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

Abstract: 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 Т =298.15K. The standard thermodynamic parameters (Δr G о, Δr H о, ТΔr S о) 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)=0.0/0.6mol fraction. The stability of [Phe18C6] and the mechanism of complexation in water were investigated using the 1Н and 13С NMR spectroscopy. The increase of EtOH concentration results in an increase of the complex stability and of the exothermicity of complexation. [Copyright &y& Elsevier]