51V Nuclear Magnetic Resonance Research Articles

NMR study of charge density wave phase in the kagome metal RbV3Sb5

The mechanism of charge-density-wave (CDW) phase in one-dimensional lattices can be well described in theory. Whether similar mechanism works in two-dimensional systems is still a mystery. In this work, we employed 51V solid-state nuclear magnetic resonance (NMR) spectroscopy combined with first-principles computations to probe atomic structure and electronic properties at V sites in a quasi-two-dimensional crystal RbV3Sb5. Clear evidence of the CDW phase transition was observed from the temperature-dependent 51V NMR measurements. The sharp transition of 51V Knight shifts and electric field gradients (EFG) across the CDW transition supports the view that energy gap is formed by the nesting of partial Fermi surface in accompany with the superlattice formation. The calculated EFG parameters were also compared with our experiments, and the results suggest that the charge modulation of the CDW order is inverse Star-of-David pattern.

Vanadium(V) complexes derived from triphenylphosphonium and hydrazides: cytotoxicity evaluation and interaction with biomolecules.

The development of coordination compounds with antineoplastic therapeutic properties is currently focused on non-covalent interactions with deoxyribonucleic acid (DNA). Additionally, the interaction profiles of these compounds with globular plasma proteins, particularly serum albumin, warrant thorough evaluation. In this study, we report on the interactions between biomolecules and complexes featuring hydrazone-type imine ligands coordinated with vanadium. The potential to enhance the therapeutic efficiency of these compounds through mitochondrial targeting is explored. This targeting is facilitated by the derivatization of ligands with triphenylphosphonium groups. Thus, this work presents the synthesis, characterization, interactions, and cytotoxicity of dioxidovanadium(V) complexes (C1-C5) with a triphenylphosphonium moiety. These VV-species are coordinated to hydrazone-type iminic ligands derived from (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride ([AH]Cl) and aromatic hydrazides ([H2L1]Cl-[H2L5]Cl). The structures of the five complexes were elucidated through single-crystal X-ray diffraction and vibrational spectroscopies, confirming the presence of dioxidovanadium(V) species in various geometries with degrees of distortion (τ = 0.03-0.50) and highlighting their zwitterionic characteristics. The molecular structural stability of C1-C5 in solution was ascertained using 1H, 19F, 31P, and 51V-nuclear magnetic resonance. Moreover, their interactions with biomolecules were evaluated using diverse spectroscopic methodologies and molecular docking, indicating moderate interactions (Kb ≈ 104 M-1) with calf thymus DNA in the minor groove and with human serum albumin, predominantly in the superficial IB subdomain. Lastly, the cytotoxic potentials of these complexes were assessed in keratinocytes of the HaCaT lineage, revealing that C1-C5 induce a reduction in metabolic activity and cell viability through apoptotic pathways.

Predicting 51V nuclear magnetic resonance observables in molecular crystals.

Solid-state nuclear magnetic resonance (NMR) spectroscopy and quantum chemical density functional theory (DFT) calculations are widely used to characterize vanadium centers in biological and pharmaceutically relevant compounds. Several techniques have been recently developed to improve the accuracy of predicted NMR parameters obtained from DFT. Fragment-based and planewave-corrected methods employing hybrid density functionals are particularly effective tools for solid-state applications. A recent benchmark study involving molecular crystal compounds found that fragment-based NMR calculations using hybrid density functionals improve the accuracy of predicted 51V chemical shieldings by 20% relative to traditional planewave methods. This work extends the previous study, including a careful analysis of 51V chemical shift anisotropy, electric field gradient calculations, and a more extensive test set. The accuracy of planewave-corrected techniques and recently developed fragment-based methods using electrostatic embedding based on the polarized continuum model (PCM) are found to be highly competitive with previous methods. Planewave-corrected methods achieve a 34% improvement in the errors of predicted 51V chemical shieldings relative to planewave. Additionally, planewave-corrected and fragment-based calculations were performed using PCM embedding, improving the accuracy of predicted 51V chemical shielding (CS) tensor principal values by 30% and values by 15% relative to traditional planewave methods. The performance of these methods is further examined using a redox-active oxovandium complex and a common 51V NMR reference compound.

