Abstract
The importance of copper as an essential element can be estimated by the wide range of copper proteins and enzymes playing different roles in biological systems. In the last decades many bioinorganic studies were developed on mimetic complexes of copper-dependent proteins, in order to verify the interrelations between structural and functional properties of active copper centers. Among the most studied copper ion ligand, diimine compounds have deserved special attention due their flexibility, facility of preparation, and ability to stabilize both oxidation states of this metal. In our laboratory, we have been investigating some Schiff base copper complexes as mimics of different proteins, with emphasis on functional aspects, trying to elucidate mechanisms of reaction, based on proposed intermediary species, in addition to molecular shapes. Particularly, mimics of the copper-zinc superoxide dismutase, and of monooxigenases and oxidases exhibiting dicopper sites are discussed in this work.
Highlights
The importance of copper as an essential element can be estimated by the wide range of copper proteins and enzymes playing different roles in biological systems (Kaim & Rall 1996)
An upper limit of 10−18 mol/L has been estimated for the concentration of free copper ions in the cell, which means that cellular pools of free copper are virtually nonexistent, and that copper ions are always inserted on suitable biomolecules (Lippard 1999)
Among the most studied copper ion ligand, diimine compounds have been deserving special at
Summary
The importance of copper as an essential element can be estimated by the wide range of copper proteins and enzymes playing different roles in biological systems (Kaim & Rall 1996). Since the pioneering studies on model systems for the action of copper monooxygenases (Karlin et al 1984), and on oxygenated species of those proteins (Kitajima et al 1989), investigations of this type of complexes have contributed to the better understanding of the oxygenation reactions in vivo Another protein extensively studied is the copper-zinc superoxide dismutase, mainly due their protective role in conditions of oxidative stress. Since its functional role has been described, many copper complexes with different ligands were prepared as mimics of this enzyme, specially macroacyclic polyimines (Gärtner & Weser 1986) These studies indicated that the catalytic cycle requires a particular conformation of the active site, between a square planar arrangement adequate for copper(II) ions, and a distorted tetrahedral form preferred by copper(I) ions. Complexes of tetradentate diimines seem to be more efficient on mimicking the SOD activity, while the tridentate ligands permit to obtain dinuclear species, which can act as monooxygenase or oxidase models
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