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.     

Decavanadate protonation degrees in aqueous solution

Aqueous solutions of vanadium(V) have been prepared at different OH⁻ vs. vanadium concentrations from both decavanadic acid and metavanadate solutions. These solutions have been extracted with an excess of tetraheptylammonium bromide in benzene. The bromide displaced has been determined in order to gain information on the average charge of the extracting species already known to be variously protonated decavanadate anions. The addition of a constant excess of supporting electrolytes has been avoided, as it is known it could affect the position of equilibria.Besides the already well known H₂V₁₀O₂₈⁴⁻, HV₁₀ O₂₈⁵⁻ and V₁₀O₂₈⁶⁻ species, strong evidence has also been obtained for the existence of H₃V₁₀O₂₈³⁻.Moreover, a slow disproportionation of V₁₀O₂₈⁶⁻ into HV₁₀O₂₈⁵⁻ and V₂O₇⁴⁻ (or HVO₄²⁻) during a first stage, and then into metavanadate, resulted.Therefore, H₆V₁₀O₂₈ proves a strong acid as triprotic instead of tetraprotic, as reported in the literature. Inconsistent results are almost certainly due to the high ionic media usually employed.     

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.     

Differences in the binding modes of phytochelatin to cadmium (II) and Zinc(II) ions

An ¹H NMR (nuclear magnetic resonance) spectroscopic structural analysis of Cd²⁺ complexes formed with the pentapeptide phytochelatin, (NH₃)⁺−(ψ-Glu-Cys)₂−Gly−COO−(PC₂), at a pH of 7.5 showed that the two thiol groups of the Cys residues and either the carbonyl or amide group of the peptide bond between Glu1 and Cys1 act as possible donor groups in the complexes at Cd²⁺/PC₂ ratios up to 0.4. As the ratio increases, the carboxylate group of Glu2 and either the carbonyl or amide group of the peptide bond between Cys1 and Glu2 comes to serve as a donor group. The manner in which Cd²⁺ forms complexes with PC₂ is distinctly different from Zn²⁺ and might account for the role of phytochelatin in Cd²⁺ detoxification. Electron absorption spectrometry demonstrated that the Cd²⁺ complexes are coordinated in a tetrahedral fashion by four thiol groups and that several sulfur atoms might bridge Cd²⁺ ions, resulting in the formation of polynuclear complexes. This contrasts with Zn²⁺ complex formation, which consists exclusively of a 1:1 complex.     

Interaction and release of soulble immune complexes from mouse B luymphocytes

Soluble immune complexes (¹²⁵I BSA-anti-BSA-C) bind to B lymphocytes and accumulate at one pole of the cells (“caps”). The complexes remain on the membrane after incubation of the cells at 37 °C in tissue culture medium for several hours. The ¹²⁵I BSA can be quantitatively removed from the cell surface by incubation with excess BSA but not with excess antibody to BSA or preformed BSA-anti-BSA-C complexes. The release of ¹²⁵I BSA is probably due to the removal of the complexes from the cell membrane and not to an exchange between unlabeled BSA in the medium and the labeled BSA present in the membrane-bound complexes. Release of ¹²⁵I BSA by excess BSA is temperature dependent. The membrane-bound complexes can also be removed by incubating the cells with papain fragments of rabbit antibody to mouse Ig (anti-γ₁, γ₂, and k Ig chains). However, after exposure to divalent [F(ab′)² or 7S Ig] rabbit antibodies to mouse Ig, the complexes remain associated with the cells. In addition, after such treatment the complexes cannot be removed by excess BSA or by Fab anti-Ig.     

