Search

A simple donor atom additivity relationship has been used to calculate the donor atom electrochemical contribution (DEC) of the Oac (acetylacetonate-enolic oxygen), OPh (phenolic oxygen), SPh (mercaptophenol sulfur), Nam (deprotonate amide nitrogen), Nim (imine nitrogen) and Npy (pyridine nitrogen) to the redox processes of the square pyramidal vanadyl complexes. The study focuses on the amidate vanadyl complexes because of (a) their biological interest and (b) the existence of data from plethora complexes studied in great details. The electrochemical contributions for the vanadyl oxidation and reduction processes increase following the same order, OPh ~ Oac(enolic) Ph ~ Nam im py. These values predict the electrochemical potentials of square pyramidal vanadyl complexes with high accuracy. Octahedral complexes with the same equatorial environment show significant shift of the oxidation potentials to lower values. The DEC influence to the square pyramidal vanadyls' electrochemical potentials has been evaluated. © 2015 Elsevier Inc. All rights reserved. 147 39 43 Cited By :5

Vanadium compounds mimic insulin actions in different cell types. The present study concerns the insulin-like effects of three vanadium(V) derivatives and one vanadium(IV) complex on osteoblast-like (UMR106 and MC3T3E1) cells in culture. The vanadium oxalate and vanadium citrate complexes hydrolyzed completely under the culture conditions, whereas more than 40% of the vanadium tartrate and nitrilotriacetate complexes remained. Vanadate, as well as vanadium oxalate, citrate, and tartrate complexes enhanced cell proliferation (as measured by the crystal violet assay), glucose consumption, and protein content in UMR106 and MC3T3E1 osteoblast- like cells. The vanadium nitrilotriacetate complex (the only peroxo complex tested) stimulated cell proliferation in UMR106 but not in MC3T3E1 cells. This derivative strongly transformed the morphology of the MC3T3E1 cells. All vanadium(V) compounds inhibited cell differentiation (alkaline phosphatase activity) in UMR106 cells. Our data are consistent with the interpretation that vanadium oxalate and citrate complexes hydrolyze to vanadate. Vanadium nitrilotriacetate would appear to be toxic for normal MC3T3E1 osteoblasts. In contrast, the vanadium tartrate complex induced a proliferative effect however, it did not alter cell differentiation. 338 1 7 14 Cited By :61

Reaction of the N,N-disubstituted bis(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2bihyat) with cis-[MoVIO2(acac)2] in tetrahydrofuran resulted in isolation of the mononuclear compound cis-[MoVIO 2(bihyat)] (1). The treatment of Na2MoVIO 4·2H2O with the ligand H2bihyat in aqueous solution gave the dinuclear compounds cis-[MoVI 2O4(bihyat)2(H2O)2] (2) and trans-[MoVI2O4(bihyat)2(H 2O)2] (3) at pH values of 3.5 and 5.5, respectively. The structures for the three molybdenum(VI) compounds were determined by X-ray crystallography. Compound 1 has a square-pyramidal arrangement around molybdenum, while in the two dinuclear compounds, each molybdenum atom is in a distorted pentagonal-bipyramidal environment of two bridging and one terminal oxido groups, a tridentate (O,N,O) bihyat2- ligand that forms two five-membered chelate rings, and a water molecule trans to the terminal oxido group. The dinuclear compounds constitute rare examples containing the {Mo 2VIO2(μ2-O2)} 4+ moiety. The potentiometry revealed that the Mo VIbihyat2- species exhibit high hydrolytic stability in aqueous solution at a narrow range of pH values, 3-5. A subtle change in the coordination environment of the five-coordinate compound 1 with ligation of a weakly bound water molecule trans to the oxido ligand (1w) renders the equatorial oxido group in 1w more nucleophilic than that in 1, and this oxido group attacks a molybdenum atom and thus the dinuclear compounds 2 and 3 are formed. This process might be considered as the first step of the oxido group nucleophilic attack on organic substrates, resulting in oxidation of the substrate, in the active site of molybdenum enzymes such as xanthine oxidase. Theoretical calculations in the gas phase were performed to examine the influence of water on the dimerization process (1 → 2/3). In addition, the molecular structures, cis/trans geometrical isomerism for the dinuclear molybdenum(VI) species, vibrational spectra, and energetics of the metal-ligand interaction for the three molybdenum(VI) compounds 1-3 have been studied by means of density functional theory calculations. © 2012 American Chemical Society. 51 24 13138 13147 Cited By :3

