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.     

Aliphatic acid dihydrazide derivatives of dicyclopentadienylzirconium(IV) dichloride and their reactions with β-diketones. Formation of cyclic compounds

The reactions of dicyclopentadienylzirconium(IV) dichloride with bidentate aliphatic acid dihydrazide (LH₂) derived from oxalic, succinic, and adipic acids (metal to ligand molar ratios 1 : 1 and 1 : 2, respectively) in anhydrous tetrahydrofuran in the presence of base led to the formation of the [Cp₂Zr(L)] and [CpZr(LH)₂Cl] complexes. The complexes were characterized by elemental analyses, electrical conductance, magnetic measurements and spectroscopic studies. These ligands appear to behave as bidentate chelate agents. All the complexes contain terminal amino or terminal hydrazinc nitrogen atoms with an unshared electron pair, enabling nucleophilic condensations. Therefore, the reactions of these complexes with β-diketones (acetylacetone, benzoylacetone, dibenzoylmethane, thenoyltrifluoroacetone) in the presence of glacial acetic acid have been studied viz., ring closure and formation of macrocyclic ligand (mac) complexes. Two types of cyclic products viz., [Cp₂Zr(mac)] and [CpZr(Mac)Cl] were isolated. The spectral studies of these cyclic products are reported.     

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.     

Synthesis and spectroscopic studies of oxovanadium(IV) and dichlorovanadium(IV) complexes of <Emphasis Type="Italic">p-</Emphasis>X-phenyl-2-picolylketones

A new series of oxovanadium(IV) complexes formulated as [(HL)₂VO]_n·nSO₄ (a), [(HL)VO(SO₄)]₂ (b), and [L₂VO] (c), where HL=phenyl-2-picolylketone and its para-substituted derivatives have been synthesized and characterized. The i.r. data suggest that the ligands are neutral bidentate in classes (a) and (b) and uninegative bidentate in (c), coordinated to the vanadyl ion via the pyridine-N and keto- or enolato-O atoms. Complexes of class (a) showed mechanochromism upon grinding. Magnetic, u.v./vis. and e.s.r. data suggest that all the complexes have a square pyramidal structure with an unpaired electron in the d_xy orbital in the solid and in solutions. Deoxygenation of the oxovanadium complexes gave the corresponding dichlorovanadium(IV) derivatives. Elemental analysis, magnetic and spectral studies indicated that the dichlorovanadium(IV) complexes are associated with a distorted trans-octahedral ligand field.     

Synthesis,spectral, thermal,and antibacterial investigation of mixed ligand complexes of oxovanadium(IV)

Novel mononuclear mixed-ligand oxovanadium(IV) complex [VO(PMFP)(Bipy)]ClO₄ was prepared by the condensation of VOSO₄ · 5H₂O with ligands 1-phenyl-3-methyl-4-formyl-2-pyrazolin-5one (PMFP) and 2,2′-bipyridyl (Bipy). The corresponding Schiff bases were prepared by the condensation of [VO(PMFP)(Bipy)]ClO₄ with ethylenediamine, ethanolamine, and glycine. All the compounds have been characterized by elemental analysis, magnetic susceptibility, X-ray crystallography, conductometry measurement, ¹H NMR, FT-IR, ESR, electronic spectra, and mass spectrometry. Electronic spectra and magnetic susceptibility measurements indicate distorted octahedral stereochemistry of the oxovanadium(IV) complexes. Thermal stability, kinetic order, heat capacity, and activation energy of thermal degradation of these complexes were determined by TGA and DSC. The presence of one coordinate water molecule is suggested from the IR and TGA studies. Hamiltonian and bonding parameters were found from ESR spectra, indicating that the metal-ligand bonding is partial covalent. Antibacterial screening is reported for the ligand and complexes of oxovanadium(IV). The text was submitted by the authors in English.     

HomoBinuclear Oxovanadium(IV) Complexes with Octaaza Macrocyclic Ligands Derived from Primary Diamines and 3,6-Dimethyl/diphenyl-4,5-diazaocta-3,5-diene-2,7-dione

The in situ reactions of 3,6-dimethyl/diphenyl-4,5-diazaocta-3,5-diene-2,7-dione with diamines (ethylenediamine, o-phenylenediamine) in the presence of vanadyl salt yielded binuclear macrocyclic complexes of type [(VO)₂mac](SO₄)₂. Attempts to synthesize the corresponding metal-free macrocyclic ligands did not prove successful. The magnetic moment of the complexes decreases from ca. 1.73 (295 K) to 1.65μ _B (91 K). The electronic spectra exhibit three bands at ca. 12 000-14 200, 18 200-19 500 and an intense band at ca. 30 000 cm^-1. The third band is probably due to a oxo → V(IV) charge-transfer transition. The infrared spectra indicate that the ligands coordinate through four aza nitrogen atoms to each V(IV). The fluid solution EPR spectra show an eight line pattern typical of a mononuclear VO(IV) compound and indicating the absence of VO…VO electron spin interaction. The electrochemical behavior of one complex with regards to oxidation has been studied by cyclic voltammetry in MeCN-MeOH solution.     

