Vanadyl Complexes Research Articles

Polaronic conduction and dielectric relaxation dynamics in V2O5 added lead bismuth silicate glass system

V2O5 doped lead bismuth silicate glasses were prepared by melt quenching technique. Initially, the spectroscopic investigations viz., optical absorption (OA) and EPR spectral studies were performed; the results of these studies suggested reduction of a part of V5+ ions into V4+ ions (that are identified to form vanadyl complexes viz., VO2+). The results further indicated the largest concentration of such complexes in the glass doped with 0.6 mol% of V2O5. Infrared spectral (IR) results suggested a progressive disintegration of the augmented glass network with increase of V2O5 concentration beyond 0.3 mol%. Later, extensive investigations on dielectric properties were carried out. Values of dielectric permittivity, ε′(ω), loss tangent and a.c. conductivity, σac, observed to be minimal for the glass containing 0.3 mol% of V2O5 (V3 glass) and found to be increased for further increase of V2O5 content at any frequency and temperature. The electric moduli components exhibited dipolar relaxation effects. Relaxation time τ for dipoles estimated from the spectra of electric moduli showed a decreasing trend as the V2O5 content increased up to 0.3 mol% and beyond that τ is found to be increased. The complexes of V4+ and Bi3+ ions with oxygen ions were predicted to be the possible dipoles responsible for the dipolar effects. A.c. conductivity variation with V2O5 concentration indicated the minimum for V3 glass and exhibited increasing trend as the content of V2O5 raised from 0.3 to 0.6 mol%. Quantitative analysis of this result indicated polaronic contribution to the conductivity (ascribed to mutual transfer of polarons between V4+and V5+ ions) is prevalent in these glasses.

Native Vanadyl Complexes in Crude Oil as Polarizing Agents for In Situ Proton Dynamic Nuclear Polarization

The presence of paramagnetic species such as vanadyl complexes (VO2+) and free carbon radicals in petroleum disperse systems (PDSs) such as crude oil, bitumen, or kerogen causes significant interes...

Synthesis, Characterization, and Anti-Diabetic Therapeutic Activity of New Vanadyl(II) Complexes with Orotic Acid and Different Amino Acids Mixed Ligands

Synthesis, Characterization, and Anti-Diabetic Therapeutic Activity of New Vanadyl(II) Complexes with Orotic Acid and Different Amino Acids Mixed Ligands

Interaction of Vanadyl Complexes in Atmospheric Residue with Their Matrixes: An ESR Study in a Temperature Range up to 170 °C

It is important to understand the interaction of vanadyl complexes in atmospheric residue (AR) with their matrixes at different conditions for demetallization processes of AR and heavy oil. An ESR study in rotational mobility of vanadyl complexes in AR was conducted at a temperature range from 20 to 170 °C with and without 1-methylnaphthalene as solvent. A complete transformation of the ESR spectrum from anisotropy to isotropy was observed at a temperature of 170 °C with decreasing AR concentration in 1-methylnaphthalene from 100 to 20 wt %, which corresponds to a transformation of the vanadyl complexes from a rigid status constrained by the surrounding matrixes to a free status. Both increase in the temperature and decrease in the AR concentration are beneficial to such transformation. The study showed that dependency of the rotational mobility of vanadyl complexes on the temperature and concentration can be classified into three domains: isotropic, transitional, and anisotropic domains. In the anisotrop...

Distribution of vanadyl complexes and free radicals in asphaltenes fractions from electron paramagnetic resonance

Structural characterization of asphaltenes in complex systems is in the focus of scientific and industrial interests since many years. Asphaltenes isolated from the high-viscous Ashal’cha oil (2500 mPa·s) were studied. Five asphaltene fractions were obtained by stepwise extraction with an alcohol-benzene solvent with different alcohol contents after precipitating the asphaltenes from the oil with hot isooctane. Redistribution of paramagnetic centers between the fractions of asphaltenes is revealed by electron paramagentic resonance (EPR) while no significant changes in EPR spectral parameters are found. The results can be used for tracking the asphatenes formation as well as following the changes of their supramolecular structure.

