Synthesis and Characterization of New Lutidinium Ionic Liquid-Supported Vanadylsalicylaldoxime Complex for Catalytic Application in Epoxidation Reaction

A new chelating task-specific ionic liquid (TSIL), lutidinium-based salicylaldoxime ( LSOH ), and its square pyramidal vanadyl(II) complex (VO(LSO)₂) have been successfully synthesized and structurally characterized using elemental (CHN), spectral, and thermal analyses. The catalytic activity of the lutidinium-salicylaldoxime complex (VO(LSO)₂) in the alkene epoxidation reactions was studied under various reaction conditions, such as solvent effect, alkene/oxidant molar ratio, pH, reaction temperature, reaction time, and the catalyst dose. The results demonstrated that the CHCl₃ solvent, 1 : 3 of the cyclohexene/H₂O₂ ratio, pH 8, temperature of 340 K, and catalyst dose of 0.012 mmol are assigned as the optimum conditions for achieving maximum catalytic activity for VO(LSO)₂. Moreover, the VO(LSO)₂ complex has the potential for application in the effective and selective epoxidation of alkenes. Notably, under optimal VO(LSO)₂ conditions, cyclic alkenes convert more efficiently to their corresponding epoxides than linear alkenes.     

Multiple reactions in vanadyl-V(IV) oxidation by H2O2

Oxidation of vanadyl sulfate by H₂O₂ involves multiple reactions at neutral pH conditions. The primary reaction was found to be oxidation of V(IV) to V(V) using 0.5 equivalent of H₂O₂, based on the loss of blue color and the visible spectrum. The loss of V(IV) and formation V(V) compounds were confirmed by ESR and⁵¹V-NMR spectra, respectively. In the presence of excess H₂O₂ (more than two equivalents), the V(V) was converted into diperoxovanadate, the major end-product of these reactions, identified by changes in absorbance in ultraviolet region and by the specific chemical shift in NMR spectrum. The stoichiometric studies on the H₂O₂ consumed in this reaction support the occurrence of reactions of two-electron oxidation followed by complexing two molecules of H₂O₂. Addition of a variety of compounds—Tris, ethanol, mannitol, benzoate, formate (hydroxyl radical quenching), histidine, imidazole (singlet oxygen quenching), and citrate—stimulated a secondary reaction of oxygen-consumption that also used V(IV) as the reducing source. This reaction requires concomitant oxidation of vanadyl by H₂O₂, favoured at low H₂O₂:V(IV) ratio. Another secondary reaction of oxygen release was found to occur during vanadyl oxidation by H₂O₂ in acidic medium in which the end-product was not diperoxovanadate but appears to be a mixture of VO ₃ ⁺ (–546 ppm), VO³⁺ (–531 ppm) and VO ₂ ⁺ (–512 ppm), as shown by the⁵¹V-NMR spectrum. This reaction also occurred in phosphate-buffered medium but only on second addition of vanadyl. The compounds that stimulated the oxygen-consumption reaction were found to inhibit the oxygen-release reaction. A combination of these reactions occur depending on the proportion of the reactants (vanadyl and H₂O₂), the pH of the medium and the presence of some compounds that affect the secondary reactions.     

Chemistry of molecular and supramolecular structures of vanadium(IV) and dioxygen-bridged V(V) complexes incorporating tridentate hydrazone ligands

Four hydrazone ligands: 2-benzoylpyridine benzoyl hydrazone (HBPB), di-2-pyridyl ketone nicotinoyl hydrazone (HDKN), quinoline-2-carbaldehyde benzoyl hydrazone (HQCB), and quinoline-2-carbaldehyde nicotinoyl hydrazone (HQCN) and four of their complexes with vanadyl salts have been synthesized and characterized. Single crystals of HBPB and complexes [VO(BPB)(μ₂-O)]₂ (1) and [VO(DKN)(μ₂-O)]₂·½H₂O (2) were isolated and characterized by X-ray crystallography. Each of the complexes exhibits a binuclear structure where two vanadium(V) atoms are bridged by two oxygen atoms to form distorted octahedral structures within cis-N₂O₄ donor sets. In most complexes, the uninegative anions function as tridentate ligands, coordinating through the pyridyl- and azomethine-nitrogen atoms and enolic oxygen whereas in complex [VO(HQCN)(SO₄)]SO₄·4H₂O (4) the ligand is coordinated in the keto form. Complexes [VO(QCB)(OMe)]·1.5H₂O (3) and 4 are found to be EPR active and showed well-resolved axial anisotropy with two sets of eight line pattern.     