Oxovanadium(IV) and ruthenium(II) carbonyl complexes of ONS‐donor ligands derived from dehydroacetic acid and dithiocarbazate: Synthesis,characterization, antioxidant activity,DNA binding and in vitro cytotoxicity

A series of new complexes of oxovanadium(IV) [VO(L)(B)] and ruthenium(II) [Ru(CO)(PPh₃)₂(L)] ( 1.1- 1.3,  2.1–2.3 ) (H₂L = dehydroacetic acid Schiff base of S‐methyldithiocarbazate, H₂smdha ( 1 ) or S‐benzyldithiocarbazate, H₂sbdha ( 2 ); B = 2,2′‐bipyridine (bpy) or 1,10‐phenanthroline (phen)) have been synthesized. The structure of these complexes was authenticated using elemental analyses and spectroscopic techniques, and their magnetic properties and electrochemical behaviour were studied. The molecular structures of oxovanadium(IV) complexes [VO(smdha)(bpy)]?CH₂Cl₂ ( 1.1 ) and [VO(sbdha)(phen)]?2H₂O ( 2.2 ) were confirmed using single‐crystal X‐ray crystallography. Analytical data showed that the ligands 1 and 2 are chelated to the metal centres in a bi‐negative tridentate fashion through azomethine N, thiol S and deprotonated hydroxyl group. The antioxidant activity of the synthesized compounds was tested against 2,2‐diphenyl‐1‐picrylhydrazyl) radical, which showed that the complexes demonstrate a better scavenging activity than their corresponding ligands. The cupric ion reducing antioxidant capacity method was also employed and the total equivalent antioxidant capacity values were found to be higher for the oxovandium(IV) complexes. DNA binding affinity of the compounds was determined using UV–visible and fluorescence spectra, revealing an intercalation binding mode. Higher cytotoxicity for the complexes compared to their ligands was found against human liver hepatocellular carcinoma (HepG2) and breast adenocarcinoma (MCF7) cell lines using MTT assay.     

Effect of ligand structure of Schiff base oxovanadium(IV) complexes on their catalytic activity in aerobic oxidation of alcohols

Two kinds of immobilized bidentate Schiff base oxovanadium(IV) complexes are prepared via polymer reactions and coordination reactions with chloromethylated cross-linked polystyrene (CMCPS) microspheres as matrix. Benzaldehyde (BA)-functionalized CPS microspheres, BA-CPS microspheres, were prepared through nucleophilic substitution with CMCPS microsphere as precursor and p-hydroxy benzaldehyde as reagent, and then Schiff base reactions were carried out with 3-aminopyridine (AP) and glycine (GL) as reagents, respectively, obtaining two kinds of bidentate Schiff base ligand-bonded microspheres, BAAP-CPS microspheres and BAGL-CPS microspheres. Finally, through coordination reactions with vanadyl sulfate (VOSO₄) as reagent, the two kinds of immobilized bidentate Schiff base oxovanadium(IV) complex microspheres, CPS-[VO(BAAP)₂] and CPS-[VO(BAGL)₂], were obtained. The two immobilized complexes, VO(BAAP)₂ and VO(BAGL)₂, are N,N- and N,O-type bidentate Schiff base oxovanadium(IV) complexes and their ligands have different chemical structures. The two catalyst microspheres were used in oxidation of cyclohexanol and benzyl alcohol with molecular oxygen as oxidant and their catalytic activities are compared. The experimental results show that both solid catalysts can catalyze the transformation reactions of cyclohexanol and benzyl alcohol to their corresponding carbonyl compounds under mild conditions. However, CPS-[VO(BAAP)₂] microspheres have much higher catalytic activity and better stability than CPS-[VO(BAGL)₂] microspheres. For the immobilized bidentate Schiff base oxovanadium(IV) catalysts, the catalytic property is closely related to the chemical structures of the ligands, and for this, a theoretical explanation is given.     

