Phospholipids are a class of amphiphilic molecules.They are the main components of biological membranes. The amphiphilic nature of these molecules defines the way in which they form membranes. They arrange themselves into bilayers by positioning their hydrophilic ends towards the surrounding aqueous medium, and their lipophilic ends towards the inside of the bilayer, defining a fatty region between two aqueous mediums.
Many other amphiphilic compounds, such as pepducins, strongly interact with biological membranes by insertion of the hydrophobic part into the lipid membrane, while exposing the hydrophilic part to the aqueous medium, altering their physical behavior and sometimes disrupting them.
Hans Meyer and Ernest Overton (university of lund) independently noticed that the chemicals which act as general anesthetics are also those soluble in both water and oil.
They interpreted this as meaning that to pass the cell membrane a molecule must be at least sparingly soluble in oil, their “lipoid theory of narcosis.” Based on this evidence and further experiments, they concluded that the cell membrane might be made of lecithin (phosphatidylcholine) and cholesterol.