Showing papers on "Vanadate published in 2015"
TL;DR: Among the enigmas to be solved with respect to the utilization of vanadium in nature is the accumulation of V(III) by some sea squirts and fan worms, as well as the purport of the nonoxido V(IV) compound amavadin in the fly agaric.
Abstract: Vanadium is special in at least two respects: on the one hand, the tetrahedral anion vanadate(V) is similar to the phosphate anion; vanadate can thus interact with various physiological substrates that are otherwise functionalized by phosphate. On the other hand, the transition metal vanadium can easily expand its sphere beyond tetrahedral coordination, and switch between the oxidation states +V, +IV and +III in a physiological environment. The similarity between vanadate and phosphate may account for the antidiabetic potential of vanadium compounds with carrier ligands such as maltolate and picolinate, and also for vanadium's mediation in cardiovascular and neuronal defects. Other potential medicinal applications of more complex vanadium coordination compounds, for example in the treatment of parasitic tropical diseases, may also be rooted in the specific properties of the ligand sphere. The ease of the change in the oxidation state of vanadium is employed by prokarya (bacteria and cyanobacteria) as well as by eukarya (algae and fungi) in respiratory and enzymatic functions. Macroalgae (seaweeds), fungi, lichens and Streptomyces bacteria have available haloperoxidases, and hence enzymes that enable the 2-electron oxidation of halide X− with peroxide, catalyzed by a Lewis-acidic VV center. The X+ species thus formed can be employed to oxidatively halogenate organic substrates, a fact with implications also for the chemical processes in the atmosphere. Vanadium-dependent nitrogenases in bacteria (Azotobacter) and cyanobacteria (Anabaena) convert N2 + H+ to NH4+ + H2, but are also receptive for alternative substrates such as CO and C2H2. Among the enigmas to be solved with respect to the utilization of vanadium in nature is the accumulation of VIII by some sea squirts and fan worms, as well as the purport of the nonoxido VIV compound amavadin in the fly agaric.
213 citations
TL;DR: In this article, temperature sensing performance was investigated by exploiting the temperature dependent fluorescence intensity ratio (FIR) of two emission bands (2 H 11/2 / 4 S 3/2 ǫ→ 4 I 15/2 ) of Er 3+ ion.
Abstract: Optical temperature sensors play a vital role in biomedical and therapeutic applications due to their reliable and unique detection sensitivity. Internal self-heating in Er 3+ /Yb 3+ doped yttrium vanadate particles is observed on optical excitation at 980 nm wavelength of a diode laser. Temperature sensing performance is investigated by exploiting the temperature dependent fluorescence intensity ratio (FIR) of two emission bands ( 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ) of Er 3+ ion. The calculated sensor sensitivity, 0.01169 K −1 at 380 K, is found the highest among the reported results for inorganic nanosensors. The temperature of the nanocrystalline sample particles is found to increase by a large value (315–460 K) within a short interval of excitation pump power (13.18–50.45 W cm −2 ). This achievement suggests potential use of the present material as an optical nanoheater for hyper-thermal treatment.
167 citations
TL;DR: The ability of vanadium to interfere with the metabolic processes involving Ca2+ and Mg2+, connected with its versatility to undergo changes in coordination geometry, allow V to influence the function of a large variety of phosphate-metabolizing enzymes and vanadate(V) salts and compounds have been frequently used either as inhibitors of these enzymes, or as probes to study the mechanisms of their reactions and catalytic cycle.
157 citations
TL;DR: In this paper, the authors investigated the mechanism of vanadate formation when vanadium slag was roasted with calcium oxide, and the effects of heating rate, added amount of CaO, holding temperature and holding time on oxidation efficiency were investigated.
119 citations
TL;DR: In this article, it was shown that most of the available X-ray structures of vanadium-phosphatase complexes contain vanadium with five coordinating atoms in trigonal bipyramidal coordination geometries.
114 citations
TL;DR: These studies demonstrated a framework for characterization of five-coordinate trigonal bipyramidal vanadium inhibitors by comparison with the reported vanadium-protein phosphatase complexes, and suggest that if effective delivery of potentially active antidiabetic compound such a the organic vanadate peptidic substrate was possible the toxicity problems currently reported for the salts and some of the complexes may be alleviated and dramatic enhancement of antidi diabetic vanadium compounds may result.
