Vesicles bilayer

Lipids also undergo rapid lateral motion in membranes. A typical phospholipid can diffuse laterally in a membrane at a linear rate of several microns per second. At that rate, a phospholipid could travel from one end of a bacterial ceil to the other in less than a second or traverse a typical animal ceil in a few minutes. On the other hand, transverse movement of lipids (or proteins) from one face of the bilayer to the other is much slower (and much less likely). For example, it can take as long as several days for half the phospholipids in a bilayer vesicle to flip from one side of the bilayer to the other. 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Antanavage, J., Cien, T. F., Ching, Y. D., Dunlap, L., Mueller, P., and Rudy, M. (1978). Formation and properties of cell-size single bilayer vesicles, Biophys. J., 21, A122. 

Brunner, J., Skrabal, P., and Hauser, H. (1976). Single bilayer vesicles prepared without sonication. Physico-chemical piwperlies, Biochim. Biophys. Acta. 455, 322-331. 

Q Studies using v- and t-SNARE ptoteins reconsti-mted into separate lipid bilayer vesicles have indicated that they form SNAREpins, ie, SNARE complexes that hnk two membranes (vesicles). SNAPs and NSF are required for formation of SNAREpins, but once they have formed they can apparently lead to spontaneous fusion of membranes at physiologic temperamre, suggesting that they are the minimal machinery required for membrane fusion. 

The lipid molecule is the main constituent of biological cell membranes. In aqueous solutions amphiphilic lipid molecules form self-assembled structures such as bilayer vesicles, inverse hexagonal and multi-lamellar patterns, and so on. Among these lipid assemblies, construction of the lipid bilayer on a solid substrate has long attracted much attention due to the many possibilities it presents for scientific and practical applications [4]. Use of an artificial lipid bilayer often gives insight into important aspects ofbiological cell membranes [5-7]. The wealth of functionality of this artificial structure is the result of its own chemical and physical properties, for example, two-dimensional fluidity, bio-compatibility, elasticity, and rich chemical composition. 

Liposomes, which are lipid bilayer vesicles prepared from mixtures of lipids, also provide a useful tool for studying passive permeability of molecules through lipid. This system has, for example, been used to demonstrate the passive nature of the absorption mechanism of monocarboxylic acids [131]. Liposome partitioning of... 

FIG. 2 A zone model of bilayer vesicles consisting of amphiphilic lipid molecules. 

Phospholipids or similar water-insoluble amphiphilic natural substances aggregate in water to form bilayer liquid crystals which rearrange when exposed to ultrasonic waves to give spherical vesicles. Natural product vesicles are also called liposomes. Liposomes, as well as synthetic bilayer vesicles, can entrap substances in the inner aqueous phase, retain them for extended periods, and release them by physical process. 

Liposomes have been, and continue to be, of considerable interest in drug-delivery systems. A schematic diagram of their production is shown in Fig. 10. Liposomes are normally composed of phospholipids that spontaneously form multilamellar, concentric, bilayer vesicles, with layers of aqueous media separating the lipid layers. These systems, commonly referred to as multilamellar vesicles (MLVs), have diameters in the range of 15 pm. Sonication of MLVs... 

Davenport LD, Knutson JR, Brand L (1986) Excited-state proton transfer of equilenin and dihydro equilenin inreractions with bilayer vesicles. Biochemistry 25 1186-1195... 

All of the above-mentioned examples describe organosiloxane hybrid sheet-like structures. However, cell-mimicry requires spherical structures that can form an inner space as a container. Liposomes and lipid bilayer vesicles are known as models of a spherical cell membrane, which is a direct mimic of a unicellular membrane. However, the limited mechanical stability of conventional lipid vesicles is often disadvantageous for some kinds of practical application. 

Construct a liposome by dissolving the desired lipids in chloroform to homogenize fully the mixture, drying them to remove solvent, and using any established method of forming bilayer vesicles in aqueous solution (i.e., sonication see Section 1, this chapter). 

The kinetic behavior of these systems is consistent with the supposition that substrate and/or catalyst molecules are freely moving around among the micelles and the bilayer vesicles much faster than the rate of reaction. However, Kunitake and Sakamoto (1978) showed that the rate of the intravesicle reaction was much faster than that of the intervesicle reaction, when p-nitrophenyl palmitate was used as substrate. Table 6 compares the rates of the intra- and intervesicle reactions in 2C12N+2C, bilayer and in CTAB micelles. A large rate difference (> 200-fold) was found in the bilayer system for the combination of cholest-Im and p-nitrophenyl palmitate. Slow transfer among vesicles of tightly bound p-nitrophenyl palmitate causes the rate difference. 

