The equilibrium of phosphatidylcholine-cholesterol in monolayers at the air/water interface

Monolayers of either cholesterol (Ch) or phosphatidylcholine (L) or their mixtures were investigated at the air/water interface. The surface tension values of pure and mixed monolayers were used to calculate the pi-A isotherms. The theory of equilibrium between components of monolayers at the air/water interface has been developed in order to obtain the stability constant of the Ch-L complex. We considered the equilibrium between L, Ch and the L-Ch complex on the basis of derived equations. We established that egg lecithin and cholesterol formed a 1: 1 complex, with stability constant equal to K = 2.56 x 10(6). (C) 2002 Elsevier Science B.V. All rights reserved.