Formation Of Radical Anion Research Articles

AP-1 Oligodeoxynucleotides Reduce Aortic Elastolysis in a Murine Model of Marfan Syndrome.

Marfan syndrome is characterized by high expression of matrix metalloproteinases (MMPs) in aortic smooth muscle cells (AoSMCs) associated with medial elastolysis and aortic root aneurysm. We aimed to reduce aortic elastolysis through decrease of MMP expression with decoy oligodeoxynucleotides (dODNs) neutralizing the transcription factor activating factor-1 (AP-1). AP-1 abundance in nuclear extracts as well as MMP-2 and MMP-9 expression were significantly increased in isolated mAoSMC of mgR/mgR Marfan mice compared to wild-type cells. Exposure to AP-1 neutralizing dODNs resulted in a significant reduction of basal and interleukin-1β-stimulated MMP expression and activity in mAoSMCs. Moreover, increased migration and formation of superoxide radical anions was substantially decreased in mAoSMCs by AP-1 dODN treatment. Aortic grafts from donor Marfan mice were treated with AP-1- dODN ex vivo and implanted as infrarenal aortic interposition grafts in mgR/mgR mice. Pretreatment of aortic grafts with AP-1 dODN led to reduced elastolysis, macrophage infiltration, and MMP activity. Permeability of the endothelial monolayer was increased for dODN in mgR/mgR aortae with observed loss of tight junction proteins ZO-1 and occludin, enabling dODN to reach the tunica media. Targeting AP-1 activity offers a new potential strategy to treat the vascular phenotype associated with Marfan syndrome.

Electrochemical reduction of organic bromides in 1-butyl-3-methylimidazolium tetrafluoroborate

The electrochemical reduction of a series of aliphatic and aromatic bromides on glassy carbon, silver and copper electrodes has been investigated by cyclic voltammetry in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4). As in polar aprotic solvents, reductive cleavage of aromatic bromides occurs by a stepwise mechanism with the formation of a transient radical anion. In contrast, concerted electron transfer/bond rupture is the preferred reaction pathway for aliphatic bromides. Both Ag and Cu show remarkable electrocatalytic activities for the activation of the carbon-bromine bond, but the catalytic effect depends on reaction mechanism and molecular structure of RBr. Catalysis is high when reduction occurs by a concerted dissociative electron transfer pathway, which is the case of alkyl bromides. When instead a stepwise mechanism is preferred, i.e., the case of all aromatic bromides, catalysis strongly decreases with the ability of the molecule to delocalize the incoming negative charge. For example, the high positive shift of peak potential (>0.7V) observed for bromobenzene on Ag decreases to <0.1V for 4-bromobenzonitrile and <0.02V for 9-bromoanthracene.Overall, [BMIm]BF4 behaves like molecular solvents such as acetonitrile and dimethylformamide but, in general, both Ag and Cu are less active in the ionic liquid than in polar aprotic solvents.

Probing Intermolecular Electron Delocalization in Dimer Radical Anions by Vibrational Spectroscopy.

Delocalization of charges is one of the factors controlling charge transport in conjugated molecules. It is considered to play an important role in the performance of a wide range of molecular technologies, including organic solar cells and organic electronics. Dimerization reactions are well-suited as a model to investigate intermolecular spatial delocalization of charges. While dimerization reactions of radical cations are well investigated, studies on radical anions are still scarce. Upon dimerization of radical anions with neutral counterparts, an electron is considered to delocalize over the two molecules. Here, by using time-resolved infrared (TRIR) detection coupled with pulse radiolysis, we show that radical anions of 4-n-hexyl-4'-cyanobiphenyl (6CB) undergo such dimerization reactions, with an electron equally delocalized over the two molecules. We have recently demonstrated that nitrile ν(C≡N) vibrations respond to the degree of electron localization of nitrile-substituted anions: we can quantify the changes in the electronic charges from the neutral to the anion states in the nitriles by monitoring the ν(C≡N) IR shifts. In the first part of this article, we show that the sensitivity of the ν(C≡N) IR shifts does not depend on solvent polarity. In the second part, we describe how probing the shifts of the nitrile IR vibrational band unambiguously confirms the formation of dimer radical anions, with Kdim = 3 × 104 M-1. IR findings are corroborated by electronic absorption spectroscopy and electronic structure calculations. We find that the presence of a hexyl chain and the formation of π-π interactions are both crucial for dimerization of radical anions of 6CB with neutral 6CB. The present study provides clear evidence of spatial delocalization of electrons over two molecular fragments.

