Pyridinium-based Building Blocks for Rotaxanes inSupramolecular Dynamic Systems

Resumo

This dissertation describes the synthesis and study of compounds derived from pyridinium salts, as well as their application in supramolecular dynamic systems. The first chapter addresses the Pd(II) and Pt(II)-directed self-assembly of nitrogenous bidentate ligands, owning different hydrophobic units and that lead to rectangular dinuclear metallocycles. Then, the dynamic equilibrium established between discrete metallocyclic species and "ring-within-ring" pseudorotaxanes was studied. In that regard, the speciation of the system can be modified following the Le Chatelier principle, or by adding a complementary substrate to the metallocyclic cavity, which leads to the formation of the corresponding inclusion complex. In the next chapter, we tackled the synthesis of pyridinic substrates capped with carboxylate end groups, and owning an appropriate aromatic central nucleus for the complexation of the macrocycle cucurbit[7]uril. The position and number of these acid groups allows the modulation, as a function of pH, of thermodynamic and kinetic parameters of the equilibrium of formation of [2]pseudorotaxanes. The third chapter describes the preparation of a new [2]rotaxane in aqueous medium, using the dynamic covalent chemistry of imines and the complementarity of biphenylpyridinium salts with the cucurbit[7]uril host. The dynamic behaviour of the obtained [2]rotaxane causes the dissociation in its components, which is favoured under acidic conditions while it is blocked by increasing the pH, changing the solvent, or by eliminating the carbonyl group in the axle component. In the last part of the thesis, three different linear components were designed that present a naphthalene unit, two viologen moieties and a polyethylene glycol chain of variable length that connects them. Self-assembly with cucurbit[8]uril leads to a zip tie-shaped superstructure, due to the simultaneous inclusion of the naphthalene unit and one of the viologens. This system can be externally controlled depending on the solvent, resulting in a [2]pseudorotaxane structure. Likewise, by means of modulation of the electric potential, the transition between the states of "tight” and "relaxed” of the molecular zip tie can be induced.