Oxovanadium Schiff Base Research Articles

Spectroscopic characterization of a mononuclear oxovanadium (IV) Schiff base complex. Oxidation catalysis applications and antibacterial activities

Herein we describe the chemical synthesis of a new oxovanadium (IV) complex of an N,N-bis(1-naphthalidimine)-o phenylenediamine (VOL). The structure has been characterized by various physiochemical and spectroscopic techniques. The single crystal X-ray diffraction confirms a tetra-coordinate chelated and a planar geometry of the complex by ONNO donor sets of the ligand. Hirshfeld's surface analysis indicates that the most important inter-molecular contact within crystal packing is C-H⋯O interaction. Density Functional Theory (DFT) calculations have been used to optimize the structure and discuss the chemical reactivity through the Frontier Molecular Orbitals (FMOs). The electrochemical properties of the complex were studied by cyclic voltammetry which shows a reversible VIV/VV redox process which is consistent with the hydrodynamic voltammograms. The complex was used as catalyst for the selective oxidation of cyclohexene to the corresponding 2-cyclohexene-1-one in DMF. Finally, antibacterial activity was determined using 3 Gram negative and 2 Gram positive bacteria using disk diffusion method, it was found to be more effective against Gram positive than the Gram negative bacteria.

Silica-coated nanomagnetite-supported oxovanadium(V) Schiff base complex: Preparation, characterization, and catalytic application for the oxidation of sulfides

In this paper, an oxovanadium(V) complex, prepared with a tridentate ONO Schiff base by reacting nicotinic hydrazide with 3-methoxysalicylaldehyde, was immobilized on the surface of the silica-coated magnetite nanoparticles. After successful preparation and complete characterization (FT–IR, SEM, XRD, TEM, VSM, EDX, and ICP), the catalytic activity of the magnetic organic–inorganic nanocomposite was explored for the green oxidation reaction of different kinds of aryl and alkyl sulfides employing hydrogen peroxide and methanol under reflux conditions. Significant features such as simple work-up, fast reaction, higher product yield, and reusability of the catalyst enhance the efficiency of this catalytic procedure economically and environmentally.

Synthesis, characterization, DFT calculations, and catalytic epoxidation of two oxovanadium(IV) Schiff base complexes

The present paper reports the synthesis, characterization, and DFT calculations of two oxovanadium (IV) Schiff base complexes symbolized as VOL1 and VOL2, which prepared by the reaction of bivalent tridentate Schiff base ligands (E)-2-((5-chloro-2-hydroxybenzylidene)amino)acetic acid and (E)-2-((2-hydoxy-5-nitrobenzylidene)amino)acetic acid and VO(acac)2 as vanadium source. The Schiff base ligands and its oxovanadium (IV) complexes were characterized by the elemental analysis (C, H, N), FTIR, 1H NMR and 13C NMR, DFT calculations were performed to derive some of their molecular properties. Schiff base ligands coordinated to vanadium center via nitrogen from the azomethine group and one oxygen from the hydroxyl attached to the benzene ring and one oxygen from hydroxyl of carboxyl group. The catalytic activity of the two complexes were tested against cyclooctene and found that both complexes were highly effective and selective in optimized conditions when used as cyclooctene epoxidation catalysts with the conversion percentage of 91.85% (with VOL1) and 87.40% (with VOL2) at 78 °C within a period of ten hours. To understand the structural properties of the two complexes, the two complexes were well optimized at B3LYP/6-31G(d,p) level of theory, structural parameters such as electron affinity, global electrophilicity, global hardness, electronegativity, ionization potential, and electron chemical potential based on HOMO and LUMO energy values were calculated.

