Investigating the copper coordination, electrochemistry, and Cu(ii) reduction kinetics of biologically relevant selone and thione compounds

Selenium- and sulfur-containing compounds can act as antioxidants by binding copper. To determine how this copper coordination results in the observed antioxidant activity, biologically relevant Cu ⁺ and Cu ²⁺ complexes with the formulae [Cu(dmit) ₃] ⁺ (3), [Cu(dmise) ₄] ⁺ (4a), and [Tpm ^iPrCu(MISeox)] ²⁺ (6) (dmise = N,N′-dimethylimidazole selone; dmit = N,N′-dimethylimidazole thione; MISeox = bis(1-methylimidazolyl)diselenide; Tpm ^iPr = tris(1,3-diisopropylpyrazolyl)methane) were synthesized, characterized, and their structures determined by single-crystal X-ray crystallography. In addition, kinetic studies using UV-vis spectroscopy indicate that dmise reduces Cu ²⁺ to Cu ⁺ three times faster than dmit. Coordination of dmise and MISeox to copper also results in more negative Cu ^2+/+ reduction potentials (-373 mV and -503 mV) compared to dmit (-217 mV). These results highlight the different complexation behaviors and reactivities of analogous selone- and thione-containing compounds, traits which likely influence their antioxidant activity.