Picolinic N-oxide Research Articles

Ligand-controlled dimensionality: 1D, 2D and 3D Gd(iii) coordination polymers based on SO42? and pyridine carboxylate N-oxide ligands

Three Gd(III)-sulfate polymers [Gd(PNO)(H2O)2(SO4)]n (1), [Gd(NNO)(H2O)2(SO4)]n (2), and [Gd(INO)(H2O)(SO4)]n (3) exhibiting a systematic variation in framework dimensionality have been hydrothermally synthesized by using three isomeric pyridine carboxylate N-oxides, PNO = picolinate N-oxide, NNO = nicotinate N-oxide, and INO = isonicotinate N-oxide, as organic components. Compound 1 comprises 1D coordination chains that are unable to propagate to higher dimensionalities due to the convergent endo PNO ligand. The structure of compound 2 consists of hydrogen-bonded layers. The formation of the 2D layer is attributed to the more divergent NNO than PNO. Compound 3 consists of a 2-fold interpenetrating “3D herringbone” framework, in which the most divergent exo ligands of INO connect the individual Gd-sulfate inorganic chains to produce the 3D coordination network. It is demonstrated that the convergence or divergence of the three isomeric ligands of the pyridine carboxylate N-oxide can be used to engineer the dimensionality of the coordination polymers.

Synthesis, characterization and thermal (tg-dsc) study of yttrium methanesulfonate coordination compounds with pyridine N-oxide and 2-,3- and 4-picoline N-oxides

The synthesis, characterization and thermal (TG and DSC) study of the coordination compounds Y(MS)3A(py-NO)2AH2O, Y(MS)3A(2-picNO)3, Y(MS)3A(3-picNO)2 and La(MS)3A(4-picNO)2 are reported (MS = methanesulfonate, py-NO = pyridine N-oxide, and 2-picNO, 3-picNO and 4-picNO are 2-, 3- and 4-picoline N-oxides, respectively). The observed thermal stability trend is: 2-picNO ≈ 4-picNO< 3-picNO< py-NO. Release of ligand molecules (endothermic) is followed by thermal degradation of the ligands (exothermic) with an increase in the exothermic values from 2-picNO to 4-picNO.

Multielectron atom transfer reactions of perchlorate and other substrates catalyzed by rhenium oxazoline and thiazoline complexes: reaction kinetics, mechanisms, and density functional theory calculations.

The title complexes, the Re(O)L(2)(Solv)(+) complexes (L = hoz, 2-(2'-hydroxyphenyl)-2-oxazoline(-) or thoz, 2-(2'-hydroxyphenyl)-2-thiazoline(-); Solv = H(2)O or CH(3)CN), are effective catalysts for the following fundamental oxo transfer reaction between closed shell molecules: XO + Y --> X + YO. Among suitable oxygen acceptors (Y's) are organic thioethers and phosphines, and among suitable oxo donors (XO's) are pyridine N-oxide (PyO), t-BuOOH, and inorganic oxyanions. One of the remarkable features of these catalysts is their high kinetic competency in effecting perchlorate reduction by pure atom transfer. Oxo transfer to rhenium(V) proceeds cleanly to afford the cationic dioxorhenium(VII) complex Re(O)(2)L(2)(+) in a two-step mechanism, rapid substrate (XO) coordination to give the precursor adduct cis-Re(V)(O)(OX)L(2)(+) followed by oxygen atom transfer (OAT) as the rate determining step. Electronic variations with PyO derivatives demonstrated that electron-withdrawing substituents accelerate the rate of Re(VII)(O)(2)L(2)(+) formation from the precursor adduct cis-Re(V)(O)(OX)L(2)(+). The activation parameters for OAT with picoline N-oxide and chlorate have been measured; the entropic barrier to oxo transfer is essentially zero. The potential energy surface for the reaction of Re(O)(hoz)(2)(OH(2))(+) with PyO was defined, and all pertinent intermediates and transition states along the reaction pathway were located by density functional theory (DFT) calculations (B3LYP/6-31G). In the second half of the catalytic cycle, Re(O)(2)L(2)(+) reacts with oxygen acceptors (Y's) in second-order reactions with associative transition states. The rate of OAT to substrates spans a remarkable range of 0.1-10(6) L mol(-)(1) s(-)(1), and the substrate reactivity order is Ph(3)P > dialkyl sulfides > alkyl aryl sulfides > Ph(2)S approximately DMSO, which demonstrates electrophilic oxo transfer. Competing deactivation and inhibitory pathways as well as their relevant kinetics are also reported.

