Concentration Effect of Sodium Chloride and Potassium Chloride on Enthalpies of Mixing of N-Glycylglycine with d-Mannitol in Aqueous Solutions at 298.15 K

Abstract

The enthalpies of mixing of N-glycylglycine with d -mannitol in aqueous sodium chloride and potassium chloride solutions have been determined by using flow-mix isothermal microcalorimetry at 298.15 K. The results, along with the enthalpies of dilution of these solutes, have been analyzed using the McMillan−Mayer theory to obtain the heterotactic enthalpic interaction coefficients (h xy , h xxy , and h xyy ). It has been found that the heterotactic enthalpic pairwise interaction coefficients h xy between N -glycylglycine and d -mannitol in aqueous sodium chloride or potassium chloride solutions are negative and become less negative as the molality of sodium chloride or potassium chloride increases. The results have been interpreted from the point of view of solute−solute interactions and solvation effects.

Solvent and pH Dependences of Mixing Enthalpies of N-Glycylglycine with Protocatechuic Acid

“…The interaction of two solvated species involves the partial dehydration of the solute molecules and the direct interaction caused by short-range molecular forces. − Palecz determined enthalpic interaction coefficients h xy of amino acid zwitterions with a urea molecule and discussed the effects of the direct interactions of the zwitterionic “head” and nonpolar side chains of the examined amino acid with the polar urea molecule and partial dehydration of hydration sheaths of the solute molecules on h xy . In our previous work, the effects of sodium chloride and potassium chloride on the enthalpies of mixing of N -glycylglycine with d -mannitol and xylitol were discussed in detail based on solute–solute interactions and solvation effects. , …”

“…42 In our previous work, the effects of sodium chloride and potassium chloride on the enthalpies of mixing of Nglycylglycine with D-mannitol and xylitol were discussed in detail based on solute−solute interactions and solvation effects. 44,45 For GlyGly−PCA−buffer system discussed here, the types of interaction can be classified in detail as follows: (1) partial dehydration of the hydration shell around solute molecules (including GlyGly and PCA molecules, positive contribution to , and Cl − , negative contribution to h xy ); (iii) hydrophobic−hydrophilic interactions between the benzene ring of PCA molecules and the hydrophilic groups of GlyGly molecules (positive contribution to h xy ). When PCA and GlyGly molecules approach each other, the inevitable interaction between the benzene ring of PCA molecules and the hydrophilic groups of GlyGly molecules require more energy to expel some solvent molecules from the solvation shell of the both types of groups, which make a positive contribution to h xy .…”

The Mixing Enthalpy Interaction Coefficients of N,N′-Hexamethylenebisacetamide with l-Alanine and l-Serine in Aqueous Glucose Solutions at 298.15 K

“…The heterotactic enthalpic pairwise interaction coefficients have been obtained from analyzing the data. These important thermodynamic parameters reflect the sum of the enthalpic effects of interactions among the species [21][22][23].…”