Hydration of the phospholipid

The dipole potential of a lipid membrane is manifested between the hydrocarbon core of the membranes and the first few water molecules adjacent to the lipid head groups (Brockman, 1994). This potential is caused by the uniform orientation of the phosphocholine moiety, the carbonyl groups of the ester union, and, to some extent, by the presence of polarizable groups in the membrane hydrocarbon phase (Voglino et al., 1998 McIntosh, 2002). Therefore, in addition to steric hindrance and electrostatic forces, the hydration of the phospholipids plays a significant role in protein-membrane interactions as a participant in the short-range repulsive forces (McIntosh, 2002). 

Hydrogels are used in the refining of edible oils to adsorb phospholipids, trace metals, and soaps (103). The adsorption capacity depends on the ease of hydration of the adsorbates, so best performance demands careful control of moisture content in the system (104). Silica hydrogel in combination with alumina has been found to be useful for purifying used cooking oils in order to extend their life and enhance the quality of the fried food (105). 

Analysis of the phospholipid fractions can also provide useful information on the quality of oilseeds as affected by stress due to environmental conditions in the field and during storage. Mounts and Nash found that the FFA content increased and the overall phospholipid content decreased as stress was applied (49). As far as individual PL classes were concerned, the content of PC and PI decreased significantly, while the PA and PE content increased, thus giving rise to an increased nonhydratable phospholipid (NHP) content in the crude oil. The NHPs refer to the phosphatides that, during degumming of crude oils with water, do not hydrate, swell, form gel, or precipitate and hence are not removed by centrifugation. 

The temperature dependence of the thickness of foam bilayers shows the occurrence of a first-order phase transition of melting of hydrocarbon tails of the phospholipid molecules. This melting is realised at a temperature very close to the temperature of the corresponding phase transition in fully hydrated water dispersions of phosphatidylcholines. This result is in agreement with the theoretical considerations of Nagle [436] for the decisive role of van der Waals attractions between hydrocarbon chains of phospholipid molecules for the chainmelting phase transition in bilayer systems. 

The exact dimensions of a phospholipid bilayer membrane in terms of the in-plane area and the height of the lipid molecules as well as the thickness of the water layer that is associated with them is dependent on the chemical identity of the phospholipid head group, the length and the degree of saturation of the acyl chains, and the degree of hydration. This information may be obtained from a combination of small-angle X-ray diffraction by MLV or oriented multi-bilayer samples of phospholipids in excess water, electron and/or neutron density profiles across lipid bilayers, and atomic level molecular dynamics simulations of hydrated lipid bilayers. H-NMR studies on selectively deuter-ated phospholipids have also been important in elucidating acyl... 

Hydration causes most of the phospholipids and gums present in a crude oil to become insoluble in the oil. Such hydration can come about from water added to the oil in the degumming step or from moisture picked up from the air by the oil during storage (116). 

Vibrational modes of the phospholipid polar head groups (in particular the symmetric and anti-symmetric PO stretching vibration) reflect their ionization and hydration state. The hydration state of the head group of DPPC was found to change under monolayer compression or by addition of cations such as Ca + There are indications that the transition at Ttg (to the solid state S, see fig. 3.6) involves ordering and dehydration of the head groups. 

Hydrated phospholipid molecules arrange themselves in the form of bilayer structures via Van-der Waals and hydrophilic/hydro-phobic interactions. In this process, the hydrophilic head groups of the phospholipid molecules face the water phase while the hydrophobic region of each of the monolayers face each other in the middle of the membrane (Fig. 2). It should be noted that formation of liposomes and nanoliposomes is not a spontaneous process and sufficient energy must be put into the system to... 

Hydrate a suitable combination of the phospholipid components, with or without cholesterol (see Note 1) in an aqueous medium for a time period of 1-2 h under an inert atmosphere such as nitrogen or argon. The nanoliposomal ingredients may be hydrated together or separately based on their solubility and r (see Note 13). 

The rate of proton dissociation was calculated from rapid kinetics measurements (decay time of < >OH, or rise time of 0- ). The rate is comparable with that measured in water, that is, 1010 sec-1, indicating that the water in the vicinity of the trapped proton emitter is out of the extensive hydration layer of the phospholipid (LeNeveu et al., 1977 Rand et al., 1980 Parsegian et al., 1979 Lis et al., 1982). 

Recently, a molecular dynamics study of the phospholipid DLPE was reported by Damodaran et al. using a united atom model. The model was built from the crystal structure of DLPE reported by Elder et al. The fully hydrated DLPE bilayer has an interlamellar water layer of 5 A. The bilayer was solvated by 553 SPCE waters ( 11 water molecules/lipid) in the head group region. This lipid has a gel-to-liquid-crystalline transition temperature of... 

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