Synthesis, ab initio calculations, thermal, thermodynamic and antioxidant properties of some oxovanadium(IV) complexes containing N2O2 set of donor atoms

The formation constants of some oxovanadium(IV) binary complexes containing Schiff bases resulting from condensation of salicylaldehyde with aniline and with its derivatives were determined spectophotometrically. The synthesized compounds were characterized by analytical and different physico-chemical techniques like ¹H NMR, IR, elemental analysis, mass and UV-Vis spectral studies. The IR spectra affirm that coordination takes place through azomethine nitrogen and phenolate oxygen. Three of the VO(IV) Schiff base complexes i.e. bis(salicylideneaniline)oxovanadium(IV), [VO(L¹)₂], bis(salicylidene-4-methoxyaniline) oxovanadium (IV), [VO(L²)₂] and bis(salicylidene-4-cyanoaniline)oxovanadium(IV), [VO(L¹⁰)₂], were studied by thermogravimetry in order to evaluate their thermal stability and thermal decomposition pathways. The number of steps and, in particular, the starting temperature of decomposition of these complexes depends on the equatorial ligand. The complexes screened for antioxidant activity and the ab initio calculations were carried out to determine the structural and the geometrical properties of a typical vanadyl salicylideneaniline complex, [VO(L¹)₂].     

Synthesis, Characterization and the Effect of Glucose-lowering of Guanidino Acid Oxovanadium（Ⅳ） Complexes

Two guanidino acid oxovanadium(Ⅳ) complexes have been synthesized. Preliminary tests in vivo have shown that the two title complexes all display lowering glucose activity in vivo to STZ-rats. The effect of glucose-lowering of guanidino acetic acid oxovanadium(Ⅳ) complex in vivo is higher than that of guanidino propanoic acid oxovanadium(Ⅳ) complex.     

Glucose-lowering Activity of Amino Acid-N-phosphonic Acid Oxovanadium Complexes and Its Interaction with DNA

Vanadium has well-documented lowering glucose properties both in vitro and in vivo.The design of newoxovanadium(IV) coordination compounds,intended for use as insulin-enhancing agents in the treatment of diabe-tes mellitus,can potentially benefit from a synergistic approach,in which the whole complex has more than an ad-ditive effect from its component parts.Biological testing with oxovanadium(IV) organic phosphonic acid,for insu-lin-enhancing potential included acute administration,by oral garage in streptozotocin (STZ) diabetic rats.Thecomplexes of oxovanadium(IV) amino acid-N-phosphonic acid exhibit higher lowering glucose activity in vivo.Theinteraction of the complexes of oxovanadium(IV) amino acid-N-phosphonic acid with DNA was investigated byagarose gel electrophoresis.The results indicated that these complexes have strong interaction with DNA.     

Glucose-lowering A ivity of Amino Acid- phosphonic Acid Oxovanadium Complexes and Its Interaction with DNA

Vanadium has well-documented lowering glucose properties both in vitro and in vivo. The design of new oxovanadium（IV） coordination compounds, intended for use as insulin-enhancing agents in the treatment of diabetes mellitus, can potentially benefit from a synergistic approach, in which the whole complex has more than an additive effect from its component parts. Biological testing with oxovanadium（IV） organic phosphonic acid, for insulin-enhancing potential included acute administration, by oral gavage in streptozotocin （STZ） diabetic rats. The complexes of oxovanadium（IV） amino acid-N-phosphonic acid exhibit higher lowering glucose activity in vivo. The interaction of the complexes of oxovanadium（IV） amino acid-N-phosphonic acid with DNA was investigated by agarose gel electrophoresis. The results indicated that these complexes have strong interaction with DNA.     

Insulin-enhancing vanadium(III) complexes

Simple, high-yield, large-scale syntheses of the V(III) complexes tris(maltolato)vanadium(III), V(ma)3, tris(ethylmaltolato)vanadium(III), V(ema)3, tris(kojato)vanadium(III) monohydrate, V(koj)3-H2O, and tris(1,2-dimethyl-3-hydroxy-4-pyridinonato)vanadium(III) dodecahydrate, V(dpp)3-12H2O, are described; the characterization of these complexes by various methods and, in the case of V(dpp)3-12H2O, by an X-ray crystal structure determination, is reported. The ability of these complexes to normalize glucose levels in the STZ-diabetic rat model has been examined and compared with that of the benchmark compound BMOV (bis(maltolato)oxovanadium(IV)), an established insulin-enhancing agent.     

