Orientation of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine at the surface of formamide and hydroxypropionitrile.

Phospholipids are a main component of cell membranes. Therefore, the experimental investigation of the self-organization of phospholipids is of great interest. Here we present results concerning the orientation of the phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at the surface of the polar solvents formamide and 3-hydroxypropionitrile (HPN), which we investigated by means of neutral impact collision ion scattering spectroscopy. It is shown that, in HPN, at low POPC surface excesses, the phospholipids are oriented with the polar headgroups pointing out of the solution. It is concluded that the behavior of lipids at the surface of liquids is more complex than expected and to a great extent dependent on the solvent. Comprehension of the behavior of POPC in the applied solvents might contribute to the understanding of the self-organization of phospholipids in water.