Water soluble calix[4]arenes. A thermodynamic investigation of proton complex formation

Abstract

Thermodynamic parameters of protonation of calix[4]arene-p-tetra sulphonate were potentiometrically and calorimetrically determined in aqueous solution at 25 °C and I = 0.1 mol dm⁻³ (NaNO₃). These values were compared with literature findings. ΔH° and ΔS° values reveal that the penta-anion protonation is energetically costly. In this connection the role played by hydrogen bonding and the cone conformation stabilization are critically discussed. Proton formation constants of the calix[4]arene-p-tetrasulphonate-tetra-carboxylate derivative in the cone conformation were also potentiometrically determined under the same experimental conditions.