Photochemical insights of TiO2 decorated mesoporous SBA-15 materials and their influence on the photodegradation of organic contaminants

Mesoporous silica, SBA-15, decorated with different amounts of TiO2 (anatase) were prepared by a sol-gel method followed by hydrothermal treatment and calcination, in the presence of a soft template, copolymer Pluronic 123. Tetraethyl orthosilicate (TEOS) was used as the SiO2 precursor and commercially available TiO2 anatase nanoparticles as the supported photocatalyst. The materials were characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDS), N2 adsorption-desorption isotherms, raman spectroscopy, ground state diffuse reflectance (GSDR), laser induced luminescence (LIL) and X-ray photoelectron spectroscopy (XPS). The zeta potentials of the pure SBA-15, TiO2/SBA-15 substrate and the commercial anatase sample were monitored through a complete range of pH values. All the nanomaterials developed in this work were studied in terms of their photoactivity in the UV range and in the visible range, separately. In the first case, hydroxyl radicals (OH) were confirmed to be the key active oxidizers in the photodegradation of the pesticide amicarbazone in aqueous medium. On the other hand, in the visible range, and following a dye sensitization process via a fluorescent rhodamine-like dye, two different mechanisms could be identified for the formation of the superoxide radical anion, O2−.

Electrochemical transformations and anti/prooxidant activity of sterically hindered o-benzoquinones

The electrochemical properties of a series of sterically hindered o-benzoquinones in aprotic solvents were examined. The reaction of O2 and KO2 with o-benzoquinones and electrogenerated o-semiquinone radical anions was studied. The formation of o-semiquinone radical anions in the reactions of KO2 with the studied o-quinones was detected using UV-visible and ESR spectroscopy. The influence of the test compounds on lipid peroxidation was considered at the molecular and tissue levels in vitro. In the most cases, o-quinones exhibit antioxidant activity, which varies depending on the type of lipid substrate.

Bottom-Up Electrochemical Deposition of Poly(styrene sulfonate) on Nanoarchitectured Electrodes.

The cathodic deposition of poly(styrene sulfonate) on nanoarchitectured TiO2 electrodes is explored by cyclic voltammetry and potentiostatic and galvanostatic experiments, showing a diffusion-controlled deposition described by Cottrell's law. The structure and composition of the polymer is evidenced by various spectroscopic techniques, including nuclear magnetic resonance, Fourier transform infrared, and X-ray photoelectron spectroscopy, and its morphology is studied by scanning electron microscopy. The average chain length can be estimated from the NMR spectra. The electropolymerization mechanism initiates by radical anion formation. The cycling behavior in half-cell batteries against Li metal is excellent, especially at high rates explored up to 10 C. The areal insertion capacity is above recent literature results, up to 80 μA h cm-2. The combination of normalized areal power density and areal energy density is one of the best reported in the literature.

H‐bonding Assisted Self‐Assembled One‐Dimensional Nanotubes of Redox Active Triphenylamine‐Benzothiadiazole Derivative

AbstractControl over the one‐dimensional (1D) nanotubular structures significant in organic electronics. Although, p‐ and n‐type derivatives have shown diverse nanostructures, however very few ambipolar derivatives reported until now because of constrained structural properties. By considering this issue, three triphenylamine‐benzothiadiazole based ambipolar derivatives (TBE, TBAc and TBAm) synthesized and TBAm forms 1D nanotubes exclusively. DFT and spectroelectrochemical studies displayed the formation of stable cation and anion radicals of TBAm under controlled potential of 1.30 V. UV‐vis, emission (steady‐state and TCSPC) and microscopic analyses revealed TBAm exists as J‐aggregates and further leads to nanotubes by utilizing directional amide H‐bonding, together with π‐π stacking and van der Waals interactions. Consequently, these properties aid to design novel materials, which pave the way towards efficient organic field effect transistors.

