Stereoselectivity in bis(α-amino-acid)copper(II) complexes: stability constants from circular dichroism and electronic spectra

Abstract

The circular-dichroism spectra of aqueous solutions containing cupric ions, N-benzyl-L-proline, and either L- or D-valine or L- or D-proline, have been measured and used to calculate the formation constants for the mixed complexes [Cu(N-benzyl-L-proline)(D-valine)], [Cu(N-benzyl-L-proline)(L-proline)], and [Cu(N-benzyl-L-proline)-(D-proline)]. The results indicate that considerable stereoselectivity occurs in the formation of these complexes, and this is confirmed by measurements of electronic absorption spectra. Careful measurements of the electronic absorption spectrum of [Cu(valine)₂] and [Cu(proline)₂] indicate that some stereoselectivity occurs even with these complexes, resulting in differences between the spectra of optically active and meso-complexes.