PtIV- or MoVI-substituted decavanadates inhibit the growth of Mycobacterium smegmatis

Abstract Inhibitory effects of two monosubstituted decavanadates by PtIV in monoplatino(IV)nonavanadate(V) ([H2PtIVV9O28]5−, V9Pt), and by MoIV in monomolybdo(VI)nonavanadate(V) ([MoVIV9O28]5−,V9Mo) were investigated against the growth of Mycobacterium smegmatis with the EC50 values of 0.0048 mM and 0.015 mM, respectively. These compare to the reported inhibitory value for decavanadate ([V10O28]6−/[HV10O28]5−, V10) on Mycobacterium smegmatis (EC50 = 0.0037 mM). Time-dependent 51V NMR spectroscopic studies were carried out for all three polyanions in aqueous solution, biological medium (7H9), heated and non-heated supernatant to evaluate their stability in their respective media, monitor their hydrolysis to form various oxovanadates over time and calculate the EC50 values. These studies allow us to calculate adjusted and maximum EC50 for the polyoxovanadate (POV) present in solution at the beginning of the study when there is most intact anions in the media and thus the EC50 values represent the initial effects of the POVs. The results have shown that V10 is 1.3 times more potent than V9Pt and 4 times more potent than V9Mo, indicating that the inhibitory effects of monosubstituted polyanions are related to the V10 structure. We attributed the minor differences in the growth inhibitory effects to the differences in charges (5- vs 6-) of V9Pt and V9Mo compared to V10 and/or the differences in the chemical composition. We concluded that the potency of the growth inhibition by V10 is mainly due to the chemical properties of the vanadium and the decametalate's unique structure even though the presence of the Mycobacterium smegmatis facilitate hydrolysis of the anions. Synopsis Two decavanadate derivatives, monoplatino(IV)nonavanadate(V) ([H2PtIVV9O28]5−), monomolybdo(VI)nonavanadate(V) ([MoVIV9O28]5−) and decavanadate are more potent growth inhibitors of Mycobacterium smegmatis than monomeric vanadate. The spectroscopic characterization carried out in the growth medium led to the conclusion that both the decavanadate structure and its properties are important for its growth effects.