Enthalpies of Solution of L–L- and D–D- Isomers of Valine in Aqueous Alkanols at 298.15 K

Abstract

The enthalpies of solution of L- and D-valines in water-ethanol, water-n-propanol, and water-i-propanol mixtures were measured calorimetrically at 298.15 K at alcohol mole fractions, x2, ranging up to 0.4. Enthalpies of transfer, ΔtrH°, from water to aqueous alkanol were calculated for each of the system studied. The enthalpic coefficients, hxy, of the solute-cosolvent pair-wise interaction in water proved to be positive and increasing in the series: ethanol, n-propanol, and i-propanol. It was shown that both the nature of the amino acid L–L- and D–D-isomerization and dimensions of linear or branched cosolvent molecules define the energetics of interaction between valine and alkanol molecules.