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[EN] We explore the potential of Tb- and Yb-doped InVO4, InTaO4, and InNbO4 for applications as phosphors for light-emitting sources. Doping below 0.2% barely change the crystal structure and Raman spectrum but provide optical excitation and emission properties in the visible and near-infrared (NIR) spectral regions. From optical measurements, the energy of the first/second direct band gaps was determined to be 3.7/4.1 eV in InVO4, 4.7/5.3 in InNbO4, and 5.6/6.1 eV in InTaO4. In the last two cases, these band gaps are larger than the fundamental band gap (being indirect gap materials), while for InVO4, a direct band gap semiconductor, the fundamental band gap is at 3.7 eV. As a consequence, this material shows a strong self-activated photoluminescence centered at 2.2 eV. The other two materials have a weak self-activated signal at 2.2 and 2.9 eV. We provide an explanation for the origin of these signals taking into account the analysis of the polyhedral coordination around the pentavalent cations (V, Nb, and Ta). Finally, the characteristic green (D-5(4) -> F-7(J)) and NIR (F-2(5/2) -> F-2(7/2)) emissions of Tb3+ and Yb3+ have been analyzed and explained.

[EN] We explore the potential of Tb- and Yb-doped InVO4, InTaO4, and InNbO4 for applications as phosphors for light-emitting sources. Doping below 0.2% barely change the crystal structure and Raman spectrum but provide optical excitation and emission properties in the visible and near-infrared (NIR) spectral regions. From optical measurements, the energy of the first/second direct band gaps was determined to be 3.7/4.1 eV in InVO4, 4.7/5.3 in InNbO4, and 5.6/6.1 eV in InTaO4. In the last two cases, these band gaps are larger than the fundamental band gap (being indirect gap materials), while for InVO4, a direct band gap semiconductor, the fundamental band gap is at 3.7 eV. As a consequence, this material shows a strong self-activated photoluminescence centered at 2.2 eV. The other two materials have a weak self-activated signal at 2.2 and 2.9 eV. We provide an explanation for the origin of these signals taking into account the analysis of the polyhedral coordination around the pentavalent cations (V, Nb, and Ta). Finally, the characteristic green (D-5(4) -> F-7(J)) and NIR (F-2(5/2) -> F-2(7/2)) emissions of Tb3+ and Yb3+ have been analyzed and explained.

A comprehensive systematic review is given of developments, trends, and advances over the past two decades in research on orthovanadates of monovalent, divalent, and trivalent metals, MI3VO4, MII3(VO4)2, and MIIIVO4, respectively. We give our perspective on the current status of the topic, and the main attention is focused on lanthanide ion (Ln3+)–activated orthovanadate-based nanostructured luminescent materials, downconversion and upconversion ones, and their reported chemical syntheses, crystal structures, and photoluminescence properties along with applications as phosphors, both existing and potential, are fully considered. In particular, downconversion and upconversion phosphors based on Ln3+-doped GdVO4 and upconversion phosphors of BiVO4, LaVO4, YbVO4, and LuVO4 are described in far more detail.

A comprehensive systematic review is given of developments, trends, and advances over the past two decades in research on orthovanadates of monovalent, divalent, and trivalent metals, MI3VO4, MII3(VO4)2, and MIIIVO4, respectively. We give our perspective on the current status of the topic, and the main attention is focused on lanthanide ion (Ln3+)–activated orthovanadate-based nanostructured luminescent materials, downconversion and upconversion ones, and their reported chemical syntheses, crystal structures, and photoluminescence properties along with applications as phosphors, both existing and potential, are fully considered. In particular, downconversion and upconversion phosphors based on Ln3+-doped GdVO4 and upconversion phosphors of BiVO4, LaVO4, YbVO4, and LuVO4 are described in far more detail.

We report a study of the high-pressure structural behavior of ZnV2O6, Zn2V2O2, and Zn3V2O8, which has been explored by means of synchrotron powder x-ray diffraction. We found that ZnV2O6 and Zn3V2O8 remain in the ambient-pressure structure up to 15 GPa. In contrast, in the same pressure range, Zn2V2O2 undergoes three phase transitions at 0.7, 3.0, and 10.8 GPa, respectively. Possible crystal structures for the first and second high-pressure phases are proposed. Reasons for the distinctive behavior of Zn2V2O2 are discussed. The compressibility of the different polymorphs has been determined. The response to pressure is found to be anisotropic in all the considered compounds and the room-temperature equations of state have been determined. The bulk moduli of Zn2V2O6 (129(2) GPa) and Zn2V2O8 (120(2) GPa) are consistent with a structural framework composed of compressible ZnO6 octahedra and uncompressible VO4 tetrahedra. In contrast, Zn2V2O2 is highly compressible with a bulk modulus of 58(9) GPa, which is almost half of the bulk modulus of the other two vanadates. The large compressibility of Zn2V2O2 and its sequence of structural transitions are related to the fact that this material is less dense than the other zinc vanadates and to the penta-coordination of Zn atoms by oxygen atoms in Zn2V2O2. A comparison to the high-pressure behavior of related compounds is presented. (C) 2020 Elsevier B.V. All rights reserved.

The performance of energy materials hinges on the presence of structural defects and heterogeneity over different length scales. Here we map the correlation between morphological and functional heterogeneity in bismuth vanadate, a promising metal oxide photoanode for photoelectrochemical water splitting, by photoconductive atomic force microscopy. We demonstrate that contrast in mapping electrical conductance depends on charge transport limitations, and on the contact at the sample/probe interface. Using temperature and illumination intensity-dependent current-voltage spectroscopy, we find that the transport mechanism in bismuth vanadate can be attributed to space charge-limited current in the presence of trap states. We observe no additional recombination sites at grain boundaries, which indicates high defect tolerance in bismuth vanadate. These findings support the fabrication of highly efficient bismuth vanadate nanostructures and provide insights into how local functionality affects the macroscopic performance.