Abstract: Studies of antidiabetic vanadium compounds, specifically the organic vanadate esters, are reviewed with regard to their chemistry and biological properties. The compounds are described from the perspective of how the fundamental chemistry and properties of organic vanadate esters impact their effects as inhibitors for phosphatases based on the structural information obtained from vanadium-phosphatase complexes. Vanadium compounds have been reported to have antidiabetic properties for more than a century. The structures and properties of organic vanadate complexes are reviewed, and the potency of such vanadium coordination complexes as antidiabetic agents is described. Because such compounds form spontaneously in aqueous environments, the reactions with most components in any assay or cellular environment has potential to be important and should be considered. Generally, the active form of vanadium remains elusive, although studies have been reported of a number of promising vanadium compounds. The description of the antidiabetic properties of vanadium compounds is described here in the context of recent characterization of vanadate-phosphatase protein structures by data mining. Organic vanadate ester compounds are generally four coordinate or five coordinate with the former being substrate analogues and the latter being transition-state analogue inhibitors. These studies demonstrated a framework for characterization of five-coordinate trigonal bipyramidal vanadium inhibitors by comparison with the reported vanadium-protein phosphatase complexes. The binding of the vanadium to the phosphatases is either as a five-coordinate exploded transition-state analogue or as a high energy intermediate, respectively. Even if potency as an inhibitor requires trigonal bipyramidal geometry of the vanadium when bound to the protein, such geometry can be achieved upon binding from compounds with other geometries. Desirable properties of ligands are identified and analyzed. Ligand interactions, as reported in one peptidic substrate, are favorable so that complementarity between phosphatase and coordinating ligand to the vanadium can be established resulting in a dramatic enhancement of the inhibitory potency. These considerations point to a frameshift in ligand design for vanadium complexes as phosphatase inhibitors and are consistent with other small molecule having much lower affinities. Combined, these studies do suggest that if effective delivery of potentially active antidiabetic compound such a the organic vanadate peptidic substrate was possible the toxicity problems currently reported for the salts and some of the complexes may be alleviated and dramatic enhancement of antidiabetic vanadium compounds may result.
99 citations
TL;DR: Sodium-ion battery (NIB) cathode performance based on ammonium vanadate is demonstrated here as having high capacity, long cycle life and good rate capability, and density functional theory calculation is envisioned for the NH4V4O10 cathode.
Abstract: Sodium-ion battery (NIB) cathode performance based on ammonium vanadate is demonstrated here as having high capacity, long cycle life and good rate capability. The simple preparation process and morphology study enable us to explore this electrode as suitable NIB cathode. Furthermore, density functional theory (DFT) calculation is envisioned for the NH4V4O10 cathode, and three possible sodium arrangements in the structure are depicted for the first time. Relevant NIB-related properties such as average voltage, lattice constants, and atomic coordinates have been derived, and the estimated values are in good agreement with the current experimental values. A screening study shows ammonium vanadate electrodes prepared on carbon coat onto Al-current collector exhibits a better electrochemical performance toward sodium, with a sustained reversible capacity and outstanding rate capability. With the current cathode with nanobelt morphology, a reversible capacity of 190 mAh g–1 is attained at a charging rate of 20...
59 citations
TL;DR: In this article, the growth process of the copper vanadate nanobelts has been proposed as the nucleation and PVP adsorption growth mechanism under acidic and alkaline conditions.
Abstract: Copper vanadate nanobelts have been successfully synthesized by a facile hydrothermal process using sodium vanadate and copper acetate as the raw materials, and the polymer polyvinyl pyrrolidone (PVP) as the surfactant by adjusting the pH value. The nanobelts are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). XRD and HRTEM show that the copper vanadate nanobelts are composed of a single crystalline monoclinic Cu2.33V4O11 phase. SEM observation shows that the copper vanadate nanobelts have the thickness, width and length of about 50 nm, 300 nm to 1 μm and several tens of micrometers, respectively. The pH value plays a key role in the formation of the copper vanadate nanobelts. The growth process of the copper vanadate nanobelts has been proposed as the nucleation and PVP adsorption growth mechanism under acidic and alkaline conditions. Copper vanadate nanobelts have been used as glassy carbon electrode (GCE) modified materials for the determination of ascorbic acid showing good electrochemical detection performance. The linear range is 0.001–2 mM and the detection limit is 0.14 μM and 0.38 μM for cvp1 and cvp2, respectively. The copper vanadate nanobelt modified GCE exhibits good stability and reproducibility.
