Counterion Affects Interaction with Interfaces: The Antidiabetic Drugs Metformin and Decavanadate

A material that contains metformium cation and decavanadate anion was synthesized and characterized. The material is not soluble in water but slightly soluble in dimethyl sulfoxide and very soluble in the inhomogeneous environment of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles, which deviates significantly from the properties of sodium decavanadate. By considering the fact that decavanadate is reported to have insulin-enhancing activity in streptozotocin (STZ)-induced diabetic rats (Pereira et al., J. Inorg. Biochem. 2009, 103, 16871692), how this oxometalate interacts with interfaces was investigated using NMR and IR spectroscopy. By using 51V NMR spectroscopy, we found only small differences between the metformium and Na+ decavanadate materials. However, by using IR spectroscopy, the decavanadatemetformin material was found to affect the water pool and water organization near the interface of the reverse micelles differently. The solubility differences and these spectroscopic studies demonstrate that the counterion to the decavanadate anion significantly affects the properties of decavanadate, even in the presence of a large excess amount of Na+ (counterions to AOT), and the implications of this work on cellular uptake is discussed.