NEW MULTIDENTATE LIGANDS .8. METAL COMPLEXES OF N,N'-DIGLYCYLETHYLENEDIAMINE IN AQUEOUS SOLUTIONS

The specific coordinating tendencies of the synthetic ligand, N,Nʹ-diglycylethylenediamine, toward Cu(II) and Ni(II) ions have been studied as a model for peptide-metal binding. The coordination compounds formed are unique in that hydrogen ions are displaced by these metal ions from the amide linkages, and in the formation of a low pH polynuclear copper(II) chelate that depolymerizes to a mononuclear chelate in alkaline solution. The copper(II) chelate, CuL2+, releases amide protons in two distinct steps, to give the species Cu2(H-1L)22+ and CuH-2L. On the other hand, the nickel(II) chelate of the neutral ligand, NiL2+, loses both amide protons simultaneously to give the chelate NiH-2L. Cobalt(II) and zinc(II) ions do not displace the peptide protons, forming only the “ordinary” complexes, ML2+, in which the metal ion is coordinated to the neutral ligand. In the types of reactions with metal ions, the ligand resembles triglycine and tetraglycine, but contrasts with these and other peptides in the manner in which it forms polynuclear copper(II) chelates. Electronic spectra of the Cu(II) and Ni(II) chelates formed are measured and discussed. © 1969, American Chemical Society. All rights reserved.