Biologically active oxovanadium(IV) Schiff base metal complex: antibacterial, antioxidant, biomolecular interaction and molecular docking studies

The oxovanadium(IV) Schiff base metal complex (ISNPV) have been synthesized as well as characterized by using micro analytical and traditional spectroscopic techniques. The spectral findings were utilized to validate the formation of ISNPV with structure exhibited square pyramidal geometry. The in vitro antibacterial activities of ISNPV were investigated to five different bacterial stains such as S. aureus, S. epidermidis, B. cereus, B. amyloliquefaciens and B. subtilis. The obtained result have suggested that the ISNPV has highest antibacterial activity against S. aureus than the other bacterial stains. The in vitro antioxidant activity like DPPH free radical scavenging assay method was studied by ISNPV in DMSO medium. Because it scavenges all free radicals, the ISNPV possesses higher antioxidant activity than the free ligand. UV-visible absorption and emission spectral techniques were used to investigate the binding of CT-DNA to the ISNPV. Both the spectral data indicate that the ISNPV binds the double helix structure of CT-DNA via an intercalation mode. Additionally, investigate the interactions of ISNPV with the protein molecules like BSA/HAS has been investigated using absorption and emission techniques. The absorption intensity of metal complex increases as well as the emission intensity of protein molecules ability decreases due to the binding nature of ISNPV with BSA/HSA protein molecules. The binding nature of ISNPV with bio molecules such as CT-DNA, BSA and HSA was also validated using molecular docking approach.

Synthesis, characterization, thermal stability, electrochemical behavior, and antioxidant activity of new oxovanadium(iv) and iron(ii) tetradentate Schiff base complexes

Two new tetradentate oxovanadium(IV) and iron(II) Schiff base complexes have been prepared by the interaction of vanadyl(IV) and iron(III) acetylacetonate with the ligand obtained from the reaction of ethylenediamine and 5′-(N-methyl-N-phenylaminomethyl)-2′-hydroxyacetophenone in methanol. These complexes have been characterized by means of different spectroscopic techniques such as UV–visible, FT-IR, mass spectrometry, and elemental analysis. In addition, thermogravimetric (TG) and differential thermogavemetric analysis (DTG) have been utilized to investigate the thermal stability of these complexes. Results showed that both Schiff base complexes decompose in five consecutive stages, and a mechanism has been proposed for each stage of thermal decomposition. Thermogravimetric analysis has been carried out using four different heating rates of 5, 10, 15, and 20 °C min−1, and the kinetic parameters of these complexes have been calculated using the Kissinger method. Cyclic voltammetry has been employed to examine the electrochemical behavior of the two synthesized complexes in dimethyl sulfoxide (DMSO) at a glassy carbon electrode. Each of these complexes displayed one quasi-reversible single electron transfer peak near 0.255 V vs. saturated calomel electrode (SCE) for the V(V)–V(IV) couple and near −0.690 V vs. SCE for the Fe(III)–Fe(II) redox couples, respectively. Finally, the antioxidant activity of the newly prepared complexes has been investigated using the 2,2-diphenyl-1-picrylhydrazyle (DPPH) free radical scavenging assay. Results revealed that the oxovanadium Schiff base complex exhibits good antioxidant activity.

Synthesis of less acidic VO-salen complex grafted onto graphene oxide via functionalization of surface carboxyl groups for the selective oxidation of norbornene

Oxidation of norbornene was carried out over oxovanadium Schiff base complex grafted on –OH and –COOH modified graphene oxide (GO) as heterogeneous catalysts using 30% H2O2 as an oxidant and ethylene glycol as a solvent. Amongst them, the carboxylic acid group modified GO was found to be better for this transformation. The lower conversion with –OH modified catalyst was ascribed to the higher acidic nature of the catalyst. NH3-TPD study confirmed the less acidic sites on the –COOH modified catalyst and this less acidic nature and controlled addition of 30% H2O2 became the centre of action for this catalytic transformation. Absolute conversion of norbornene (100%) with 98.8% 2,3-epoxy norbornane was achieved at 60 °C in 1 h. This catalyst was recycled four times without significant loss of activity. This durability of the catalyst was believed to be due to strong π–π stacking interaction of GO sheet and an unsaturated ring of ligand and cyclic structure of ligand which protect the metal to leach out.

