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PubMed1998

Facile Syntheses of Titanium(II), Tin(II), and Vanadium(II) Porphyrin Complexes through Homogeneous Reduction. Reactivity of trans-(TTP)TiL(2) (L = THF, t-BuNC).

Facile syntheses of the meso-tetra-p-tolylporphyrin (TTP) complexes trans-(TTP)Ti(THF)(2) (1), (TTP)Sn (2), and trans-(TTP)V(THF)(2) (3) are achieved through homogeneous reduction of high-valent precursors using NaBEt(3)H. The composition of the new compound trans-(TTP)Ti(THF)(2) was determined by spectroscopic and chemical characterization. Ligand displacement reactions of trans-(TTP)Ti(THF)(2) with t-BuNC produced a new Ti(II) complex, trans-(TTP)Ti(t-BuNC)(2). The ligand-binding preference of (TTP)Ti(II)L(n)() (n = 1, 2) is picoline approximately pyridine > t-BuNC > PhC&tbd1;CPh > EtC&tbd1;CEt > THF.

Journal Article↗
PubMed1986

Cellular basis for the species differences in sensitivity to cardiac glycosides (digitalis).

The relative toxicity of numerous cardiotonic steroids (viz. ouabain, digitoxin, digoxin, convallatoxin, SC4453, bufalin, gitaloxin, digoxigenin, actodigin, oleandrin, digitoxigenin, gitoxin, strophanthidin, gitoxigenin, lanatosides A, B and C, alpha- and beta-acetyl digoxin, alpha- and beta-methyl digoxin) and related compounds towards a number of independent cell lines established from human, monkey, mouse, Syrian hamster, and Chinese hamster have been determined. All cardiac glycosides and their genins, as well as the cardiotonic alkaloid cassaine, exhibited greater than 100-fold higher toxicity towards cultured human and monkey cells in comparison to the cell lines of mouse, Syrian hamster, and Chinese hamster origins. These differences are species-related as all cell lines (both normal as well as transformed) from any one species, as well as cells from the closely related species (e.g., man and monkey or mouse, Chinese hamster, and Syrian hamster), showed similar sensitivity towards these drugs. The failure to see any significant differences in cellular toxicity for a larger number of other compounds which either bear limited structural resemblance to cardiac glycosides (viz. estradiol 17-beta-acetate, testosterone propionate, 21-acetoxy pregnenolone, beta-estradiol, digitonin, tigogenin, and tomatine) or interact with the Na+/K+ ATPase in a different manner (viz. veratridine, sanguinarine nitrate, penicillic acid, vanadium pentoxide, harmaline-HCI,5,5'-diphenyl hydantoin, quindonium bromide, and methyl quinolizinum bromide) provides strong evidence that the observed species-related differences are highly specific for cardiotonic steroids. Studies on the binding of [3H]ouabain show that, in comparison to human and monkey cell lines, no significant binding of the drug is observed in cells derived from the resistant species (i.e., mouse and Chinese hamster). The Na+/K+ ATPase from cells of the resistant species is inhibited at much higher concentrations of ouabain and digitoxin in comparison to the enzyme from human cells, and a good correlation is observed between these concentrations and those reported for inhibition of the enzyme from isolated heart muscles of the same species. These results provide strong evidence that the species-related differences in sensitivity to digitalis have a cellular basis and that the cultured cells from various mammalian species provide a useful model system for investigating the mechanism of action of cardiac glycosides.

Animals↗
PubMed1997

Identification of a novel phosphatase sequence motif.

We have identified a novel, conserved phosphatase sequence motif, KXXXXXXRP-(X12-54)-PSGH-(X31-54)-SRXXXXX HXXXD, that is shared among several lipid phosphatases, the mammalian glucose-6-phosphatases, and a collection of bacterial nonspecific acid phosphatases. This sequence was also found in the vanadium-containing chloroperoxidase of Curvularia inaequalis. Several lines of evidence support this phosphatase motif identification. Crystal structure data on chloroperoxidase revealed that all three domains are in close proximity and several of the conserved residues are involved in the binding of the cofactor, vanadate, a compound structurally similar to phosphate. Structure-function analysis of the human glucose-6-phosphatase has shown that two of the conserved residues (the first domain arginine and the central domain histidine) are essential for enzyme activity. This conserved sequence motif was used to identify nine additional putative phosphatases from sequence databases, one of which has been determined to be a lipid phosphatase in yeast.

