Syntheses, structures, stability, and insulin-like activities of peroxovanadium(V) complexes with a heteroligand

Several peroxovanadium(V) complexes were prepared with a tripodal or a quasi-tripodal tetradentate ligand. The structures of K(2)[VO(O(2))(nta)].2H(2)O and K[VO(O(2))(DL-cmhist)].H(2)O have been determined by X-ray crystallography (nta, nitrilotriacetate; cmhist, N-carboxymethylhistidinate). The structure of Cs[VO(O(2))(pda)].2H(2)O (pda, N-pyridylmethyliminodiacetate) has been estimated to be similar to that of K[VO(O(2))(DL-cmhist)].H(2)O. Each complex anion in these compounds adopts a distorted pentagonal bipyramidal structure, which is typical for heptacoordinate oxoperoxovanadium(V) complexes. The peroxide ion binds in a side-on fashion to the vanadium(V) center in the pentagonal plane. The peroxide anion in the cmhist complex dissociates rather easily in an acidic solution (pH approximately 3), while that in the other complexes stays intact under similar conditions. The in vitro insulin mimetic effect of the peroxovanadium(V) complexes has been evaluated by the inhibitory effect on free fatty acid (FFA) release in isolated rat adipocytes treated with epinephrine. The cmhist complex is effective, while the others are almost totally ineffective.