he Influence of Aspartic or Glutamic acid Residues in Tetrapeptides on the Formation of Complexes with Nickel (II) and Zinc (II)
Onindo, Charles O.
Pettit, L. D.
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The formation of the complexes formed by NiII and ZnII with Asp-Asp-Asp and a series of tetrapeptides containing one or two Asp residues or one Glu residue are reported. Stability constants were measured pH-metrically. The particular species and the metal ion binding sites were determined using 1H NMR, UV-vis and CD spectroscopy. The β-carboxylate group of the Asp residue stabilizes the complexes significantly, particularly when present as the N-terminal residue. As a result the tendency for NiII to deprotonate and bind to amide-nitrogen atoms, forming planar diamagnetic complexes, is reduced and their formation delayed to a significantly higher pH when compared to other peptides. The side chain of the Glu residue has a much smaller effect. As anticipated, ZnII was unable to deprotonate and bind to peptide nitrogens.