Although dogma states that vanadate is readily reduced by glutathione, cysteine, and other thiols, there are several examples documenting that vanadium(V)-sulfur complexes can form and be observed. This conundrum has impacted life scientists for more than two decades. Investigation of this problem requires an understanding of both the complexes that form from vanadium(IV) and (V) and a representative thiol in aqueous solution. The reactions of vanadate and hydrated vanadyl cation with 2-mercaptoethanol have been investigated using multinuclear NMR, electron paramagnetic resonance (EPR), and UV-vis spectroscopy. Vanadate forms a stable complex of 2:2 stoichiometry with 2-mercaptoethanol at neutral and alkaline pH. In contrast, vanadate can oxidize 2-mercaptoethanol this process is favored at low pH and high solute concentrations. The complex that forms between aqueous vanadium(IV) and 2-mercaptoethanol has a 1:2 stoichiometry and can be observed at high pH and high 2-mercaptoethanol concentration. The solution structures have been deduced based on coordination induced chemical shifts and speciation diagrams prepared. This work demonstrates that both vanadium(IV) and (V)-thiol complexes form and that redox chemistry also takes place. Whether reduction of vanadate takes place is governed by a combination of parameters: pH, solute- and vanadate-concentrations and the presence of other complexing ligands. On the basis of these results it is now possible to understand the distribution of vanadium in oxidation states (IV) and (V) in the presence of glutathione, cysteine, and other thiols and begin to evaluate the forms of the vanadium compounds that exert a particular biological effect including the insulin-enhancing agents, antiamoebic agents, and interactions with vanadium binding proteins. © 2010 American Chemical Society. 49 9 4245 4256 Cited By :59

Reaction of the non-innocent dinucleating ligand 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]hydroquinone (H 6bicah) with VO (2+) and VO 4 (3-) salts in water in the pH range 2 to 4.5 provides a series of novel tetranuclear V (IV) and/or V (V) macrocycles with the main core consisting of the anions [V (V) 4O 4(mu-O) 2(mu-bicah) 2] (4-) isolated at pH = 2.5 and [V (IV) 2V (V) 2O 4(mu-O) 2(mu-bicas)(mu-bicah)] (5-) and [V (IV) 4O 4(mu-O) 2(mu-bicas) 2] (6-) isolated at pH = 4.5 (bicas (*5-) = 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]- p-semiquinonate), whereas at pH = 2 the dinuclear [(V (IV)O) 2(OH 2) 2(mu-bicah)] (2-) was obtained. All vanadium compounds have been characterized, and the charge of the ligand has been assigned in solid state by X-ray crystallography and infrared spectroscopy. The structures of the tetranuclear anions consist of four vanadium atoms arranged at the corners of a rectangle with the two bridging bicas (*5-) and/or bicah (6-) ligands on the long and the two V (IV/V)-O-V (IV/V) bridges on the short sides of the rectangle. UV-vis, (51)V and (1)H NMR spectroscopy and electrochemistry showed that these complexes interconvert to each other by varying the pH. This pH induced redox transformation of the tetranuclear anions has been attributed to the shift of the reduction potential of the bicas (*5-) to higher values by decreasing the pH. The electron is transferred intramolecularly from the metal ion to the electron accepting semiquinones resulting in reduction of bicas (*5-) to bicah (6-) and concurrent oxidation of the V (IV) to V (V). The resulting complexes are further oxidized by atmospheric oxygen. This system as a model for the H (+) coupled redox reactions in metalloenzymes and its relevance is discussed briefly.

