Metallokinetic characteristics of antidiabetic bis(allixinato)oxovanadium(IV)-related complexes in the blood of rat

The antidiabetic effect of vanadium is a widely accepted phenomenon; some oxovanadium(IV) complexes have been found to normalize high blood glucose levels in both type 1 and type 2 diabetic animals. In light of the future clinical use of these complexes, the relationship among their chemical structures, physicochemical properties, metallokinetics, and antidiabetic activities must be closely investigated. Recently, we found that among bis(3-hydroxypyronato)oxovanadium(IV) [VO(3hp)₂] related complexes, bis(allixinato)oxovanadium(IV) [VO(alx)₂] exhibits a relatively strong hypoglycemic effect in diabetic animals. Next, we examined its metallokinetics in the blood of rats that received five VO(3hp)₂-related complexes by the blood circulation monitoring–electron paramagnetic resonance method. The metallokinetic parameters were obtained from the blood clearance curves based on a two-compartment model; most parameters, such as area under the concentration curve and mean residence time, correlated significantly with the in vitro insulinomimetic activity in terms of 1/IC₅₀ (IC₅₀ is the 50% inhibitory concentration of the complex required for the release of free fatty acids in adipocytes) and the lipophilicity of the complex (log P _com). The oxovanadium(IV) concentration was significantly higher and the species resided longer in the blood of rats that received VO(alx)₂ than in the blood of rats that received VO(3hp)₂ or bis(kojato)oxovanadium(IV); VO(alx)₂ also exhibited higher log P _com and 1/IC₅₀ values. On the basis of these results, we propose that the introduction of lipophilic groups at the C2 and C6 positions of the 3hp ligand is an effective method to enhance the hypoglycemic effect of the complexes, as supported by the observed in vivo exposure and residence in the blood.     

Preparation and characterization of oxovanadium(IV), acetatomanganese(III), chloroiron(III), nickel(II), copper(II), zinc(II) and palladium(II) complexes of 3,3′-(1,2-phenylenediimino)diacrolein

The oxovanadium(IV), acetatomanganese(III), chloroiron(III), nickel(II), copper(II), zinc(II) and palladium(II) of 3,3′-(1,2-phenylenediimino)diacrolein were prepared and investigated by means of mass, electronic, vibrational, NMR and ESR spectroscopy as well as magnetic susceptibility measurements. The acetatomanganese(III) and chloroiron(III) complexes were confirmed to be of high spin type. The absorption bands appearing in the energy range greater than 23 000 cm⁻¹ were attributed to π→π^* transitions within a ligand molecule and charge- transfer transitions from metal to ligand. The metal complexes assume the square-planar configuration type since the ligand-field bands were detected in the 12 700–18 500 cm⁻¹ region. Strong bands appearing at 1601 and 1627 cm⁻¹ were assigned to the CC and CO stretching vibrational modes, respectively, and were shifted to lower frequency upon metal-coordination. A VO stretching band was observed at 982 cm⁻¹ for the oxovanadium(IV) complex and a CO stretching band was observed at 1547 cm⁻¹ for the acetatomanganese(III) complex. Upon complex formation the amine proton signal is found to vanish and the aldehydic methine proton signal in the lowest field is shifted upfield for the nickel(II), zinc(II) and palladium(II) complexes. ¹³C NMR spectra support the coordination structure of the complexes which is revealed by ¹H NMR spectra. As judged by the spin Hamiltonian parameters, the oxovanadium(IV) complex is of a square- planar type with an unpaired electron in the d_xy orbital and the copper(II) complex assumes a distorted square-planar coordination due to the presence of five- and six-membered chelate rings with an unpaired electron in the d_x2−y2 orbital.     

Structural characterization and electrochemical behavior of oxovanadium(V) complexes with N-salicylidene hydrazides

