Paraquat Dication Research Articles

Solvent‐dependent mechanistic aspects for the redox reaction of paraquat in basic solution

AbstractDetailed mechanisms for the redox cycling of paraquat in basic solutions have been revealed computationally. The reduction of paraquat dication (PQ2+) undergoes via the successive additions with two hydroxide (OH−) anions to form the neutralized intermediates, which can decompose to generate the cation radical (PQ+) by releasing either OH or the hydrated O−radical.PQ+is neutralized by one OH−, converting molecular oxygen into superoxide (O2−) anion to regeneratePQ2+. The reduction ofPQ2+by OH−is an energy‐directive process whereas the oxidation ofPQ+prefers an entropy‐driving path in which OH−acts as a catalyst. It is found that the Gibbs free‐energy reaction paths are strongly solvent dependent. The redox cycle is energetically preferable in the solvents with low dielectric constants. The yellow‐blue‐transparent color‐changing sequence in the clock reaction of paraquat has been understood by means of the electronic absorption spectra of the cations and the neutral intermediates. Atomic radical anion O−is predicted besides the known OH and O2−radicals to stimulate experimental studies on the redox chemistry of paraquat.

Theoretical prediction of structures and inclusion properties of heteroatom-bridged pillar[n]arenes

In this paper, the heteroatom-bridged pillar[n]arene derivatives, namely bora-, aza-, and oxa-pillar[n]arenes (PnX, X = B, N, and O respectively, n = 4 − 6) are studied by quantum chemical calculations at the ωB97XD/6-311G(d,p) level of theory. The geometries, energetics, electronic structures, absorption spectra, solvent effects, and the inclusion complexation with paraquat dication are discussed in detail. The calculated results show the structures of pentamers (P5X) are more stable compared with tetramers (P4X) and hexamers (P6X) and the PnB have relatively loose and irregular geometry structures. The molecular cavities of PnX are electron-rich and capable of accommodating cationic guests. Absorption spectra of PnN and PnO are very similar to those of Pn with one intense peak (λmax) at around 260 nm, while PnB indicates another characteristic peak between 300 and 400 nm. P5X can form inclusion complexes of 1:1 stoichiometry with paraquat dication, and P5N exhibits strongest combination ability with paraquat dication among them. These thorough understanding of the structure and properties of heteropillar[n]arenes will broaden the designs, syntheses, and applications of pillararenes.

An Ionic Liquid-based Microextraction Method for Ultra-High Preconcentration of Paraquat Traces in Water Samples Prior to HPLC Determination.

An ionic liquid (IL)-based microextraction method was developed for the preconcentration of paraquat traces in water samples prior to HPLC determination. On the basis of the relationship between the aqueous solubility and the extractability of known ILs, 1-ethyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)amide ([EMIm][NNf2]) was selected as the extractant for paraquat. The distribution ratio of paraquat dication in the [EMIm][NNf2]/water biphasic system was theoretically estimated to be nearly 108 at its maximum level, indicating that [EMIm][NNf2] was suitable for the ultra-high preconcentration (a maximum of 106-fold concentration) of paraquat with a quantitative recovery (more than 99%). The extraction procedure could be performed easily and quickly following the in situ solvent formation microextraction technique, and the paraquat traces in the IL phase could be determined by hydrophilic interaction chromatography with good detection limits and linearity ranges (0.16 and 1 - 50 ng mL-1 for paraquat, respectively). The combined method was successfully applied to four real environmental water samples spiked with paraquat and its analog, diquat at 5.0 ng mL-1.

The laws governing ionic liquid extraction of cations: partition of 1-ethylpyridinium monocation and paraquat dication in ionic liquid/water biphasic systems.

To find the laws governing the extraction of cations from aqueous solutions into hydrophobic ionic liquids (ILs), we investigated the partition of 1-ethylpyridinium monocation and paraquat (1,1'-dimethyl-4,4'-bipyridinium) dication in various IL/water biphasic systems. Ten different ILs of 1-butyl-3-methylimidazolium-based or bis(trifluoromethanesulfonyl)amide-based salts were used. The distribution ratio of the target cations (T(n+)) was dependent on the initial concentration in the aqueous phase and also very sensitive to the kind of IL. The behavior was quantitatively explained on the basis of a model in which the extraction goes through both the ion exchange and ion pair transfer processes, while keeping the product of the aqueous concentrations of the IL constituent ions a constant value (solubility product, Ksp). The distribution ratio of T(n+) is expressed as a function of the difference between the initial and equilibrium concentrations of T(n+) in the aqueous phase (Δ[T(n+)]W), the aqueous solubility of IL (Ksp(1/2)), and the cation valence n. The distribution ratio is a nearly constant value (D0) when Δ[T(n+)]W ≪ Ksp(1/2)/n and decreases inversely proportional to the nth power of Δ[T(n+)]W when Δ[T(n+)]W ≫ Ksp(1/2)/n. The log D0 versus log Ksp(1/2) plot gives a linear relationship with a slope of +n for the ILs with the same anion but different cations and that with a slope of nearly -n for the ILs with the same cation but different anions. This means that the extractability dependence on the kinds of IL constituent ions is greater for the divalent cation than for the monovalent one.

