Chiral recognition in aqueous solutions between enantiomeric a-amino acids bearing substituted alkyl chains at 25°C: the preferential configuration model.

Calorimetric, densimetric, and nuclear relaxation time measurements were carried out at 25°C on binary and ternary aq. solns. contg. L and D forms of the following amino acids bearing substituted alkyl chains: lysine, glutamine, arginine, asparagine, serine, and homoserine. For three of them (lysine, glutamine, and arginine), very high differences were found between the values of the homochiral and heterochiral pairwise enthalpic interaction coeffs. Vol. and spectroscopic data showed that it is possible to detect chiral recognition by techniques other than calorimetric. The role of the zwitterionic interaction and of the substituted side chain is discussed to explain the enhanced chiral recognition of these a-amino acids in respect to those bearing unsubstituted alkyl chains (alanine, a-aminobutyric acid, valines and leucines).