58 citations
TL;DR: In this article, the authors reported the long-term cycling stability and high-rate capability of the as-prepared K 025 V 2 O 5 with a unique layer-by-layer stacked flake-like structure.
56 citations
TL;DR: Mature 3T3-L1 adipocytes showed a higher propensity to form VIV species, despite the prevalence of VV in the medium, and may also point to an endogenous role of V in adipocytes.
Abstract: The antidiabetic activities of vanadium(V) and -(IV) prodrugs are determined by their ability to release active species upon interactions with components of biological media. The first X-ray absorption spectroscopic study of the reactivity of typical vanadium (V) antidiabetics, vanadate ([VVO4]3–, A) and a vanadium(IV) bis(maltolato) complex (B), with mammalian cell cultures has been performed using HepG2 (human hepatoma), A549 (human lung carcinoma), and 3T3-L1 (mouse adipocytes and preadipocytes) cell lines, as well as the corresponding cell culture media. X-ray absorption near-edge structure data were analyzed using empirical correlations with a library of model vanadium(V), -(IV), and -(III) complexes. Both A and B ([V] = 1.0 mM) gradually converged into similar mixtures of predominantly five- and six-coordinate VV species (∼75% total V) in a cell culture medium within 24 h at 310 K. Speciation of V in intact HepG2 cells also changed with the incubation time (from ∼20% to ∼70% VIV of total V), but it ...
54 citations
TL;DR: The zinc vanadate nanorods have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), TEM, high-resolution TEM (HRTEM), and solid UV-vis diffuse reflectance spectrum as discussed by the authors.
TL;DR: 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 was investigated as mentioned in this paper.
TL;DR: Transmembrane ion fluxes of H(+) , Ca(2+) and K(+) are recorded in guard cells of wild-type Arabidopsis, the CORONATINE INSENSITIVE1 (COI1) mutant coi1-1 and the PM H (+) -ATPase mutants aha1-6 and aha 1-7, using a non-invasive micro-test technique.
Abstract: Methyl jasmonate (MeJA) elicits stomatal closure in many plant species. Stomatal closure is accompanied by large ion fluxes across the plasma membrane (PM). Here, we recorded the transmembrane ion fluxes of H(+) , Ca(2+) and K(+) in guard cells of wild-type (Col-0) Arabidopsis, the CORONATINE INSENSITIVE1 (COI1) mutant coi1-1 and the PM H(+) -ATPase mutants aha1-6 and aha1-7, using a non-invasive micro-test technique. We showed that MeJA induced transmembrane H(+) efflux, Ca(2+) influx and K(+) efflux across the PM of Col-0 guard cells. However, this ion transport was abolished in coi1-1 guard cells, suggesting that MeJA-induced transmembrane ion flux requires COI1. Furthermore, the H(+) efflux and Ca(2+) influx in Col-0 guard cells was impaired by vanadate pre-treatment or PM H(+) -ATPase mutation, suggesting that the rapid H(+) efflux mediated by PM H(+) -ATPases could function upstream of the Ca(2+) flux. After the rapid H(+) efflux, the Col-0 guard cells had a longer oscillation period than before MeJA treatment, indicating that the activity of the PM H(+) -ATPase was reduced. Finally, the elevation of cytosolic Ca(2+) concentration and the depolarized PM drive the efflux of K(+) from the cell, resulting in loss of turgor and closure of the stomata.
TL;DR: The hierarchical transition-metal vanadate nanosheets supported on metal meshes are used as monolith catalysts for the selective catalytic reduction of NO with NH3 and shows excellent de-NOx performance with high efficiency and stability in the presence of SO2 and H2O, which provide a promising monolith de- NOx catalyst for stationary source at medium temperatures.
