Spectroscopic studies on the interactions between a bioactive diperoxovanadate complex and pyridine

The role of nano-sized manganese oxides in the oxygen-evolution reactions by manganese complexes: towards a complete picture

Eighteen Mn complexes with N-donor and carboxylate ligands have been synthesized and characterized. Three Mn complexes among them are new and are reported for the first time. The reactions of oxygen evolution in the presence of oxone (2KHSO5·KHSO4·K2SO4) and cerium(iv) ammonium nitrate catalyzed by these complexes are studied and characterized by UV-visible spectroscopy, X-ray diffraction spectrometry, dynamic light scattering, Fourier transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, transmission electron microscopy, scanning electron microscopy, membrane-inlet mass spectrometry and electrochemistry. Some of these complexes evolve oxygen in the presence of oxone as a primary oxidant. CO2 and MnO4(-) are other products of these reactions. Based on spectroscopic studies, the true catalysts for oxygen evolution in these reactions are different. We proposed that for the oxygen evolution reactions in the presence of oxone, the true catalysts are both high valent Mn complexes and Mn oxides, but for the reactions in the presence of cerium(iv) ammonium nitrate, the active catalyst is most probably a Mn oxide.

Spectroscopic investigation of the interaction between diperoxovanadate complexes and benzimidazole-like ligands

To understand the effects of benzimidazole substitution on reaction equilibrium, the interactions between a series of benzimidazole-like ligands and [OV(O₂)₂(D₂O)]⁻/[OV(O₂)₂(HOD)]⁻ in solution were explored by a combination of multinuclear ((1)H, (13)C, and (51)V) magnetic resonance and variable temperature NMR in 0.15 mol/L NaCl ionic medium for mimicking the physiological condition. Some direct NMR data are reported for the first time. These results show that the relative reactivity among the organic ligands is 2-methyl-1H-benzo[d]imidazole>(1H-benzo[d]imidazol-2-yl)methanol>1-(1H-benzo[d]imidazol-2-yl)ethanol>1H-benzo[d][1,2,3]triazole. Both the steric effect and the electron effect of the 2-position substituted groups in benzimidazole ring affect the reaction equilibrium. The competitive coordination results in the formation of a series of new six-coordinated peroxovanadate species [OV(O₂)₂L]⁻(L=benzimidazole-like ligands). Moreover, the results of density functional calculations provided a reasonable explanation on the relative reactivity of the benzimidazole-like ligands as well as the important role of solvation in these reactions.

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.

NMR and theoretical study on interactions between diperoxovanadate complex and pyrazole-like ligands

To understand the effects of pyrazole substitution on reaction equilibrium, the interactions between a series of pyrazole-like ligands and [OV(O(2))(2)(D(2)O)](-)/[OV(O(2))(2)(HOD)](-) were explored by using multinuclear ((1)H, (13)C, and (51)V) magnetic resonance, HSQC, and variable temperature NMR in 0.15 mol/L NaCl ionic medium mimicking physiological conditions. These results show that the relative reactivities among the pyrazole-like ligands are 3-methyl-1H-pyrazole approximately 4-methyl-1H-pyrazole approximately 1H-pyrazole>1-methyl-1H-pyrazole. As a result, the main factor which affects the reaction equilibrium is the steric effect instead of the electronic effect of the methyl group of these ligands. A pair of isomers has been formed resulting from the coordination of 3-methyl-1H-pyrazole and a vanadium complex, which is attributed to different types of coordination between the vanadium atom and the ligands. Thus, the competitive coordination leads to the formation of a series of six-coordinate peroxovanadate species [OV(O(2))(2)L](-) (L, pyrazole-like ligands). Moreover, the results of density functional calculations provided a reasonable explanation on the relative reactivity of the pyrazole-like ligands as well as the important role of solvation in these reactions.

Solution structure of a seven coordinated manganese(II) complex via electrospray ionization mass spectrometry

The mononuclear complex [Mn(tptz)(CH(3)COO)(OH(2))(2)]NO(3) (1) was investigated by electrospray ionization mass spectrometry in aqueous solution at pH 4.5. Electrospray ionization mass spectrometry shows that mononuclear and dinuclear manganese cationic species are present in solution, probably in equilibrium with neutral 1. An experiment showed that the most important reaction in the presence of oxone (2KHSO(5).KHSO(4).K(2)SO(4)) is decoordination.

Multinuclear NMR and theoretical investigation on interactions between diperoxovanadate complex and 4-picoline-like ligands

To understand the 4-substituting group effects of organic ligands in pyridine ring on the reaction equilibrium, the interactions between a series of 4-picoline-like ligands and [OV(O(2))(2)(D(2)O)](-)/[OV(O(2))(2)(HOD)](-) in solution were explored by the combined use of multinuclear ((1)H, (13)C, and (51)V) magnetic resonance, DOSY, and variable-temperature NMR in 0.15 mol/L NaCl ionic medium for mimicking the physiological condition. Some direct NMR data are given for the first time. The reactivity among the 4-picoline-like ligands is 4-picoline>isonicotinate>isonicotinamide>ethyl isonicotinate. The competitive coordination results in the formation of a series of new six-coordinated peroxovanadate species [OV(O(2))(2)L](n-) (L=4-picoline-like ligands, n=1 or 2). The results of density functional calculations provide a reasonable explanation on the relative reactivity of the 4-picoline-like ligands. Solvation effects play an important role in these reactions.