The performance of energy materials hinges on the presence of structural defects and heterogeneity over different length scales. Here we map the correlation between morphological and functional heterogeneity in bismuth vanadate, a promising metal oxide photoanode for photoelectrochemical water splitting, by photoconductive atomic force microscopy. We demonstrate that contrast in mapping electrical conductance depends on charge transport limitations, and on the contact at the sample/probe interface. Using temperature and illumination intensity-dependent current-voltage spectroscopy, we find that the transport mechanism in bismuth vanadate can be attributed to space charge-limited current in the presence of trap states. We observe no additional recombination sites at grain boundaries, which indicates high defect tolerance in bismuth vanadate. These findings support the fabrication of highly efficient bismuth vanadate nanostructures and provide insights into how local functionality affects the macroscopic performance.

Structural characterization of Ni3VxP2−xO8 (0 ≤ x ≤ 2) and Ni2VyP2−yO7 (0 ≤ y ≤ 2) compositions was made and colour parameters of these materials measured. Ni(II) diphosphate and divanadate crystalline phases are not stables at high temperature. Solid solutions in Ni3P2O8 and Ni3V2O8 are obtained by incorporation of V(V) in Ni orthophosphate and P(V) in Ni orthovanadate structures. Solid solutions with Ni3V2O8 structure are formed in a greater compositional interval than solid solutions with Ni3P2O8 structure. These materials might be used as ceramic pigments because of its thermal and chemical stability. Tan brown colorations were obtained in glazed tiles when the fired compositions were 4% weight enamelled with a commercial glaze.

Lanthanide-doped GdVO4 nanorods that exhibit upconversion emission under 982 nm excitation have been prepared by a facile room-temperature chemical co-precipitation method followed by a subsequent annealing at temperatures of 600 degrees C, 800 degrees C and 1000 degrees C. Multicolor upconversion emission, including white, was achieved by tuning the concentrations of dopant lanthanide ions (Ho3+, Er3+, Tm3+ and Yb3+) in GdVO4. It is found that four GdVO4 samples emit light with the white chromaticity coordinates of (0.326, 0.339), (0.346, 0.343), (0.323, 0327) and (0.342, 0.340) respectively, under a single-wavelength NIR excitation. These coordinates are very close to the standard equal energy white light coordinates (0333, 0.333) according to the 1931 CIE diagram. By varying dopant lanthanide concentrations in nanorods it is possible to produce upconversion emission with colors between red (0.504, 0369), green (0.282, 0.577) and blue (0.142, 0.125) coordinates. (C) 2015 Elsevier Ltd. All rights reserved.

A self-activated yellow emitting zinc vanadate (Zn2 Y20 1) was synthesized by combustion method. The influence of the processing parameters such as synthesis temperature and dopants concentration on the structure, morphology and luminescence properties was investigated. The X-ray diffraction (XRD) analysis confirmed that the samples have a tetragonal structure and no significant structural change was observed in varying both the synthesis temperature and the dopants concentration. The estimated average grain size was 78 nm for the samples synthesized at different temperatures and 77 nm for the doped samples. Scanning electron microscope (SEM) images show agglomerated hexagonal-like shape particles with straight edges at low temperatures and the shape of the particles changed to cylindrical-like structures at moderate temperatures but were destroyed at higher temperatures. The microstructure retained its original structure when the phosphor was doped with Ba, Ca and Sr. The photoluminescence (PL) of the product exhibited broad emission bands ranging from 400 to 800 nm. The best luminescence intensity was observed for the undoped Zni Y20 1 samples and those synthesized at 600°C. Any further increase in synthesis temperature and concentration of dopants, respectively, led to a decrease in the luminescence intensity. The broad band emission peak of Zn2 Y201 consist of two broad band's corresponding to emission from the Em1 (3T2-1A1) and Em2(3T1 - 1A1) transitions. The Zn2 Y20 1 phosphor was prepared by a sol-gel method. The effect of annealing temperature on the structure and photoluminescence of Zn2 Y201 was investigated. The XRD results showed the single monoclinic phase of Zn2Y201. The crystallinity of the Zn2Y201 phosphor improved while the full width at half maximum of (022) XRD peak was decreased with the increase in annealing temperature. SEM showed that the grains size increased with the increase in annealing temperature, which is due to the improvement in cryst, National Research Foundation (NRF), University of the Free State (UFS)

Lanthanide-doped GdVO4 nanorods that exhibit upconversion emission under 982 nm excitation have been prepared by a facile room-temperature chemical co-precipitation method followed by a subsequent annealing at temperatures of 600 degrees C, 800 degrees C and 1000 degrees C. Multicolor upconversion emission, including white, was achieved by tuning the concentrations of dopant lanthanide ions (Ho3+, Er3+, Tm3+ and Yb3+) in GdVO4. It is found that four GdVO4 samples emit light with the white chromaticity coordinates of (0.326, 0.339), (0.346, 0.343), (0.323, 0327) and (0.342, 0.340) respectively, under a single-wavelength NIR excitation. These coordinates are very close to the standard equal energy white light coordinates (0333, 0.333) according to the 1931 CIE diagram. By varying dopant lanthanide concentrations in nanorods it is possible to produce upconversion emission with colors between red (0.504, 0369), green (0.282, 0.577) and blue (0.142, 0.125) coordinates. (C) 2015 Elsevier Ltd. All rights reserved.