High-Field (3.4 T) ENDOR Investigation of Asphaltenes in Native Oil and Vanadyl Complexes by Asphaltene Adsorption on Alumina Surface

Vanadyl porphyrin complexes in asphaltenes from heavy (Karmalinskoye) oil and in asphaltene films obtained as a result of adsorption on the surface of aluminum oxide were studied by electron paramagnetic resonance (EPR) and double electron-nuclear resonance (ENDOR) in the W-band frequency range (microwave frequency of 95 GHz, magnetic field of 3.4 T). Mims ENDOR spectra from 1H and 27Al nuclei are observed. ENDOR spectra are different for native oil and asphaltenes from one side and the adsorbed samples from the other side while no significant changes in X- (microwave frequency of 9 GHz) or W-band EPR spectra are found. The results allow supposing that vanadyl porphyrin complexes (at least in the studied asphaltene films) participate in the formation of asphaltene aggregates through the functional groups rather than π−π interactions. The data show the feasibility of the commercial pulsed ENDOR approaches for the investigation of crude oils and their constituents under external influence.

Structural characterization of vanadium terpyridine complexes for the study of in-situ ligand cyclization reaction

Vanadyl complex [VIVO(hmfc)(terpy)]3.5H2O (1) (hmfc=5-hydroxy-3-methyl-2(5H)-furanone-5-carboxylate; terpy=2,2′:6′,2-terpyridine) has been isolated, which the hmfc ligand was formed through in-situ cyclization of lactate. X-ray structural analysis shows that hydroxyfuranone carboxylate chelates to vanadium through hydroxy group and carboxy group. Under the same condition, a peroxo vanadium terpyridine [VVO(O2)(terpy)(H2O)]Cl⋅H2O (2) could also be isolated, which is directly formed by molecular oxygen. In addition, a mixed-valence complex [V2O3(terpy)2]Cl3⋅9H2O (3) was isolated with two dimensional water units. These three complexes were characterized by elemental analysis, IR, UV-Vis, EPR, TGA, bond valence calculations and X-ray structural analyses. The formation of hydroxyfuranone carboxylate ligand may provide a new approach for one-pot synthesis of γ-hydroxy butenolide derivatives.

Synthesis of new antidiabetic agent by complexity between vanadyl (II) sulfate and vitamin B1: Structural, characterization, anti‐DNA damage, structural alterations and antioxidative damage studies

Complexity between thiamine (vitamin B1) and VSO4.xH2O salt with the suggest formula, [VO (vitB1)2] has been synthesized by the chemical reaction in neutralization media pH = 7.5 at 70 °C. The assignments of the elemental analysis, conductivity measurements, FT‐IR, UV–Vis, ESR spectroscopy, thermal analyses (TGA‐DTA) and magnetic moment data visualize the stoichiometry, formula and chelation of the vanadyl (II) complex. The spectroscopic analyses revealed that vitamin B1 reacted with vanadyl (II) ions as a bidentate ligand via hydroxyl ethyl‐oxygen and sulfur of the thiazole group. New vanadyl (II) complex has the protective effect against pancreatic toxicity induced by STZ. The target of this investigation was to assess the enhancement effect of new vanadyl (II)complex in two doses on pancreatic toxicity, oxidative stress, DNA damage and hyperglycemia persuade by STZ. The rats were divided into 7 groups; control group, STZ (diabetic untreated group) (50 mg/kg), STZ plus thiamine (10 mg/Kg) (Low dose), STZ plus thiamine (50 mg/Kg) (High dose), STZ plus VSO4. xH2O (15 mg/kg), STZ + vanadyl (II) complex (10 mg/Kg) (Low dose), STZ+ vanadyl (II) complex (50 mg/Kg) (High dose). Vanadyl (II) complex in high dose afforded a significant decline in MDA level parallel to significant elevation in antioxidant enzymes (SOD, CAT, MPO and XO) in pancreas homogenates. It may be due to the capturing activities of reactive oxygen species by the new complex, which reduces oxidative damage and enhance antioxidant capacities. The novel complex succeeded in the restoration of lipid parameters to its normal levels beside lowering TNF‐α and CRP levels. The new complex also reduces hyperglycemia induced by STZ greatly and improve histological and ultrastructure of pancreas and has a high potency in reducing DNA damage in pancreatic tissues.

