Molecular recognition properties of new chiral molecular tweezers based on deoxycholic acid 1～3 have been investigated using amino acid methyl esters. The association constants (K~a) and gibbs free energy changes (-△G°) have been measured by UV-visible spectroscopic titration for inclusion complexation of molecular tweezers 1～3 with some D/L-amino acid methyl esters in CHCl~3 at 25℃ . The results indicate that the molecular tweezers 1 and 2 are favorable for complexation with D-amino acid methyl esters and molecular tweezer 3 fails to recognize all amino acid methyl esters examined. the supramolecular complexes formed from host 1 or 2 with various guest D/L-amino acid methyl esters consist of 1 : 1 host and guest molecules. The molecular recognition ability and enantioselectivity of receptors for amino acid methyl esters are discussed from in terms of size/shape-fit, complementary geometrical relationship and the weak intermolecular forces. A computer-aided study has been employed to elucidate the binding behavior of these molecular tweezers. Molecular modeling suggests that in these molecular tweezers the recognition ability come mainly from hydrogen bonding and van der Waals interaction. The size/shape-fit and geometrical complementary relationship between receptor and substrate play a pivotal role in the inclusion complexation of amino acid methyl esters with rceptor 1～3.

Key words: OLECULAR RECOGNITION, AMINO ACID, ENANTIOMORPH, STEROIDS, COMPUTERIZED SIMULATION