Studies on 2,6-diacetylpyridine bis(2-furoylhydrazone) complexes of bivalent 3d-metal ions

Summary The chelating behaviour of neutral and deprotonated 2,6-diacetyl-pyridine bis(2-furoylhydrazone), H₂dapf, has been investigated in some new complexes of oxovanadium(IV), manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II). The hydrazone reacts with the metal salts to yield complexes of two types; the addition compounds [VO(H₂dapf)]SO₄, [M(H₂dapf)Cl]Cl and the deprotonated complexes [M(dapf)H₂O] [M=manganese(II), cobalt(II), nickel(II), copper(II) or zinc(II)] in neutral and alkaline media, respectively. The complexes have been characterized by elemental analyses, molar conductance, magnetic susceptibility, electronic, i.r. and e.s.r. studies and their stereochemistries are discussed.     

Synthesis,characterization and oxidase catalytic activity of vanadium(IV) and oxovanadium(IV) complexes with Schiff base ligands derived from β-diketones

New complexes of vanadium(IV) and oxovanadium(IV) with Schiff base ligands derived from -diketones and ethanolamine or o-aminophenol have been prepared and characterized by elemental analyses, electrical conductance, magnetic moment measurements, and by i.r., u.v.–vis. and e.p.r. spectroscopy. A distorted octahedral environment was proposed for the vanadium(IV) and oxovanadium(IV) complexes. The spectroscopic results were utilized to compute the important ligand field parameters. Three adduct complexes were isolated owing to the interaction of one oxovanadium complex with Lewis-bases in MeOH. Vanadium(IV) complexes exhibit promising catalytic activity towards the aerobic oxidation of p-phenylenediamine (PPD) to the corresponding semi-oxidized form (PPD⁺). A linear correlation exists between the oxidase catalytic activity and the Lewis acidity of the central vanadium(IV) ion created by the donating properties of the parent ligand.     

Mononuclear and binuclear lanthanum(III) complexes of macrocyclic ligands derived from 2,6-diacetylpyridine

Two novel series of complexes of types [La(DAPCH)X₂]X and [La(DAPTC)X₂]X (DAPCH = a potentially pentadentate ligand derived from 2,6-diacetylpyridine and carbohydrazide; DAPTC = a potentially tridentate ligand derived from 2,6-diacetylpyridine and thiocarbohydrazide; X = Cl, Br or NO₃) have been synthesized and characterized by elemental analyses, conductance measurements and IR spectral data. All these complexes contain terminal hydrazinic nitrogen atoms with an unshared electron pair and may take part in nucleophilic condensations. Therefore, the reactions of these complexes with 2,6-diacetylpyridine have also been studied which cause ring closure and formation of macrocyclic ligand complexes. Two types of cyclic products, viz. mononuclear [La(mac)X₂]X, [La(mac′)X₂]X and binuclear [La₂(mac)X₄]X₂, [La₂(mac′)X₄]X₂ (mac- = macrocyclic ligand derived from DAPCH and 2,6-diacetylpyridine; mac′ = macrocyclic ligand derived from DAPTC and 2,6-diacetylpyridine; X = Cl, Br or NO₃) have been isolated by carrying out the reactions by different methods. The IR spectra of these cyclic products are reported.     

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, 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 magnetic properties of novel μ-isophthalato oxovanadium(IV) binuclear complexes

Four novel oxovanadium(IV) binuclear complexes have been synthesized, namely [(VO)₂(IPHTA) (L)₂SO₄ (L denotes 2,2′-bipyridine (bpy); 1,10-phenanthroline (phen); 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy) and 5-nitro-1,10-phenanthroline (NO₂-phen)), where IPHTA is the isophthalate dianon. Based on elemental analyses, molar conductivity measurements, IR and electronic spectra studies, it is proposed that these complexes have IPHTA-bridged structures and consist of two vanadium(IV) atoms in a square-pyramidal environment. The complexes [(VO)₂(IPHTA)(Me₂bpy)₂]SO₄ (1) and [(VO)₂(IPHTA)(bpy)₂]SO₄ (2) were characterized by variable temperature magnetic susceptibility (4–300 K) and the data could be well fitted by the least-squares method to a susceptibility equation derived from the spin Hamiltonian operator, . The exchange integral, J, was found to be −26.8 cm⁻¹ for (1) and −31.0 cm⁻¹ for (2). These results are commensurate with antifferomagnetic interactions between two oxovanadium(IV) ions within each molecule. The influence of different terminal ligands on magnetic interactions between the metals of this kind of complexes is also discussed.     

