Calix[6]arene Derivatives as Pivotal Components of Working Devices and Molecular Machine Prototypes

This Ph.D. thesis describes the synthesis, characterization and study of calix[6]arene derivatives as pivotal components for the construction of molecular machine prototypes. Initially, the ability of a calix[6]arene wheel to supramolecularly assist and increase the rate of a nucleophilic substitution reaction was exploited for the synthesis of two constitutionally isomeric oriented rotaxanes. Then, the synthesis and characterization of several hetero-functionalised calix[6]arene derivatives and the possibility to obtain molecular muscle prototypes was reported. The ability of calix[6]arenes to form oriented pseudorotaxane towards dialkyl viologen axles was then exploited for the synthesis of two calixarene-based [2]catenanes. As last part of this thesis, studies on the electrochemical response of the threading-dethreading process of calix[6]arene-based pseudorotaxanes and rotaxanes supported on glassy carbon electrodes are reported.

Synthesis and Characterisation of Functional Magnetic and Plasmonic Nanomaterials

The main aim of this thesis is the controlled and reproducible synthesis of functional materials at the nanoscale. In the first chapter, a tuning of morphology and magnetic properties of magnetite nanoparticles is presented. It was achieved by an innovative approach, which involves the use of an organic macrocycle (calixarene) to induce the oriented aggregation of NPs during the synthesis. This method is potentially applicable to the preparation of other metal oxide NPs by thermal decomposition of the respective precursors. Products obtained, in particular the multi-core nanoparticles, show remarkable magnetic and colloidal properties, making them very interesting for biomedical applications. The synthesis and functionalisation of plasmonic Au and Ag nanoparticles is presented in the second chapter. Here, a supramolecular approach was exploited to achieve a controlled and potentially reversible aggregation between Au and Ag NPs. This aggregation phenomena was followed by UV - visible spectroscopy and dynamic light scattering. In the final chapters, the conjugation of plasmonic and magnetic functionalities was tackled through the preparation of dimeric nanostructures. Au - Fe oxide heterodimeric nanoparticles were prepared and their magnetic properties thoroughly characterised. The results demonstrate the formation of FeO (wustite), together with magnetite, during the thermal decomposition of the iron precursor. By an oxidation process that preserves Au in the dimeric structures, wustite completely disappeared, with the formation of either magnetite and / or maghemite, much better from the magnetic point of view. The plasmon resonance of Au results damped by the presence of the iron oxide, a material with high refractive index, but it is still present if the Au domain of the nanoparticles is exposed towards the bulk. Finally, remarkable hyperthermia, also in vitro, was found for these structures.

Molecular approaches to smart materials via interface recognition and conformationally switchable cavitands

In this thesis the molecular level design of functional materials and systems is reported. In the first part, tetraphosphonate cavitand (Tiiii) recognition properties towards amino acids are studied both in the solid state, through single crystal X-ray diffraction, and in solution, via NMR and ITC experiments. The complexation ability of these supramolecular receptors is then applied to the detection of biologically remarkable N-methylated amino acids and peptides using complex dynamic emulsions-based sensing platforms. In the second part, a general supramolecular approach for surface decoration with single-molecule magnets (SMMs) is presented. The self-assembly of SMMs is achieved through the formation of a multiple hydrogen bonds architecture (UPy-NaPy complexation). Finally we explore the possibility to impart auxetic behavior to polymeric material through the introduction of conformationally switchable monomers, namely tetraquinoxaline cavitands (QxCav). Their interconversion from a closed vase conformation to an extended kite form is studied first in solution, then in polymeric matrixes via pH and tensile stimuli by UV-Vis spectroscopy.

Stabilization of APIs and nutraceuticals through cocrystallization and molecular confinement

Cocrystallization of the molecule of interest could be a smart and dainty way to tune solubility properties of solid phases leaving the molecule chemically unchanged, hence it is widely investigated by companies and by solid state scientists. Despite of this extremely high interest towards cocrystallization no particular emphasis has been paid to using it as a means to stabilize liquid molecules. In this work we define a benchmark of relevant molecules for human health that have been combined with suitable partners according to crystal engineering methods in order to obtain cocrystals. Solubility properties in different solvents of cocrystals new solid phases have been tested and compared to the properties of the drugs. A further approach to deal with volatile compounds is molecular confinement inside molecular scaffold. Nowadays metal organic frameworks (MOFs) are studied in many fields ranging from catalysis to trapping or storage of gases, such as hydrogen, methane, CO2 thanks to their extremely high porosity. Our goal is to confine liquid guests of biological relevance inside MOF pores, monitoring via X-ray diffraction, spectroscopy and thermal analysis the stabilization of the molecule of interest inside the cavities.