Emergent charge order in pressurized kagome superconductor CsV3Sb5.

The discovery of several electronic orders in kagome superconductors AV3Sb5 (A means K, Rb, Cs) provides a promising platform for exploring unprecedented emergent physics1-9. Under moderate pressure (<2.2 GPa), the triple-Q charge density wave (CDW) order is monotonically suppressed by pressure, while the superconductivity shows a two-dome-like behaviour, suggesting an unusual interplay between superconductivity and CDW order10,11. Given that time-reversal symmetry breaking and electronic nematicity have been revealed inside the triple-Q CDW phase8,9,12,13, understanding this CDW order and its interplay with superconductivity becomes one of the core questions in AV3Sb5 (refs. 3,5,6). Here, we report the evolution of CDW and superconductivity with pressure in CsV3Sb5 by 51V nuclear magnetic resonance measurements. An emergent CDW phase, ascribed to a possible stripe-like CDW order with a unidirectional 4a0 modulation, is observed between Pc1 ≅ 0.58 GPa and Pc2 ≅ 2.0 GPa, which explains the two-dome-like superconducting behaviour under pressure. Furthermore, the nuclear spin-lattice relaxation measurement reveals evidence for pressure-independent charge fluctuations above the CDW transition temperature and unconventional superconducting pairing above Pc2. Our results not only shed new light on the interplay of superconductivity and CDW, but also reveal new electronic correlation effects in kagome superconductors AV3Sb5.

Pascoite Minerals and Potential Application of NMR Spectroscopy

The 20 minerals encompassing the pascoite family of decavanadate isopolyanion-containing [V10O28]6− minerals include a few minerals, such as rakovanite, that have been described as containing a protonated decavanadate anion. Rakovanite was originally assigned the formula Na3[H3V10O28]•15H2O and now is redefined with an ideal formula (NH4)3Na3[V10O28]•12H2O. Nuclear magnetic resonance (NMR) and particularly 51V NMR spectroscopy is an informative method used to describe the protonation state and speciation in both solid and solution states of materials in the chemical and life sciences. However, 51V NMR spectroscopy has not yet been used experimentally to distinguish the protonation state of the decavanadate ion of leaching solutions and thus contributing to the discussion regarding the controversial protonation states of decavanadate ions in gunterite, rakovanite, and nashite. In contrast, the morphology and crystal structure for apatites, vanadinite, pyromorphite, and mimetite was related to 207Pb NMR chemical shifts, assisting in describing the local environments of these minerals. NMR spectroscopy could be a useful method if used in the future for decavanadate-containing minerals. Currently, partial reduction of two Pascoite minerals (caseyite and nashite) is proposed and accordingly could now effectively be investigated using a different magnetic resonance technique, EPR spectroscopy.

Possible star-of-David pattern charge density wave with additional modulation in the kagome superconductor CsV3Sb5

AV3Sb5 (A = K, Rb, Cs) is a novel kagome superconductor coexisting with the charge density wave (CDW) order. Identifying the structure of the CDW order is crucial for understanding the exotic normal state and superconductivity in this system. Here, we report 51V nuclear magnetic resonance (NMR) and 121/123Sb nuclear quadrupole resonance (NQR) studies on kagome-metal CsV3Sb5. Below the CDW transition temperature TCDW ~ 98 K, an abrupt change of spectra was observed, indicating that the transition is of the first order. By further analyzing the spectra, we find that the CDW order is commensurate. And most remarkably, the obtained experimental results suggest that the charge modulation of the CDW order is of star-of-David pattern and accompanied by an additional charge modulation in bulk below T* ~ 40 K. Our results revealing the unconventional CDW order provide new insights into AV3Sb5.

