Synthesis, crystal structure, computational and solution studies of a new phosphotetradecavanadate salt. Assessment of its effect on U87 glioblastoma cells

The new benzylammonium (C₇H₁₀N) salt of the phosphotetradecavanadate (PV14) anion PV₁₄O₄₂^9-, (C₇H₁₀N)₆[H₃PV₁₄O₄₂]∙7H₂O (1), is synthesized under mild conditions and characterized by a combination of physicochemical techniques such as Fourier transform infrared spectroscopy, powder X-ray diffraction, elemental analyses and cyclic voltammetry. As evaluated by ⁵¹V NMR spectroscopy, at milimolar concentrations and pH ∼2.5 the PV14 anions decompose slowly, thus demonstrating kinetic stability, but at pH ∼7 this process takes place much faster. However, in the presence of human serum albumin, the ⁵¹V NMR peaks of PV14 anions broaden significantly and their decomposition becomes much slower, this being due to a direct interaction between both components. The structure of 1 is elucidated by single-crystal X-ray diffraction and reveals the presence of three-fold protonated, bicapped Keggin type [H₃PV₁₄O₄₂]^6- anions. The supramolecular interactions governing the crystal packing are further studied using the Hirshfeld surface analysis. Computational studies using density functional theory were effective in determining the electronic and protonation states of PV14 clusters, as well as the multi-electron redox behavior of compound 1 in acidic aqueous solutions. Molecular dynamics calculations confirm the high hydrophilicity and absence of aggregation between protonated PV14 anions in aqueous medium. Notably, this compound shows high inhibitory effect on the viability of the U87 glioblastoma cell line with IC₅₀ values of 3.2 ± 0.6 μM and 1.10 ± 0.04 μM after 24 h and 72 h treatments. The mode of action of compound 1 is mediated by the pro-apoptotic process. These data provide evidence on the potential therapeutic use of PV14 compounds against glioblastoma.