Stability in solution and chemoprotection by octadecavanadates(IV/V) in E. coli cultures.

Two mixed-valence octadecavanadates, (NH)(MeN)[VVOI]·MeNI·5HO (VI) and [{K(OH)VVO(PO)·4HO}] (VP), were synthesized and characterized by single-crystal X-ray diffraction analysis and FTIR, Raman, V NMR, EPR and UV/Vis/NIR spectroscopies. The chemoprotective activity of VI and VP towards the alkylating agent diethyl sulfate was assessed in E. coli cultures. The complex VI was nontoxic in concentrations up to 5.0 mmol L, while VP presented moderate toxicity in the concentration range 0.10 - 10 mmol L. Conversely, a ca. 35% enhancement in culture growth as compared to cells treated only with diethyl sulfate was observed upon addition of VI (0.10 to 2.5 mmol L), while the combination of diethyl sulfate with VP increased the cytotoxicity presented by diethyl sulfate alone. V NMR and EPR speciation studies showed that VI is stable in solution, while VP suffers partial breakage to give low nuclearity oxidometalates of vanadium(V) and (IV). According to the results, the chemoprotective effect depends strongly on the direct reactivity of the polyoxidovanadates (POV) towards the alkylating agent. The reaction of diethyl sulfate with VI apparently produces a new, rearranged POV instead of poorly-reactive breakage products, while VP shows the formation and subsequent consumption of low-nuclearity species. The correlation of this chemistry with that of other mixed-valence polyoxidovanadates, [HVVOPO] (V) and [VVOCl] (V), suggests a relationship between stability in solution and chemoprotective performance.