Oxidation of sulfides including DBT using a new vanadyl complex of a non‐innocent o‐aminophenol benzoxazole based ligand

Reaction of a non‐innocent o‐aminophenol benzoxazole based ligand HLBAP with VOCl3 afforded a vanadyl complex, VOLBIS (SQ), in which SQ is a 2,4‐di‐tert‐butylsemiquinone produced from hydrolysis of HLBAP. The crystal structure of VOLBIS (SQ) exhibits an octahedral geometry with the VO2+ center coordinated by two nitrogen and one oxygen atoms of LBAP and two oxygen atoms of SQ. Electrochemical studies showed quasi‐reversible metal‐centered reduction and ligand‐centered oxidation of complex. The magnetic moment of VOLBIS (SQ) is consistent with the spin‐only value expected for S = 1/2 system. The neutral species of VOLBIS (SQ) is EPR active, which is consistent with a paramagnetic electronic ground state (S = 1/2). This result is in accordance with the vanadyl (IV) moiety surrounded by tridentate iminobenzosemiquinonate anion radical (HLBIS)•‐ and benzosemiquinone ligand (SQ)•. The theoretical calculations confirm the experimental results. Furthermore, we present the optimal conditions for maximum efficiency of sulfide oxidation for oxidative desulfurization with hydrogen peroxide and 6 times reusability of catalyst for sulfoxidation of dibenzothiophene.

XPS and IR Spectroscopic Studies of Titanyl and Vanadyl Complexes with Etioporphyrin II

XPS and IR Spectroscopic Studies of Titanyl and Vanadyl Complexes with Etioporphyrin II

DNA binding, cytotoxic effects and probable targets of an oxindolimine–vanadyl complex as an antitumor agent

The vanadyl–oxindolimine complex as an antitumor agent.

Vanadium (IV) complexes with Schiff base ligands derived from 2,3-diaminopyridine as catalyst for the oxidation of sulfides to sulfoxides with H2O2

Sulfoxides are substances used in the synthesis of valuable complexes and as drugs in medicine. Sulfides were selectively oxidized to the corresponding sulfoxides in proper yields with (H2O2) hydrogen peroxide applying a vanadium (IV) Schiff base complex in the role of a catalyst in glacial acetic acid in the role of solvent beneath mild conditions. For the conversion of sulfides to sulfoxides of various catalysts are applied. It must be noted that in our previous article, the vanadyl complexes (VOY1) synthesized were applied as a catalyst in the epoxidation of styrene (Zabardasti and Shangaie, J Iran Chem Soc 13:1875–1886, 2016) but in the new work, vanadium (IV) complexes with Schiff base ligands derived from 2,3-diaminopyridine were used to as catalyst for the oxidation of sulfides to sulfoxides with H2O2. To the most of our information, there is not any literature description on the selective oxidation of sulfides to sulfoxides by means of a vanadium (IV) Schiff base complex with N, O donor ligand derived from 2,3-diaminopyridine catalyst beneath these conditions. Dimethyl sulfide was chosen as a pattern substrate for optimization experiments. Oxidation of sulfides was functioned at 25 °C temperature in the attendance of a catalytic quantity of the vanadium (IV) complex or (VOY1) utilizing 20% H2O2 in the role of the oxidant, Scheme 1 and glacial acetic acid in the role of the solvent.

VAOS, a novel vanadyl complexes of alginate saccharides, inducing apoptosis via activation of AKT-dependent ROS production in NSCLC

Previous studies have confirmed that protein tyrosine phosphatase 1B (PTP1B) can promote tumour progression in non-small cell lung cancer (NSCLC). Vanadyl alginate oligosaccharides (VAOS) is a new coordination compounds that possesses a good PTP1B inhibitory activity. However, the potent anticancer efficacy of VAOS in human NSCLC requires further study. In this study, VAOS exhibited effective inhibitory effects in NSCLC both in cultured cells and in a xenograft mouse model. VAOS was further identified to induce NSCLC cell apoptosis through activating protein kinase B (AKT) to elevate intracellular reactive oxygen species (ROS) levels by increasing in oxygen consumption and impairing the ROS-scavenging system. Neither silencing of PTP1B by siRNA nor transient overexpression of PTP1B had an effect on the AKT phosphorylation triggered by VAOS, indicating that PTP1B inhibition was not involved in VAOS-induced apoptosis. Through phosphorus colorimetric assay, we demonstrated that VAOS notably inhibited phosphatase and tensin homologue deleted on chromosome 10 (PTEN) dephosphorylation activity, another member of the protein tyrosine phosphatases (PTPases)-upstream factor of AKT. Interestingly, PTEN knockdown sensitized cells to VAOS, whereas ectopic expression of PTEN markedly rescued VAOS-mediated lethality. In vivo, VAOS treatment markedly reduced PTEN activity and tumour cell burden with low systemic toxicity. Thus, our data not only provided a new therapeutic drug candidate for NSCLC, but presented new understanding into the pharmacological research of VAOS.

