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Dilution enthalpies of enantiomers of four α-amino acids,namely L-proline vs D-proline,and L-hydroxyproline vs D-hydroxyproline,in water-rich regions of dimethyl formamide (DMF)+H2O and dimethylsulfoxide (DMSO)+H2O mixtures (mass fractions of cosolvents wCOS=0-0.30) have been determined respectively at 298.15 K by isothermal titration calorimetry (ITC).The successive values of dilution enthalpy obtained in a single run of ITC determination were used to calculate homochiral enthalpic pairwise interaction coefficients (hxx) at the corresponding composition of mixed solvents according to the McMillan-Mayer’ statistical thermodynamic approach.The sign and magnitude of hxx were interpreted in terms of solute-solute interactions mediated by solvent and cosolvent,and preferential configurations of homochiral pairwise interactions (L-L or D-D pairs) in solutions.The variations of hxx with wCOS were considered to depend greatly on the competition equilibrium between hydrophobic and hydrophilic interactions,as well as the structural alteration of water caused by the two highly polar aprotic cosolvents (DMF and DMSO).Especially,it was found that when one of the two kinds of interactions (hydrophobic or hydrophilic interactions) preponderates over the other in solutions,enthalpic effect of homochiral pairwise interactions is always remarkable and characterized by a large value of hxx,positive or negative,which corresponds to the prevailing interactions of hydrophobicity or hydrophilicity respectively.Interestingly,it was also found that the hxx values of L-enantiomers are generally larger than those of D-enantiomers across the whole studied composition range of mixed solvents,i.e.|hLL|>|hDD|,which is defined as enthalpic discrimination and attributed to the effect of preferential configuration on homochiral pairwise interactions in aqueous solutions.