The interactions of cholesterol and dipalmitoyl-phosphatidylcholine in bilayers were investigated by differential scanning dilatometry and related techniques. Dipalmitoyl-phosphatidylcholine bilayers ranging from 0 to 50 mol % cholesterol were studied over a temperature range of 0-50 degrees C. These investigations allowed construction of a three-dimensional surface with dimensions of mole fraction of cholesterol, temperature, and apparent partial specific volume. Much of the phenomenology reported for dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylcholine-cholesterol bilayers appears and can be interrelated on this surface. In addition to the thermotropic events associated with the system, two cholesterol-induced events at 17.5-20 and 29 mol % cholesterol are particularly in evidence.

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