262,216 research outputs found
EPR and potentiometric reinvestigation of copper(II) complexation with simple oligopeptides and related compounds
No full textThe coordination modes of Cu(II) to Di-, Tri-, and Tetra-glycine and related ligands were investigated, within the entire measurable pH range and over a wide range of ligand excess, by means of electron paramagnetic resonance, electron spectroscopy, and in some cases, pH potentiometry. The results, besides allowing the identification of the complex species involved and the attribution of distinctive spectral data set to the various structures, provide significant insight in relation to: i) the coordination ability of the zwitterionic AH form of simple oligopeptides to yield COO-- or 2COO(-)-complexes or species with mixed [(NH2,CO)(COO-)] or [(NH2,N-, COO-)(COO-)] coordination;) the influence of the size of the (NH2,CO), (NH2,N-), and (N-, COO-) chelated rings on the stability and structure of the complex species; iii) the bis-complex formation processes taking place with Gly-beta-ala, beta-Alagly, Tri-, and Tetra-glycine
Copper(II) complexes of N-terminal protected tri- and tetrapeptides containing histidine residues
No full textCopper(II) complexes of peptides containing two or three histidyl residues (Ac-HisGlyHis-OH, Ac-HisGlyHis-NHMe, Ac-HisHisGlyHis-OH and Ac-HisHisGlyHis-NHMe) have been studied by potentiometric, UV-Vis, EPR and CD spectroscopic measurements. The imidazole nitrogen atoms are described as the primary metal binding sites of all ligands resulting in the formation of various macrochelates in the pH range 4 to 7. The (N-im, N-, N-im)-co-ordinated [CuH-1L](0(+)) complexes were mainly detected in samples containing free carboxylates at the C-termini, whilst the [CuH-2L](-(0)) complexes were the predominant species in slightly alkaline solution and their binding modes were described via 4N-co-ordination (N-im, N-, N-, N-im) in (7,5,6)- membered fused chelate rings. Deprotonation and co-ordination of the third amide nitrogens were detected above pHsimilar to9 in all cases
Potentiometric and spectroscopic studies on transition metal complexes of GlyLys(Gly) and Asp-epsilon-Lys
No full textCopper(II), nickel(II) and zinc(II) complexes of the peptides GlyLys(Gly) and Asp-epsilon-Lys, containing the amide functions at the c-amino groups of the lysyl residues were studied by potentiometric, UV-VIS and EPR spectroscopic methods. The stoichiometry of the major species formed in the copper(II)-GlyLys(Gly) system is [CuH-1L] and the EPR spectroscopic data indicate the existence of two isomeric forms of the complex. The nickel(II) and zinc(II)-GlyLys(Gly) systems have been characterised by the formation of stable [ML](+) complexes containing bis(NH2,CO) co-ordination and a macrochelate. Deprotonation and co-ordination of the amide groups were detected in the copper(II) and nickel(II) complexes. The co-ordination chemistry of Asp-epsilon-Lys is best described by the metal binding ability of the amino acid residues and it's high affinity for dimerisation. The stoichiometry of the dinuclear complexes can be given as [M2L2]. containing only amino acid binding sites. Deprotonation and co-ordination of the amide functions were suggested only in the copper(II)-containing systems, resulting in the formation of the [Cu2H-2L2](2-) dinuclear complex
Copper(II) complexes of oligopeptides containing aspartyl and glutamyl residues. Potentiometric and spectroscopic studies
No full textCopper(II) complexes of di-, tri- and tetra-peptides built up from Asp and/or Glu residues were studied by potentiometric and various spectroscopic techniques including UV-visible, circular dichroism and electron paramagnetic resonance measurements. The ligands contain two to five carboxylate functions and it generally results in the enhanced metal binding ability of the ligands, which is especially true for the oligopeptides of aspartic acid. In the case of peptides containing aspartyl residue in the N-terminal position the stability enhancement is reflected in the equilibrium data of the species [CuL] containing the (NH2, beta-COO-)-coordination mode in a 6-membered chelate. In the case of AspAsp and AspAspAsp the (NH2, N-, beta-COO-) and (NH2, N-, N-, beta-COO-)-coordination modes will be favoured, which contain (5,6) and (5,5,6)-joined chelate ring systems, respectively. The outstanding stability of the latter binding mode and the high negative charge of the corresponding species suppresses the metal ion coordination of the third amide function of AspAspAspAsp. It is also important to note that the presence of side chain carboxylate functions results in the formation of carboxylato-bridged polynuclear complexes in medium pH range. The extent of oligomerisation can be significantly enhanced by the increase of concentration and by the decrease of temperature. (c) 2005 Elsevier Inc. All rights reserved
