Journal of Lipid Research, Vol 18, 1-5, Copyright © 1977 by Lipid Research, Inc.
Surface phase separation and collapse of the stearate anion--alkaline earth cation complex
GS Patil and DG Cornwell
The surface properties of fatty acid and fatty acid-alcohol mixtures were
examined at 22-24 degrees C. At pH 12, sodium stearate forms a rigid
surface film that generates an equilibrium spreading pressure of 16.5
dynes/cm. At pH 12, stearate-alkaline earth cation films collapse at the
air-water interface and do not generate significant equilibrium spreading
pressures. The rate of film collapse depends on the counterion decreasing
in the sequence Ba2+ greater than Sr2+ greater than Ca2+. Stearate-stearyl
alcohol mixtures form solid (condensed) films that are relatively stable
and behave initially as homogeneous surfaces in their selectivities for
counterions. Stearate-oleyl alcohol mixtures form fluid (expanded) films
that are unstable. Lateral phase separations occur rapidly in fluid films
and the stearate-alkaline earth cation phase collapses. The rate of film
collapse in the fluid mixtures also depends on the counterion decreasing in
the sequence Ba2+ greater than Ca2+. These surface properties suggest how a
lipid anion may function as an ionophore in the translocation of alkaline
earth cations.