DNA/BSA binding of a new oxovanadium (IV) complex of glycylglycine derivative Schiff base ligand

In this study, a new oxovanadium (IV) Schiff base complex was synthesized by the reaction of {[5-(triethylammoniummethyl)salicylaldehyde]chloride}triethylammonium and vanadyl sulfate. The complex was characterized by elemental analysis, FT-IR and UV–Vis spectroscopy. The interaction between the complex and bovine serum albumin (BSA) was studied by absorption and emission titration methods. The quality of the spectral changes and the large calculated value of both the binding constant (Kb = 7.53 × 104 M−1) and the Stern-Volmer quenching constant (KSV = 7.65 × 104 M−1) proved the strong affinity of the complex to BSA. The static quenching mechanism was confirmed by comparing the calculated Kb values at four different temperatures. The negative changes in enthalpy and Gibbs free energy, proved that the BSA-complex binding is exothermic and spontaneous. The fluorescence data also indicated 1:1 binding stoichiometry of the complex on one binding site of BSA. Competitive experiments with site markers (phenylbutazone and ibuprofen) and synchronous measurements identified site I of BSA as the main binding site. Molecular docking results confirmed the binding pocket of site I (subdomain IIA) as the binding site. In the second part of the work, the binding of the complex to fish sperm DNA (FS-DNA) was investigated by UV–Vis absorption spectroscopy, fluorescence spectroscopy, viscosity measurement and cyclic voltammetry. The Stern-Volmer quenching and bimolecular quenching rate constants (KSV = 6.13 × 102 M−1, kq = 6.13 × 1010 M−1S−1) were calculated. Absorption and emission studies could present types of interactions for example groove binding and electrostatic. A minor changes in viscosity showed a groove binding mode. In cyclic voltammogram study, decrease in current and also shift of peak potentials positively after adding DNA supported a partial intercalation mode. Theoretical docking study proposed the minor groove as the main part for DNA-complex binding.

Mononuclear oxovanadium(IV) Schiff base complex: Synthesis, spectroscopy, electrochemistry, DFT calculation and catalytic activity

A new complex of oxovanadium, VOL has been synthesized from Schiff base ligand obtained by the condensation of o-phenylenediamine and 5-bromo-salicylaldehyde. All new compounds have been characterized by 1H NMR, IR spectra, UV–Vis spectroscopy, elemental analysis and mass spectrometry. The molar conductance data revealed that the metal complex is a non-electrolyte. Thermal analysis techniques (TGA/DTA) of the ligand and the complex were performed. The proposed structures for the free ligand and the corresponding vanadium complex were corroborated by the use of geometry optimization and conformational analysis. The solid state structure of complex VOL was fully determined by single crystal X-ray diffraction analysis.Similar electrochemical behavior for both the ligand and the corresponding complex have been observed by cyclic voltammetry (CV). The complex gave a metal-based one-electron quasi-reversible redox couple at 606 mV/SCE corresponding to the VOIV/VOV redox process which was consistent with the hydrodynamic voltammograms. Additional peaks in the CVs that were growing with the scan rate have been attributed to consecutive one-electron reduction of the ligand. The catalytic activity of the oxovanadium Schiff base complex VOL was tested in the oxidation reaction of cyclohexene. The efficiency of the catalyst was influenced by the nature of the oxidant. The results showed that the complex was highly active and selective for cyclohexenone in optimized conditions.

Spectroscopic, electrochemical, docking and molecular dynamics studies on the interaction of three oxovanadium (IV) Schiff base complexes with bovine serum albumin and their cytotoxicity against cancer

This study was designed to investigate the interaction of three oxovanadium (IV) Schiff base complexes with bovine serum albumin (BSA) by means of various spectroscopic and electrochemical methods along with molecular docking study and molecular dynamics simulations. Binding constants were estimated by fluorescence and UV-Vis spectroscopy. The results indicated a good affinity of the complexes for BSA in which furyl derivative had more activity. Molecular docking study showed that these complexes have the similar binding modes and located within subdomain IB in site III of BSA. The supporting of molecular docking and molecular dynamics results by experimental data, confirms the validity of the interactions data obtained by these methods. Biological activity against cancer cell showed that furyl derivative has higher activity than other complexes. Pharmaceutical analysis also showed that, these complexes potentially can be used as anticancer agents.

