Volumetric Investigations on Molecular Interactions of Glycine/l-alanine in Aqueous Citric Acid Solutions at Different Temperatures

Apparent molar volumes [Formula: see text] of glycine/l-alanine in water and in aqueous citric acid (CA) solutions of varying concentrations, i.e. (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg(−1) were determined from density measurements at temperatures T = (288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure. Limiting partial molar volumes [Formula: see text] and their corresponding partial molar volumes of transfer [Formula: see text] have been calculated from the [Formula: see text] data. The negative [Formula: see text] values obtained for glycine/l-alanine from water to aqueous CA solutions indicate the dominance of hydrophilic–hydrophobic/hydrophobic–hydrophilic and hydrophobic–hydrophobic interactions over ion/hydrophilic–dipolar interactions. Further, pair and triplet interaction coefficients, i.e. [Formula: see text] along with hydration number [Formula: see text] have also been calculated. The effect of temperature on the volumetric properties of glycine/l-alanine in water and in aqueous CA solutions has been determined from the limiting partial molar expansibilities [Formula: see text] and their second-order derivative [Formula: see text] . The apparent specific volumes [Formula: see text] for glycine and l-alanine tend to approach sweet taste behavior both in the presence of water and in aqueous CA solutions. The [Formula: see text] values for glycine/l-alanine increase with increase in concentration of CA at all temperatures studied. This reveals that CA helps in enhancing the sweet taste behavior of glycine/l-alanine which also supports the dominance of hydrophobic–hydrophobic interactions. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10953-018-0829-6) contains supplementary material, which is available to authorized users.