mesogenic units and a common flexible spacer

Four closely related polyesters, with aromatic ester triads and decamethylene spacers, were prepared and characterized for their thermotropic liquid crystalline properties. Two of the polymers, which were based on linear biphenols, formed stable nematic phases, whereas one of the two based on nonlinear biphenols formed a poorly defined nematic phase; the other was not liquid crystalline. Several polymerization reactions and methods were evaluated and structure-property relationships of the polymers are discussed. The concept of “degree of liquid crystallinity” for polymers with poorly defined thermotropic behavior is considered.     

SYNERGETIC EFFECT OF SUCROSE AND ETHANOL ON FORMATION OF TRIGLYCERIDE MICROEMULSIONS

The phase behavior of soybean oil, a nonionic surfactant (ethoxylated monodiglycerides) and an aqueous phase of water containing ethanol, and sucrose was investigated at 35 and 40°C. A minimum concentration of 20 wt% ethanol was required for the formation of isotropic solutions. Addition of sucrose to the aqueous phase decreased the amount of ethanol required to form these solutions. The solubilization mechanism of the oil was investigated by small angle x-ray diffraction and polarized light microscopy. A stable lamellar liquid crystalline phase was formed for a mixture of 75/25 surfactant/sucrose solution (2.5 wt% sucrose). This phase was destabilized with increased concentrations of sucrose and liquid crystalline phases having hexagonal structures were favored at 8.75 wt% sucrose. At a ratio of 55/45 wt% of surfactant/sucrose solution (9 wt% sucrose) hexagonal structures were formed and could be destabilized or destroyed by addition of ethanol. The concept of stabilization and destabilization of liquid crystalline mesophases was applied to the solubilization of triglycerides in aqueous solutions. Two microemulsion regions were identified; oil-in-water (L₁) and water-in-oil (L₂) in systems containing soybean oil, ethoxylated monodiglycerides, and 20 wt% ethanol solution. At 55/45 wt% surfactant/20 wt% ethanol solution,7.5 wt% of soybean oil was solubilized. Addition of 10, 20, and 30 wt% sucrose, at the same ratio of surfactant to ethanol solution, increased the solubility of the oil to 9, 13.5, and 18 wt% respectively. In addition, the size of the L₁ phase increased and moved to the aqueous corner of the phase diagram and the size of the L₂ phase decreased.     

Dispersed lipid liquid crystalline phases stabilized by a hydrophobically modified cellulose

Aqueous dispersions of monoolein (MO) with a commercial hydrophobically modified ethyl hydroxyethyl cellulose ether (HMEHEC) have been investigated with respect to the morphologies of the liquid crystalline nanoparticles. Only very low proportions of HMEHEC are accepted in the cubic and lamellar phases of the monoolein-water system. Due to the broad variation of composition and size of the commercial polymer, no other single-phase regions were found in the quasi-ternary system. Interactions of MO with different fractions of the HMEHEC sample induced the formation of lamellar and reversed hexagonal phases, identified from SAXD, polarization microscopy, and cryogenic TEM examinations. In excess water (more than 90 wt %) coarse dispersions are formed more or less spontaneously, containing particles of cubic phase from a size visible by the naked eye to small particles observed by cryoTEM. At high polymer/MO ratios, vesicles were frequently observed, often oligo-lamellar with inter-lamellar connections. After homogenization of the coarse dispersions in a microfluidizer, the large particles disappeared, apparently replaced by smaller cubic particles, often with vesicular attachments on the surfaces, and by vesicles or vesicular particles with a disordered interior. At the largest polymer contents no proper cubic particles were found directly after homogenization but mainly single-walled defected vesicles with a peculiar edgy appearance. During storage for 2 weeks, the dispersed particles changed toward more well-shaped cubic particles, even in dispersions with the highest polymer contents. In some of the samples with low polymer/MO ratio, dispersed particles of the reversed hexagonal type were found. A few of the homogenized samples were freeze-dried and rehydrated. Particles of essentially the same types, but with a less well-developed cubic character, were found after this treatment.     