Thermolysis of brown coal in the presence of alkali metal hydroxides

The thermolysis (≤500°C) of brown coal impregnated with alkali metal hydroxides MOH was studied. Alkalis cause the cleavage of a three-dimensional coal framework into fragments similar to humic acids. The initial rate of the process increases with the diameter of a cation. For the brown coal–KOH compound, an increase in the temperature from 110 to 400°C increased the rate of fragmentation by a factor of ~200 to cause the almost complete (≥90 wt %) decomposition of coal. The promotion of condensational reactions that cause a decrease in the yield of low-molecular-weight volatile organic products is a competing process. In the presence of MOH, the buildup of radicals is changed: a local maximum (at 200–250°C) is formed in the temperature dependence of the concentration of unpaired electrons; the temperature of this maximum and the values of [e –] depend on the nature of MOH. In the series of alkalis from LiOH to CsOH, the EPR signal broadened from 0.63 to 0.84 mT due to the formation of semiquinone radical anions and the interaction of an unpaired electron with a cation. A reaction scheme was proposed for the processes of the thermolysis (to 400°C) of brown coal with MOH; it includes the cleavage of a coal framework by the simultaneous heterolysis and homolysis of C–O and C–C bonds with the subsequent formation of a secondary lattice due to polycondensation and radical polymerization.

Photoinduced electron transfers after t-stilbene incorporation in zeolite. Effect of the presence of an electron acceptor on the reactivity

Diffuse reflectance UV–vis absorption and EPR spectroscopies are used to study photoinduced electron transfers in supramolecular assemblies composed of donor (t-stilbene, t-St) and acceptor (dicyanobenzene, DCB) guest molecules incorporated in MFI zeolites. By using Al-free silicalite-1, it clearly appears that the presence of the acceptor has no effect on the reactivity and that no electron transfer occurs to DCB after t-St photoionization and radical cation (t-St●+) formation. On the contrary, we show evidence for the striking slowing down of the recombination reaction in the presence of the acceptor molecule in the channels of MZSM-5 (M = Na+, Cs+). In these Al-rich zeolites, electron transfers are mediated by the framework which does not remain passive after photoexcitation. Indeed, zeolite acts both as an electron acceptor and as an electron donor and strongly influences the reaction mechanisms. The donor character is put forward to explain the indirect recombination of the radical cation to form an electron/hole pair. Concerning the acceptor ability of zeolite, we show that the attracting and stabilizing character of NaZSM-5 competes with the acceptor property of dicyanobenzene and then, does not allow total electron transfer to the guest. Even if the DCB●− radical anion formation does not occur, HYSCORE experiments show strong electron density in the surrounding of DCB indicating partial electron transfer and explaining the trapping of electron and the slowing down of the charge recombination.

Contaminant salts as enhancers of sonocatalytic degradation of organic water pollutants: Effect of concentration, reaction time and adsorption on the efficiency of enhancement and the fate of concurrently formed H2O2

The effect of salts/anions on ZnO-mediated sonocatalytic degradation of phenol in water is investigated. Anions such as CH3COO−, SO42−, CO32−, HCO3−, NO3−, F−, Cl− and PO43− enhance the degradation. However, the effect is dependent on concentration of the anion and duration of reaction. The enhancing effect in sonocatalysis is different from and contradictory to the inhibiting effect of anions in photo- and sonophoto- catalysis. The enhancement is maximum in the presence of F−, SO42− and CH3COO− and the least in the presence of HCO3− and PO43− though minor exceptions are there depending on the experimental conditions. The basic mechanism of enhancement involves the formation of reactive radical anions by interaction of the anions with the highly reactive .OH radicals and their reaction with phenol. The lower reactivity of the radical anions compared to OH is compensated by the relatively higher concentration. Moreover, they interact exclusively with the substrate whereas the .OH participates in many reactions simultaneously including recombination and self- deactivation. Other effects of dissolved salts/anions such as increasing the ionic strength of the medium, modification in the partition coefficient, decreasing vapor pressure, increase in hydrophilicity etc. also favor sonocatalytic degradation of phenol. The concentration of concurrently formed H2O2 does not increase corresponding to the degradation of phenol and varies in a wave-like fashion (oscillation) due to the simultaneous formation and decomposition with either of them dominating periodically. The anions also influence the nature of the oscillation curve. Possible reasons for the anion effect and potential practical application are discussed.

