An analytic treatment of the condensation of phospholipid chains

A theory relating hydrocarbon chain length to temperature is developed and applied to the liquid crystalline to crystalline phase transiion in phospholipids. Interactions in both the chains and head groups are considered. The hydrocarbon tails are treated as freely jointed chains and the heads as a system of interacting dipoles. Analytic expressions are obtained for the internal energy, entropy, free energy and specific heat of the combined system. The free energy is minimized to obtain a relationship between straightening force and chain length. Agreement is good with experiments involving variation of water content and % cholesterol.Work was supported by a grant from the National Research Council of Canada.