Enthalpic pairwise interactions of isomers of 2,4-pentanediol and 2,5-hexanediol in dimethylsulfoxide+water mixtures at 298.15K

Abstract The dilution enthalpies of four chiral diols, namely (2S,4S)-(+)-2,4-pentanediol vs (2R,4R)-(−)-2,4-pentanediol and (2S,5S)-(+)-2,5-hexanediol vs (2R,5R)-(−)-2,5-hexanediol in dimethylsulfoxide (DMSO) + water mixtures at 298.15 K have been determined respectively, using isothermal titration calorimeter (ITC). On the basis of the McMillan–Mayer theory, homochiral enthalpic pairwise interaction coefficients ( h xx ) of the four diols in the mixed solvents of various mass fractions ( w  = 0–0.3) have been calculated. It is found amazedly that across the whole studied composition range of mixed solvent values of h xx for S-enantiomer are almost higher than R-enantiomer for each diol. The results are discussed from the point of view of solute–solute interaction and solute–solvent interaction accompanied by chiral discrimination effect. The variations of h xx with w for the four chiral diols depend largely on the competition equilibrium between hydrophobic–hydrophobic, hydrophilic–hydrophilic and hydrophobic–hydrophilic interactions in the ternary solution systems.