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We prepared and characterized [meso-tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4−), [VO(tpps)], and its in vitro insulin-mimetic activity, metallokinetic features in the blood of healt...

The oxygen atom exchange reaction between the terminal oxygen atom (V=O) of tetradentate Schiff base-oxovanadium(IV) complexes and water slowly proceeds in DMSO solutions. The rate constants kobs for the isotopic oxygen atom exchange reaction in DMSO solutions containing excess H218O at 50 °C under an argon atmosphere were obtained for several complexes (6×10-7 to 6×10-5 s-1). The reaction proceeds faster for those complexes with electron-withdrawing groups at the Schiff base ligand moieties, and slower for the complexes with bulky hydrophobic groups. The oxygen atom exchange reaction and isomerization reaction under an argon atmosphere and in air were investigated for oxovanadium(IV) complexes that have two geometrical isomers. Water molecules attack the vanadium atom mainly from the same side of the oxo ligand for the oxovanadium(IV) complexes, whereas mainly from the opposite side of the oxo ligand for the oxovanadium(V) complexes produced by oxidation with air.

Two geometrical isomers, exo- and endo-[VO(3-EtOsal-meso-stien)] (H2(3-EtOsal-meso-stien) = N,N′-di-3-ethoxysalicylidene-(R,S)(S,R)-1,2-diphenyl-1,2-ethanediamine), were selectively prepared separately. X-Ray structure analyses were carried out for two different crystals of the endo-isomer: endo-[VO(3-EtOsal-meso-stien)]·3H2O, (A), monoclinic P21/c, a = 10.435(3), b = 9.696(3), c = 30.948(3) A, β = 94.87(2)°, V = 3120(1) A3 and Z = 4; endo-[VO(3-EtOsal-meso-stien)]·CH3CN, (B), monoclinic P21/c, a = 15.935(3), b = 9.510(2), c = 20.891(2) A, β = 100.58(1)°, V = 3112(1) A3 and Z = 4. Under an argon atmosphere, the endo-isomer in both crystals A and B isomerized to the exo-isomer completely upon heating at 210 °C for 20 h. The X-ray powder diffraction patterns of the heated crystals A′ and B′ were approximately identical with that of exo-[VO(3-EtOsal-meso-stien)]·H2O (C). In the latter the V=O bonds are arranged in crystals to form a fairly weak linear chain structure (V=O···V=O···). The drastic rearrangement...

The isomerization between the two diastereomers of [VIVO{3-MeOsal,sal-(RR)-chxn}] (H2{3-MeOsal,sal-(RR)-chxn} = N-salicylidene-N′-3-methoxysalicylidene-(RR)-1,2-cyclohexanediamine) in acetonitrile-water(95:5 v/v) was observed under aerobic conditions. The reaction was accelerated by the addition of [VVO(salen)]ClO4 (H2salen = N,N′-disalicylidene-1,2-ethanediamine), but the complex did not isomerize in dry acetonitrile. The mechanism of the isomerization was investigated.

In the presence of a catalytic amount of oxovanadium(IV) complexes coordinated with 1,3-diketone ligands, fused aromatic compounds such as naphthalenes and naphthol derivatives are smoothly oxygenated into the corresponding 1,4-naphthoquinones by combined use of molecular oxygen and crotonaldehyde under an atmospheric pressure.

Vanadyl-meso-tetrakis(4-sulfonatophenyl)porphyrin, VOTPPS, was synthesized and evaluated for its in vitro and in vivo insulin-mimetic activities in streptozotocin (STZ)-induced diabetic mice. Based...

A new purple vanadyl complex, bis(1-oxy-2-pyridinethiolato)oxovanadium(IV), VO(OPT), with VO(S2O2) coordination mode, was prepared by mixing 2-mercaptopyridine-N-oxide or 1-hydroxy-2-pyridinethione and VOSO4, and characterized by UV, IR and EPR spectra, magnetic susceptibility and partition coefficient. Based on the higher in vitro insulin-mimetic activity of VO(OPT) (IC50 = 0.19 mM) than that of VOSO4 (IC50 = 0.9 mM), the complex was found to be a potent agent for treating insulin-dependent diabetes mellitus in rats when given by daily intravenous injection or oral administration.