Enantioselective epoxidation of styrene with TBHP catalyzed by bis(oxazoline)–vanadyl–laponite materials

Bis(oxazoline)-vanadyl complexes have been prepared from two precursors, VO(acac)2 and VOSO4, and immobilized on laponite by cation exchange. These catalysts have been tested in the enantioselective epoxidation of styrene with TBHP. The catalytic activities are always much higher in the case of VO(acac)2. The ligand improves the catalytic activity, with similar or slightly better selectivity to styrene oxide (up to 42%) and up to 63% ee in solution. Laponite support is also beneficial in most cases, with selectivities to styrene oxide up to 60%. Moderate enantioselectivities are obtained, better with VOSO4 solids, up to 72% ee.

Anti-diabetic vanadyl complexes reduced Alzheimer's disease pathology independent of amyloid plaque deposition.

Association of Alzheimer's disease (AD) with cerebral glucose hypometabolism, likely due to impairments of insulin signaling, has been reported recently, with encouraging results when additional insulin is provided to AD patients. Here, we tested the potential effects of the anti-diabetic vanadium, vanadyl (IV) acetylacetonate (VAC), on AD in vitro and in vivo models. The experimental results showed that VAC at sub-micromolar concentrations improved the viability of neural cells with or without increased β-amyloid (Aβ) burden; and in APP/PS1 transgenic mice, VAC treatment (0.1 mmol kg-1 d-1) preserved cognitive function and attenuated neuron loss, but did not reduce brain Aβ plaques. Further studies revealed that VAC attenuated Aβ pathogenesis by (i) activation of the PPARγ-AMPK signal transduction pathway, leading to improved glucose and energy metabolism; (ii) up-regulation of the expression of glucose-regulated protein 75 (Grp75), thus suppressing p53-mediated neuronal apoptosis under Aβ-related stresses; and (iii) decreasing toxic soluble Aβ peptides. Overall, our work suggested that vanadyl complexes may have great potential for effective therapeutic treatment of AD.

α-AMYLASE INHIBITION AND ELECTROCHEMICAL BEHAVIOR OF SOME OXOVANADIUM (IV) COMPLEXES OF L-AMINO ACIDS

Objective: Diabetes is complex metabolic disease having a symptom of hyperglycemia. Oxovanadium (IV) and l-amino acids are used to normalize the hyperglycemic condition. The aim of this study was to screen the α-amylase inhibitory activity of l-amino acids, their oxovanadium (IV) complexes, and electrochemical activity of oxovanadium (IV) complexes.Methods: All the oxovanadium (IV) complexes were synthesized according to the solubility of l-amino acids; the molar ratio of metal to l-amino acid was 1:2. The synthesized oxovanadium (IV) complexes were examined for their electrochemical behavior in 0.01 M sodium perchlorate solution. Further, the oxovanadium (IV) complexes of l-amino acids and l-amino acids were screened for their α-amylase inhibitory activity using spectrophotometric assay system.Results: The synthesized complexes were divided into four groups according to nature of amino acids. Entire complexes show simple irreversible wave for VO redox couples in −900–50 mV potential range and scan rate was 300 mV/S. All the complexes and l-amino acids were screened for their α-amylase inhibitory activity. L-Histidine and their oxovanadium (IV) complex show the minimum IC50 value, i.e. 4199.05 μM and 101.015 μM, respectively, in their respective groups.Conclusion: The data obtained from our study, it reveals that the entire oxovanadium (IV) complexes are an irreversible wave for VO redox system and the l-histidine and its oxovanadium (IV) complex is the most potent inhibitor for the α-amylase. Further, the complexes show minimum IC50 value on comparing their respective ligands due to the interaction of Vanadyl complex to the enzyme, at the sixth vacant position of Vanadyl complex.

Vanadyl complexes discriminate between neuroblastoma cells and primary neurons by inducing cell-specific apoptotic pathways

Vanadium compounds have arisen as potential therapeutic agent for the treatment of cancers over the past decades. A few studies suggested that vanadyl complexes may discriminate between the cancerous and the normal cells. Here, we reported the investigation on the pro-apoptotic effect and the underlying mechanism of bis(acetylacetonato) oxovanadium(IV) ([VO(acac)2]) on SH-SY5Y neuroblastoma cells in comparison with that of mouse primary cortex neurons. The experimental results revealed that [VO(acac)2] showed about 10-fold higher cytotoxicity (IC50 ~16 μM) on the neuroblastoma cells than on normal neurons (IC50 ~250 μM). Further analysis indicated that the vanadyl complex suppressed the growth of neuroblastoma cells via different pathways depending on its concentration. It induced a special cyclin D-mediated and p53-independent cell apoptosis at <50 μM but cell cycle arrests at >50 μM. In contrast, [VO(acac)2] promoted cell viability of primary neurons in the concentration range of 0–150 μM; while [VO(acac)2] at hundreds of μM would cause neuronal death possibly via the reactive oxygen species (ROS)-mediated signal pathways. The extraordinary discrimination between neuroblastoma cells and primary neurons suggests potential application of vanadyl complexes for therapeutic treatment of neuroblastoma. In addition, the p53-independent apoptotic pathways induced by vanadyl complexes may provide new insights for future discovery of new anticancer drugs overcoming the chemo-resistance due to p53 mutation.