The hydrazone ligands derived from salicylaldehyde and aliphatic carbonic acid hydrazides react with equimolecular amounts of ammonium metavanadate and 8-hydroxyquinoline in refluxing methanol to yield oxovanadium(V) complexes. The synthesis can alternatively be performed starting from [VO(acac)₂] followed by aerial oxidation to form the corresponding oxovanadium(V) complexes. The molecular structures determined by X-ray crystallography feature in all cases a oxovanadium(V) moiety in an distorted octahedral arrangement with an oxygen and nitrogen rich environment. The obtained compounds posses very good solubility in organic solvents, permitting electrochemical investigation. Square wave voltammetric measurements revealed two reversible one-electron reduction steps at 0.355 and −1.638 V. The reduction of the oxovanadium(V) complexes to the corresponding vanadium(IV) species occurs at relatively positive potential, which is independently verified by ESR spectroscopy. While the second reduction step appears to be accompanied by a pre-wave exhibiting an unusual frequency dependence which can be attributed to ligand addition/elimination equilibria related to the 8-hydroxyquinoline coligand. The oxovanadium(V) complexes can be converted into the corresponding cis-dioxovanadium(V) compounds by reaction with aqueous NaOH. ⁵¹V NMR monitoring of this reaction reveals that one equivalent of base results in a full conversion with the cis-dioxovanadium(V) complex being the only species present in solution.     

Reactions of Cr(III) tetraphenylporphyrin complex with superoxide ion: ESR evidence for the formation of a new superoxide adduct of Cr(IV) porphyrinate and its reactive character

The electron spin resonance (ESR) spectrum of the reaction product of superoxide ion, O₂⁻, with chloro-5,10,15,20-tetraphenylporphyrinatochromium(III) [Cr(III)(TPP)Cl] shows strong hyperfine interactions with the metal nucleus and the metal ligand, indicating the formation of a superoxide adduct, Cr(IV)(TPP)(Cl)(O₂⁻). The formation of this superoxide adduct was also confirmed by UV-Vis spectroscopy. The reactive character of this superoxide adduct was investigated by ESR spectrometry. It was found that Cr(IV)(TPP)(Cl)(O₂⁻) can oxidize t-butylamine and triphenylphosphine to give the corresponding radical species, respectively, but not pyridine, 4-cyanopyridine or imidazole. These results indicate that the reactive character of Cr(IV)(TPP)- (Cl)(O₂⁻) resembles that of the free superoxide ion.     

Preparation and spectroscopic properties of oxovanadium(IV) and dioxomolybdenum(VI) complexes with tetraaza[14]annulenes containing pyridine rings

The reaction of 5,14-dihydro-7,16-diethyl-(E)- or -(Z)-dipyrido [b, i] [ 1,4,8,11 ] tetraazacyclotetradecine with vanadium(III) chloride led to the corresponding oxovanadium(IV) complexes, while reaction with tetracarbonylbis(piperidine)molybdenum(O) gave the corresponding dioxomolybdenum(VI) complexes. The oxovanadium(IV) complexes showed mass spectra with prominent parent peaks in the El mode. On the other hand the FD mass spectra for the dioxomolybdenum(VI) complexes exhibited the expected parent and parent-O peaks. A VO stretching band was observed at ca. 970 cm⁻¹ for the oxovanadium(IV) complexes. The dioxomolybdenum(VI) complexes had strong bands at 855 and 885 cm⁻¹ in the NaCl region, which are attributable to the MoO symmetric and asymmetric stretching modes. The absorption bands observed above 20 000 cm⁻¹ range were attributed to the CT and π→π^* transitions. Judging from the spin Hamiltonian parameters, the oxovanadium(IV) complexes are of square-planar types with an unpaired electron in the d_xy orbital. The downfield shifts for the dioxomolybdenum(VI) complexes are much larger in magnitude than those observed for the corresponding oxochromium(IV) complexes. This is primarily dependent on the fact that the magnitude of the positive charge fed by molybdenum(VI) is greater than that by chromium(IV).     

Oxovanadium(IV) and dioxouranium(VI) complexes with thiocarbohydrazones

Oxovanadium(IV) and dioxouranium(VI) complexes with thiocarbohydrazones have been prepared in an ethanolic medium and characterised by elemental analysis and molecular weight determination. They have 1:1 stoichiometry. The IR observations suggest that the ligands have coordinated through azomethine nitrogen atoms and reacted through hydroxy groups. The v(MN) and v(MO) vibrations have been assigned. The PMR spectral information supports the IR inference. The oxovanadium(IV) complexes show magnetic moments in the range of 1.74–1.94 B.M. The electronic spectra have been interpreted in the light of the BG model. Various NSH parameters have been calculated. The ESR spectra also render support for the spectral information. On the basis of this information it is suggested that oxovanadium(IV) complexes exhibit coordination number five and dioxouranium coordination number six.     

