Cholesterol-lecithin mixtures

Infrared Spectra. The effect of composition on infrared absorption of cholesterol-lecithin mixtures was striking in two regions of the spectrum—near 2.8 and 9.2 microns—which are associated with O-H and P-O-C stretching frequencies, respectively (Figure 4). 

To calculate activity coefficients, yu we apply the data of Figure 6 to Equation 1. Values for the two cholesterol-lecithin mixtures are presented in Table I as a function of mole fractions. The activity coefficients are greater than 1 in all instances of cholesterol mixtures. 

The molecular areas on the transitional line FF in Figures 3-5 are presented as a function of the mole fraction in the condensed film in Figure 7 for the cholesterol-lecithin mixtures there is a decrease in area ... 

Egg Oil. Oil of egg yolk. Obtained from fresh egg yolks by extraction with ethylene dicbloride. Contains fatty glycerides, cholesterol, lecithin. The glyceride fraction is a mixture of the glycerides of satd and unsatd fatty acids. Palmitic, stearic, oleic, Linoleic and dupanodonic acids have been isolated from both the glyceride and lecithin fractions. Preparation Levin, Lenman, J. Am, Oil Chem. Soc. 28, 441 (1951) U.S. pat. 2,503,312 (to Vb-Bin Corp ). 

In a 1 1 molar mixture of cholesterol and lecithin the OH stretching band of cholesterol lies at 3250cm , having been shifted from 3420-3400cm in the spectrum of cholesterol alone. These workers have cited some of the evidence supporting the idea that cholesterol-lecithin interactions may be important in cellular membranes and in certain other biological systems. 

Fig. 3 Cholesterol monohydrates crystal dissolution In a mixture of tauroursodeoxycholate Lecithin (80 20) at 37 C, observed by polarized light microscope. After 3 hours (B) the edges of the crystal are covered by birefringent liquid crystals made of cholesterol-lecithin in molar proportion of about one[11]. 

The yolk is separated from the white by the vitelline membrane, and is made up of layers that can be seen upon careful examination. Egg yolk is a complex mixture of water, Hpids, and proteias. Lipid components iaclude glycerides, 66.2% phosphoUpids, 29.6% and cholesterol [57-88-5] 4.2%. The phosphohpids consist of 73% lecithin [8002 3-5] 15% cephahn [3681-36-7], and 12% other phosphohpids. Of the fatty acids, 33% are saturated and 67% unsaturated, including 42% oleic acid [112-80-1] and 7% linoleic acid [60-33-3]. Fatty acids can be changed by modifying fatty acids ia the laying feed (see... 

Example Separation of mixture of fatty acids, cholesterols and their esters lecithins and polar... 

Liposomes (SUVs) were prepared by probe sonication according to standard procedures (31) in the presence of STPP. A mixture of lecithin, cholesterol, and STPP (PC/Ch/STPP = 65/15/20, molar ratio final total lipid 25 mg/ mL) was dissolved in chloroform followed by removal of the organic solvent using a rotary evaporator. After adding 5 mM HEPES (pH 7.4) to the dry lipid film, the sample was probe sonicated with a Sonic Dismembrator (Model 100, Fischer Scientific) at a power output of approximately 10 W for 30 minutes. To remove any titanium particles, which have been shed from the tip of the probe during sonication, the sample was centrifuged for 10 minutes at 3000 X g. The formed liposomes were separated from free, i.e., nonincorporated, STPP by gel filtration chromatography on a Sephadex G-15 column. 

N3. Nichols, A. V., and Gong, E. L., Use of sonicated dispersions of mixtures of cholesterol with lecithin as substrates for lecithin cholesterol acyltransferase. Biochim. Biophys. Acta 231, 175-184 (1971). 

Our present ideas about the nature of biological membranes, which are so fundamental to all biochemical processes, are based on the Singer-Nicholson mosaic model. This model of the membrane is based on a phospholipid bilayer that is, however, asymmetrical. In the outside monolayer, phosphatidylcholine (lecithin) predominates, whereas the inner monolayer on the cytoplasmic side is rich in a mixture of phos-phatidylethanolamine, phosphatidylserine, and phosphatidylinositol. Cholesterol molecules are also inserted into the bilayer, with their 3-hydroxyl group pointed toward the aqueous side. The hydrophobic fatty acid tails and the steran skeleton of cholesterol... 

Two complementary experiments show that the orientation and hiding of one or the other face of the steroid ring of cholate can occur when mixtures of lecithin and bile salt are considered. One of these experiments was performed by Etienne (4), who observed the following facts incidentally while extracting lipids from the serum lipoproteins by Delsal s method. This method utilizes a mixture of methanol and methylal (1 to 4) in the cold. The proteins are precipitated, while the lipids are dissolved in the methanol-methylal solvent mixture. If this solution of the lipids is evaporated, the residue is soluble in nonpolar solvents, such as chloroform. However, if sodium cholate is added to the lipoproteins before their extraction, the residue obtained after the methylal-methanol solvent evaporates is insoluble in chloroform. More precisely, while cholesterol and the triglycerides of the lipidic residue are extracted by chloroform, all of the lecithin remains insoluble, associated to the bile salt. The explanation is probably as follows. During evaporation, methylal with its low boiling point (44°C.), evaporates first, and the solvent becomes more and more concentrated with methanol and the residual water from the lipoprotein aqueous solution. Therefore, in the lecithin plus... 

