EPR and potentiometric reinvestigation of copper(II) complexation with simple oligopeptides and related compounds (original) (raw)
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Spectrochimica Acta Part A: Molecular Spectroscopy, 1993
The complex formation between copper(II) and the tetrapeptide glycyl-glycyI-L-histidyI-L-alanine ([H3L] z+) has been studied in aqueous solution at t = 25°C and 1= 0.1 tool dm -3 by potentiometric, visible spectrophotometric and circular dichroism measurements. All the experimental techniques show that the complex [CuLH_z]-is predominant over a wide pH range, while the monodentate [CuLH] 2+ is formed in the acidic region and a further deprotonated [CuLH_3] z-species exists at pH higher than 10. The formation constants of the three above complexes are reported and a structure is proposed on the basis of spectroscopic results. The structure of [CuLH_2]-species very probably involves four nitrogen donors in the plane, excluding coordination by the L-alanine residue, while it seems likely that [CuLH_a] 2-is formed by simple dissociation of the N-1 pyrrole hydrogen.
Spectrochimica Acta Part a Molecular Spectroscopy, 1993
The complex formation between copper(II) and the tetrapeptide glycyl-glycyI-L-histidyI-L-alanine ([H3L] z+) has been studied in aqueous solution at t = 25°C and 1= 0.1 tool dm-3 by potentiometric, visible spectrophotometric and circular dichroism measurements. All the experimental techniques show that the complex [CuLH_z]-is predominant over a wide pH range, while the monodentate [CuLH] 2+ is formed in the acidic region and a further deprotonated [CuLH_3] z-species exists at pH higher than 10. The formation constants of the three above complexes are reported and a structure is proposed on the basis of spectroscopic results. The structure of [CuLH_2]-species very probably involves four nitrogen donors in the plane, excluding coordination by the L-alanine residue, while it seems likely that [CuLH_a] 2-is formed by simple dissociation of the N-1 pyrrole hydrogen.
Polyhedron, 2001
The formation constants and the isotropic ESR parameters (g-factors, 63 Cu, 65 Cu, 14 N hyperfine coupling constants and relaxation parameters) of the various species were determined by the simultaneous analysis of a series of spectra, taken in a circulating system at various pH and ligand-to-metal concentration ratio. For both systems the new [CuLH] 2 + complex was identified in acidic solutions. With the glycyl-L-serine ligand below pH 11.5 the same complexes and coordination modes are formed than with simple dipeptides. The side-chain donor group is bound only over pH 11.5 in the complex [CuLH − 2 (OH)] 2 − , where it is deprotonated and substitutes the carboxylate O in the third equatorial site. For the bis complex [CuLH − 1 (L)] − an isomeric equilibrium was shown, where the difference between the isomers was based on which of the donor atoms of the 'L' ligand, the peptide O or the amino N, occupies the fourth equatorial position, and which one is coordinated axially. The L-seryl-glycine ligand forms the same species as simple dipeptides and glycyl-L-serine up to pH 8. The only difference is that the axial binding of the alcoholic OH group fairly stabilizes the bidentate equatorial coordination of the 'L' ligand through the amino N and peptide O atoms in the [CuL] + complex as well as in the major isomer of the [CuLH − 1 (L)] − complex. For this system we showed that (1) proton loss and the equatorial coordination of the alcoholic OH group occurs at relatively low pH (over pH 8-9), which results in the [CuL 2 H − 2 ] 2 − complex with excess ligand, and also the newly identified species [Cu 2 L 2 H − 4 ] 2 − : (2) this process is in competition with the proton loss of a coordinated water molecule. For both systems, the ESR-inactive species [Cu 2 L 2 H − 3 ] − was also shown.
