Critical Pressures in Multicomponent Lipid Monolayers

John P. Hagen, Stanford University
Harden M. McConnell, Stanford University

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Copyright © 1996 Elsevier. The definitive version is available at http://dx.doi.org/10.1016/0005-2736(96)00009-0.

NOTE: At the time of publication, the author John P. Hagen was not yet affiliated with Cal Poly.

Abstract

Epifluorescence microscopy has been used previously to study coexisting liquid phases in lipid monolayers of dihydrocholesterol and dimyristoylphosphatidylcholine at the air/water interface. This binary mixture has a critical point at room temperature (22°C), a monolayer pressure of approx. 10 mN/m, and a composition in the vicinity of 20-30 mol% dihydrocholesterol. It is reported here that this critical pressure can be lowered, raised, or maintained constant by systematically replacing molecules of this phosphatidylcholine with molecules of a phosphatidylethanolamine, or an unsaturated phosphatidylcholine, or mixtures of the two, while maintaining the dihydrocholesterol concentration at 20 mol%. Thus, even complex mixtures of lipids may be characterized by a single, well-defined second-order phase transition. In principle, such transitions might be found in biological membranes.