Construction of asymmetric cell-sized lipid vesicles from lipid-coated water-in-oil microdroplets

We present a simple, rapid, and robust method for preparing asymmetric cell-sized lipid bilayer vesicles using water-in-oil (W/O) microdroplets transferred through an oil-water interface. The efficiency for producing cell-sized model membranes is elucidated in relation to the vesicular size and the weight of contained water-soluble molecules. We demonstrate the biological asymmetric nature and the formation of lipid raft microdomain structures using fluorescence microscopy.     

Budding dynamics of multicomponent tubular vesicles

Real-time budding dynamics of multicomponent, tubular lipid vesicles was investigated. By using a fluorescence microscope, three typical growth modes of the buds were observed, corresponding, respectively, to bud growth through coalescence between flat patches, a bud and a patch, as well as that of two buds. The spatial and temporal scales measured in the observation were used to estimate the bending rigidity of the membrane. In the late stage, the continuing coalescence between the buds resulted in large shape deformation of the vesicles, from tubular to spherical vesicles, and the number of the buds decayed with time as N approximately t-2/3. This scaling relation was observed for the first time in experiment and confirmed early theoretical predictions. Our observation showed a difference between the diffusivity of the buds on the lipid membrane and that of the embedded membrane proteins.     

Reversible photoswitching in a cell-sized vesicle

A photosensitive amphiphilic molecule can switch the shape of an assembled vesicle as determined by microscopic observation. Photoisomerization induces a change in membrane fluctuation behavior or a morphological transition between ellipsoid and bud shapes, depending on the asymmetrical degree of the initial shape. The mechanism of this reversible photoswitching in the vesicle morphology is interpreted in terms of a change in the effective cross-sectional area of the photosensitive molecule.     

Deposition of a photosensitive complex within a lecithin bilayer lipid membrane

In this paper the phenomenon of a photosensitive ion complex of Brilliant Yellow and ferric ions formation in the electrolyte phase and its subsequent deposition within a bilayer lipid membrane (BLM) is described. Deposition of light sensitive complex into the BLM considerably increases its mechanical stability and drastically changes its electrochemical and photoelectrical properties as well.     

Formation and coexistence of the micelles and vesicles in mixed solution of cationic and anionic surfactant

In the aqueous mixtures of sodium alkylcarboxylate and alkyltrimethylammonium bromide, large unilamelar vesicles can be formed spontaneously or by sonication as the total carbon number in the HC chains is 19 (or larger). Vesicle formation can be influenced by changes of pH, molar ratio of the two surfactant components, and the polar head group of cationic surfactant. Micelles may coexist with the vesicles in these mixed systems. The larger hydrodynamic radius (200 nm) and aggregation number (800) illustrate that the shape of the micelle in 1:1 C₉H₁₉COONa–C₁₀H₂₁N(CH₃)₃Br is rod-like. In some mixed systems, the micelles can be transformed into stable vesicles by sonication — a phenomenon revealed for the first time. The surface-chemical properties of these catanionic surfactant solutions and the stabilities of vesicle have been studied systematically.     

Chemical potential of a nonionic surfactant in solution

The chemical potential of a surfactant in solution can be calculated from the Gibbs adsorption equation when the surface excess of the surfactant and the surface tension of the solution as a function of surfactant concentration are known. We have investigated a solution of the nonionic surfactant 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the polar solvent 3-hydroxypropionitrile at concentrations below and above the critical micelle concentration (cmc). Neutral impact collision ion scattering spectroscopy was applied for the direct measurement of the surface excess of POPC as a function of concentration. The Gibbs adsorption equation was applied in conjunction with surface tension measurements to evaluate the chemical potential and the activity coefficients of POPC, respectively. We find that the solution shows ideal behavior up to the cmc and that the chemical potential remains constant at concentrations larger than the cmc.     

Formation of reverse vesicles in silicone surfactant systems

This study deals with the formation of reverse vesicles based on the phase behavior of silicone surfactants. The surfactants, polyoxyethylene–polydimethylsiloxane and polyoxyethylene–polyoxypropylene–polydimethylsiloxane copolymer, were found to form lamellar liquid crystal phases in three different types of silicone oil upon the addition of a certain amount of water. A conventional method in which reverse vesicles are prepared by physically dispersing this lamellar liquid crystal phase in oil was employed in addition to a technique based on a temperature-induced phase transition. The particle sizes and stabilities of the resulting reverse vesicles were evaluated.     

