Calorimetric study of the molecular complex formation of glycyl–glycyl–glycine with 18-crown-6 in aqueous organic solvents

Abstract

The influence of water–ethanol (H₂O–EtOH), water–acetone (H₂O–MeAc) and waterdimethylsulfoxide (H₂O–DMSO) solvents on the reaction of the molecular complex formation between ether 18-crown-6 (18C6) and small peptide glycyl–glycyl–glycine (3Gly) has been studied at T = 298.15 K. The thermodynamic parameters for the reaction (log K, Δ_rG, Δ_rH, Δ_rS) were obtained from calorimetric titration experiments carried out by means of the calorimetric system TAM III (TA Instruments, USA). 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 sоlvation-thermodynamic approach.