Abstract: A facile method is developed for the large-scale growth of hierarchical transition-metal (Cu, Fe, and Ni) vanadate nanosheets on corresponding metal mesh as supports. The hierarchical transition-metal vanadate nanosheets were in situ grown on the metal meshes through an orientational etching process and simultaneous nucleation and growth process. Interestingly, the morphologies of the vanadate nanosheets are governed by the balance between dissolution rate and nucleation rate. Thus, the sizes and the thicknesses of the nanosheets could be facilely controlled by the reaction duration, the acidity of the solution and the concentration of vanadate precursor. Furthermore, the hierarchical transition-metal vanadate nanosheets supported on metal meshes are used as monolith catalysts for the selective catalytic reduction (SCR) of NO with NH3. The iron mesh based monolith catalyst shows excellent de-NOx performance with high efficiency and stability in the presence of SO2 and H2O, which provide a promising monolith de-NOx catalyst for stationary source at medium temperatures.
TL;DR: In this paper, vanadate compounds showed self-activated photoluminescence (PL) based on the VO4 clusters against the ultraviolet (UV) light irradiation, where the vanadates included chloride vanadsates (MII2VO4Cl), pyrovanadates (mII2V2O7), orthovanadates(MII3(VO4)2) with divalent cations MII of Mg, Sr, Ba, and Zn, and oxofluorovanads (AIVOF4) with an
Abstract: Rare-earth-free phosphors based on vanadate compounds were investigated, where the vanadates included chloride vanadates (MII2VO4Cl), pyrovanadates (MII2V2O7), orthovanadates (MII3(VO4)2) with divalent cations MII of Mg, Sr, Ba, and Zn, and oxofluorovanadates (AIVOF4) with an alkali metal AI. A chloride pyrolysis method and a liquid phase precipitation method were proposed for preparing the chloride vanadates and pyro- and orthovanadates, respectively. These vanadate compounds showed self-activated photoluminescence (PL) based on the VO4 clusters against the ultraviolet (UV) light irradiation. The colors of PL covered almost the whole visible-light region from blue to yellow as Sr2VO4Cl (deep blue), Ca2VO4Cl (sky blue), Ba2V2O7 (green), Sr2V2O7 (yellowish green), Zn3(VO4)2 (yellow), and Mg3(VO4)2 (yellow). A correlation was suggested from these compounds between the luminescent colors and the structural feature as the longer V–O distances in the VO4 tetrahedra in the crystal structures led to the longer wavelength in PL. This seemed to be also applicable for the oxofluorovanadates AIVOF4 (AI = K and Cs) which contain the VOF4 polyhedra with one O2− ion and four F- ions as the ligands, as they exhibited the reddish PL.
TL;DR: In this paper, a self-activated vanadate phosphor of Na2YMg2(VO4)3 was prepared using a sol-gel method and phase formation was verified through X-ray diffraction studies.
TL;DR: In this paper, the authors compared the hot corrosion performance of yttria-stabilized zirconia (ZIRconia-3-4Yttria, YSZ), ceria stabilized zirconsistency (Ceria-24 Ceria-2.5YSZ, CSZ), and titania stabilized yttrium oxide (Y2O3), and titanium vanadate (TiSZ) coatings in the presence of molten mixture of sodium sulfate + vanadium oxide at 1050°C.
Abstract: This paper compares the hot corrosion performance of yttria-stabilized zirconia (Zirconia-3-4Yttria, YSZ), ceria stabilized zirconia (Zirconia-24Ceria-2.5Yttria, CSZ), and titania stabilized zirconia (Zirconia-18Titania-10Yttria, TiSZ) coatings in the presence of molten mixture of sodium sulfate + vanadium oxide at 1050 °C. These coatings were prepared by air plasma spray (APS). Characterizations using X-ray diffraction (XRD) and scanning electron microscope (SEM) indicate that in the case of YSZ, the reaction between sodium vanadate (NaVO3) and yttrium oxide (Y2O3) produces yttrium vanadate (YVO4) and leads to the transformation of tetragonal zirconia to monoclinic zirconia. For the CSZ coatings, by the formation of cerium vanadate (CeVO4), the amount of yttrium vanadate formed on the CSZ coating is significantly reduced, thus the amount of monoclinic phase in the TBC coating is substantially reduced. For TiSZ coating, although some minor reactions happened and some titanium vanadate (TiVO4) ribbons formed on the surface of coating, tetragonal zirconia was stable after hot corrosion test and no monoclinic zirconia was formed. Comparing to YSZ and CSZ under a temperature of 1050 °C, TiSZ coating is found to be more stable, both thermally and chemically, and exhibits a better hot corrosion resistance.