Oxidative transformation of a tunichrome model compound provides new insight into the crosslinking and defense reaction of tunichromes

Tunichromes, small oligopeptides with dehydrodopa units isolated from the blood cells of ascidians, have been implicated in the defense reactions, metal binding, wound repair, or tunic formation. Their instability and high reactivity has severely hampered the assessment of their biological role. Experiments conducted with the model compound, 1,2-dehydro-N-acetyldopamine, indicated that the instability of tunichromes is due to this basic structure. Exposure of this catecholamine derivative to even mild alkaline condition such as pH 7.5 causes rapid nonenzymatic oxidation. High performance liquid chromatography and mass spectrometry studies confirmed the production of dimeric and other oligomeric products in the reaction mixture. The nonenzymatic reaction seemed to proceed through the intermediary formation of semiquinone free radical and superoxide anion. Ultraviolet and visible spectral studies associated with the oxidation of tunichromes isolated from Ascidia nigra by tyrosinase indicated the probable formation of oligomeric tunichrome products. Attempts to monitor the polymerization reaction by mass spectrometry ended in vain. Tunichrome also exhibited instability in mild alkaline conditions generating superoxide anions. Based on these studies, a possible role for oxidative transformation of tunichrome in defense reaction, tunic formation and wound healing is proposed.

Superoxide Radical Anion‐Mediated Aerobic Oxidative Synthesis of 2‐Substituted Quinazolines under Visible Light

AbstractA facile and efficient one‐pot reaction for the aerobic oxidative synthesis of 2‐substituted quinazolines using visible‐light catalysis has been developed. A variety of substituted aldehydes and 2‐aminobenzylamines are amenable to producing the corresponding quinazolines in good to excellent yields under metal‐free conditions. Electron paramagnetic resonance (EPR) measurements provide clear evidence on the formation of a superoxide radical anion (O2⋅−), which is responsible for this transformation.

Probing the redox process of p-benzoquinone in dimethyl sulphoxide by using fluorescence spectroelectrochemistry

Quinones are common organic compounds frequently used as model dissolved organic matters in water, and their redox properties are usually characterized by either electrochemical or spectroscopic methods separately. In this work, electrochemical methodology was combined with two fluorescence spectroelectrochemical techniques, cyclic volta- fluorescence spectrometry (CVF) and derivative cyclic volta- fluorescence spectrometry (DCVF), to determine the electrochemical properties of p-benzoquinone in dimethyl sulfoxide, an aprotic solution. The CVF results show that the electrochemical reduction of p-benzoquinone resulted in the formation of radical anion and dianion, which exhibited a lower fluorescence intensity and red-shift of the emission spectra compared to that of p-benzoquinone. The fluorescence intensity was found to vary along with the electrochemical oxidation and reduction of p-benzoquinone. The CVF and DCVF results were in good consistence. Thus, the combined method offers a powerful tool to investigate the electrochemical process of p-benzoquinone and other natural organic compounds. Open image in new window

Significantly enhanced base activation of peroxymonosulfate by polyphosphates: Kinetics and mechanism

