Films lecithin

Similarly, a marked discontinuity was found at 50 mole % in the curve relating An to the composition of cholesterol-lecithin films (Figure 3). Up to 50 mole % cholesterol the magnitude of An was the same as with lecithin alone above this, An increased linearly with cholesterol concentration. 

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. 

Figure 1. Lipid spread on the electrolyte solution. Change of AV with the surface pressure of lecithin films spread on 150 mequiv NaCl (O) and CaClg (%), pH 5.6, 25°C DML, DPL,andDSL. Deviations 5 mV ...

Electrolyte Injected under the Lipid Film. There is a marked difference in the AV response of phosphatidyl choline films to the electrolyte, depending on whether the lipid film is spread onto the electrolyte solution or the electrolyte is injected under the lecithin film that was spread first onto distilled H20 (I). 

In various attempts at establishing the stoichiometry of an eventual interaction of Ca++ with lecithin films, the increases in surface radioactivity observed in the presence of 45Ca++ in the aqueous phase were ascribed to adsorption of Ca+ Apart from the interpretations, the data themselves in this field are interestingly discordant (13,14,15). To appreciate the significance of the statement, we first present our own data from experiments in which the excess surface radioactivity in counts per minute (A cpm) in the presence of DPL film (cpm with DPL — cpm without DPL) are related to the hypophase pH the aqueous phase contained 150mM NaCl and 93/xM CaCl2 carrier (see Figure 6). 

Stable, very thick films, approximately 100 nm in thickness, characteristic of the single-component soya bean lecithin film ... 

These experiments are characterized by that extreme selectivity usually associated only with biological processes. This led Hughes to trace a parallelism with hemolysis caused by the venoms. He found that blacksnake venom reacted with the lecithin film at a rate which was indeed related to the speed of hemolysis of washed guinea-pig cells. Further experiments, however, showed that the ability of a venom to react with a lecithin monolayer did not necessarily imply hemolytic activity towards the red cells of any given species. Black tiger venom, for example, was only very slightly reactive towards red cells, even after sixteen hours, while the venoms of copperhead and cobra as well as of blacksnake were strongly hemolytic within two hours in concentrations as low as 0.2 mg. ml. . ... 

Table I. Area and Surface Pressure at which Phase Separation Begins in Distearoyl Lecithin Films at Various Hydrocarbon /Aqueous NaCl Interfaces...

The effects of lecithin monolayers on Atr and r at different Cp s are shown in Figures 2 and 3. The lecithin monolayers were spread to initial film pressures (t ) of 10 dynes/cm so that the molecular areas for the dibehenoyl and egg yolk lecithins were about 50 and 88 A2/molecule. When Cp is less than 10 5 %, lecithin monolayers give larger values of Att than are observed at the clean air-water interface. In this region r is probably reduced, but the adsorption of protein is so limited that it approaches the limits of experimental error. However, when 10"5 < Cp < 4 X 10 3 %, the lecithin monolayers cause large reductions in Y and Att, and the condensed dibehenoyl lecithin film has the greater effect. The reduction in T is real and not an artifact caused by the lipid monolayer... 

Joos data on distearoyl lecithin (DSL)-cholesterol mixed films (35) coincide with data from our DPL-cholesterol system in the sense that cholesterol reduced the viscosity of the lecithin film, and the surface viscosity decreased with increasing cholesterol concentrations. However, the comparison and interpretation of surface viscosity data require caution (2,6). For example, in Joos experiments the lipid was distearoyl lecithin (DSL), the subphase was distilled water, phospholipid and cholesterol were premixed, and viscosity was measured by the rotational surface Couette method. By the torsion oscillation method, at all film pressures... 

A typical island or cluster structure for the lecithin film transferred... 

Figure 3. Electron micrographs of lecithin films transferred at various surface pressures. The scale shows I/x, and the arrows indicate the direction of shadowcasting.

The effect of a dc potential applied across brain cephalin and lecithin films has been studied with infrared methods (May and Kamble, 1968). When an electric... 

Fig. 5. Temperature-induced chain-melting transition of lecithin film at the electrode can be monitored by a change in the imaginary admittance component. Critical temperature T<- is estimated from the inflexion point.

The influence of the orientation of the adsorbed film of 1,3-dipalmi-toyllecithin on the phase transition temperature was described. The inhibition of the reduction of Cd by lecithin film at various temperatures can also be used for the transition temperatures determination. The possible formation of a complex between Cd and lecithin is suggested [126]. 

Pethica, B. A. Phospholipid monolayers at the -heptane/water interface. Part 2. Dilute monolayers of saturated 1,2-diacyl-lecithins and -cephahns. J. Chem. Soc. Faraday Trans. 1 1976, 72, 2694-2702. (d) Yue, B. Y. T., Jackson, C. M., Taylor, J. A. G., Mingins, J., Pethica, B. A. Phospholipid monolayers at non-polar oU/water interfaces. Part 1. Phase transitions in distearoyl-lecithin films at the -heptane aqueous sodium chloride interface. J. Chem. Soc. Faraday Trans. 1 1976, 72, 2685-2693. 

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