Bioactivity of Decavanadate Compounds: Can Their <i>In Vitro</i> and <i>In Vivo</i> Effects Be Assessed in a Simple Manner?

Two decavanadate anions with 4-dimethylaminopyridinium and one with 1-methylimidazolium cations are isolated and characterized by single-crystal X-ray diffraction. The Hirshfeld surfaces and associated 2D-fingerprint plots confirm the propensity of V₁₀ anions to undergo hydrogen-bonding interactions. DFT calculations demonstrate the tendency for protonation of decavanadates and, for the first time, the possibility of one or two-electron reduction maintaining the V₁₀-cluster structure. Moreover, the tendency of V₁₀ species to gain electrons increases with ion pairing, this effect depending on the counterion involved. The computed proton-coupled electron transfer energies indicate the prevalence of [HV^V₉V^IVO₂₈]^6-, [H₂V^V₈V^IV₂O₂₈]^6-, or [H₂V^V₉V^IVO₂₈]^5- species over V₁₀. Decavanadates at total vanadium concentrations ([V]_total) in the range 720-800 μM undergo extensive hydrolysis within a few hours when added to RPMI cell incubation media. With the cell media in contact with A2780 ovarian cancer cells, V₁₀ hydrolysis occurs much faster. Notably, the cytotoxicity and the vanadium uptake observed on A2780 cells for equal [V]_total values are similar to solutions containing or not V₁₀ anions, but preincubation with the V^V solutions affect the biological activities, decreasing cell viability. These conclusions support the complexity of factors to be analyzed when discussing any biological effect observed, namely, protonation, redox processes, hydrolysis, ageing, counterions, and composition of the biological medium.