Ingegärd Andersson

Speciation in peroxovanadate systems

Detailed and thorough potentiometric and 51V-NMR spectroscopic investigations of H+–H2VO4−–H2O2–Ligand systems have been performed at 25 °C in 0.15 M Na(Cl) ionic medium. Extensive ranges of vanada ...

Speciation in vanadium bioinorganic systems. 6. Speciation study of aqueous peroxovanadates, including complexes with imidazole.

Using a combination of potentiometry (glass electrode) and quantitative 51V NMR spectroscopy, the full speciation in the vanadate-peroxide and vanadate-peroxide-imidazole systems was determined in the pH range 1-10 (0.150 M Na(Cl) medium, 25 degrees C). Using the computer program LAKE, the pKa value of imidazole and the formation constants for 10 peroxovanadate species and also for three more species where a single imidazole moiety is also bound, have been calculated. The experimental data show a good fit to the calculated speciation model, even for the less abundant species. The species are either monomeric or dimeric in vanadium, and four resonances of the dimeric species have been unambiguously assigned via 2D 51V NMR. Diperoxovanadates are the favoured species at pH 2-10, when sufficient peroxide is present. Imidazole is found to bind strongly to them at pH 6-9. The equilibrium conditions are illustrated in distribution diagrams.

A Potentiometric and51V NMR Study of the Aqueous H+/H2VO4−/H2O2/L-α-Alanyl-L-histidine System

The speciation in the quaternary aqueous H+/H2VO4−/H2O2/L-α-alanyl-L-histidine (Ah) system has been determined from quantitative 51V NMR measurements and potentiometric data (glass electrode). The study was performed in 0.150 M Na(Cl) medium at 25 °C. Data were evaluated with the computer program LAKE, which is able to treat combined EMF and NMR data. The pKa values for Ah were determined as 8.06, 6.72 and 2.64. In the ternary H+/H2VO4−/Ah system, two complexes, (H+)p(H2VO4−)q(Ah)r, for which (p, q, r) values of (0, 1, 1) and (1, 1, 1) with log β0,1,1=2.52±0.03 and log β1,1,1=9.40±0.05 (pKa=6.88), respectively, explain all data. The errors given are 3σ. In the quaternary H+/H2VO4−/H2O2/Ah system, eight complexes were determined in addition to all binary and ternary complexes, four with a V/X/Ah ratio 1:1:1 and four with a ratio 1:2:1 (X=peroxo ligand). VX2Ah2− and VX2Ah− (pKa=8.19) are the main complexes and predominate in the pH range 5 to 9. Three additional minor species have also been found but their compositions could not be determined owing to their small amounts. Equilibria are slow, significant decomposition of peroxide occurs only in acidic solutions. Data in the pH range 5 to 10 have been used for the LAKE calculations. Chemical shifts, compositions, and formation constants for the eight quaternary complexes are given, and equilibrium conditions are illustrated in distribution diagrams. Structural proposals for VX2Ah2− and VX2Ah− are made from 1H and 13C NMR measurements.

Speciation in the aqueous H+/H2VO4–/H2O2/L-(+)-lactate system

A detailed study of the quaternary aqueous H+/H2VO4−/H2O2/L-(+)-lactate (Lac−) system has been performed at 25 °C in 0.150 M Na(Cl) medium, representing the ionic strength of human blood, using quantitative 51V NMR and potentiometric data (glass electrode). Data were evaluated with the computer program LAKE, which is able to treat combined EMF and NMR data. The pKa-value for lactic acid was determined as 3.653 ± 0.002. The error given is 3σ. In the ternary H+/H2VO4−/Lac− system, eight complexes were found in the pH region 1.1–10.9; only half of them are mononuclear. Owing to the fast reduction of vanadium(V) in acidic solutions and to the slow equilibria of the inorganic vanadates under certain conditions, the final model of this ternary system presented in the study is limited to pH > 3.1. Solutions, in which reduction occurred to any extent, were excluded from all calculations, hence the study is limited to vanadium(V). In the quaternary H+/H2VO4−/H2O2/Lac− system, seven complexes could be found in addition to all binary and ternary complexes over the pH region 2.1–10.0, only two of which were mononuclear. Equilibrium is fast, but significant decomposition of peroxide occurs in acidic solutions over very short time, limiting the final model to pH > 4. Chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Simple biological tests were carried out to check the resistance of different peroxovanadate complexes (including the ones with Lac−) against human catalase and the results are being presented here.