A thermal behaviour and structural study of bis(hydroxamato)oxovanadium(IV) complexes

The bis(hydroxamato)oxovanadium(IV) complexes of composition [VO(IAH)₂)] (I), [VO(IBH)₂)] (II) and [VO(ICH)₂)] (III) (where IAH = indole-3-acetohydroxamate; (C₉H₈NCONHO^?); IBH = indole-3-butyrohydroxamate; (C₁₁H₁₂NCONHO^?); ICH = indole-2-carbohydroxamate; (C₈H₆NCONHO^?)) synthesized form the reactions of VOSO₄·5H₂O with bi-molar amounts of potassium salts of the respective hydroxamic acids in methanol have been characterised by elemental analyses, magnetic moment measurements and IR spectral studies. The thermal behaviour of complexes has been studied by TG and DTA techniques. Thermograms indicated that all complexes decompose in two steps yielding [VO(IAH)], [VO(IBH)] and [VO(ICH)] as intermediate of respective complexes and VO₂ as the final product of decomposition in each case. From the initial decomposition temperatures (IDT), the order of thermal stability for the complexes has been inferred as II > I > III.     

Flexible ligand synthesis, characterization and liquid phase hydroxylation of phenol by H2O2 with host (nanopores of zeolite-Y)/guest [VO([R]2–N2X2)]2+ (R = H, CH3; X = NH, O, S) nanocomposite materials

Encapsulation of Oxovanadium(IV) complexes of 12-membered macrocyclic ligands having N₂O₂, N₂S₂ and N₄ donor atoms in the nanocavity of zeolite-Y by the Flexible-Ligand Method (FLM) have been described. Oxovanadium(IV) complexes with macrocyclic ligands were entrapped in the nanocavity of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of precursor ligand; 1,2-di(o-aminophenyl-, amino, oxo, thio)ethane, (N₂X₂); in the supercages of VO(IV)-Y; ([VO(N₂X₂)]²⁺-Y (X = NH, O, S); and (ii) in situ condensation of the oxovanadium(IV) precursor complex with glyoxal or biacetyl; [VO([R]₂–N₂X₂)]²⁺-Y (R = H, CH₃). The new Host–Guest Nanocomposite Materials (HGNM, [VO([R]₂–N₂X₂)]²⁺-Y) have been characterized by FT-IR, DRS and UV–Vis spectroscopic techniques, XRD and elemental analysis, as well as nitrogen adsorption. Liquid-phase selective hydroxylation of phenol with H₂O₂ to a mixture of catechol and hydroquinone in CH₃CN has been reported using [VO([R]₂–N₂X₂)]²⁺-Y as catalysts. Reaction conditions have been optimized by considering the concentration of substrate and oxidant, amount of catalyst, effect of time, volume of solvent and temperature. Under the optimized reaction conditions, [VO([H]₂–N₄)]²⁺-Y gave 50.1% conversion of phenol after 6 h. All these catalysts are more selective toward catechol formation.     

Nano-sized, ternary oxovanadium(IV) complexes containing electron-rich oxygen-based ligands

Some mononuclear mixed-carboxylato ??-diketonato oxovanadium(IV) complexes of the general formula [VO(??-dike)(RCOO)] (where H??-dike?=?acetylacetone; benzoylacetone or dibenzoylmethane, R?=?C₁₅H₃₁ or C₁₇H₃₅) have been synthesized from VO(acac)₂ by stepwise substitutions of acetylacetonate ion with straight chain fatty acids (RCOOH) and ??-diketones in p-xylene under reflux. The substituted acetylacetone could be fractionated out with p-xylene as an azeotrope. These were characterized by elemental analyses, molecular weight determinations, spectral (electronic, infrared, ¹H NMR, EPR and powder XRD) studies, magnetic susceptibility measurements and cyclic voltammetry. Molar conductance values indicated the complexes to be non-electrolytes in nitrobenzene. Bidentate chelating nature of ??-diketonate and carboxylate ligands in the complexes was established by infrared and NMR spectra. Molecular weight determinations confirmed mononuclear nature of the complexes. The EPR spectra illustrated coupling of the unpaired electron with ⁵¹V nucleus (I?=?7/2). Cyclic voltammograms of all the complexes displayed one-step oxidation processes. The oxidation peak potential corresponded to the quasireversible one-electron oxidation process of the metal center, yielding V(V) species. Powder XRD and transmission electron microscopy (TEM) studies indicated the particles of these were lying in the nano-size range. The synthesized complexes are a new type of mixed-ligand complexes in which vanadium is having coordination number 5. A square pyramidal geometry around vanadium has been assigned in all the complexes.     