The oxidation of fullerene[C 60] with various amine N-oxides under ultrasonic irradiation

The reaction of C 60 with various amine N-oxides such as 3-picoline N-oxide (Aldrich 98.0%), pyridine N-oxide hydrate (Aldrich 95.0%), quinoline N-oxide (Aldrich 97.0%), isoquinoline N-oxide (Aldrich 98.0%) under ultrasonic irradiation in air at 25–43 °C causes the oxidation of fullerene[C 60(O) n ] ( n=1–2 or n=1). The MALDI-TOF MS, UV–vis spectra, and HPLC profile confirmed that the products of fullerene oxidation are [C 60(O) n ] ( n=1–2 or n=1).

Synthesis, Structure, and Reactivity of Osmium Silyl and Silylene Complexes Cp*(Me3P)2OsSiR2X and [Cp*(Me3P)2OsSiR2][B(C6F5)4] (R = Me, iPr; X = Cl, OTf)

Reaction of Cp*(Me3P)2OsCH2SiMe3 (1, Cp* = C5Me5) with an excess of iPr2Si(H)Cl afforded Cp*(Me3P)2OsSiiPr2Cl (2) in good yield, without the formation of Os(IV) products. Treatment of 2 with Me3SiOTf (OTf = triflate, OSO2CF3) afforded the corresponding triflatosilyl complex Cp*(Me3P)2OsSiiPr2OTf (3), which appears to possess substantial silylene character, as determined by structural and spectroscopic measurements. The synthetic route to these complexes is analogous to that employed for the previously reported dimethylsilyl compounds Cp*(Me3P)2OsSiMe2X (X = Cl (4), OTf (5)). Complexes 2−5 were converted to the corresponding base-free silylene complexes [Cp*(Me3P)2OsSiR2][B(C6F5)4] (R = Me (6), iPr (7)) by anion metathesis with Li[B(C6F5)4]·3Et2O. Both 6 and 7 were characterized by multinuclear NMR spectroscopy and X-ray crystallography. The silylene complexes feature a trigonal planar environment for silicon, short Os−Si contacts (2.257(7) Å for 6, 2.263(1) Å for 7), and 29Si NMR resonances that are shifted to very low field (350 ppm for 6; 363 ppm for 7). The spectroscopic and structural differences between these silylene complexes and their precursors are discussed. While stable in fluorobenzene, 6 and 7 are rapidly oxidized by chlorocarbons via a radical pathway to form cationic Os(III) chlorosilyl species. Reactions of 7 with oxygen atom sources such as N2O and 2-picoline N-oxide afforded the N2-bridged diosmium complex [Cp*(Me3P)2Os−NN−Os(PMe3)2Cp*][B(C6F5)4]2 (8) and the cyclic siloxane (OSiiPr2)3. Reaction of 7 with elemental sulfur provided the turquoise, S2-bridged diosmium complex [Cp*(Me3P)2Os−S−S−Os(PMe3)2Cp*][B(C6F5)4]2 (9) and unidentified silicon-containing products.

A non-radical chain mechanism for oxygen atom transfer with a thiorhenium(V) catalyst.

The compound MeRe(S)(mtp)(PPh3), 2, where mtpH2 is 2-(mercaptomethyl)thiophenol, was used to catalyze the reaction between pyridine N-oxides, PyO, and triphenylphosphine. The rate law is -d[PyO]/dt=kc'[2].[PyO](1/2), with kc' at 25.0 degrees C in benzene=0.68 (4-picoline N-oxide) and 3.5x10(-3) dm(3/2) mol(-1/2) s(-1) (4-NO2-pyridine N-oxide). A chain mechanism with three steady-state thiorhenium species as chain carriers is implicated.

Preparation and characterization of nanocrystalline zinc oxide by a novel solvothermal oxidation route

A novel solvothermal oxidation route has been used to prepare hydroxyl-free nanocrystalline zinc oxide via the oxidation of zinc powder with trimethylamine N-oxide (Me 3N→O) or 4-picoline N-oxide (4-picN→O) in different organic solvents under dry nitrogen atmosphere. It is found that both oxygen sources and solvents have great effect on morphologies and sizes of nanocrystalline ZnO. The role of the small amount of water in wet solvent in the formation of nanocrystalline ZnO is also studied. The products are characterized by X-ray diffraction, transmission election microscopy. Possible mechanisms of the formation of the nanocrystalline ZnO are discussed.

Methyloxorhenium(V) complexes with two bidentate ligands: syntheses and reactivity studies.