The Effect of the ring size of fused chelates on the thermodynamic and spectroscopic properties of peptide complexes of copper(II)
No full textCopper(II) complexes of the tripeptides GlyGly-β-Ala, Gly-β-AlaGly, β-AlaGlyGly, Gly-β-Ala-β-Ala, β-AlaGly-β-Ala, β-Ala-β-Ala-β-Ala and the tetrapeptides GlyGlyGly-β-Ala, GlyGly-β-AlaGly, Gly-β-AlaGlyGly and β-AlaGlyGlyGly were studied by potentiometric, EPR and UV-Vis spectroscopic methods. The stoichiometry of the complexes of peptides containing β-alanine residues are very similar to those of oligoglycines; [CuL]+, [CuL2], [CuH-1L], [CuH-2L]-, [CuH-1L2]- and [CuH-3L]2- were detected as the major species in all cases. The presence of -alanine residues, however, influenced both thermodynamic stability and coordination geometry of various complexes. In most cases the formation of six-membered chelate rings resulted in a decrease of thermodynamic stability and distortion of coordination geometry of peptide complexes, especially if β-alanine residues were present in N-terminal or adjacent positions. On the contrary, the formation of the mixed (5,6,5) and (5,5,6) linked chelate systems of tripeptides is favoured over the pure five-membered rings
POTENTIOMETRIC AND SPECTROSCOPIC STUDIES ON THE COPPER(II) COMPLEXES OF PEPTIDE-HORMONES CONTAINING DISULFIDE BRIDGES
No full textCopper(II) complexes of oxytocin, 4-Glu-oxytocin, 5-Asp-oxytocin, and GlyGlyGly-Lys(8)-vasopressin were studied by potentiometric, EPR, and UV-visible spectroscopic methods. The formation of 4N-coordinated complexes was characteristic of all ligands. This type of coordination is especially favored for oxytocin due to the specific conformation of the ring coupled by the disulfide bridge. The coordination of the gamma-carboxylate group of 4-Glu-oxytocin and a disulfide sulfur atom of GlyGlyGly-Lys(8)-vasopressin was reported to occur in the 2N-complexes over medium pH range
Potentiometric and spectroscopic studies on the copper(II) complexes formed by oligopeptides containing histidine with a protection at the terminal amino group
No full textCopper(II) complexes of oligopeptides with protected amino groups (Z-His-OH, Z-HisGly-OH, Z-GlyHis-OH and Z-GlyGlyHis-OH) were studied by potentiometric and spectroscopic methods. The involvement of the imidazole nitrogen in metal binding was proved in slightly acidic media. The deprotonation and coordination of the amide nitrogen atoms from the carbamate or peptide CONH--- moieties occurred around pH 7, which resulted in the formation of 2N (Z-His-OH and Z-HisGly-OH), 3N (Z-GlyHis-OH) and 4N (Z-GlyGlyHis-OH) complexes supporting the anchoring ability of the imidazole rings. Ternary complexes with 2,2′-bipyridine, L -histidine or glycine (B) were also studied. The major species contained chelated B ligands, whereas the oligopeptide behaved as N-monodentate or 2N-bidentate. The outstanding stability of the 4N complex of Z-GlyGlyHis-OH ([CuH−3A]2−) ruled out mixed complex formation at high pH values
Acid-base properties and copper(II) complexes of di-peptides containing histidine and additional chelating bis(imidazol-2-yl) residues
No full textCopper(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 [Cu(2)L(2)](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 [NH(2), N(-)(amide), N(Im)] tridentate coordination of the ligand is favoured and results in the formation of di- and trinuclear complexes [Cu(2)H(-1)L](3+) and [Cu(3)H(-2)L(2)](4+) in equimolar solutions. The presence of these coordination modes shifts the formation of "tripeptide-like" ([NH(2), 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(I)H groups does not occur below pH 10. (C) 2003 Elsevier Inc. All rights reserved
New insights into the metal ion-peptide hydroxamate interactions: Metal complexes of primary hydroxamic acid, derivatives of common dipeptides in aqueous solution
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