A Potentiometric and (31P, 51V) NMR Study of the Aqueous Molybdovanadophosphate System

The equilibrium speciation of the quaternary system H+/MoO42-/HVO42-/HPO42- in aqueous 0.600 M Na(Cl) at 25 °C and 90 °C was studied by pH potentiometry and 31P (202.5 MHz) and 51V (131.6 MHz) 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.

Speciation in Aqueous Vanadate – Ligand and Peroxovanadate – Ligand systems

In the present focused review, the speciation studies of aqueous vanadate-ligand (L) and peroxovanadate-L systems are addressed. The paper focuses solely on the systems studied at our department in the context of potential insulin-enhancing effects, including the following ligands: imidazole, alanylhistidine, alanylserine, lactate, picolinate, citrate, phosphate, maltol, and uridine. We summarise the results of detailed and thorough potentiometric (glass electrode) and (51)V NMR (Bruker AMX-500MHz) spectroscopic studies, performed at 25 degrees C in 0.150 M Na(Cl), a medium representing human blood. The importance of experimental conditions is discussed and illustrated. A detailed overview of our methodology, based on combining potentiometric and (51)V integral and chemical shift data by means of the computer program LAKE, is also given. We list the important steps of equilibrium analysis and the kinds of information available from different sets of NMR spectra. The ligand picolinate is chosen to exemplify our working method, but conclusions are drawn from all systems, reviewing trends and common features. An overview of all systems is given in two tables, including e.g. types and number of species formed. Previously unpublished modelling results at physiological conditions are also shown for all peroxovanadate-ligand systems.

Glyphosate complexation to aluminium(III). An equilibrium and structural study in solution using potentiometry, multinuclear NMR, ATR-FTIR, ESI-MS and DFT calculations

The stoichiometries and stability constants of a series of Al(3+)-N-phosponomethyl glycine (PMG/H(3)L) complexes have been determined in acidic aqueous solution using a combination of precise potentiometric titration data, quantitative (27)Al and (31)P NMR spectra, ATR-FTIR spectrum and ESI-MS measurements (0.6M NaCl, 25 degrees C). Besides the mononuclear AlH(2)L(2+), Al(H(2)L)(HL), Al(HL)(2)(-) and Al(HL)L(2-), dimeric Al(2)(HL)L(+) and trinuclear Al(3)H(5)L(4)(2+) complexes have been postulated. (1)H and (31)P NMR data show that different isomers co-exist in solution and the isomerization reactions are slow on the (31)P NMR time scale. The geometries of monomeric and dimeric complexes likely double hydroxo bridged and double phosphonate bridged isomers have been optimized using DFT ab initio calculations starting from rational structural proposals. Energy calculations using the PCM solvation method also support the co-existence of isomers in solutions.

Speciation in the aqueous H+/H2VO4−/H2O2/citrate system of biomedical interest

The speciation in the quaternary aqueous H+/H2VO4-/H2O2/citrate (Cit3-) and H+/H2VO4-/Cit3-/L-(+)-lactate (Lac-) systems has been determined at 25 degrees C in the physiological medium of 0.150 M Na(Cl). A combination of 51V NMR integral intensities and chemical shift (Bruker AMX500) as well as potentiometric data (glass electrode) have been collected and evaluated with the computer program LAKE, which is able to treat multimethod data simultaneously. The pKa-values for citric acid have been determined as 2.94, 4.34 and 5.61. Altogether six vanadate-citrate species have been found in the ternary H+/H2VO4-/Cit3- system in the pH region 2-10, only two of which are mononuclear. Reduction of vanadium(V) becomes more pronounced at pH < 2. Solutions, in which reduction occurred to any extent, were excluded from all calculations. In the quaternary H+/H2VO4-/H2O2/Cit3- system, eight complexes have been found in addition to all binary and ternary complexes over the pH region 2-10, including three mononuclear species. Equilibria in general are fast, but the significant and rapid decomposition of peroxide in acidic solutions limited the final model to pH > 4. In the quaternary H+/H2VO4-/Cit3-/Lac- system, two mixed-ligand species have been determined, with the compositions V2CitLac2- and V2CitLac3- (pKa = 5.0). To our knowledge, this is the first time such complexes have been reported for vanadium(V). 51V NMR chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. When suitable, structural proposals are given, based on 13C NMR measurements and available literature data of related compounds.

[CA1]Speciation in the vanadate–alanylhistidine–peroxide system

The speciation in the quaternary aqueous H+–H2VO4−–H2O2–-α-alanyl--histidine (Ah) system has been determined from quantitative 51V NMR measurements and potentiometric data (glass electrode). The st ...