Eugenio Garribba
Vanadium compounds (VCs) in solution are distinguished by a significant tendency to transform, allowing processes, such as hydrolysis, ligand exchange, and redox reactions, to occur. These features have implications for their biological role and pharmacological applications. In aqueous and biological media, VCs rarely maintain a single, well-defined identity, but participate in interconversion processes that depend on pH, (bio)ligand availability, and vanadium concentration. Electron paramagnetic resonance (EPR) spectroscopy has emerged as a powerful and selective technique that sheds light on these processes, owing to the capability to reveal the paramagnetic species formed by many transition metals, including vanadium. EPR can provide valuable insights into the electronic structure, coordination geometry, and transformation in solution of VCs. In this Perspective article, we present the information that EPR spectroscopy provides on the characterization of biologically relevant systems containing mono-, di-, or polynuclear VCs, with a particular emphasis on biologically relevant and EPR-active V IV species. The possibility of evaluating the transformation of VCs in the presence of biomolecules, such as amino acids, reducing agents, or proteins, is presented. In addition to the classical foundations, we discuss recent methodological advances and representative case studies, highlighting the advantages and limitations of EPR in chemical biology, including speciation in complex biological media, integration with other instrumental techniques, studies under near-physiological conditions, and prediction with computational methods.