Mixed Langmuir Monolayers of C18 Fatty Acids: Effect of Degree of Saturation

Abstract

The degree of unsaturation of hydrocarbon chains in the lipid diversity of biological membrane will greatly influence the membrane protein function. Lipid-lipid interactions in the membrane domain are crucial in the development of novel liposomal nanocarrier as the stability and function of liposomes are important points to be considered. The embedded therapeutic proteins are dependent on lipid membrane composition and their physical properties. In this study, we elucidated lipid-lipid interactions in the biological membrane domain with energetic quantitative data by mixing any two C18 fatty acids namely, stearic acid (SA), oleic acid (L1), linoleic acid (L2), and linolenic acid (L3) in Langmuir-Blodgett trough with water subphase. In general, SA has a saturated hydrocarbon chain; meanwhile, L1, L2 and L3 have increasing degree of unsaturation in their respective hydrocarbon chain. The tail-to-tail interactions were studied by the combinations of SA/L1, SA/L2, SA/L3, L1/L2, L1/L3 and L2/L3 at various mole ratios ranging from 9:1, 8:2, 7:3 ... to 1:9. Among the mixtures of C18 fatty acids, L2/L3 is considered as the energetically stable at the optimum amount of XL2 and XL3 = 0.5 respectively, at all discrete surface pressure.