Dipalmitoyl lecithin

Materials. The water used for all purposes was double-distilled (once with glassware) and deionized (final conductance was less than 1 X 10"6 ohm1 cm."1). Stearic acid (obtained from Sigma Chemical Co.) was at least 99% pure as determined by silica gel thin-layer chromatography (4), and the synthetic L-a(/ ,y-dipalmitoyl) lecithin was about 90% pure (see Ref. 13 for analysis). The ATP-14C and its derivatives were obtained from Nuclear-Chicago or New England Nuclear Corp. and were found to be 95-98% pure as determined by cellulose thin-layer chromatography (16). 

A Dioleoyl lecithin shows internal salt linkage between phosphate and trimethyl-ammonium groups. Broken lines in egg lecithin diagram represents weak interactions of phosphate with Ca2+ and trimethylammonium group. Solid line between Ca + and phosphate group in dipalmitoyl lecithin diagram represents strong interaction... 

Dipalmitoyl Lecithin—Cholesterol Monolayers. The average area per molecule in dipalmitoyl lecithin-cholesterol monolayers shows deviation at low surface pressures, whereas at 30 dynes per cm. it follows the additivity rule (Figures 8 and 9) (42). The surface pressure—area curve of dipalmitoyl lecithin monolayers is liquid-expanded up to 30 dynes per cm., whereas above this surface pressure it is relatively incompressible (42). Figures 10b and c represent the structures of the dipalmitoyl... 

Figure 8. Average area per molecule of dipalmitoyl lecithin-cholesterol monolayers at various surface pressures...

The optimum condensation at molecular ratios of 3 to 1 and 1 to 3 in egg lecithin-cholesterol monolayers and 1 to 1 in dipalmitoyl lecithin-cholesterol monolayers (42) do not imply complex formation between lecithin and cholesterol but rather suggest average geometrical arrangements of these molecules. 

On Mechanisms of Interaction of Ca++ with Dipalmitoyl Lecithin at the Air-Water Interface... 

Penetration of electrolytes into both the air-water interface and films of dipalmitoyl lecithin is accompanied by a relatively small surface potential increase, whereas hydrolysis of CaCl% produces accumulation of Ca(OH)t and related species at the interface (l). Although in the absence of ionic lipids a correlation between interfacial ionic populations of the electrolyte and the surface potential changes is not yet possible, the marked surface potential effects of CaCU accompanying the presence of small quantities of acidic phospholipids in dipalmitoyl lecithin films suggest that the acidic lipid contaminants are still the only certifiable species whose interaction with CaCl2 produces an appreciable surface potential increase. Surface radioactivity and IR absorption spectra of dipalmitoyl lecithin in the presence of CaCU produced no evidence of Ca -dipalmitoyl lecithin interaction. 

Data on emulsion film formation from insoluble surfactant monolayer are rather poor. It is known, however, that such films can be obtained when a bubble is blown at the surface of insoluble monolayers on an aqueous substrate [391,392]. Richter, Platikanov and Kretzschmar [393] have developed a technique for formation of black foam films which involves blowing a bubble at the interface of controlled monolayer (see Chapter 2). Experiments performed with monolayers from DL-Py-dipalmitoyl-lecithin on 510 3 mol dm 3 NaCl aqueous solution at 22°C gave two important results. Firstly, it was established that foam films, including black films, with a sufficiently long lifetime, formed only when the monolayer of lecithin molecules had penetrated into the bubble surface as well, i.e. there are monolayers at both film surfaces on the contrary a monolayer, however dense, formed only at one of the film surfaces could not stabilize it alone and the film ruptured at the instant of its formation. Secondly, relatively stable black films formed at rather high surface pressures of the monolayer at area less than 53A2 per molecule, i.e. the monolayer should be close-packed, which corresponds to the situation in black films stabilized with soluble surfactants. 

Jain, M. K. and Wu, N. M. Effect of small molecules on the dipalmitoyl lecithin liposomal bilayer. Journal of Membrane Biology 54 157-201, 1977. 

Hill, M. W. The effect of anaesthetic-like molecules on the phase transition in smectic mesophases of dipalmitoyl lecithin. I. The normal alcohol up to C = 9 and three inhalation anesthetics. Biochimica et Biophysica Acta 556 117, 1974. 

Lecithins, soaps and surfactants can form bilayer structures in water, resembling those in cell membranes, and NMR has been used to determine the degrees of molecular mobility at the interior and surface of the bilayer. The proton spectrum of dipalmitoyl-lecithin (12) shows very... 

Phase transitions may be a particularly important property of membranes as they occur at around physiological temperatures and may result in large permeability changes in the membrane. The crystalline/liquid crystalline transition in dipalmitoyl lecithin has been examined in detail [147] using the spin labelled androstane derivative (D). 

Antonis (A3) has estimated phospholipids by a procedure for determining fatty acids. This technique requires a total serum extract and a phospholipid-free extract for the measurement of both total and free fatty acids, the difference between them being a measure of the phospholipid content. Free fatty acids (A4) are determined on a phospholipid-free extract by a procedure based on partitioning the fatty acids as copper soaps into chloroform, and subsequent photometric determination of the copper with diethyldithiocarbamate. Phospholipids, as well as the free fatty acids present in the total lipid-extract, are measured by the same method, since they also form a complex with copper that is soluble in chloroform. A criticism of this technique is that equal response is not given by dipalmitoyl lecithin, dipalmitoyl cephalin, or beef brain sphingomyelin. 

Results. Similar absorbances are found for triolein, cholesterol oleate, dipalmitoyl lecithin, and dipalmitoyl cephalin. Sphingomyelin, which has an amide fatty acid linkage, does not undergo hydroxylaminolysis. The standard error of the method is 0.36 mEq for an acyl ester concentration of 7-20 mEq/liter serum. 

Lipids. The chromatographically pure 1,2-dibehenoyl lecithin (C22) was synthesized in this laboratory and described before (15). The 1,2-dipalmitoyl lecithin (Ci6) was purchased from Fluka AG Chemical Co., Buchs, Switzerland, and further purified by passage through a silicic acid column. Chromatographically pure hen egg lecithin and phosphatidyl-... 

Figure 1. Surface pressure (ir)- molecular area (A) isotherms for dibehenoyl lecithin (A), dipalmitoyl lecithin (B), and egg yolk lecithin (C) on phosphate buffer (pH 7,1 = 0.1) at room temperature...

The tt-A curves at room temperature for dibehenoyl, dipalmitoyl, and egg yolk lecithins are shown in Figure 1. The condensed isotherm for dibehenoyl lecithin and the curve for dipalmitoyl lecithin which undergoes a two-dimensional condensation at 5.6 dynes/cm at 20.5 °C are consistent with earlier investigations (15, 17). The fully expanded isotherm for egg yolk lecithin was expected in view of the high level of unsaturation of this lipid. 

Figure 5. Dependence of A7r (O) and T (X) of l-14C-acetyU p-casein (Cpl = 10r4 %) on the iri of dipalmitoyl lecithin monolayers at 20.5°C. The film pressure at which the two-dimensional condensation starts is shown by the vertical dashed line. The other conditions were as described in Figure 2.

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