Interaction of calcium ions with lecithin and sphingomyelin monolayers.

Dipalmitoyl lecithin and sphingomyelin monolayers have similar limiting areas, whereas their surface potentials are strikingly different. The double bond at the 4-5 position in sphingomyelin acts as an induced dipole in relation to the surface potentials. This was confirmed by the surface potential of hydrogenated sphingomyelin. The binding of calcium to lecithin and sphingomyelin monllayers resulted in an increase in surface potential. This increase was greater for the dipalmitoyl lecithin monolayer as compared to that for sphingomyelin. It is concluded that the binding of calcium ions to springomyelin monolayers is significantly reduced by the presence of the hydroxyl group at the 3-carbon position of the molecule.