Crystal structure and bio-catalytic potential of oxovanadium(IV) Schiff base complexes derived from 2-hydroxy-4-(prop-2-yn-1-yloxy)benzaldehyde and alicyclic/aromatic diamines

Syntheses, structures, electronic properties and bio-catalytic activities of oxovanadium(IV) complexes [VOL1,VOL2] containing N,O-donor Schiff base ligands (L1=2,2′-{cyclohexane-1,2-diylbis[nitrilo(E)methylylidene]}bis[5-(prop-2-yn-1-yloxy)phenol] and L2=2,2′-{1,2-phenylenebis[nitrilo(E)methylylidene]}bis[5-(prop-2-yn-1-yloxy)phenol]) are presented. The single crystal XRD analyses show distorted square pyramidal based geometry for VOL1 and VOL2. The structure and electronic properties of the complexes were analyzed using DFT and TD-DFT calculations. The topological analysis of the electron density was carried out to analyze the bonding nature in the complexes. The bio-relevant catalytic activities (catecholase, phenoxazinone synthase and haloperoxidases) of the complexes have been investigated. The X-band EPR studies show that the oxidation of 3,5-DTBC and 2-aminophenol catalyzed by VOL1 and VOL2 are due to the formation of ligand-centered radical pathway. DFT studies support the ligand-centered radical formation in the reduced metal complexes with significant elongation of the imine bond length.

Ni(II) and V(IV) Schiff base complexes derived from 2,2′-dimethylpropandiamine: the crystal structure, electrochemical properties and catalytic activities in oxidation of sulfides

Tetradentate Schiff base (H2L) derived from 2,2′-dimethylpropandiamine and its nickel(II) and oxo-vanadium(IV) complexes (NiL, VOL) have been prepared and characterized. The crystal structure of NiL has been determined. The reported structure contains two molecules of the complex revealing slightly different conformation and the coordination sphere around nickel is distorted square planar. The electrochemical properties of the Ni and oxo-vanadium Schiff base complexes were investigated in CH3CN by cyclic voltammetry. The catalytic activities of the complexes were studied in the oxidation of sulfides in ethanol. Under the optimized reaction conditions, in the presence of NiL, 89% and VOL, 100% conversion of methyl phenyl sulfide with 100% selectivity for sulfoxide were obtained.

Renewable waste rice husk grafted oxo-vanadium catalyst for oxidation of tertiary amines to N-oxides

Low cost renewable waste rice husks (RH) have been used as a support for grafting of an oxo-vanadium Schiff base via covalent attachment for the oxidation of tertiary amines to N-oxide.

A new oxovanadium(IV) complex containing an O,N-bidentate Schiff base ligand: Synthesis at ambient temperature, characterization, crystal structure and catalytic performance in selective oxidation of sulfides to sulfones using H2O2 under solvent-free conditions

A new bidentate ON Schiff base ligand, HL, was synthesized by simple condensation reaction of isopropylamine and salicylaldehyde. Then by reaction of HL and VO(acac)2 in the ratio of 2:1 at ambient temperature, a new oxovanadium(IV) Schiff base complex, VOL2, was synthesized. The Schiff base ligand and its oxovanadium(IV) complex were characterized by elemental analyses, FT-IR, 1H NMR, 13C NMR and UV–visible spectroscopies. The crystal structure of oxovanadium(IV) complex, VOL2, was also determined by single crystal X-ray analysis. The vanadium center in this structure is coordinated to two bidentate Schiff base ligands with the two nitrogen and two phenolate oxygen atoms in equatorial positions and one oxo oxygen in the axial position to complete the distorted trigonal bipyramidal N2O3 coordination sphere.Catalytic performance of the VOL2 complex was studied in the selective oxidation of thioanisole with the green oxidant 35% aqueous H2O2 under solvent-free conditions and under organic solvents (EtOH, CHCl3, CH2Cl2, DMF, CH3CN, EtOAc) as a model. Due to better catalytic performance of the VOL2 complex under solvent-free conditions, this complex used for the oxidation of the different sulfides to the corresponding sulfones under solvent-free conditions. The use of hydrogen peroxide as oxidant and the absence of solvent makes these reactions interesting from environmental and economic points of view.

