Two macrocyclic pentaaza compounds containing pyridine evaluated as novel chelating agents in copper(II) and nickel(II) overload

• Published in: Journal of inorganic biochemistry Vol. 105; no. 3; pp. 410 - 419
• Main Authors: Fernandes, Ana S., Cabral, M. Fátima, Costa, Judite, Castro, Matilde, Delgado, Rita, Drew, Michael G.B., Félix, Vitor
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2011
• Subjects: Cations, Divalent; Chelating Agents - chemical synthesis; Chelating Agents - chemistry; Chelation therapy; Copper - chemistry; Copper(II) complex; Hydrogen Bonding; Inhibitory Concentration 50; Ligands; Macrocyclic compounds; Macrocyclic Compounds - chemistry; Nickel - chemistry; Nickel(II) complex; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Pyridines - chemistry; Spectrum Analysis; Stability constants; X-Ray Diffraction; Copper(II) complex; Nickel(II) complex; Macrocyclic compounds; Stability constants; Chelation therapy
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/j.jinorgbio.2010.11.014

Two pentaaza macrocycles containing pyridine in the backbone, namely 3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),14,16-triene ([15]pyN 5), and 3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),15,17-triene ([16]pyN 5), were synthesized in good yields. The acid–base behaviour of these compounds was studied by potentiometry at 298.2 K in aqueous solution and ionic strength 0.10 M in KNO 3. The protonation sequence of [15]pyN 5 was investigated by 1H NMR titration that also allowed the determination of protonation constants in D 2O. Binding studies of the two ligands with Ca 2+, Ni 2+, Cu 2+, Zn 2+, Cd 2+, and Pb 2+ metal ions were performed under the same experimental conditions. The results showed that all the complexes formed with the 15-membered ligand, particularly those of Cu 2+ and especially Ni 2+, are thermodynamically more stable than with the larger macrocycle. Cyclic voltammetric data showed that the copper(II) complexes of the two macrocycles exhibited analogous behaviour, with a single quasi-reversible one-electron transfer reduction process assigned to the Cu(II)/Cu(I) couple. The UV–visible-near IR spectroscopic and magnetic moment data of the nickel(II) complexes in solution indicated a tetragonal distorted coordination geometry for the metal centre. X-band EPR spectra of the copper(II) complexes are consistent with distorted square pyramidal geometries. The crystal structure of [Cu([15]pyN 5)] 2+ determined by X-ray diffraction showed the copper(II) centre coordinated to all five macrocyclic nitrogen donors in a distorted square pyramidal environment. The synthesis and characterization of two pentaaza macrocyclic compounds containing pyridine in the backbone, [15]pyN 5 and [16]pyN 5, as well as the study of their copper(II) and nickel(II) complexes, are reported in order to evaluate their possible use as chelating agents. [Display omitted]