Thermodynamic hydration behaviour of glycine below room conditions using time domain reflectometry

Abstract

The present work reports the concentration-dependent hydrophobicity of glycine below room temperature. The dynamics of aqueous glycine have been studied by means of dielectric relaxation spectroscopy using Time Domain Reflectometry (TDR) technique in the frequency region of 10 MHz–30 GHz. Complex permittivity spectra are obtained using TDR that allowed evaluation of the static dielectric constant (ε0) and average relaxation time (τ). As dielectric relaxation spectroscopy provides information on the average relaxation time (τ) related to the mechanism of hydrogen bond (HB) formation and breaking, therefore the concentration-temperature dependence of τ was used to evaluate and study hydration behaviour through dielectric parameters such as dipole moment (μ), correlation factor (g), and the dynamics of irrationally bound water molecules (Zib). Aqueous glycine relaxes in two different relaxation modes in the broad microwave frequency region from MHz to GHz. The low-frequency relaxation process (l-process) observed is associated with glycine relaxation, while the detected peak in the high-frequency relaxation process (h-process) is attributed to water associated with glycine. We have attempted a concentration-temperature-dependent hydrogen bonding mechanism in both relaxation processes, and the results were corroborated with thermodynamical parameters such as molar entropy of activation (∆Sj), molar enthalpy of activation (∆Hj), and molar free energy of activation (∆Fj).