Dielectric relaxation studies of aqueous L-glutamine-ethanol mixtures in the microwave frequency range

摘要

A study on the dielectric properties of various molar concentration levels of aqueous L-glutamine, ethanol mixtures at microwave frequency region (0.02 < nu/GHz < 20) is carried out in the temperature range of 298 K to 323 K. Dielectric parameters such as dielectric permittivity, dielectric loss of different molar concentrations of L-glutamine in water, ethanol medium are evaluated. It is noticed that the real and imaginary part of dielectric permittivity increases with increase in molar concentration levels of L-glutamine in water and ethanol medium and decreases with increase in temperature. From these parameters, average relaxation time (tau), excessive inverse relaxation time (1/tau)(E), excessive dielectric permittivity (epsilon(E)) are determined and their behavior is analyzed in terms of the distribution of hydrogen bond network in the liquid medium. The theoretical dipole moments of L-glutamine in both aqueous and ethanol medium are determined by using DFT-B3LYP method with different solvation models. Mean molecular polarizability (alpha(M)) of the system is calculated from the Lippincott delta function potential model and compared with the Lefevre method. The activation entropy (Delta S*), activation enthalpy (Delta H*), Helmholtz energy (Delta F-E) parameters have also been evaluated and the results are correlated. (C) 2019 Elsevier B.V. All rights reserved.