Bactericidal activity of different oxovanadium(IV) complexes with Schiff bases and application of chelation theory

Oxovanadium(IV) complexes have been synthesized and characterized the general composition [VOL(A)], where H₂L = salicylidene-o-aminothiophenol A¹ = bis(benzylidene)ethylenediamine, A² = bis(acetophenone)ethylenediamine, A³ = 2,2′-bipyridylamine, A⁴ = bis(benzylidene) ? 1,8-diaminonaphthalene, A⁵ = thiophene-o-carboxaldeneaniline and A⁶ = thiophene-o-carboxaldene-p-anisidine. Spectral studies indicate that the oxovanadium(IV) complexes assume a six-coordinate octahedral geometry. The antibacterial activities of the complexes against Salmonella typhi, Escherichia coli and Serratia mercescens are higher as compared to the free ligands, vanadyl sulphate, and the control (DMSO) but of moderate activity as compared to the standard drug (tetracycline).     

Oxovanadium(IV) complex formation by simple sugars in aqueous solution.

The binding of oxovanadium(IV) to simple sugars in neutral or basic aqueous solution, as studied by EPR and electronic absorption spectroscopy, is reported. The complexation is favored in basic media and involves the coordination of the metal ion to couples of adjacent deprotonated hydroxyls of the sugar molecule. However, only the ligands provided with cis couples can adopt this chelating ligand behavior. The ability of the cis hydroxyl couples to yield chelated complexes has been related to the structural rearrangement (decrease of the O-C-C-O torsion angle in the five-membered chelated ring) needed to permit the oxovanadium(IV) coordination by the sugar molecule.     

Synthesis, X-ray structure, and anti-leukemic activity of oxovanadium(IV) complexes

In a systematic effort to identify and develop effective anticancer agents, four oxovanadium(IV) complexes with 1,10-phenanthroline (Phen) or 4,7-dimethyl-1,10-phenanthroline (Me2-Phen) as ligand(s) were synthesized and characterized. Among the four oxovanadium(IV) complexes synthesized, the crystal structure of the bis(phenanthroline)oxovanadium(IV) complex bis(1,10-phenanthroline)sulfatooxovanadium(IV) ([VO(SO4)(Phen)2], compound 1) has been determined. Compound 1 crystallized in the space group P2(1)/n with unit cell parameters a = 14.2125(17) A, b = 10.8628(13) A, c = 20.143(2) A, alpha = 90 degrees, beta = 102.569(2) degrees, gamma = 90 degrees, V = 3035.3(6) A3, and Z = 4. The refinement of compound 1 by full-matrix least-squares techniques gave an R factor of 0.0785 for 4356 independent reflections. The structure contains two enantiomorphous molecules, lambda and delta, which are related by an inversion center. Compound 1 exhibited 3.5-fold more potent cytotoxic activity against NALM-6 human leukemia cells than the mono(phenanthroline)oxovanadium(IV) complex (diaqua)(1,10-phenanthroline)sulfatooxovanadium(IV) ([VO(SO4)(Phen)(H2O)2], compound 2) (IC50 values: 0.97+/-0.10 microM versus 3.40+/-0.20 microM: P=0.0004). Methyl substitution in the phenanthroline ligand enhanced the anti-leukemic activity of the mono(phenanthroline)oxovanadium(IV) complex 4.4-fold (IC50 values: 0.78+/-0.10 microM, compound 4, versus 3.40+/-0.20 microM, compound 2; P=0.0003) and the anti-leukemic activity of the bis(phenanthroline)oxovanadium(IV) complex 5.7-fold (IC50 values: 0.17+/-0.02 microM, compound 3, versus 0.97+/-0.10 microM, compound 1; P=0.001). The leading oxovanadium compound, bis(4,7-dimethyl-1,10-phenanthroline)sulfatooxovanadium(IV) ([VO(SO4)(Me2-Phen)2], compound 3) triggered the production of reactive oxygen species (ROS) in human leukemia cells, caused G1-arrest and inhibited clonogenic growth at nanomolar concentrations.     

