Gel to liquid-crystal transitions in synthetic amphiphile vesicles (original) (raw)
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The effects of chain flexibility on the properties of vesicles formed from di-n-alkyl phosphates
Recueil des Travaux Chimiques des Pays-Bas, 1996
This paper describes a study of the effects of chain flexibility and chain packing on the properties of vesicles formed from sodium di-n-alkyl phosphates. Three di-n-alkyl phosphates with a constant chain length but with different degrees of unsaturation have been synthesized: dioleyl phosphate (DOP) and dielaidyl phosphate (DEP) having, respectively, a cis and a trans double bond at C-9 and the saturated distearyl phosphate (DSP). These surfactants form vesicles, as confirmed by transmission electron microscopy (EM). The gel to liquid-crystalline phase transition was studied using both fluorescence polarization and differential scanning microcalorimetry. According to fluorescence polarization, using trans,trans,trans-1,6-diphenyl-hexa-1,3,5-triene (DPH) as a probe, DSP vesicles undergo a cooperative transition from a gel to a liquid-crystalline state at 72°C. The polarization of the probe captured in DOP or DEP vesicles decreased gradually in the temperature range 0-40°C, indicating a non-cooperative phase transition. It appears that the vesicle bilayer is in a gel state below 0°C and in a liquid-crystalline state above 40°C. A temperature-dependent 31 P NMR study failed to identify the exact phase-transition temperature. The effect of the fusogenic cation Ca 2+ was studied qualitatively using EM. Calcium induces fusion of DEP vesicles but, within a short time, tubules are formed which are most probably anhydrous crystals of the calcium salts. For DSP vesicles the latter process is extremely fast and fused vesicles cannot be detected. In contrast, DOP vesicles fuse under the influence of calcium, but no crystallization takes place. The fused DOP vesicles are stable for more than one week in the presence of 4 mM Ca 2+ stored at room temperature or at 60°C. Addition of EDTA to DOP vesicles leads to chelation of the calcium ions and to a transition to multilamellar vesicles.
Characterization of vesicles prepared with various non-ionic surfactants mixed with cholesterol
Colloids and Surfaces B: Biointerfaces, 2003
The vesicles (niosomes) prepared with hydrated mixture of various non-ionic surfactants and cholesterol were studied. The bilayer formation was characterized by X-cross formation under light polarization microscope and the ability of the vesicles to entrap water-soluble substance. Membrane rigidity was measured by means of mobility of fluorescence probe as a function of temperatures. The entrapment efficiencies of the vesicles and microviscosities of the vesicular membrane depended on alkyl chain length of non-ionic surfactants and amount of cholesterol used to prepare vesicles. The stearyl chain (C 18) non-ionic surfactant vesicles showed higher entrapment efficiency than the lauryl chain (C 12) non-ionic surfactant vesicles. Cholesterol was used to complete the hydrophobic moiety of single alkyl chain nonionic surfactants for vesicle formation. Niosome prepared with Tween 61 bearing a long alkyl chain and a large hydrophilic moiety in the combination with cholesterol at 1:1 molar ratio was found to have the highest entrapment efficiency of water soluble substances.
1995
Interactions of both cationic and anionic surfactants with vesicles formed by dimethyldioctadecylammonium bromide (DOAB) and by sodium didodecylphosphate (DDP) have been probed using differential scanning microcalorimetry. The scans show that the surfactants are incorporated into the vesicle bilayers. The change in the melting temperature, Tm, characterising the gel to liquid-crystal transition depends on whether the charges on the head groups of surfactant ion and vesicular ion have either similar or opposite signs.
Spontaneous Vesicles Formed in Aqueous Mixtures of Two Cationic Amphiphiles
Langmuir, 2000
The spontaneous formation of vesicles was detected in aqueous mixtures of two cationic amphiphiles: the double-tailed didodecyldimethylammonium bromide, DDAB, and the single-tailed dodecyltrimethylammonium chloride, DTAC. These aggregates appear in a high-dilution region of the system, intermediate between those where monomers and micelles prevail, and are most easily formed at a considerable excess of the single-chained surfactant (DTAC/DDAB molar ratios ≈ 2-20). Vesicles were characterized at 25°C by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light-scattering (DLS) measurements: they present a well-defined contour, are mostly spherical and unilamellar, but show a large size polydispersity, with the more frequent population distributions of diameters from ≈40-50 to ≈500-600 nm. Apart from intact vesicles (and in most cases coexisting with them), vesicles with ruptured membranes, small bilayer disks (probably discoidal micelles, rarely found), and globular micelles were also visualized by cryo-TEM. Ruptured vesicles and disks were assigned to intermediate structures between intact vesicles and globular micelles. We propose that the main factor which drives the appearance of vesicles in this bicationic system is the difference in the spontaneous curvature (or packing parameter) of the two long-chained surfactant ions.