Catalysis in protein tyrosine phosphatases (PTPs) involves movement of a protein loop called the WPD loop that brings a conserved aspartic acid into the active site to function as a general acid. Mutation of the tryptophan in the WPD loop of the PTP YopH to any other residue with a planar, aromatic side chain (phenylalanine, tyrosine, or histidine) disables general acid catalysis. Crystal structures reveal these conservative mutations leave this critical loop in a catalytically unproductive, quasi-open position. Although the loop positions in crystal structures are similar for all three conservative mutants, the reasons inhibiting normal loop closure differ for each mutant. In the W354F and W354Y mutants, steric clashes result from six-membered rings occupying the position of the five-membered ring of the native indole side chain. The histidine mutant dysfunction results from new hydrogen bonds stabilizing the unproductive position. The results demonstrate how even modest modifications can disrupt catalytically important protein dynamics. Crystallization of all the catalytically compromised mutants in the presence of vanadate gave rise to vanadate dimers at the active site. In W354Y and W354H, a divanadate ester with glycerol is observed. Such species have precedence in solution and are known from the small molecule crystal database. Such species have not been observed in the active site of a phosphatase, as a functional phosphatase would rapidly catalyze their decomposition. The compromised functionality of the mutants allows the trapping of species that undoubtedly form in solution and are capable of binding at the active sites of PTPs, and, presumably, other phosphatases. In addition to monomeric vanadate, such higher-order vanadium-based molecules are likely involved in the interaction of vanadate with PTPs in solution.

The challenge of fine compositional tuning and microstructure control in complex oxides is overcome by developing a general two-step synthetic approach. Antimony-alloyed bismuth vanadate, which is identified as a novel light absorber for solar fuel applications, is prepared in a wide compositional range. The bandgap of this quaternary oxide linearly decreases with the Sb content, in agreement with first-principles calculations.

In this paper, we studied the effects of Er3+/Yb3+ concentration ratio on structural, morphological and luminescence properties of GdVO4:Er3+/Yb3+ green phosphors prepared by a high-temperature solid state method. The samples with different concentrations (between 0.5 to 2 mol%) of dopant Er3+ emitting ions and different concentrations (between 5 to 20 mol%) of sensitizer ions (Yb3+) were studied. The phosphors were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. For all samples, XRD diffraction patterns confirmed a formation of a pure GdVO4 phase, while the SEM showed that the materials are comprised of chunks of deformed particles with an average diameter ranging from approximately 2 mu m to 8 mu m. Both, down-conversion and up-conversion emission spectra of GdVO4: Er3+/Yb3+ samples, under near UV and IR excitations, exhibit two strong emission bands in the green spectral region at 525 nm and 552 nm wavelengths corresponding to H-2(11/2) - gt I-4(15/2) and S-4(3/2) - gt I-4(15/2) electronic transitions of Er3+ ions. The intensity of the green emission was changed by changing the Er3+/Yb3+ concentration ratio. This dual-mode luminescence makes these materials ideal as green phosphors for a wide variety of applications in the fields of bioanalysis and biomedical.

In this paper, we studied the effects of Er3+/Yb3+ concentration ratio on structural, morphological and luminescence properties of GdVO4:Er3+/Yb3+ green phosphors prepared by a high-temperature solid state method. The samples with different concentrations (between 0.5 to 2 mol%) of dopant Er3+ emitting ions and different concentrations (between 5 to 20 mol%) of sensitizer ions (Yb3+) were studied. The phosphors were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. For all samples, XRD diffraction patterns confirmed a formation of a pure GdVO4 phase, while the SEM showed that the materials are comprised of chunks of deformed particles with an average diameter ranging from approximately 2 mu m to 8 mu m. Both, down-conversion and up-conversion emission spectra of GdVO4: Er3+/Yb3+ samples, under near UV and IR excitations, exhibit two strong emission bands in the green spectral region at 525 nm and 552 nm wavelengths corresponding to H-2(11/2) - GT I-4(15/2) and S-4(3/2) - GT I-4(15/2) electronic transitions of Er3+ ions. The intensity of the green emission was changed by changing the Er3+/Yb3+ concentration ratio. This dual-mode luminescence makes these materials ideal as green phosphors for a wide variety of applications in the fields of bioanalysis and biomedical.

The challenge of fine compositional tuning and microstructure control in complex oxides is overcome by developing a general two-step synthetic approach. Antimony-alloyed bismuth vanadate, which is identified as a novel light absorber for solar fuel applications, is prepared in a wide compositional range. The bandgap of this quaternary oxide linearly decreases with the Sb content, in agreement with first-principles calculations.

Catalysis in protein tyrosine phosphatases (PTPs) involves movement of a protein loop called the WPD loop that brings a conserved aspartic acid into the active site to function as a general acid. Mutation of the tryptophan in the WPD loop of the PTP YopH to any other residue with a planar, aromatic side chain (phenylalanine, tyrosine, or histidine) disables general acid catalysis. Crystal structures reveal these conservative mutations leave this critical loop in a catalytically unproductive, quasi-open position. Although the loop positions in crystal structures are similar for all three conservative mutants, the reasons inhibiting normal loop closure differ for each mutant. In the W354F and W354Y mutants, steric clashes result from six-membered rings occupying the position of the five-membered ring of the native indole side chain. The histidine mutant dysfunction results from new hydrogen bonds stabilizing the unproductive position. The results demonstrate how even modest modifications can disrupt catalytically important protein dynamics. Crystallization of all the catalytically compromised mutants in the presence of vanadate gave rise to vanadate dimers at the active site. In W354Y and W354H, a divanadate ester with glycerol is observed. Such species have precedence in solution and are known from the small molecule crystal database. Such species have not been observed in the active site of a phosphatase, as a functional phosphatase would rapidly catalyze their decomposition. The compromised functionality of the mutants allows the trapping of species that undoubtedly form in solution and are capable of binding at the active sites of PTPs, and, presumably, other phosphatases. In addition to monomeric vanadate, such higher-order vanadium-based molecules are likely involved in the interaction of vanadate with PTPs in solution.

