Calorimeteric and NMR binding studies of hydrogen-bonding receptors for carboxylates

Two receptors (1 and 2) were designed and prepared to bind carboxylate anions through donor–donor hydrogen-bonding motifs provided by thiourea (1) and squaramide (2) groups. The binding efficacy of each receptor was studied using NMR and isothermal calorimetric titrations in DMSO and CH3CN/CHCl3 solvent systems. Binding constants and changes in enthalpy and entropy of the binding process were calculated and evaluated.