Calix[n]arene-based Monolayer Protected Clusters (MPCs): Synthesis, Studies and Applications

This thesis deals with the synthesis, characterization and study of metallic nanoparticles (M = Au, Pd, Ag, Cd-Se) functionalized on their surface with calix[n]arene derivatives. These hybrid organic-inorganic materials, more commonly called "monolayer-protected clusters" (MPCs), have recently attracted a growing scientific interest for their potential applications in catalysis, in the realization of optical devices, electrical or magnetic sensors or more in general in the field of nanotechnology. In each of these applications the control, during the preparation, of the size of the nanoparticles obtained is important. The idea of preparing MPCs stabilized on their surface with macrocyclic receptors came from the possibility of combining the recognition properties of calix[n]arene derivatives with the typical properties of metal colloids in order to obtain "smart" material capable of interesting functions, that are able to perform actions in response to external chemical or electrochemical stimuli. In the first phase of the thesis it has developed new synthetic methodologies of calix[n]arene derivatives functionalized at the lower rim with alkyl chain bearing, at their ends, thiols functional groups suitable for covalent binding on metal surfaces. In a second phase it has developed reproducible synthetic methodologies for the preparation of metal nanoparticles having a core size between 0.8 -7 nm functionalized with calix[n]arene derivatives. This study has allowed us to evaluate various experimental parameters that lead to obtain size controlled and monodisperse gold nanoparticles, such as reaction temperature, duration, stochiometry of thiols and gold etc.. These studies have highlighted in particular the "denticity" of the ligand (number of thiolic chains on macrocycle) on the size and stability of such systems. All prepared nonosystems are studied by microscopic (TEM), superficial analysis (XPS, XRD), spettrometric techniques (NMR, UV-vis) and chemical techniques (elemental analysis and TGA). These thiolic derivatives were also used for the surface coating of Cd-Se semiconductor nanoparticles for the preparation of Quantum Dots-in collaboration with the University of Miami (USA). Such synthesized organic-inorganic hybrid materials were subsequently used for processes of self-assembly in solution exploiting the receptor capabilities of calix[n]arene derivatives on the surface with piridinium salts. These studies, conducted at the University of Konstanz (Germany), had been conducted using optical techniques (UV-vis and Dynamic Light Scattering) and have shown the aggregation processes in solution and the structural properties of such systems.