Partial volumes of cholesterol and monounsaturated diacylphosphatidylcholines in mixed bilayers

• Monounsaturated diacylphosphatidylcholines Cn-1PC (n-number of carbons in chain) in fluid phase mix ideally with cholesterol.
• Average thermal expansivity for Cn-1PC with n = 18, 20 and 22 is (71.5 ± 1.1) 10−5 K−1.
• Partial volume of cholesterol slightly decreases with the lengthening of the Cn-1PC host molecule.
• The phase boundary at ∼23 mol% of cholesterol was observed for C24-1PC bellow the main phase transition.

Dispersions of multilamellar liposomes prepared from monounsaturated diacylphosphatidylcholines having 18–24 carbons and from varying amounts of cholesterol were studied by densitometry. Ideal mixing of the studied phosphatidylcholines with cholesterol in the fluid phase was observed. The temperature dependence of partial volumes of both phosphatidylcholines and cholesterol was determined. A slight decrease in the partial volume of cholesterol with the lengthening of the acyl chain of the host phosphatidylcholine was observed. By measuring the density of multilamellar liposomes of dinervonoylposphatidylcholine and cholesterol below the main phase transition temperature, the phase boundary between the solid ordered phase and the area of coexistence of the solid ordered and liquid ordered phases was detected.