In this paper, we studied the effects of Er3+/Yb3+ concentration ratio on structural, morphological and luminescence properties of GdVO4:Er3+/Yb3+ green phosphors prepared by a high-temperature solid state method. The samples with different concentrations (between 0.5 to 2 mol%) of dopant Er3+ emitting ions and different concentrations (between 5 to 20 mol%) of sensitizer ions (Yb3+) were studied. The phosphors were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. For all samples, XRD diffraction patterns confirmed a formation of a pure GdVO4 phase, while the SEM showed that the materials are comprised of chunks of deformed particles with an average diameter ranging from approximately 2 mu m to 8 mu m. Both, down-conversion and up-conversion emission spectra of GdVO4: Er3+/Yb3+ samples, under near UV and IR excitations, exhibit two strong emission bands in the green spectral region at 525 nm and 552 nm wavelengths corresponding to H-2(11/2) - gt I-4(15/2) and S-4(3/2) - gt I-4(15/2) electronic transitions of Er3+ ions. The intensity of the green emission was changed by changing the Er3+/Yb3+ concentration ratio. This dual-mode luminescence makes these materials ideal as green phosphors for a wide variety of applications in the fields of bioanalysis and biomedical.

In this paper, we studied the effects of Er3+/Yb3+ concentration ratio on structural, morphological and luminescence properties of GdVO4:Er3+/Yb3+ green phosphors prepared by a high-temperature solid state method. The samples with different concentrations (between 0.5 to 2 mol%) of dopant Er3+ emitting ions and different concentrations (between 5 to 20 mol%) of sensitizer ions (Yb3+) were studied. The phosphors were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. For all samples, XRD diffraction patterns confirmed a formation of a pure GdVO4 phase, while the SEM showed that the materials are comprised of chunks of deformed particles with an average diameter ranging from approximately 2 mu m to 8 mu m. Both, down-conversion and up-conversion emission spectra of GdVO4: Er3+/Yb3+ samples, under near UV and IR excitations, exhibit two strong emission bands in the green spectral region at 525 nm and 552 nm wavelengths corresponding to H-2(11/2) - GT I-4(15/2) and S-4(3/2) - GT I-4(15/2) electronic transitions of Er3+ ions. The intensity of the green emission was changed by changing the Er3+/Yb3+ concentration ratio. This dual-mode luminescence makes these materials ideal as green phosphors for a wide variety of applications in the fields of bioanalysis and biomedical.

A series of SCR catalysts of mixed iron-erbium vanadates supported on TiO2-WO3-SiO2 were prepared and their reduction, textural, structural and morphological properties characterized by temperature programmed reduction, X-ray powder diffraction, B.E.T. methods and transmission electron microscopy. The influence of Fe/Er ratio in the vanadate as well as the effect of aging conditions on their activity in ammonia SCR reaction was investigated. SCR activity at medium/low temperature was found to correlate directly with the Fe loading of the catalyst, with supported FeVO4 resulting the most active material. This behavior might be correlated with the characteristics of Fe3+-O-V5+ bond and the acidity of the V-O moiety. Supported FeVO4 suffers a strong deactivation following thermal aging due to rutile formation in TiO2-based support and consequent collapse of surface area. The effect of Er is that of blocking transformation to rutile, thus enhancing activity after thermal treatment. Mixed composition FexEr1-xVO4 with x = 0.5 represents the best compromise between activity and stability and are potential candidates for deNO(x) process when a higher stability is requested. (C) 2014 Elsevier B.V. All rights reserved., Postprint (published version)

Damaging thermal stimuli trigger long-lasting variation potentials (VPs) in higher plants. Owing to limitations in conventional plant electrophysiological recording techniques, recorded signals are composed of signals originating from all of the cells that are connected to an electrode. This limitation does not enable detailed spatio-temporal distributions of transmission and electrical activities in plants to be visualised. Multi-electrode array (MEA) enables the recording and imaging of dynamic spatio-temporal electrical activities in higher plants. Here, we used an 8 × 8 MEA with a polar distance of 450 μm to measure electrical activities from numerous cells simultaneously. The mapping of the data that were recorded from the MEA revealed the transfer mode of the thermally induced VPs in the leaves of Helianthus annuus L. seedlings in situ. These results suggest that MEA can enable recordings with high spatio-temporal resolution that facilitate the determination of the bioelectrical response mode of higher plants under stress.

A versatile assay for protein tyrosine phosphatases (PTP) employing 3-nitrophosphotyrosine containing peptidic substrates is described. These therapeutically important phosphatases feature in signal transduction pathways. The assay involves spectrophotometric detection of 3-nitrotyrosine production from 3-nitrophosphotyrosine containing peptidic substrates, which are accepted by many PTPs. Compared to conventional chromogenic phosphate derivatives, the more realistic peptidic substrates allow evaluating substrate specificity. The assay's applicability is demonstrated by determining kinetic parameters for several PTP-substrate combinations and inhibitor evaluation, as well as detection of PTP activity in lysates. The convenient new assay may assist further adoption of PTPs in drug development.

A versatile assay for protein tyrosine phosphatases (PTP) employing 3-nitrophosphotyrosine containing peptidic substrates is described. These therapeutically important phosphatases feature in signal transduction pathways. The assay involves spectrophotometric detection of 3-nitrotyrosine production from 3-nitrophosphotyrosine containing peptidic substrates, which are accepted by many PTPs. Compared to conventional chromogenic phosphate derivatives, the more realistic peptidic substrates allow evaluating substrate specificity. The assay's applicability is demonstrated by determining kinetic parameters for several PTP-substrate combinations and inhibitor evaluation, as well as detection of PTP activity in lysates. The convenient new assay may assist further adoption of PTPs in drug development.

Includes bibliographical references (leaves 98-100)., Includes abstract and appendix.

Includes bibliographical references (leaves 98-100)., Includes abstract and appendix.

We report what is believed to be the first laser operation based on Ho(3+)-doped yttrium orthovanadate (YVO(4)). The cryogenic (77 K) Ho(+3):YVO(4) was resonantly diode-pumped at approximately 1.93 microns to produce up to 1.6 W of continuous wave (CW) output power at approximately 2.054 microns. The laser had a slope efficiency of approximately 38% with respect to absorbed power. We have measured the absorption and stimulated emission cross sections of the Ho(+3):YVO(4) at 77 K, 175 K, and 300 K and present the calculated gain cross section spectrum at 77 K for different excited state inversion levels., The original document contains color images.

