Speciation in the aqueous peroxovanadate-maltol and (peroxo)vanadate-uridine systems

• The speciation in the aqueous H+/H2VO4-/H2O2/maltol (Ma), H+/H2VO4-/uridine (Ur) and H+/H2VO4-/H2O2/Ur systems was determined in the physiological medium of 0.150 M Na(Cl) at 25 °C. A combination of quantitative 51V NMR (Bruker AMX500) and potentiometric data (glass electrode) was collected and treated simultaneously by the computer program LAKE. In the quaternary maltol system, the two species VXMa2- and VX2Ma2- (where X denotes the peroxo ligand) were found in the pH region 5-10, in addition to all binary and ternary complexes. Their formation was fast. In the ternary uridine (H+/H2VO4-/Ur) subsystem, altogether three vanadate-uridine (V-Ur) species were found in the pH region 4-10, with compositions VUr2-, V2Ur22- and V2Ur23-. Equilibrium was fast except in weakly acidic solutions when slowly decomposing decavanadates formed. In the quaternary H+/H2VO4-/H2O2/Ur system, five additional species were found at pH > 7. They were of VXUr and VX2Ur compositions. Their formation was fast. Formation constants, compositions and 51V NMR chemical shifts are given for all the species found in the systems, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Biological and medical relevance of the species (in the treatment of diabetes) are also discussed, with pseudo-physiological conditions modelled.

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