The kinetics of the electron-transfer reaction between [VO{3-MeOsal-(RR) or (SS)-chxn}] and [VO{sal-(RR)-chxn}]+ were studied using the stopped-flow method in acetonitrile over the temperature range of 5 – 25 °C. The reactions were enantioselective. The ratio of the rate constant of the electron-transfer between [VO{3-MeOsal-(SS)-chxn}] and [VO{sal-(RR)-chxn}]+ (kSS-RR) and that between [VO{3-MeOsal-(RR)-chxn}] and [VO{sal-(RR)-chxn}]+ (kRR-RR) was 2.0 (kSS-RR / kRR-RR) at 25 °C.

Binuclear oxovanadium(IV) complex, [(VO)2L(OCH3)], has been synthesized, where H3L denotes 2,6-diformyl-4-methylphenol bis(benzoylhydrazone). Two metal ions are bridged by the phenolic oxygen of L3 and a methoxide oxygen. Cryomagnetic measurements (80–300 K) indicated the operation of an antiferromagnetic spin-exchange interaction (J=−191.3 cm−1) between the oxovanadium(IV) ions.

Binuclear oxovanadium(IV) and copper(II) complexes, M2(fsalap-R)(OMe) (R=H, CH3, Cl, and NO2) were synthesized and characterized, where H3fsalap-R denotes 2,6-bis[N-(2-hydroxy-5-substituted-phenyl)iminomethyl]-4-methylphenol and the metal ions are connected by the phenolic oxygen and a methanolate ion. The cryomagnetic properties of the complexes except Cu2(fsalap-NO2)(OMe) could be interpreted on the basis of the Bleaney-Bowers equation. It was found that the -2J values for the oxovanadium(IV) complexes increase in the order (VO)2(fsalap-CH3)(OMe) Cu2(fsalap-H)(OMe)>Cu2(fsalap-Cl)(OMe). These facts could be reasonably explained in terms of the difference in structures and spin-exchange mechanisms between the oxovanadium(IV) and the copper(II) complexes. (VO)2(fsalap-NO2)(OMe) showed a very strong antiferromagnetic spin-exchange interaction (−2J=545 cm−1) compared with the other...

The kinetics of malonate exchange on VO(mal)22− has been studied by the NMR line-broadening method. The reaction was found to be dependent on the Hmal and hydrogen-ion concentrations, and the mechanism producing the intermediate complexes, where malonic acid was coordinated partly as an unidentate ligand, was estimated from the rate law. The activation parameters were determined for the acid-independent and acidcatalyzed paths as: ΔH\eweq=8.6 kcal/mol, ΔS\eweq=−16.2 e.u., and ΔH\eweq=8.9 kcal/mol, ΔS\eweq=−13.5 e.u.

The effect of temperature on the visible absorption spectra of oxovanadium(IV) β-diketonates [VO (β-dik)2] (β-dik=aca, bza, tfa, and dpm*) were studied in organic solvents. The results together with the spectral and thermogravimetric data of the pyridine and dioxane adducts of these chelates lead to the conclusion that the ease of taking up a solvent molecule to form a six-coordinate solvated chelate in solution increases in the order: VO(tfa)2>VO(bza)2≈VO(aca)2>VO(dpm)2. Various proofs for the existence of a polymeric structure of VO(tfa)2, which was formerly indicated on the basis of its IR spectrum, were found.

The correspondence of the reduction potential of vanadyl acetylacetonate and the wavelength of the optical absorption band was well recognized from the solvent effect on the ligand configuration. However, the noticeable deviation of the data in the aqueous solution was observed. The corelation to the donor number is also discussed.

All the patterns from the isotropic ESR spectrum to the anisotropic one of bis(acetylacetonato)oxovanadium(IV) and related chelates are recorded by employing molten o-terphenyl as a solvent and by changing the temperature above and below the melting point. The results are qualitatively explained in terms of the anisotropic molecular motion and are considered to be evidence for the presence of clusters in the melt. Similar observations are made with some derivatives of 2,4,6-trinitrodiphenylamine, but only partially with m-terphenyl and the 3′-methoxy and 3′-ethoxy derivatives of 2,4-dinitrodiphenylamine. The implications of the results concerning the structure of the melts are discussed.

The asymmetric oxidation of sulfides into the corresponding sulfoxides was achieved with organic hydroperoxides in the presence of a catalytic amount of optically active Schiff base-oxovanadium(IV) complexes; in most cases the optical yields (e.e.) ranged between 20 and 40%.

