The influence of water-ethanol mixture on the thermodynamics of complex formation between 18-crown-6 ether and L-phenylalanine

The influence of water-ethanol mixture composition on the complex formation between 18-crown-6 ether and L-phenylalanine was studied by titration calorimetry at T = 298.15 K. The standard thermodynamic parameters (DrGo, DrHo, TDrSo) of formation of [Phe18C6] molecular complex were calculated from data obtained by means of the microcalorimetric system TAM III (TA Instruments, USA) at X(EtOH) = 0.0/0.6 mol fraction. The stability of [Phe18C6] and the mechanism of complexation in water were investigated using the 1H and 13C NMR spectroscopy. The increase of EtOH concentration results in an increase of the complex stability and of the exothermicity of complexation.