Synthesis, characterization and liquid-phase hydroxylation of phenol with hydrogen peroxide over host (nanopores of zeolite-Y)/guest (oxovanadium(IV) complexes of tetraaza macrocyclic ligands) nanocatalyst

Oxovanadium(IV) tetraaza complexes of [14]aneN₄: 1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane; [16]aneN₄: 1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane; Bzo₂[14]aneN₄: dibenzo-1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane and Bzo₂[16]aneN₄: dibenzo-1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane have been encapsulated in the nanopores of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of [bis(diamine)VO(IV)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [VO(N-N)₂]²⁺-NaY; in the nanopores of the zeolite-Y and (ii) in situ condensation of the oxovanadium(IV) precursor complex with ethylcinnamate. The new host-guest nanocatalysts were characterized by several techniques: chemical analysis and spectroscopic methods (FT-infrared (FT-IR), ultraviolet-visible (UV-Vis), X-ray diffraction (XRD), nitrogen adsorption and diffuse reflectance spectra (DRS)) technique. The analytical data indicated a composition corresponding to the mononuclear complex of tetraaza ligand. The characterization data showed the absence of extraneous complexes, retention of zeolite crystalline structure and encapsulation in the nanopores. Liquid-phase selective hydroxylation of phenol with H₂O₂ to a mixture of catechol and hydroquinone in CH₃CN have been reported using oxovanadium(IV) tetraaza complexes encapsulated in zeolite-Y as catalysts. All these catalysts are more selective toward catechol formation.     

Model complexes for amavadine,a vanadium natural product

Amavadine is a vanadium natural product from the mushroom Amanita muscaria. Earlier reports have characterized the compound as a vanadyl (VO²⁺) complex with two N-hydroxy-αα-iminodipropionic acid ligands, but no hypothesis as to its function has yet been put forward. We report here the synthesis, isolation, and properties of bis(iminodiacetato)oxovanadium(IV) and bis(αα-iminodipropionato)oxovanadium(IV). The complex bis(ββ-iminodipropionato)oxovanadium(IV) has been prepared in solution. These complexes serve as models for Amavadine. The structures of the models are analogous to that of Amavadine, with two bidentate, singly charged ligands bonding through one oxygen and one nitrogen atom. The visible spectra suggest the possibility of 1:1 complexes in solution in addition to the 2:1 ligand to metal complexes. Preliminary electrochemical data suggest reversible V(IV) ? V(III) couples.     

Reduction of vanadium(V) with ascorbic acid and isolation of the generated oxovanadium(IV) species

The interaction of sodium metavanadate and VOCl₃ with ascorbic acid, one of the possible natural reducing agents of vanadium(V) to oxovanadium(IV), has been investigated. Three new VO²⁺ complexes could be isolated as microcrystalline powders. One of them, of composition K_1.5Na_0.5[VO(HAsc)(OH)₃], contains ascorbic acid as a monodentate ligand. In the other two, K[VO(Diketo)(OH)]·H₂O and Na₃[VO(Diketo)₂(OH)], the enolized form of 2,3-diketogulonic acid (one of the oxidation products of ascorbic acid), acts as a bidentate ligand. The complexes were characterized by means of electronic (absorption and reflectance) and infrared spectroscopy and magnetic susceptibility measurements. Their thermal behavior was investigated by thermogravimetric and differential thermal analyses. The interest of the investigated system in relation to vanadium detoxification is also discussed.     

Structural characterization of pentadentate salen-type Schiff-base complexes of oxovanadium(IV) and their use in sulfide oxidation

Pentadentate Schiff-base complexes of oxovanadium(IV), the ligands of which were derived from salicylaldehyde derivatives with a variety of substituents and two kinds of amines (2,2^′-bis(aminoethyl)amine and 3,3^′-bis(aminopropyl)amine), were prepared, and their coordination geometries in the solid state were determined by X-ray diffraction and IR measurements and those in CH₂Cl₂ by EPR measurements. They were found to retain distorted octahedral coordination in the solid state. They showed the structural change depending on the type of the substituent. The complexes which reacted with tert-butylhydroperoxide converted methyl phenyl sulfide to the corresponding sulfoxide at lower rates of reaction than tridentate N-salicylidene-2-aminoethanolato oxovanadium(IV) ([VO(salae)]) and tetradentate (N,N^′-bis(salicylidene)ethylenediaminato)oxovanadium(IV) ([VO(salen)]).     