Investigations of the Magnetic and Spectroscopic Properties of V(III) and V(IV) Complexes.

Herein, we utilize a variety of physical methods including magnetometry (SQUID), electron paramagnetic resonance (EPR), and magnetic circular dichroism (MCD), in conjunction with high-level ab initio theory to probe both the ground and ligand-field excited electronic states of a series of V(IV) ( S = 1/2) and V(III) ( S = 1) molecular complexes. The ligand fields of the central metal ions are analyzed with the aid of ab initio ligand-field theory (AILFT), which allows for a chemically meaningful interpretation of multireference electronic structure calculations at the level of the complete-active-space self-consistent field with second-order N-electron valence perturbation theory. Our calculations are in good agreement with all experimentally investigated observables (magnetic properties, EPR, and MCD), making our extracted ligand-field theory parameters realistic. The ligand fields predicted by AILFT are further analyzed with conventional angular overlap parametrization, allowing the ligand field to be decomposed into individual σ- and π-donor contributions from individual ligands. The results demonstrate in VO2+ complexes that while the axial vanadium-oxo interaction dominates both the ground- and excited-state properties of vanadyl complexes, proximal coordination can significantly modulate the vanadyl bond covalency. Similarly, the electronic properties of V(III) complexes are particularly sensitive to the available σ and π interactions with the surrounding ligands. The results of this study demonstrate the power of AILFT-based analysis and provide the groundwork for the future analysis of vanadium centers in homogeneous and heterogeneous catalysts.

W-band EPR of vanadyl complexes aggregates on the surface of Al2O3

Structural characterization of metalloporphyrins, asphaltenes and their aggregates in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since many years. We present W-band (95 GHz) electron paramagnetic resonance (EPR) study in the magnetic field of about 3.4 T and temperature of 100 K for Karmalinskoe oil, asphaltens and asphaltenes deposited on the surface of Al2O3. Features of the obtained spectra are described. Shift to the higher frequencies allows to separate spectrally the contributions from paramagnetic complexes of different origin and define the EPR parameters more accurately comparing to the conventional X-band (9 GHz). Changes of the EPR parameters are tracked. We suggest that the proposed approach can be used for the investigation of structure of vanadyl complexes aggregates in crude oil and their fractions.

Selective ionization by electron-transfer MALDI-MS of vanadyl porphyrins from crude oils

Petroporphyrins are biomarkers derived from chlorophyll, bacteriochlorophyll and the heme group, commonly present in crude oils as vanadyl or nickel complexes. These compounds, which despite of the organic matter maturation process preserve the tetrapyrrolic core of their precursors, show low polydispersity, concentration and are commonly used in geochemistry to assess oil lithology, oxidation-reduction conditions, geothermal maturation, conversion of organic matter, and burial depth. The physicochemical characteristics of petroporphyrins make them excellent analytes for MALDI-MS. Electron transfer (ET) ionization in MALDI, using novel electron transfer matrices based on cyano-phenylenevinylenes (e.g. CNPV-CH3), allows direct observation of labile compounds such as polyaromatics and porphyrin-like compounds, chlorophylls and pigments, as has been previously demonstrated by our group. In this work, we analyze petroporphyrins from two South American heavy oils using CNPV-CH3 as ET MALDI matrix. Petroporphyrins were isolated by Soxhlet extraction, with acetonitrile, followed by fractionation using normal-phase column chromatography. UV–Vis measurements showed a strong absorption band at 408 nm assigned to porphyrin Soret band for some chromatographic fractions. The fractions enriched with petroporphyrins were subjected to ET MALDI analysis. We demonstrate the suitability of the CNPV-CH3 MALDI matrix for the efficient and selective desorption and ionization of vanadyl porphyrins, when compared with a commercial MALDI matrix (DCTB) and LDI conditions.