Aqueous Chemistry of Ammonium (Dipicolinato)oxovanadate(V): The First Organic Vanadium(V) Insulin-Mimetic Compound

Abstract

The aqueous speciation, formation constants, and solution structure were determined for a new insulin-mimetic organic vanadium(V) compound (ammonium (dipicolinato)oxovanadate(V)). The solution properties of the system were characterized by using potentiometry, 1H, 13C, and 51V NMR 1D and 2D spectroscopy, and UV/visible spectroscopy. These studies were conducted using the crystalline compound as well as combinations of the free ligand and the metal salt. The major complex is most stable in the acidic pH range, although it does protonate at low pH. It protonates at pH ∼1 and decomposes below pH 0. The dipic ligand is coordinated in a tridentate manner throughout the pH range studied. Protonation at low pH takes place on one of the oxo groups. Dynamic processes were explored using 1H and 13C EXSY NMR spectroscopy. VO2dipic- was found to exchange between the complex and the ligand at high and at low pH values. In the intermediate-pH range, no evidence for exchange processes was obtained, documenting the inert...