M. Fátima Cabral

Protective role of ortho-substituted Mn(III) N-alkylpyridylporphyrins against the oxidative injury induced by tert-butylhydroperoxide.

Abstract The present work addresses the role of two ortho-substituted Mn(III) N-alkylpyridylporphyrins, alkyl being ethyl in MnTE-2-PyP5+ and n-hexyl in MnTnHex-2-PyP5+, on the protection against the oxidant tert-butylhydroperoxide (TBHP). Their protective role was studied in V79 cells using endpoints of cell viability (MTT and crystal violet assays), intracellular O2•– generation (dihydroethidium assay) and glutathione status (DTNB and monochlorobimane assays). MnPs per se did not show cytotoxicity (up to 25 μM, 24 h). The exposure to TBHP resulted in a significant decrease in cell viability and in an increase in the intracellular O2•– levels. Also, TBHP depleted total and reduced glutathione and increased GSSG. The two MnPs counteracted remarkably the effects of TBHP. Even at low concentrations, both MnPs were protective in terms of cell viability and abrogated the intracellular O2•– increase in a significant way. Also, they augmented markedly the total and reduced glutathione contents in TBHP-treated cells, highlighting the multiple mechanisms of protection of these SOD mimics, which at least in part may be ascribed to their electron-donating ability.

Protonation and metal complexation studies on some oxa-diaza macrocyclic ligands

Abstract Some 9- and 10-membered oxa-diaza macrocyclic ligands and their N-acetate derivatives have been synthesized and their protonation patterns studied by 1 H NMR and potentiometric techniques. The stability constants of the complexes formed by these ligands with several alkaline-earth and first-series transition metal ions, zinc, cadmium and lead, were determined by potentiometry and the values were compared with those formed with the analogous 9-membered tri-aza macrocyclic ligands and with 12-membered oxa-triaza ligands. The substitution of one nitrogen by an oxygen atom in the backbone of the macrocyclic ring has pronounced effects both on the kinetics of the complexation reactions (faster equilibration) and on the stability of the metal complexes formed (decreased stability). The differences in this last case are analysed for two pairs of cyclic amines ([9]aneN 3 /[9]aneN 2 O and [12]aneN 4 /[12]aneN 3 O) with the first transition metal ions and for the corresponding N-acetate derivatives with the first transition and alkaline-earth metal ions.

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

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.

Cytotoxic effects of cadmium in mammary epithelial cells: protective role of the macrocycle [15]pyN5.

Human exposure to cadmium (Cd) occurs via different routes, including diet. The increasing amount of data linking Cd with different cellular effects in the mammary gland justifies additional toxicological assessments using human mammary epithelial cells. This work aimed therefore to assess the cytotoxic effects of Cd in MCF10A cells and to characterize the cytoprotective role of the macrocycle [15]pyN(5) in the form of calcium salt. Cadmium chloride revealed to be cytotoxic to MCF10A cells, decreasing cell viability and proliferation in a concentration-dependent manner. Comparable dose-response curves and IC50 values (57-63 μM, 24h treatment) were obtained using the MTT reduction, crystal violet and BrdU assays. In terms of reactive oxygen species formation, only a slight increase in superoxide radical anion was observed at very high Cd concentrations (≥100 μM). Chelation should thus constitute the primary strategy to mitigate the cytotoxic effects induced by Cd in mammary cells. In this context, [15]pyN(5) which presents appropriate chemical and thermodynamic features was studied as a Cd chelator. This macrocycle (25 and 50 μM) significantly reduced or even abolished Cd-induced cytotoxicity. Protective effects were observed in terms of cell viability, cell proliferation and morphological alterations, being the protection mostly attributed to a chelating-based mechanism.

Tetraazamacrocycle bearing quinoline pendant arms and its complexation properties

AbstractA new tetraazamacrocycle containing two 5-chloro-8-hydroxyquinoline side arms, L 1 , was synthesized. The protonationconstants of L 1 and the stability constants of its complexes with Cu 2 ,Zn 2 ,Cd and Pb were determined by potentiometric orspectrophotometric methods, at 20 8C in methanol:water (5:1, v/v) and ionic strength 0.10 mol dm 3 in tetrabutylammonium nitrate(TBAN). Compound L 1 has three high protonation constants, the most basic centres being both phenolates of the arms. Mono- anddinuclear complexes were found in solution for all the metal ions, the complexes of copper are thermodynamically very stable, andthe dinuclear complexes of lead(II) are the predominant species even in 1:1 mixtures. UV / Vis spectra of some complexes and EPRof the copper ones confirmed the presence of dinuclear complexes.# 2003 Elsevier B.V. All rights reserved. Keywords: Tetraazamacrocycle; Stability constants; Dinuclear complexes; EPR copper complexes; 8-Hydroxyquinolinyl groups 1. IntroductionMacrocycles containing quinoline side arms havefound many applications as analytical reagents inabsorption spectrophotometry, fluorometry, solvent ex-traction, and partition chromatography [1,2]. Thesecompounds are also used as pesticides [2].The 8-hydroxyquinoline (HQ) forms a stable five-membered chelate ring with metal centres and verystable complexes with divalent transition and post-transition metal ions of the type M(HQ) , M(HQ)

4,7,10,13-Tetrakis(carboxymethyl)-1-oxa-4,7,10,13-tetraazacyclopentadecane and properties of its metal complexes

Abstract A new N-carboxymethyl derivative of the oxa-tetraaza macrocyle, 4,7,10,13-tetrakis-(carboxymethyl)-1-oxa-4,7,10,13-tetraazacyclopentadecane, has been synthesised. The protonation constants of this compound and the stability constants of its complexes with several di- and trivalent metal ions were determined by potentiometric or spectrophotometric methods, at 25°C and ionic strength 0.10 M in tetramethyl ammonium nitrate. The ligand exhibits two high or fairly high values of protonation constants and two low ones, and its overall basicity is about 27 in log units. Mono- and dinuclear complexes were found. The stability constant values of the 1:1 complexes with most of the metal ions studied are lower than expected, but not those of the dinuclear complexes. This was interpreted, in the case of mononuclear complexes, as the non-involvement in the co-ordination to these metal ions of two nitrogen atoms of the macrocycle backbone and, probably also, of one or two carboxylate groups. The Cu2+ ion has an exceptional behaviour, its 1:1 complex exhibits a high stability constant value. Spectroscopic data have indicated, for the last complex, the presence of two octahedral isomers in solution, one of them having only two nitrogens in the co-ordination sphere, while in the other three nitrogen donor atoms of the macrocyclic framework are co-ordinated in the equatorial plane. A third species appears at pH values higher than 7. These features suggest that the presence of four carboxymethyl arms and the relatively large size of the macrocycle severely constrains the geometric arrangement of the nitrogen donor atoms of the macrocyclic backbone around the metal centre decreasing the co-ordination number or leading to a preferred co-ordination with oxygen atoms. Another consequence of these structural features, is their easy ability to form dinuclear complexes, as found in the equilibria studies in solution and also by EPR spectroscopy of the Cu2+ complexes where the presence of two types of signals in the ΔMs=1 and ΔMs=2 regions, clearly reveals the presence of the dinuclear complex.