Abstract
Infrared absorption spectra in aqueous (D2O) solution are employed to elucidate the nature of coordinate bonding in copper(II)- and nickel(II)-polyglycine chelates formed over the full pH range from strongly acid to strongly alkaline solution. These assignments provide the first microscopic evidence for metal-polyglycine coordinate sites in acid solution. Shifts in peptide carbonyl and terminal carboxylate frequencies are interpreted as indications of the conformational changes in both copper(II) and nickel(II) chelates as dissociation of hydrogen ion takes place to convert the initial complexes to the ultimate high pH forms, MH−nL1–n and MH−nLOH−n where n is the number of peptide linkages in the ligand.