CHIRAL RECOGNITION IN AQUEOUS-SOLUTIONS - ON THE ROLE OF UREA IN HYDROPHILIC AND HYDROPHOBIC INTERACTIONS OF UNSUBSTITUTED ALPHA-AMINO-ACIDS

Calorimetric and nuclear relaxation time measurements were carried our at 25 degrees C on concentrated aqueous solutions of urea containing the L. and D forms of the following alpha-aminoacids: alanine, alpha-a minobutyric acid, norvaline, and norleucine. Glycine was also studied under the same experimental conditions. The enthalpic interaction coef ficients were rationalized according to the preferential configuration model. The trends of the homochiral coefficients at increasing concen tration of urea underline an interaction mechanism not different from that occurring in water. Chiral recognition is the quantity more affec ted by the nature of the solvent Among the amino acids studied, only n orleucine presents this effect, which vanishes at the highest concentr ations of urea because the attenuated electrostatic interactions canno t impose preferential configurations.