This research deals with the development of two unconventional preparation routes to AVO4 vanadates and ANbO4 niobates which are luminescent materials when doped with lanthanide ions. In addition, the preparation of A3NbO7 niobates was also implemented because of the great interest of such materials in the field of ion conductivity. The two developed preparation routes are based on coordination compounds which are used as precursors to incorporate the metals A, V and/or Nb. These precursors were either implemented alone in an aqueous preparation route called molecular precursors method or blended into a cellulose derivative matrix (hybrid precursor route). In this work, the two different routes were first used for the synthesis of bulk metallates and secondly for the preparation of thin films. Finally, an adaptation of the molecular precursor method was developed for the preparation of YVO4:Eu coated submicrometric silica spheres. This research has been therefore subdivided in five main parts. The first part deals with the synthesis of stoichiometrically well-defined coordination compounds of formula (NH4)A(EDTA)(H2O)x (A = Y, La, Pr, Sm, Eu, Gd, Dy, Er, Tm, Lu), (gu)3[Nb(O2)2(EDTAO2)]•2.5H2O and (NH4)[V(O)2(EDTA)]•0,5H2O. Secondly, these complexes were involved in the molecular precursor route. The method consists in using, for the different elements to be incorporated, molecular precursors which are coordination compounds. The final compound is obtained by an appropriate thermal treatment under dry air of a solid homogeneous mixture of the different complexes. This process was implemented for the preparation of bulk AVO4, ANbO4 and A3NbO7 as well as for the synthesis of solid solutions Y1-xAxVO4 and doped vanadates AVO4:Ln and Y1-xAxVO4:Eu. Luminescent properties of these doped materials were investigated and a significant effect of the host lattice composition was put forward. The hybrid precursor route was developed in the third part of this work. This method co, Cette recherche traite du développement de deux méthodes non conventionnelles de préparation de vanadates AVO4 et de niobates ANbO4 pouvant, lorsqu’ils sont dopés avec des ions de lanthanides, présenter des propriétés de luminescence. En outre, les niobates A3NbO7 ont également été étudiés car ils présentent un intérêt particulier dans le domaine de la conductivité ionique. Les deux méthodes développées ici consistent à utiliser des composés de coordination comme précurseurs pour l’incorporation des métaux A, V et/ou Nb. Ces précurseurs ont soit été employés comme tels dans une voie de préparation en solution aqueuse (méthode des précurseurs moléculaires), soit incorporés dans une matrice cellulosique (méthode des précurseurs hybrides). Ces deux méthodes de préparation ont été premièrement utilisées pour la préparation de matériaux massiques, puis également pour la préparation de films minces. Des matériaux « supportés » sur sphères de silice submicrométriques ont également été synthétisés en adaptant la méthode des précurseurs moléculaires. Dès lors, le travail s’est articulé en cinq grandes parties. La première partie traite de la synthèse de composés de coordination à stœchiométrie bien définie et de formulation (NH4)A(EDTA)(H2O)x (A = Y, La, Pr, Sm, Eu, Gd, Dy, Er, Tm, Lu), (gu)3[Nb(O2)2(EDTAO2)]•2,5H2O et (NH4)[V(O)2(EDTA)]•0,5H2O. Dans la deuxième partie de ce travail, ces composés de coordination ont été introduits dans la méthode des précurseurs moléculaires. Celle-ci est basée sur l’utilisation d’un mélange solide homogène des précurseurs moléculaires que sont les composés de coordination. Ce mélange homogène solide est obtenu par préparation d’une solution mixte contenant les précurseurs puis par élimination du solvant. Il est par la suite calciné afin de former le métallate désiré. Cette méthode a été appliquée ici à la synthèse des composés AVO4, ANbO4 et A3NbO7 ainsi qu’à des solutions solides Y1 xAxVO4 et des matériaux dopés YVO4 :Ln et Y1-xAxVO4 :Eu., (CHIM 3) -- UCL, 2011

Rare earth orthovanadates are being used as substitute for traditional solid state laser hosts such as yttrium aluminium garnet (YAG). While the most common of these is yttrium orthovanadate, other rare earth vanadates such as lutetium vanadate and gadolinium vanadate are being used for their special properties in certain applications. We report new measurements of the refractive indices and thermo-optics coefficients of these materials which will aid in the design of laser cavities and other nonlinear optical elements., Work Unit no. M07R5000

Neutron and x-ray reflectivity are used to determine the composition profile of vanadate and trivalent chromium process (TCP) inhibitor films. In both cases, the films have a complex structure consisting of at least two layers. For vanadate films, a porous, hydrophilic layer exists at the interface between the film and the metal substrate. For TCP films, the interfacial layer is very thin and dense if the film is deposited electrochemically. The films also differ in hydration. Vanadate films are un-hydrated whereas TCP films exist as hydrates of the form Crf2O3-4H2O. In both cases, the bulk of the films is not fully dense. Densification is observed, however, at high temperature and when dried after exposure to liquid water. The differences in film morphology imply different mechanisms of film formation. Mechanisms are described that are consistent with the observations., The original document contains color images. Supported in part by DOE contract DEAC05-00OR22725.

ONGOING WORK (1) Artificial scratch cell: The artificial scratch cell setup is being used to further evaluate whether meta-vanadates released from the coating could protect bare Al surfaces. (2) Coating degradation: A detailed EIS analysis on coatings with and without intentional defects is also being conducted. Results thus far have shown lower break point frequencies and larger Z(10mHz) values when vanadates were added to the primer in line with the results of ASTM B117 testing. (3) Inhibition studies on aeronautical magnesium alloys by meta-vanadates are being conducted. CONCLUSIONS: Adding NaVO3 to plain epoxy primers greatly improved coating performance. In the presence of meta-vanadates no blistering or corrosion products were found after 2 weeks of exposure to the salt fog chamber. Vanadium was found along the scribe, likely suggesting diffusion of the inhibitor from the coating to the bare Al surface. The slightly alkaline environment of the chamber could reduce the risk of deca-vanadate precipitation., Presented at the U.S. Army Corrosion Summit, held in Clearwater Beach Resort, FL, on 3-5 Feb 2009. Prepared in cooperation with Det Norske Veritas, Columbus, OH, and with Institute of Technology, Buenos Aires, Argentina. Document consists entirely of briefing charts. The original document contains color images.