NEW CROWNOPHANES CONTAINING 2,7-DIOXYFLUORENONE AND 2,7-DIOXYNAPHTHALENE

New crownophanes containing 2,7-dioxyfluorenone and 2,7-dioxynaphthalene fragments linked by tri- and tetraethylene glycol linkers have been obtained. The formation of “hostguest”-type complexes upon interaction with paraquat dication was detected by UV-Vis and FAB-MS spectrometry.

New fluorenonocrownophanes containing azobenzene: synthesis, properties and interaction with paraquat

New crownophanes containing 2,7-dioxyfluorenone and 4,4′-azobiphenoxy moieties linked by di-, tri-, tetra-, and pentaethylene glycol residues were synthesized. Just in case of obtaining largest crownophane with pentaethyleneglycol linkers, the dimeric cyclization product was also isolated in low yield. Obtained crownophanes, according to 1H NMR spectral data exist in conformations with closed intramolecular cavity in solution. Photoinduced E–Z isomerization of crownophane containing triethylene glycol linkers were investigated. The azobenzene fragment inclusion into crownophane reduces the photoisomerization rate compared to model 4,4′-dimethoxyazobenzene. In all the obtained crownophanes according to NMR, UV–Vis and X-ray data 4,4′-azobiphenoxy fragment is in E-configuration in solution as well as in the solid state. Crystal packing of all crownophanes has distinct feature—stacking arrangement of fluorenone moieties probably due to electrostatic dipole–dipole interactions. The formation of pseudorotaxane-type host–guest complexes of these crownophanes with paraquat dication was detected by FABMS and 1H NMR spectroscopy. UV–Vis spectra show no significant changes upon complex formation.

Unique binding behaviour of water-soluble polycationic oxacalix[4]arene tweezers towards the paraquat dication.

The first water-soluble polycationic oxacalix[4]arene molecular tweezers able to recognize - under pH control - the paraquat dication as a result of a delicate balance between electrostatic repulsion, Coulombic shielding and attractive π-stacking interactions are reported.

Complex I Is the Major Site of Mitochondrial Superoxide Production by Paraquat

Paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) is widely used as a redox cycler to stimulate superoxide production in organisms, cells, and mitochondria. This superoxide production causes extensive mitochondrial oxidative damage, however, there is considerable uncertainty over the mitochondrial sites of paraquat reduction and superoxide formation. Here we show that in yeast and mammalian mitochondria, superoxide production by paraquat occurs in the mitochondrial matrix, as inferred from manganese superoxide dismutase-sensitive mitochondrial DNA damage, as well as from superoxide assays in isolated mitochondria, which were unaffected by exogenous superoxide dismutase. This paraquat-induced superoxide production in the mitochondrial matrix required a membrane potential that was essential for paraquat uptake into mitochondria. This uptake was of the paraquat dication, not the radical monocation, and was carrier-mediated. Experiments with disrupted mitochondria showed that once in the matrix paraquat was principally reduced by complex I (mammals) or by NADPH dehydrogenases (yeast) to form the paraquat radical cation that then reacted with oxygen to form superoxide. Together this membrane potential-dependent uptake across the mitochondrial inner membrane and the subsequent rapid reduction to the paraquat radical cation explain the toxicity of paraquat to mitochondria.

Synthesis and properties of first representatives of crownophanes containing the f luorenone and naphthalene fragments

A new family of crownophanes containing the fluorenone and naphthalene fragments linked by oligo(oxyethylene) bridges were synthesized. Reactions of these ligands with the paraquat dication gave inclusion complexes of the pseudorotaxane type that were detected by FAB mass spectrometry, 1H NMR spectroscopy, and electronic absorption spectroscopy.