Orbital ordering and fluctuations in a kagome superconductor CsV3Sb5

Recently, competing electronic instabilities, including superconductivity and density-wave-like order, have been discovered in vanadium-based kagome metals AV3Sb5 (A = K, Rb, Cs) with a nontrivial band topology. This finding stimulates considerable interest to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state. Here, we performed 51V and 133Cs nuclear magnetic resonance (NMR) measurements on a CsV3Sb5 single crystal to clarify the nature of density-wave-like transition in these kagome superconductors. A first-order structural transition is unambiguously revealed below Ts ∼ 94 K by observing the sudden splitting of Knight shift in 51V NMR spectrum. Moreover, combined with 133Cs NMR spectrum, the present result confirms a three-dimensional structural modulation. By further analyzing the anisotropy of Knight shift and 1/T1T at 51V nuclei, we proposed that the orbital order is the primary electronic order induced by the first-order structural transition, which is supported by further analysis on electric field gradient at 51V nuclei. In addition, the evidence for possible orbital fluctuations is also revealed above Ts. The present work sheds light on a rich orbital physics in kagome superconductors AV3Sb5.

Kinetic and Interaction Studies of Adenosine-5′-Triphosphate (ATP) Hydrolysis with Polyoxovanadates

The reactivity of polyoxovanadates towards adenosine-5′-triphosphate (ATP) hydrolysis at pH 2, 4, 6 and 7 is reported. Detailed kinetic investigation of ATP hydrolysis in the presence of polyoxovanadates was performed through multinuclear nuclear magnetic resonance (NMR) spectroscopy. In general, rate acceleration of up to five orders of magnitude was observed in the presence of vanadates compared to spontaneous ATP hydrolysis, with the greatest acceleration observed for reactions carried out at pH 2. Interestingly, the effectiveness of vanadates in promoting ATP hydrolysis decreased as the pH of the reaction solution increased; nevertheless, at pH = 7, the rate increase of one order of magnitude in comparison to blank reactions was still observed. Interactions between vanadate species in solution and ATP were investigated by means of 31P and 51V NMR spectroscopy, and this pointed towards the preferential interaction of vanadium with the phosphate groups rather than other regions of the ATP molecule.

S-Wave Superconductivity in Kagome Metal CsV3Sb5 Revealed by 121/123Sb NQR and 51V NMR MeasurementsSupported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0302901, 2018YFE0202600, and 2016YFA0300504), the National Natural Science Foundation of China (Grant Nos. 11921004, 11634015, 11822412, and 11774423), the Beijing Natural Science Foundation (Grant No. Z200005), and the Strategic Priority Research Program and Key

We report 121/123Sb nuclear quadrupole resonance (NQR) and 51V nuclear magnetic resonance (NMR) measurements on kagome metal CsV3Sb5 with T c = 2.5 K. Both 51V NMR spectra and 121/123Sb NQR spectra split after a charge density wave (CDW) transition, which demonstrates a commensurate CDW state. The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first-order phase transition. At low temperature, electric-field-gradient fluctuations diminish and magnetic fluctuations become dominant. Superconductivity emerges in the charge order state. Knight shift decreases and 1/T 1 T shows a Hebel–Slichter coherence peak just below T c, indicating that CsV3Sb5 is an s-wave superconductor.

Oxido- and Dioxido-Vanadium(V) Complexes Supported on Carbon Materials: Reusable Catalysts for the Oxidation of Cyclohexane.

Oxidovanadium(V) and dioxidovanadium(V) compounds, [VO(OEt)L] (1) and [Et3NH][VO2L] (2), were synthesized using an aroylhydrazone Schiff base (5-bromo-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H2L). They were characterized by elemental analysis, Fourier-transform infrared spectroscopy (FT-IR), (1H and 51V) nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS) and single crystal X-ray diffraction analyses. Both complexes were immobilized on functionalized carbon nanotubes and activated carbon. The catalytic performances of 1 and 2, homogenous and anchored on the supports, were evaluated for the first time towards the MW-assisted peroxidative oxidation (with tert-butylhydroperoxide, TBHP) of cyclohexane under heterogeneous conditions. The immobilization of 1 and 2 on functionalized carbon materials improved the efficiency of catalytic oxidation and allowed the catalyst recyclability with a well-preserved catalytic activity.

