Speciation in the Aqueous H+/ H2VO4--/ Uridine/ Imidazole and H+/H2VO4-/H2O2/Uridine Systems

ANA CECILIA GONZALEZ BARO; ANDERSSON, I.; PETTERSSON, L.

Antalya, Turquía

Congreso; 9th Eurasia Conference on Chemical Sciences; 2006

The speciation in the aqueous H+/H2VO4-/ Uridine (Ur), H+/H2VO4-/Ur/Imidazole (Im) and H+/H2VO4-/H2O2/Ur systems has been determined in the physiological medium of 0.150 M Na(Cl) at 25 °C. A combination of quantitative 51V NMR data (Bruker AMX500) and potentiometric data (glass electrode) have been collected and treated simultaneously by the computer program LAKE. The pKa-value for uridine has been determined by potentiometric titrations to be 9.163. Altogether, three vanadate – uridine species have been found in the pH region 4 – 10, with compositions: VUr2-, V2Ur22- and V2Ur23-. In the mixed ligand uridine and imidazole system, two additional species were identified in the pH region 6 – 10, with compositions VUrIm- and VUrIm2-. Equilibrium is fast, except in weakly acidic solutions, where slowly decomposing decavanadates form. In the quaternary H+/H2VO4-/H2O2/Ur system, five new species have been found in addition to all species in the binary and ternary subsystems. They are of VXUr and VX2Ur compositions, where X denotes the peroxo ligand. Their formation is fast. Formation constants and 51V NMR chemical shifts are given for all species in the systems. Equilibrium conditions, including physiological, are illustrated in distribution diagrams as well as the fit of the model to the experimental data.