Stereoselectivity in bis(α-amino acid)copper(II) complexes—II[5] spectrophotometric and spectropolarimetric investigation of the solvent effect

Abstract

Abstract Stereoselectivity phenomena have been studied in the copper(II) bis-complexes of a series of natural bidentate α-amino acids substituted at the nitrogen atom with methyl and benzyl groups in different proportions. The difference in the free energy of formation of complexes with the two ligands of similar and of opposite configurations can be as high as 2·1 ± 0·5 kcal/mole as in the case of a mixed complex of N-benzylproline with N,N-dimethylvaline. Changing the solvent may result not only in a change of the magnitude of stereoselectivity but even in a change of its sign. The efficiencies of spectrophotometry, polarimetric titration and circular dichroism measurements for the quantitative evaluation of stereoselectivity effects are compared.