Structural conformation of lipids at the oil–water interface

Abstract

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 A, which is much larger than a fully extended DSPC molecule (∼30 A). 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.