Interactions of nitrogen-donor biomolecules with copper(II) complexes in Tris buffer

Abstract

Comprehensive mole-ratio, kinetic, EPR and X-ray studies were performed to investigate substitution reactions between square-planar [CuCl₂(en)] (en = ethylenediamine) and square-pyramidal [CuCl₂(terpy)] (terpy = 2,2’:6’,2”-terpyridine) complexes with bio-relevant nucleophiles at 295 K in 0.010 M Tris-HCl buffer (pH = 7.4) in the presence of 0.010 M NaCl. According to mole-ratio and EPR studies, Tris buffer reacts with [CuCl₂(en)], and likely the complex geometry remains square-planar. Kinetic results have shown that the order of reactivity of nucleophiles towards [CuCl₂(en)] in solution for both reaction steps is 1,2,4-triazole > imidazole > pyrazine. The order of reactivity of the azole and diazine ligands toward [CuCl₂(terpy)] for the first reaction step is imidazole > 1,2,4-triazole > pyrazine, while for the second one is pyrazine > 1,2,4-triazole > imidazole. X-ray studies indicate great affinity of ethylenediamine toward Cu(II), which results in crystal structures of [Cu(en)₂]Cl₂·H₂O and [Cu(en)₂][ZnCl₄], instead of dinuclear or heteronuclear complexes with a bridging pyrazine ligand. The recorded EPR spectra demonstrate that all ligands interact with Cu(II) complexes, except in the case of the [CuCl₂(en)] complex, where the competition between ligand and Tris molecules might be observed.

Graphical Abstract

Keywords:

• Cu(II) complexes
• Tris buffer
• structure – reactivity correlation
• bio-relevant nucleophiles

Acknowledgement

EPR measurements were conducted in Magnetic Resonance Research Center in the Research Park of Saint-Petersburg State University with the kind help from S.M. Sukharzhevskii. Diffraction experiments were performed at the Centre for X-ray Diffraction Studies of Research park of Saint-Petersburg State University.

Disclosure statement

There are no conflicts of interest to declare.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

E. Selimović and T. Soldatović gratefully acknowledge financial support from State University of Novi Pazar, Novi Pazar, Republic of Serbia.