Formation of vesicles in block copolymer-fluorinated surfactant complexes

Spherical micellar aggregates have been obtained in chloroform by mixing poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers with perfluorinated surfactants (FS) bearing a carboxylic acid head. These micellar aggregates are resulting from the self-assembly of the insoluble P4VP/fluorinated complexes into a core surrounded by the soluble PS coronal chains. Their characteristic features have been studied as a function of various parameters including the composition of the PS-b-P4VP copolymer, the tail length of the fluorinated surfactant, the 4VP/FS molar ratio, the number of carboxylic acid group (1 or 2) on the surfactant, the presence of the PS block and of the fluorine atoms on the surfactant. Dilution of these initial micellar aggregates triggers a morphological reorganization resulting in the formation of more stable vesicles. The extent of this morphological transition is related to the solubility of the P4VP/fluorinated complexes during the dilution process. This transition is complete for short P4VP/FS complexes, incomplete for long P4VP/FS complexes, and not observed whenever an alpha,omega-difunctional FS is used in P4VP/FS complexes, leading to a cross-linked core. Finally, the spheres-to-vesicles transition has been advantageously used in order to encapsulate molecules, as demonstrated by confocal fluorescence microscopy.     

Migration of a cationic polymer between lipid vesicles

The adsorption of a synthetic polycation, poly(N-ethyl-4-vinylpyridinium bromide) (PEVP), on the surface of bilayer lipid vesicles (liposomes) and the migration of adsorbed macromolecules between the liposomes are studied. Liposomes of three types are used, including (1) traditional two-component liposomes composed of neutral phosphatidylcholine (PC) and anionic cardiolipin (CL); (2) three-component liposomes consisting of PC, CL, and cationic dicetyldimethylammonium bromide (DCMAB); and (3) anionic PC/CL liposomes with a nonionic surfactant, poly(ethylene oxide)-cetyl alcohol ether (Briij 58), incorporated into their bilayers. The adsorption of PEVP on the surface of PC/CL liposomes is accompanied by their aggregation. Using the fluorescence method, it is shown that the units (segments) of the polycation undergo partial redistribution between the liposomes inside the aggregates formed from PC/CL liposomes (with and without a fluorescent label) and PEVP. On the contrary, three-component PC/CL/DCMAB and PC/CL/Briij liposomes are not aggregated, even with the complete neutralization of their charges by adsorbed PEVP. In both cases, the migration of PEVP molecules between individual (nonaggregated) liposomes is observed. Possible reasons for the aggregative stability of the three-component PC/CL/DCMAB and PC/CL/Briij liposomes and the mechanism of interliposome migration of PEVP in such systems are discussed.     

Preparation and characterization of bolaform surfactant vesicles

Vesicular formulations (liposomes and niosomes) play an increasingly important role since they can be used as drug delivery and targeting systems. We described the formation of two niosomal systems based on synthetic bolaform surfactants (4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecanedioc acid diamide (BD-16) and alpha,omega-(4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecane (BC-16). Systems containing BD-16 or BC-16 and different amount of cholesterol (CH) were prepared by aqueous dispersion of films, followed by examination of methylene blue (MB) entrapment, particle size and morphology. Indeed, we also studied the hydration in the distilled water and physiological solution, in order to investigate the complexing ability on vesicle formation. The results obtained in this study show a high encapsulation capacity and this ability and the size depends on cholesterol content.     

Simulations of lipid transfer between a supported lipid bilayer and adsorbing vesicles

Recent experiments demonstrate transfer of lipid molecules between a charged, supported lipid membrane (SLB) and vesicles of opposite charge when the latter adsorb on the SLB. A simple phenomenological bead model has been developed to simulate this process. Beads were defined to be of three types, ‘n’, ‘p’, and ‘0’, representing POPS (negatively charged), POEPC (positively charged), and POPC (neutral but zwitterionic) lipids, respectively. Phenomenological bead–bead interaction potentials and lipid transfer rate constants were used to account for the overall interaction and transfer kinetics. Using different bead mixtures in both the adsorbing vesicle and in the SLB (representing differently composed/charged vesicles and SLBs as in the reported experiments), we clarify under which circumstances a vesicle adsorbs to the SLB, and whether it, after lipid transfer and changed composition of the SLB and vesicle, desorbs back to the bulk again or not. With this model we can reproduce and provide a conceptual picture for the experimental findings.     

The reactivity of substrate functionalized surfactant vesicles

The hydrolysis and thiolysis of active ester-functionalized cationic surfactant vesicles proceed without kinetic resolution of distinct exovesicular and endovesicular reactions.     

Redox-photosensitized reaction of indene using photosensitive surfactant in emulsion: dependence on oil droplet size and surfactant charge

A redox-photosensitized reaction of indene 2 using a photosensitive surfactant 1a in an oil-in-water emulsion proceeded efficiently to give alcohol 3 as a major product and is strongly influenced by the oil droplet size and surfactant charge.     

Use of a water solution of surfactant in Knoevenagel reaction

In reaction of vanillin with active methylene compounds in the presence of detergent Oksipav AP the corresponding substituted alkenes were formed in high yields.     