TL;DR: The exact mechanism of the effect of vanadium compounds on protein tyrosine phosphatases (PTP), epidermal growth factor receptor (EGFR), PLCγ, Src, mitogen-activated protein kinase (MAPK) cascades, transcription factor NF-κB, and more are described.
Abstract: This paper discusses how the activity and expression of cyclooxygenases are influenced by vanadium compounds at anticancer concentrations and recorded in inorganic vanadium poisonings. We refer mainly to the effects of vanadate (orthovanadate), vanadyl and pervanadate ions; the main focus is placed on their impact on intracellular signaling. We describe the exact mechanism of the effect of vanadium compounds on protein tyrosine phosphatases (PTP), epidermal growth factor receptor (EGFR), PLCγ, Src, mitogen-activated protein kinase (MAPK) cascades, transcription factor NF-κB, the effect on the proteolysis of COX-2 and the activity of cPLA2. For a better understanding of these processes, a lot of space is devoted to the transformation of vanadium compounds within the cell and the molecular influence on the direct targets of the discussed vanadium compounds.
TL;DR: Single-crystal temperature-dependent magnetic studies on Ba2V(VO4)2(OH) reveal a broad feature over a wide temperature range with maximum at ∼100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies.
Abstract: A new series of transition metal vanadates, namely, Ba2M(VO4)2(OH) (M = V3+, Mn3+, and Fe3+), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba2V(VO4)2(OH) is monoclinic in space group P21/m, a = 7.8783(2) A, b = 6.1369(1) A, c = 9.1836(2) A, β = 113.07(3)°, V = 408.51(2) A3. The other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the b-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba2Mn(VO4)2(OH) analogue yielded a new understanding of the Jahn–Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Single-crystal temperature-dependent magnetic studies on Ba2V(VO4)2(OH) reveal a broad feature over a wide temperature range with maximum at...
TL;DR: In this article, the effect of different Cu sources and pH on the size, morphology and size distribution of copper vanadate nanostructures was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrum, Electron Dispersive Xray spectroscopy (EDX) and ultraviolet-visible (UV-Vis) spectrography.
Abstract: Copper vanadate nanostructures were prepared via ex-situ precipitation approach in presence of Schiff-base ligand (N,N׳ -buthylenebis(acetylacetone iminato)dianion = acacbn) as a new capping agent. The effect of different Cu sources and pH on the size, morphology and size distribution of copper vanadate nanostructures was investigated. The as-prepared products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrum, Electron Dispersive X-ray spectroscopy (EDX) and ultraviolet– visible (UV–Vis) spectroscopy. The optical properties of different samples were compared.
TL;DR: In this article, two vanadates, Ag2Sr(VO3)4 and SRSV3, have been studied as visible-light-driven water oxidation photocatalysts with the help of density-functional theory calculations.
Abstract: Two vanadates, Ag2Sr(VO3)4 and Sr(VO3)2, have been studied as visible-light-driven water oxidation photocatalysts with the help of density-functional theory calculations. Our computational results for the density of states and partial charge densities implied that Ag2Sr(VO3)4 and Sr(VO3)2 possess desirable electronic structures for the water oxidation reaction, i.e., the valence band (VB) maximum of Ag2Sr(VO3)4 consists of multiple orbitals of Ag d and O p, while Sr(VO3)2 has a broad VB associated with oxygen non-bonding states. We have experimentally demonstrated that these vanadates efficiently oxidize water to O2 under irradiation of visible light in the presence of the sacrificial agent.
