Liquid Crystalline Phase Region Research Articles

Formation of bilayer membrane and niosomes by double-tailed polyglyceryl-type nonionic surfactant.

Vesicles with synthetic nonionic surfactants are called niosomes or NSVs, and these have been the focus of attention as an alternative to phospholipid liposomes as drug carriers. Especially it is demanded to discover novel niosomal systems with polyol-type nonionic surfactants from the viewpoint of environmental aspects. In this paper, a novel series of double-tailed nonionic surfactants, polyglyceryl dialkyl ethers, (C12)2Gn (n = 2.3, 5.4, 9.4, and 13.8), was synthesized, and its aqueous phase behavior and niosome formation were studied. Because of its double-tailed molecular structure, a lamellar liquid crystalline phase was dominant in the binary phase diagrams for different polyglyceryl chain lengths. The single lamellar liquid crystalline phase region was expanded as the polymerization degree in the hydrophilic moiety increased. Small-angle X-ray scattering spectra revealed the lamellar structure for the (C12)2G2.3 was extremely loose. Molecular packing in the lamellar phase was analyzed except for the (C12)2G2.3 system by using a geometrical model of the lamellar phase. The effective cross-sectional area per molecule at the interface increased extensively as dilution for the (C12)2G13.8 system but remained almost unchanged for the (C12)2G5.4 system. From the molecular parameters, water-holding ability in the lamellar phase was evaluated, and the results indicated strong hydration ability of the long polyglyceryl chain. In a dilute region, micron-sized giant niosomes and small niosomes of about 100 nm were formulated by vortex mixing and ultrasonication, respectively. The multilamellar structure of the small niosomes was confirmed by transmission electron microscopy. Cholesterol addition in the present surfactant lamellar phase induced the phase transition to the liquid ordered phase, which is the same phenomenon in a phospholipid-cholesterol mixture. The stability of niosomes with/without cholesterol was monitored by the niosome size change. In both cases, the niosomes were stable for at least 100 days.

Single Molecule Tracking of Annexin V in Cushioned DMPC Assemblies

Using single molecule imaging, this study describes the phase behavior and mobility of individual transmembrane (TM) proteins and compares those results with the bulk phase behavior of the biomimetic membrane in which they have been incorporated. To accomplish this a TM protein, Annexin V, was incorporated into a cushioned planar supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) / L-α-lysophosphatidyl-serine (Brain-PS) biomimetic assembly and its mobility between 30 and 16 C was measured. Fluorescence microscopy and Fluorescence Recovery After Photobleaching (FRAP) were used to verify the structural integrity and the phase behavior (median melting temperature, TC = 22 C) of the lipid assembly. The spatial confinement of individual Annexin V molecules was measured in three distinct phase regions: (1) a homogenous liquid crystalline phase region (Lα) in which Annexin V was unconfined (≥ 25 C), (2) a two-phase region (Lα + gel-phase-Pβ′) in which Annexin V displayed intermediate confinement (24 - 20 C), and (3) a gel-phase region (Pβ′) with included nanoscopic domains that are enriched with PS and surround a single Annexin V TM protein (19 - 16 C); the mobility of Annexin V in these domains is highly confined. At early time lags, Annexin V moves with apparent Brownian-like behavior at all temperatures but the diffusion coefficients have very different magnitudes and temperature dependence. A possible mechanism for nanoscopic domain formation will be discussed.

Effect of Salts on the Phase Behavior and the Stability of Nano-Emulsions with Rapeseed Oil and an Extended Surfactant

For many decades, the solubilization of long-chain triglycerides in water has been a challenge. A new class of amphiphiles has been created to overcome this solubilization problem. The so-called "extended" surfactants contain a hydrophilic-lipophilic linker to reduce the contrast between the surfactant-water and surfactant-oil interfaces. In the present contribution, the effects of different anions and cations on the phase behavior of a mixture containing an extended surfactant (X-AES), a hydrotrope (sodium xylene sulfonate, SXS), water, and rapeseed oil were determined as a function of temperature. Nanoemulsions were obtained and characterized by conductivity measurements, light scattering, and optical microscopy. All salting-out salts show a transition from a clear region (O/W nanoemulsion), to a lamellar liquid crystalline phase region, a clear phase (bicontinuous L(3)), and again to a lamellar liquid crystalline phase region with increasing temperature. For the phase diagrams with NaSCN and Na(2)SO(4), only one clear region (O/W nanoemulsion) was observed, which turns into a lamellar phase region at elevated temperatures. Furthermore, the stability of the nanoemulsions was investigated by time-dependent measurements: the visual observation of phase separation, droplet size by dynamic light scattering (DLS), and optical microscopy. The mechanism of the different phase transitions is also discussed.

