| 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. |
- Andersson, Ingegärd, et al.
(författare)
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Speciation in vanadium bioinorganic systems 6. Speciation study of aqueous peroxovanadates, including complexes with imidazole
- 2000
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Ingår i: Journal of Inorganic Biochemistry. ; 80:1-2, s. 51-8
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Tidskriftsartikel (refereegranskat)abstract
- 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 °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.
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| 3. |
- Boström, Dan, et al.
(författare)
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Sodium trirubidium metavanadate monohydrate
- 2003
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Ingår i: Acta Crystallographica Section E. - : International Union of Crystallography. - 1600-5368. ; E59:11, s. i151-i153
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Tidskriftsartikel (refereegranskat)abstract
- The title compound, sodium trirubidium metavanadate monohydrate, NaRb3(VO3)4(H2O), crystallizes in the orthorhombic space group Pnma. The structure, which represents a rare type of catena-vanadate, is built up of strongly folded chains of corner-sharing [VO4] tetrahedra, running in the [010] direction with a periodicity of four. A three-dimensional framework is obtained by sodium ions linking adjacent chains in the [001] direction and by rubidium ions linking adjacent chains in the [100] direction. The single water molecule binds to the sodium ion and to two rubidium ions.
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| 4. |
- 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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| 5. |
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| 6. |
- 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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| 7. |
- 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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| 8. |
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| 9. |
- Howarth, Oliver W, et al.
(författare)
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Aqueous Peroxoisopolyoxometalates
- 2001
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Ingår i: Polyoxometalate Chemistry From Topology via Self-Assembly to Applications. - Dordrecht : Kluwer Academic Publishers. - 9780792370116 - 9780306476259 ; , s. 145-59
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Bokkapitel (refereegranskat)abstract
- New 17O NMR, potentiometry and ESI-MS measurements on aqueous peroxomolybdates and peroxotungstates reveal many new species, including diperoxo hepta-anions and also confirm other proposals based on potentiometry alone, such as a monoperoxo monomer. They also show the presence of many anions previously identified only in the solid state, including both forms of the Mo2(peroxide)4 anion. Comparison with recent work on peroxovanadates and peroxoniobates shows a marked preference in all cases for each metal atom to be coordinated to two peroxo ligands. Peroxotungstates, like tungstates themselves, are generally more complex than peroxovanadates and -molybdates.
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| 10. |
- Lyxell, Dan-Göran, et al.
(författare)
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Multicomponent Polyanions. 57. Large-Angle X-ray Scattering Study of Aqueous Molybdophenylphosphonate Solutions
- 2001
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 40:4, s. 584-92
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Tidskriftsartikel (refereegranskat)abstract
- The radial distribution functions are calculated from large-angle X-ray scattering (LAXS) measurements for one concentrated aqueous molybdate/heptamolybdate solution and five aqueous molybdophenylphosphonate solutions (lithium chloride medium). Besides water and hydrated lithium, chloride, and molybdate ions, five species in all, having different nuclearities, are postulated to exist in the solutions, according to equilibrium studies using potentiometry and 31P NMR spectroscopy. The structures of the three polymolybdate species Mo7O246-, Mo8O264-, and (C6H5P)2Mo5O214-, for which the structures are determined crystallographically, are confirmed to exist also in aqueous solution. The principal structures of the remaining two complexes, (C6H5P)Mo6O21(OH2)52- and (C6H5P)Mo7O25(OH2)4-, are elucidated with the use of structures of related species. Both anions have one group of four edge-sharing MoO6 octahedra and another group of two MoO6 octahedra connected by sharing corners, forming a bent unsymmetric six-membered ring, with the C6H5PO3 group placed on the crowded side of the ring. In the former, the group of two MoO6 octahedra is edge-shared, while in the latter, the group is face-shared, resulting in a ring small enough to tetrahedrally coordinate to the seventh molybdenum opposite the phenyl group.
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