| In the past three decades, the interactions between peroxovanadates and organic ligands have attracted great interest in both chemistry and biology. In this work, multinuclear NMR (1H, 13C and 51V), multidimensional (DOSY and 1H-1H COSY), and variable temperature NMR were used to study the above interaction systems. Through the combination of these methods, structures of all species in interaction systems were obtained and a better understanding of the experimental phenomena was achieved. The possible interaction modes and mechanism of the interaction systems are discussed. The main conclusions are summarized as follows:1. To understand the substituting effects of organic ligands on the reaction equilibrium, the interactions between diperoxovanadate complex [OV(O2)2(D2O)]-/[OV(O2)2(HOD)]-(abbr. bpV) and a series of N-substituted-picolinamide ligands in solution were explored for mimicking the physiological conditions. The order of reactive capability of the picolinamide-like ligands with bpV is as follows: N-methylpicolinamide≈N-(2-hydroxyethyl)-picolinamide > N-ethylpicolinamide > N-propylpicolinamide. The substituting group influences the reactivity by an electron effect. Competitive coordination interactions result in a series of new seven-coordinated peroxovanadate species.2. To understand the effects of organic ligands of the diperoxovanadate complexes on the reaction equilibrium, the interactions between a series of diperoxovanadate complexes [OV(O2)2LL']n- (LL' = oxalate, picolinate, 2,2'-bipyridine and 1,10-phenanthroline, the corresponding peroxovanadate species abbreviate bpV(oxa), bpV(pic), bpV(bipy)) and 1-methylimidazole (N-Me-Imi) in solution were explored for mimicking the physiological conditions. The experimental results indicated the activity order of these complexes with 1-methylimidazole as follows: bpV(oxa) > bpV(pic) > bpV(bipy) > bpV(phen). Both the coordinating capability and the steric effect of the organic ligands affect the reaction equilibrium. At the same time, a new six-coordinated peroxovanadate species [OV(O2)2(N-Me-Imi)]- is formed due to the competitive coordination.3. To understand the substituting effects of imidazole ring on the reaction equilibrium, the interactions between diperoxovanadate complex NH4[OV(O2)2(2-(2'-Py)-Imi)] 2222 4H2O (abbr. bpV(Imi-Py)) and a series of imidazole-like ligands (imidazole, 2-methyl-imidazole, 4-methyl-imidazole, and histidine) in solution were explored for mimicking the physiological conditions. The experimental results indicated that the activities of bpV(Imi-Py) and organic ligands as follows: imidazole≈4-methyl-imidazole > 2-methyl-imidazole > histidine. The steric effect of the organic ligands affects the reaction equilibrium. At the same time, new six-coordinated peroxovanadate species [OV(O2)2L]- were formed due to the competitive coordination between 2-(2'-Py)-Imi and the imidazole-like ligands. When the ligand was 4-methyl-imidazole or histidine, a pair of isomers was formed.4. To understand the substitutinged effects of pyridine ring on the reaction equilibrium, the interactions between diperoxovanadate complex bpV and 4-substituted pyridine for mimicking the physiological conditions. The experimental results indicated that the activities of bpV and organic ligands as follows: pyridine > isonicotinate > N-methyl isonicotinamide > methyl isonicotinate. Both the electron-withdrawing induction effect and electron-withdrawing conjugated effects of the organic ligands affect the reaction equilibrium.NMR were used to study the interactions between diperoxovanadates and small organic molecules. A spectroscopic method was 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 system. |
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