Síntese e caracterização do complexo de cobre (II) com o ligante bipiridina, [cu(bipy)2]2+ , e avaliação de sua atividade antioxidante.

Abstract

Oxidative stress is characterized by an imbalance between the production of reactive oxygen species and the antioxidant capacity of the organism, resulting in cellular damage associated with diseases such as cancer, neurodegenerative disorders, and cardiovascular conditions. In this context, copper(II) complexes have attracted increasing attention as potential antioxidant agents due to their structural versatility, redox reactivity, and ability to mimic antioxidant enzymes, such as superoxide dismutase. This study aimed to synthesize, characterize, and evaluate the antioxidant activity of a copper(II) complex containing the ligand 2,2′-bipyridine ([Cu(bipy)₂]²⁺), investigating the influence of its chemical structure on free radical neutralization. The complex was synthesized in a hydroalcoholic medium from copper(II) chloride and 2,2′-bipyridine, followed by precipitation as a hexafluorophosphate salt. Characterization was performed by infrared and ultraviolet–visible spectroscopy. Antioxidant activity was evaluated using the in vitro DPPH free radical scavenging assay, with Trolox as the reference standard. Infrared results confirmed complex formation through the presence of Cu–N stretching bands and characteristic vibrations of the hexafluorophosphate counterion. In the ultraviolet–visible region, an intense absorption band attributed to metal-to-ligand charge transfer transitions was observed, with a high molar absorptivity value, indicating strong electronic interaction and structural stability in solution. In the antioxidant assay, the complex exhibited dose-dependent behavior, with inhibition percentages above 50%, indicating moderate to high antioxidant activity. The free ligand showed nearly constant and lower values, with no clear dose–response relationship. These results demonstrate that coordination to the copper(II) ion significantly enhances free radical scavenging ability, attributed to metal–ligand synergism and the involvement of the copper(II)/copper(I) redox pair in electron transfer processes. It is concluded that the [Cu(bipy)₂]²⁺ complex presents superior antioxidant properties compared to the free ligand, highlighting its potential for the development of new bioinorganic compounds with possible application in the prevention of oxidative stress-related damage.