Molecular containers based on aryl-extended calix[4]Pyrroles

Identifier:  TDX:3010

Handle: https://hdl.handle.net/20.500.11797/TDX3010

Authors:  Escobar González, Luis

Abstract:
This Thesis deals with the design and synthesis of concave receptors possessing hydrophilic cavities: covalent receptors, metallo-cages and non-covalent capsules. For their construction, we chose the aryl-extended calix[4]pyrrole scaffold (AE-C[4]P), which delivers a deep aromatic cavity closed at one end by a polar binding site and opened at the opposite end. We investigated the binding properties of the synthesized receptors in both organic solvents and water. Specifically, we describe a synthetic approach for the elongation of the cavity of AE-C[4]Ps leading to super aryl-extended derivatives (SAE-C[4]P). First, we prepared a tetra-ester SAE-C[4]P and conducted binding studies with a series of N-oxides in chloroform solution. The SAE-C[4]P complexes had 1:1 stoichiometry and were thermodynamically and kinetically highly stable. The results highlight the superior binding properties of the SAE-C[4]P receptor versus the parent aryl-extended. Next, we synthesized SAE-C[4]Ps bearing eight ionizable (octa-acid) or charged (octa-pyridinium) groups. The later SAE-C[4]Ps were soluble in basic or neutral water. We determined the thermodynamic stability of their inclusion complexes with a series of pyridyl N-oxides, having different non-polar residues at their para-position. Based on these results, we quantified the magnitude of the hydrophobic effect operating in these SAE-C[4]P complexes. We also report the self-assembly of metallo-cages and non-covalent capsules, featuring enclosed cavities. In this regard, we show that a tetra-pyridyl SAE-C[4]P ligand self-assembles into a mono-metallic Pd(II)/Pt(II)-cage. We studied the encapsulation of neutral polar guests in the cage’s cavity. The results obtained in the kinetic characterization of the cage complexes allowed us to propose viable mechanisms for the guest inclusion/exchange processes. Finally, we describe the dimerization studies of a tetra-urea SAE-C[4]P into dimeric capsules stabilized through hydrogen-bonding interactions.