Chiral recognition between enantiomeric a-amino acids. A calorimetric study at 25° C.

Homotactic and heterotactic enthalpic pair interaction coefficients were determined at 25°C from the enthalpies of dilution of binary and ternary aqueous solutions containing the L and D forms of -aminoacids bearing alkyl chains of increasing length (alanine, -aminobutyric acid, valine, norvaline, leucine, isoleucine and norleucine). Significant differences were found between the values of the homotactic (h DD or h LL ) and heterotactic (h DL ) pairwise coefficients, for the enantiomers of leucine and its isomers. The role of the zwitterionic interactions is discussed to explain the nature of the chiral recognition.