Four new methyloxorhenium(V) complexes were synthesized: MeReO(PA)(2) (1), MeReO(HQ)(2) (2), MeReO(MQ)(2) (3), and MeReO(diphenylphosphinobenzoate)(2) (4) (in which PAH = 2-picolinic acid, HQH = 8-hydroxyquinoline, and MQH = 8-mercaptoquinoline). Although only one geometric structure has been identified crystallographically for 1, 2, and 3, two isomers of 3 and 4 in solution were detected by NMR spectroscopy. These compounds catalyze the sulfoxidation of thioethers by pyridine N-oxides and sulfoxides. The rate law for the reaction between pyridine N-oxides and thioethers, catalyzed by 1, shows a first-order dependence on the concentrations of pyridine N-oxide and 1. The second-order rate constants of a series of para-substituted pyridine N-oxides fall in the range of 0.27-7.5 L mol(-)(1) s(-)(1). Correlation of these rate constants by the Hammett LFER method gave a large negative reaction constant, rho = -5.2. The next and rapid step does not influence the kinetics, but it could be explored with competition experiments carried out with a pair of methyl aryl sulfides, MeSC(6)H(4)-p-Y. The value of each rate was expressed relative to the reference compound that has Y = H. A Hammett analysis of k(Y)/k(H) gave rho = -1.9. Oxygen-18 labeled 1 was used in a single turnover experiment for 4-picoline N-oxide and dimethyl sulfide. No (18)O-labeled DMSO was found. We suggest that the reaction proceeds by way of two intermediates that were not observed during the reaction. The first intermediate contains an opened PA-chelate ring; this allows the pyridine N-oxide to access the primary coordination sphere of rhenium. The second intermediate is a cis-dioxorhenium(VII) species, which the thioether then attacks. Oxygen-18 experiments were used to show that the two oxygens of this intermediate are not equivalent; only the new oxygen is attacked by, and transferred to, SR(2). Water inhibits the reaction because it hydrolyzes the rhenium(VII) intermediate.

Electrical and Spectral Properties of Complexes of Pyridine N-Oxide Derivatives with Iron Trichloride

Complexes (1 : 2) of iron trichloride with N-oxides of pyridine, picolines, and 2,6-lutidine were studied by optical spectroscopy, dielectrometry, and conductometry. In solid complexes, three crystalline phases are in equilibrium; the nuclei of each of these phases can be detected in the oily state. The enthalpies of the coordination bonds are different in different phases. One of the phases of the 3-picoline N-oxide complex shows a strong orientation disorder; disappearance of the short-range order causes weakening of the coordination bonds by ∼1.6 kcal. The thermal motion of free base molecules in two phases of the 2,6-lutidine N-oxide complex is gaslike. In the solid phase of this complex, there is a strong distribution of the relaxation frequencies; the mean relaxation frequency is close to 220 Hz. Upon irradiation of the complexes with solar or UV light, specific coloration centers can form. Weak alternating electric fields initiate in some compounds reversible chemical reactions. The intermolecular and charge equilibria in the compounds are very labile; the energy of generation of the low-temperature electrical conductivity in them is close to 0.9 eV.

The Synthesis of Liquid Crystalline Copolymers with Block Copolymer Grafts

The synthesis of novel copolymers consisting of a side-group liquid crystalline backbone and poly(tetrahydrofuran)-poly(methyl methacrylate) block copolymer grafts was realized by using cationic-to-free-radical transformation reactions. Firstly, photoactive poly(tetrahydrofuran) macroinimers were prepared by cationic polymerization of tetrahydrofuran and subsequent termination with 2-picoline N-oxide. Secondly, the macroinimers and acrylate monomers containing different spaced cyanobiphenyl mesogenic groups were copolymerized to yiel the respective graft copolymers. Eventually, these were used for indirect photochmical polymerization of methyl methacrylate by UV irradiation in the presence of anthracene as a photosensitizer leading ti the final copolymers with block copolymer grafts. The liquid crystalline, semi-crystalline, and amorphous blocks were micro-phase separated in the graft copolymers.

Physicochemical properties of complexes of zinc iodide with pyridine N-oxides

Polycrystalline 1 : 2 complexes of ZnI2 with N-oxides of pyridine, picoline, and 2,6-lutidine were studied by IR spectroscopy, dielectrometry, and conductometry. An equilibrium between three solid phases was observed. These phases are characterized by different enthalpies of formation of intermolecular bonds and different mechanism of electronic effect transmission via these bonds. Gas-like thermal molecular motion in one of the phases of the 2,6-lutidine N-oxide complex was observed. Reversible chemical reactions on the surface of the crystalline 3-picoline N-oxide complex are initiated on exposure to an alternating electric field. Two complexes, similarly to the ZnCl2 complexes, are ionized in the cumulative mode on fast heating from 18-19 to 26-45°C. Partial activation energies of electrical conductivity of different ions were determined for a number of complexes and inorganic salts.

