Energy calculations related to aliphatic chain-packing modes

X-ray measurements reveal that the orthorhombic gel phase of long-chain lipids shows a large variation in structural properties. These can be classified by systematic lattice energy calculations. Typical Values are reported for the space group Pbnm. The experimental X-ray data of two samples (dihexadecylphos-phatidylethanolamine, n-docosyl-phosphocholine) are used to obtain energy data for different indexing combinations in each phase. The most probable polymorphism was selected by applying a continuous energy criterion. It allows a discussion of packing frustration or freedom of the respective lipid in the bilayer or monolayer structure on heating.