Application of mass spectrometry for study of the adsorption of multicomponent surfactant mixtures at the solid/solution interface

The selective adsorption of the components of a polydisperse gemini surfactant blend (alkylbenzenesulfonate-Jeffamine salt, ABSJ) in aqueous solution onto Berea sandstone, a reference material in enhanced oil recovery (EOR), was investigated. The individual adsorption isotherms of the four, benzene-ring containing ABSJ components with different alkyl chain lengths (ranging from decyl to tridecyl of the alkyl chain length) were simultaneously determined by using a four-channel electrospay ionization mass spectrometer (ESI-MS) for concentration analysis. This analytical device provided selective information (based on the differences in the mass to charge ratio) on the adsorption of each component in the mixed surfactant system. The overall isotherm obtained from the superposition of the individual isotherms determined by ESI-MS agreed well with the isotherm determined by UV spectrometry; the UV equipment is benzene-ring sensitive, irrespective of the alkyl chain length. The S-shaped isotherms reached a plateau at the critical micelle concentration. Longer-chain surfactants adsorbed preferentially over the short chain homologs, independently of solution concentration. This analytical device provided the net adsorption isotherm. Most analytical methods are not component selective, and thus they are not able to measure the individual isotherms in multicomponent solutions. Here, we report on a novel method which describes the selective determination of the individual adsorption isotherms of surfactants in a multicomponent mixture. The theoretical background of the method is described in detail.     

Heterogeneous molecular distribution in supported multicomponent lipid bilayers

Membrane domains contribute important structural and functional attributes to biological membranes. We describe the heterogeneous nanoscale distribution of lipid molecules within microscale membrane domains in multicomponent lipid bilayers composed of dipalmitoylphosphatidylcholine (DPPC), dilauroylphosphatidylcholine (DLPC), and cholesterol (chol). The lipids were labeled with the fluorescent lipid analogues Bodipy-PC and DiI-C20:0 to identify the distribution of individual membrane components. We used a near-field scanning optical microscope (NSOM) at room temperature to identify the nanoscale structures in the membrane. Simultaneous multicolor NSOM imaging at the emission maxima of the fluorescent analogues revealed a patchy distribution of Bodipy-PC and DiI-C20:0 indicative of phase separations in the bilayer. In a cholesterol-free system (DPPC/DLPC = 1:1), NSOM images proved that the two phosphatidylcholine molecules can coexist in domains at the micrometer level but form nanoscopic patches within the domains; DPPC occurs at the edge of the domains, whereas DLPC is present throughout the domains. In the presence of cholesterol (DPPC/DLPC = 7:3, chol = 18.9%), the two lipid molecules were more miscible but incomplete phase separations also occurred. The average domain sizes were 140-200 nm, well below the resolution capabilities of diffraction-limited light microscopy techniques; the domains were unresolvable by confocal microscopy. Our high-resolution NSOM studies of membrane domain behavior provide a better understanding of complex membrane phase phenomena in multicomponent biological membranes.     

Dynamic assembly of anionic surfactant into highly-ordered vesicles

A highly-efficient dynamic assembly method for the transformation of the initial spongy lamellar structure of concentrated linear alkylbenzene sulfonate, LAS, incorporated with sodium silicate, into spherulitic vesicles is presented. A combination of drag and pressure flows, via twin screw extrusion, was used to mitigate the ubiquitous viscoplasticity and the wall slip behavior of the anionic surfactant paste and gave rise to the dynamic assembly of stable vesicular nanostructures within a narrow size range, that was not possible with either pure drag or pure pressure flows. Concomitantly with the structure transformation of the paste during assembly under the combination of pressure and drag flows, significant changes in its viscoelasticity, i.e., order of magnitude increases in storage and loss moduli and magnitude of complex viscosity, were observed. The demonstrated dynamic assembly of stable vesicular nanostructures, with vesicle diameters within the relatively narrow range of 300-600 nm, from a commodity surfactant is relevant to myriad templating and encapsulation applications, as well as shedding light on the mechanisms of the deformation-induced planar lamellar to vesicle transformation of concentrated amphiphiles.     

Phase behavior of mixed solution of a glycerin-modified cationic surfactant and an anionic surfactant

The phase behavior of mixed solution of newly synthesized monoglycerylcetyldimethylammonium chloride (MGCA) and sodium octyl sulfate (SOS) in water was investigated by cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), differential scanning calorimetry (DSC), and fluorescence polarizing for evaluation of the microviscosity of bilayers. No precipitate was observed in the mixed solution except at concentrations below 20 mM over all mixing ratios, and stable vesicles were formed in a considerably wide range of mixing ratio, even at the equimolar ratio. Vesicles formed in aqueous 1/1 MGCA/SOS mixture were found to exhibit no phase transition, and fluorescence polarizing measurements showed that the vesicle bilayers have a high fluidity. This flexibility allows the bilayers to have a spontaneous curvature, and thus vesicles rather than flat lamellae can be stabilized in the mixture even at the equimolar ratio. In addition, because the glycerin group of MGCA interacts strongly with water, the hydration repulsion contributes to prevent the bilayers consisting of MGCA and SOS from adhering and flocculating even though the charge neutralization between MGCA and SOS occurs at the equimolar ratio.