title: Copper(II), nickel(II) and zinc(II) complexes of N-acetyl-His-Pro-His-His-NH2: equilibria, solution structure and enzyme mimicking.
abstract: The copper(II), nickel(II) and zinc(II) binding ability of the multi-histidine peptide N-acetyl-His-Pro-His-His-NH(2) has been studied by combined pH-potentiometry and visible, CD and EPR spectroscopies. The internal proline residue, preventing the metal ion induced successive amide deprotonations, resulted in the shift of this process toward higher pH values as compared to other peptides. The metal ions in the parent [ML](2+) complexes are exclusively bound by the three imidazole side chains. In [CuH(-1)L](+), formed between pH 6-8, the side chains of the two adjacent histidines and the peptide nitrogen between them are involved in metal ion binding. The next deprotonation results in the proton loss of the coordinated water molecule (CuH(-1)L(OH)). The latter two species exert polyfunctional catalytic activity, since they possess superoxide dismutase-, catecholase- (the oxidation of 3,5-di-tert-butylcatechol) and phosphatase-like (transesterification of the activated phosphoester 2-hydroxypropyl-4-nitrophenyl phosphate) properties. On further increase of the pH rearrangement of the coordination sphere takes place leading to the [CuH(-3)L](-) species, the deprotonated amide nitrogen displaces a coordinated imidazole nitrogen from the equatorial position of the metal ion. The shapes of the visible and CD spectra reflect a distorted arrangement of the donor atoms around the metal ion. In presence of zinc(II) the species [ZnL](2+) forms only above pH 6, which is shortly followed by precipitation. On the other hand, the [NiL](2+) complex is stable over a wide pH range, its deprotonation takes place only above pH 8. At pH 10 an octahedral NiH(-2)L species is present at first, which transforms slowly to a yellow square planar complex.
authors.affiliation: Department of Inorganic and Analytical Chemistry, University of Szeged, P.O. Box 440, H-6701 Szeged, Hungary.
authors.forename: Noémi I
authors.initials: NI
authors.lastname: Jakab
authors.forename: Attila
authors.initials: A
authors.lastname: Jancsó
authors.forename: Tamás
authors.initials: T
authors.lastname: Gajda
authors.forename: Béla
authors.initials: B
authors.lastname: Gyurcsik
authors.forename: Antal
authors.initials: A
authors.lastname: Rockenbauer
mesh_terms: D002413:Cations, Divalent; D003300:Copper; D004798:Enzymes; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000737:chemistry*; D018716:Molecular Mimicry; D015394:Molecular Structure; D009532:Nickel; D009842:Oligopeptides / Q000737:chemistry*; D011199:Potentiometry; D012996:Solutions; D013057:Spectrum Analysis; D015032:Zinc
chemical_list: D002413:Cations, Divalent; D004798:Enzymes; D008670:Metals; D009842:Oligopeptides; D012996:Solutions; D003300:Copper; D009532:Nickel; D015032:Zinc