Many new oxovanadium(IV) complexes (abbreviated as VO(X-sal.R)2) of Schiff bases obtained from substituted salicylaldehydes and alkylamines have been synthesized as crystals, where X=H and 3-CH3O and R=CH3, C2H5, n-C3H7, n-C4H9, iso-C3H7, CH(CH3)(C2H5), CH2CH-(CH3)2 and cyclohexyl. Since all these complexes show similar electronic spectra, it is considered that they take an essentially similar configuration, that is, a square-pyramidal one in the solid state and in chloroform, even for R=α-branched alkyls. This result is different from that of the copper (II) complexes. It is also concluded that these oxovanadium(IV) complexes, when dissolved in pyridine, take up one pyridine molecule to form a six-coordinated species. The configuration of the pyridine solvate depends upon R.

The interaction of bis(O,O′-diethyldithiophosphato)oxovanadium(IV), VOdtp2, with pyridine bases has been studied in toluene by ESR. It has been found that the four-membered chelate structure of VOdtp2 is disrupted by pyridine bases to form the complex species identified as VOdtp2·Py and VOdtp2·Py2 by their characteristic ESR spectra. The coordination structures of the newly-formed complexes are discussed in association with the substitution equilibria involved.

Oxovanadium(IV) malonate tetrahydrate, VO(malon)·4H2O and oxovanadium(IV) maleate dihydrate, VO(mal)·2H2O are prepared and characterised. Magnetic moments agree with quadrivalent vanadium. The differential thermal analysis and infrared spectra of both the complexes have been studied. Molar conductance, molecular weight by cryoscopic method and the electronic spectrum of the malonate have also been obtained. A comparison of oxalate, malonate and maleate complexes of the type VO(LL)·x H2O (LL, being one of the bidentates) is attempted to arrive at a series from cryoscopic data, thermal decomposition temperature and vanadium-oxygen stretching frequency. The series obtained showing the ‘stability’ is: oxalate>malonate>maleate and is expected to be the same as the naphelauxetic series.

Oxovanadium(IV) complexes of Schiff bases obtained from salicylaldehyde derivatives and arylamines (abbreviated as VO(X-SAL.R)2) have been synthesized, where X=H, 5,6-benzo, 5-Cl, and 5-Br, and R=Ph, CH3-Ph, 2,6-(CH3)2-Ph and 2,6-(C2H5)2-Ph, Ph being phenyl nucleus. Complexes of the type VO(5-X-SAL.Ph)2 in the solid state, X being Cl and Br, consist of the species having a different configuration from that of the other complexes. For the latter complexes, distortion from the square-pyramidal configuration is not apparent in the solid state or in non-donor solvents, but in pyridine they combine with one pyridine molecule to form six-coordinate vanadium(IV) complexes. Comparison shows that the tendency toward the distortion in the solid state is lower with R=aryl than with R=α-branched alkyl groups.

The interaction of bis(O,O′-diethyldithiophosphato)oxovanadium(IV), VOdtp2, with pyridine has been studied in toluene by means of the optical absorptions. It has been found that the visible absorption band characteristic of VOdtp2 was shifted toward longer wavelengths upon the formation of the complex species identified as VOdtp2·Py and VOdtp2·Py2. The equilibrium constants and enthalpy and entropy changes for the formation of VOdtp2·Py were determined from the spectral characteristics, measured as a function of the solvent composition and the temperature. The results obtained were then discussed in comparison with those for the base addition of other oxovanadium complexes.

The copper(II) and oxovanadium(IV) complexes of a new Schiff base derived from heptane-2,4,6-trione and ethylenediamine were prepared. Of a macrocyclic two-to-two and an open jaw-shaped two-to-one (trione to diamine) condensation product, only the latter gave mononuclear copper (II) and oxovanadium(IV) complexes. The coordinating sites to the metal ion in each complex are discussed referring to the spectroscopic results.

The magnetic properties of oxovanadium(IV) complexes of Schiff bases(I) are reported. Contrary to an earlier report that these complexes are involved in magnetic exchange, the complexes are found to be magnetically dilute. The complexes display μeff in the range 1.68–1.71 B. M. at 78–297 K with θ=2–4 K, and exhibit 8 line ESR spectra.

An oxovanadium(IV) complex with N,N′-bis(1-methyl-2-bromo-3-oxobutylidene)ethylenediamine gave green and yellow forms in the solid state, depending upon the solvents used for recrystallization. A polymeric structure was proposed for the yellow form.

The kinetics of ligand exchange in [VO(dmso)5]2+ (dmso = dimethyl sulfoxide) has been studied by the high pressure NMR method. The volume of activation ΔV≠ for the dmso exchange at the basal positions of [VO(dmso)5]2+ was determined to be (−5.3±0.4) cm3/mol. This negative value of ΔV≠ is consistent with associative behavior in the ligand substitution processes of oxovanadium(IV) complexes.