Chain length dependence of lipid partitioning between the air/water interface and its subphase: thermodynamic and structural implications.

We have investigated phosphatidylcholines with the same two saturated hydrocarbon chains of 12, 10 and 8 C-atoms. Langmuir trough data could be evaluated towards even small lipid subphase desorption when applying a novel approach that had recently been developed in our laboratory. The C12 lipid turned out to form a nearly insoluble monolayer with slight desorption only beyond 15 mN/m for an area/volume ratio around 1 cm(-1). Above 22 mN/m micellation in the subphase apparently terminates further accumulation in the interface forcing additionally added lipid to enter the bulk volume. A comparatively substantial increase of solubilization was observed for the C10 monolayer. When turning to the C8 lipid partitioning proved to take place in nearly equal parts. In that case, strong multimeric aggregation is indicated to occur in both the interfacial and the bulk volume domains. All the results are quantitatively discussed in the light of basic thermodynamic and structural considerations.