Thermodynamics of mixed-ligand complex formation of copper(II) ethylenediaminetetraacetate with amino acids in solution
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Thermodynamics of mixed-ligand complex formation of copper(II) ethylenediaminetetraacetate with amino acids in solution M. A. Bazanova • D. F. Pyreu • E. V. Kozlovskii
Received: 17 April 2012 / Accepted: 21 August 2012 / Published online: 28 September 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
Abstract The mixed-ligand complex formation in the systems Cu2?–Edta4-–L (L = His, Lys, Orn, Arg, Im) has been calorimetrically, pH-potentiometrically, and spectrophotometrically studied in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO3). The thermodynamic parameters of formation of the CuEdtaL, CuEdtaHL, and (CuEdta)2L complexes have been determined. The probable coordination mode for the complexone and the ancillary ligand in the mixed-ligand complexes was discussed. Keywords Thermodynamic parameters Mixed-ligand complex Copper (II) ethylenediaminetetraacetate Amino acid Denticity
Introduction EDTA has a widespread clinical application as a so-called chelation therapy agent. Owing to its strong complexing capability, in particular with respect to transition metal ions and radionuclides, it has been used in vivo to remove toxic metal ions or an excess of biometal ions. The formation of relatively stable mixed complexes of the type CuEdtaL at a physiologic pH value should be accounted under chelation therapy and its excretion from the human organism [1]. The account of the interaction of copper (II) complexonate with amino acid and peptide molecules can make the application of chelating agents (complexones) more effective. The sufficiently strong affinity of copper (II) ion to ligands with N donor atoms makes the amino acids containing the so-called additional donor group (His, Lys, M. A. Bazanova D. F. Pyreu (&) E. V. Kozlovskii Ivanovo State University, Ermak 39, Ivanovo 153025, Russia e-mail: [email protected]
Arg, and some others) an interesting object of mixed complexes formation research. The presence of several donor atoms in amino acids being studied results in various coordination modes. Earlier, the stability of mixed-ligand complexes of Hg(II) ethylenediaminetetraacetate with the above-mentioned amino acids had been studied [2]. It was noted that the chelation number (denticity) of amino acid in mononuclear mixed complexes did not achieve the maximum. The presence of an uncoordinated group of amino acid in HgEdtaL leads to the formation of a binuclear complex in which amino acid has a bridge function. Such effect has been revealed in the systems including histidine, lysine, cysteine, and methionine. Copper (II)–EDTA–amino acid interaction has been previously studied in [3] by potentiometric titration. The mixed complexes CuEdtaL formation and their possible role in blood plasma models have been investigated. The possible coordination mode of ligands and structure of mixed complexes have not been proposed by the authors. It was interesting to continue the study of systems Cu2?– Edta4-–amino acids in aqueous solution in a wide range of pH in order to reveal the coordination mode
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