Journal of Dispersion Science and Technology, 2018
We report herein, the aggregation behavior of 3, 4-di(dodecyloxy)benzoic acid-4-hydroxy phenyl ester (DDBE), a synthetic amphiphile and a true non-ionic surfactant system as per the geometrical considerations. The true surfactant nature of the system stems from its hydrophilic-lipophilic-balance (HLB ¼ 4.7), comparable to that of Span-60, also a true non-ionic surfactant. This compound undergoes spontaneous vesicle formation in THF:water binary solvent mixtures which further underwent fission at lower DDBE concentrations and fusion at higher concentrations, leading to giant vesicles of the order of 3000 nm. These vesicles are sensitive to the polarity of their environment. The predominant mode of interaction as observed from the molecular dynamics simulations were found to be p-p stacking with the phenyl rings of the molecule. Further, the system, upon complete extraction into water, formed spherical aggregates of size 50 nm based on the good solvent-poor solvent combination as the necessary condition for the vesicle formation.
Journal of Polymer Science Part A: Polymer Chemistry, 1995
Certain phosphate bipolar amphiphiles, both monomeric (I and 11) and polymeric or rather oligomeric (poly-I and poly-11), were used as basic materials for the preparation of simple and mixed vesicles. Specifically, it was found that oligomeric phosphate bipolar amphiphiles form stable vesicles in aqueous media. The same oligomeric bolaamphiphiles in mixture with their monomeric counterparts also form stable mixed vesicles with sonication; they are relatively less stable with the "thin film method." Furthermore, it was shown that the method of spanning the membrane of didodecylphosphate vesicles with the dipolar amphiphile I1 is not effective for enhancing stability.
Langmuir, 2005
Two N-acyl amino acid surfactants, sodium N-(11-acrylamidoundecanoyl)-glycinate (SAUG) and L-alaninate (SAUA), were synthesized and characterized in aqueous solution. A number of techniques, such as surface tension, fluorescence probe, light scattering, and transmission electron microscopy were employed for characterization of the amphiphiles in water. The surface and interfacial properties were measured. The amphiphiles have two critical aggregation concentrations. The results of surface tension and fluorescence probe studies suggested formation of bilayer self-assemblies in dilute aqueous solutions of the amphiphiles. The magnitudes of free energy change of aggregation have indicated that bilayer formation is more favorable in the case of SAUG. Steady-state fluorescence measurements of pyrene and 1,6-diphenyl-1,3,5-hexatriene (DPH) were used to study the microenvironment of the molecular selfassemblies. Temperature-dependent fluorescence anisotropy change of DPH probe revealed phase transition temperature of the bilayer self-assemblies. The effects of pH on the structure of the self-assemblies of SAUG and SAUA have been studied. The role of intermolecular hydrogen bonding between amide groups upon aggregation toward microstructure formation in solution has been discussed. Circular dichroism spectra suggested the presence of chiral aggregates in an aqueous solution of SAUA. The transmission electron micrographs revealed the presence of closed spherical vesicles in aqueous solutions of the amphiphiles. Dynamic light scattering measurements were performed to obtain average size of the aggregates. Kawasaki, H.; Souda, M.; Tanaka, S.; Nemoto, N.; Karlsson, G.; Almgren, M.; Maeda, H.
Surfactant Effects on Lipid-Based Vesicles Properties
Journal of pharmaceutical sciences, 2018
Understanding the effect of surfactant properties is critical when designing vesicular delivery systems. This review evaluates previous studies to explain the influence of surfactant properties on the behavior of lipid vesicular systems, specifically their size, charge, stability, entrapment efficiency, pharmacokinetics, and pharmacodynamics. Generally, the size of vesicles decreases by increasing the surfactant concentration, carbon chain length, the hydrophilicity of the surfactant head group, and the hydrophilic-lipophilic balance. Increasing surfactant concentration can also lead to an increase in charge, which in turn reduces vesicle aggregation and enhances the stability of the system. The vesicles' entrapment efficiency not only depends on the surfactant properties but also on the encapsulated drug. For example, the encapsulation of a lipophilic drug could be enhanced by using a surfactant with a low hydrophilic-lipophilic balance value. Moreover, the membrane permeabilit...
Size and Charge Modulation of Surfactant-Based Vesicles
The Journal of Physical Chemistry B, 2011
Nonstoichimetric mixtures of two oppositely charged surfactants, such as sodium dodecylsulfate and hexadecyltrimethylammonium bromide or tetradecyltrimethylammonium bromide and tetraethylammonium perfluorooctanesulfonate, a fluorinated species, form vesicles in dilute concentration regimes of the corresponding phase diagrams. Vesicles size and charge density are tuned by changing the mole ratio between oppositely charged species, at fixed overall surfactant content. They are also modulated by adding neutral electrolytes, or raising T. In the investigated regions, mixtures made of sodium dodecylsulfate/hexadecyltrimethylammonium bromide show ideality of mixing, the other non ideality and phase separation. The formation of unilamellar vesicles occurs in the sodium dodecylsulfate/hexadecyltrimethylammonium bromide mixture, but not in the other. DLS, viscosity, and electrophoretic mobility quantified the above effects. Surface charge density, surface tension, elasticity, and osmotic pressure concur to the stability of unilamellar vesicles and a balance between the above contributions is demonstrated. The results are relevant for practical applications of vesicles as carriers in biomedicine.