Dioxo- and oxovanadium(V) complexes of thiohydrazone ONS donor ligands: synthesis, characterization, reactivity, and antiamoebic activity

As a contribution to the development of novel vanadium complexes with pharmacologically interesting properties, two neutral dioxovanadium(V) complexes [VO2(Hpydx-sbdt)] (1) and [VO2(Hpydx-smdt)] (3) [H2pydx-sbdt (I) and H2pydx-smdt (II) are the Schiff bases derived from pyridoxal and S-benzyl- or S-methyldithiocarbazate] have been synthesized by the reaction of [VO(acac)2] and the potassium salts of the ligands in methanol followed by aerial oxidation. Heating of the methanolic solutions of these complexes yields the oxo-bridged binuclear complexes [{VO(pydx-sbdt)}2mu-O] (2) and [{VO(pydx-smdt)}2mu-O] (4). The crystals and molecular structures of 1, 3 x 1.5H2O, and 4 x 2CH3OH have been determined, confirming the ONS binding mode of the dianionic ligands in their thioenolate form. The ring nitrogen of the pyridoxal moiety is protonated in complexes 1 and 3. Acidification of 1 and 3 with HCl dissolved in methanol afforded oxohydroxo complexes, while in a methanolic KOH solution, the corresponding dioxo species K[VO2(pydx-sbdt/smdt)] are formed. Treatment of 1 and 3 with H2O2 yields (unstable) oxoperoxovanadium(V) complexes, the formation of which has been established spectrophotometrically. In vitro antiamoebic activities (against HM1:1MSS strain of Entamoeba histolytica) were established for all of the dioxo- and oxovanadium(V) complexes. The complexes 1, 2, and 4 were more effective than metronidazole, a commonly used drug against amoebiasis, suggesting that oxovanadium(V) complexes derived from thiohydrazones may open a new dimension in the therapy of amoebiasis.     

Vanadium complexes with thiosemicarbazones: Synthesis,characterization, crystal structures and anti-Mycobacterium tuberculosis activity

The development of more efficient anti-tuberculosis drugs is of interest. Three oxovanadium(IV) and three cis-dioxovanadium(V) complexes with thiosemicarbazone derivatives bearing moieties with different lipophilicity have been prepared and had their inhibitory activity against Mycobacteriumtuberculosis H₃₇Rv ATCC 27294 evaluated. The analytical methods used by the complexes’ characterization included IR, EPR, ¹H, ¹³C and ⁵¹V NMR spectroscopies, elemental analysis, cyclic voltammetry, magnetic susceptibility measurement and single crystal X-ray diffractometry. [VO(acac)(aptsc)], [VO(acac)(apmtsc)] and [VO(acac)(apptsc)] (acac = acetylacetonate; Haptsc = 2-acetylpyridinethiosemicarbazone; Hapmtsc = 2-acetylpyridine-N(4)-methyl-thiosemicarbazone and Happtsc = 2-acetylpyridine-N(4)-phenyl-thiosemicarbazone) are paramagnetic and their EPR spectra are consistent with the monoanionic N,N,S-tridentate coordination of the thiosemicarbazone ligands, resulting in octahedral structures of rhombic symmetry and with the oxidation state +IV for the vanadium atom. As result of oxidation of the vanadium(IV) complexes above, the diamagnetic cis-dioxovanadium(V) complexes [VO₂(aptsc)], [VO₂(apmtsc)] and [VO₂(apptsc)] are formed. Their ¹H, ¹³C and ⁵¹V NMR spectra were acquired and support a distorted square pyramidal geometry for them, in accord with the solid state X-ray structures determined for [VO₂(aptsc)] and [VO₂(apmtsc)]. In general, the vanadium compounds show comparable or larger anti-M. tuberculosis activities than the free thiosemicarbazone ligands, with MIC values within 62.5–1.56 (μg/mL).     

Synthesis,spectroscopic studies and crystal structures of two new vanadium complexes of 2-benzoylpyridine containing hydrazone ligands

The reaction of VO(acac)₂ with 2-benzoylpyridine substituted aroylhydrazones is studied. Oxovanadium(IV) and (V) complexes are obtained, indicating the binding of ligands to the metal ion through the imine nitrogen, enolate oxygen and pyridyl nitrogen. The oxovanadium(IV) compound [VOL¹(OCH₃)] · 0.14H₂O (1a) gets oxidized to dioxovanadium(V) species [VO₂L¹] (1b) upon crystal formation. The crystal structures of the ligand and the two vanadium complexes are reported. Single crystal X-ray diffraction studies of the compound [VO(HL²)(μ₂-O)]₂ (2) revealed a centrosymmetric dimer.