S. J. Morris, D. Bradley, and R. Blumenthal, The use of cobalt ions as a collisionsl quencher to probe surface charge and stability of fluorescently labeled bilayer vesicles, Biochim. Biophys. Acta 818, 365-372 (1985). 

Strauss G, Schurtenberger P, Hauser H. The interaction of saccharides with lipid bilayer vesicles stabilization during freeze-thawing and freeze-drying. Bio-chim Biophys Acta 1986 858 169. 

Figure 1. Various physical states of phospholipids in aqueous solution. Note the following features (a) phospholipids residing at the air/water interface are arranged such that their polar head groups maximize contact with the aqueous environment, whereas apolar side chains extend outward toward the air (b) solitary phospholipid molecules remain in equilibrium with various monolayer and bilayer structures (c) bilayer vesicles and micelles remain in equilibrium with solitary phospholipid molecules, provided that the total lipid content exceeds the critical micelle concentration.

AA Omran, K Kitamura, S Takegami, A-AY El-Sayed, M Abdel-Mottaleb. Determination of partition coefficients of diazepam and flurazepam between phosphatidylcholine bilayer vesicles and water by second derivative spectro-photometric method. J Pharm Biomed Anal 25 319-324, 2001. 

Fendler JH (1982) Membrane mimetic chemistry characterizations and applications of micelles, microemulsions, monolayers, bilayers, vesicles, host-guest systems, and polyions. Wiley, New York... 

Nonviral systems have been developed and used to deliver genes in vivo. Delivery of genes by means of liposomes—artificial lipid bilayer vesicles—overcomes the potential safety hazards associated with viral gene sequences required for packaging. DNA-Uposome complexes have been... 

The above data suggest that a crosslinked bilayer vesicle is essentially a single polymer molecule (really two, one in each half of the bilayer). In other words the polymerization of the lipid monomers exceeded a gel-point. This concept raises the question of what mole fraction of bis-substituted lipid is necessary to achieve a gel-point for a bilayer composed of a crosslinker lipid, i.e. bis-lipid, and a mono-substituted lipid. Approximately 30% of the lipids in a bilayer vesicle of SorbPCs must be bis-SorbPC (4) in order to produce a polymerized vesicle that could not be dissolved by detergent or organic solvent [29], A complementary study of Kolchens et al. found that the lateral diffusion coefficient, D, of a small nonreactive lipid probe in a polymerized bilayer of mono- and bis-AcrylPC was dramatically reduced when the mole fraction of the bis-AcrylPC, was increased from 0.3 to 0.4 [24]. The decreased freedom of motion of the probe molecule indicates the onset of a crosslinked bilayer in a manner consistent with a 2-dimensional gel-point. 

In 1985 Tyminski etal. [55, 56] reported that two-component lipid vesicles of a neutral phospholipid, e.g. DOPC, and a neutral polymerizable PC, bis-DenPC (15), formed stable homogeneous bilayer vesicles prior to photopolymerization. After photopolymerization of a homogeneous 1 1 molar lipid mixture, the lipid vesicles were titrated with bovine rhodopsin-octyl glucoside micelles in a manner that maintained the octyl glucoside concentration below the surfactant critical micelle concentration. Consequently there was insufficient surfactant to keep the membrane protein, rhodopsin, soluble in the aqueous buffer. These conditions favor the insertion of transmembrane proteins into lipid bilayers. After addition and incubation, the bilayer vesicles were purified on a... 

The CD band intensity originated from the host (8) is enhanced in the bilayer vesicle ([0] -i-1.5 x 10 deg cm dmol at 247 nm) relative to the corresponding value in the HEPES buffer at 30.0 °C. In addition, no CD spectral change was observed for at least one day at 30.0 °C. This result indicates that the four pyridinium moieties bound to the chiral L-valine residues in 8 assume highly restricted conformations in the bilayer membrane. Thus, the hybrid assembly seems to furnish a chiral guest-binding site different from that provided by 8 alone in aqueous media without the vesicle. 

The stoichiometry for the complexes formed with host 8 embedded in the bilayer membrane and the guest was investigated by the molar ratio method [62]. A plot of the [0] value for 8 against the concentration of Orange G reveals that 8 embedded in the bilayer vesicle forms a complex with Orange G in a 1 1 molar ratio. The same 1 1 stoichiometry was confirmed for other complexes. The formation constants (K) for the 1 1 host-guest complexes in the bilayer... 

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