Amino Acid Sequence↗
PubMed2002

Open-framework and microporous vanadium silicates.

A series of novel vanadium silicates with open-framework and microporous structures has been synthesized under mild hydrothermal conditions. Ten distinct framework types have been identified that all have structures based on cross-linking single silicate sheets with square pyramidal V(IV)O(5) units to give compounds with the general formula A(r)[(VO)(s)(Si(2)O(5))(p)(SiO(2))(q)].tH(2)O, where A is Na, K, Rb, Cs, or a combination. The vanadosilicate (VSH-n) structures have free channel diameters up to 6.5 A and show good thermal stability, absorption, and ion-exchange properties, suggesting their potential for technological applications as molecular sieves or in catalysis.

Journal Article↗
PubMedDate not supplied

Toxicity of selenium compounds to alveolar macrophages.

Selenium compounds released into urban atmospheres as a result of fossil fuel combustion may pose an inhalation hazard to people. Two chemical forms of selenium produced during coal combustion and present in combustion effluent are selenious acid. H2SeO3, and elemental selenium, Se. In an attempt to determine the toxicity of selenium compounds relative to other trace elements, the cytotoxicity of H2SeO3 and Se to rabbit alveolar macrophages in vitro was investigated. Macrophages were obtained by lung lavage and exposed in tissue culture after 20 h. Neither selenious acid nor elemental selenium caused cell lysis at concentrations which decreased total cell viability. Selenious acid was an order of magnitude more toxic then elemental selenium. Elemental selenium was similar in toxicity to environmental contaminants such as CdCl2 and V2O5. These in vitro cytotoxicity data can be used to predict the risk posed to people inhaling selenium compounds at levels found in urban atmospheres.

Animals↗
PubMed2002

Intercalation of cyclic ethers into vanadyl phosphate.

Two cyclic ethers, tetrahydrofuran (THF) and tetrahydropyran (THP), were intercalated into vanadyl phosphate and characterized by X-ray powder diffraction, thermogravimetry, and IR and Raman spectroscopy. Both compounds contain one molecule of ether per formula unit of VOPO(4) and show high thermal stability in comparison with VOPO(4) intercalates with other organic guest molecules. Both ethers are anchored to the VOPO(4) host layers by their oxygen atoms, which are coordinated to the vanadium atoms of the host. The probable arrangement of the tetrahydropyran molecules in the host interlayer space is derived from molecular simulations by the Cerius(2) 4.5 program.

Journal Article↗
PubMed2003

Self-assembly of a polar open-framework uranyl vanadyl hexaoxoiodate(VII) constructed entirely from distorted octahedral building units in the first uranium hexaoxoiodate: K2[(UO2)2(VO)2(IO6)2O].H2O.

The reaction of UO(3) with V(2)O(5) and KIO(4) under mild hydrothermal conditions produces K(2)[(UO(2))(2)(VO)(2)(IO(6))(2)O].H(2)O (1) in the form of orange acicular crystals. The structure of 1 consists of UO(6), VO(6), and IO(6) distorted octahedra that are assembled into a polar, open-framework structure. The distorted VO(6) and IO(6) octahedra edge-share to form chains that run down the c-axis. Each VO(6) octahedron also shares a vertex with an adjacent vanadium atom to link the chains together into a ribbon. The IO(6) units also partake in corner-sharing with the UO(6) units to create interconnected elliptical tubes. The major channels in 1 are filled with K(+) cations and water molecules. The polarity of this compound is caused by alignment of distorted vanadyl hexaoxoiodate ribbons and UO(6) trapezoidal bipyramids resulting in a large second-harmonic generation response of 300 times that of alpha-quartz. Crystallographic data: 1, orthorhombic, space group Pba2, a = 9.984(2) A, b = 16.763(3) A, c = 4.977(1) A, Z = 4 (T = 193 K).

