Turning Bonding into Function: the Emerging Role of the Bioactive Selenium─Metal Motif in Toxicology and Medicinal Chemistry

The synthesis and characterization of organo-selenium compounds have attracted considerable interest for decades, driven by the search for efficient catalysts and bioinspired antioxidants; the investigation and exploitation of selenium─metal motifs in biological and medicinal chemistry represent a recent development and constitute the focus of this review. Selenoproteins are targets of metal ions like mercury and cadmium, whose toxicity is associated with the formation of stable selenium─metal bonds impairing protein function. On the other hand, selenium─metal bonding provides a strategy for tuning both chalcogen and metal reactivity, potentially enhancing the pharmacological performance of metallodrugs. Coordination to transition metals can modify redox potentials, bond polarization, and reactivity, thereby enabling multifunctional compounds combining metal-based pharmacophores with the redox activity of selenium. These systems may modulate reactive oxygen species, inhibit enzymes, and enhance selective cytotoxicity toward cancer cells. The formation of selenium─metal bonds in biological environment can also alter the function of metalloproteins, accounting for the toxicity of organoselenides. By combining experimental structural and reactivity properties with mechanistic insights from computational chemistry, we highlight the unifying concepts that govern selenium─metal bonding and to illustrate how these concepts can guide the rational design of new classes of selenium-based functional molecules.