title: Acid-base properties and copper(II) complexes of dipeptides containing histidine and additional chelating bis(imidazol-2-yl) residues.
abstract: Copper(II) complexes of dipeptides of histidine containing additional chelating bis(imidazol-2-yl) agent at the C-termini (PheHis-BIMA [N-phenylalanyl-histidyl-bis(imidazol-2-yl)methylamine] and HisPhe-BIMA [N-histidyl-phenylalanyl-bis(imidazol-2-yl)methylamine]) were studied by potentiometric, UV-Visible and Electron Paramagnetic Resonance (EPR) techniques. The imidazole nitrogen donor atoms of the bis(imidazol-2-yl)methyl group are described as the primary metal binding sites forming stable mono- and bis(ligand) complexes at acidic pH. The formation of a ligand-bridged dinuclear complex [Cu2L2]4+ is detected in equimolar solutions of copper(II) and HisPhe-BIMA. The coordination isomers of the dinuclear complex are described via the metal binding of the bis(imidazol-2-yl)methyl, amino-carbonyl and amino-imidazole(His) functions. In the case of the copper(II)-PheHis-BIMA system the [NH2, N-(amide), N(Im)] tridentate coordination of the ligand is favoured and results in the formation of di- and trinuclear complexes [Cu2H(-1)L]3+ and [Cu3H(-2)L2]4+ in equimolar solutions. The presence of these coordination modes shifts the formation of "tripeptide-like" ([NH2, N-, N-, N(Im)]-coordinated) [CuH(-2)L] complexes into alkaline pH range as compared to other dipeptide derivatives of bis(imidazol-2-yl) ligands. Although there are different types of imidazoles in these ligands, the deprotonation and coordination of the pyrrole-type N(1)H groups does not occur below pH 10.
authors.affiliation: Department of Inorganic and Analytical Chemistry, University of Debrecen, P.O. Box 21, H-4010 Debrecen, Hungary.
authors.forename: Katalin
authors.initials: K
authors.lastname: Osz
authors.forename: Katalin
authors.initials: K
authors.lastname: Várnagy
authors.forename: Helga
authors.initials: H
authors.lastname: Süli-Vargha
authors.forename: Antal
authors.initials: A
authors.lastname: Csámpay
authors.forename: Daniele
authors.initials: D
authors.lastname: Sanna
authors.forename: Giovanni
authors.initials: G
authors.lastname: Micera
authors.forename: Imre
authors.initials: I
authors.lastname: Sóvágó
mesh_terms: D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D004151:Dipeptides / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006639:Histidine / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D015394:Molecular Structure; D011199:Potentiometry; D013056:Spectrophotometry, Ultraviolet
chemical_list: D004151:Dipeptides; D007093:Imidazoles; D008024:Ligands; D006639:Histidine; D003300:Copper