title: Two macrocyclic pentaaza compounds containing pyridine evaluated as novel chelating agents in copper(II) and nickel(II) overload.
abstract: 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 298.2K in aqueous solution and ionic strength 0.10 M in KNO(3). The protonation sequence of [15]pyN(5) was investigated by (1)H NMR titration that also allowed the determination of protonation constants in D(2)O. 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.
authors.affiliation: iMed.UL, Faculdade de Farmácia, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal.
authors.forename: Ana S
authors.initials: AS
authors.lastname: Fernandes
authors.forename: M Fátima
authors.initials: MF
authors.lastname: Cabral
authors.forename: Judite
authors.initials: J
authors.lastname: Costa
authors.forename: Matilde
authors.initials: M
authors.lastname: Castro
authors.forename: Rita
authors.initials: R
authors.lastname: Delgado
authors.forename: Michael G B
authors.initials: MG
authors.lastname: Drew
authors.forename: Vitor
authors.initials: V
authors.lastname: Félix
mesh_terms: D002413:Cations, Divalent; D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D006860:Hydrogen Bonding; D020128:Inhibitory Concentration 50; D008024:Ligands; D047028:Macrocyclic Compounds / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D013057:Spectrum Analysis; D014961:X-Ray Diffraction
chemical_list: D002413:Cations, Divalent; D002614:Chelating Agents; D008024:Ligands; D047028:Macrocyclic Compounds; D009942:Organometallic Compounds; D011725:Pyridines; D003300:Copper; D009532:Nickel; C023666:pyridine