Novel receptors based on calix [4] arene for cation complexation: Synthesis, characterisation and binding properties.

Following an introduction on calixarene chemistry and their metal-ion complexes including some of their applications, the aim of the work are described. Thus this thesis concentrates on the synthesis and characterisation of two new lower rim calix(4)arene derivatives containing mixed pendent arms as well as an investigation on the solution properties of their metal-ion complexes. Macrocycles namely, 5, 11, 17, 23 tetrakis (1, 1 dimethylethyl) 25, 27- bis [(2-methylthio) ethoxy] 26, 28-bis [2- pyridyl methyloxy] calix(4)arene, L1 and 5, 11, 17, 23 tetrakis (1, 1 dimethylethyl) 25, 27- bis [(2- methylthio) ethoxy] 26, 28-bis [3-pyridyl methyloxy] calix(4)arene, L2, are structurally (1H NMR and X-ray crystallography) and thermodynamically (solubility, Gibbs energy, enthalpy and entropy) characterised. The complexing ability of these ligands for metal cations is investigated using a variety of techniques. Solubility measurements and derived standard transfer Gibbs energies of these isomers indicate that these macrocycles undergo selective solvation in non-aqueous media. 1H NMR studies were performed to obtain information about the active site of interaction of these ligands with metal cations. Conductance measurements were used to establish the composition of the metal-ion complexes in dipolar aprotic media. Potentiometric and calorimetric measurements were carried out to derive the thermodynamic parameters of complexation of L1 and L2 and metal-ions in acetonitrile and benzonitrile at 298.15 K. Based on stability constant data, two metal- ion complexes of L1 were isolated and the structure of the Na+ complex determined by X-ray diffraction methods. Thus, the cation was found in the hydrophilic cavity while the hydrophobic cavity hosts a molecule of acetonitrile. The crystallographic results confirm the key role played by the ethereal oxygens in the complexation process. Thus, while L1 is able to interact with alkali metal cations, no complexation was found for L2 and these cations. This is attributed to an increase in the distance between the pyridyl nitrogen and the ethereal oxygen in moving from L1 to L2. Conclusions and suggestions for further research in this area are given