Influence of α-hydroxylation of glycolipids on domain formation in lipid monolayers

By means of fluorescence and scanning force microscopy (SFM), we investigated the phase behavior of lipid monolayers composed of a mixture of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, sphingomyelin, and cholesterol (5/2/3) with either α-hydroxylated or nonhydroxylated galactocerebroside. Fluorescence images of lipid monolayers at the air−water interface demonstrate that, independent of the lipid mixture, phase separation occurs at low surface pressure up to 4−6 mN m-1, while an almost homogeneous phase is observed at larger surface pressures. However, by means of SFM of lipid monolayers transferred by the Langmuir−Blodgett technique at around 30 mN m-1, nanometer-sized domains became discernible in those lipid mixtures that contained galactocerebroside, while, in that without a glycolipid, no such domain formation was visible. Moreover, the α-hydroxy group of the galactocerebroside alters the size and the total area of the domains significantly.