Binding Properties of Cu +/2+ -(glycyl) n glycine Complexes ( n = 1−3)
The Journal of Physical Chemistry A, 2008
The structure, relative energies, and binding energies of the complexes formed by the interaction of Cu + (d 10 , 1 S) and Cu 2+ (d 9 , 2 D) cations with the (glycyl) n glycine (n) 1-3) oligomers have been theoretically determined by means of density functional methods. The most stable structures of the Cu + systems present linear dicoordination geometries, in agreement with a recent X-ray absorption spectroscopic study of Cu(I) interacting with model dipeptides. This is attributed to an efficient reduction of metal-ligand repulsion through sd σ hybridization in dicoordinated linear structures. In contrast, for Cu 2+ systems the lowest energy structures are tricoordinated (n) 1), tetracoordinated (n) 2), and pentacoordinated (n) 3). For both copper cations, binding energy values show that the interaction energies increase when the peptide chain is elongated. Differences on the coordination properties of the ligands are discussed according to their length as well as to the electronic configuration of the metal cations, which are compared to the Cu +/2+-glycine systems.
Polyhedron, 2002
Stabilities of the mixed-ligand complexes of Cu 2 + ion with N, N,N%,N¦,N¦-pentamethyldiethylenetriamine [N,N,N%,N¦,N¦-pentamethyl-{bis(2-aminoethyl)amine}, Me 5 dien] as a primary ligand and a-alaninehydroxamic acid [2-amino-N-hydroxypropanamid, a-Alaha] or b-alaninehydroxamic acid [3-amino-N-hydroxypropanamid, b-Alaha] as a secondary ligand L and their absorption and EPR spectra at various pH values are reported. The visible spectra exhibit a characteristic red shift and a shoulder at lower energies indicating a five-coordinate structure of the formed complexes. The change of the EPR spectral parameters as a function of pH reflects two modes of an equatorial-axial chelation by the aminohydroxamic acid ligand L in the [Cu(Me 5 dien)(HL)] 2 + and [Cu(Me 5 dien)(L)] + species.
Journal of Molecular Structure, 2010
The energies of various Cu(II) complexes have been computed at the MM and DFT levels of theory. These complexes are constituted of Cu(II) ion used as a central ion, an enantiomer of an amino acid and L-proline or trans-4-L-Hydroxy-proline (THLP) used as chiral selectors in Ligand Exchange Capillary Electrophoresis (LECE). The energy differences of the diastereomeric complexes containing implicit water molecules computed at the DFT/B3LYP/LANL2DZ level are in good agreement with the observed enantioseparations using LECE.
Theoretical study of dipeptide complexes of copper(II)
Journal of Molecular Structure: THEOCHEM, 2006
The L,L-Phe-Leu-Cu(II), L,L-Leu-Phe-Cu(II), L,L-Phe-Met-Cu(II), and L,L-Met-Phe-Cu(II) systems were studied using molecular modelling. The results obtained, which are in good agreement with results obtained by potentiometric studies show a significant increase in stability of copper complexes, when an aromatic residue is located in C-terminal (compared to the L,L-dipeptides containing the same amino acid residues), this phenomenon is attributed to the interaction between the d-orbital of copper and the p-electrons of the aromatic ring.
INDIAN …, 1994
; revisedand accepted7 October1993 The stabilities of mixed ligand complexes of Cu(II)-diamine(A)-amino acid(B) systems, where diamine refers to 1,2-diaminopropane (dp) or 1,3-diaminopropane (tp) and amino acid to DL-2-amipobutyric acid (2-aba), DL-3-aminobutyric acid (3-aba), 4-aminobutyric acid (4-aba) or DL-4-amino-3-hydroxybutyric acid (ahba) have been studied by computer based analysis of thepH-metric data at 3rC and I = 0.15 mol dm-3 (NaCI04). In the Cu(II)-dp(A)-2-aba, 3-aba and 4-aba (B) systems only CuAB type of ternary species is detected, whMein the corresponding tp(A) systems in addition CuABH is also present. The tendency of mixed complex formation decreases in the order 3-aba > 2-aba > 4-aba in the former systems, while in the latter systems the order is 2-aba> 3-aba > 4-aba. These trends are explained on the basis of the chelate ring size. In the Cu(II)-dpjtp(A)-ahba (B) systems only CuAB type of ternary species has been detected. In this speciesahba(B) ligand binds the metal in a bidentate manner, though it is tridentate in its binary species with Cu(II).