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 51V NMR (Bruker AMX-500 MHz) spectroscopic studies, performed at 25 °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 51V 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.

Single crystals of dysprosium-doped gadolinium orthovanadate (Dy:GdVO4) were successfully grown by the floating zone method and their fluorescence properties were investigated. The as-grown crystals did not contain any macroscopic defects such as cracks and inclusions for any Dy-concentration of up to 4 at%. Every crystal showed optical homogeneity under observation with a polarizing microscope; that is, no low-angle grain boundaries and growth striations were detected. In the visible region two distinct, fluorescence bands were observed around 480 and 575 nm, corresponding to F-4(9/2) → H-6(15/2) and F-4(9/2) → H-6(13/2) transitions, respectively. The excitation spectrum for the emission of 573 nm indicates the possibility to use a commercially available laser diode of 450 nm as a pumping source for solid-state yellow laser.

Single crystals of dysprosium-doped gadolinium orthovanadate (Dy:GdVO4) were successfully grown by the floating zone method and their fluorescence properties were investigated. The as-grown crystals did not contain any macroscopic defects such as cracks and inclusions for any Dy-concentration of up to 4 at%. Every crystal showed optical homogeneity under observation with a polarizing microscope; that is, no low-angle grain boundaries and growth striations were detected. In the visible region two distinct, fluorescence bands were observed around 480 and 575 nm, corresponding to F-4(9/2) → H-6(15/2) and F-4(9/2) → H-6(13/2) transitions, respectively. The excitation spectrum for the emission of 573 nm indicates the possibility to use a commercially available laser diode of 450 nm as a pumping source for solid-state yellow laser.

The aims of this research were the scientific understanding of the environmental degradation of thermal barrier systems by molten deposits, as relevant to the US Navy aircraft and marine engines, and the application of this understanding to develop mitigation strategies. The program had two thrusts, one addressing molten deposits of calcium-magnesium alumino silicates (CMAS), and the other corrosive sulfate/vanadate (S/V) melts resulting from salt ingestion combined with fuel contaminants. In principle, both types of deposits can penetrate the coating and reduce its compliance upon freezing, leading to thermomechanical damage, but also attack thermochemically the TBC by dissolving the barrier oxide and reprecipitating undesirable phases. The program successfully elucidated the mechanisms and identified mitigating strategies for both problems. The proposed CMAS mitigation is based on reaction with a rare earth zirconate layer, which leads to the precipitation of solid phases in sufficient volume to inhibit the capillary-driven flow of CMAS into the pore spaces of the coating. The approach for S/v relied on reducing the Y activity by co-doping with Ta. The latter compositions also offer phase stability at considerably higher temperatures than 7YSZ and attractive toughness.

Heteronuclear NMR experiments, in particular 51V, wereperformed with the aim to elucidate the nature of vanadates and peroxovanadates in hydrophilic ionic liquids (i.e., [bmim][BF4], [bmim][TfO] and [bdmim][BF4]). The data so far reported clearly indicate that ionic liquids have a strong influence on the solution chemistry of vanadate in water both for the formation of the aggregates (with and without H2O2) and for the rate of peroxide consumption catalyzed by vanadium. In BF4- containing ionic liquids, formation of vanadate-fluoride adducts is suggested. The obtained results are also discussed in the light of the reactivity data of peroxovanadates in ionic liquids., Published Online 27 October 2008

The processes for recovery of vanadium from boiler residues, fly ash and petroleum coke are similar to those for treating ores and spent catalysts; however, some of the materials may contain high levels of carbon that must be removed. The conventional route for processing vanadium-bearing materials comprises roasting in the presence of a sodium salt and water, alkali or acid leaching of the calcine followed by solvent extraction/ion exchange, purification to eliminate Fe, P, Si and Mg and recovery of vanadium pentoxide by various routes. The salt roasting processes are the ones used at industrial scale; others remain at pilot or laboratory scale. Other processes for recovery from fly ash include conventional sulphuric acid leaching; variants discussed include the Petrofina process, the Sotex process, processes described by Giavarini and by Tokuyuma et al, processes for treatment of oil sand or tar sand fly ash (GCOS fly ash), an acid pressure leaching process, and one developed by Mintek. Prospects for industrial scale use are considered., The processes for recovery of vanadium from boiler residues, fly ash and petroleum coke are similar to those for treating ores and spent catalysts; however, some of the materials may contain high levels of carbon that must be removed. The conventional route for processing vanadium-bearing materials comprises roasting in the presence of a sodium salt and water, alkali or acid leaching of the calcine followed by solvent extraction/ion exchange, purification to eliminate Fe, P, Si and Mg and recovery of vanadium pentoxide by various routes. The salt roasting processes are the ones used at industrial scale; others remain at pilot or laboratory scale. Other processes for recovery from fly ash include conventional sulphuric acid leaching; variants discussed include the Petrofina process, the Sotex process, processes described by Giavarini and by Tokuyuma et al, processes for treatment of oil sand or tar sand fly ash (GCOS fly ash), an acid pressure leaching process, and one developed by Mintek. Prospects for industrial scale use are considered.

