The (biological) speciation of vanadate(V) as revealed by (51)V NMR: A tribute on Lage Pettersson and his work

Four decades of research carried out by Lage Pettersson, his group and his coworkers are reviewed, research that has been directed predominantly towards the speciation of vanadate and systems containing, along with vanadate and co-reactants such as phosphate and peroxide, biologically relevant organics. In particular, those organics have been addressed that either are (potential) ligands for vanadate-derived coordination compounds generated at physiological conditions and/or function as constituents in medicinally interesting oxidovanadium compounds. Examples for molecules introduced in the context of the physiological vanadate-ligand interaction include the dipeptides Pro-Ala, Ala-Gly, Ala-His and Ala-Ser, the serum constituents lactate and citrate, and the nucleobases adenosine and uridine. The speciation in the vanadate-picolinate and vanadate-maltol systems is geared towards insulin-enhancing vanadium drugs. The speciation as a function of pH, ionic strength and the concentration of vanadate and the ligand(s) is based on potentiometric and (51)V NMR investigations, a methodical combination that allows reliable access to composition, formation constants and, to some extent, also structural details for the manifold of species present in aqueous media at physiological pH and beyond. The time frame 1971 to 2014 is reviewed, emphasizing the interval 1985 to 2006, and thus focusing on biologically interesting vanadium systems. Figurative representations from the original literature have been included.

Spectroscopic and theoretical study on the interaction between diperoxovanadate complexes and glycyl-histidine

The interaction between diperoxovanadate complexes (K₃)[VO(O₂)₂(C₂O₄)]·H₂O and [VO(O₂)₂(D₂O)](-)/[VO(O₂)₂(HOD)](-)) and glycyl-histidine (abbr. GlyHis) in solution was studied by 1D NMR including variable-temperature NMR, 2D diffusion ordered spectroscopy (DOSY), HMQC and density functional theory (DFT) calculations. The results indicate that a pair of [VO(O₂)₂(GlyHis)](-) isomers is formed. The vanadium in the new species is coordinated by either the ɛ-N or δ-N in the imidazole ring. The relative ratio of the isomers was affected by temperature. Theoretical calculation results provide a reasonable explanation on the relative coordination capability of different nitrogen sites. Solvation effect is shown to be important for the reactivity of the interaction system.

Investigation on the interactions between diperoxovanadate and substituted phenanthroline

Detailed investigations were carried out to explore the interaction systems of NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline and NH4VO3/H2O2/5-methyl-1,10-phenanthroline in aqueous solution under physiological conditions by NMR spectroscopy, such as 1D 1H, 13C, 51V variable temperature, and 2D COSY, NOESY, HETCOR, COLOC techniques as well as density functional calculations. New species [OV(O2)2(5,6-dimethyl-1,10-phenanthroline)]- and [OV(O2)2(5-methyl-1,10-phenanthroline)]- including isomers were formed in a bidentate coordination fashion which were stable under the experimental conditions. The solution structures of these new species were proposed based on the direct NMR experimental information and confirmed by the theoretical calculations. All the 1H and 13C NMR peaks were assigned. The calculated 1H and 13C chemical shifts on the whole are in fair agreement with the experimental values. The methyl groups on the aromatic ring of the three new complexes were found to have a steric hindrance effect on the coordination process. Experimental results show that the order of coordination capability of phenanthroline and its derivants was: 1,10-phenanthroline>5-methyl-1,10-phenanthroline>5,6-dimethyl-1,10-phenanthroline.

Investigation on the complex of diperoxovanadate with 2-(2′-pyridyl)-imidazole

A novel diperoxovanadate complex NH4[OV(O2)2{2-(2'-pyridyl)-imidazole}] x 4H2O was synthesized in aqueous solution under physiological conditions. The solution structure of the complex was characterized by multinuclear (1H, 13C, 14N, and 51V) as well as multi-dimensional (DOSY and C-H COSY) NMR techniques in the interaction system of NH4VO3/H2O2/2-(2'-pyridyl)-imidazole at room temperature. The crystal structure of the complex was determined at 173K by single-crystal X-ray diffraction method. It belongs to the monoclinic space group P21/c with a = 13.048(4), b = 6.984(2), c = 17.814(5) A, beta = 104.695(5), V = 1570.3(8) A3 and Z = 4. The crystal is composed of ammonium ions, {2-(2'-pyridyl)-imidazole}oxodiperoxovanadate(V) ions, and water molecules, which are held together by ionic and hydrogen bond forces. The metal atom in the complex is seven-coordinated with a distorted pentagonal bipyramidal geometry. It is the first mononuclear diperoxovanadate complex with a N, N'-chelating biheteroaromatic ligand and its 51V chemical shift is at the highest field among the known mononuclear diperoxovanadate(V) complexes.

