Thermodynamics of molecular complexation of glycyl–glycyl–glycine with cryptand [2.2.2] in water–dimethylsulfoxide solvent at 298.15 K

The influence of water–dimethylsulfoxide (H 2 O–DMSO) solvent on the reaction of the molecular complex formation between cryptand [2.2.2] (L) and glycyl–glycyl–glycine (3Gly) was studied at T = 298.15 K. The thermodynamic parameters for the reaction (lg K 0 , Δ r G 0 , Δ r H 0 , T Δ r S 0 ) were obtained from calorimetric titration experiments carried out by means of the calorimetric system TAM III (TA Instruments, USA). The binding mode of 3Gly–L complexation in H 2 O–DMSO solvent was determined by NMR spectroscopy, and the spectroscopic data were also used to calculate the [3GlyL] stability constants. A slight increase in complex stability and reaction exothermicity was observed at increasing DMSO content. The thermodynamic parameters for [3GlyL] are compared with thermodynamic parameters of complex formation of 18-crown-6 with amino acids and 3Gly in mixed solvents using the solvation-thermodynamic approach.