Oleamide and Oleamide–Lipid Mixed Monolayers

Abstract

Oleamide (OA) and its mixtures with other lipids are of interest in some biological systems, such as the tear film or the cerebrospinal fluid. In this work, the behavior of OA, OA–dipalmitoylphospatidylcholine (DPPC), and OA–cholesterol films is studied using surface pressure–area isotherms and atomic force microscopy, and analyzing the collapse pressure vs. composition, the compressibility, and the mean area vs. composition for several surface pressures. It is observed that OA forms homogeneous monolayers in a liquid-expanded state until the collapse surface pressure and the mixing with DPPC and cholesterol. The collapse surface pressure changes with the mixture composition, and in the case of DPPC, a noticeable influence of OA in the liquid-expanded/liquid-condensed phase change of DPPC is observed. The excess area is positive for the OA/DPPC films, but mostly negative for the OA–cholesterol films. These results are of interest for the target of formulation of artificial tears containing lipids.