| 1. |
- Andersson, Ingegärd, et al.
(författare)
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Speciation in the aqueous H+/H2VO4–/H2O2/picolinate system relevant to diabetes research
- 2004
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Ingår i: Dalton Transactions. - Cambridge : Royal Society of Chemistry, Thomas Graham House. - 1477-9226 .- 1477-9234. ; :3, s. 421-428
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the quaternary aqueous H+/H2VO4−/H2O2/picolinate (Pi−) system has been performed at 25 °C in 0.150 M Na(Cl) medium using quantitative 51V 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 13C NMR data and available crystal structures.
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| 2. |
- Gorzsás, András, et al.
(författare)
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A speciation study of the aqueous H+/H2VO4–/H2O2/L--alanyl-L-serine system
- 2003
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; , s. 1161-7
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the quaternary aqueous H+/H2VO4–/H2O2/L--alanyl-L-serine (Alaser) 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-values for Alaser were determined as 8.04 ± 0.01 and 3.07 ± 0.01. The errors given are 3. In the ternary H+/H2VO4–/Alaser system, two complexes, (H+)p(H2VO4–)q(Alaser)r, having (p, q, r) values (0, 1, 1) and (–1, 1, 1) with log0,1,1= 2.42 ± 0.01 and log–1,1,1=–5.80 ± 0.05 explain all data in the pH region 2.5–9.5. Equilibrium conditions are illustrated in distribution diagrams and structure proposals are given based on 1H and 13C NMR investigations. In the quaternary H+/H2VO4–/H2O2/Alaser system, six complexes could be found in addition to all binary and ternary complexes over the pH region 2.6–11.1, four with a V/X/Alaser ratio 1 1 1 and two with a ratio 1 2 1 (X = peroxo ligand). The formation of the monoperoxo vanadium species is very slow, requiring up to 10 days for complete equilibrium. Significant decomposition of peroxide occurs only in acidic solutions. Chemical shifts, compositions and formation constants for the six quaternary complexes are given, and equilibrium conditions are illustrated in distribution diagrams. The H+/H2VO4–/H2O2/Alaser/Alahis system, where Alahis denotes L--alanyl-L-histidine, was briefly investigated and no mixed ligand species were detected.
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| 3. |
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| 4. |
- Gorzsás, András, et al.
(författare)
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Speciation in the aqueous H+/H2VO4–/H2O2/citrate system of biomedical interest
- 2004
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Ingår i: Dalton Transactions. - Cambridge : Royal Society of Chemistry, Thomas Graham House. - 1477-9226 .- 1477-9234. ; :18, s. 2873-2882
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Tidskriftsartikel (refereegranskat)abstract
- The speciation in the quaternary aqueous H+/H2VO4–/H2O2/citrate (Cit3–) and H+/H2VO4–/Cit3–/L-(+)-lactate (Lac–) systems has been determined at 25 °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.
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| 5. |
- Gorzsás, András, et al.
(författare)
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Speciation in the aqueous H+/H2VO4–/H2O2/L-(+)-lactate system
- 2003
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). ; , s. 2503-11
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Tidskriftsartikel (refereegranskat)abstract
- 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 3. 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.
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| 6. |
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| 7. |
- Pettersson, Lage, et al.
(författare)
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Speciation in peroxovanadate systems
- 2003
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Ingår i: Coordination Chemistry Reviews. ; 237:1-2, s. 77-87
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Tidskriftsartikel (refereegranskat)abstract
- 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 vanadate, hydrogen peroxide and ligand concentration and of pH have been covered. The medium was chosen to represent the physiological conditions in human blood. The computer program , designed to treat different types of data simultaneously, has been used to establish the entire speciation in the systems. Before studying systems containing the ligand (L), the complete speciation in the subsystem H+–H2VO4−–H2O2 must be known under the same experimental conditions. The formation constants in this subsystem have earlier been determined and it was found that hydrogen peroxide interacts with vanadate in the whole pH range studied (0.5–10.5). In all, 10 peroxovanadate species were identified and diperoxovanadate species were found to be exceptionally stable at physiological pH. The ligands studied so far include imidazole (Im), -α-alanyl--histidine (Ah), -α-alanyl--serine (As), picolinic acid (Pi), and -(+)-lactic acid (La). In these five systems, as many as 3, 8, 6, 8, and 5 different peroxovanadate—L species (isomers included) were identified. A feature common to all these systems is that V(H2O2)2L species are formed at physiological pH. Notably, the 51V chemical shift values of diperoxovanadate moieties are always found in the range −670 to −770 ppm, and those of monoperoxovanadate from −540 to −670 ppm. The equilibrium conditions are illustrated in distribution diagrams and the effectiveness of the different ligands as complexation agents are compared. In the case of diperoxovanadate complexes, ligands with aromatic nitrogen (Im, Pi, Ah) are the most effective, the one with both aliphatic nitrogen and oxygen (As) is less effective, and the one with oxygen only (La) is the least preferred.
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