Interactions of vanadyl(IV) with dithiothreitol and thioglycolic acid. Their action on alkaline phosphatase activity

The interactions between the VO2+ cation and dithiothreitol and thioglycoli c acid were investigated in aqueous solution and also in the solid state fo r the latter ligand. Spectral measurements in solution show the coordinatio n of VO2+ through deprotonated thiol and hydroxyl groups (pH = 8.5-12) for the first ligand, and carboxylate and deprotonated thiol groups for the sec ond (pH = 4-11). Elemental analysis, IR and diffuse reflectance spectroscop y, magnetic susceptibility and thermal behavior measurements support the ch aracterization of [VO(TGA)(2)]. H2O. In this complex, obtained at pH = 3.5, the coordination involves the carboxylate and thiol groups giving a five-m embered chelate ring (alpha-SH/beta-COO- donor groups). In order to have an insight into the biological properties of simple VO(IV) complexes, the dir ect effect of these complexes upon alkaline phosphatase activity was invest igated The free ligands caused inhibition of the enzyme activity with stati stically lesser potency than that of the vanadyl complexes. The VO/dithioth reitol complex was a stronger inhibitor of the alkaline phosphatase activit y than the VO/thioglycolic acid complex. (C) 1999 Elsevier Science Inc. All rights reserved.