Temperature-dependent dielectric relaxation and hydration dynamics of γ-aminobutyric acid in aqueous solution: A broadband dielectric spectroscopy and QTAIM study.

Abstract

The complex permittivity of aqueous solutions of γ-Aminobutyric Acid (GABA) is measured in the span of 0.5 < GHz < 50 by varying the molal concentration (0-1.0865 mol.kg-1) at T = 298.15 K - 323.15 K. The dielectric spectra were analyzed using a two-relaxation Cole-Cole model to determine the relaxation times, dielectric strengths, and distribution parameters. At lower GABA concentrations (0-0.3078 mol.kg-1), the dielectric response is predominantly governed by hydration-water dynamics, whereas at higher concentrations (0.4136-1.0865 mol.kg-1), an additional slower relaxation contribution emerges, associated with GABA reorientation and its hydration environment. The volumetric and transport data suggest strong intermolecular interactions and progressive ordering of water in the vicinity of GABA molecules. DFT (B3LYP) with D3/6-311G ++ (d, p) calculation was performed in both gas and water medium to assess the strength of hydrogen-bonding, while the mean molecular polarizabilities were estimated using the Lippincott δ-function model and were further validated through LeFevre method. QTAIM analysis demonstrated the presence of strong intermolecular hydrogen-bonding interactions, as evidenced by the identification of bond critical points and their associated topological parameters. These findings provide insights into GABA hydration, molecular interactions, biological functions, neurotransmitter transport, and potential pharmaceutical applications.