Lecithin membrane containing

The lipid bilayer of a cell membrane contains two layers of a phospholipid such as lecithin, arranged tail-to-tail. 

The basic characteristic of the membrane structure is its asymmetry, reflected not only in variously arranged proteins, but also in the fact that, for example, the outside of cytoplasmatic (cellular) membranes contains uncharged lecithin-type phospholipids, while the polar heads of strongly charged phospholipids are directed into the inside of the cell (into the cytosol). 

Lecithin is another food constituent which has been shown to cause neurobehavioral teratogenic effects in rats. It is added to foods as an emulsifier, but it is also present in soy lecithin preparations which are consumed as healthy food supplements. Soy lecithin preparations contain various phospholipids which can be incorporated into the brain as membrane constituents or acetylcholine, and conceivably may affect brain development if available in high levels. Pregnant dams were fed a lecithin-enriched diet (prepared by adding a commercial soy lecithin preparation) from gestational day 7 until weaning. Subsequently, the pups were also fed this diet. Treated pups showed faster rightening responses on postnatal days 1 and 2 and slower... 

Natural vesicles, in particular endosomes for the fransport of proteins and nucleotides through cell membranes, contain about 50 mol% cholesterol in a bilayer where the lipids closely resemble the mixtures foimd in egg lecithins. Typ-... 

Most cell membranes contain about 60% lipid and 40% protein. Phosphoglycerides (such as lecithin and cephalin), sphingomyelin, and cholesterol are the predominant types of lipids found in most membranes. Precisely how the lipids and proteins are organized to form membranes has been the subject of a great deal of research. A widely accepted model called the fluid-mosaic model is diagrammed in I Figure 8.11. The lipids are organized... 

The conduction properties of bilayer lecithin membranes in iodine-containing solutions have been examined from a potentiodynamic experimental approach. 

A PhoE porin-lecithin membrane-BPG electrode was prepared as follows n-decane containing 0.5% egg lecithin and 0.25% cholesterol was brushed on the BPG electrode and dried in air. The resulting lecithin membrane-BPG electrode was inserted in 10 ml, 50 mM Tris-HCL buffer (pH 7.0), and coated again with the n-decane solution containing lecithin and cholesterol. After the lecithin membrane turned black, extracted PhoE porin was added to the lecithin membrane-BPG electrode and Tris-HCl buffer solution system. The anion-selective polymer membrane electrode was an Ag/AgCl electrode (0.422 cm2) coated with a PVC membrane containing 6% methyltridodecyl ammonium chloride and 30% nitrophenyloctyl ether. A PhoE porin-lecithin membrane-anion selective membrane electrode was prepared in the same way as the PhoE porin-lecithin membrane-BPG electrode described above. 

The identity of the moiety (other than glycerol) esterified to the phosphoric group determines the specific phosphoHpid compound. The three most common phosphoHpids in commercial oils are phosphatidylcholine or lecithin [8002-45-5] (3a), phosphatidylethanolamine or cephalin [4537-76-2] (3b), and phosphatidjlinositol [28154-49-7] (3c). These materials are important constituents of plant and animal membranes. The phosphoHpid content of oils varies widely. Laurie oils, such as coconut and palm kernel, contain a few hundredths of a percent. Most oils contain 0.1 to 0.5%. Com and cottonseed oils contain almost 1% whereas soybean oil can vary from 1 to 3% phosphoHpid. Some phosphoHpids, such as dipaLmitoylphosphatidylcholine (R = R = palmitic R" = choline), form bilayer stmetures known as vesicles or Hposomes. The bdayer stmeture can microencapsulate solutes and transport them through systems where they would normally be degraded. This property allows their use in dmg deHvery systems (qv) (8). 

Lecithin is a phospholipid, a class of compounds that make up cell membranes throughout the body. It is produced in the liver if the diet contains enough of the raw ingredients. 

In the first example, procaine penicillin, an aqueous vehicle containing the soluble components (such as lecithin, sodium citrate, povidone, and polyoxyethylene sorbitan monooleate) is filtered through a 0.22 pm membrane filter, heat sterilized, and transferred into a presterilized mixing-filling tank. The sterile antibiotic powder, which has previously been produced by freeze-drying, sterile crystallization, or spray-drying, is aseptically added to the sterile solution while mixing. After all tests have been completed on the bulk formulation, it is aseptically filled. 

Without an artificial sink, the membrane retentions are very high, with many basic probe molecules showing R > 80%. With the imposed sink, many of the retentions dropped by as much as 50%. Furthermore, just 0.5% wt/vol cholesterol in dodecane (in addition to the sink) caused increased retention to drop by at least a further 10-30%. It was not possible to form stable cholesterol-containing lipid models under sink conditions with Avanti s egg lecithin acceptor buffer solutions turned significantly turbid in the untenable model 13.1. 

The correct ratio of lipid constituents is important to form stable liposomes. For instance, a reliable liposomal composition for encapsulating aqueous substances may contain molar ratios of lecithin cholesterol negatively charged phospholipid (e.g., phosphatidyl glycerol (PG)) of 0.9 1 0.1. A composition that is typical when an activated phosphatidylethanolamine (PE) derivative is included may contain molar ratios of phosphatidylcholine (PC) cholesterol PG derivatized PE of 8 10 1 1. Another typical composition using a maleimide derivative of PE without PG is PC male-imide-PE cholesterol of 85 15 50 (Friede et al., 1993). In general, to maintain membrane stability, the PE derivative should not exceed a concentration ratio of about l-10mol PE per lOOmol of total lipid. 

The illustration shows a model of a small section of a membrane. The phospholipids are the most important group of membrane lipids. They include phosphatidylcholine (lecithin), phosphatidylethanolamine, phos-phatidylserine, phosphatidylinositol, and sphingomyelin (for their structures, see p. 50). in addition, membranes in animal cells also contain cholesterol (with the exception of inner mitochondrial membranes). Clycoli-pids (a ganglioside is shown here) are mainly found on the outside of the plasma membrane. Together with the glycoproteins, they form the exterior coating of the cell (the gly-cocalyx). 

Ogawa, S., Decker, E.A., McClements, D.J. (2003). Influence of environmental conditions on the stability of oil-in-water emulsions containing droplets stabilized by lecithin-chitosan membranes. Journal of Agricultural and Food Chemistry, 51, 5522-5527. 

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