For mixtures of lecithin plus Na cholate it appears possible to infer the molecular arrangement in the dispersed micelles from the most likely structure of the liquid crystalline phase suggested by x-ray analysis. However, there are cases where dispersion is not possible because neither component is sufficiently hydrophilic to be dispersed even when alone in water. This is shown by the association of cholesterol and lecithin in the presence of water. The ternary diagram of Figure 4 is relative to these systems. Here only the lamellar liquid crystalline phase is obtained (region 1< in Figure 4). This phase is already given by lecithin alone, which can absorb up to 55% water. Cholesterol can be incorporated within this lamellar phase up to the proportion of one molecule of choles-... 

Discontinuities are seen in the relationship between increase in film pressure, An, and lipid composition following the injection of globulin under monolayers of lecithin-dihydro-ceramide lactoside and lecithin-cholesterol mixtures. The breaks occur at 80 mole % C 16-dihydrocaramide lactoside and 50 mole % cholesterol. Between 0 and 80 mole % lactoside and between 0 and 50 mole % cholesterol the mixed films behave as pure lecithin. Two possible explanations are the formation of complexes, having molar ratios of lecithin-lactoside 1 to 4 and lecithin-cholesterol 1 to 1 and/or the effect of monolayer configurations (surface micelles). In this model, lecithin is at the periphery of the surface micelle and shields the other lipid from interaction with globulin. 

Although glycosphingolipids are the specific lipid components in the antigen-antibody complex, their activity is markedly enhanced by other (auxiliary) lipids such as lecithin and lecithin-cholesterol mixtures (15). The present study deals with the effect of lipid composition on the penetration of lactoside—cholesterol and lactoside—lecithin monolayers by rabbit y-globulin. We also investigated the lecithin-cholesterol system. Furthemore, since criteria for the existence of lipid-lipid complexes in monolayers are still few (8, 17), we have used infrared spectroscopy to examine lipid mixtures for the presence of complexes. 

Pure cholesterol in CHC13 solution has a sharp peak at 2.8 microns, owing to the free O-H group. Lecithin has a broad absorption between 2.9 and 3.2 microns, attributed to bound water (2). The peak at 2.8 microns disappeared in mixtures containing 50 mole % or more of... 

Figure 4. Infrared absorption spectra of cholesterol (C)-lecithin(L) mixtures...

The infrared evidence for hydrogen bonding between cholesterol and lecithin in chloroform solution is no evidence of a similar complex in the monolayer but suggests such a possibility. It does not exclude the hydrophobic bonding suggested by Chapman from NMR studies of the aqueous suspensions of equimolar mixtures of cholesterol and lecithin (3). 

Film penetration studies show unequivocally that lecithin-cholesterol mixtures containing from 0 to 50 mole % cholesterol and lecithin—lactoside mixtures containing from 0 to 80 mole % Ci6-dihydroceramide lactoside have the same effect as pure lecithin. This suggests the presence of a lipid complex in which lecithin prevents the interaction of the cholesterol or ceramide lactoside with globulin. Over these ranges of composition the lipid film would consist of a mixture of the lecithin-cholesterol or the lecithin-lactoside complex with excess lecithin. One may picture two models in which the protein contact is restricted to molecules of lecithin. In one, individual polar groups of the protein interact with the excess lecithin molecules as well as with the lecithin portions of the complex. In the other model, the protein as a whole interacts with the lecithin sites of polymeric lipid structures. The latter, which could be referred to as surface micelles (I), are visualized also through the term "mono-... 

Since cholesterol is an important component of many biological membranes mixtures of polymerizable lipids with this sterol are of great interest. In mixed monolayers of natural lipids with cholesterol a pronounced condensation effect , i.e. a reduction of the mean area per molecule of phospholipid is observed68. This influence of cholesterol on diacetylenic lecithin (18, n = 12), however, is not very significant (Fig. 32). Photopolymerization indicates phase separation in this system. Apparently due to the large hydrophobic interactions between the long hydrocarbon chains of... 

Figure 6. Observed 23Na quadrupole splitting for lamellar mesophase samples of dimyristoyllecithin-cholesterol-2H20 as a function of the cholesterol concentration at four different temperatures 16°C ( ), 30°C (V), 40°C ( ), and 48°C (O). In all samples the salt solution (0.8M NaCl in 2H20) accounted for 25% of the total sample weight. The concentration of cholesterol is expressed as the percentage (by weight) of cholesterol in the lecithin-cholesterol mixture.

To test and measure the retention rate of liposomes, carboxyfluorescein (CF) can be used. Ausborn and Nuhn [3.38] studied different lipid vesicles, e.g. egg lecithin (EPC), hydrated egg lecithin (HEPC), cholesterol (CHOL) and mixtures thereof. For... 

At large surfactant concentrations emulsion films as well as foam films exhibit a layer-by-layer thinning (stratification) and metastable black films are formed [31,347,512], Such a behaviour has been reported for hydrocarbon films obtained from solutions of lecithin in either benzene or a mixture of chloroform and decane at concentration higher than 0.6-0.8% as well as in films from oxidised cholesterol in decane [31,512]. Manev et. al. [347] have reported stratification of O/W type emulsion films, toluene being added as a disperse phase, occurring within a surfactant (NaDoS) concentration range of 0.017-0.14 mol dm 3. The number of metastable states was 5-6. Compared to foam films of analogous composition, the respective emulsion films were thicker, due to the weaker intermolecular attraction and the stratification occurred at lower surfactant concentrations. 

Heuman, D.M., Bajaj, R.S., and Lin, Q. (1996) Adsorption of mixtures of bile salt taurine conjugates to lecithin-cholesterol membranes implications for bile salt toxicity and cytoprotection. Journal of Lipid Research, 37 (3), 562-573. 

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