Determination and comparison of how the chain number and chain length of a lipid affects its interactions with a phospholipid at an air/water interface.

We determined how the number of chains in a lipid and its chain length affects its interactions with a phospholipid model membrane, and whether the number of chains or the chain length of lipids affects their interactions with the phospholipids more. This was achieved by using a Langmuir trough and a fluorescence microscope to study the interactions of mono-, di-, and triglycerides with a phospholipid monolayer at an air/water interface. The effect of the number of chains in a lipid on its interactions with phospholipids at air/water interfaces was shown by surface pressure-area per molecule isotherms and their thermodynamic analysis to worsen as the number of alkyl chains was increased to be greater than one. An increase in the packing density decreased the mixing ability of the lipids with the phospholipids, resulting in the formation of aggregates in the mixed monolayer. The aggregation was explained by the intermolecular hydrophobic and van der Waals attractions between the lipid molecules. Fluorescence microscopy revealed partial mixing without aggregation for monoglycerides, but the presence of lipid aggregation for diglycerides and triglycerides. The effect of decreasing the chain length of triglycerides from a long chain to a medium chain caused the interactions of the lipids with the phospholipid molecules at the air/water interface to significantly improve. Decreasing the chain length of monoglycerides from a long chain to a medium chain worsened their interaction with the phospholipid molecules. The effect of decreasing the triglyceride chain length on their interactions with phospholipids was much greater than the effect of decreasing the number of alkyl chains in the lipid.