NMR and Theoretical Study on the Coordination and Solution Structures of the Interaction between Diperoxovanadate Complexes and Histidine-like Ligands

To simulate the types of coordination and solution structures of the active site of haloperoxidases, the interaction systems between diperoxovanadate complexes [OV(O2)2L]n- (n = 1 or 3, L = oxalate or H2O) and a series of histidine-like ligands in solution have been studied by using 1D multinuclear (1H, 13C, and 51V) NMR, 2D diffusion ordered spectroscopy, and variable-temperature NMR in 0.15 mol/L NaCl ionic medium, representing the physiological conditions of human blood. Some direct NMR data are given for the first time. The reactivity among the histidine-like ligands is imidazole > 2-methylimidazole > carnosine approximately 4-methylimidazole > histidine. Competitive coordination interactions result in a series of new peroxovanadate species [OV(O2)2L']- (L' = histidine-like ligands). When the ligands are 4-methylimidazole, histidine, and carnosine, a pair of isomers have been observed, which are attributed to different types of coordination between vanadium atom and ligands. The results of density functional theory calculations provided a reasonable explanation on the relative reactivity of the histidine-like ligands and the molar ratios of isomers. Theoretical results signify the importance of the solvation effect for the reactivity and stability of the interaction systems.

Molecular and supramolecular features of oxo-peroxovanadium complexes containing O3N, O2N2and ON3donor sets

The complexes [VO(O2)Hbpa]+ (1a), [VO(O2)bpa] (1b, Hbpa = bis(picolyl)-beta-alanine), [VO(O2)heida]- (2, H2heida =N-(2-hydroxyethyl)iminodiacetic acid), [VO(O2)(3OH-pic)2]- (3a), [VO(O2)(3OH-pic)2]-/[V(O2)2(3OH-pic)2]- (3b, 3OH-pic = 3-hydroxypicolinic acid), [VO(O2)(3OH-pa)2] (6, 3OH-pa = 3-hydroxypicolylamide), [VO2(3OH-pic)2]- (4), [VO(tBuO2)(3OH-pic)2] (5) and [VO(tBuO2)(3OH-pa)2]2+ (7) have been characterised. The structures of 21a[ClO4].1b.2.25H2O, K.2H2O, [NH4].H2O and [nBu4]3b are reported. Supramolecular patterns arise from intermolecular hydrogen bonds, the relevance of which for the peroxo/hydroperoxo intermediates in oxo transfer reactions catalysed by vanadate-dependent haloperoxidases is addressed. Specific solution patterns have been analysed by 51V and 17O NMR.

Speciation in the aqueous H+/H2VO4-/H2O2/picolinate system relevant to diabetes research

A detailed study of the quaternary aqueous H+/H2VO4-/H2O2/picolinate (Pi-) system has been performed at 25 degrees C in 0.150 M Na(Cl) medium using quantitative 51 V NMR (500 MHz) and potentiometric data (glass electrode). In the ternary H+/H2VO4-/Pi- system, six complexes have been found in the pH region 1-10. In the quaternary H+/H2VO4-/H2O2/Pi- system, eight additional complexes have been found. Generally, equilibria are fast in both systems. The rate of peroxide decomposition depends on the species in solution. Chemical shifts, compositions and formation constants for the species are given. Equilibrium conditions and the fit of the model to the experimental data are illustrated in distribution diagrams. Possible formation of mixed ligand species with imidazole, lactic acid and citric acid have been investigated and ruled out under the same experimental conditions. Structural proposals are given, based on 1)C NMR data and available crystal structures.