TL;DR: (51)V-based NMR crystallography can be used to derive the detailed coordination environments of vanadium centers in large biological molecules to help explain the different reactivities of the wild-type and mutant VCPO and their pH-dependence.
Abstract: Vanadium-dependent haloperoxidases (VHPOs) perform two-electron oxidation of halides using hydrogen peroxide. Their mechanism, including the factors determining the substrate specificity and the pH-dependence of the catalytic rates, is poorly understood. The vanadate cofactor in the active site of VHPOs contains “spectroscopically silent” V(V), which does not change oxidation state during the reaction. We employed an NMR crystallography approach based on 51V magic angle spinning NMR spectroscopy and Density Functional Theory, to gain insights into the structure and coordination environment of the cofactor in the resting state of vanadium-dependent chloroperoxidases (VCPO). The cofactor environments in the wild-type VCPO and its P395D/L241V/T343A mutant exhibiting 5–100-fold improved catalytic activity are examined at various pH values. Optimal sensitivity attained due to the fast MAS probe technologies enabled the assignment of the location and number of protons on the vanadate as a function of pH. The va...
TL;DR: The developed procedure was successfully applied to the analysis of leachable concentrations of chromate, molybdate, tungstate and vanadate in alkaline extracts of manual metal arc (MMA) welding fumes loaded on filters.
TL;DR: The speciation as a function of pH, ionic strength and the concentration of vanadate and the ligand(s) is based on potentiometric and NMR investigations, a methodical combination that allows reliable access to composition, formation constants and, to some extent, also structural details for the manifold of species present in aqueous media at physiological pH and beyond.
TL;DR: The results show that anion transport imposes an upper limit on mitochondrial Ca2+ uptake and modifies the [Ca2+]mito response in a complex manner.
TL;DR: This work has demonstrated that uranyl vanadate extended structures are excellent hosts for further incorporation of trivalent lanthanide/actinide cations and has provided a new way to create new heterobimetallic 4f-5f and 5f- 5f compounds.
Abstract: Two new uranyl vanadates have been prepared from hydrothermal reactions and structurally characterized by single-crystal X-ray diffraction. The structure of (H3O)UO2VO4 (UVO-1) consists of anionic layers containing UO2(2+) pentagonal bipyramids coordinated by edge-sharing VO5 square pyramids, with the charge balanced by interlaminar H3O(+) cations. Vanadium in (UO2)3(VO4)2(H2O)3 (UVO-2) exists as monomeric VO4 tetrahedra coordinating to UO2(2+) pentagonal bipyramids, forming a 3D uranyl(VI) vanadate framework. Similar reactions with the addition of Ln(NO3)3 (Ln = Nd, Eu) afford the three heterobimetallic lanthanide uranyl vanadate frameworks Nd(UO2)3(VO4)3(H2O)11 (NdUVO-1), Eu(UO2)3(VO4)3(H2O)10 (EuUVO-1), and Eu2(UO2)12(VO4)10(H2O)24 (EuUVO-2). In NdUVO-1 and EuUVO-1, Ln(3+) cations are inserted into the interlayer space of UVO-1 substituting for H3O(+) and further bridging adjacent layers into 3D frameworks. Similarly, EuUVO-2 adopts the same sheet topology as UVO-2, with Eu(3+) ions replacing some of the interlayer uranyl ions in UVO-2. Our work has demonstrated that uranyl vanadate extended structures are excellent hosts for further incorporation of trivalent lanthanide/actinide cations and has provided a new way to create new heterobimetallic 4f-5f and 5f-5f compounds.
TL;DR: In this article, the authors investigated the metal catalyzed intramolecular 1,2 carbon shift reaction, usually associated with the epimerization of sugars, using the density functional theory.
