A novel packing of the hydrocarbon chains in lipids. The low temperature phases of dipalmitoyl phosphatidyl-glycerol.

The system dipalmitoyl phosphatidylglycerol-water displays several phases in the temperature-concentration range explored in this work. All the phases are lamellar; they differ by the organization of the hydrocarbon chains. In the high temperature phase the conformation of the chains is liquid-like. In the low temperature phases the chains are stiff and parallel and they interdigitate (in other words the CH3 ends of the chains of one layer are near to the polar groups of the opposite layer). Moreover, several types of packings of the stiff chains are observed which differ by the symmetry of the two-dimensional lattices. The observed lattices are p6, cmm and pgg.