Oxovanadium(IV) salicylidene Schiff base complex anchored on mesoporous silica MCM-41 as hybrid materials: a robust catalyst for the oxidation of sulfides

Oxovanadium(IV) Schiff base complex have been anchored onto the surface of purely siliceous MCM-41 and tested for its activity as catalyst for the oxidation of sulfides. This catalyst could alter this oxidation reaction extremity, exhibiting excellent yields with 100 % selectivity. The intercalation of the complex inside the silica matrix was supported by various characterization techniques like X-ray diffraction, differential thermogravimetric (TG-DTA), BET measurements, UV–Vis diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy (FT-IR). The stability of the catalyst during the course of the reaction was confirmed from its post catalytic FT-IR and XRD analysis. The catalyst could be reused five times without notable loss of its catalytic activity and efficiency which indicates that the metal-Schiff base moiety is intact and the coordination environments are not altered during the reaction.

Co(II), Fe(III) or VO(II) Schiff base metal complexes immobilized on graphene oxide for styrene epoxidation

Cobalt(II), iron(III) or oxovanadium(II) Schiff base metal complexes have been covalently grafted onto graphene oxide (GO) previously functionalized with 3‐aminopropyltriethoxysilane. Potential catalytic behaviors were tested in the epoxidation of styrene, using air as the oxidant. The catalysts were characterized using infrared (IR) and Raman spectroscopies, thermogravimetric analyses, inductively coupled plasma atomic emission spectrometry (ICP‐AES), X‐ray diffraction, nitrogen adsorption–desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). IR spectroscopy, thermogravimetric analyses and ICP‐AES confirmed the successful incorporation of the metal Schiff base complexes onto GO. X‐ray diffraction, nitrogen adsorption–desorption, Raman spectroscopy, SEM and TEM showed the intact structure of the GO. Co-GO and Fe-GO showed high styrene conversion (90.8 versus 86.7%) and epoxide selectivity (63.7 versus 51.4%). Nevertheless, VO-GO showed poorer catalytic performance compared with Co-GO and Fe-GO. The recycling results of these heterogeneous catalysts showed good recoverability without significant loss of activity and selectivity within four successive runs. Copyright © 2015 John Wiley & Sons, Ltd.

Sodium borohydride reduction of aldehydes catalyzed by an oxovanadium(IV) Schiff base complex encapsulated in the nanocavity of zeolite-Y

Selective reduction of a wide range of aromatic and aliphatic aldehydes to the corresponding alcohols with NaBH4 was achieved in the presence of an oxovanadium(IV) Schiff base complex encapsulated in the nanopores of zeolite Y (VOL-Y). For most of the aldehydes, a conversion of 100% was observed after less than 5min. High chemoselectivity of the reduction for aldehydes over ketones was verified by a competitive reduction between 4-methylbenzaldehyde and acetophenone.

Immobilized oxo-vanadium Schiff base on graphene oxide as an efficient and recyclable catalyst for the epoxidation of fatty acids and esters

Oxo-vanadium Schiff base was covalently immobilized onto chemically functionalized graphene oxide (GO) using 3-aminopropyltriethoxysilane as a coupler. The loading of vanadyl Schiff base onto GO nanosheets was confirmed by FTIR, XRD, TGA, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The synthesized heterogeneous catalyst was found to be efficient and selective for the epoxidation of fatty acids and esters using t-butyl hydroperoxide (TBHP) as an oxidant. Interestingly, the immobilized catalyst showed a higher catalytic efficiency than the homogeneous vanadyl acetylacetonate. The recycling experiment results indicated that the catalyst was highly stable and maintained very high activity, and selectivity even after being used for six cycles.