Journal Article↗
PubMed2003

Vanadium(V) complexes of a chelating dianionic [ONNO]-type amine bis(phenolate) ligand: synthesis and solid state and solution structures.

The reaction between VO(OR)(3) (R = (i)()Pr, (t)()Bu, CH(2)CF(3)) and the chelating dianionic bis(phenoxy)amine ligand [ONNO]H(2) affords a mixture of two isomers (A and B in a ratio A:B approximately 3:1) formulated as VO(OR)[ONNO] (1a-c) (R = (i)()Pr (1a), (t)Bu (1b), CH(2)CF(3) (1c)). Multinuclear and NOESY NMR spectroscopy experiments were able to determine the structure in solution of the complexes. Both isomers have the symmetry-related phenolate groups in a trans configuration, the difference arising from the different configuration of the oxo and alkoxo ligands being located either cis (in isomer A) or trans (in isomer B) to the tripodal amino nitrogen donor atom and the (dimethylamino)ethyl sidearm respectively for the oxo and the alkoxo ligands. Crystals of isomer A (cis-1a) were obtained, and the structure determination confirms the arrangement of the ligands around the vanadium center. Analogue complexes VO(X)[ONNO] (X = Cl (2); X = N(3) (3)) were prepared by reacting equimolar amount of [ONNO]H(2) and VO(X)(n)(OR)(3-n) (X = Cl, R = Et, n = 1; X = N(3), R = (i)Pr, n = 2) at ambient temperature. Compounds 2 and 3 were further characterized by NMR spectroscopy experiments and X-ray structure determination. For both 2 and 3, a single isomer is obtained, having a trans-(O,O) configuration for the phenolate groups and a trans configuration of the oxo ligand in respect to the tripodal amino nitrogen donor atom. Finally, complex 2 could also be obtained by chlorination of 1a or 3 using a large excess of ClSiMe(3) in refluxing toluene.

Journal Article↗
PubMed1979

[Molybdocene dichloride as an antitumor agent (author's transl)].

The antitumor activity of molybdocene dichloride is tested against Ehrlich ascites tumor in CF1 mice. The application of 75 of 100 mg/kg 24 h after transplantation achieves 100% tumor inhibition until day 30. Following the d0 and d1 metallocene dichlorides of titanium and vanadium, molybdocene dichloride is the first analogous d2 system revealing similar antineoplastic properties.

Animals↗
PubMed1998

Stimulation of MAP kinase and S6 kinase by vanadium and selenium in rat adipocytes.

To explore the mechanism underlying the insulin-mimetic actions of vanadium and selenium we examined their effects on the mitogen activated protein/myelin basic protein kinases (MAPK) and ribosomal S6 protein kinases, which are among the best characterized of the kinases that comprise the phosphorylation cascade in insulin signal transduction. We observed a transient activation of MAPK and S6 kinases by insulin in rat adipocytes, while both sodium selenate and vanadyl sulphate produced prolonged activation of the kinases. Vanadyl sulphate stimulated the activity of MAPK and S6 kinase by as much as 6 fold and 15 fold, respectively. Pretreatment of the cells with genistein did not affect the activation of MAPK by insulin, but partially blocked the effects of sodium selenate and vanadyl sulphate. Genistein did not change the activation of S6 kinase by insulin, but blocked the activation in vanadyl sulphate- and sodium selenate-treated-cells, suggesting that a genistein sensitive tyrosine kinase may be involved in the activation by these two compounds. Rapamycin, a specific inhibitor of the p70s6k isoform of S6 kinase, partially reduced the activation of S6 kinase activity by sodium selenate, indicating a role for this kinase in the overall activity of the S6 kinase in sodium selenate-treated cells. A similar trend was noted in vanadyl sulphate-treated cells. Thus, this study supports the involvement of MAPK and S6 kinases in the insulin-mimetic actions of vanadium and selenium.

