Abstract: In the past two decades, the interactions between peroxovanadates and organic ligands have attracted great interest in both chemistry and biology. In this work, multinuclear NMR (¹H, ¹³C, ¹⁴N, ¹⁵N, and ⁵¹V), multidimensional (DOSY, ¹H-¹H COSY, and ¹³C-¹H COSY), and variable temperature NMR, together with ESI-MS and theoretical calculations were utilized to study the above interaction systems. Through the combination of these methods, structures of all species in the interaction systems were obtained and a better understanding of the experimental phenomena was achieved. These studies shed some light on the essence of the vanadium-contained enzyme such as chloroperoxidase. The main conclusions are summarized as follows:
1. NMR study on the interactions between diperoxovanadates and histidinelike ligands shows that histidine or carnosine coordinates to vanadate(V) by its ε-N, which is the same as His496 in the active site of chloroperoxidase from the fungus Curvularia inaequalis. Theoretical study indicates that the solvation effect plays a key role in stabilizing the products. ESI-MS and theoretical calculations were also performed to explore the different behaviors of the species in the interaction systems in solution and gas phases. The species [OV(O₂)₂(L)₂]^- in gas phase, ever reported to be seven-coordinated, was found to be actually six-coordinated, the same as in solution. The second ligand links to the oxo or peroxo groups through hydrogen bonds.
2. NMR and ESI-MS techniques were used to study the interactions between diperoxovanadates and small organic molecules such as pyridine, imidazole, arginine, picoline ester, and picoline amide. Spectroscopic methods were established to explore this type of interactions. It is worth mentioning that DOSY can be used to analyze the chemical structures and components of mixtures without chemical separation．This makes it important for the investigation of complicated mixtures avoiding time-consuming separation and purification that may destroy the inspected systems.
3. A new diperoxovanadate crystal NH₄{OV(O₂)₂{2-(2′-pyridyl)-imidazole}}·4H₂O was synthesized. The crystal was obtained from the interaction system, NH₄VO₃/H₂O₂/ 2-(2′-pyridyl)imidazole, in aqueous solution under the physiological conditions, and the complex was characterized by solution NMR, IR, X-ray crystal diffraction and elementary analysis. The complex may be of great chemical interest because it is the first diperoxovanadate complex having an asymmetrical N,N′-chelating biheteroaromatic ligand. To the best of our knowledge, its ⁵¹V NMR chemical shift is at the highest field among this kind of complexes reported in the literature.

Key words: diperoxovandate, small molecular, interaction, NMR, ESI-MS, theoretical calculation