Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

The apparent molar volume of glutamine dipeptides (glycyl-L-glutamine and L-alanyl-L-glutamine) and the molar conductivity (poundsN) of sodium caproate (NaC6) have been determined from density and conductance measurements. The values of apparent molar volume of glutamine dipeptides were utilized to deduce the standard partial molar volumes, standard partial molar volumes of transfer for glutamine dipeptides from water to aqueous sodium caproate solutions, hydration number and volumetric interaction coefficients. An increase in transfer volumes and a decrease in hydration number of the dipeptide with increasing sodium caproate concentration have been explained due to stronger interactions of sodium caproate with the charged center and polar groups of the peptides compared to the sodium caproate-nonploar group of peptide interactions. From the molar conductivity of sodium caproate, the limiting molar conductivity of sodium caproate and Walden products were calculated. The decrease in the limiting molar conductivity of sodium caproate and Walden products with increase in dipeptide concentration is attributed to the interaction of sodium caproate with dipeptides and the friction resistance of the solvent medium. Both the hydration number for dipeptides and Walden products values in peptide-sodium carboxylate-water systems are in the order: sodium acetate greater than sodium butyrate greater than sodium caproate. This can be ascribed to the fact that the interactions of dipeptides with sodium carboxylate increase with the increase in the size of side chain of carboxylic anions.