Synthesis and spectral investigation of manganese(II), cadmium(II) and oxovanadium(IV) complexes with 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone): Crystal structure of manganese(II) and cadmium(II) complexes

The chelating behavior of 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone) (H₂dapa) towards manganese(II), cadmium(II) and oxovanadium(IV) ions has been studied by elemental analyses, conductance measurements, magnetic properties and spectral (IR, ¹H NMR, UV-Vis and EPR) studies. The IR spectral studies suggest the pentadentate nature of the ligand with pyridine nitrogen, two azomethine nitrogens and two carbonyl oxygen atoms as the ligating sites. Six coordinate structure for [VO(H₂dapa)]SO₄ · H₂O and seven coordinate structures for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)Cl₂] · H₂O complexes have been proposed. Pentagonal bipyramidal geometry for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)(Cl₂)] · H₂O complexes was confirmed by single crystal analysis. The X-band EPR spectra of the oxovanadium(IV) and manganese(II) complexes in the polycrystalline state at room (300 K) and also at liquid nitrogen temperature (77 K) were recorded and their salient features are reported.     

Oxovanadium(IV) complexes with Knoevenagel Schiff base condensate as impending chemotherapeutic agents: Synthesis,characterization, biological screening and anti-proliferative assay

Two novel oxovanadium(IV) complexes [VOL1]SO₄ (1) and [VOL2]SO₄ (2) containing Knoevenagel condensate Schiff base ligand (L1/L2) have been synthesized and characterized by physical, spectral and analytical methods. These complexes are reported as ionic in nature on the basis of elemental composition and molar conductance, and possess square pyramidal geometry around the central metal ions. The binding interactions of (1) and (2) with calf thymus DNA (CT DNA) were explored by absorption spectrophotometric titration, cyclic voltammetry data and viscosity measurements. The calculated intrinsic binding constant values (K_b) for (1) and (2) obtained from UV–Vis absorption studies are 0.4 × 10⁵ and 5.6 × 10⁵ (M⁻¹) respectively. These experimental results indicate that (1) and (2) are intercalative binders and avid binder to CT DNA with different affinities. These complexes exhibit significant oxidative cleavage of supercoiled plasmid (pUC18) DNA in the presence of activators. In particular, the in vitro antimicrobial efficacy of oxovanadium(IV) complexes reveal that they are more active than free ligands. Besides, the in vitro cytotoxic effect of the titled complexes were examined on a bundle of human tumor cell lines such as MCF-7 and HeLa cancerous cell lines by the MTT method. Interestingly, complex (2) exhibits more potent cytotoxic activity than the other complex and standard drug (cisplatin). The mode of cell death was assessed by Hoechst 33258 staining morphological studies.     

Polyoxovanadates: The missing link between simple paramagnets and bulk magnets?

Oxovanadium clusters provide novel examples of large magnetic clusters, which may showin nuce the typical behavior of bulk magnetic materials.The paper reviews the magnetic properties of V₁₅, comprising fifteen oxovanadium(IV); V₁₄, comprising fourteen oxovanadium(IV); V₃₊₁, comprising three localized oxovanadium(IV), six localized oxovanadium(V), and one oxovanadium(IV) delocalized over three sites; V₄₊₂ and V₄₊₄ which comprise four localized and two and four delocalized oxovanadium(IV), respectively. The different observed magnetic behaviors are discussed on the basis of several models of different sophistication.     

The influence of a new vanadium compound, bis(2,2'-bipyridine)oxovanadium(IV) sulphate on liver golgi complexes from control and streptozotocin-diabetic rats.

Among the previously studied organic vanadium derivatives showing an anti-diabetic action, we investigated a new complex, bis(2,2'-bipyridine)oxovanadium(IV) sulphate. We tested its ability to normalise parameters previously described for streptozotocin (STZ)-diabetes, such as lower yields of Golgi-rich membrane fraction isolation, decreased activity of Golgi membrane marker enzyme - galactosyltransferase (GalT) - and altered morphology of rat liver Golgi complexes. Oral application as a drinking solution of 1.8 mmol bis(2,2'-bipyridine)oxovanadium(IV) (dissolved in 0.09 M NaCl) caused a similar dispersion of GalT activities in both vanadium treated groups, control and diabetic. Very low activities of the enzyme (characteristic for untreated diabetes) we found only in approximately 35 % of the STZ-diabetic rats treated with the new vanadium compound. The morphology of liver Golgi complexes in diabetic rats treated with bis(2,2'-bipyridine)oxovanadium(IV) sulphate was improved, which manifested itself in the reappearance of vacuoles with VLDL and coated and uncoated secretory vesicles. In view of biochemical and morphological parameters of normalised diabetic rat liver Golgi apparatus, the new vanadium complex was more effective than bis(oxalato)oxovanadium(IV) or bis(kojato)oxovanadium(IV), but in our experimental model, the best anti-diabetic, orally applied drug was the bis(maltolato)oxovanadium(IV) previously investigated.     