Adipose Tissue↗
PubMed2002

Oxovanadium(V) and cobalt(III) complexes of dithiocarbazate-based Schiff base ligands: formation of a thiadiazole ring by vanadium-induced cyclization of the coordinated ligand.

S-Methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate (H(2)L(1)) and its bromo derivative (H(2)L(2)), which are traditionally biprotic tridentate (ONS) ligands, behave in an unprecedented manner when allowed to react with [VO(acac)(2)] under an oxidative environment in acetonitrile-water medium containing a catalytic amount of alkali metal ion. The products obtained are oxovanadium(V) compounds [VOL(L(cyclic))] (L = L(1), 1a, and L(2), 1b) that contain one molecule of ligand which undergoes metal-induced cyclization to form a thiadiazole ring. Compound 1a crystallizes in the triclinic space group P(-)1 with a = 9.1830(9) A, b = 9.4165(12) A, c = 12.700(2) A, alpha = 100.988(8)(o), beta = 100.195(7)(o), gamma = 78.774(8)(o), V = 1046.3(2) A(3), and Z = 2. With cobalt(III), however, the products [CoL(HL)].H(2)O (L = L(1), 2a, and L(2), 2b) have hydrogen-bonded dimeric structures with each ligand virtually carrying 1.5 units of negative charge as confirmed by X-ray crystal structure analysis of 2a. It also crystallizes in triclinic space group P(-)1 with a = 12.0842(8) A, b = 13.5251(9) A, c = 14.1960(10) A, alpha = 78.122(6)(o), beta = 73.888(6)(o), gamma = 78.255(6)(o), V = 2154.7(3) A(3), and Z = 4. In solution, 2a is a symmetric molecule as indicated by (1)H NMR, involving a characteristic hydrogen-bonded O-H-O broad feature in the downfield (at 14.5 ppm) connecting both monoprotonated (LH(-)) and deprotonated (L(2-)) forms of the ligand--a situation somewhat analogous to the classic H-F-H case as observed in bifluoride ion.

Journal Article↗
PubMed2004

Speciation in the aqueous H+/H2VO4-/H2O2/citrate system of biomedical interest.

The speciation in the quaternary aqueous H+/H2VO4-/H2O2/citrate (Cit3-) and H+/H2VO4-/Cit3-/L-(+)-lactate (Lac-) systems has been determined at 25 degrees C in the physiological medium of 0.150 M Na(Cl). A combination of 51V NMR integral intensities and chemical shift (Bruker AMX500) as well as potentiometric data (glass electrode) have been collected and evaluated with the computer program LAKE, which is able to treat multimethod data simultaneously. The pKa-values for citric acid have been determined as 2.94, 4.34 and 5.61. Altogether six vanadate-citrate species have been found in the ternary H+/H2VO4-/Cit3- system in the pH region 2-10, only two of which are mononuclear. Reduction of vanadium(V) becomes more pronounced at pH < 2. Solutions, in which reduction occurred to any extent, were excluded from all calculations. In the quaternary H+/H2VO4-/H2O2/Cit3- system, eight complexes have been found in addition to all binary and ternary complexes over the pH region 2-10, including three mononuclear species. Equilibria in general are fast, but the significant and rapid decomposition of peroxide in acidic solutions limited the final model to pH > 4. In the quaternary H+/H2VO4-/Cit3-/Lac- system, two mixed-ligand species have been determined, with the compositions V2CitLac2- and V2CitLac3- (pKa = 5.0). To our knowledge, this is the first time such complexes have been reported for vanadium(V). 51V NMR chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. When suitable, structural proposals are given, based on 13C NMR measurements and available literature data of related compounds.

Citrates↗
PubMed1989

Long-term effects of vanadyl treatment on streptozocin-induced diabetes in rats.

