Dimyristoyl lecithin

Eight binary systems are reported. Six include cholesterol as one component of the mixed film. The second components in these six films were myristic acid, methyl palmitate, ethyl palmitate, 1,2-dimyristin, 1,2-dimyristoyl-3-lecithin, and l,2-didecanoyl-3-lecithin. In addition, the systems trilaurin-dimyristoyl lecithin and triolein-dimyristoyl lecithin... 

Figure 5. Mixed monolayers of cholesterol-1,2-dimyristoyl-3-lecithin system at 23°C., pH 6, and 5 dynes per cm.

Figure II. Surface pressure-area and surface potential-area plots for 1,2-dimyristoyl-3-lecithin, trilaurin, and a 1 to 1 molar mixture at 22°C.

Particular phospholipids display characteristic transition temperatures (Tm). As shown in Table 9.1, increases with chain length, decreases with unsaturation, and depends on the nature of the polar head group. For pure phospholipid bilayers, the transition occurs over a narrow temperature range. The phase transition for dimyristoyl lecithin has a peak width of about 0.2°C. 

Figure 12.7t-A isotherm for 1,2-dimyristoyl lecithin at an n-heptane-aqueous NaCl solution interface. The numerals on the curves are the temperatures given in Celsius.

Katz, Y. and Diamond, J. M. (1974). Thermodynamic constants for nonelectrolyte partition between dimyristoyl lecithin and water, J. Membr. Biol., 17, 101-120. 

Table II. Thermodynamic Excess Functions for an Equimolar Mixed Monolayer of Trilaurin—Dimyristoyl Lecithin...

Type II is represented by line LOM in Figure 12, with a sharp change in slope at point O. Either this behavior or Type III behavior can be found when the pure expanded component ejdiibits a fully expanded tt-A curve. The cholesterol-dimyristoyl lecithin system, illustrated in Figure 5, is an example of Type II behavior. 

We also report here mean molecular area plots for two further systems which exhibited Type III behavior trilaurin-dimyristoyl lecithin... 

Figure 7. Area per molecule at the amphiphilic surface (calculated from x-ray data by K. Fontell) as a function of the mole fraction of dimyristoyl-lecithin (DML) in the lecithin-cholesterol bilayer...

Thermodynamic parameters for the mixing of dimyristoyl lecithin (DML) and dioleoyl lecithin (DOL) with cholesterol (CHOL) in monolayers at the air-water interface were obtained by using equilibrium surface vapor pressures irv, a method first proposed by Adam and Jessop. Typically, irv was measured where the condensed film is in equilibrium with surface vapor (V < 0.1 0.001 dyne/cm) at 24.5°C this exceeded the transition temperature of gel liquid crystal for both DOL and DML. Surface solutions of DOL-CHOL and DML-CHOL are completely miscible over the entire range of mole fractions at these low surface pressures, but positive deviations from ideal solution behavior were observed. Activity coefficients of the components in the condensed surface solutions were greater than 1. The results indicate that at some elevated surface pressure, phase separation may occur. In studies of equilibrium spreading pressures with saturated aqueous solutions of DML, DOL, and CHOL only the phospholipid is present in the surface film. Thus at intermediate surface pressures, under equilibrium conditions (40 > tt > 0.1 dyne/cm), surface phase separation must occur. 

M. J. Janiak, D. M. Small, G. G. Shipley, Temperature and compositional dependence of the structure of hydrated dimyristoyl lecithin, J. Biol. Chem., 1979, 254, 6068-6078. 

Hitchcock et al. (1974) reported the first crystal structure of a phospholipid, that of dilauroylphos-phatidylethanolamine. Later the structure of dimyristoyl-lecithin was determined by Pearson and Pascher (1979). The structure of two monoacyl-phospholipids has also been determined. Hauser et al. (1980) reported the crystal structure of a lysophosphatidylcholine analogue and Pascher and Sundell have determined the crystal structure of a lysophosphatidylethanolamine (Sundell, 1980). 

The L -phase dominates in all lecithin-water systems. Tardieu et al., (1973) found a phase below the chain melting transition in dimyristoyl-lecithin with two sets of long-spacing values, one corresponding to the bilayer thickness and the other considerably larger. The structure was proposed... 

Figure 8.60 Phase diagram of egg lecithin of low water content (a) and of the dimyristoyl-lecithin-water system (b) after Tardieu et al. (1973).

The polymer is expected to be at least occasionally cross-linked Since the polymer chains are very flexible, the amphiphilic polybutadienes represent a better approach to biological membranes than the corresponding polydiacetylenes In particular of interest are partially polymerized membranes, which consist of polymerizable butadiene lecithines and saturated lecithines (e.g. dimyristoyl-lecithin, DMPC). While vesicles of DMPC exhibit a typical ripple structure, the surface of the polymerized vesicles appears homogeneous. Electron micrographs of mixed vesicles show a phase separation, indicated by the simultaneous presence of regions with a smooth surface due to the polymer, and rippled regions due to DMPC Instead of... 

Inoue, K., 1974, Permeability properties of liposomes prepared from dipabnitoyl lecithin, dimyristoyl lecithin, egg lecithin, rat liver lecithin and beef brain sphingomyelin, Biochim. Biophys. Acta 339 390. 

However, the site of action was shown not to be purely lipoidal by the following work. Nitrous oxide, halothane, and cyclopropane (in the concentrations found during surgery) were led over a film of cholesterol (40%) in dimyristoyl lecithin, a composition designed to represent nerve membranes. Neither X-ray nor neutron diffraction analysis showed any change, even when concentrations of the anaesthetics were increased tenfold. The authors suggest that these drugs act at a lipid-protein interface, presumably in ion pores (Franks and Lieb, 1978). 

Dimyristoyl-sn-glycero-3-phosphocholine monohydrate (dimyristoyl-L-a-lecithin)... 

Materials. The samples of l,2-dimyristoyl-3-lecithin (L-configura-tion) and l,2-didecanoyl-3 lecithin (L-configuration) were respectively donated by Erich Baer, Banting and Best Institute, Toronto, Canada, and D. Chapman, Unilever Research Laboratories, Welwyn Garden City, England. All other materials were obtained from the Applied Science Laboratories, State College, Pa. All materials examined were synthesized and purified chromatographically. 

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