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

Apparent molar volumes $$ of glycine/l-alanine in water and in aqueous citric acid (CA) solutions of varying concentrations, i.e. (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg^-1 were determined from density measurements at temperatures T = (288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure. Limiting partial molar volumes $$ and their corresponding partial molar volumes of transfer $$ have been calculated from the $$ data. The negative $$ values obtained for glycine/l-alanine from water to aqueous CA solutions indicate the dominance of hydrophilic-hydrophobic/hydrophobic-hydrophilic and hydrophobic-hydrophobic interactions over ion/hydrophilic-dipolar interactions. Further, pair and triplet interaction coefficients, i.e. $$ 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.