Structural conformation of lipids at the oil-water interface

A neutron reflectivity study of the phospholipid 1,2-distearoyl- sn-glycero -3-phosphocholine at the hexadecane-water interface is reported as a function of spread amount. Two isotopic contrasts have been used to determine the structure of the phospholipid molecule in the buried interfacial region. The results indicate a roughened or diffuse monolayer at low spread amounts of phospholipid at the oil-water interface. An increase in the spread amount of phospholipid results in combination of a monolayer plus micelle-like aggregates formation at the interface. There is a transition from a monolayer to a more complex monolayer and micelle-like aggregates conformation as the amount of spread phospholipid increases. The total layer thickness for these fits is about 70 Å, which is much larger than a fully extended DSPC molecule (30 Å). This is indicative of rough molecular packing at the oil-water interface. This roughened or diffuse interface is suggested to be because of the solvation effect of the hydrocarbon tails and the resultant hydrophobic interactions. In addition, a minor contribution may originate from the accommodation of the charges in the head groups. Schematic representation of the conformation of DSPC at low (left) and high (right) spread amounts. A change in conformation is observed as the spread amount increases.