Molecular complexation of some amino acids and triglycine with 18-crown-6 ether in H2O-EtOH solvents at 298.15 K

The influence of composition of H2O-EtOH solvent on the reaction of formation of a molecular complex of 18-crown-6 ether (18C6) with triglycine (3Gly) has been studied at 298.15 K by a thermochemical method. The standard thermodynamic parameters (Delta(r) GA degrees, Delta(r) HA degrees, and T Delta(r) SA degrees) of the reaction of [3Gly18C6] complex formation in water-ethanol (H2O-EtOH) solvents having an EtOH mole fraction of 0.0, 0.1, 0.15, 0.2, 0.25, 0.30, and 0.50 have been calculated from the data of calorimetric measurements performed on a TAM III titration microcalorimeter. It has been found that an increase in EtOH concentration in the mixed solvent results in an increase in stability of [3Gly18C6] and in an enhancement in exothermicity of its formation reaction. The water-ethanol solvent has an analogous effect on the stability and energetics of the reactions of formation of molecular complexes of 18C6 with glycine, D,L-alanine, and L-phenylalanine.