The vanadyl (VO2+) chelate bis(acetylacetonato)oxovanadium(IV) potentiates tyrosine phosphorylation of the insulin receptor

We have compared the insulin-like activity of bis(acetylacetonato)oxovanadium(IV) [VO(acac)₂], bis(maltolato)oxovanadium(IV) [VO(malto)₂], and bis(1-N-oxide-pyridine-2-thiolato)oxovanadium(IV) [VO(OPT)₂] in differentiated 3T3-L1 adipocytes. The insulin-like influence of VO(malto)₂ and VO(OPT)₂ was decreased compared with that of VO(acac)₂. Also, serum albumin enhanced the insulin-like activity of all three chelates more than serum transferrin. Each of the three VO²⁺ chelates increased the tyrosine phosphorylation of proteins in response to insulin, including the β-subunit of the insulin receptor (IRβ) and the insulin receptor substrate-1 (IRS1). However, VO(acac)₂ exhibited the greatest synergism with insulin and was therefore further investigated. Treatment of 3T3-L1 adipocytes with 0.25 mM VO(acac)₂ in the presence of 0.25 mM serum albumin synergistically increased glycogen accumulation stimulated by 0.1 and 1 nM insulin, and increased the phosphorylation of IRβ, IRS1, protein kinase B, and glycogen synthase kinase-3β. Wortmannin suppressed all of these classical insulin-signaling activities exerted by VO(acac)₂ or insulin, except for tyrosine phosphorylation of IRβ and IRS1. Additionally, VO(acac)₂ enhanced insulin signaling and metabolic action in insulin-resistant 3T3-L1 adipocytes. Cumulatively, these results provide evidence that VO(acac)₂ exerts its insulin-enhancing properties by directly potentiating the tyrosine phosphorylation of the insulin receptor, resulting in the initiation of insulin metabolic signaling cascades in 3T3-L1 adipocytes.     

Synthesis,characterization and catalytic oxidations of oxovanadium(IV), oxotitanium(IV) and dioxomolybdenum(VI) complexes with chiral imines of L-amino acids

Representative oxovanadium(IV), oxotitanium(IV), and dioxomolybdenum(VI) complexes of N-salicylidene-L-amino acids (the amino acids are: valine, leucine, except for Mo(VI), and histidine) have been synthesized and characterized by various spectroscopic techniques. It has been found that while in the histidine complexes of titanium(IV) and vanadium(IV) the amino acid residue is bound in the expected glycine-like mode, in the molybdenum(VI) complex it is bound in the unusual histamine-like mode. Also, the structure of this molybdenum(VI) complex contains imidazolate-bridged polymeric units in the solid state, while the carboxyl group of the amino acid residue is protonated. In solution the polymeric structure is cleaved and the monomers contain carboxylate and protonated imidazole groups at the histidine residue. The histamine-like structure of the histidine complex was probcd by comparison with that of the chiral dioxomolybdenum(VI) complex of N-salicylidene-L-histidinol. While the structure of the metal centers is six-coordinate for the dioxomolybdenum(VI) complexes and the histidine complexes of oxotitanium(IV) and oxovanadium(IV), it is likely that the complexes of the latter metals derived from nonpolar amino acids do not achieve coordination numbers higher than five. The present oxometal complexes are catalytically active in the sulfoxidation of sulfides and in the epoxidations of activated olefins by tert-butyl hydroperoxide, but in general exhibit a low degree of asymmetric induction in these reactions.     

DNA cleavage,binding and intercalation studies of drug-based oxovanadium(IV) complexes

The complexes of oxovanadium(IV) with ciprofloxacin and various uni-negative bidentate ligands have been prepared and their structure investigated using spectral, physicochemical and elemental analyses. The viscosity measurement suggest that the complexes bind to DNA by intercalation. The DNA binding efficacy was determined using absorption titration to obtain the binding constant (K_b). The DNA cleavage efficacy was determined using gel electrophoresis. The DNA binding and cleavage efficacy were increased in the complexes relative to the parental ligands and metal salts. Antibacterial activity has been assayed against two Gram^{( ? ve)} i.e. Escherichia coli, Pseudomonas aeruginosa and three Gram^{( + ve)} Staphylococcus aureus, Bacillus subtilis, Serratia marcescens microorganisms using the doubling dilution technique. The results show a significant increase in antibacterial activity in the complexes compared with parental ligands and metal salts.