(527g) Morphological and Mechanical Studies of Multicomponent Phospholipid Monolayers Containing 27-Hydroxycholesterol

27-Hydroxycholesterol (27OH) is structurally similar to cholesterol with the addition of a hydroxyl group located at the 27th carbon of cholesterol. This oxysterol is part of the biosynthetic pathway for the synthesis of bile salts. 27OH is also implicated in a host of pathologies including Chronic Obstructive Pulmonary Disease (COPD) where airways are found to have elevated levels of 27OH. The biological relevance of this sterol is paired with unique phase behavior in model lipid membranes making 27OH an attractive molecule to investigate. Like cholesterol, 27OH induces liquid-liquid immiscibility in phospholipid monolayers. However, the morphology of these systems is strikingly different from cholesterol/phospholipid systems. These monolayers can exhibit regions of miscibility at low surface pressures as well as high surface pressures. Additionally, the size distribution of liquid domains is significantly sharper than in other sterol/phospholipid systems. Here we will utilize traditional Langmuir film balance techniques to extract thermodynamic parameters and molecular packing densities. We report the elastic and viscous modulus for these monolayers measured using the oscillatory mode of our pendant drop tensiometer. Finally, we report morphological changes as the monolayer undergoes a symmetric compression to collapse.