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pH-Potentiometric Investigation towards Chelating Tendencies of p-Hydroquinone and Phenol Iminodiacetate Copper(II) Complexes.

Stylianou M, Keramidas AD, Drouza C - Bioinorg Chem Appl (2010)

Bottom Line: The results reveal that the iminodiacetic phenol ligand forms mononuclear complexes with Cu(2+) at acidic and alkaline pHs, and a binuclear O(phenolate)-bridged complex at pH range from 7 to 8.5.The binucleating hydroquinone ligand forms only 2 : 1 metal to ligand complexes in solution.The pK values of the protonation of the phenolate oxygen of the two ligands are reduced about 2 units after complexation with the metal ion and are close to the pK values for the copper-interacting tyrosine phenol oxygen in copper enzymes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Cyprus, 1678 Nicosia, Cyprus.

ABSTRACT
Copper ions in the active sites of several proteins/enzymes interact with phenols and quinones, and this interaction is associated to the reactivity of the enzymes. In this study the speciation of the Cu(2+) with iminodiacetic phenolate/hydroquinonate ligands has been examined by pH-potentiometry. The results reveal that the iminodiacetic phenol ligand forms mononuclear complexes with Cu(2+) at acidic and alkaline pHs, and a binuclear O(phenolate)-bridged complex at pH range from 7 to 8.5. The binucleating hydroquinone ligand forms only 2 : 1 metal to ligand complexes in solution. The pK values of the protonation of the phenolate oxygen of the two ligands are reduced about 2 units after complexation with the metal ion and are close to the pK values for the copper-interacting tyrosine phenol oxygen in copper enzymes.

No MeSH data available.


Species distribution (% formation relative to Cu2+) in the Cu(II)-H4cacp system at equimolar concentration (5.00 mmol dm−3) as a function of pH over the range 2.00–10.0 (25°C, I = 0.10 mol dm−3 KCl, pKw = 13.78, γ = 0.78). The Cu(II) species are as follows: (a) [Cu(H2cacp)(H2O)], (b) [Cu(H2cacp)2]2−, (c) [Cu(Hcacp)(H2O)]−, (d) [Cu2(Hcacp)2]2−, and (e) [Cu(Hcacp)(OH)]2−.
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fig3: Species distribution (% formation relative to Cu2+) in the Cu(II)-H4cacp system at equimolar concentration (5.00 mmol dm−3) as a function of pH over the range 2.00–10.0 (25°C, I = 0.10 mol dm−3 KCl, pKw = 13.78, γ = 0.78). The Cu(II) species are as follows: (a) [Cu(H2cacp)(H2O)], (b) [Cu(H2cacp)2]2−, (c) [Cu(Hcacp)(H2O)]−, (d) [Cu2(Hcacp)2]2−, and (e) [Cu(Hcacp)(OH)]2−.

Mentions: The Cu(II)-H4cacp titration curves were evaluated on the assumption of the formation of various 1 : 1, 1 : 2 and 2 : 1 metal to ligand species with different protonation steps. The extensive crystallographic study of the isolated complexes from solutions of Cu(II)-H4cacp at various pHs reported by Stylianou et al. [25] was also used for the better suggestion of the species in solution (Scheme 2). The best fit with the experimental data (Figure 2(a)) was obtained with the speciation model listed in Table 1. Species distribution curves for the complexes formed in the Cu(II)-H4cacp system as a function of pH are depicted in Figure 3.


pH-Potentiometric Investigation towards Chelating Tendencies of p-Hydroquinone and Phenol Iminodiacetate Copper(II) Complexes.

Stylianou M, Keramidas AD, Drouza C - Bioinorg Chem Appl (2010)

Species distribution (% formation relative to Cu2+) in the Cu(II)-H4cacp system at equimolar concentration (5.00 mmol dm−3) as a function of pH over the range 2.00–10.0 (25°C, I = 0.10 mol dm−3 KCl, pKw = 13.78, γ = 0.78). The Cu(II) species are as follows: (a) [Cu(H2cacp)(H2O)], (b) [Cu(H2cacp)2]2−, (c) [Cu(Hcacp)(H2O)]−, (d) [Cu2(Hcacp)2]2−, and (e) [Cu(Hcacp)(OH)]2−.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2901618&req=5

fig3: Species distribution (% formation relative to Cu2+) in the Cu(II)-H4cacp system at equimolar concentration (5.00 mmol dm−3) as a function of pH over the range 2.00–10.0 (25°C, I = 0.10 mol dm−3 KCl, pKw = 13.78, γ = 0.78). The Cu(II) species are as follows: (a) [Cu(H2cacp)(H2O)], (b) [Cu(H2cacp)2]2−, (c) [Cu(Hcacp)(H2O)]−, (d) [Cu2(Hcacp)2]2−, and (e) [Cu(Hcacp)(OH)]2−.
Mentions: The Cu(II)-H4cacp titration curves were evaluated on the assumption of the formation of various 1 : 1, 1 : 2 and 2 : 1 metal to ligand species with different protonation steps. The extensive crystallographic study of the isolated complexes from solutions of Cu(II)-H4cacp at various pHs reported by Stylianou et al. [25] was also used for the better suggestion of the species in solution (Scheme 2). The best fit with the experimental data (Figure 2(a)) was obtained with the speciation model listed in Table 1. Species distribution curves for the complexes formed in the Cu(II)-H4cacp system as a function of pH are depicted in Figure 3.

Bottom Line: The results reveal that the iminodiacetic phenol ligand forms mononuclear complexes with Cu(2+) at acidic and alkaline pHs, and a binuclear O(phenolate)-bridged complex at pH range from 7 to 8.5.The binucleating hydroquinone ligand forms only 2 : 1 metal to ligand complexes in solution.The pK values of the protonation of the phenolate oxygen of the two ligands are reduced about 2 units after complexation with the metal ion and are close to the pK values for the copper-interacting tyrosine phenol oxygen in copper enzymes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Cyprus, 1678 Nicosia, Cyprus.

ABSTRACT
Copper ions in the active sites of several proteins/enzymes interact with phenols and quinones, and this interaction is associated to the reactivity of the enzymes. In this study the speciation of the Cu(2+) with iminodiacetic phenolate/hydroquinonate ligands has been examined by pH-potentiometry. The results reveal that the iminodiacetic phenol ligand forms mononuclear complexes with Cu(2+) at acidic and alkaline pHs, and a binuclear O(phenolate)-bridged complex at pH range from 7 to 8.5. The binucleating hydroquinone ligand forms only 2 : 1 metal to ligand complexes in solution. The pK values of the protonation of the phenolate oxygen of the two ligands are reduced about 2 units after complexation with the metal ion and are close to the pK values for the copper-interacting tyrosine phenol oxygen in copper enzymes.

No MeSH data available.