Monolayer configurations

Figure 8.7 Structures of TaS2-n-alkylamine intercalates (a) bilayer and (b) monolayer configuration of the intercalated amine.

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. 

Since these effects probably result from the organization of lipids in the monolayer, we must first consider criteria for ascertaining the nature of lipid-lipid associations. Moreover, since the discontinuities in the An—composition curves probably reflect transitions in monolayer configurations, we discuss these from the standpoint of penetration of protein into the lipid film and its relation to specific lactoside-antibody interaction. 

An alternative explanation for these data may be found by consider-ing monolayer configurations. In a suitable model, the protein as a whole would penetrate between the surface micelles. Two new parameters should thus become important in studying film penetration intermicellar area, and structure and orientation of lipid molecules at the periphery of the surface micelles. 

The concept of monolayer configurations is particularly useful in explaining penetration of the protein as a unit, in a form in which it has more structure than in solution. Studies of interactions between protein and monolayers of mixed lipids are very useful for examining the nature of lipid-lipid associations. 

For protein units in the condensed monolayer configuration (see Section III, A, 1, a) ratio bla estimated from models is about 1/4 for... 

Adsorption of dispersants at the soHd—Hquid interface from solution is normally measured by changes in the concentration of the dispersant after adsorption has occurred, and plotted as an adsorption isotherm. A classification system of adsorption isotherms has been developed to identify the mechanisms that may be operating, such as monolayer vs multilayer adsorption, and chemisorption vs physical adsorption (8). For moderate to high mol wt polymeric dispersants, the low energy (equiUbrium) configurations of the adsorbed layer are typically about 3—30 nm thick. Normally, the adsorption is monolayer, since the thickness of the first layer significantly reduces attraction for a second layer, unless the polymer is very low mol wt or adsorbs by being nearly immiscible with the solvent. 

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