Dependence of chiral recognition of a-amino acids and their derivatives on the nature of functional groups. Calorimetric and spectroscopic studies.

Calorimetric and nuclear relaxation time measurements were carried out at 25° on binary and ternary aq. solns. contg. the L and D forms of the N-acetyl derivs. of the a-amino acids alanine, valine, leucine, methionine, aspartic acid and proline. The interaction coeffs. of the virial expansion of the excess enthalpy were evaluated. Only the acetyl derivs. of leucine and proline present chiral recognition, namely a difference in the energetics of interaction between the LL and DL forms. This chiral recognition is larger in magnitude with respect to the corresponding free amino acids and changes sign. The role of the functional group is discussed and the results are interpreted using the preferential configuration model. Like-like interactions between functional groups seem to be responsible for the inversion of chiral recognition.