The effect of a phase transition on single molecule tracks of Annexin V in cushioned DMPC assemblies

Using single molecule imaging, this study describes the phase behaviour and mobility of individual transmembrane (TM) proteins and compares those results with the bulk phase behaviour of the biomimetic membrane in which they have been incorporated. To accomplish this a TM protein, Annexin V, was incorporated into a cushioned planar supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/L-α-lysophosphatidyl-serine (Brain-PS) biomimetic assembly and its mobility between 30 and 16 °C was measured. Fluorescence microscopy and Fluorescence Recovery After Photobleaching (FRAP) were used to verify the structural integrity and the phase behaviour (median melting temperature, TC = 22 °C) of the lipid assembly. The spatial confinement of individual Annexin V molecules was measured in three distinct phase regions: (1) a homogeneous liquid crystalline phase region (Lα) in which Annexin V was unconfined (≥25 °C), (2) a two-phase region (Lα + gel-phase-Pβ′) in which Annexin V displayed intermediate confinement (24–20 °C), and (3) a gel-phase region (Pβ′) with included nanoscopic domains that are enriched with PS and surround a single Annexin V TM protein (19–16 °C); the mobility of Annexin V in these domains is highly confined. At early time lags, Annexin V moves with apparent Brownian-like behaviour at all temperatures but the diffusion coefficients have very different magnitudes and temperature dependence. A possible mechanism for nanoscopic domain formation will be discussed.

Phase Behavior and Hydrated Solid Structure in Lysophospholipid/Long-chain Alcohol/Water System and Effect of Cholesterol Addition

Phase behavior in lysophospholipid/long-chain alcohol/water system at 80°C was investigated using hexanol and oleyl alcohol as the long-chain alcohol. Similarly to hydrophilic surfactant, a micellar phase in a lysophospholipid/water system transitioned to a lamellar liquid-crystalline phase by the addition of long-chain alcohol. In the oleyl alcohol system the lamellar liquid-crystalline phase was observed in wider region compared to the hexanol system. The effect of cholesterol addition on the phase behavior was also studied. The region of liquid-crystalline phase and (reverse micellar + liquid-crystalline + water) phase shifted towards higher lysophospholipid concentrations. The structure of hydrated solid as well as the transition between lamellar liquid-crystalline phase and hydrated solid was analyzed by X-ray scattering measurement and differential scanning calorimetry measurement. It was revealed that the hydrated solid was α-type crystals with lamellar structure. The hydrated solid (gel)-liquid crystal transition temperature gradually decreased with increasing oleyl alcohol concentration and the decrement was enhanced by the addition of cholesterol.

Phase behavior and viscous properties of cetyltrimethylammonium bromide and sodium dodecyl sulfonate aqueous mixtures

Phase behavior of cetyltrimethylammonium bromide (CTAB)/sodium dodecyl sulfonate (AS)/water systems at 318.15 K with the total surfactant mole fraction x T ≤ 0.020 was investigated. In addition to the seven phase regions in the lower concentration range, two new phase regions, i.e. the hexagonal liquid crystalline phase region and its adjacent aqueous two-phase region were obtained in the higher concentration range. Shear viscosities of some isotropic single-phase systems, aqueous two-phase systems and lamellar liquid crystalline systems were measured. The experimental results indicate that at either isotropic single-phase region, under certain x T, there exists one shear viscosity maximum peak. As x T increases, the shear viscosity maximum peak shifts to the position far from the equimolar ratio of CTAB and AS, and meanwhile the value of the shear viscosity maximum peak increases. At each x T, the value of shear viscosity peak at the isotropic single-phase region with excess AS is less than that at the isotropic single-phase region with excess CTAB. The rheological behavior of the isotropic single-phase systems around the shear viscosity peak and that of lamellar liquid crystalline systems are complicated. Thixotropic, antithixotropic and complex thixotropic behaviors were all observed for these systems. Experimental results illustrate that both the isotropic single-phase systems and lamellar liquid crystalline systems located at position very close to the boundaries of the aqueous two-phase systems, as well as the coexisted phases in aqueous two-phase systems are not very viscous. When x T ≤ 0.005, their shear viscosities are usually several to dozens mPa s. In order to understand the rheological behaviors of the mixed systems, TEM micrographs of some isotropic single-phase systems and aqueous two-phase systems were investigated.

