Mixed bilayers hydration

The interaction between an acidic phospholipid, the natural (wheat) phosphatidylinositolmonophosphate PI and a linear cationic polysoap the poly(2-methyl-5-vinyl-hexylpyridinium bromide) PVPC6 has been studied with mixed spread monolayers and with hydrated (40%, w/w) mixed bilayers. The "electrostatic" interaction between PI and PVPC6 involves monolayer condensation and affects the bilayers hydration. In addition, the free energy of the bilayers structural water is modulated by this interaction. 

In practice, van der Waals forces appear within a mix of forces. Measured between bilayers in free suspension, they are mixed with lamellar motions as well as with repulsive hydration forces. 

The formation of liposomes [or better arsonoliposomes (ARSL)], composed solely of arsonolipids (Ars with R=lauric acid (C12) myristic acid (C14) palmitic acid (C16) and stearic acid (C18) (Fig. 1) have been used for ARSL construction), mixed or not with cholesterol (Choi) (plain ARSL), or composed of mixtures of Ars and phospholipids (as phosphatidylcholine [PC] or l,2-distearoyl- -glyceroyl-PC [DSPC]) and containing or not Choi (mixed ARSL), was not an easy task. Several liposome preparation techniques (thin-film hydration, sonication, reversed phase evaporation, etc.) were initially tested, but were not successful to form vesicles. Thereby a modification of the so called one step or bubble technique (8), in which the lipids (in powder form) are mixed at high temperature with the aqueous medium, for an extended period of time, was developed. This technique was successfiil for the preparation of arsonoliposomes (plain and mixed) (9). If followed by probe sonication, smaller vesicles (compared to those formed without any sonication [non-sonicated]) could be formed [sonicated ARSL] (9). Additionally, sonicated PEGylated ARSL (ARSL that contain polyethyleneglycol [PEG]-conjugated phospholipids in their lipid bilayers) were prepared by the same modified one-step technique followed by sonication (10). 

When a substance such as sodium chloride is dissolved in water, the ions that form become completely surrounded by water molecules, which form structures called hydration spheres. When the sodium salt of a fatty acid is mixed with water, the caiboxylate group of the molecule becomes hydrated but the hydrophobic hydrocarbon portion of the molecule is poorly hydrated, if at all. The hydrocarbon chains from numerous fatty acids tend to clump together in spherical structures called micelles or, if large numbers are present, into bilayer sheets. Using a circle to represent the carboxylate group and an attached squiggly line to represent the hydrocarbon chain of a fatty acid, draw a picture of a micelle and a bilayer. 

The preparation methods of these vesicles are various. In some cases, the liposomal suspension is firstly prepared and then amphiphilic CyDs are inserted inside the phospholipid-bilayer, for example by sonication [93]. Another method mixes phospholipid (+/— cholesterol) and amphiphilic CyD solutions, to form hposomes by conventional methods [92, 94]. Lastly, vesicles consisting of bilayers of purely amphiphilic CyDs as raw material can be prepared applying a technique used to prepare hposomes, i.e. hydration of lipidic film followed by sonication [99-101]. 

An improved united atom force field for simulation of mixed lipid bilayers has been introduced and compared to X-ray and NMR structures. The dynamics of hydration-water in several phospholipids membranes of different compositions was studied by 2D H P heteronuclear correlation NMR under MAS using a H T2 filter before and a H mixing time after the evolution period and P detection so that inter-bilayer water is selectively... 

The interaction of hydrocarbon and fluorocarbon surfactants on the surface of dispersed particles has been studied through a flocculation and redispersion process [65-67]. Dispersions of positively charged particles can be flocculated with an anionic surfactant. An excess of the anionic surfactant forms a bilayer on the particle surface and causes redispersion of the flocculated sol. This flocculation reversal was used to study the interaction between mixed surfactants on a solid surface. A dispersion of iron(ITI) oxide hydrate particles was flocculated with an anionic hydrocarbon or fluorocarbon surfactant at pH 3.5, where the sols had a positive zeta potential. Subsequently, a second fluorocarbon or hydrocarbon surfactant was added to the flocculated sol. The extent of redispersion depended on the interaction between the two surfactants on the solid particle surface. 

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