Effect of saturation degree on the interactions between fatty acids and phosphatidylcholines in binary and ternary Langmuir monolayers

Fatty acids molecules have strong influence on membrane properties. In this work the interactions between fatty acids and phosphatidylcholines were studied in mixed binary and ternary Langmuir monolayers. The compounds investigated, both fatty acids and phospholipids were of the same hydrocarbon chain length and differed in their saturation degree (stearic acid (C18:0)), oleic acid (C18:1)), linoleic acid (C18:2) and distearoylphosphatidylcholine—DSPC and dioleoylphosphatidylcholine—DOPC). It was found that the investigated fatty acids interact more strongly with saturated phospholipid (DSPC) and more strongly affect the molecular organization of DSPC films as compared to DOPC monolayer. The saturated fatty acid (stearic acid) makes the phospholipid monolayers more rigid, while unsaturated fatty acids decrease the condensation of phospholipid films. The differences in the effect of the respective fatty acids on phosphatidylcholines monolayers were thoroughly analyzed from the point of view of geometry of the lipids molecules, which is determined by the saturation of the hydrocarbon chain.