Application of isothermal titration calorimetry for evaluation of water–acetone and water–dimethylsulfoxide solvent influence on the molecular complex formation between 18-crown-6 and triglycine at 298.15 K

Abstract

The influence of water–acetone (H2O–MeAc) and water–dimethylsulfoxide (H2O–DMSO) solvents on the reaction of the molecular complex formation between 18-crown-6 ether (18C6) and small peptide triglycine (3Gly) has been studied at T = 298.15 K. The thermodynamic parameters for the reaction (lgK, ΔrG, ΔrH, ΔrS) were obtained from calorimetric titration experiments carried out by means of the calorimetric system TAM III (TA Instruments, USA). The binding mode of 3Gly–18C6 complexation in H2O–MeAc and in H2O–DMSO solvents was determined by 1H NMR spectroscopy, and the spectroscopic data were also used to calculate the [3Gly18C6] stability constants. The increase in MeAc and DMSO concentrations in solvents results in an increase in the [3Gly18C6] complex stability and in the exothermicity of complexation. The thermodynamics of the [3Gly18C6] molecular complex formation is discussed in comparison with thermodynamic parameters of complex formation between 18C6 and amino acids in mixed solvents using the solvation-thermodynamic approach.