Urea–picoline N-oxide (4:2) cocrystal: an unusual channel inclusion compound

The crystal structure of urea–picoline N-oxide cocrystal reveals urea channel formation in which two independent picoline N-oxide molecules are stacked with their charge-transfer axes aligned approximately at 60° toward the crystallographic b-axis.

2:1 Complex of 3-PicolineN-Oxide and Hydroquinone

The title system, 2C 6 H 7 NO.C 6 H 6 O 2 , belongs to a series of molecular complexes formed from 3-picoline N-oxide and diverse hydrogen-bond donors. The molecular complex owes its formation to a hydrogen bond between the O atom of the N-oxide group of each 3-picoline N-oxide molecule and the O atom of an OH group of the hydroquinone molecule. The complex has a dihedral angle of 48.16 (5)° between the aromatic rings and exhibits overlap between the hydroquinone and 3-picoline N-oxide molecules in the [001] direction. The structural characteristics of the title complex are compared with those of similar systems.

Induction of cytochromes P450 2B and 2E1 in rat liver by isomeric picoline N-oxides

Pyridine derivatives are widely used solvents and precursors for the synthesis of chemicals of industrial importance. Oxidized metabolites have been implicated in the observed toxicity of pyridines and are known to induce drug-metabolizing enzymes in rat liver. In this study the three isomeric picoline (methylpyridine) N-oxides, as major oxidized metabolites of 2-, 3- and 4-picoline, were evaluated as inducers of cytochrome P450 (CYP) enzymes in rat liver. After a single dose of 100 mg/kg 24 h before sacrifice the 3- and 4-isomers were effective inducers of microsomal substrate oxidations associated with the phenobarbital-inducible CYPs 2B; upregulation of CYP2B protein was confirmed by immunoblotting. In contrast, the 2-isomer did not increase CYP2B protein or activity in rat liver but CYP2E1 protein expression was upregulated by the isomers to 160–200% of control. The three chemicals increased aniline 4-hydroxylation activity in rat liver, which is consistent with induction of CYPs 2B or 2E1 and 4-nitrophenol 2-hydroxylation activity was increased in microsomal fractions from 3- and 4-picoline N-oxide-treated rats. The activities of several other CYPs were also determined and CYP1A-dependent 7-ethylresorufin O-deethylation was increased (to ∼6- and 2-fold of control) by the 3- and 4-isomer, respectively, whereas the activity of CYP3A-mediated androstenedione 6 β-hydroxylation was decreased by the agents-most notably by the 2-isomer. During NADPH-supported oxidation of CCl 4, lipid peroxidation was increased in microsomes from 3- and 4-picoline N-oxide-pretreated rats and was modulated in vitro by the CYP2B inhibitor orphenadrine, but not by the CYP2E1 inhibitor 4-methylpyrazole. These findings establish that particular isomers of picoline N-oxide rapidly upregulate CYP2B or, to a lesser extent, CYP2E1 and implicate CYP2B in the enhanced lipid peroxidation observed in microsomes from rats treated with 3- and 4-picoline N-oxides. Such induction process may contribute to the hepatotoxicity of pyridines by enhancing the capacity for microsomal lipid peroxidation.

The 1:1 Complex Formed by 2-PicolineN-Oxide and 3-Chlorobenzoic Acid

The title co-crystal, C6H7NO.C7H5ClO2, belongs to a series of molecular complexes based on the N—O group and was studied in order to establish its possible non-linear optical behavior. The 2-picoline N-oxide and 3-chlorobenzoic acid moieties are held together by an intermolecular hydrogen bond between the N—O and O—H groups. This system shows a transparency in the visible region of spectra.

The 1:1 Complex Formed by 3-PicolineN-Oxide andp-Toluic Acid

The title co-crystal, C6H7NO.C7H5ClO2, belongs to a series of molecular complexes based on the N—O group and was studied in order to establish its possible nonlinear optical behaviour. The 2-picoline N-oxide and 3-chlorobenzoic acid moieties are held together by an intermolecular hydrogen bond between the N—O and O—H groups. This system shows a transparency in the visible region of spectra.

1:1 Complex Formed by 2-Picoline N-Oxide and 4-Nitrophenol

The 2-picoline N-oxide and 4-nitrophenol moieties in the title complex, C6H7NO.C6H5NO3, are held together by an intermolecular O-H⋯CN hydrogen bond. This crystal structure exhibits partial overlap between the rings of the molecules, in the [110] direction. The complex formed may be described by two planes which contain the 2-picoline N-oxide and 4-nitrophenol molecules, respectively.

