Squeeze-out from mixed monolayers of dipalmitoylphosphatidylcholine and egg phosphatidylglycerol |
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Authors: | A. Boonman F. H. J. Machiels A. F. M. Snik J. Egberts |
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Affiliation: | 1. Key Laboratory of Health Cultivation of the Ministry of Education, Beijing University of Chinese Medicine, Beijing, 100029, China;2. Dongfang Hospital, Beijing University of Chinese Medicine, Beijing, 100078, China |
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Abstract: | Plots of surface pressuer (π) vs surface area (A) are taken from mixed monolayers of dipalmitoylphosphatidylcholine (DPPC) and “egg” phosphatidylglycerol (egg PG) with the concentration of egg PG (X) ranging from 0 to 100%, the temperatures (T) from 37 to 41°C, and the compression rate (dA/dt) from −13.6 to −688 mm2s−, and at a relative humidity of over 90%. Between limiting values of X, T, and dA/dt the π-A plots of compression show regions of nearly constant π (plateaus) which start at values of π (πpb) of 48 ± 2 mN m−1, and which can be followed by an increase in π until collapse occurs at 70 mN m−1. πpb is independent of X, T, and dA/dt. The plateau is correlated with a loss of molecules from the monolayer, which increases strongly with X and T and decreases with dA/dt. The quantitative results are not in agreement with separate collapse of the components. A model is presented stating that plateaus occur when the transition from the liquid-expanded (LE) to the liquid-condensed phase (LC) is incomplete at πpb. During plateau formation a mixed LE phase is squeezed out at its collapse pressure. The remaining LC phase can be compressed to 70 mN m−1. Results of calculations based on this model are in agreement with the experimental results and predict slight enrichment of the squeezed-out phase with respect to egg PG. |
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