Influence of 2-hydroxyethylammonium acetate-based protic ionic liquids on the thermophysical properties of aqueous DL-alanine solutions

Abstract

Understanding the hydration behavior of amino acids is fundamental to gaining insights into protein solvation mechanisms. Within this framework, examining the solvation properties of amino acids in aqueous media containing protic ionic liquids (PILs) a novel class of environmentally friendly solvents is crucial for characterizing their hydration dynamics. This research focuses on the influence of ammonium-based PILs, specifically mono-, bis-, and tris-(2-hydroxyethyl) ammonium acetate, on the hydration characteristics of DL-alanine. By employing COSMO computational analysis alongside thermophysical property measurements, the study evaluates the hydration energies and σ-profiles of DL-alanine and the PILs. The thermophysical behavior of DL-alanine in aqueous solutions containing varying concentrations of protic ionic liquids (PILs) was systematically analyzed using experimental data and modeling approaches. The density, speed of sound, viscosity, and refractive index were measured for ternary solutions of DL-alanine, water, and PILs across a temperature range of (298.15 to 318.15) K under atmospheric pressure. The standard partial molar volume ([Formula: see text]) measured over the studied temperature range indicates that the solute-solvent interactions between [2-HEA]Ac and DL-alanine in the presence of water is 63.119 cm³·mol^-1. Additionally, the hydration layer surrounding DL-alanine is notably influenced by temperature, as higher temperatures lead to the release of more water molecules relative to PIL-containing solutions. This temperature-dependent effect is especially pronounced in the presence of (2-hydroxyethyl) ammonium acetate, underscoring its significant impact on the hydration behavior of DL-alanine.

Keywords: DL-alanine; COSMO Analysis; Molar refractionon; Protic ionic liquids; Viscosity; Volumetric properties.

Fig. 1

Sigma profiles of DL-alanine, water, [2-HEA] Ac, [BHEA] Ac, and [THEA] Ac

Fig. 2

Variation of apparent molar volumes( )with, a) temperature, b) concentration of PILs and c) cation size of the PILs

Fig. 3

Variation of apparent molar isentropic compressibility ( ) with, a) temperature, a) concentration of PILs and c) cation size of the PILs

Fig. 4

molar refraction variation of ternary solutions with, a) temperature, b) concentration of PILs and c) cation size of the PILs