Enantioselectivity measurements of copper(II) amino acid complexes using isothermal titration calorimetry

Enantioselectivity experiments for the binding to chiral Cu(II) complexes h ave been performed for several alpha -amino acids using isothermal titratio n calorimetry. To a system containing nonionic micelles, Cu(II) ions, and c holesteryl glutamate as chiral selector, either the D- or L-amino acid was titrated. The highest enantioselectivities (K-D/K-L) were measured for the amino acids with relatively bulky R-groups [phenylalanine (1.24) and phenyl glycine (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 ala nine 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 selec tor is an entropically driven process.