Green oxidation of olefins and methyl phenyl sulfide with hydrogen peroxide catalyzed by an oxovanadium(IV) Schiff base complex encapsulated in the nanopores of zeolite-Y

Oxovanadium(IV) complex of a Schiff base ligand derived from 2,4-dihydroxyacetophenone and 2,2′-dimethylpropanediamine has been encapsulated in the nanopores of zeolite-Y by flexible ligand method and characterized by metal analysis, IR spectroscopic studies and X-ray diffraction patterns. The encapsulated complex [VOL-Y] catalyzes the oxidation of various olefins and methyl phenyl sulfide using hydrogen peroxide as a green oxidant in good yield. Under the optimized reaction conditions, in the presence of VOL-Y, 86 % conversion of cyclooctene with 100 % selectivity for epoxide and 51 % conversion for methyl phenyl sulfide with 92 % selectivity for sulfone were obtained.

Rod shaped oxovanadium(IV) Schiff base complexes: Synthesis, mesomorphism and influence of flexible alkoxy chain lengths

A series of oxovanadium(IV) complexes of bidentate [N,O] donor Schiff-base ligands of the type [VO(L)2], [L=N-(4-n-alkoxysalicylaldimine)-4′-octadecyloxyaniline, n=8, 10, 12, 14, 16 and 18] have been synthesized. The compounds were characterized by elemental analyses, Fourier transform infrared spectroscopy (FTIR), 1H, 13C nuclear magnetic resonance (NMR), ultraviolet–visible spectroscopy (UV–Vis), and fast atom bombardment (FAB) mass spectrometry. The mesomorphic behavior of the compounds was studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The ligands and complexes are all thermally stable exhibiting smectic mesomorphism. The ligands 8-OR to16-OR show SmC phase at ∼113–118°C and an unidentified SmX phase reminiscent of soft crystal at ∼77–91°C whereas the complexes all showed SmA phases. Interestingly the complexes with C10 and C12 alkoxy chain length exhibited additionally SmC phases also. The melting points of the ligands linearly increases whereas mesophase to isotropic transition temperature decreases as a function of increasing carbon chain length of alkoxy arm while no trend was apparently noticeable for the complexes.

Oxovanadium (IV) Schiff base complex immobilized on CPS microspheres as heterogeneous catalyst for aerobic selective oxidation of ethyl benzene to acetophenone

In this work, chloromethylated crosslinked polystyrene microspheres (CMCPS microspheres) were used as starting carrier, and a new immobilized bidentate Schiff base oxovanadium (IV) complex catalyst was prepared. The chloromethyl groups of CMCPS microspheres were first transformed into aminomethyl groups via Delepine reaction with hexamethylene tetramine (HMTA) as reagent, obtaining aminomethylated (AM) microspheres AMCPS. And then the Schiff base reaction between the primary amino group of AMCPS microspheres and salicylaldehyde (SA) was allowed to be conducted, resulting in Schiff base-type resin microspheres, SAAM-CPS, on which bidentate Schiff base ligand SAAM were chemically anchored. Subsequently, the coordination reaction between the ligand SAAM of SAAM-CPS microspheres and vanadyl sulfate (VOSO4) was carried out, obtaining a new immobilized bidentate Schiff base-type oxovanadium (IV) complex, CPS-[VO(SAAM)2] microspheres, namely a new heterogeneous oxovanadium (IV) complex catalyst was prepared. On the basis of fully characterizing the microspheres CPS-[VO(SAAM)2], they were used in the catalytic oxidation of ethyl benzene with molecular oxygen. The experimental results show that in the oxidation reaction of ethylbenzene with molecular oxygen as oxidant, the heterogeneous oxovanadium (IV) complex catalyst, CPS-[VO(SAAM)2], has high catalytic activity and excellent catalytic selectivity. Under the mild conditions such as at ordinary pressure of dioxygen and at a relatively low temperature of 110°C, ethyl benzene can be transformed to acetophenone as a single product with a yield of 43%. It was found that the reaction temperature and the used amount of the solid catalyst effect on the oxidation reaction greatly. The catalyst CPS-[VO(SAAM)2] has excellent recycle and reuse property.