Synthesis, characterization and antimicrobial activity of 3d transition metal complexes of a biambidentate ligand containing quinoxaline moiety

A new series of oxovanadium(IV), chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), and copper(II) complexes of the 3-hydrazino quinoxaline-2-one (HQO) were prepared and characterized. The ligand exhibits biambidenticity. It behaves as a bidentate ON donor in oxovanadium(IV), iron(III) and copper(II) complexes and as a bis bidentate ONNN donor in chromium(III), manganese(II), cobalt(II) and nickel(II) complexes. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, thermal, infrared, ¹H NMR, electronic spectra, magnetic susceptibility and conductivity measurements. An octahedral geometry was suggested for all the complexes. All the complexes show subnormal magnetic moments. The ligand, HQO, and its complexes were tested against one strain Gram +ve bacteria (Staphylococcus aureus), Gram −ve bacteria (Escherichia coli). The prepared metal complexes exhibited higher antimicrobial activities than the parent ligand.     

Synthesis and Spectral Investigation of Some Transition Metal Complexes Containing Pentadentate Macroacyclic <Emphasis Type="Italic">NNNNN</Emphasis>-donor Schiff Base Ligands

A new Schiff base, 2,6-diacetylpyridine bis(2-hydrazinobenzothiazole) (DPHB), has been designed, and synthesized by the condensation of 2,6-diacetylpyridine with 2-hydrazinobenzothiazole, and structurally characterized. Copper(II), cobalt(II), nickel(II), manganese(II), zinc(II), cadmium(II) and oxovanadium(IV) complexes of DPHB have been synthesized for the first time. Their structures have been elucidated on the basis of elemental analyses, conductance measurements, magnetic properties, spectral (i.r., ¹H-n.m.r., u.v.–vis., e.p.r. and FAB-mass) and thermal studies. The complexes exhibit an octahedral geometry around the metal centre. The conductance data of all the complexes suggest them to be 1:1 electrolytes. The X-band e.p.r. spectra of the copper(II) and oxovanadium(IV) complexes in the polycrystalline state at room (300 K) and liquid nitrogen temperature (77 K) were recorded and their salient features are reported. Thermal stabilities of the manganese(II) and zinc(II) complexes have been studied.     

Asymmetric sulfoxidation of phenacyl phenyl sulfide using chiral vanadium(IV) complexes

Asymmetric sulfoxidation of phenacyl phenyl sulfide was performed in the presence of bis(acetylacetonanto) oxovanadium(IV) complexes with chiral Schiff bases, which were generated in situ. Chlorine dioxide and hydrogen peroxide as oxidants were compared.     

Coordination chemistry and insulin-enhancing behavior of vanadium complexes with maltol C6H6O3 structural isomers

Syntheses of vanadium complexes using the naturally occurring ligands isomaltol (Hima) and allomaltol (Hama), as well as a newly synthesized, potentially tetradentate diaminodipyrone [H(2)(en(ama)(2)], are reported. Complete characterization of the resulting compounds [trans-VO(ima)(2)(H(2)O), VO(ama)(2), V(ima)(3), V(ama)(3) and VO(en(ama)(2))], including X-ray crystallography analyses for trans-VO(ima)(2)(H(2)O) and V(ima)(3), are presented herein. Potentiometric titrations (25 degrees C, I = 0.16 M NaCl) were used to measure stability constants in the V(IV)-Hima system; these data were compared to previous data collected on the V(IV)-L (L = Hma, Hama) systems. The in vivo efficacy of these compounds to lower the blood glucose levels of STZ-diabetic rats was tested; all but VO(en(ama)(2)) produced significant decreases in plasma glucose levels. The results were compared to those of the benchmark compound BMOV [VO(ma)(2), bis(maltolato)oxovanadium(IV)], a known insulin-enhancing agent.     

Synthesis,spectral characterization,and antidiabetic study of new furan-based vanadium(IV) complexes

We have synthesized furan-based vanadium complexes, bis(5-nitrofuran-2-carboxylato)oxovanadium(IV) – [VO(5NF)₂], bis(1-furan-2-yl-ethanonato)oxovanadium(IV) sulfate – [VO(2AF)₂]SO₄, and bis(5-methyl-2-furalato)oxovanadium(IV) sulfate – [VO(MFFA)₂]SO₄ possessing [VO(O₄)] coordination mode. These complexes are characterized by physico-chemical and spectroscopic methods. Based on electron paramagnetic resonance parameters, the proposed geometry is close to a distorted square pyramid. Animal study was carried out using standard protocol and the complete profile of glucose, protein, and total cholesterol levels were analyzed followed by an oral glucose tolerance test.     

