Supramolecular sensing at the solid-liquid interface with phosphonate cavitands

The base of supramolecular chemistry rests on molecular recognition, that is the selective recognition of substrate molecules (guest) by synthetic receptors (host). The present thesis deals with the selective recognition properties of tetraphosphonate cavitands towards N-methylpyridinium and N-alkylammonium salts. In the first part of the thesis an extensive study of the thermodynamics of the complexation properties of tetraphosphonate cavitands towards N-methylpyridinium salts in solution via Isothermal Titration Calorimetry (ITC) is reported. The information obtained by the ITC in the recognition process of the receptor towards N-methylpyridinium salts were then exploited for the design of a new type of non-covalently linked-cavitand-stopped rotaxane. In the second part of the work, the complexation properties of cavitands were assessed towards N-alkylammonium salts at the solid-liquid interface via microcantilevers reaching an unprecedented real-time label-free selectivity. ITC was used as an independent tool for confirmation and rationalization of the results obtained with microcantilevers-based sensor. This approach has been then benchmarked by differentiating biological important molecules like sarcosine and glycine in water, reaching unique performances. The results obtained for the N-alkylammonium salts series opened the route to use microcantilevers for the online monitoring and the label-free sensing of biologically active ammonium-based molecules like drugs. The first experiments performed to test the recognition properties of tetraphosphonate cavitands towards drugs at the solid-liquid interface are described.