Accurate fragment-based 51-V chemical shift predictions in molecular crystals

Nuclear magnetic resonance (NMR) spectroscopy plays a crucial role in determining molecular structure for complex biological and pharmaceutical compounds. NMR investigations are increasingly reliant on computation for mapping spectral features to chemical structures. Here we benchmark the accuracy of fragment-based 51V chemical shielding tensor calculations using a training set comprised of 10 biologically and pharmaceutically relevant oxovanadium complexes. Using our self-consistent reproduction of the Madelung potential (SCRMP) electrostatic embedding model, we demonstrate comparable performance between fragment methods and computationally demanding cluster-based techniques. Specifically, fragment methods employing hybrid density functionals are capable of reproducing the experimental 51V isotropic chemical shifts with a training set rms error of ~9 ​ppm, representing a 20% improvement over traditional plane wave techniques. We provide training set-derived linear regression models for mapping the absolute shieldings obtained from computation to the experimentally determined chemical shifts using four common density functionals; PBE0, B3LYP, PBE, and BLYP. Finally, we establish the utility of fragment methods and the reported regression parameters examining four oxovanadium structures excluded from the training set including the tetracoordinate oxovanadium silicate (Ph3SiO)3VO, VO15NGlySalbz which contains redox-active ligands, and the solid-state form of the common 51V NMR reference compound VOCl3.

Role of vanadium oxide on the lithium silicate glass structure and properties

AbstractThe structural role of V in 28Li2O–72SiO2 (in mol%) lithium silicate glass doped with 0.5 mol% V2O5 was assessed using 29Si and 51V Nuclear Magnetic Resonance (NMR), Fourier‐transform infrared (FTIR), and X‐ray photoelectron (XPS) spectroscopy techniques. Despite the low amount of V2O5 used, the structural information obtained or deduced from the statistical analysis of the NMR data could explain the evolution of glass properties after V2O5 addition. The XPS results indicated that all vanadium exists in 5+ oxidation state. Both the 29Si NMR and FTIR data point toward an increase in the polymerization of the silicate network, caused by the V2O5 acting as network former, capable to form various tetrahedral units (for n = 0, 1, and 2) in the glasses. These units, which are similar to phosphate units, scavenge the Li+ ions and cause the silicate network to polymerize. However, in an overall balance, the entire glass network is depolymerized due to the additional nonbridging oxygens contributed by the vanadium polyhedra. The addition of vanadium causes the network to expand and increases the ionic conductivity.

The Influence of Free Acid in Vanadium Redox‐Flow Battery Electrolyte on “Power Drop” Effect and Thermally Induced Degradation

A series of vanadium redox‐flow battery (VRFB) electrolytes at 1.55 m vanadium and 4.5 m total sulfate concentration are prepared from vanadyl sulfate solution and tested under conditions of appearance of “power drop” effect (discharge at high current density from high state‐of‐charge). A correlation between the initial electrolyte composition, the thermal stability of catholyte, and the susceptibility of VRFB to exhibit a “power drop” effect is derived. The increase in total acidity to 3 m, expressed as concentration of sulfuric acid in precursor vanadyl sulfate solution, enables “power drop”‐free operation of VRFB at least at 75 mA cm−2. Thermally‐induced degradation of electrolyte is evaluated based on decrease in vanadium concentration in the electrolyte series after exposure to the temperature of 45 °C and based on characterization of catholytes series using 51V, 17O, and 1H nuclear magnetic resonance spectroscopy.