Stability and isomerization of complexes formed by metal ions and cytosine isomers in aqueous phase

We present a systematic study of the stability of the formation of complexes produced by four metal ions (M^+/2+) and 14 cytosine isomers (C_n). This work predicts theoretically that predominant product complexes are associated with higher-energy C₄M^+/2+ and C₅M^+/2+ rather than the most stable C₁M^+/2+. The prediction resolves successfully several experimental facts puzzling two research groups. Meanwhile, in-depth studies further reveal that direct isomerization of C₁?C₄ is almost impossible, and also that the isomerization induced by either metalation or hydration, or by a combination of the two unfavorable. It is the single water molecule locating between the H1(?N1) and O2 of the cytosine that plays the dual roles of being a bridge and an activator that consequently improves the isomerization greatly. Moreover, the cooperation of divalent metal ion and such a monohydration actually leads to an energy-free C₁←C₄ isomerization in the gas phase. Henceforth, we are able to propose schemes inhibiting the free C₁←C₄ isomerization, based purely on extended hydration at the divalent metal ion.

Structural analysis of the anti-arthritic drug Auranofin: Its complexes with cysteine, selenocysteine and their fragmentation products

Positive mode electrospray mass spectrometry was used to investigate complexes of cysteine and selenocysteine with the metallo-drug Auranofin and the analogous chlorotriethylphosphine gold. Evidence for all the complexes, with the exception of the Auranofin-selenocysteine complex, was obtained. Several fragmentation products were examined and their proposed structures reported. Structural details of many experimentally observed ions including [Auranofin + H]⁺, [(CH₃CH₂)₃P-Au-cysteine]⁺ and [(CH₃CH₂)₃P-Au-methylselenocysteine]⁺ were examined by means of hybrid density functional theory at the B3LYP/DZVP level. Structural information and relative free energies are presented for several isomers of each ion considered.     

Conformational peculiarities of rRNA inff supMet from E. coli as revealed by fluorescent methods

Conformational transitions in several individual tRNAs (tRNA _inff ^supMet , tRNA^Phe from E. coli, tRNA _inf1 ^supVal , tRNA^Ser, tRNA^Phe from yeast) have been studied under various environmental conditions. The binding isotherms studies for dyes-tRNA complexes exhibited similarities in conformational states of all tRNAs investigated at low ionic strength (0.01 M NaCl). By contrast, at high ionic strength (0.4 M NaCl or 2×10^-4 M Mg²⁺) a marked difference is found in structural features of tRNA _inff ^supMet as compared with other tRNAs used. The tRNA _inff ^supMet is the only tRNA species that does not reveal the strong type of complexes with ethidium bromide, acriflavine and acridine orange.     

Synthesis,FT-IR and 1H NMR studies of alkali and alkaline earth metal complexes with guanosine

The synthesis of complexes of Li(I), K(I), Mg(II), Ca(II) and Ba(II) with guanosine in basic non aqueous solutions is described. The complexes were of two types: (1) complexes having the general formula, M(Guo)_nX_m·YH₂O·ZC₂H₅OH, where M = Mg(II), Ca(II), Ba(II) and Li(I), n = 1,2,4, X = Cl^?, Br^?, NO₃^?, ClO₄^? and OH^?, m = 1,2, Y = 0?6 and X = 0?2, and (2) complexes with the general formula, M(GuoH-1)(OH)_n^?1·YH₂O, where M = K(I), Ca(Il) and Ba(II), GuoH-1 =Ionized guanosine at N₁, n = 1,2 and Y = 1?3. The complexes are characterized by their proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared (FT-IR) spectra. The FT-IR and ¹H NMR data of the non ionized nucleoside complexes suggest that the metal binding is through the N₇-site of guanine and that the anion (X) is hydrogen bonded to N₁H and NH₂ groups. In the N₁-ionized guanosine complexes the metal binding is via the O₆^? of guanine. All the complexes formed exhibited a transition of the sugar conformation from C₂′-endo/anti in the free nucleoside to C₃′-endo/anti in the metal complexes.     

