Importance of hydrogen‐bonding sites in the chiral recognition mechanism between racemic D 3 terbium(III) complexes and amino acids

The perturbation of the racemic equilibrium of luminescent D 3 terbium(III) complexes with chelidamic acid (CDA), a hydroxylated derivative of 2,6‐pyridine‐dicarboxylic acid (DPA), by added chiral biomolecules such as L ‐amino acids has been studied using circularly polarized luminescence and 13 C NMR spectroscopy. It is shown in this work that the chiral‐induced equilibrium shift of [Tb(CDA) 3 ] 6− by L ‐amino acids (i.e. L ‐proline or L ‐arginine) was largely influenced by the hydrogen‐bonding networks formed between the ligand interface of racemic [Tb(CDA) 3 ] 6− and these added chiral agents. The capping of potential hydrogen‐bonding sites by acetylation in L ‐proline led to a ∼100‐fold drop in the induced optical activity of the [Tb(CDA) 3 ] 6− : N ‐acetyl‐ L ‐proline system. This result suggested that the hydrogen‐bonding networks serve as the basis for further noncovalent discriminatory interactions between racemic [Tb(CDA) 3 ] 6− and added L ‐amino acids. Chirality, 2009. © 2008 Wiley‐Liss, Inc.