Yttrium(III) and lanthanide(III) vanadates corresponding to the general formula AVO(4) (A = Y, Pr, Sm, Eu, Gd, Dy, Er) were prepared by a nonconventional soft chemistry route in which coordination compounds of the different elements to be incorporated were used as molecular precursors. In this case, EDTA-based yttrium(III), lanthanide(III) and vanadium(V) complexes were synthesised, characterised and used as precursors for the preparation, of zircon-type AVO(4) materials at a moderate temperature of 800 degrees C, as evidenced by XRD and Raman analyses. Solid solutions such as Y1-x-PrxO4 and Y1-x-GdxVO4 were also obtained. Linear correlations between chemical compositions and lattice parameters or Raman shifts were observed. SEM was used to characterise the particle size and morphology. ((D Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

A new type of mixed-valence polyoxoanionic cluster, [V(V)13V(IV)3O42(Cl)]8-, composed of 14 {VO5} square pyramids and 2 {VO4} tetrahedral units, hosting a chloride ion has been synthesized and characterized.

A new type of mixed-valence polyoxoanionic cluster, [V(V)13V(IV)3O42(Cl)]8-, composed of 14 {VO5} square pyramids and 2 {VO4} tetrahedral units, hosting a chloride ion has been synthesized and characterized.

T cell receptor (TCR) internalization by clathrin-coated vesicles after encounter with antigen has been implicated in the regulation of T cell responses. We demonstrate that TCR internalization after receptor engagement and TCR signaling involves inducible phosphorylation of clathrin heavy chain (CHC) in both CD4+ and CD8+ human T cells. Studies with mutant Jurkat T cells implicate the Src family kinase Lck as the responsible enzyme and its activity in this process is influenced by the functional integrity of the downstream signaling molecule ZAP-70. CHC phosphorylation positively correlates with ligand-induced TCR internalization in both CD4+ and CD8+ T cells, and CHC phosphorylation as a result of basal Lck activity is also implicated in constitutive TCR endocytosis by CD4+ T cells. Remarkably, irreversible CHC phosphorylation in the presence of pervanadate reduced both constitutive and ligand-induced TCR internalization in CD4+ T cells, and immunofluorescence studies revealed that this inhibition affected the early stages of TCR endocytosis from the plasma membrane. Thus, we propose that CHC phosphorylation and dephosphorylation are involved in TCR internalization and that this is a regulatory mechanism linking TCR signaling to endocytosis.

T cell receptor (TCR) internalization by clathrin-coated vesicles after encounter with antigen has been implicated in the regulation of T cell responses. We demonstrate that TCR internalization after receptor engagement and TCR signaling involves inducible phosphorylation of clathrin heavy chain (CHC) in both CD4+ and CD8+ human T cells. Studies with mutant Jurkat T cells implicate the Src family kinase Lck as the responsible enzyme and its activity in this process is influenced by the functional integrity of the downstream signaling molecule ZAP-70. CHC phosphorylation positively correlates with ligand-induced TCR internalization in both CD4+ and CD8+ T cells, and CHC phosphorylation as a result of basal Lck activity is also implicated in constitutive TCR endocytosis by CD4+ T cells. Remarkably, irreversible CHC phosphorylation in the presence of pervanadate reduced both constitutive and ligand-induced TCR internalization in CD4+ T cells, and immunofluorescence studies revealed that this inhibition affected the early stages of TCR endocytosis from the plasma membrane. Thus, we propose that CHC phosphorylation and dephosphorylation are involved in TCR internalization and that this is a regulatory mechanism linking TCR signaling to endocytosis.

Previous enzyme kinetic and structural studies have revealed a critical role for Asp181 (PTP1B numbering) in PTP (protein-tyrosine phosphatase)-mediated catalysis. In the E-P (phosphoenzyme) formation step, Asp181 functions as a general acid, while in the E-P hydrolysis step it acts as a general base. Most of our understanding of the role of Asp181 is derived from studies with the Yersinia PTP and the mammalian PTP1B, and to some extent also TC (T-cell)-PTP and the related PTPa and PTPe. The neighbouring residue 182 is a phenylalanine in these four mammalian enzymes and a glutamine in Yersinia PTP. Surprisingly, little attention has been paid to the fact that this residue is a histidine in most other mammalian PTPs. Using a reciprocal single-point mutational approach with introduction of His182 in PTP1B and Phe182 in PTPH1, we demonstrate here that His182-PTPs, in comparison with Phe182-PTPs, have significantly decreased kcat values, and to a lesser degree, decreased kcat/Km values. Combined enzyme kinetic, X-ray crystallographic and molecular dynamics studies indicate that the effect of His182 is due to interactions with Asp181 and with Gln262. We conclude that residue 182 can modulate the functionality of both Asp181 and Gln262 and therefore affect the E-P hydrolysis step of PTP-mediated catalysis.

Previous enzyme kinetic and structural studies have revealed a critical role for Asp181 (PTP1B numbering) in PTP (protein-tyrosine phosphatase)-mediated catalysis. In the E-P (phosphoenzyme) formation step, Asp181 functions as a general acid, while in the E-P hydrolysis step it acts as a general base. Most of our understanding of the role of Asp181 is derived from studies with the Yersinia PTP and the mammalian PTP1B, and to some extent also TC (T-cell)-PTP and the related PTPa and PTPe. The neighbouring residue 182 is a phenylalanine in these four mammalian enzymes and a glutamine in Yersinia PTP. Surprisingly, little attention has been paid to the fact that this residue is a histidine in most other mammalian PTPs. Using a reciprocal single-point mutational approach with introduction of His182 in PTP1B and Phe182 in PTPH1, we demonstrate here that His182-PTPs, in comparison with Phe182-PTPs, have significantly decreased kcat values, and to a lesser degree, decreased kcat/Km values. Combined enzyme kinetic, X-ray crystallographic and molecular dynamics studies indicate that the effect of His182 is due to interactions with Asp181 and with Gln262. We conclude that residue 182 can modulate the functionality of both Asp181 and Gln262 and therefore affect the E-P hydrolysis step of PTP-mediated catalysis.