Novel Discrete Micellar Cubic Phase From a Mixture of GMO/Ethanol/Water

During the reconstruction the ternary phase diagram of glycerol monooleate (GMO)/ethanol/water, we detected a novel structure not previously seen. The new phase, denoted QL (micellar cubic liquid), is located within the 49–54 wt.-% water/41–33 wt.-% GMO binary mixture line and at 10–13 wt.-% EtOH in a small island within the phase diagram close to the cubic liquid-crystalline phase region. The QL phase is transparent (not tinted), of a low viscosity (36.6 Pa s), non-birefringent, and stable at room temperature. Evidence from severe centrifugation, synchrotron small-angle X-ray scattering (SAXS) measurements, and rheological behavior revealed that the sample is a single phase. SAXS reflections suggest that two types of domain may coexist. The symmetry of the QL phase is Pm3n. A cubic micellar structure is the dominant mesostructure of this unique sample. Cryo-TEM images show highly ordered domains with cubic symmetry, of lattice parameter 103 ± 2 Å. A possible transformation pathway to the QL phase is a ‘rupture and refusion’ mechanism, as the phase seems to have discontinuous symmetry.

Effects of pressure-induced membrane phase transitions on inactivation of HorA, an ATP-dependent multidrug resistance transporter, in Lactobacillus plantarum.

The effects of pressure on cultures of Lactobacillus plantarum were characterized by determination of the viability and activity of HorA, an ATP-binding cassette multidrug resistance transporter. Changes in the membrane composition of L. plantarum induced by different growth temperatures were determined. Furthermore, the effect of the growth temperature of a culture on pressure inactivation at 200 MPa was determined. Cells were characterized by plate counts on selective and nonselective agar after pressure treatment, and HorA activity was measured by ethidium bromide efflux. Fourier transform-infrared spectroscopy and Laurdan fluorescence spectroscopy provided information about the thermodynamic phase state of the cytoplasmic membrane during pressure treatment. A pressure-temperature diagram for cell membranes was established. Cells grown at 37 degrees C and pressure treated at 15 degrees C lost >99% of HorA activity and viable cell counts within 36 and 120 min, respectively. The membranes of these cells were in the gel phase region at ambient pressure. In contrast, cells grown at 15 degrees C and pressure treated at 37 degrees C lost >99% of HorA activity and viable cell counts within 4 and 8 min, respectively. The membranes of these cells were in the liquid crystalline phase region at ambient pressure. The kinetic analysis of inactivation of L. plantarum provided further evidence that inactivation of HorA is a crucial step during pressure-induced cell death. Comparison of the biological findings and the membrane state during pressure treatment led to the conclusion that the inactivation of cells and membrane enzymes strongly depends on the thermodynamic properties of the membrane. Pressure treatment of cells with a liquid crystalline membrane at 0.1 MPa resulted in HorA inactivation and cell death more rapid than those of cells with a gel phase membrane at 0.1 MPa.

The Phase Behavior and the Structural Properties of Triton X-100/n-C8H17OH/PEG1000aq System

The phase behavior and the structural properties of Triton X-100/n-C8H17OH/PEG1000aq system indicate that with increasing PEG1000, the partial phase diagram can be simplified, i.e. the lamellar liquid crystalline phase region (LLC) is gradually reduced. In Triton X-100 micelles and Triton X-100/n-C8H17OH/PEG1000aq O/W microemulsion droplets, PEG1000 molecules can locate either in the surfactant interfacial layer or be adsorbed on this layer. In the LLC region, PEG1000 molecules exist in the aqueous layer or in the amphiphile bilayer. This collocation of the surfactant molecules results in less order and reduced stability of the LLC phase.

STUDIES ON THE PHASE DIAGRAM OF THE SURFACTANT/1-PENTANOL / WATER TERNARY SYSTEM II: THE LIQUID CRYSTALLINE PHASE

ABSTRACT The phase behavior of liquid crystalline in the ternary system of dodecyl dimethyl ammonium hydroxyl propyl sulfonate(DDAHPS)/1pentanol(C5HnOH) / water deuteron(D2O) has been investigated by polarizing optical microscopy, 2H NMR spectroscopy methods. The results indicate that two kinds of liquid crystals (the lamellar, and the hexagonal) exist in the liquid crystalline phase region. In this paper, we also use the polarized Raman spectroscopy method to measure the values of the order/ disorder parameters and the values of the environment polarity parameters for the samples selected from the liquid crystalline phase region, and compare these two parameters of the samples with those of solid state DDAHPS and liquid state pentan-l-ol.

