DESIGN, SYNTHESIS AND CHARACTERIZATION OF POLYAMINE- AND SQUARAMIDE-BASED FLUORESCENT CHEMOSENSORS FOR SELECTIVE RECOGNITION OF ORGANIC MOLECULES AND METAL CATIONS IN SOLUTION

The present thesis describes two class of optical receptor able to be used as chemosensors for anionic species: the first class is constituted by seven squaramide-based system (L1-L7), the second one lies to two tetraazaprifane systems (L8-L9). Bis-squaramide ligands L1-L4 bearing a dansyl moiety were synthesised and their potential applications as fluorescent probes were investigated towards non-steroidal anti-inflammatory drugs Naproxen and Ketoprofen. Each ligand contains two squaramide units connected via a dipropylenamine spacer bearing a dansyl group as fluorescent signaling unit linked to the central nitrogen atom. The four ligands show different structural features: L1 and L2 have a macrocyclic topology while L3 and L4 are open-chain ligands. The non-fluorescent ligand L5 showing the same macrocyclic topology of L1 has been also studied for comparison. The aim of the study is to understand how and at which extent the molecular topology and the number of HB donors of the receptors influence the selectivity and the signaling efficiency towards the selected targets analytes NPX and KET in their anionic forms. Ligands L6 and L7 showed excellent ability to selectively bind NSAIDs through converging hydrogen bonds with a clear spectrophotometric output. They represent the single-arm and the double-arm version of the same ligand. They are both open-chain sensors in which the coordinating unit is represented by a squaramide covalently bonded to a 7-amino-4-(trifluoromethyl)coumarin. In the case of L6 the spacer that connects the two equivalent branches is a m-xylylenediamine, therefore a benzylamine was used for the synthesis of L7. The rationale in the design of these two ligands lies in looking for an eventual selectivity between the anions of four specific NSAIDs – Ibuprofen, Ketoprofen, Diclofenac and Naproxen – and a possible synergistic effect of the two branches in the case of the double sensor with respect to its single analogue. The receptor L8 consists of two “scorpiand” polyamine subunits connected by a luminescent biphenol spacer. The receptor has been salified with HCl making it perfectly soluble in an aqueous environment as well as characterizing by potentiometric means. The coordination and the fluorescence behavior of the binuclear species [Zn2L] in an aqueous environment both in the total pH range and in a buffered environment was studied. The focus of the project was to try to understand and explain the unusual fluorescence behavior of L8 in the presence of Zn2+ using different characterization techniques. Preliminary studies have also been carried out in the presence of organic molecules such as L-aspartic acid, L-glutamic acid, succinic acid and glutaric acid. The scorpiand-type polyamine chemosensor L9, bearing a fluorescent acridine moiety as signalling unit, has been designed and synthesized to selectively recognize nucleotides in aqueous media. L9 has a 12-membered polyamine macrocycle and the sensing material is connected to the acridinine-based fluorescent signal transducer via an N1-ethylpropane-1,3-diamine chain. The chosen nucleotides were those of the “triphosphate” series: ATP, GTP and UTP to which was also added the “monophosphate” GMP.