The reaction of Cu2+ acetate monohydrate with 2-[N,N′-bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H 4cacp), 2-[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H 4cah) and the dinucleating 2,5-bis[N,N-bis(carboxymethyl)aminomethyl] hydroquinone (H6bicah) in water results in the formation of several Cu2+ species, which are in dynamic equilibrium in aqueous solution and their stability is pH dependent. A systematic crystallographic study of these species was pursued, resulting in the characterization of most of the species. Additional techniques were employed to characterize the molecules in the solid state (infrared spectroscopy) and in solution (UV-vis spectroscopy and electrochemistry). These measurements show that the Cu2+ ions are ligated mainly to the iminodiacetate at pH 6, the phenol oxygen was deprotonated and dinuclear-bridged species, from the phenolate oxygen complexes exhibiting a Cu2+2O2 core, were isolated. The coordination environment around the copper ions varies between trigonal bipyramidal, tetragonal pyramidal and distorted octahedral geometries. The two unpaired electrons of the Cu2+ ions are found to be antiferromagnetically coupled. A survey of the magnetic and structural properties of the dinuclear phenoxide bridged Cu2+ complexes shows that the strength of the antiferromagnetic coupling is linearly dependent on the Cu-Ophenolate bond lengths, at bond distances below 1.98 . The effect of the Cu-O-Cu angles on the magnetic properties of the complexes is also discussed. © The Royal Society of Chemistry 2008. 44 6188 6204 Cited By :25

Reaction of the ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5- triazine (H2bihyat) with NaVVO3 in aqueous solution followed by addition of either Ph4PCl or C(NH 2)3Cl, respectively, gave the mononuclear vanadium(V) compounds Ph4P[VVO2(bihyat)]·1.5H 2O (1) and C(NH2)3[VVO 2(bihyat)] (2). Treatment of VIVOSO4· 5H2O with the ligand H2bihyat in methyl alcohol under specific conditions gave the oxo-bridged dimer [VV2O 2(μ2-O)(bihyat)2] (3). The structures for 1 and 3 were determined by X-ray crystallography and indicate that these compounds have distorted square-pyramidal arrangement around vanadium. The ligand bihyat2- is bonded to vanadium atom in a tridentate fashion at the pyridine-like nitrogen atom and the two deprotonated hydroxylamino oxygen atoms. The high electron density of the triazine ring nitrogen atoms, which results from the resonative contribution of electrons of exocyclic nitrogen atoms (Scheme 4), leads to very strong V-N bonds. The cis-[VVO 2(bihyat)]- species exhibits high hydrolytic stability in aqueous solution over a wide pH range, 3.3-11.0, as it was evidenced by 1H and 51V NMR spectroscopy and potentiometry. The high affinity of the H2bihyat ligand for the VVO 2+ unit, its tridentate character, as well as its small size, paves the way for potential applications in medicine, analysis, and catalysis for the C(NH2)3[VVO 2(bihyat)] compound. The molecular structures, vibrational and electronic spectra, and the energetics of the metal-ligand interaction for compounds 1 and 3 have been studied by means of density functional calculations. © 2008 American Chemical Society. 47 24 11698 11710 Cited By :17

Surface-active metalorganic complexes can be used to construct organic thin films with excellent electronic and catalytic properties. We have recently introduced a new versatile surface-active ligand, which can efficiently coordinate a wide range of transition metals. In the present work we report an investigation of Langmuir monolayers of VV, MoVI and TiIV complexes of this ligand, using surface pressure-area isotherms, Brewster-angle microscopy, and Grazing incidence X-ray diffraction. The monolayers of these complexes are stable enough over broad temperature ranges to allow efficient transfer to solid substrates. © 2007 Elsevier Inc. All rights reserved. 317 2 544 555 Cited By :4

Vitamin E succinate selenium-conjugated molecules were synthesized and their apoptogenic properties were evaluated. 4-Methyl-2-phenylselenyl succinate (4) was prepared by the reaction of sodium benzeneselenolate with 2-bromosuccinic anhydrite in methanol solution. The methyl ester was converted to the acid (5) by hydrolysis with aqueous hydrochloric acid. Reaction of the 2-phenylselenyl succinic anhydrite (6) with α-tocopherol (1a), γ-tocopherol (1c), and γ-tocotrienol (2c) in acidic conditions gave the respective esters. The free radical scavenging properties of α-tocopheryl-2-phenylselenyl succinate (7), γ-tocopheryl-2- phenylselenyl succinate (8), and γ-tocotrienyl-2-phenylselenyl succinate (9) were evaluated in comparison with those of α-tocopheryl succinate (10), γ-tocopheryl succinate (11), and γ-tocotrienyl succinate (12), respectively, and the free tocopherols and γ-tocotrienol. Compounds 7-9 induced a statistically significant decrease in prostate cancer cell viability compared to 10-12, respectively, or 5, exhibiting features of apoptotic cell death and associated with caspase-3 activation. These data show that structural modifications of vitamin E components by 5 enhance their apoptogenic properties in cancer cells. © 2005 Elsevier Ltd. All rights reserved. 14 8 2684 2696 Cited By :23

