Thermodynamic and structural characterization of the macrochelates formed in the reactions of copper(II) and zinc(II) ions with peptides of histidine

Copper(II) complexes of the peptides Ac-HisSarHis-NH2, Ac-HisSarHisSarHis-NH2 and Ac-HisSarHisSarHisSarHis-NH2 have been studied by potentiometric, UV–Vis, CD and EPR spectroscopic methods. Stability constants for the corresponding zinc(II) complexes have also been reported. The formation of M(II)–2Nim, M(II)–3Nim and M(II)–4Nim bonded macrochelates was suggested in the pH range 5–7. The macrochelates were, however, not stable enough to prevent metal ion hydrolysis in slightly alkaline solutions. In the case of copper(II) complexes, the metal ion promoted deprotonation and coordination of the amide groups of histidyl residues were also suggested. The stability constants of macrochelate complexes were compared to the literature data reported for the macrochelates of the other peptides of histidine. It was found that the thermodynamic stability of macrochelate species is largely influenced by the number and location of histidyl residues in the peptide backbone. The highest stability was obtained for the HXHYH-type sequences, while the distant arrangement of histidyl residues resulted in a significant reduction of the stability constants.

Multihistidine peptides can form stable macrochelates with copper(II) and zinc(II) ions and the stability constants of these species are the function of the number and location of histidyl residues in the peptide backbone. In the case of 3-histidine peptides the sequences Ac-HisXaaHisYaaHis-NH2 are the best suited for macrochelation.Figure optionsDownload as PowerPoint slide