Hydrogen Bonding and Solvent Effects on Calixarene Coordination Reactions

Abstract

Calixarenes are macrocyclic compounds comprising phenolic units ortho-linked by methylene bridges. Many calixarene derivatives are known to be very efficient and in some cases selective binders of ions and neutral molecules. The complexation reactions of calix[4]arene derivatives in several solvents were extensively investigated by means of an integrated thermodynamic, structural, and computational approach. Thermodynamic data (complex stability constants and derived reaction Gibbs energies, enthalpies and entropies) were determined using several experimental techniques, and correlated with structural results obtained by X-ray crystallography, NMR, and computational methods (DFT and molecular dynamics). The solvation and transfer parameters of the ligands and their complexes were also determined and discussed. The intra- and intermolecular hydrogen bonding and solvent effects on the equilibria of binding reactions were particularly addressed. The results clearly indicate how remarkable and complex the influence of solvent on the ion-hosting abilities of calixarene derivatives can be.