293(2) K) are as follows: (1) monoclinic space group C2/c, a = 14.561(7) Å, b = 14.871(9) Å, c = 7.250(4) Å, β = 95.40(4)°, Z = 4 (2) monoclinic space group P21/c, a = 19.080(2) Å, b = 9.834(1) Å, c = 15.156(2) Å, β = 104.62(1)°, Z = 4. 1H NMR measurements indicate that complex 2 retains its structure in CD3CN solution Reaction of [UO2(NO3)2] with the hydroxy ketones 3-hydroxy-2-methyl-4-pyrone (Hma) and 3-hydroxy-1,2-dimethyl-4(1H)- pyridone (Hdpp)(Hdpp) in aqueous acidic solutions (pH ∼ 3) yields the compounds [UO2(ma)2(H2O)]·H2O (1·H2O) and [UO2(dpp)(Hdpp)2(H 2O)]ClO4 (2), respectively. X-ray diffraction shows that the geometry around the metal ion in both complexes is pentagonal bipyramid. Uranium ion in the crystal structure of 1 were found to be ligated with two chelate ma- groups and one unidentate H2O molecule (C coordination mode) at the equatorial plane, while in 2 with two single-bonded Hdpp there were one chelate dpp- and one H2O molecule (P coordination mode). Crystal data (Mo Kα however, in DMSO-d6 both complexes adopt the C structure. Line-shape analysis for the 1H NMR peaks of 2 at various temperatures shows a fast intramolecular exchange process between the chelate dpp- and one of the single bonded Hdpp ligands and one slower exchange between all three ligands. The activation parameters and the decrease of the exchange rate by replacing unidentate ligand with DMSO indicate the dissociation of the unidentate ligand as the rate-determining step for the former exchange. Density functional calculations (DFT) support this mechanism and give a quantitative interpretation of the electronic structure of the two ligands and the geometries adopted by the complexes. 43 26 8336 8345 Cited By :9

Reaction of the non-oxo VIV species [VIVCl2(LOO)2] [LOO = acetylacetonate (acac-) or benzoylacetonate (bzac-)] with a chelate nitrogen-donor ligand LNN in acetonitrile leads to the reduction of VIV to VIII and the formation of the mononuclear VIII compounds of the general formula [VIIICl2(LOO)(LNN)] (LOO and LNN are acac- and bipy for 1 acac- and 5,5′-me2bipy for 2 acac- and 4,4′-tb2bipy for 3 acac- and phen for 4 bzac- and bipy for 5 bzac- and phen for 6). The reduction of the VIV complexes was monitored by GC-MS and 1H NMR spectroscopy. Both one- and two-dimensional (2D COSY and 2D EXSY) 1H NMR techniques were used to assign the observed 1H NMR resonances of 1-6 in CD2Cl2 or CDCl3 solution. It appeared that in solution these VIII complexes form two isomers which are in equilibrium: cis-[VIIICl2(LOO)(LNN)] ⇌ trans-[VIIICl2(LOO)(LNN)]. 2D EXSY cross-peaks were clearly observed between bipy- and acac-hydrogen atoms of the two geometrical isomers of 1-3 as well as between bipy and acac- protons of the cis isomer, indicating a dynamic process that corresponds to cis-trans isomerization and a cis-cis racemization. The thermodynamic and kinetic parameters of the equilibrium between these two isomers were calculated for compounds 1 and 2 by using variable temperature (VT) NMR data. Both cis-trans isomerization and cis-cis racemization processes probably proceed with an intramolecular twist mechanism involving a trigonal prismatic transition state. Density functional calculations (DFT) also indicated such a rearrangement mechanism. 42 15 4640 4649 Cited By :7

