AMPHIPHILIC DENDRIMERS AS BUILDING-BLOCKS IN SUPRAMOLECULAR ASSEMBLIES

The self-assembly of amphiphilic dendrimers based on poly(propylene im ine) dendrimers of five different generations with up to 64 end groups modified with long hydrophobic chains has been studied. At the air-wa ter interface stable monolayers form in which the dendritic surfactant s presumably adopt a cylindrical shape; all the chains are aligned per pendicular to the water surface, and the dendritic poly(propylene imin e) core faces the aqueous phase. Electron microscopy and dynamic light -scattering measurements performed on aqueous solutions of the amphiph iles at pH = 1 showed the formation of small spherical aggregates with diameters varying between 20 and 200 nm. X-ray diffraction of cast fi lms of these aggregates revealed bilayer thicknesses of 48-54 Angstrom . A phase transition was detected by measuring fluorescence anisotropy . The theoretical volumes of the dendritic amphiphiles were in good ag reement with those calculated from the monolayer experiments and X-ray diffraction data. Hence, the amphiphilic dendrimers within the aggreg ates in solution have the same highly asymmetric conformation as that proposed at the air-water interface. Calculations showed that the shap e of the dendritic poly(propylene imine) core in the aggregates is dis torted and that the axial ratio (r(b):r(a)) ranges from 1:2.5 for the first generation to approximately 1:8 for the three highest generation of dendrimer. This behavior illustrates the high flexibility of the p oly(propylene imine) dendrimers.