Synthesis and Experimental-Computational Characterization of a Copper/Vanadium Compound with Potential Anticancer Activity

Cancer represents a major worldwide public health problem. While significant advances in different fronts are being made to combat the disease, the development of new metal-based drugs with cytotoxic capabilities is of high relevance. This work presents a heterobimetallic molecule comprising two moieties with a structure similar to Casiopeina II-gly. One of them has a cyclotetravanadate anion that functions as an inorganic bridge coordinating two Cu (II) atoms resulting in a hexanuclear [Cu(phen)(Gly)-µ2-V4O12-Cu(phen)(Gly)]2− complex, which is counterbalanced by two isolated [Cu(phen)(Gly)(H2O)]1+ cations. Ten water molecules arranged in two sets of five-member chains also play an essential role in the 3D supramolecular structure of the compound. The molecule was designed to provide Cu and V, two metals with proven anticancer capabilities in the same molecular structure. The compound was synthesized and characterized by elemental analysis; visible, FTIR, and Raman spectroscopies; 51V Nuclear Magnetic Resonance; cyclic voltammetry; and monocrystalline X-ray diffraction. The structural, spectroscopic, and electronic properties of the compound were calculated through the density functional theory (DFT) using the Minnesota functional M06-2X and the Def2TZVP/LANL2TZ(f) basis sets with an effective core potential (ECP) for metals. Noncovalent interactions were analyzed using a natural population analysis (NPA) and Hirshfeld surfaces. The compound upon dissociation provides two metals that can interact with important biological targets in a variety of cancer cell models.

MnOx-decorated VOx/CeO2 catalysts with preferentially exposed {110} facets for selective catalytic reduction of NOx by NH3

Highly dispersed MnOx-decorated VOx/CeO2 catalysts with preferentially exposed {110} facets were chosen to improve the low-temperature (200−250 °C) NH3-SCR activity. In this work, the catalytic data on NH3-SCR performance indicated that the improved catalytic activity were achieved when both VOx and MnOx were presented on the {110} facet of CeO2 nanorods. It could be deduced that the highly dispersed surface monomeric vanadium species were the reason for the high NH3-SCR activity from 51V-Nuclear Magnetic Resonance (NMR), Raman, X-ray diffraction (XRD) and Transmission electron microscopy (TEM). It was also suggested that CeO2{110} facet and surface oxygen vacancy defects had significant effects on the promotion of NH3-SCR performance. Furthermore, the redox cycle of V5+/V4+ and the quantities of NH3(L) species and bridging nitrate species were increased by the introduction of Mn. The Langmuir-Hinshelwood mechanism is possible because abundant surface NH3(L), NH4+(B) and bridging nitrate species were produced as intermediates studied via in situ DRIFTs.

51V and 25Mg NMR Study of the Kagome Staircase Compound Mg3V2O8

The 51V and 25Mg nuclear magnetic resonance (NMR) spectra have been obtained and magnetic susceptibility has been measured in polycrystalline Mg3V2O8. The analysis of 51V NMR spectra has shown that the line shift, δ(51V) = − 555 ppm, does not depend on temperature. It has been established that vanadium ions V5+ have a zero magnetic moment in this structure. The 25Mg NMR spectrum consists of two lines corresponding to two crystallographically nonequivalent positions of magnesium ions in the Kagome structure: Mg(1) are « spine » and Mg(2) are « cross tie » . Quadrupole frequencies and asymmetry parameters of 25Mg and 51V NMR spectra have been determined. The magnetic susceptibility is turn out to be zero (within the error) and remains constant over at a whole temperature range.

Structural properties of alumina-doped lithium borovanadate glasses and glass-ceramics

This study elucidates the role of Al2O3 in the lithium borovanadate (LBV) system, Li2O-B2O3-V2O5, in improving the glass-forming region of LBV glass. This increased glass-forming tendency is likely due to formation of [AlO4]− units. 11B, 27Al, and 51V nuclear magnetic resonance measurements suggest an importance of V-O-Al linkages and distribution of Li for charge compensation of [AlO4]− and [BO4]− units. Intense 51V NMR signals and resolved hyperfine coupling patterns in the electron paramagnetic resonance (EPR) spectra indicate that the majority of vanadium is pentavalent (V5+) and minor amounts of paramagnetic vanadium (V4+) are present. The EPR interaction parameters suggest that the vanadyl-like environments can be described as tetragonally compressed distorted octahedra. Based on V-2p3/2 X-ray photoelectron spectroscopy, the V4+ concentration is estimated at <3%. These vanadate glasses are attractive for energy storage applications, as they have higher specific capacities than commercial lithium-ion battery cathodes.