Studies of mononuclear and dinuclear complexes of dibromodimethylplatinum(IV): Preparation, characterization and crystal structures

A number of complexes of the types [PtBr₂Me₂(N^?N)] (N^?N = 4,4′-di-Me-2,2′-bpy (1); 4,4′-di-t-Bu-2,2′-bpy (2); 2,2′-bpz (3); bpym (4)) and [PtBr₂Me₂(L)₂] (L = H-pz (5); 4-Me-H-pz (6); H-idz (7); H-im (8); H-bim (9); quaz (10)) are reported. Characterization by NMR (¹H, ¹³C and ¹⁹⁵Pt), IR and EI-MS is given. In addition, crystal structures of several of these complexes are described. Furthermore, interactions within these structures including intramolecular hydrogen bonding and π-π stacking interactions are reported. The reactivity of selected mononuclear complexes was investigated and yielded two dinuclear complexes [PPh₄][(PtBrMe₂)₂(μ-Br)(μ-pz)₂] (11) and [(PtBr₂Me₂)₂(μ-bpym)] (12), respectively. The latter complex is accompanied by a solid-state structure. Finally, the thermal stability of all complexes is reported.     

Calorimetric studies of the interaction between the insulin-enhancing drug candidate bis(maltolato)oxovanadium(IV) (BMOV) and human serum apo-transferrin

Bis(maltolato)oxovanadium(IV) (BMOV), and its ethylmaltol analog, bis(ethylmaltolato)oxovanadium(IV) (BEOV), are candidate insulin-enhancing agents for the treatment of type 2 diabetes mellitus; in mid-2008, BEOV advanced to phase II clinical testing. The interactions of BMOV and its inorganic congener, vanadyl sulfate (VOSO₄), with human serum apo-transferrin (hTf) were investigated using differential scanning calorimetry (DSC). Addition of BMOV or VOSO₄ to apo-hTf resulted in an increase in thermal stability of both the C- and N-lobes of transferrin as a result of binding to either vanadyl compound. A series of DSC thermograms of hTf solutions containing different molar ratios of BMOV and VOSO₄ were used to determine binding constants; at 25 °C the binding constants of BMOV to the C- and N-lobes of apo-hTf were found to be 3 (±1) × 10⁵ and 1.8 (±0.7) × 10⁵ M⁻¹, respectively. The corresponding values for VOSO₄ were 1.7 (±0.3) × 10⁵ and 7 (±2) × 10⁴ M⁻¹. The results show that the vanadium species initially presented as either BMOV or VOSO₄ had similar affinities for human serum transferrin due to oxidation of solvated vanadyl(IV) prior to complexation to transferrin. Binding of metavanadate () was confirmed by DSC and isothermal titration calorimetry (ITC) experiments of the interaction between sodium metavanadate (NaVO₃) and hTf.     

Metal ion biomolecule interactions. VI: Synthesis and spectroscopic properties of methylmercury(II) complexes of xanthosine

The interaction of MeHg(II) with xanthosine (Xanth H₂, 1) in aqueous medium has been found to lead to several methylmercurated complexes depending on the reactant stoichiometries and the pH. The N-bound complexes [(MeHg)(Xanth H)] (2), [(MeHg)₂Xanth] (3), [(MeHg)₃(Xanth)]NO₃ (4), [(MeHg)(Xanth H₂)]NO₃ (5), and the N- and C-bound complex [(MeHg)₄(Xanth)]NO₃ (6) have thus been prepared. The complexes were characterized by means of ¹H and ¹³C nuclear magnetic resonance and infrared as well as elemental analysis. Formation of the carbon-bound methylmercurated species 6 is in accord with our previous results obtained with inosine and imidazole derivatives, thus substantiating our proposal that activation through electrophilic coordination at N₇ is a requirement for C₈-H abstraction. Correlations are drawn between ²J(¹H-¹¹⁹Hg) values and pK_a as well as ¹³C chemical shifts.     

Synthesis of green emissive terbium(III) complexes for displays: Optical,electrochemical and photoluminescent analysis

A series of heteroleptic terbium(III) complexes with fluorinated 2-thenoyltrifluoroacetone (TTFA) and other heteroaromatic units have been synthesized. The developed heteroleptic complexes were inspected via elemental study, cyclic voltammetry, thermal analysis and spectroscopic investigations. Optical band-gap data proposed the conducting property of prepared complexes. The photoluminescence emission profiles illustrated peaks based on terbium(III) cation (Tb³⁺) positioned at ~617, 586, 546 and 491 nm, imputed to ⁵D₄ to ⁷F_J (J = 3,4,5,6) transitions separately. Most intense peak at 546 nm corresponding to ⁵D₄ → ⁷F₅ transition is accountable for the green emissive character of developed complexes. The luminous character of complexes reveals the sensitization of Tb³⁺ by ligands. Color parameters further corroborates the green emanation of Tb³⁺ complexes. The photometric characteristics of complexes recommended their usages in designing display devices.     

