Transfer Properties of Diglycine from Water to Aqueous Alkali Metal Nitrate Solutions

Abstract

Enthalpies of solution and densities of diglycine in aqueous solutions of LiNO3, NaNO3 and KNO3 were measured at 298.15 K. Transfer enthalpies ( $$ \Delta_{\text{tr}} H $$ ) and transfer partial molar volumes ( $$ \Delta_{\text{tr}} V_{\phi }^{0} $$ ) were derived for diglycine. The transfer enthalpies of diglycine from water to the three alkali metal nitrates solutions are negative while the transfer partial molar volume values are positive. The absolute values of $$ \Delta_{\text{tr}} H $$ and $$ \Delta_{\text{tr}} V_{\phi }^{0} $$ from water to the same concentration in salt solutions in both cases vary in the relative order LiNO3 < KNO3 < NaNO3. The results are discussed in terms of electrostatic interaction and structural interactions. Electrostatic interaction between the diglycine zwitterion and salts gives large contributions to Δtr H and $$ \Delta_{\text{tr}} V_{\phi }^{0} $$ . But, structursal interaction is responsible for the abnormal behavior of diglycine in aqueous LiNO3 solutions.