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

Two mixed-valence octadecavanadates, (NH4)2(Me4N)5[VIV12VV6O42I]·Me4NI·5H2O (V18I) and [{K6(OH2)12VIV11VV7O41(PO4)·4H2O}n] (V18P), were synthesized and characterized by single-crystal X-ray diffraction analysis and FTIR, Raman, 51V NMR, EPR and UV/Vis/NIR spectroscopies. The chemoprotective activity of V18I and V18P towards the alkylating agent diethyl sulfate was assessed in E. coli cultures. The complex V18I was nontoxic in concentrations up to 5.0 mmol L−1, while V18P presented moderate toxicity in the concentration range 0.10 - 10 mmol L−1. Conversely, a ca. 35% enhancement in culture growth as compared to cells treated only with diethyl sulfate was observed upon addition of V18I (0.10 to 2.5 mmol L−1), while the combination of diethyl sulfate with V18P increased the cytotoxicity presented by diethyl sulfate alone. 51V NMR and EPR speciation studies showed that V18I is stable in solution, while V18P 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 V18I apparently produces a new, rearranged POV instead of poorly-reactive breakage products, while V18P shows the formation and subsequent consumption of low-nuclearity species. The correlation of this chemistry with that of other mixed-valence polyoxidovanadates, [H6VIV2VV12O38PO4]5- (V14) and [VIV8VV7O36Cl]6- (V15), suggests a relationship between stability in solution and chemoprotective performance. The chemoprotective activity of the mixed-valence octadecavanadates [{K6(OH2)12VIV11VV7O41(PO4)·4H2O}n] (V18P) and (NH4)2(Me4N)5[VIV12VV6O42I]·Me4NI·5H2O (V18I) against diethyl sulfate was assessed in E. coli cultures. V18I counteracts the alkylating agent more efficiently than V18P. Speciation studies suggest that chemoprotection relates to the ability of polyoxidovanadates to rearrange in solution following reaction with diethyl sulfate. [Display omitted] •Two mixed-valence octadecavanadates were synthesized and characterized.•V18P is [{K6(OH2)12VIV11VV7O41(PO4)·4H2O}n] and V18I is (NH4)2(Me4N)5[VIV12VV6O42I]·Me4NI·5H2O.•The chemoprotective activity of V18P and V18I against diethyl sulfate was assessed.•V18I counteracts the alkylating agent and provides 35% enhancement in culture growth.•Halide-encapsulated POVs offer higher chemoprotection than phosphate analogs.