Feasibility study for the rapid screening of target molecules using translational diffusion coefficients: diffusion-ordered NMR spectroscopy of biological toxins

A panel of 15 biological toxins ranging between approximately 60-28,000 g/mol was used to evaluate the feasibility of screening aqueous samples for toxin analytes based on their translational diffusion coefficients, D(t). Toxin D(t) values were measured by pulsed-field gradient (1)H NMR spectroscopy using a bipolar pulse pair, longitudinal eddy current delay pulse sequence incorporating water suppression to achieve the maximum dynamic range for toxin signals. To collect data for an effective screening protocol, reference D(t) values were determined from five independent measurements at both 25 and 37 degrees C for all toxins in the panel. In the protocol, D(t) values are measured at both temperatures for a suspected toxin target in a sample, and for assignment as a potential toxin analyte, the measurements are required to fall within +/-0.25 x 10(-6) cm(2)/s of both reference D(t) values for at least one toxin in the panel. Only solution viscosity was found to influence sample D(t) measurements appreciably; however, the measurements are easily corrected for viscosity effects by calculating the D(t) value of the suspected toxin at infinite dilution. In conclusion, the protocol provides a rapid and effective means for screening aqueous samples for all toxins in the panel, narrowing toxin identification to < or = 2 possibilities in virtually all cases.

Investigation on the complex of diperoxovanadate with picolinamide

A novel diperoxovanadate complex NH(4)[OV(O(2))(2)(picolinamide)].H(2)O was synthesized from aqueous solution under physiological conditions. The solution structure of the complex was characterized by multinuclear ((1)H, (13)C, (14)N, and (51)V), variable temperature as well as two-dimensional (DOSY) NMR techniques in the interaction system of NH(4)VO(3)/H(2)O(2)/picolinamide at room temperature. The crystal structure of the complex was determined at 223K by single-crystal X-ray diffraction method. It belongs to the monoclinic space group P21/c with a=7.323(3)A, b=14.255(7)A, c=10.022(5)A, beta=99.524(9) degrees , V=1031.7(8)A(3), and Z=4. The crystal is composed of ammonium ions, picolinamide oxodiperoxovanadate(V) ions, and water molecules, which are held together by ionic and hydrogen bond forces. The species [OV(O(2))(2)(picolinamide)](-) is seven-coordinated with a distorted pentagonal bipyramidal geometry both in solution and in crystal.

NMR and theoretical study on interactions between diperoxovanadate complex and 4-substituted pyridines

To understand the substituting group effects of organic ligands on the reaction equilibrium, the interactions between diperoxovanadate complex [OV(O2)2(D2O)]-/[OV(O2)2(HOD)](-) and a series of 4-substituted pyridines in solution were explored using multinuclear (1H, 13C, and 51V) magnetic resonance, DOSY, and variable temperature NMR in 0.15 mol/L NaCl ionic medium for mimicking the physiological condition. Some direct NMR data are given for the first time. The reactivity among the 4-substituted pyridines is pyridine > isonicotinate > N-methyl isonicotinamide > methyl isonicotinate. The competitive coordination results in the formation of a series of new six-coordinated peroxovanadate species [OV(O2)2L](n-) (L = 4-substituted pyridines, n = 1 or 2). The results of density functional calculations provide a reasonable explanation on the relative reactivity of the 4-substituted pyridines. Solvation effects play an important role in these reactions.

Spectroscopic and theoretical study on the interaction between diperoxovanadate and oxazole

Detailed investigations were carried out to explore the interaction systems of NH(4)VO(3)/H(2)O(2)/oxazole in aqueous solution under physiological conditions by a combined use of multinuclear NMR ((1)H, (13)C, (14)N and (51)V), diffusion ordered spectroscopy (DOSY), variable temperature NMR, electrospray ionization mass spectrometry (ESI-MS), spin-lattice relaxation and density functional calculations. The results indicated the formation of a new peroxovanadate species [OV(O(2))(2)(oxazole)](-) with oxazole coordinating to vanadium through nitrogen atom. The solution structure of the new species was predicted from theoretical calculations.

Interactions between diperoxovanadate complex and amide ligands in aqueous solution

Multinuclear ((1)H, (13)C, (14)N, and (51)V) NMR spectroscopy has been used to study the reactions between the diperoxovanadate complex K(3)[OV(O(2))(2)(C(2)O(4))] x H(2)O (abbr. bpV(ox)) and ethylenediamine or diethylamine in aqueous solution. The interaction between bpV(ox) and diethylamine was very weak and no new complex was formed. However, bpV(ox) reacted with ethylenediamine giving a new product in which ethylenediamine attached to the vanadium atom via one nitrogen atom in a monodentate manner. Diffusion ordered spectroscopy (DOSY) measurements and theoretical calculations proved the formation of new product in bpV(ox) and ethylenediamine. The vanadium atoms in both [OV(O(2))(2)(C(2)O(4))](3-) and [OV(O(2))(2)(en)](-) species are six coordinated in solution state.

Multinuclear NMR spectroscopic and theoretical study on the interactions between diperoxovanadate complex and picoline-like ligands

To understand the substituting effects of organic ligands on the reaction equilibrium, the interactions between diperoxovanadate complex [OV(O(2))(2)(H(2)O)](-) and a series of picoline-like ligands in solution were explored using 1D multinuclear ((1)H, (13)C, and (51)V) magnetic resonance, 2D diffusion ordered spectroscopy (DOSY), and variable temperature NMR in 0.15 mol/l NaCl ionic medium for mimicking the physiological conditions. The order of reactive capability of the picoline-like ligands with [OV(O(2))(2)(H(2)O)](-) is found to be picolinamide>N-methylpicolinamide>methyl picolinate>ethyl picolinate approximately propyl picoliniate>isopropyl picolinate. The substituting group influences the reactivity by either steric effect or electron-donating effect. Competitive coordination interactions result in a series of new seven-coordinated peroxovanadate species [OV(O(2))(2)L](-) (L=picoline-like ligands). Their coordination ways were confirmed by density functional calculations.

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.