Abstract
Enantioselectivity experiments for the binding to chiral Cu(II) complexes have been performed for several -amino acids using isothermal titration calorimetry. To a system containing nonionic micelles, Cu(II) ions, and cholesteryl glutamate as chiral selector, either the D- or L-amino acid was titrated. The highest enantioselectivities (KD/KL) were measured for the amino acids with relatively bulky R-groups [phenylalanine (1.24) and phenylglycine (1.26)], while an increase in enantioselectivity from 1.00 to 1.21 was measured upon increasing the size of the R-group in the amino acids alanine to leucine. For serine, no enantioselectivity was measured. Reciprocal enantioselectivities have been measured with phenylalanine upon inversion of the chirality of the glutamate headgroup of the chiral selector. Finally, it was found that the binding of the amino acid to the chiral-metal selector is an entropically driven process.