A strategy to improve the cancer therapies involves agents that cause the depletion of the endogenous antioxidant glutathione (GSH), increasing its efflux out of cells and inducing apoptosis in tumoral cells due to the presence of reactive oxygen species. It has been shown that Casiopeina copper complexes caused a dramatic intracellular GSH drop, forming disulfide bonds and reducing Cu^II to Cu^I. Herein, through the determination of the [Cu^II]–SH bond before reduction, we present evidence of the adduct between cysteine and one Casiopeina as an intermediate in the cystine formation and as a model to understand the anticancer activity of copper complexes. Evidence of such an intermediate has never been presented before.

This work explores the effect of geometry and the presence of a site available for carbon dioxide coordination in molecular catalysis of CO₂ reduction for cobalt complexes using electrochemical and spectroelectrochemical studies. The octahedral complexes [Co^II(bztpen)Br]PF₆ and [Co^II(bpy)₃](BF₄)₂, along with the trigonal bipyramidal complex [Co^II(TPA)Cl]Cl, were selected for this study (where bztepen = N-benzyl-N,N′,N′-tris-(pyridine-2-ylmethyl)-ethylenediamine), TPA = tris (2-pyridimethyl)-amine, and bpy = 2′-2′- pyridine). DFT calculations were performed to predict the geometries of the complexes and to propose the sites at which electron transfer occurs. Among the studied compounds, [Co^II(bpy)₃(BF₄)₂] exhibited the highest catalytic rate constant for CO₂ reduction (k = 1.22 × 10² M⁻¹·s⁻¹) compared to [Co^II(bztpen)Br]PF₆ (k = 8.93 × 10¹ M⁻¹·s⁻¹). The trigonal bipyramidal complex [Co^II(TPA)Cl]Cl presented the lowest catalytic rate constant for CO₂ reduction (k = 1.47 × 10¹ M⁻¹·s⁻¹). UV-Vis spectroelectrochemical studies and DFT calculations suggested the formation of [Co^I(bztpen)(CO)]⁺ and [Co^I(tpa)(CO)]⁺ species, which are associated with catalyst deactivation and may account for the lower performance of CO₂ reduction.