The balance between electronic and steric effects in the template-directed syntheses of [2]catenanes

Three bis- p-phenylene-34-crown-10 (BPP34C10) derivatives bearing ester groups on one or both of their two aromatic rings have been synthesized. These ester-substituted macrocyclic polyethers bind the paraquat dication in solution more strongly than BPP34C10. In contrast, however, acyclic analogs of these macrocyclic polyethers form much weaker complexes with cyclobis(paraquat- p-phenylene) (CBPQT 4+). Likewise, catenane formation is diminished, in parallel with the number and disposition of the ester substituents on the hydroquinone rings of the macrocyclic polyethers. These observations suggest that complex and catenane formation are controlled by opposing recognition features, according to whether the ester-substituted hydroquinone rings assume either a guest or host role in 1:1 complexes with bipyridinium-based species, or lie inside or alongside the CBPQT 4+ component in the[2]catenanes. Steric and electronic factors associated with the ester substituents probably account for the opposing trends in the inter-component recognition behavior.

Laser desorption/ionization coupled to tandem mass spectrometry for real-time monitoring of paraquat on the surface of environmental particles.

Aerosol mass spectrometry with laser desorption/ionization was investigated as a possible tool for real-time monitoring of the presence of the pesticide paraquat on the surface of airborne soil particles. Laser desorption/ionization of paraquat dication produced only singly charged ions. The most abundant species were [M](+.), [M - H](+), and [M - CH3](+). Operation of the ion trap mass spectrometer in the MS(3) mode allowed the reduction of the signal dependence on laser fluence fluctuations and permitted the detection of the analyte with good sensitivity and high selectivity. The estimated limit of detection in terms of surface coverage was 0.016 monolayers, approximately 1 attomole of paraquat on the surface of a single micron-sized soil particle.

Bajo nivel de exposición e inhalación de paraquat con el uso correcto de la bomba de mochila

Se realizaron cuatro experimentos de campo en donde se aplicaron mezclas de paraquat y oxifluorfen, utilizando una bomba de mochila, al cultivo de plátano (Musa acuminata x M. balbisiana AAB) para evaluar la exposición a inhalación de los aplicadores de paraquat, y determinar posibles medios de reducir la misma. En el primer experimento con cuatro adjuvantes y el segundo experimento con cuatro tipos de boquillas, el nivel de paraquat encontrado mediante análisis de los respiradores de los aplicadores estuvo muy por debajo del nivel de detección (menos de 0.018 mg). Para corroborar el bajo nivel de paraquat encontrado anteriormente, se llevaron a cabo dos experimentos adicionales comparando dos boquillas seleccionadas para aplicar paraquat más el adyuvante X-77 bajo condiciones de campo diferentes. Cada aplicador utilizó un respirador para asperjar tres parcelas, en lugar de una parcela, para un volumen total de 55.5 L. Los análisis de los respiradores en estos dos experimentos revelaron que el nivel de paraquat estuvo por debajo del nivel de detección. Los resultados de estos dos últimos experimentos corroboraron que la exposición de los aplicadores al paraquat estaba por debajo de 0.10 mg/m3, el nivel establecido por el NIOSH. El método analítico para el di-catión de paraquat consistió en pasar los extractos de los respiradores por sus filtros para remover microparticulas. Se empleó una determinación estándar de colorimetría para detectar el nivel de paraquat por cada respirador. Se sustrajo la absorbancia sin añadir un reactivo de color desde la absorbancia con reactivo para poder detectar el nivel de paraquat a 0.018 mg.

Crystal structures of the hydrated disodium and paraquat salts of 1,8-disulfonato-3,4,5,6-acridinetetracarboxylic acid

Two hydrated salts of 1,8-disulfonato-3,4,5,6-acridinetetracarboxylic acid, H2L, have been characterized by single-crystal X-ray analysis. Compound 1, Na2L·9\( - \frac{1}{2}\)H2O, crystallizes in the monoclinic space group C2/c with a = 42.005(1), b = 6.838(1), c = 23.807 (1) A, β = 122.71 (1)°, and Z = 8. Compound 2, (paraquat)L·2H2O, belongs to the triclinic space group \({P\bar 1}\) with a = 9.940(1), b = 11.543(1), c = 14.033(1) A, α = 105.45(1), β = 95.82(1), γ = 100.14(1)° and and Z = 2. All four carboxyl groups in the 3,4,5,6-tetracarboxyacridine-1,8-disulfonate dianion L2− are un-ionized. In 1 the distorted octahedrally coordinated sodium cations, the anions, and the lattice water molecules are joined together by hydrogen bonds to generate a three-dimensional network. In the crystal structure of 2, a host framework composed of L2− ions and water molecules accommodate the paraquat dications within two channel systems running parallel to the a and b axes.