Hydrothermal synthesis and structural characterization of bimetallic organic-inorganic hybrid materials: Copper vanadate-1,4-Carboxy-phenylphosphonate phases

The hydrothermal reactions of V₂O₅, a copper(II) source, 1,4-carboxy-phenylphosphonic acid, a bidentate organonitrogen ligand and HF provided a series of bimetallic organic-inorganic hybrid materials. [Cu(bpy)VO₂(O₂CC₆H₄PO₃)] (1) is one-dimensional, while [Cu(bpa)VO(OH)(O₂CC₆H₄PO₃)] (2) and [Cu(phen)V₂O₄F(O₂CC₆H₄PO₃)] (3) are two-dimensional. In the absence of V₂O₅, a number of copper-organophosphonates were isolated. Compound 4 [Cu(phen)(H₂O)(O₂CC₆H₄PO₃H)] is one-dimensional while [Cu₃(bpy)₂(O₂CC₆H₄PO₃)₂] (5) is two-dimensional. Molecular structures were observed for [CuF(bpy)(H₂O)(HO₂CC₆H₄PO₃H)] (6) and [Cu(bpa)(O₂CC₆H₄PO₃H)]·3H₂O (7·3H₂O).     

Nanostructured copper oxides and phosphates from a new solid-state route

Nanostructured copper containing materials of CuO, Cu₃(PO₄)₃ and Cu₂P₂O₇ have been prepared by solid-state pyrolysis of molecular CuCl₂·NC₅H₄OH (I), CuCl₂·CNCH₂C₆H₄OH (II), oligomeric [Cu(PPh₃)Cl]₄ (III), N₃P₃[OC₆H₄CH₂CN·CuCl]₆[PF₆] (IV), N₃P₃[OC₆H₅]₅[OC₅H₄N·Cu][PF₆] (V), polymeric chitosan·(CuCl₂)_n (VI) and polystyrene-co-4-vinylpyridine PS-b-4-PVP·(CuCl₂) (VII) precursors. The products strongly depend on the precursor used. The pyrolytic products from phosphorus-containing precursors (III), (IV) and (V) are Cu phosphates or pyrophosphates, while non-phosphorous-containing precursors (VI) and (VII), result in mainly CuO. The use of chitosan as a solid-state template/stabilizer induces the formation of CuO and Cu₂O nanoparticles. Copper pyrophosphate (Cu₂P₂O₇) deposited on Si using (IV) as the precursor exhibits single-crystal dots of average diameter 100 nm and heights equivalent to twice the unit cell b-axis (1.5-1.7 nm) and an areal density of 5.1-7.7 Gigadots/in.². Cu₂P₂O₇ deposited from precursor (VI) exhibits unique labyrinthine high surface area deposits. The morphology of CuO deposited on Si from pyrolysis of (VI) depends on the polymer/Cu meta ratio. Magnetic measurements performed using SQUID on CuO nanoparticle networks suggest superparamagnetic behavior. The results give insights into compositional, shape and morphological control of the as-formed nanostructures through the structure of the precursors.     

Hydrothermal syntheses and structures of vanadium oxyfluorides templated by organic and metal organic cations

The hydrothermal reactions of V₂O₅, HF and an organodiphosphonic acid, in the presence of appropriate templating organoammonium or metal-organic complex cations provided three new oxyfluorovanadate compounds. The V(IV) species [H₃N(CH₂)₂NH₂(CH₂)₂NH₂(CH₂)₂NH₃][V₃O₃F₂(H₂O){O₃PCH₂PO₃}₂]·2H₂O (1·2H₂O) exhibits a three-dimensional anionic framework constructed from {VO(O₃PCH₂PO₃)}_n²ⁿ⁻ chains and {VF₂O₄} octahedra. The molecular structure of [N(CH₂CH₂NH₃)₃]₂[NH₄][V₃O₂F₆(O₃PCH₂PO₃)₂]·2H₂O (2·2H₂O) is characterized by the presence of unique {V₃O₂F₆(O₃PCH₂PO₃)₂}⁷⁻ clusters. The bimetallic phase [{Cu(ophen)}VOF{HO₃P(CH₂)₅PO₃}] (3) is one-dimensional with {Cu₂V₂O₂F₂(HO₃PR)₂(O₃PR)₂} cluster building blocks.     

