Nanostructured surfaces created by the interactions of dendrimers and oppositely charged amphiphiles

Abstract: The research described in this thesis aims to understand the interactions between cationic poly(amidoamine) (PAMAM) dendrimers and small oppositely charged amphiphiles at the solid-liquid and air-liquid interfaces in relation to the bulk solution behavior. There is high interest in PAMAM dendrimers because they are well-defined polymers with a hierarchical architecture which makes them promising materials as nanocapsules and gene vectors. In the first part of the work, the bulk solution and interfacial properties of mixtures of PAMAM dendrimers of generations 2, 4 and 8 and the anionic surfactant sodium dodecyl sulfate (SDS) were studied. At the solid-liquid interface, the structure and composition of the adsorbed layers depend on the dendrimer generation, the bulk composition and the pathway of adsorption. At the air-water interface, there is a synergistic enhancement of adsorbed surfactant in the presence of PAMAM dendrimers and the interfacial behavior depends on the non-equilibrium properties of the aggregates formed in the bulk solution. The implications of the interfacial properties of the layers formed by PAMAM/SDS mixtures are discussed with respect to their possible applications. The interactions of PAMAM dendrimers and negatively charged lipid bilayers were also investigated. The aim was to understand the transport mechanism of dendrimers across anionic model biomembranes. The addition of PAMAM dendrimers of generation 4 to solid supported and droplet interface bilayers showed that the dendrimer makes the membranes more permeable and this allows them to translocate through the membranes. The results are employed to evaluate the use of PAMAM dendrimers as delivery vehicles. The last section is dedicated to the examination of the interactions between PAMAM dendrimers of generation 4 and the nucleolipids dilauroylphospholiponucleosides based on adenosine (DLPA) and uridine (DLPU) at the silica-water interface. The aim was to develop ‘smart’ complexes on surfaces to achieve selective binding of nucleic acids. The layer structure and functionality depend on the method of adsorption and the type of nucleolipid. Only PAMAM/DLPA layers showed selective hydrophobic and hydrogen bonding base pairing interactions with different strands of nucleic acids through the formation of nucleolipid/nucleic acid multilayers.