The vanadate and vanadyl forms of vanadium have been shown by many investigators to have insulinlike effects on glucose metabolism. Many investigators have shown that vanadium, or its salts, counteracts the hyperglycemia associated with streptozocin-induced diabetes (STZ-D) in the rat, although insulin secretion remains depressed. Studies of the action of vanadate on insulin secretion and glucose metabolism have not addressed the question of possible long-term effects of this compound on glucose metabolism extending beyond the period of oral administration. This study was undertaken to assess the effects of treatment (3 wk) and withdrawal of vanadyl sulfate (13 wk) on glucose metabolism, insulin secretion, and islet insulin content of STZ-D rats. Our results indicate that STZ-D rats that have had blood glucose levels normalized by 3 wk of vanadyl treatment remain normoglycemic after 13 wk of withdrawal from treatment. Normal glucose tolerance was observed in vanadyl-treated diabetic animals despite depressed fasting and glucose-stimulated plasma insulin levels. Insulin secretion from the isolated perfused pancreas was greater after vanadyl treatment than in untreated diabetic rats, although it was only 12% of values from controls. Three weeks of vanadyl treatment of STZ-D rats, followed by 13 wk of withdrawal, yielded islets close in size and insulin content of control islets, even though in vivo and in vitro insulin secretion was impaired. This study has shown that short-term vanadyl treatment of STZ-D rats yields normalization of glucose tolerance and protection of islets from destruction by STZ.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMedDate not supplied

Inhibitory effects of vanadium pentoxide on respiration of rat liver mitochondria.

The bioenergetic functions of liver mitochondria were studied following the acute and chronic exposure of rats to vanadium pentoxide via respiratory tract. The mitochondrial respiration with glutamate or succinate as substrate was inhibited significantly when compared to the control animals. No inhibition was found with ascorbate. The same effects were observed in vitro. Vanadium (V) was responsible for these inhibitory effects. It is postulated that significant amounts of vanadate are accumulated in the intermembrane space of liver mitochondria of the exposed rats. The process of "detoxification" by reduction of vanadate in the tissue may be insufficient to prevent the deleterious action of this compound on liver mitochondria.

Animals↗
PubMed2004

Nonoxovanadium(IV) and oxovanadium(V) complexes with mixed O, X, O-donor ligands (X = S, Se, P, or PO).

Ligating properties of four potentially tridentate bisphenol ligands containing [O, X, O] donor atoms (X = S 1, Se 2, P 3, or P=O 4) toward the vanadium ions in +IV or +V oxidation states have been studied. Each ligand with different heterodonor atoms yields as expected nonoxovanadium(IV) complexes, V(IV)L(2), whose structures have been determined by X-ray diffraction methods as having six-coordinate V(IV), VO(4)X(2), core. Compounds 1-4 have also been studied with electrochemical methods, variable-temperature (2-295 K) magnetic susceptibility measurements, X-band electron paramagnetic resonance (EPR) (2-60 K) spectroscopy, and magnetic circular dichroism (MCD) (5 K) measurements. Electrochemical results suggest metal-centered oxidations to V(V) (i.e., no formation of phenoxyl radicals from the coordinated phenolates). A combination of density functional theory calculations and experimental EPR investigations indicates a dramatic effect of the heteroatoms on the electronic structure of 1-4 with consequent reordering of the energy levels; 1 and 3 possess a trigonal ground state (d(z)()(2))(1), but 4 with the phosphoryl oxygen as the heterodonor atom in contrast exhibits a tetragonal ground state, (d(xy)())(1). On the basis of the intense electronic transitions in absorption spectra, all electronic transitions observed for 4 have been assigned to ligand-to-metal charge-transfer transitions, which have been confirmed by preliminary resonance Raman measurements and C/D ratios obtained from low-temperature MCD spectroscopy. Moreover, diamagnetic complexes 5 and 6 containing mononuclear and dinuclear oxovanadium(V) units have also been synthesized and structurally and spectroscopically ((51)V NMR) characterized.

Journal Article↗
PubMed1988

Organ distribution and pharmacokinetics of titanium after treatment with titanocene dichloride.