Abstract: We investigate the metal catalyzed intramolecular 1,2 carbon shift reaction, usually associated with the epimerization of sugars, using the density functional theory. Metals like molybdenum (Mo), tungsten (W) and vanadium (V), in their oxoanion complex forms (molybdate, tungstate, vanadate) are investigated. The experimentally observed difference in the activity of these metal complexes, in catalyzing 1,2 carbon shift in glucose, at different pH is explained. Formation of larger (polynuclear) metal oxoanions (“metalates”) at higher pH reduces the structural flexibility of the metal complex. Thus, upon binding with glucose, their ability to rearrange the carbon backbone in sugar molecules decreases, resulting in lower activity towards 1,2 carbon shift at higher pH. For example, the activation barrier for 1,2 carbon shift catalyzed by “active” di-nuclear molybdate (exists at pH 2.5–3.5) is 21.1 kcal/mol; whereas it is 26.8 kcal/mol for the tetra-nuclear molybdate (exists at pH 4–5.5). Bonding interaction analysis has been carried out to quantify the flexibility/rigidity of the metal oxoanion complexes. Comparison of catalytic activities of Mo, W and V (as dimetalate) showed that vanadate is more active than the popular molybdate complex and W is the least active of them all. The trend in the catalytic activities of these metals is explained on the basis of the participation of higher orbitals in the complexation of metal oxoanions with glucose. Additionally, the flexibility/rigidity of the metal complex is also shown to be a descriptor of its catalytic activity for the 1,2 carbon shift reaction.
TL;DR: In this article, a promising nuclear waste form for the immobilization of I-129, was irradiated with energetic ions, electrons, and gamma rays, to investigate its radiation stability.
Abstract: Spark-plasma-sintered lead vanadate iodoapatite Pb9.85(VO4)6I1.7, a promising nuclear waste form for the immobilization of I-129, was irradiated with energetic ions, electrons, and gamma rays, to investigate its radiation stability. In situ TEM observation of the 1 MeV Kr2+ irradiation shows that lead vanadate iodoapatite generally exhibits higher tolerance against ion irradiation-induced amorphization than lead vanadate fluorapatite, and the spark plasma sintering can further enhance its radiation stability attributed to the enhanced crystallinity, reduced defect concentration, and denser microstructure. The critical amorphization dose and critical temperature for the SPS-densified iodoapatite at 700°C are determined to be 0.25 dpa at room temperature and 230°C, respectively. No significant phase transformation or microstructural damage occurred under energetic electron and gamma irradiations. Raman spectra of gamma-ray-irradiated iodoapatite indicate improved V–O bond order at 500 kGy dose. Generally, the spark-plasma-sintered iodoapatite exhibits excellent radiation stability for nuclear waste form applications. The significantly enhanced radiation stability of the SPS-densified iodoapatite suggests that SPS holds great promise for fabricating iodoapatite waste form with minimum iodine loss and optimized radiation tolerance for effective management of highly volatile I-129.
TL;DR: In this paper, a plausible hypothesis, i.e., ATP dyssynthesis, is proposed to elucidate the potential toxicity mechanism of the VO2 nanomaterial via vanadate-phosphate antagonism.
Abstract: A thermochromic vanadium dioxide (VO2) film holds great promise for intelligent windows owing to marvelous semiconductor-metal transitions (SMT), an active response to external temperature stimuli and near-infrared irradiation. To date, however, its potential biological effect on human cells has not been well characterized. In this work, homogeneous high quality VO2 films with different thicknesses (30, 80, 120 nm) were prepared on a quartz glass substrate. Afterwards, for the first time, we demonstrate the time-dependent and dose-dependent cytotoxicity of the VO2 film to human cells. Speciation analysis by 51V NMR spectra and surface zeta potentials revealed the formation of vanadate(+5) and ADPV, an analogue of ATP. On the basis of energy metabolism or bioenergetics, a plausible hypothesis, i.e., “ATP dyssynthesis”, is proposed here to elucidate the potential toxicity mechanism of the VO2 nanomaterial via vanadate-phosphate antagonism including two steps: (i) vanadate speciation from VO2 surface chemistry; (ii) vanadate disturbing ATP synthesis as a phosphate analogue. ATP stores energy to carry out various life processes; once its synthesis is hindered, vital movement will be impaired. From the perspective of surface modification and bioactivation, some practical methods are recommended to compensate for the potential cytotoxicity of the VO2 material. We expect this work can stimulate scientific interest to search for more versatile material design strategies to balance the energy-saving efficiency and environmental safety of VO2 intelligent window coatings.