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

Apparent molar volumes of glycine/l-alanine in water and in aqueous citric acid (CA) solutions of varying concentrations, (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg were determined from density measurements at temperatures  = (288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure. Limiting partial molar volumes and their corresponding partial molar volumes of transfer have been calculated from the data. The negative 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, along with hydration number 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 and their second-order derivative . The apparent specific volumes for glycine and l-alanine tend to approach sweet taste behavior both in the presence of water and in aqueous CA solutions. The 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.