A novel supramolecular compound 2,2′-bipyridyl-phosphotungstic acid: synthesis and catalysis

A new supramolecular compound (C₁₀H₈N₂)_3.2·H₃PW₁₂O₄₀·25.6H₂O (Bipy-PW₁₂) was synthesized by self-assembly design, and characterized by elemental analysis, Fourier-transform infrared spectra (FTIR), and ³¹P NMR spectra. Bipy-PW₁₂ can effectively catalyze oxidative degradation of chitosan with H₂O₂ in heterogeneous phase. To obtain water-soluble chitosan with an average molecular weight of 5000, the optimum reaction conditions were determined as follows: reaction temperature, 80 °C; reaction time, 13 min; H₂O₂ concentration, 2.7 mol/L; and mass ratio of Bipy-PW₁₂ to chitosan, 0.01.     

Ethanol-dependent oxygen consumption and acetaldehyde formation during vanadyl oxidation by H2O2

Sequential addition of vanadyl sulfate to a phosphate-buffered solution of H₂O₂ released oxygen only after the second batch of vanadyl. Ethanol added to such reaction mixtures progressively decreased oxygen release and increased oxygen consumption during oxidation of vanadyl by H₂O₂. Inclusion of ethanol after any of the three batches of vanadyl resulted in varying amounts of oxygen consumption, a property also shared by other alcohols (methanol, propanol and octanol). On increasing the concentration of ethanol, vanadyl sulfate or H₂O₂, both oxygen consumption and acetaldehyde formation increased progressively. Formation of acetaldehyde decreased with increase in the ratio of vanadyl:H₂O₂ above 2:1 and was undetectable with ethanol at 0.1 mM. The reaction mixture which was acidic in the absence of phosphate buffer (pH 7.0), released oxygen immediately after the first addition of vanadyl and also in presence of ethanol soon after initial rapid consumption of oxygen, with no accompanying acetaldehyde formation. The results underscore the importance of some vanadium complexes formed during vanadyl oxidation in the accompanying oxygen-transfer reactions.     

The effect of Mg2+ and Ca2+ on urea-catalyzed phosphorylation reactions

Summary When struvite (MgNH₄PO₄ 6H₂O) is heated with urea at 65–100°C, inorganic pyrophosphate is formed in good yield. Under similar conditions pyro-phosphate is formed much more slowly from ammonium phosphate or hydroxylapatite. The major products formed by the reaction of nucleotides with urea and either ammonium phosphate or hydroxylapatite are derivatives phosphorylated on the 2 or 3 position. With struvite, on the other hand, the main reaction is pyrophosphate bond formation. Yields of up to 25% of uridine diphosphate can be obtained at temperatures as low as 65°C.     

VO(acac)(2)/H(2)O(2)/NaI: a mild and efficient combination for the cleavage of dithioacetal derivatives of sugars

A wide variety of dithioacetal derivatives of sugars can be cleaved easily into the corresponding open-chain aldehydo sugars using an efficient combination of VO(acac)₂/H₂O₂/NaI at 0–5 °C. Some of the salient features of this protocol are mild reaction conditions, good yields, short reaction times, easy work-up procedures, and non-involvement of toxic chemicals.     

A series of oxo-vanadium(IV) complexes containing mixed ligands of poly(pyrazolyl)borate and organic carboxylic acid: Synthesis, structural characterization and primary study of bromination reaction activities

