Miscibility of phosphatidylcholine and sulphatide in monolayers

Compression isotherms of mixed monolayers of phosphatidylcholine (PC) and sulphatides (S) were carried out, with the lipids being spread on subphases of different pH and different ionic composition. Several common trends can be observed. All monolayers when compressed reach collapse. Collapse pressures are directly related to the molar fractions of the lipids in the monolayer. Miscibility is not ideal, in general, and is independent on the surface pressure of the monolayer, the mixed monolayers being always (with some exceptions) in a more expanded state than those of the pure components. The thermodynamic parameters corresponding to the mixing interactions have been calculated at the molar composition that gives a maximum deviation from ideality.