Nuovi fluorofori e chemosensori per anioni e cationi metallici e carrier per anioni; sintesi e studi di sensing e di trasporto

Supramolecular chemistry is the basis of many fundamental biological processes, such as chelation of metals, transmembrane ion transport, host-guest interactions and catalysis. Our group is involved since years in the development and the study of synthetic chemosensors for metal sensing and ions coordination. The work presented in this thesis is focused in the development and study of fluorescent sensing unit and novel chemosensors for metal cations and ions. In particular, the fluorophores developed are characterised by a high fluorescent quantum yield and presence of donator atoms, such as nitrogen and oxygen, required for metal complexation. The first class of ligands is based on [1,3,4]oxadiazole ring, the fluorophore units 2-phenyl-5- pyridyl[1,3,4]oxadiazole (PyPD) and 2,5-dipyridyl[1,3,4]oxadiazole (PyPyD) were tethered with polyamines-based framework to obtain L1, L2 and L3. The second series is based on the framework 2-(2-hydrossi-3-naftyl)-4-metylbenzozazole (HNBO) used to get L3 and L5. The coordination and optical behavior of compounds in aqueous or organic solutions have been studied towards different analysis and with several transition metal ions in order to evaluate proprieties and applications of ligands as chemical sensors for metals. Results have been discussed focusing to three crucial points: the thermodynamic stability of the ligands and the complexes, the photochemical response to coordination mainly at physiological pH 7.4 and the structural aspect of the complexes formed. In addition, the afforded metal complexes can function as sensors for anions; the fluorescent optical response of this metallo-based sensor with different anions has been discussed. A parallel project was carried on in collaboration with Professor Gale, from University of Southampton. Based on a promising tris(thiourea) receptor previously synthetized with selectivity for chloride over proton or hydroxide, a series of tripodal tris(thiourea) as anion transporters were developed. The main aim of the work was to enhance the encapsulation of complexed target to improve the transport selectivity of Cl− over H+/OH−. Four novel compounds based on a tripodal (thiourea)trien structure have been successfully synthetized. By using a series of different liposome-based transport assays the carrier behaviour of receptors was studied; and the effect of macrocyclisation of two transporters (T1 e T3) versus the analogous acyclic transporters (T2 e T4) in the modulation of transport selectivity for Cl− over H+/OH− has been discussed.