Phospholipid vesicles physical properties

The chemical compositions and isomeric structures of the fatty acid chains of phospholipids is well known to have large effects on the physical properties of lipid bilayers, such as the temperatures of endothermic chain melting phase transitions. Lipid vesicles sensitized with lipid haptens can be agglutinated with specific antibodies directed against the haptens (see Fig. 1). 

Fig. 23.3. (a) Schematic depiction of the creation of a lipid nanotube by application of a point force, allowing interconnection of vesicles, (b) Mechanical stresses and physical properties of planar phospholipid assemblies... 

Up until 1977, the non-covalent polymeric assemblies found in biological membranes rarely attracted any interest in supramolecular organic chemistry. Pure phospholipids and glycolipids were only synthesized for biophysical chemists who required pure preparations of uniform vesicles, in order to investigate phase transitions, membrane stability and leakiness, and some other physical properties. Only very few attempts were made to deviate from natural membrane lipids and to develop defined artificial membrane systems. In 1977, T. Kunitake published a paper on A Totally Synthetic Bilayer Membrane in which didodecyl dimethylammonium bromide was shown to form stable vesicles. This opened the way to simple and modifiable membrane structures. Since then, organic chemists have prepared numerous monolayer and bilayer membrane structures with hitherto unknown properties and coupled them with redox-active dyes, porous domains and chiral surfaces. Recently, fluid bilayers found in spherical vesicles have also been complemented by crystalline mono-... 

The experiments described in Sections VI,A,B show that two physical properties of the synthetic LamB signal peptides correlate with their in vivo export function tendency to adopt an a-helical conformation in hydrophobic environments, and tendency to insert into lipid mono-layers. These properties may be involved in the same step in the secretion process, or in different steps. An a-helical conformation may be required to generate a structure sufficiently hydrophobic to allow mono-layer insertion. Alternatively, these properties may reflect separate roles of the signal sequence in protein secretion. For instance, an a-helical conformation may be necessary for binding to a proteinaceous site, while the ability to interact with lipids may be important for another step in the secretion process. We have studied the conformations of the synthetic LamB signal peptides in phospholipid vesicles and monolayers by CD and IR spectroscopy. 

Hillard CJ, Harris RA, Bloom AS (1985) Effects of the cannabinoids on physical properties of brain membranes and phospholipid vesicles fluorescence studies. J Pharmacol Exp Ther 232 579-588... 

In the presence of amphiphilic bilayers, such as phospholipid vesicles or biological membranes, water-soluble amphiphiles partition between the bilayer and the aqueous media. Many studies have been devoted to the partitioning of alcohols between bilayers and water as well as to the enthalpy associated with the introduction of alcohols into bilayers, the effects of the alcohols on the physical properties of the bilayers, and the dependence of all these factors on the structure and properties of both the bilayers and the alcohols. 

Artificial vesicles formed by phospholipids are of interest as models of biological membranes. The inner aqueous core and the lipid bilayer of vesicles are effective media for the entrapment of biomacromolecules. Various vesicle preparation methods have been reported [1-8], and the physical properties of the vesicles formed to some degree depend on the way they are prepared [9,10],... 

Phospholipids are a major component of living cell membranes. Physical and chemical properties of bilayer structure composed of phospholipids have been well studied, (ij.2) One of the intriguing properties of phospholipids is that they form a closed structure hereafter referred to as vesicles. Vesicles have attracted much attention since they are considered to mimic biocelIs. 

Liposomes are a heterogeneous class of compounds that can be synthesized so that they possess a wide variety of physical and chemical properties. They can consist of sheets and long cylinders of reasonably circular vesicles such structures are the result of combining phospholipids with a fatty acid tail and hydrophilic head groups. There are two classes of these compounds that have been extensively studied as vectors for gene transfer anionic liposomes and cationic liposomes. 

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