Improved All-Vanadium Redox Flow Batteries using Catholyte Additive and a Cross-linked Methylated Polybenzimidazole Membrane

Through controlling the cross-linking and thickness of low-cost methylated polybenzimidazole anion exchange membranes and by using imidazolium chloride as a catholyte additive, we improved the energy efficiency at a current density of 100 mA cm–2 for all-vanadium redox flow batteries (RFBs) to 82%, compared to 76% with a Nafion 212 membrane and 67–78% for previously reported polybenzimidazole membranes with standard electrolyte. Moreover, thermal stability analysis of the charged catholytes, by direct observations of vanadium precipitation and variable temperature 51V nuclear magnetic resonance, confirmed an optimized content of 0.16 M of the electrochemically inert additive in 1.6 M vanadium solution, consistent with the electrochemical data. The imidazolium chloride additive with such a low concentration is sufficient to induce interaction with vanadium species in catholyte. This explains the improved electrolyte stability and enhanced cycling efficiency.

Dynamic signature of orbital selective Mott transition in the metallic phase of VO2

An orbital-selective technique, nuclear magnetic resonance (NMR) spectroscopy, which could simultaneously probe the atomic structure and electronic properties, was employed to address the ‘bad metal’ behaviors, i.e., negligible electron thermal conductivity in the metallic phase of VO2. The measured electric field gradients at V sites by 51V NMR were found to evolve significantly in the pure metallic phase within the vicinity of structural phase transition temperatures, unexpected in a simple metal within this temperature region according to structural analysis by diffraction. This abnormal temperature-dependent local symmetry evolution can be well explained by a simple phenomenological model of orbital selective Mott transition in this multiorbital system.

Lanthanum vanadate catalysts for selective and stable methane oxybromination

A series of lanthanum vanadium oxides, LaVxO2.5x+1.5, with molar V:La ratios in the range of x = 0–1.2 have been synthesized using the citrate method and evaluated in the oxybromination of methane. This reaction aims at valorizing natural gas by its selective conversion into bromomethanes (CH3Br and CH2Br2) that can be used as a platform for the production of fuels and chemicals. In order to establish relationships between the composition, structure, and catalytic performance, the materials in fresh and equilibrated forms have been characterized by X-ray diffraction, N2 sorption, scanning transmission electron microscopy, elemental mapping, and Raman, 51V nuclear magnetic resonance, and X-ray photoelectron spectroscopies. At x = 1, the catalyst comprises nanocrystals of monoclinic-LaVO4, which are accompanied by crystalline hexagonal-La2O3 or amorphous vanadium oxide at sub-stoichiometric (x < 1) or over-stoichiometric (x > 1) ratios, respectively. Pure LaVO4 displays a pretty high selectivity to bromomethanes (86–78% at methane conversions of 15–25%) and stable structural and catalytic behavior. The selectivity is increased to 92–95% when a certain excess of lanthanum is used (e.g., LaV0.5O2.75) due to synergistic effects of the mixture of LaVO4 and tetragonal-LaOBr nanocrystals, formed by partial bromination of La2O3. In this catalyst, LaOBr moderates the oxidation potential of LaVO4 and minimizes the formation of carbon oxides, while LaVO4 avoids agglomeration of the LaOBr phase and secures stable operation. Catalysts outside the compositional window of x = 0.2–1 deactivate due to sticking of LaOBr particles (x < 0.2) or the volatilization of free vanadium oxide (x > 1). These results emphasize that the tuning the composition of LaVxO2.5x+1.5 enables to attain catalysts competing with the best reported oxybromination systems.