Elucidation of molecular interactions of aspartic acid with aqueous potassium sorbate and sodium benzoate: Volumetric, viscometric and FTIR spectroscopic investigation

Abstract

Aspartic acid (Asp), a nonessential amino acid has been taken for the present study. Solutions of different concentrations of aspartic acid were prepared by dissolving it in water and {water + (1.5, 2.0 and 2.5 m) Potassium sorbate (PS)/sodium benzoate (SB)}. Density and viscosity of the solutions were experimentally determined at T = (293.15, 298.15, 303.15, 308.15 and 313.15) K. Volumetric parameters like apparent molar volume (V∅), partial apparent molar volume (V∅0), partial apparent molar expansibility (E∅0) were computed by using standard formulations. Stronger ion-ion, ion-hydrophilic and hydrophilic-hydrophilic interactions between zwitterionic centers (COO- and NH3+) and polar groups of aspartic acid (COOH and NH2) and ions present in aqueous PS/SB are found to dominate the hydrophobic interactions between the nonpolar organic segments of amino acid and PS/SB. Structure building character of aspartic acid in presence of PS/SB are established by the positive values of Hepler’s constant (∂2V∅0/∂T2)P for all compositions of solutions. Positive viscosity B-coefficient (BJ) and negative (∂BJ/∂T)values further establish the structure building character of aspartic acid. Thermodynamic parameters for viscous flow (Δμ20,#,ΔS0,#andΔH0,#) suggest that transition state for viscous flow is less stable than the ground state and formation of transitions state is not thermodynamically favoured. Shifting of IR absorption band for O-H stretching due to H-bonding at 3300–3340 cm-1 confirms changes in solvent structure due to ion-ion and ion–solvent interactions occurring in the investigated systems.