Spectroscopic and potentiometric study of the SOD mimic system copper(II)/acetyl-L-histidylglycyl-L-histidylglycine

Stoichiometry, stability constants and solution structures of the copper(II) complexes of the N-acetylated tetrapeptide HisGlyHisGly were determined in aqueous solution in the pH range 2-11. The potentiometric and spectroscopic data (UV-Vis, CD, EPR and Raman scattering) show that acetylation of the amino terminal group induces drastic changes in the coordination properties of AcHGHG compared to HGHG. The N-3 atoms of the histidine side chains are the first anchoring sites of the copper(II) ion. At pH 4.7 and 5.6 both the imidazole rings cooperate in the formation of a 2N equatorial set, while, at higher pH values, 3N and 4N complexes are formed through the coordination of peptide N- atoms. The log beta values of the copper complexes of AcHGHG are by far lower than those of the corresponding species in the parent Cu-II-HGHG system. (C) 2002 Elsevier Science Inc. All rights reserved.