Single-lamellar vesicles

Various forms of vesicles have been characterized, including single-walled (or single-lamellar) vesicles (SLVs) and multi-walled vesicles (MLVs) (see... 

Figure 3.2. Schematic representation of the sonication of mul-tilamellar vesicles to single-lamellar vesicles (not to scale)...

A droplet characterized by the presence at its surface of a lipid bi-molecular film (bi-layer) or series of concentric bi-layers. A vesicle can be single or multi-lamellar and stabilized by natural or synthetic surfactants. Multi-lamellar vesicles are also termed liposomes. See also Bi-molecular Film. 

If we come back to smaller (single-walled) vesicles, we are on more familiar ground. The experimental situation is nevertheless unresolved. Some believe that vesicles are always thermodynamically unstable, the stable state being the lamellar phase. Monodisperse vesicles of the size given by simple... 

HPTS fluorescence has been employed in the study of proton diffusion within inverted micelles [24], in liposomes [4a], in apomyoglobin and the inter-membranal hydration layers of multi-lamellar vesicles [4b]. The simplest case for analysis involves the HPTS molecule in the center of a sphere (inverted micelle, liposome) whose walls are impermeable to protons on the timescale of the experiment. This outer wall is therefore described by an additional reflective boundary condition. Inside such a sphere, even a single proton/anion pair ultimately reaches an equilibrium situation The long-time tail approaches a plateau, rather than decaying to zero. The smaller the radius of the sphere, the higher the expected asymptotic plateau. 

Replacement of the organic solvent by D2O yielded multi-lamellar structures with no high resolution characteristics. Sonica-tion of these suspensions led to the formation of single bilayered vesicles which contained either A -THG or CBD. In these vesicles no signals from the cannabinoid protons could be detected at concentrations of A -THC or CBD twice as high as those for which PMR signals are easily determined in CDCl solution (Fig. IB). 

J Suurkuusk, BR Lentz, Y Barenholz, RL Biltonen, TE Thompson. A calorimetric and fluorescent probe study of the gel-liquid crystalline phase transition in small, single-lamellar dipahnitoylphosphatidylcholine vesicles. Biochemistry 75 1393-1401 (1976). 

The effect characteristic of a multi-chain hydrophobe, that is, increase in the cmc and simultaneous decrease in the cloud point, appears to be inconsistent with the well-known HLB concept in surfactants. Tanford has pointed out that based on geometric considerations of micellar shape and size, amphiphilic molecules having a double-chain hydrophobe tend to form a bilayer micelle more highly packed rather than those of single-chain types ( ). In fact, a higher homologue of a,a -dialkylglyceryl polyoxyethylene monoether has been found to form a stable vesicle or lamellar micelle (9 ). Probably, the multi-chain type nonionics listed in... 

When lamellar phases are sheared, e.g. by flowing through a narrow tube, the membranes are disrupted and the resulting fragments close to form spherical shells, termed vesicles [4]. These vesicles can consist of a single shell... 

Figure 5.2 Top-diagramatic representation of a detergent molecule, (a) Single tailed (b) double tailed (c) zwitterionic (d) bolamphiphilic. Bottom - different types of surfactant aggregates in solution (A) monolayer (B) bilayer (C) liquid-crystallin phase lamellar (D) normal micelles (E) cylindrical micelles (hexagonal) (F) vesicles (liposomes) (G) reversed micelles.

Liquid crystals, liposomes, and artificial membranes. Phospholipids dissolve in water to form true solutions only at very low concentrations ( 10-10 M for distearoyl phosphatidylcholine). At higher concentrations they exist in liquid crystalline phases in which the molecules are partially oriented. Phosphatidylcholines (lecithins) exist almost exclusively in a lamellar (smectic) phase in which the molecules form bilayers. In a warm phosphatidylcholine-water mixture containing at least 30% water by weight the phospholipid forms multilamellar vesicles, one lipid bilayer surrounding another in an "onion skin" structure. When such vesicles are subjected to ultrasonic vibration they break up, forming some very small vesicles of diameter down to 25 nm which are surrounded by a single bilayer. These unilamellar vesicles are often used for study of the properties of bilayers. Vesicles of both types are often called liposomes.75-77... 

Transfersomes are vesicles prepared from lipids and an edge activator that might be a single-chain lipid or surfactant. The edge activator renders the vesicles elastic. As a result of the hydration force in the skin, elastic vesicles can squeeze through SC lipid lamellar regions [47], Transfersomes were much more effective than conventional liposomes when applied nonocclusively with respect to mass flow of lipid across the skin. After 8 h of transfersome application... 

Figure 21 Effect of macroscopic orientation on 3,P NMR spectra of PL membranes. (A) Multi-lamellar PL vesicles yield 31P NMR spectra that are characterised by an axially symmetric shielding tensor. If lamellar lipid membranes are oriented between glass plates, a single 3,P NMR signal is obtained for any given orientational angle between the membrane normal and the external magnetic field B0. 31P NMR spectra for (B) perpendicular and (C) parallel orientations are shown. Taken from Ref. [86].

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