Spectroscopic and Electrochemical Behavior of the Methyl and Ethyl Derivatives of Bis(acetylacetonato) oxovanadium(IV)

The infrared, Raman and electronic spectra of the oxovanadium (IV) complexes of the 3‐methyl and 3‐ethyl substituted acetylacetone were recorded and discussed in detail, in comparison with that of the bis(acetylacetonato) complex and on the basis of the known structural data of these compounds. The electrochemical behavior of the three complexes was investigated by cyclic voltammetry in DMSO solutions, and the mechanism of the involved processes is briefly discussed.     

双（α－呋喃甲酸）氧钒的合成和抗糖尿病活性研究

设计和合成了一种新型的有机羧酸氧钒配合物双（α－呋喃甲酸）氧钒。运用 元素分析、红外光谱、紫外光谱、质谱和核磁共振氢谱对配合物的结构进行了初步 确证。在实验性动物模型上研究了这个配合物的初步毒性和降血糖作用。结果表明 ：双（α－呋喃甲酸）氧钒具有活性高，安全性好的优点，对糖尿病的治疗显示出 潜在的开发应用前景。     

Vibrational spectra of bis(maltolato)oxovanadium(IV): a potent insulin mimetic agent

The FTIR and FT-Raman spectra of the oxovanadium(IV) complex of 3-hydroxy-2-methyl-4-pyrone (maltol) bis(maltolato)oxovanadium(IV) were recorded and briefly discussed by comparison with the spectra of uncoordinated maltol and with some related species.     

DSC determination of the sublimation enthalpy of bis(2,4-pentanedionato)oxovanadium(IV) and tetrakis(2,4-pentanedionato)zirconium(IV)

The sublimation enthalpies of bis(2,4-pentanedionato)oxovanadium(IV) and tetrakis(2,4-pentanedionato)zirconium(IV) have been determined by differential scanning calorimetry as 140.7 ± 4.0 and 132.0 ± 6.8 kJ mol⁻¹, respectively. The fusion enthalpy of the latter complex has also been determined as 33.68 ± 2.5 kJ mol⁻¹. A summary of “selected” sublimation enthalpy data for first-row transition metal acetylacetonate complexes is included.     

Vanadium-Komplexe mit dreizähnigen diaciden Liganden. Die Kristallstrukturen von Bis[acetylacetonthiobenzoylhydrazonato(2-)]vanadium(IV), Methoxo-oxo-[salicylaldehydthiobenzoylhydrazonato(2-)]vanadium(V) und Methoxo-oxo-[salicylaldehydbenzoylhydrazonato(2-)]methanolvanadium(V)

Vanadium Complexes with Tridentate Diacidic Ligands. The Crystal Structures of Bis[acetylacetonato-thiobenzoylhydrazonato(2-)]vanadium(IV), Methoxo-oxo-[salicylaldehyd-thiobenzoylhydrazonato(2-)]vanadium(V), and Methoxo-oxo-[salicylaldehydbenzoylhydrazonato(2-)]methanol Vanadium(V) By template reactions of bis(acetylacetonato)oxovanadium(IV) and bis(salicylaldehydato)oxo-vanadium(IV), respectively, with benzoylhydrazine, thiobenzoylhydrazine, and 2-aminophenol the vanadium(IV) complexes V(LLL)₂ of tridentate azomethine ligands LLL were synthesized. The complexes were characterized by EPR spectroscopy and by absorption spectroscopy. From the complex V(LLL)₂ ( 1 ), in which LLL is acetyl-aceton-thiobenzoydrazonate(2-), the crystal structure analysis was solved. The vanadium atom in 1 is coordinated trigonal-prismatically by two N, 0 and S atoms. Furthermore, the 0x0 vanadium(V) complexes[VO(LLL)(OCH,)] (6) with LLL = salicylaldehyd-thio-benzoylhydrazonato(2-) and [VO(LLL)(OCH₃)· -CH₃OH] (7) with LLL = salicylaldehydbenzoylhydrazonato(2-) were identified by X-ray diffraction and by IR spectroscopy in the reaction products. Crystallographic data for 1, 6 , and 7 see ?Inhaltsübersicht”?.     

Synthesis and mesomorphic properties of some platinum(II) and oxovanadium(IV) complexes

The synthesis and mesomorphic properties of a homologous series of N-(2-hydroxy-4-n-alkoxybenzylidene)-4'-n-decylphenylanilines and their platinum(II) and oxovanadium(IV) complexes are reported. All the ligands and their metal chelates exhibit enantiotropic mesophases, predominantly smectic A and smectic C phases. The transition temperatures and enthalpies have been determined for most of the compounds. The platinum(II) complexes have higher melting points and mesophase thermal stabilities. However, the oxovanadium(IV) complexes have a wider thermal range for the mesophase. Both platinum(II) and oxovanadium(IV) complexes containing only a chain on the biphenyl moiety exhibit a nematic phase.     