Chromium(III) complexes and their relationship to the glucose tolerance factor. Part II. Structure and biological activity of amino acid complexes

A number of octahedral chromium complexes with amino acids are ligands have been prepared and their structures assigned on the basis of their chromatographic and spectral properties. These include complexes with the general structure Cr(AA)₂(H₂O)₂ where the amino acids glycine, glutamic acid and glutamine act as bidentate ligands. The analogous compound with cysteine as ligand is stable at low pH, but at high pH a terdentate cysteine complex, Cr(cysteine)₂^?, is formed. These complexes, as well as a solution of monodentate glycine aquo complexes, and Cr-nicotinic acid-glycine and Cr-nicotinic acid-cysteine complexes of undetermined structure, have been assayed for glucose tolerance factor activity using a yeast assay. Only Cr(glutamine)₂- (H₂O)₂⁺, Cr-nicotinic acid-glycine and the mixture of complexes Cr(glycine)_n(H₂O)_6-n⁺³ showed significant activity. It is proposed that a trans arrangement of the non-coordinated nitrogen atoms in the ligands of these complexes can mimic the structural features of the glucose tolerance factor which are essential for biological activity.     

Synthesis and characterization of tertiary phosphine Pd(0) complexes

The synthesis of PdL_n complexes (L = tertiary phosphine; n = 2,3,4) is reported. The coordination number results to be a function of the steric hindrance of the phosphine. Two-coordinate, 14-electron complexes, have been isolated with bulky phosphines (PPrⁱ₃, P (cyclohexyl)₃, PBu^t₂Ph). The behaviour in solution of the PdL_n complexes has been studied by ¹³C NMR spectroscopy.     

Transformation of vanadinite [Pb5(VO4)3Cl] by fungi

Saprotrophic fungi were investigated for their bioweathering effects on the vanadium‐ and lead‐containing insoluble apatite group mineral, vanadinite [Pb₅(VO₄)₃Cl]. Despite the insolubility of vanadinite, fungi exerted both biochemical and biophysical effects on the mineral including etching, penetration and formation of new biominerals. Lead oxalate was precipitated by Aspergillus niger during bioleaching of natural and synthetic vanadinite. Some calcium oxalate monohydrate (whewellite) was formed with natural vanadinite because of the presence of associated ankerite [Ca(Fe²⁺,Mg)(CO₃)₂]. Aspergillus niger also precipitated lead oxalate during growth in the presence of lead carbonate, vanadium(V) oxide and ammonium metavanadate, while abiotic tests confirmed the efficacy of oxalic acid in solubilizing vanadinite and precipitating lead as oxalate. Geochemical modelling confirmed the complexity of vanadium speciation, and the significant effect of oxalate. Oxalate–vanadium complexes markedly reduced the vanadinite stability field, with cationic lead(II) and lead oxalate also occurring. In all treatments and geochemical simulations, no other lead vanadate, or vanadium minerals were detected. This research highlights the importance of oxalate in vanadinite bioweathering and suggests a general fungal transformation of lead‐containing apatite group minerals (e.g. vanadinite, pyromorphite, mimetite) by this mechanism. The findings are also relevant to remedial treatments for lead/vanadium contamination, and novel approaches for vanadium recovery.     

Chemical and biological evaluation of 153Sm and 166Ho complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylphosphonic acid monoethylester) (H4 dotp OEt)

The novel methylphosphonic acid monoethylester (H₄dotp^OEt) has been synthesized and characterized and their complexes with Sm(III) and Ho(III) ions were studied. Dissociation constants of the ligand are lower than those of H₄dota. The stability constants of the Ln(III)-H₄dotp^OEt complexes are surprisingly much lower that those of H₄dota (H₄dota = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) probably due to a lower coordination ability of the phosphonate monoester groups. Acid-assisted decomplexation studies have shown that both complexes are less kinetically inert than the H₄dota complexes, but still much more inert than complexes of open-chain ligands. Nevertheless, the synthesis of ¹⁵³Sm and ¹⁶⁶Ho complexes with this ligand led to stable complexes both in vitro and in vivo. A very low binding of these complexes to hydroxyapatite (HA) and calcified tissues was observed confirming the assumption that a fully ionized phosphonate group(s) is necessary for a strong bone affinity. Both complexes show similar behaviour in vivo and, in general, follow the biodistribution trend of the H₄dota complexes with the same metals.     

