Calcium action on fatty acid and phospholipid monolayers and its relation to the cell membrane

Abstract

Calcium ions interact with stearic and palmitic acid monolayers producing a solid-condensed film which is rigid, has no measurable surface viscosity, and has a high solid-to-liquid transition temperature measured by the talc test. This effect can be explained by charge destruction, formation of di-soap molecules, or formation of a copolymeric soap lattice. Surface viscosity experiments indicate that charge destruction has a measurable but minor effect on film properties. Di-soap analogs have increased surface viscosities. However, these analogs form plastic films with moderate transition temperatures. The data suggest that the unusual properties of calcium stearate and palmitate films are most readily explained by a copolymeric lattice structure. Calcium has no effect on the surface viscosity of cis-and trans-monoethenoic acid and phospholipid monolayers. Saturated fatty acid soaps thus have unique surface properties which depend on their packing mode and crosssectional area and limit their value as model systems for calcium interactions with the cell membrane.