Interactions between beta-cyclodextrin and insoluble glyceride monomolecular films at the argon/water interface: application to lipase kinetics.

A study of the desorption rate of insoluble monomolecular films of oleic acid (OA), monoolein (MO), 1,2-diolein (1,2-DO), 1,3-diolein (1,3-DO) and triolein (TO) at the argon/water interface by water-soluble beta-cyclodextrin (beta-CD) is reported. The desorption of OA and MO involves probably the complexation of the single acyl chain with beta-CD and sequestering of the formed soluble OA/beta-CD and MO/beta-CD complexes from the argon/water interface. In the case of monolayers of multiple acyl chain molecules such as DO and TO, no detectable change in the surface pressure occurred after beta-CD injection. The surface rheological dilatational properties of the monolayers of DO and TO in the presence of beta-CD in the subphase were studied. The elasticity of the DO monolayer remained unchanged, whereas the decrease in the surface elasticity of the TO film was attributed to the formation of a water-insoluble TO/beta-CD complex. With the 'tuning fork' model, one acyl chain of TO can be included in the beta-CD cavity. The formed TO/beta-CD complex present at the interface retarded the propagation of the dilatational deformation along the plane of the monolayer. Schematic models have been proposed in an attempt to explain the different complexation of these lipids by beta-CD at the argon/water interface. In addition to the above results, the presence of beta-CD in the water subphase makes it possible for the first time to perform kinetic measurements of the lipase hydrolysis rates of long-chain glycerides forming monomolecular films.