Mixed monolayers of cholesteric acid and lipid molecules

The studies on Langmuir monolayer of cholesteric acid (ChA) at the air-water (A-W) interface show many interesting results. We have observed different two-dimensional (2D) phases like L′1, L ′ 2 and L2. In this chapter, we describe our studies on the stability of the phases and miscibility of binary mixture of ChA and lipid molecules of different structures. We have chosen the lipid molecules like cholesterol (Ch), stearic acid (SA) and L-αdipalmitoyl phosphatidylcholine (DPPC). Lipids are important constituents of the biological membranes. They have a broad classification which primarily includes the phopholipids, fatty acids and sterols (cholesterol, ergosterol, dehydrocholsterol). Fatty acids are known to regulate the blood pressure [1]. They also reduce the risk of hypercholesterolemia by lowering the level of low density lipoprotein-bound cholesterol [2]. Stearic acid (a fatty acid) possesses a linear alkyl chain with a carboxylic head group. Phopholipids are the main constituents of the lung surfactant. The phospholipids monolayers mimic the biological membranes and have been extensively studied [3]. DPPC (a phospholipid) is one of the most commonly studied compound. It has two aliphatic tails and a bulkier phosphocholine head group. The phosphocholine head group acquires a large value of dipole moment in the polar solvent like water. It is interesting to study the 2D miscibility of the ChA with lipid molecules of different structures like Ch,