Copper complexes for biomedical applications: Structural insights, antioxidant activity and neuron compatibility.

Copper coordinated with amino acid residues is essential for the function of many proteins. In addition, copper complexed to free l-Histidine, as [Cu(His) ₂ ], is used in the treatment of the neurodegenerative Menkes disease and of cardioencephalomyopathy. This study was aimed to coordinate copper(II) with four small ligands (l-Serine, l-Histidine, Urea and Biuret) and to evaluate structural features, stability, antioxidant activity and neuronal compatibility of the resulting complexes. All complexes were synthesized with CuCl ₂ and purified by precipitation in alcohol. Elemental composition, X-rays diffraction and FTIR indicated that the complexes were in form of [Cu(ligand) ₂ ] and exhibited tridentate (l-Histidine), bidentate (l-Serine and Biuret) or monodentate (Urea) coordination with copper. UV-Vis absorbance profiles in physiologically relevant solutions and cyclic voltammetry revealed that, contrarily to [Cu(Urea) ₂ Cl ₂ ] and [Cu(Biuret) ₂ Cl ₂ ], the [Cu(Ser) ₂ ] and [Cu(His) ₂ Cl ₂ ] complexes were stable in different media including water, physiological saline and intestinal-like solutions. All complexes and their ligands had antioxidant capacity as evaluated by DPPH (1,1-diphenyl-2,2-picrylhydrazyl) and DPD (N,N-diethyl-p-phenylenediamine) methods, and the [Cu(His) ₂ Cl ₂ ] complex was the most potent. Neuronal compatibility was assessed through cell viability measurements using cultured neurons derived from mouse P19 stem cells. Although only [Cu(His) ₂ Cl ₂ ] showed a good neurocompatibility (about 90% at concentrations up to 200 μM), the cytotoxicity of the other copper complexes was lower compared to equivalent concentrations of CuCl ₂ . These findings open new perspectives for the use of these copper complexes as antioxidants and possibly as therapeutic agents for neurodegenerative diseases. Furthermore, study of these complexes may help to improve chelation therapy for copper dysfunctions.
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