Mixing behavior of saturated short-chain phosphatidylcholines and fatty acids: Eutectic points, liquid and solid phase immiscibility, non-lamellar phases

Phase diagrams of the hydrated pseudo-binary mixtures dilauroylphosphatidylcholine (DLPC)/lauric acid (LA) and dimyristoylphosphatidylcholine (DMPC)/myristic acid (MA) have been constructed using high-sensitivity DSC and time-resolved X-ray diffraction. They are of a different type compared to those of the longer chain phosphatidylcholine (PC)/fatty acid (FA) mixtures, the latter being of maximum azeotropic point type. Eutectic points were distinguished in the phase diagrams, at 75 mol% MA and 49°C for the DMPC/MA mixture, and at ca. 67 mol% LA and 29°C for the DLPC/LA mixture. Regions of liquid–liquid and solid–solid phase separation have been located according to the shape of the phase diagrams and observed by X-ray diffraction. Limited regions (2–4°C) of liquid–liquid phase immiscibility exist at compositions with slightly prevailing fatty acid molar content. For instance, at 67 mol% MA, a phase separation between L α phase enriched in DMPC and H II phase enriched in MA takes place in the temperature range 51–55°C. Solid phase immiscibility is detected between 60 and 90 mol% fatty acid. The studied PC/FA mixtures form compound subgel polymorphic phases (one in the DMPC/MA mixture, with DMPC/MA 1:2 molar stoichiometry, and two in the DLPC/LA mixture, with about 40 and 60 mol% LA, respectively) upon low-temperature equilibration. In the liquid crystalline phase region, non-lamellar phases dominate the phase diagrams, especially in their fatty acid-rich part. With increasing FA content, the nonlamellar phases arrange in the sequence: bicontinuous cubic phases (Ia3d, Pn3m, Im3m)→hexagonal phase (H II)→micellar cubic phase (Fd3m)→isotropic phase (I). With the eutectic composition (75 mol% MA), only H II phase is detected above the melting transition in the DMPC/MA mixture. At higher FA content (85 mol%), micellar cubic phase of space group Fd3m form in the two PC/FA mixtures. At lower FA content (<75 mol%), at least three cubic phases (Ia3d, Pn3m, Im3m) form. The order of their appearance with increasing temperature varies with the PC/FA ratio. They exist either as single phases or concurrently to the H II phase.

The influence of liquid crystalline phases on drug percutaneous absorption. II. Permeation studies through excised human skin.

The influence of liquid crystalline (LC) phases on the percutaneous absorption of a model compound (ploxicromil; PXC) was studied with the use of the phase diagram for the surfactant, oil, and water comprising the vehicles. Two separate sets of vehicles, representing two different tie lines lying in the L1 + LC phase region, were prepared in which the concentration of LC was varied over the range 0 to 100% along each tie line. In vitro permeation studies of PXC from these systems were conducted using excised human skin and the flux values determined as a function of the percentage LC present in the vehicles. In virtually all cases, the flux reached a peak at 5-10% LC and then decreased significantly as the fraction of LC present increased further. The pattern of behavior observed is discussed in terms of current theories describing membrane-controlled and vehicle-controlled diffusion, none of which adequately model the results obtained.

Phase equilibria and microemulsion structure for a triple-chained soap: Sodium di-2-butyldecanoate

An alkyl carboxylate with a very voluminous hydrophobic part, sodium di-2-butyldecanoate, was prepared and its phase behavior investigated in mixtures with water (25–100°C) and in mixtures with both water and decane (25°C). Furthermore, the homogeneous phases formed were characterized on the basis of NMR and self-diffusion studies. In the two-component water-surfactant system there is an extensive lamellar liquid crystalline phase region as well as two isotropic solution regions, one at lower and one at higher surfactant concentrations than the lamellar liquid crystalline region. The latter solution phase has unusual features in respect to location in the phase diagram, solution structure, and the formation of metastable lamellar phase, transforming slowly into isotropic solution. Sodium di-2-butyldecanoate can mix equal amounts of water and hydrocarbon into homogeneous solution and the water-to-hydrocarbon ratio of the microemulsions can be varied over very large ranges. Depending on composition, the microemulsion microstructure is of the water droplet-in-oil type or bicontinuous.