Comparison of Crystal Field Dependent and Independent Methods to Analyse Lanthanide Induced NMR Shifts in Axially Symmetric Complexes. Part II: Systems with a C4 Symmetry Axis

Analysis of the LIS data for several series of Ln³⁺ complexes of C₄ symmetry in terms of structural changes, crystal-field effects and/or variation of hyperfine constants along the lanthanide series was undertaken using a combination of the two-nuclei and three-nuclei techniques together with the classical onenucleus technique. Isostructurality of whole series of complexes, with changes of the F_i, and B₀² parameters, was clearly defined for the complexes of L by the combination of the two first methods. Small changes, involving the three F_i, G_i and B₀² parameters, are observed for the series of complexes of L-L4, using the three data plotting methods. Some of the plots according to the two- and three-nuclei methods are accidentally linear, without necessarily implying isostructurality of the complexes, as they involve parameters, which may be insensitive to any small structural changes occurring in these systems. These parameter variations could result from a magnification, by the present graphical analysis, of the breaks expected from the gradual structural changes along the series due to the lanthanide contraction. The α and β parameters of the three-nuclei method are not diagnostic of the type of structures the complexes have in solution, due to their very indirect dependence on the geometric factors.     

Template synthesis and characterization of hexaaza nickel(II) complex nanoparticles entrapped within the zeolite-Y

Some complexes containing “[Ni([18]py₂N₄)]²⁺, [Ni([20]py₂N₄)]²⁺, [Ni(Bzo₂[18]py₂N₄)]²⁺ and [Ni(Bzo₂[20]py₂N₄)]²⁺” were successfully prepared by the template synthesis of 2,6-diacetylpyridine with [bis(diamine)nickel(II)]; [Ni(N-N)₂]²⁺; within the zeolite-Y. These complexes were entrapped in the supercage of Y-zeolite by a two-step process in the liquid phase: (i) inclusion of a Ni(II) precursor complex, [Ni(diamine)₂]²⁺@NaY, and (ii) template synthesis of the nickel(II) precursor complex with 2,6-diacetylpyridine. The new complex nanoparticles entrapped within the zeolite-Y “[Ni([18]py₂N₄)]²⁺@NaY, [Ni([20]py₂N₄)]²⁺@NaY, [Ni(Bzo₂[18]py₂N₄)]²⁺@NaY, [Ni(Bzo₂[20]py₂N₄)]²⁺@NaY” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV-Vis, XRD, BET, DRS). Analysis of the data indicates that the Ni(II) complexes are encapsulated within the zeolite-Y and exhibit different property from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix.     

Molecular Structure and Cytotoxicity of 3D-Transition Metal Complexes Capable to Form a Stable Metal-Nitrogen Bond

Abstract

The cytotoxicity of several Co(II), Ni(II), Cu(II) and Zn(II) complexes with various molecular structures and geometries, has been tested on LoVo and 2008 cells at 1–100 μM concentration for 24 h exposure. On the basis of 24 h results, the exposure time was prolonged to 48 and to 72 hours. The most potent complexes result [Cu(tren)(H₂O)]²⁺ 2Cl^?, E, [CoCl₃(H₂Meppz)], G, and [CoCl₃(HMe₂ppz)], H, (tren=tris(2-aminoethyl)amine, H₂Meppz=1-methylpiperazin-1-ium, HMe₂ppz=1,4-dimethylpiperazin-1-ium cations). Nevertheless, these complexes are able to induce cell growth reduction of about 50% at highest doses tested (1-100 μM) and after 72 h exposure.