Thermodynamic aspects of the host–guest chemistry of pyrogallol[4]arenes and peralkylated ammonium cations

The stability constants (K), standard free energy (ΔGo), enthalpy (ΔHo), and entropy changes (ΔSo) for the complexation of pyrogallol[4]arenes with ammonium cations of different size and shape have been determined in ethanol at 298 K by isothermal titration calorimetry. The trends observed in the thermodynamic parameters for 1:1 and/or 1:2 host–guest complexation correspond to the systematic structural changes of the guest molecules. On the basis of the results obtained we compare the complexation properties with two other resorcin[4]arenes and discuss the thermodynamic aspects of this supramolecular host–guest interactions.