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 hydro carbon chains of 12, 10 and 8 C-atoms. Langmuir trough data could be evalua ted towards even small lipid subphase desorption when applying a novel appr oach that had recently been developed in our laboratory. The C12 lipid turn ed out to form a nearly insoluble monolayer with slight desorption only bey ond 15 mN/m for an area/volume ratio around 1 cm(-1). Above 22 mN/m micella tion in the subphase apparently terminates further accumulation in the inte rface forcing additionally added lipid to enter the bulk volume. A comparat ively substantial increase of solubilization was observed for the C10 monol ayer. When turning to the C8 lipid partitioning proved to take place in nea rly equal parts. In that case: strong multimeric aggregation is indicated t o occur in both the interfacial and the bulk volume domains. All the result s are quantitatively discussed in the light of basic thermodynamic and stru ctural considerations. (C) 2001 Elsevier Science Ireland Ltd. All rights re served.