A series of oxo-vanadium(IV) complexes: Tp^∗VO(pzH^∗)(CH₃COO) (1), Tp^∗VO(pzH^∗)(CCl₃COO) (2), Tp^∗VO(pzH^∗)(C₆H₅COO) (3), Tp^∗VO(pzH^∗)(m-NO₂-C₆H₄COO)·CH₃CN (4) and [Tp^∗VO(pzH^∗)(H₂O)]⁺[m-NO₂-C₆H₄-SO₃]⁻·CH₃OH (5) (Tp^∗ = hydrotris(3,5-dimethylpyrazolyl)borate; pzH^∗ = 3,5-dimethylpyrazole) are synthesized in methanol solution under physiological conditions. They are characterized by elemental analysis, IR, UV-Vis and X-ray crystallography. Structural analyses show that the vanadium atoms in complexes 1-5 are all in a distorted-octahedral environment with the N₄O₂ donor set, and intra- or inter-hydrogen bonding linkages have been also observed in each complex. Bromination reaction activity of the complexes has been evaluated by the method with phenol red as organic substrate in the presence of H₂O₂, Br⁻ and phosphate buffer, indicating that they can be considered as potential functional model vanadium-dependent haloperoxidases. In addition, thermal analysis and quantum chemistry calculations were also performed and discussed in detail.     

Peroxidase-Like Catalytic Activity of Ag3PO4 Nanocrystals Prepared by a Colloidal Route

Nearly monodispersed Ag₃PO₄ nanocrystals with size of 10 nm were prepared through a colloidal chemical route. It was proven that the synthesized Ag₃PO₄ nanoparticles have intrinsic peroxidase-like catalytic activity. They can quickly catalyze oxidation of the peroxidase substrate 3, 3, 5, 5-tetramethylbenzidine (TMB) in the presence of H₂O₂, producing a blue color. The catalysis reaction follows Michaelis-Menten kinetics. The calculated kinetic parameters indicate a high catalytic activity and the strong affinity of Ag₃PO₄ nanocrystals to the substrate (TMB). These results suggest the potential applications of Ag₃PO₄ nanocrystals in fields such as biotechnology, environmental chemistry, and medicine.     

Solid state coordination chemistry of organodiphosphonates with copper(II) and auxilliary aromatic nitrogen heterocyclic ligands

The hydrothermal reactions of CuSO₄ · 5H₂O, a phosphonate ligand and an appropriate aromatic nitrogen heterocycle yield a series of materials of the Cu(II)/phosphonate/nitrogen ligand donor family. Two of the materials [Cu(2,2′-bpy)(HO₃PCH₂CH₂CH₂PO₃H)] (1) and [Cu(4,4′-bpy)(H₂O)₂(HO₃PCH₂CH₂CH₂CH₂PO₃H)] (2) are two-dimensional, while [{Cu(2,2′-bpy)}₂(O₃PC₆H₄PO₃)] · 8H₂O (3 · 8H₂O) is three-dimensional. When 1,3,5-benzenetricarboxylic acid is introduced as a reactant, the one-dimensional material [Cu(2,2′-bpy){OC₆H₂(CO₂H)₃}(HOPC₆H₅)] (4) is isolated. This is an example of an in situ hydrothermal ligand transformation in which the 1,3,5-benzene tricarboxylic acid is hydroxylated to give 1,3,5-benzene tricarboxylic acid-2-hydroxide. Compound 5 [Cu(terpy)(HO₃PC₆H₄PO₃H] is molecular.     

Media optimization studies for glucose isomerase production by arthrobacter species

Media optimization studies are carried out with the objective of maximising glucose isomerase production by Arthrobacter sp. The recommended media consists of 1.0% (w/v) xylose, 1.0% peptone, 0.5% yeast extract, 0.025% MgSO₄·7H₂O, 0.6% (NH₄)₂HPO₄ and 0.2% KH₂PO₄. Activity of the enzyme produced in this media is 11.2 units/ml. Growth cycle for batch cultivation is studied and the lag period is 2 hours, followed by exponential phase extending upto 32 hours.     

Catalytic conversion of cellulose to chemicals in ionic liquid

A simple and effective route for the production of 5-hydroxymethyl furfural (HMF) and furfural from microcrystalline cellulose (MCC) has been developed. CoSO₄ in an ionic liquid, 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (IL-1), was found to be an efficient catalyst for the hydrolysis of cellulose at 150 °C, which led to 84% conversion of MCC after 300 min reaction time. In the presence of a catalytic amount of CoSO₄, the yields of HMF and furfural were up to 24% and 17%, respectively; a small amount of levulinic acid (LA) and reducing sugars (8% and 4%, respectively) were also generated. Dimers of furan compounds were detected as the main by-products through HPLC-MS, and with the help of mass spectrometric analysis, the components of gas products were methane, ethane, CO, CO_2, and H₂. A mechanism for the CoSO₄-IL-1 hydrolysis system was proposed and IL-1 was recycled for the first time, which exhibited favorable catalytic activity over five repeated runs. This catalytic system may be valuable to facilitate energy-efficient and cost-effective conversion of biomass into biofuels and platform chemicals.     

