THE INFLUENCE OF ASPARTIC OR GLUTAMIC ACID RESIDUES IN TETRAPEPTIDES ON THE FORMATION OF COMPLEXES WITH NICKEL(II) AND ZINC(II)

摘要

The formation of the complexes formed by Ni-II and Zn-II 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 H-1 NMR, UV-vis and CD spectroscopy. The beta-carboxylate group of the Asp residue stabilizes the complexes significantly, particularly when present as the N-terminal residue. As a result the tendency for Ni-II 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, Zn-II was unable to deprotonate and bind to peptide nitrogens. [References: 16]