ON THE LIPID HEAD GROUP HYDRATION OF FLOATING SURFACE MONOLAYERS BOUND TO SELF-ASSEMBLED MOLECULAR PROTEIN LAYERS

The structure of monomolecular layers of the protein streptavidin, spe cifically bound to biotin-functionalized lipid monolayers at aqueous s urfaces, has been characterized. Neutron and X-ray reflectivity measur ements allowed an assessment of the organization of these self-assembl ed systems with molecular resolution. Emphasis here is placed on the h ydration of the lipid head groups in the bound state. For three functi onalized lipids with spacers of different lengths between the biotin a nd their chains it was observed that the head groups were dehydrated i n monolayers of the pure lipids, which were kept at low surface pressu re before protein adsorption. The introduction of dipole moments at th e interface by the admixture of phospholipids or the application of la teral pressure on the lipid monolayer before protein adsorption were f ound to impose an extension of the spacer moieties. The biotin groups were thus presented further away from the interface, and a hydration l ayer between the protein and the functionalized interface was observed in the self-assembled supramolecular structures.