Phospholipids are a class of amphiphilic lipid which has a hydrophilic negatively charged phosphate group, and two hydrophobic hydrocarbon tails linked by a glycerol residue. The phosphate group can be modified with simple organic molecules such as choline, ethanolamine or serine.
Phospholipids are the key component of cell membranes. In aqueous solutions, phospholipids are driven by hydrophobic interactions, which result in the hydrophobic fatty acid tails aggregating to minimize interactions with the water molecules. The result is a phospholipid bilayer: a membrane that comprises two layers of oppositely oriented phospholipid molecules, with their heads exposed to the liquid on both sides, and with the tails directed into the membrane. Phospholipids can be produced commercially and have been used in nanotechnology delivery and materials science.