In-plane structures of synthetic oligolactose lipid monolayers--impact of saccharide chain length.

Abstract

Grazing incidence X-ray diffraction (GIXD) was used to investigate the in-plane structure of monolayers of synthetic glycolipids with oligolactose head groups (Lac N, with N = number of lactose units) at the air/water interface. The Lac 1 monolayer exhibits three sharp diffraction peaks. One peak can be deconvoluted into two diffraction peaks, which suggests that alkyl chains in the monolayer form an orthorhombic lattice. On the other hand, the other two peaks are related to bulk crystalline materials residing at the interface. Another weak peak from the head group correlation, either in a monolayer or in bulk crystals, can also be observed in some experiments. The scattering patterns of the Lac 2 monolayer indicate that the alkyl chains order in an orthorhombic lattice, where a shift in the hydrophilic/hydrophobic balance seems to fluidize the film. Alkyl chains in the Lac 3 monolayer also seem to assume an orthorhombic lattice; however, a weak diffraction peak from the correlation between trilactose head groups can also be observed. The estimated lattice dimensions are compared systematically to those of bulk dispersions, as well as to the viscoelastic properties of the monolayer. The obtained results strongly suggest that the in-plane structure of synthetic glycolipid monolayers can provide a well-defined basis to understand the impact of the chemical structure on the cooperativity and function of the glycocalix of cellular surfaces.