A novel viscoelastic system from a cationic surfactant and a hydrophobic counterion

The phase behavior of 2-hydroxy-1-naphthoic acid (2,1-HNC) mixed with cetyltrimethylammonium hydroxide (CTAOH) is reported. This novel system is compared with the published one of 3-hydroxy-2-naphthoic acid (3,2-HNC) mixed with CTAOH. We investigated the phase behavior and properties of the phases in aqueous solutions of 100 mM CTAOH with 2,1-HNC. In both systems a multilamellar vesicle phase is formed when the naphthoate/surfactant ratio (r) reaches unity. When an increasing amount of 2,1-HNC is mixed with a micellar solution of 100 mM CTAOH, an isotropic low-viscous micellar solution, a viscoelastic gel (consisting of rodlike micelles), a turbid region (two-phase region), and a viscoelastic liquid crystalline gel (consisting of multilamellar vesicles, MLV) were formed. The vesicular phase is highly viscoelastic and has a yield stress value. The transition from the micellar to the vesicle phase occurs for CTAOH/2,1-HNC over a two-phase region, where micelles and vesicles coexist. Also it was noticed that 2,1-HNC is dissolved in 100 mM CTAOH until the naphthoate/surfactant ratio reaches approximately 1.5, and the liquid crystalline phases were found to change their color systematically when they were viewed between two crossed polarizers. The vesicles have been characterized by differential interference contrast microscopy, freeze-fracture electron microscopy, and cryo-electron microscopy (cryo-TEM). The vesicles were polydisperse and their diameter ranged from 100 to 1000 nm. The interlamellar spacing between the bilayers was determined with small angle neutron scattering and agrees with the results from different microscopical methods. The complex viscosity rises by six orders of magnitude when rodlike micelles are formed. The complex viscosity decreases again in the turbid region, and then rises approximately six orders of magnitude above the water viscosity. This second rising is due to the formation of the liquid crystalline MLV phase.     

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.     

Self-organization of double-chained and pseudodouble-chained surfactants: counterion and geometry effects

Self-organization in aqueous systems based on ionic surfactants, and their mixtures, can be broadly understood by a balance between the packing properties of the surfactants and double-layer electrostatic interactions. While the equilibrium properties of micellar systems have been extensively studied and are understood, those of bilayer systems are less well characterized. Double-chained and pseudodouble-chained (or catanionic) surfactants are among the amphiphiles which typically form bilayer structures, such as lamellar liquid–crystalline phases and vesicles. In the past 10–15 years, an experimental effort has been made to get deeper insight into their aggregation patterns. With the double-chained amphiphiles, by changing counterion, adding salt or adding anionic surfactant, there are possibilities to depart from the bilayer aggregate in a controlled manner. This is demonstrated by several studies on the didodecyldimethylammonium bromide surfactant. Mixtures of cationic and anionic surfactants yield the catanionics, surfactants of the swelling type, and also show a rich phase behavior per se. A variety of liquid–crystalline phases and, in dilute regimes, equilibrium vesicles and different micellar shapes are often encountered. Phase diagrams and detailed structural studies, based on several techniques (NMR, microscopy and scattering methods), have been reported, as well as theoretical studies. The main features and conclusions emerging from such investigations are presented.     

Phase Behavior of Commercial AES/Ethanol/H2O Ternary System

Phase behavior containing alkyl ethoxysulfates (AES), ethanol, and H₂O over the whole concentration range was explored at 25°C. The system exhibited an isotropic solution phase (L), two different liquid crystalline phases: hexagonal phase (H), lamellar phase (Lα), and a biphasic region appearing with the ethanol concentration increasing. Polarized optical microscopy and small angle x-ray scattering were applied to characterize liquid crystalline phases. Direct two-phase titration and liquid chromatography–mass spectrometry (LC–MS) were employed to analyze the AES activity and homologues composition of the particles appearing in two-phase region.     

Molecular packing in sphingomyelin bilayers and sphingomyelin/phospholid mixtures

The molecular packing properties of sphingomyelin (SM) from egg yolk were studied. The influence of the spontaneous curvature of SM on the phase behaviour of SM/dodecane/water systems was investigated. A comparison was made to a previous study by Lindblom et al. (Liq. Cryst. 3 (1988) 783), of the phase behaviour of dipalmitoylphosphatidylcholine (DPPC)/dodecane/water systems, where a reversed hexagonal liquid crystalline was shown to form at high water contents (60-80%, w/w). In contrast, SM/dodecane/water systems mainly maintained a lamellar liquid crystalline phase at all compositions and temperatures >35 degrees C. This suggests that the spontaneous curvature of SM is larger than for DPPC. To further examine the packing properties of SM and DPPC, the phase behaviour of SM/dioleoylphosphatidylethanolamine (DOPE)/water and DPPC/DOPE/water systems were investigated. Aqueous dispersions of DOPE normally form a reversed hexagonal liquid crystalline phase, while an isotropic phase was formed at small additions (20 mol.%) of SM or DPPC and a lamellar liquid crystalline phase was maintained at higher fractions (>35 mol.%) of SM or DPPC.     

