Distearoyl lecithin monolayers

In the vibrating plate studies the liquid surface was formed in a waxed Langmuir-Adam trough in which the surface could be cleaned by waxed slides. Details of how cleanliness was controlled, how monolayers were spread, and how surface pressures were measured are described elsewhere (25). We studied numerous monolayers but only report sodium octadecyl sulfate and distearoyl lecithin monolayers. 

Some Effects of Hydrocarbon Solvent Structure on the Phase Behavior of Distearoyl Lecithin Monolayers at the Hydrocarbon/Water Interface... 

Figure 5. Current bias (E-EJ relation for a clean 0.1M NaCl surface—O and for a surface with a monolayer of distearoyl lecithin at a surface pressure of 30.4 dynes/cm at 20°C—(A).

Monolayers of distearoyl lecithin at hydrocarbon/water interfaces undergo temperature and fatty acid chain length dependent phase separation. In addition to these variables, it is shown here that the area and surface pressure at which phase separation begins also depend upon the structure of the hydrocarbon solvent of the hydrocarbon oil/aqueous solution interfacial system. Although the two-dimensional heats of transition for these phase separations depend little on the structure of the hydrocarbon solvent, the work of compression required to bring the monomolecular film to the state at which phase separation begins depends markedly upon the hydrocarbon solvent. Clearly any model for the behavior of phospholipid monolayers at hydrocarbon/water interfaces must account not only for the structure of the phospholipid but also for the influence of the medium in which the phospholipid hydrocarbon chains are immersed. 

Representative surface pressure/area per molecule isotherms from monolayers of distearoyl lecithin at the interface between 0.1M NaCl and cyclohexane, n-heptane, and isooctane at 20 °C and n-nonane and isooctane at 3°C are shown in Figure 1. Two completely independent isotherms which were actually determined some months apart for the n-heptane/O.lM NaCl interface are plotted to illustrate the precision and reproducibility of the method and the data. Quite clearly the area and surface pressure at which phase separation begins depend on the hydrocarbon component of the oil/water interfacial system. The areas and surface pressures at which phase separation occurs for these and the other solvents which have been investigated are summarized in Table I. 

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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