A new dinuclear unsymmetric copper(II) complex as model for the active site of catechol oxidase |
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Authors: | Christiane Fernandes, Ademir Neves, Adailton J. Bortoluzzi, Ant nio S. Mangrich, Eva Rentschler, Bruno Szpoganicz,Erineu Schwingel |
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Affiliation: | a Laboratório de Bioinorgânica e Cristalografia, Departamento de Química, LABINC CAMPUS-TRINIDADE, Universidade Federal de Santa Catarina, 88040-900 Florianópolis SC, Brazil b Departamento de Química, Universidade Federal do Paraná, 81531-970 Curitiba PR, Brazil c Max-Planck Institut für Strahlenchemie Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany d Centro de Ciências Exatas, Agrárias e das Engenharias, Universidade do Sul de Santa Catarina, UNISUL, 88130-000 Florianópolis SC, Brazil |
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Abstract: | The crystal structure, magnetic, redox and spectroscopic properties of a novel unsymmetrical dinuclear copper(II) complex, prepared by the reaction between copper(II) perchlorate, sodium acetate and the unsymmetrical, binucleating ligand HTPPNOL, where HTPPNOL is N,N,N′-tris-(2-pyridylmethyl)-1,3-diaminopropan-2-ol, is reported. HTPPNOL (1 equiv.) reacted with 1 equiv. of copper(II) ion, in methanol, and produced the mononuclear copper complex [Cu(TPPNOL)](ClO4)(BPh4) (1). On the other hand, the reaction of 1 equiv. of HTPPNOL with 2 equiv. each of copper (II) ion and acetate, in methanol, produced the dinuclear complex [Cu2(TPPNOL)(OOCCH3)](ClO4)2 (2), whose structure has been determined by X-ray diffraction. In complex 2, as a result of the inherent asymmetry of the ligand HTPPNOL, one copper ion is five-coordinated (distorted trigonal-bipyramidal) while the other copper is four-coordinated (distorted square-planar). Then, as a result of the presence of distinct geometries for the metal centres, complex 2 exhibits a ferromagnetic coupling (J=+25.41 cm−1). Titration experiments carried out on the dinuclear complex suggest a pKa=8.0, which was related to the aquo/hydroxo equilibrium. Complex 2 is able to oxidise 3,5-di-tert-butylcatechol to the respective o-quinone. The oxidation reaction was studied by following the appearance of the quinone spectrophotometrically, at pH 8.0 and 25 °C. |
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Keywords: | Crystal structures Copper complexes Unsymmetrical ligand complexes Catecholase activity |
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