Interplay between H‐Bonding and Alkyl‐Chain Ordering in Self‐Assembly of Monodendritic L‐Alanine Derivatives

This paper reports on the synthesis and self‐organizing properties of monodendrons consisting of L ‐alanine at the focal point and alkyl chains with different length at the periphery. The structures of thin films and monolayers are studied by temperature‐resolved grazing‐incidence X‐ray diffraction and scanning force microscopy. The interplay between H‐bonding and ordering of the alkyl chains results in a rich temperature‐dependent phase behavior. The monodendrons form H‐bonded stabilized clusters with the number of molecules depending on the length of the aliphatic chains and temperature. The clusters play the role of constitutive units in the subsequent self‐assembly. Short alkyl chains allow the material to form thermodynamically stable crystalline phases. The molecules with longer side groups exhibit additional transitions from the crystalline phase to thermotropic columnar hexagonal or columnar rectangular liquid‐crystalline phases. In monolayers deposited on highly ordered pyrolytic graphite, the materials show ordering similar to thin films. However, for the compound bearing hexadecyl chains the affinity of the alkyl groups to graphite dominates the self‐assembly and thereby allows epitaxial growth of a 2D lattice with flat‐on oriented molecules.     

Properties of mixed DOTAP-DPPC bilayer membranes as reported by differential scanning calorimetry and dynamic light scattering measurements

We have investigated the effect of a cationic lipid [DOTAP] on both the thermotropic phase behavior and the structural organization of aqueous dispersions of dipalmitoyl-phosphatidylcholine [DPPC] by means of high-sensitivity differential scanning calorimetry and dynamic light scattering measurements. We find that the incorporation of increasing quantities of DOTAP progressively reduces the temperature and the enthalpy of the gel-to-liquid crystalline transition. We are further showing that, in mixed DOTAP-DPPC systems, the reduction of the phase transition temperature is accompanied by a reduction of the average size of the structures present in the aqueous mixtures, whatever the DOTAP concentration is. These results, which extend a previous investigation by Campbell et al. (Campbell, R. B.; Balasubramanian, S. V.; Straubinger, R. M.; Biochim. Biosphys. Acta 2001, 27, 1512.) limited to a DOTAP concentration below 20 mol %, confirm that the insertion of cationic head groups in zwitterionic phosphatidylcholine bilayers facilitates the formation of stable, relatively small, unilamellar vesicles. This self-assembling restructuring from an aqueous multilamellar structure toward a liposomal phase is favored by decreasing the phospholipid phase transition temperature and by increasing the temperature of the system. This reduction of the average size and the appearance of a stable liposomal phase is also promoted by a heating and cooling thermal treatment.     

Hydrogels from phospholipid vesicles

It is shown that phospholipid dispersions with a few percent of diacylphosphocholine PC in water can be swollen to single-phase lyotropic liquid crystalline L_α-phases by the addition of co-solvents like glycerol, 1,3-butyleneglycol BG or 1,2-propyleneglycol PG. The birefringent L_α-phases contain small unilamellar and multilamellar vesicles if the temperature of the samples is above the Krafft-Temperature T_m of the phospholipid. When such transparent birefringent viscous samples are cooled down below T_m the samples are transformed into birefringent gels. Cryo-TEM and FF-TEM measurements show that the bilayers of the vesicles are transformed from the liquid to the crystalline state during the transformation while the vesicle structure remains. The bilayers of the crystalline vesicles form adhesive contacts in the gel. Pulsed-field gradient NMR measurements show that two different kinds of water or co-solvent can be distinguished in the gels. One type of solvent molecules can diffuse like normal solvent in a continuous bulk phase. A second type of water diffuses much more slowly. This type of solvent is obviously trapped in the vesicles. The permeability of the crystalline vesicles for water and solvent molecules is much lower in the crystalline state than in the fluid state.     

Nonaqueous lyotropic liquid-crystalline phases formed by gemini surfactants in a protic ionic liquid

The aggregation behaviors of three Gemini surfactants [(C(s)H(2s)-α,ω-(Me(2)N(+)C(m)H(2m+1)Br(-))(2), s = 2, m = 10, 12, 14] in a protic ionic liquid, ethylammonium nitrate (EAN), have been investigated. The polarized optical microscopy and small-angle X-ray scattering (SAXS) measurements are used to explore the lyotropic liquid crystal (LLC) formation. Compared to the LLCs formed in aqueous environment, the normal hexagonal and lamellar phases disappear. However, with increasing the surfactant concentration, a new reverse hexagonal phase (H(II)) can be mapped over a large temperature range except for other ordered aggregates including the isotropic solution phase and a two-phase coexistence region. The structural parameters of the H(II) are calculated from the corresponding SAXS patterns, showing the influence of surfactant amount, alkyl chain length, and temperature. Meanwhile, the rheological profiles indicate a typical Maxwell behavior of the LLC phases formed in EAN.