The Design and Self-Assembly of a Furan-Containing [2]Catenane

The bisfuran-containing crown ether 8 has been incorporated, along with bis(paraquat-p-phenylene), into a [2]catenane 2.4PF6 using a self-assembly approach. The presence of the furan units in 8 has a disruptive influence upon the hydrogen bonding interactions involving this crown ether receptor and the paraquat dication. The perturbation of the hydrogen bonding interactions within the furan-containing [2]catenane 2.4PF6 results in changes in the dynamic properties of the relative ring motions compared with those observed for the molecular components of the [2]catenane 1.4PF6.

Paraquat on Carvone Biosynthesis inMentha

ABSTRACT The bipyridinium herbicide paraquat (1,1′-dimethyl-4,4′-bipyridinium chloride), NADPH2 and superoxide dismutase (SOD) were applied to leaf discs of Mentha x verticillata strain No. 21, a strain particularly rich in carvone and trans-carveol. Paraquat affected the carvone biosynthesis and induced leaking of monoterpenes from the oil secreting structures. The addition of NADPH2 to the paraquat treatment increased both the limonene and total monoterpene content probably by supplying the loss of endogenous NADPH2 which was oxidized by paraquat di-cations and thereby affecting monoterpene biosynthesis. Exogeneous SOD increased the total monoterpene content by partly scavenging the toxic effect of paraquat induced superoxide activity on carvone biosynthesis.

1H NMR and visible spectroscopic studies on the complexation of paraquat dication with cyclotetrachromotropylene in water

Cyclotetrachromotropylene forms a 1:1 complex with paraquat dication in water. The stability constant of the complex is 1.1×10 4 M −1 at 25°C.

Difunctional paraquat dications (viologens) and their crown complexes: a new class of rotaxane monomers

Difunctional paraquat dications (viologens) and their crown complexes: a new class of rotaxane monomers

Studies on crown ether based potentiometric sensors for 4,4′-dipyridinium and related dications

Electrodes based on PVC matrix membranes containing one of six crown ethers with 2-nitrophenyl octyl ether or dibutyl phthalate solvent mediator have been studied for their potentiometric response to 4,4′-dipyridyl (DPy), diquat (DQT) and paraquat (PQT) dications. The data are discussed in terms of quality of potentiometric response related to conformational phenomena of crown ethers in their complexation with these dications.Good ion-selective electrode properties were characteristic of the 4,4′-DPy systems based on bis(metaphenylene-32-crown-10)(BMP32C10), bis(metaphenylene-38-crown-12)(BMP38C12), bis(paraphenylene-34-crown-10)(BPP34C10), bis(paraphenylene-37-crown-11)(BPP37C11) and dinaphthalene-36-crown-10 (DN36C10). The calibration slope was between 33 and 41 mV decade–1, extending down to 1.7–6 µM. Interferences from potassium, ammonium, guanidinium, barium, DQT and PQT ions were low except for the BPP34C10 electrode where DQT caused some interference. A sixth electrode, based on dibenzo-30-crown-10 (DB30C10), showed similar calibration behaviour towards 4,4′-DPy but was much less selective.

Complexation of Diquat by a bisparaphenylene-34-crown-10 derivative

The Paraquat dication forms a 1:1 molecular inclusion complex both in acetone solution and in the solid state with the bisparaphenylene-34-crown-10 derivative (BPP34C10) as a result of intra-complex stabilisation from charge transfer interactions as well as from hydrogen and electrostatic bonding.

ChemInform Abstract: EXCIPLEX PROCESSES INVOLVING TRANS‐NAPHTHYLETHYLENES. IMPLICATIONS OF GROUND‐STATE CONFORMERIC EQUILIBRIUMS

Five arylethylenes with 1-naphthyl, 2-naphthyl, and phenyl groups in 1,2-positions have been studied for singlet-mediated charge-transfer interactions with several amines and paraquat dication. 1-Phenyl-2-(2-naphthyl)ethylene and 1,2-di(2-naphthyl)ethylene exhibit distinct dependence of exciplex emission maxima and lifetimes, and fluorescence quenching constants, on excitation and/or monitoring wavelengths; this is in conformity with the existence of ground-state rotamers for these systems, wtih distinguishable absorption-emission spectra and fluorescence lifetimes. The fluorescence quenching by aromatic amines and paraquat dication occurs with rate constants in the limit of diffusion control and is accompanied by the formation of radical ions in polar solvents (acetonitrile). The transient spectra and kinetics associated with the radical ions, observed by 337.1- and 355-nm laser flash photolysis, are also reported. 10 figures, 4 tables.