Structural models of vanadate-dependent haloperoxidases and their reactivity

Vanadium(V) complexes with hydrazone-based ONO and ONN donor ligands that partly model active-site structures of vanadate-dependent haloperoxidases have been reported. On reaction with [VO(acac)₂] (Hacac = acetylacetone) under nitrogen, these ligands generally provide oxovanadium(IV) complexes [VO(ONO)X] (X = solvent or nothing) and [VO(acac)(ONN)], respectively. Under aerobic conditions, these oxovanadium(IV) species undergo oxidation to give oxovanadium(V), dioxovanadium (V) or μ-oxobisoxovanadium(V) species depending upon the nature of the ligand. Anionic and neutral dioxovanadium(V) complexes slowly deoxygenate in methanol to give monooxo complexes [VO(OMe)(MeOH)(ONO)]. The anionic complexes [VO₂(ONO)]^- can also be convertedin situ on acidification to oxohydroxo complexes [VO(OH)(HONO)]⁺ and to peroxo complexes [VO(O₂)(ONO)]^-, and thus to the species assumed to be intermediates in the haloperoxidases activity of the enzymes. In the presence of catechol (H₂cat) and benzohydroxamic acid (H₂bha), oxovanadium (IV) complexes, [VO (acac)(ONN)] gave mixed-chelate oxovanadium(V) complexes [VO(cat)(ONN)] and [VO(bha)(ONN)] respectively. These complexes are not very stable in solution and slowly convert to the corresponding dioxo species [VO₂(ONN)] as observed by⁵¹V NMR and electronic absorption spectroscopic studies.     

Characterization of the Potent Insulin Mimetic Agent Bis(maltolato)oxovanadium(IV) (BMOV) in Solution by EPR Spectroscopy

Bis(maltolato)oxovanadium(IV) (abbreviated BMOV or VO(ma)(2)) has been characterized by electron paramagnetic resonance (EPR) spectroscopy in CH(2)Cl(2), H(2)O, MeOH, and pyridine at both room and low temperatures. Spin Hamiltonian parameters for mono- and bis(maltolato)oxovanadium(IV) complexes [VO(ma)](+) (=[VO(ma)(H(2)O)(n)()](+), n = 2 or 3) and VO(ma)(2) (Hma = 3-hydroxy-2-methyl-4-pyrone, maltol) have been obtained by computer simulation (SOPHE). Configurations of solvated vanadyl/maltol complexes, VO(ma)(2)S, in solution (S = solvent) are proposed on the basis of a comparison of their hyperfine coupling constants with those obtained for related vanadium(IV) compounds in the literature. Whereas at room temperature pyridine coordinates to VO(ma)(2) in a position cis to the oxo ligand (cis isomer), in H(2)O or in MeOH solvated and unsolvated cis and trans adducts of VO(ma)(2) are all formed, with the cis isomer dominant. As expected, the coordinating ability was found to be in the order py > H(2)O approximately MeOH > CH(2)Cl(2). In aqueous solutions at room temperature and neutral pH, cis- and trans-VO(ma)(2)(H(2)O) complexes are present as major and minor components, respectively.     

Thermal decomposition of oxovanadium(IV) complexes with substituted pyridines

The kinetics of decomposition of solid complexes of bis(dibenzoylmethanato) oxovanadium(IV) with pyridine and several methyl, dimethyl and aminopyridines has been studied using differential scanning calorimetry. Activation energies have been determined and, in general show an increase with increasing basicity of the ligands. A linear relationship exists between pK_b values of the bases and the temperatures for the decomposition, except for the complexes obtained with 4 aminopyridine and 4 methylpyridine. These complexes are less stable than expected from the basicity of the ligands. These observations are discussed in terms of the nature of the metalligand bond.     

Adducts of bis(8-quinolinate) oxovanadium(IV) with organic bases

We report the synthesis and study of bis(8-quinolinol) oxovanadium(IV) adducts with pyridine and substituted pyridines. These complexes were identified by IR and electronic spectra, magnetic susceptibility measurements and analytical data. The relation between the basicity of the pyridines and the VO stretching frequency has also been studied. The effects of steric hindrance and the inductive effects exercised by the functional groups, amino and methyl of the pyridine, in the formation of the adducts are discussed.