Hydrothermal synthesis and structure of [Ni(tpyrpyz)2]2[Mo4O12F2][Mo6O19] · 2H2O, a material exhibiting an unusual tetranuclear polyoxofluoromolybdate cluster [Mo4O12F2]

The hydrothermal reaction of a solution of Ni(CH₃CO₂)₂ · 4H₂O, MoO₃, tetra-4-pyridylpyrazine, H₂O₃PCH₃, and HF at 200 °C for 96 h yields orange crystals of [Ni(tpyrpyz)₂]₂[Mo₄O₁₂F₂][Mo₆O₁₇] · 2H₂O (1 · 2H₂O). The structure consists of discrete {Ni(tpyrpyz)₂}²⁺ cations and {Mo₆O₁₉}²⁻ and {Mo₄O₁₂F₂}²⁻ anionic clusters. The hexamolybdate is the well-documented octahedron of octahedra, that is, six {MoO₆} octahedra in a compact edge-sharing arrangement. The novel oxyfluoride cluster {Mo₄O₁₂F₂}²⁻ features two {MoO₄F₂} octahedra, sharing the edge defined by the fluoride ligands; the octahedral Mo sites corner-share to two {MoO₄} tetrahedra in the μ₂-O, O^′ bridging mode.     

Cyclic and acyclic compartmental Schiff bases, their reduced analogues and related mononuclear and heterodinuclear complexes

[1+1] macrocyclic and [1+2] macroacyclic compartmental ligands (H₂L), containing one N₂O₂, N₃O₂, N₂O₃, N₄O₂ or O₂N₂O₂ Schiff base site and one O₂O_n (n=3, 4) crown-ether like site, have been prepared by self-condensation of the appropriate formyl- and amine precursors. The template procedure in the presence of sodium ion afforded Na₂(L) or Na(HL) · nH₂O. When reacted with the appropriate transition metal acetate hydrate, H₂L form M(L) · nH₂O, M(HL)(CH₃COO) · nH₂O, M(H₂L)(X)₂ · nH₂O (M=Cu²⁺, Co²⁺, Ni²⁺; X=CH₃COO⁻, Cl⁻) or Mn(L)(CH₃COO) · nH₂O according to the experimental conditions used. The same complexes have been prepared by condensation of the appropriate precursors in the presence of the desired metal ion. The Schiff bases H₂L have been reduced by NaBH₄ to the related polyamine derivatives H₂R, which form, when reacted with the appropriate metal ions, M(H₂R)(X)₂ (M= Co²⁺, Ni²⁺; X=CH₃COO⁻, Cl⁻), Cu(R) · nH₂O and Mn(R)(CH₃COO) · nH₂O. The prepared ligands and related complexes have been characterized by IR, NMR and mass spectrometry. The [1+1] cyclic nature of the macrocyclic polyamine systems and the site occupancy of sodium ion have been ascertained, at least for the sodium (I) complex with the macrocyclic ligand containing one N₃O₂ Schiff base and one O₂O₃ crown-ether like coordination chamber, by an X-ray structural determination. In this complex the asymmetric unit consists of one cyclic molecule of the ligand coordinated to a sodium ion by the five oxygen atoms of the ligand. The coordination geometry of the sodium ion can be described as a pentagonal pyramid with the metal ion occupying the vertex. In the mononuclear complexes with H₂L or H₂R the transition metal ion invariantly occupies the Schiff base site; the sodium ion, on the contrary, prefers the crown-ether like site. Accordingly, the heterodinuclear complexes [MNa(L)(CH₃COO)_x] (M=Cu²⁺, Co²⁺, Ni², x=1; M=Mn³⁺, x=2) have been synthesised by reacting the appropriate formyl and amine precursors in the presence of M(CH₃COO)_n · nH₂O and NaOH in a 1:1:1:2 molar ratio. The reaction of the mononuclear transition metal complexes with Na(CH₃COO) · nH₂O gives rise to the same heterodinuclear complexes. Similarly [MNa(R)(CH₃COO)_x] have been prepared by reaction of the appropriate polyamine ligand H₂R with the desired metal acetate hydrate and NaOH in 1:1:2 molar ratio.     