Mechanism in Polyoxometalate-Catalyzed Homogeneous Hydrocarbon Oxo Transfer Oxidation. The [Co4(H2O)2P2W18O68]10-/p-Cyano-N,N-dimethylaniline N-Oxide Selective Catalytic Epoxidation System

The Co-substituted heteropolyanions [Co4P2W18O68]10- and [CoPW11O39]5- catalyze the highly selective epoxidation of disubstituted alkenes and stilbenes by p-cyano-N,N-dimethylaniline N-oxide (CDMANO). Terminal alkenes are not readily epoxidized. The following d-electron transition metal-substituted (TMSP) complexes are less selective and two orders of magnitude less reactive than the Co complexes: [MnIIIPW11O39]4-, [MnIIPW11O39]5-, [FeIIIPW11O39]4-, and [NiIIPW11O39]5-. The system (TBA)8H2[Co4P2W18O68] (TBA = n-Bu4N+) (TBA1)/CDMANO/alkene/CH3CN solvent is homogeneous throughout. The values for K1 (constant for 1:1 association of the following ligands with 1 under the catalytic conditions in these studies = acetonitrile solution, 25 or 50 °C) are 275 ± 13 (N-methylimidazole), 4.3 ± 0.1 (pyridine), 59 ± 3 (4-picoline N-oxide), 22 ± 1 (4-cyanopyridine N-oxide), and 57 ± 5 (N-methylmorpholine N-oxide, MMNO, a model for CDMANO). Comparisons of the electronic absorption spectra of 1 under catalytic turnover and several other conditions indicate formation of the 1:1 CDMANO adduct, a result also consistent with thermodynamic binding and kinetic data. Chromatographic separation and spectral (UV−visible, NMR) evidence indicate that the brown color in the epoxidation reactions evident after many turnovers results from condensed heterocyclic structures from oxidation of the principal product derived from CDMANO during catalysis, p-cyano-N,N-dimethylaniline (CDMA). Evaluation of the kinetics of cyclohexene epoxidation by CDMANO over a wide range of conditions affords the following empirical rate law: +{d[epoxide]/dt}initial = k‘[cyclohexene]i[CDMANO]i[1]total)/(k‘‘[CDMANO]i + k‘‘‘[cyclohexene]i + k‘‘‘‘[cyclohexene]i[CDMANO]i + k‘‘‘‘‘). This is inconsistent with several common catalytic oxygenation mechanisms but consistent with a three-step mechanism: an initial pre-equilibrium association of 1 and CDMANO; loss of CDMA and formation of a reactive high-valent cobalt intermediate; and then transfer of oxygen from the intermediate to alkene.

Potential mechanism-based tyrosine kinase inhibitors. Part 1. Phosphorylation chemistry of pyridine N-oxides

Phosphorylated derivatives of 4-picoline N-oxide have been observed on treatment with both phos-phorylating and phosphitylating agents. These intermediates were trapped by external nucleophiles. Propane-1-thiol reacted preferentially at carbon to yield a propylsulfanylpyridine whereas propylamine reacted preferentially at phosphorus. This chemistry carries implications for the design of mechanism-based tyrosine kinase inhibitors.

Purification and properties of trimethylamine N-oxide reductase from aerobic photosynthetic bacterium Roseobacter denitrificans.

Trimethylamine N-oxide (TMAO) reductase was purified from an aerobic photosynthetic bacterium Roseobacter denitrificans. The enzyme was purified from cell-free extract by ammonium sulfate fractionation, DEAE ion exchange chromatography, hydrophobic chromatography, and gel filtration. The purified enzyme was composed of two identical subunits with molecular weight of 90,000, as identified by SDS-polyacrylamide gel electrophoresis, containing heme c and a molybdenum cofactor. The molecular weight of the native enzyme determined by gel filtration was 172,000. The midpoint redox potential of heme c was +200 mV at pH 7.5. Absorption maxima appeared at 418,524, and 554 nm in the reduced state and 410 nm in the oxidized state. The enzyme reduced TMAO, nicotine acid N-oxide, picoline N-oxide, hydroxylamine, and bromate, but not dimethyl sulfoxide, methionine sulfoxide, chlorate, nitrate, or thiosulfate. Cytochrome c2 served as a direct electron donor. It probably catalyzes the electron transfer from cytochrome b-c1 complex to TMAO reductase. Cytochrome c552, another soluble low-molecular-weight cytochrome of this bacterium, also donated electrons directly to TMAO reductase.