Thermodynamic study of p-sulfonated calixarene complexes in aqueous solution

Abstract

Association equilibrium constants and thermodynamic parameters (i.e., ΔH and ΔS) for complexation between N,N-dimethylindoaniline and p-sulfonated calix[n]arenes in aqueous solution have been determined by means of UV–VIS spectroscopy. Equilibrium constants corresponding to calix[n]arene-p-sulfonates increase in the order [4] < [6] ≈ [8]. ΔH and ΔS values, which are interpreted in terms of the importance of the various interactions responsible for complexation, lead to a linear ΔH – TΔS relationship. Such a linear correlation is interpreted in terms of the extent of calixarene conformational change and of host and guest desolvation involved in the complexation process.