Cre recombinase exchanges DNA strands at the LoxP recognition site via transphosphorylation reactions that involve pentacoordinate transition states. We demonstrate that meta-vanadate ion (VO(3)(-)) and appropriate DNA substrates assemble a transition-state analog-like complex in the Cre active site. Meta-vanadate inhibits recombination of LoxP-derived oligonucleotide substrates that contain a gap at either or both scissile phosphates, but does not inhibit reactions with intact LoxP. The 3(')-hydroxyl group of the gapped substrate is required for inhibition, suggesting that vanadate is ligated by three oxo ligands. Assembly of the inhibited complex is slow (t(1/2)=19min at 4mM NaVO(3)) and requires Cre, substrates, and meta-vanadate. Holliday junction intermediates accumulated at lower meta-vanadate concentrations, suggesting that the second strand exchange is inhibited more readily than the first. The apparent K(D) for meta-vanadate is 1.5-2mM and binding shows positive cooperativity. This methodology may have general application for mechanistic studies of recombinase/topoisomerase-mediated strand exchange reactions.

When the solubility products or other thermodynamic data are not known, the optimum experimental procedures for preparing complex mixed oxides/hydroxides can be approximately predicted by extrapolation of the solubility behaviours of individual metal ions in aqueous solutions. This simple approach determined a probable co-precipitation domain ranging from pH = 0.7 to pH = 4 for FeIII-VV-H2O system. To control the kinetic aspect of condensation mechanisms in order to obtain crystallized compounds, three different experimental protocols were developed leading to successful syntheses of FeVO4·1.1 H2O, Fe4V6 O21·3 H2O and FeV3O9 ·2.6 H2O. These vanadates were characterized by X-ray diffraction (XRD), thermal analysis, scanning or transmission electron microscopy (SEM/TEM), and Brunauer-Emmett-Teller (BET) surface area measurements. The results notably revealed that FeVO4· 1.1 H2O and FeV3O9·2.6 H2O have close structural similarities with two minerals fervanite and kazakhstanite, respectively. © 2003 Académie des sciences. Published by Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Deficiency of alkaline and acid DNase is a hallmark in all non-necrotic cancer cells in animals and humans. These enzymes are reactivated at early stages of cancer cell death by vitamin C (acid DNase) and vitamin K(3) (alkaline DNase). Moreover, the coadministration of these vitamins (in a ratio of 100:1, for C and K(3), respectively) produced selective cancer cell death. Detailed morphological studies indicated that cell death is produced mainly by autoschizis, a new type of cancer cell death. Several mechanisms are involved in such a cell death induced by CK(3), they included: formation of H(2)O(2) during vitamins redox cycling, oxidative stress, DNA fragmentation, no caspase-3 activation, and cell membrane injury with progressive loss of organelle-free cytoplasm. Changes in the phosphorylation level of some critical proteins leading to inactivation of NF-kappaB appear as main intracellular signal transduction pathways. The increase knowledge in the mechanisms underlying cancer cells death by CK(3) may ameliorate the techniques of their in vivo administration. The aim is to prepare the introduction of the association of vitamins C and K(3) into human clinics as a new, non-toxic adjuvant cancer therapy.

When the solubility products or other thermodynamic data are not known, the optimum experimental procedures for preparing complex mixed oxides/hydroxides can be approximately predicted by extrapolation of the solubility behaviours of individual metal ions in aqueous solutions. This simple approach determined a probable co-precipitation domain ranging from pH = 0.7 to pH = 4 for FeIII-VV-H2O system. To control the kinetic aspect of condensation mechanisms in order to obtain crystallized compounds, three different experimental protocols were developed leading to successful syntheses of FeVO4·1.1 H2O, Fe4V6 O21·3 H2O and FeV3O9 ·2.6 H2O. These vanadates were characterized by X-ray diffraction (XRD), thermal analysis, scanning or transmission electron microscopy (SEM/TEM), and Brunauer-Emmett-Teller (BET) surface area measurements. The results notably revealed that FeVO4· 1.1 H2O and FeV3O9·2.6 H2O have close structural similarities with two minerals fervanite and kazakhstanite, respectively. © 2003 Académie des sciences. Published by Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Cre recombinase exchanges DNA strands at the LoxP recognition site via transphosphorylation reactions that involve pentacoordinate transition states. We demonstrate that meta-vanadate ion (VO(3)(-)) and appropriate DNA substrates assemble a transition-state analog-like complex in the Cre active site. Meta-vanadate inhibits recombination of LoxP-derived oligonucleotide substrates that contain a gap at either or both scissile phosphates, but does not inhibit reactions with intact LoxP. The 3(')-hydroxyl group of the gapped substrate is required for inhibition, suggesting that vanadate is ligated by three oxo ligands. Assembly of the inhibited complex is slow (t(1/2)=19min at 4mM NaVO(3)) and requires Cre, substrates, and meta-vanadate. Holliday junction intermediates accumulated at lower meta-vanadate concentrations, suggesting that the second strand exchange is inhibited more readily than the first. The apparent K(D) for meta-vanadate is 1.5-2mM and binding shows positive cooperativity. This methodology may have general application for mechanistic studies of recombinase/topoisomerase-mediated strand exchange reactions.

When the solubility products or other thermodynamic data are not known, the optimum experimental procedures for preparing complex mixed oxides/hydroxides can be approximately predicted by extrapolation of the solubility behaviours of individual metal ions in aqueous solutions. This simple approach determined a probable co-precipitation domain ranging from pH = 0.7 to pH = 4 for FeIII-VV-H2O system. To control the kinetic aspect of condensation mechanisms in order to obtain crystallized compounds, three different experimental protocols were developed leading to successful syntheses of FeVO4·1.1 H2O, Fe4V6 O21·3 H2O and FeV3O9 ·2.6 H2O. These vanadates were characterized by X-ray diffraction (XRD), thermal analysis, scanning or transmission electron microscopy (SEM/TEM), and Brunauer-Emmett-Teller (BET) surface area measurements. The results notably revealed that FeVO4· 1.1 H2O and FeV3O9·2.6 H2O have close structural similarities with two minerals fervanite and kazakhstanite, respectively. © 2003 Académie des sciences. Published by Éditions scientifiques et médicales Elsevier SAS. All rights reserved.