The pharmacokinetics and organ distribution of titanium (Ti) were analyzed at various intervals up to 96 h after a single i.p. injection of a therapeutic dose of the antitumor agent titanocene dichloride (TDC, 60 mg/kg) by use of flameless atomic absorption spectroscopy in dried organ specimens. Highest organ concentrations were found in the liver and the intestine where 80-90 mg Ti/kg dry weight were accumulated at 24 and 48 h, corresponding to liver/blood and intestine/blood ratios of 8-9. However, at no time point after the TDC application, the Ti concentrations in brain tissue exceeded those of control animals. In solid tumors growing subcutaneously in mice, increasing amounts of Ti were found during the course of the experiment, reaching concentrations between 10 and 15 mg Ti/kg at 24 and 96 h after single i.p. application of TDC. These results confirm a typical pattern of organ distribution of Ti-containing metabolites of TDC, which clearly differs from that observed for vanadium after application of vanadocene dichloride or for platinum after treatment with cisplatin.

Animals↗
PubMed2006

A new structural motif for biological iron: iron K-edge XAS reveals a [Fe4-mu-(OR)5(OR)(9-10)] cluster in the ascidian Perophora annectens.

The Phlebobranch ascidian Perophora annectens surprisingly exhibited a biological Fe/V ratio of approximately 15:1 on multichannel X-ray fluorescence analysis of two independent collections of organisms. Iron K-edge X-ray absorption spectroscopy (XAS) indicated a single form of iron. The XAS K-edge of the first collection of blood cells was shifted approximately +1 eV relative to that of the second, indicating redox activity with average iron oxidation states of 2.67+ and 2.60+. The first-derivative iron XAS K-edge features at 7120.5, 7124, and 7128 eV resembled the XAS of magnetite but not of ferritin or of dissolved Fe(II) or Fe(III). Pseudo-Voigt fits to blood-cell iron K-edge XAS spectra yielded 12.4 integrated units of preedge intensity, indicating a noncentrosymmetric environment. The non-phase-corrected extended X-ray absorption fine structure (EXAFS) Fourier transform spectrum showed a first-shell O/N peak at 1.55 angstroms and an intense Fe-Fe feature at 2.65 angstroms. Fits to the EXAFS required a split first shell with two O at 1.93 angstroms and three O at 2.07 angstroms, consistent with terminal and bridging alkoxide ligands, respectively. More distant shells included three C at 2.87 angstroms, two Fe at 3.08 angstroms, three O at 3.29 angstroms, and one Fe at 3.8 angstroms. Structural models consistent with these findings include a [Fe4(OR)13](2-/3-) broken-edged Fe4O5 cuboid or a [Fe4(OR)14](3-/4-) "Jacob's ladder" with three edge-fused Fe2(OR)2 rhombs. Either of these models represents an entirely new structural motif for biological iron. Vanadium domination of blood-cell metals cannot be a defining trait of Phlebobranch tunicates so long as P. annectens is included among them.

Animals↗
PubMed1995

Roles of protein-tyrosine phosphatases in Stat1 alpha-mediated cell signaling.

Different Stat proteins are activated through phosphorylation of unique tyrosine residues in response to different cytokines and growth factors. Interferon-gamma activates Stat1 molecules that form homodimers and bind cognate DNA elements. Here we show that treatment of permeabilized cells with 200-500 microM peroxo-derivatives of vanadium, molybdenum, and tungsten results in the accumulation of constitutively phosphorylated Stat1 alpha molecules. In contrast, treatment of permeabilized cells with orthovanadate, vanadyl sulfate, molybdate, and tungstate at the same range of concentrations does not result in the accumulation of activated Stat1 alpha molecules in the absence of ligand. However, these compounds inhibit the inactivation of interferon-gamma-induced DNA-binding activity of Stat1 alpha. A 4-6-h exposure of the permeabilized cells to orthovanadate, molybdate, and tungstate, but not vanadyl sulfate, results in a ligand-independent activation of Stat1 alpha, which is blocked by the inhibition or depletion of NADPH oxidase activity in the cells, indicating that NADPH oxidase-catalyzed superoxide formation is required for the bioconversion of these metal oxides to the corresponding peroxo-compounds. Interestingly, ligand-independent Stat1 alpha activation by peroxo-derivatives of these transition metals does not require Jak1, Jak2, or Tyk2 kinase activity, suggesting that other kinases can phosphorylate Stat1 alpha on tyrosine 701.

Animals↗