Reaction of the p-hydroquinone derivative H2Na4bicah·4H2O with either VIVOSO4·3H2O and NaVVO3 in equivalent quantities or with NaVVO3 yields the tetranuclear VIVO2+ macrocycle-semiquinonate compound Na6{(VIVO)4-(μ2-O) 2[μ2-bicas·(-5)-N,O,O,O]2}·Na 2SO4·20H2O (1·Na2SO4·20H2O) and the dinuclear cis-VVO2+-hydroquinone species Na4{(VVO2)2[μ2- bicah(-6)-N,O,O,O]}·11H2O (2·11H2O) respectively. Compounds 1·Na2SO4·20H2O and 2·11H2O were characterized by X-ray structure analysis and ab initio calculations. 23 2786 2787 Cited By :21

Reaction of the multifunctional phenolic ligands 2,5-bis[ N , N -bis(carboxymethyl)aminomethyl]hydroquinone (H 6 cahq), 2,2′-bis[ N , N -bis(carboxymethyl)aminomethyl]-4,4′-isopropylidenediphenol (H 6 capd), 2,2′,2″-tris[ N , N -bis(carboxymethyl)aminomethyl]-1,1,1-tris(4-hydroxyphenyl)ethane (H 9 catp) and the monofunctional 2-[ N,N -bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H 3 cacp), with VOSO 4 and NaVO 3 affords the oxo-bridged mixed-valence vanadium(IV/V) Na 6 [(VO) 4 (μ-O) 2 (μ-cahq) 2 ]·Na 2 SO 4 ·20H 2 O ( 1 ), H n Na 3− n [(VO) 2 (μ-O)(μ-cacp) 2 ] ( 2 ), H n Na 3− n [(VO) 4 (μ-O) 2 (μ-capd) 2 ] ( 3 ), H n Na 9− n [(VO) 6 (μ-O) 3 (μ 3 -catp) 2 ] ( 4 ). In addition to the synthesis, we report the infrared, magnetic, optical and electrochemical properties of these complexes. The hydrolytic stability at different pH values was also investigated using visible spectroscopy.

A novel series of vanadium(V) hydroxylamido complexes with weak ligands including glycine, [VO-(NH2O)2(Glycine)]· H2O (1) serine, [VO(NH2O)2(Serine)]·H2O (2) glycylglycine, [VO(NH2O)2(GlyGly)]·H2O (3) and imidazole, [VO(NH2O)2(imidazole)2]Cl (4) were prepared and characterized both in solution and in the solid state. All complexes were prepared in aqueous solution at neutral pH at ambient temperature and as crystalline solids. The vanadium atom in these four complexes is seven-coordinate with pentagonal bipyramidal geometry. In complexes 1-3 the hydroxylamido groups are coordinated side-on with the hydroxylamido nitrogen cis to the organic ligand in the equatorial plane. In complex 4, the hydroxylamido groups are coordinated side-on with the hydroxylamido nitrogen trans to the imidazole ligand in the equatorial plane. The UV/vis spectra of these complexes were also examined, and the absorbance peaks show similarities between the properties of the vanadium(V) hydroxylamido complexes and known side-on peroxovanadium complexes. Multinuclear NMR studies were conducted to characterize the solution structure and properties of compounds 1-4. A particularly detailed study of compound 3 was carried out since the analogous vanadium(V) peroxo complex could also be prepared. Complex 4 was less labile and more stable than the corresponding diperoxovanadium(V)-imidazole complex, H[VO(O2)2(imidazole)] (5). In solution the inherent asymmetry of the hydroxylamido ligand has facilitated an in-depth study of ligand exchange. Upon dissolution, compound 4 forms three isomeric complexes, all of which have one of the original two-coordinated imidazole groups in the complex dissociated. 1D and 2D EXSY and multinuclear NMR spectroscopies were used to examine the stoichiometry of the isomers, their structures, and the dynamics of their ligand exchanges. Specifically, both inter- and intramolecular exchanges were observed for the dihydroxylamine-vanadium(V)-imidazole involving both the coordinated imidazole and the coordinated hydroxylamido groups. The intramolecular exchange of the coordinated imidazole in 5 was compared to the exchange in the hydroxylamido complex, and the hydroxylamido compounds were found to have some properties that may be advantageous over those of the diperoxovanadium(V) complexes. In summary, evidence was generated to support the existence of a novel and unprecedented asymmetric hydroxylamido-metal complex as well as the first isolation and characterization of a vanadium(V)-imidazole complex not enjoying stabilization by other organic ligands. 119 38 8901 8915 Cited By :91