Copper(II) complexes of peptide-group-containing amino acids Bis(N-acetyl- l-alaninate)copper(II) complexes and their amine adducts

Abstract

The bis(N-acetyl- l-alaninate)copper(II) monohydrate, for which magnetism and electronic and IR spectra suggest a copper-acetate monohydrate type structure, was prepared. The substitution of the water molecule with some amines was made to investigate their effect on the amino acid coordination and on the geometry around the copper ion. For the adducts of monodentate heterocyclic amines such as N-methylpiperazine, piperidine, morpholine, pyridine, 3- and 4-methylpyridine (CuL 2B 2) and of bidentate amines such as piperazine, ethylenediamine, 2,2′- and 4,4′-bipyridine (CuL 2B) in the solid state or chloroform solution, magnetic properties, electronic spectra (one d− d band in the 14500–18700 cm −1 spectral region, depending on the basicity or steric interference of the amines) and IR spectra suggest a square-planar or strongly distorted tetragonal arrangement around the copper ion with a CuN 2O 2 or CuN 4 chromophore. For the Cu(N-ac- l-ala) 2B 2 (BN-methypiperazine, piperidine and morpholine) adducts in chloroform solution in presence of excess amine, electronic (two d− d bands) and IR spectra indicate tetragonal arrangement around the copper ion with a CuN 4O 2 chromophore, while for the Cu(N-ac- l-ala) 2· o-phen adduct in the solid state and chloroform solution they suggest the presence of 6-coordinate cis-octahedral species, with CuN 2O 4 chromophores. In all the adducts studied the IR spectra exclude any interaction between the peptide group and the metal ion.