Thermochemical Characteristics of the Dissolution of d-Valine in Aqueous Solutions of Some Amides at T = 298.15 K

Abstract

Enthalpies of the dissolution of d-valine in the mixtures of water with formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) with the mole fraction (x2) of amides ranging up to 0.3 have been measured at T = 298.15 K. The standard enthalpies of the dissolution (ΔsolH°) and the transfer enthalpies (ΔtrH°) of d-valine have been calculated. On the basis of McMillan–Mayer’s theory, the enthalpic coefficients of pairwise interaction (hxy) have been calculated. The enthalpic coefficients (hxy) of the solute–amide pairwise interaction in the water proved to be positive and increasing in the series: FA < MFA < DMF. It is associated with the increasing of the hydrophobic properties of amides and the energy of intermolecular interactions between components of water+organic mixtures in the same sequence.