Neutralization of Reactive Oxygen Species at Dinuclear Cu(II)-Cores: Tuning the Antioxidant Manifold in Water by Ligand Design

Abstract

Dinuclear Cu 2 (II,II)-cores stabilized by the N 3 O donorset of HL 1 = (2-{[[di(2-pyridyl)methyl](methyl)amino]methyl}phenol), HL 2 = 2-({[di(2-pyridyl)methyl]amino}methyl)phenol), and HL 3 = 2-({[di(2-pyridyl)methyl]amino}methyl)-4-nitrophenol display a unique superoxide dismutase (SOD) combined with catalase (CAT)-like activity in water, at neutral pH. The Cu 2 L 1 2 < Cu 2 L 2 2 < Cu 2 L 3 2 structure− reactivity trend puts a spotlight on the electron-deficient core of Cu 2 L 3 2 that exhibits the highest SOD (log k cat (O 2 •− ) = 7.55) and CAT-like (k H 2 O 2 = 0.66 M −1 s −1 ) performance. Time-lapse ESI-MS and EPR experiments indicate that a dimeric core is essential for oxygenic turnover upon H 2 O 2 decomposition.

Dinuclear Zn Complex: Phenoxyl Radical Formation Driven by Superoxide Coordination

“…The X-ray analysis of Zn 2 L 2 shows a C i point-group symmetry for the complex, with a distorted octahedral geometry for the metal centers, analogously to the structure previously reported for the Cu 2 (II)L 2 complexes (Figure 1). [7] Each Zn(II) atom is coordinated in a facial configuration by the three N atoms of the tetradentate ligand, while the phenolate ligands act as a bridge between the two metal centers. The metal coordination sphere is completed by two MeOH molecules (Figure 1).…”

“…[8] This ligand has been recently reported in the literature to form mono and dimeric complexes with first row transition metals (Mn, Cu, Fe) exhibiting excellent properties in the processes of H 2 O 2 and O 2 * À dismutation and proton reduction. [7,9] The tetradentate N 3 O donor-set provided by the ligand can bind Zn(II) with a bis-pyridyl, tertiary amine and phenolate terminals. The Zn 2 L 2 complex has been obtained by reacting the ligand HL with zinc perchlorate and triethylamine in methanol (Scheme 1).…”

“…The Zn 2 L 2 complex has been obtained by reacting the ligand HL with zinc perchlorate and triethylamine in methanol (Scheme 1). [7,9] Colourless crystals suitable for X-ray analysis have been isolated upon addition of acetonitrile and cooling to 4°C. The X-ray analysis of Zn 2 L 2 shows a C i point-group symmetry for the complex, with a distorted octahedral geometry for the metal centers, analogously to the structure previously reported for the Cu 2 (II)L 2 complexes (Figure 1).…”

“…[6] Herein the reactivity of the Zn 2 L 2 complex, a structural analogue of the highly reactive SOD mimic Cu 2 L 2 , with O 2 * À has been investigated in order to evaluate the interaction and the contribution of the Zn center in the process of superoxide activation. [7]…”

Versatile Activity of a Copper(II) Complex Bearing a N4‐Tetradentate Schiff Base Ligand with Reduced Oxygen Species

“…However, at pH 7, mononuclear Cu(II) complexes are much less reactive than dinuclear Cu(II) complexes, thus reinforcing the requirement of two Cu(II) centers for CAT activity. [55] When the complex is left to react with H 2 O 2 in DMF and the reaction mixture is frozen, the low-temperature X-band EPR spectrum displays the characteristic pattern of distorted squarepyramidal Cu(II) complexes (Figure 7b). [16,26] Inspection of the spectrum reveals the presence of two paramagnetic species with two sets of g k values with distinct A k .…”