Phosphatidylcholine - Mg2+ equilibria in a monolayer at the air/water interface

Abstract

The interaction between Mg2+ and a phosphatidylcholine (lecithin, L) monolayer at the air/water interface was investigated. Surface tension measurements (Langmuir method) of phosphatidylcholine monolayers as a function of Mg2+ concentration were carried out at 22 C using a Teflon trough and a Nima 9000 tensiometer. Interactions between phosphatidylcholine and Mg2+ result in significant deviations from additivity. An equilibrium theory was developed to obtain the stability constants and areas occupied by one molecule of LMg+ and L 2Mg. The stability constants were K 1 = 9.95×10 2 m2 mol-1 and K 2 = 3.87×104 m2 mol-1. The area occupied by LMg+ is 77 Å2 molecule-1, while that occupied by L2Mg is 109 Å2 molecule-1. The Gibbs free energies of complexation for LMg+ and L2Mg are -16.91 ± 0.51 and -25.88 ± 0.76 kJ mol-1. © 2012 Versita Warsaw and Springer-Verlag Wien.