Vanadyl tetradentate Schiff base complexes as catalyst for C-H bond activation of olefins with tert-butylhydroperoxide: Synthesis, characterization and structure

Three N₂O₂ tetradentate Schiff base ligands (H₂L^1-3) were prepared by reaction of 1,2-propylenediamine and appropriate aldehyde and ketone and characterized by FT-IR, ¹H and ¹³C NMR. The vanadyl complexes were synthesized by treating an ethanolic solution of the appropriate ligand and one equivalent of VO(acac)₂ to yield VOL^1-3. These oxovanadium (IV) complexes were characterized on the basis of their FT-IR, UV-Vis spectroscopy and elemental analysis. The crystal structure of VOL³ has been determined. The metal center in VOL³ is a deformed tetragonal pyramidal N₂O₃ coordination sphere. These complexes are used as catalyst for the selective epoxidation of olefins. High selectivity of epoxidation for cyclooctene observed from oxidation data. The catalytic activity increases as the number of electron-donor groups increases, and the catalytic selectivity is varied by changing the substituents on the ligands. The catalytic system described here is an efficient and inexpensive method for the oxidation of olefins, with the advantages of high activity, selectivity, re-usability and short reaction time.     

Identification and characterization of VPO1, a new animal heme-containing peroxidase

Animal heme-containing peroxidases play roles in innate immunity, hormone biosynthesis, and the pathogenesis of inflammatory diseases. Using the peroxidase-like domain of Duox1 as a query, we carried out homology searching of the National Center for Biotechnology Information database. Two novel heme-containing peroxidases were identified in humans and mice. One, termed VPO1 for vascular peroxidase 1, exhibits its highest tissue expression in heart and vascular wall. A second, VPO2, present in humans but not in mice, is 63% identical to VPO1 and is highly expressed in heart. The peroxidase homology region of VPO1 shows 42% identity to myeloperoxidase and 57% identity to the insect peroxidase peroxidasin. A molecular model of the VPO1 peroxidase region reveals a structure very similar to that of known peroxidases, including a conserved heme binding cavity, critical catalytic residues, and a calcium binding site. The absorbance spectra of VPO1 are similar to those of lactoperoxidase, and covalent attachment of the heme to VPO1 protein was demonstrated by chemiluminescent heme staining. VPO1 purified from heart or expressed in HEK cells is catalytically active, with a K_m for H₂O₂ of 1.5 mM. When co-expressed in cells, VPO1 can use H₂O₂ produced by NADPH oxidase enzymes. VPO1 is likely to carry out peroxidative reactions previously attributed exclusively to myeloperoxidase in the vascular system.     

Temperature insensitive O2 in blood of the tree frogChiromantis petersi

Summary Respiratory gas exchange and blood respiratory properties have been studied in the East-African tree frogChiromantis petersi. This frog is unusually xerophilous, occupies dry habitats and prefers body temperatures near 40°C and direct solar exposure. Total O₂ uptake was low at 81 l O₂·g^–1·h^–1±19.0 (SD) at 25°C increasing to 253.5 l O₂·g^–1·h^–1±94.8 (SD) at 40°C giving aQ ₁₀ value of 2.1. Skin O₂ uptake at 25°C was 38.5% of total. The gas exchange ratio was 0.71 for whole body gas exchange, 0.61 for the lungs and 1.02 for the skin at 25°C.Blood O₂ affinity was low with aP ₅₀ of 47.5 mmHg at 25°C and pH 7.65. Then _H-value at 25°C increased from 2.7 aroundP ₅₀ to 5.0 at O₂ saturations exceeding 70–80%. Surprisingly, blood O₂ affinity was nearly insensitive to temperature expressed by a H value of ±1.0 kcal·mole between 25 and 40°C.The adaptive significance of the low O₂ affinity, the increase ofn _H with O₂ saturation and the temperature insensitive O₂-Hb binding is discussed in relation to the high and fluctuating body temperatures ofChiromantis.