Base activation of peroxydisulfate (PDS) is a common process aiming for water treatment, but requires high doses of PDS and strongly basic solutions. Peroxymonosulfate (PMS), another peroxygen of sulfurate derived from PDS, may also be activated by a less basic solution. However, enhancing the base-PMS reactivity is still challenging. Here it is reported that pyrophosphate (PA) and tripolyphosphate (PB) can efficiently enhance PMS activation under weakly alkaline conditions (pH 9.5) via the formation of superoxide anion radical (O2•−) and singlet oxygen (1O2). The rate constant of Acid Orange 7 (AO7) degradation in PA/PMS system (kPA/PMS) was nearly 4.4–15.9 fold higher than that in PMS/base system (kPMS/base) without any polyphosphates. Increases in PA (or PB) concentration, PMS dose and pH favored the rapid dye degradation. Gas chromatograph-mass spectrometer (GC-MS) data confirmed AO7 and 2,4,6-trichlorophenol (2,4,6-TCP) were decomposed to a series of organic intermediates. The radical quenching and probe oxidation experiments indicate the degradation of organic compounds in the PA/PMS and PB/PMS processes was not reliant on sulfate radical (SO4•−) and hydroxyl radical (OH) species but on O2− and 1O2 reactive species. Comparison experiments show that the polyphosphate/PMS process was much more favorable than PDS/base process. The present work provides a novel way to activate PMS for contaminant removal using industrial polyphosphate wastewaters.

Synthesizing a CuIIcomplex of tinidazole to tune the generation of the nitro radical anion in order to strike a balance between efficacy and toxic side effects

Synthesis, characterization, enzyme assay, DNA binding and antimicrobial activity of a monomeric complex of CuIIwith tinidazole: significance of the controlled formation of the nitro radical anion.

Recent developments in transition-metal photoredox-catalysed reactions of carbonyl derivatives.

Single-electron reduction of C[double bond, length as m-dash]O and C[double bond, length as m-dash]N bonds of aldehydes, ketones, and imines results in the formation of ketyl and α-aminoalkyl anion radicals, respectively. These reactive intermediates are characterized by an altered electronic character with respect to their parent molecules and undergo a diverse range of synthetically useful transformations, which are not available to even-electron species. This Review summarizes the reactions of ketyl and α-aminyl radicals generated from carbonyl derivatives under transition-metal photoredox-catalysed conditions. We primarily focus on recent developments in the field, as well as give a brief overview of catalytic enantioselective transformations that provide a means to achieve precise stereocontrol over the reactivity of ion radicals.

Effects of Substitution of Fish Meal with Black Soldier Fly (Hermetia illucens) Larvae Meal, in Yellow Catfish (Pelteobagrus fulvidraco) Diets

An 8-week feeding trial was conducted to evaluate effects of replacing fish meal (FM) with black soldier fly larvae meal (BSF) on growth performance, feed utilization, and plasma parameters, for juvenile yellow catfish, Pelteobagrus fulvidraco. Six isonitrogenous and isolipidic diets were prepared substituting the FM protein with BSF protein in the following amounts: 0 (control group), 10% (BSF10), 15% (BSF15), 20% (BSF20), 25% (BSF25) and 30% (BSF30). Three replicate groups of juvenile yellow catfish (initial weight of 1.20 ± 0.01 g) were stocked in circular tanks at a rate of 30 fish per tank. The results showed that 20% of the FM in the control diet could be replaced with BSF without significantly reducing weight gain, feed conversion ratio, or whole body and muscle proximate composition. Apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude lipids, gross energy, or amino acids were not affected by 10% FM replacement. 30% FM replacement in the BSF30 diet significantly increased the concentration of cholesterol (CHO) and nitric oxide (NO) in the plasma, and significantly reduced the inhibition of superoxide radical anion formation. In conclusion, it appears that up to 20% of the FM in conventional yellow catfish diets can be replaced with BSF, and thus account for up to 8.9% of the total protein in the diet without causing a significant reduction in growth performance.

Effects of Substitution of Fish Meal with Black Soldier Fly (Hermetia illucens) Larvae Meal, in Yellow Catfish (Pelteobagrus fulvidraco) Diets

An 8-week feeding trial was conducted to evaluate effects of replacing fish meal (FM) with black soldier fly larvae meal (BSF) on growth performance, feed utilization, and plasma parameters, for juvenile yellow catfish, Pelteobagrus fulvidraco. Six isonitrogenous and isolipidic diets were prepared substituting the FM protein with BSF protein in the following amounts: 0 (control group), 10% (BSF10), 15% (BSF15), 20% (BSF20), 25% (BSF25) and 30% (BSF30). Three replicate groups of juvenile yellow catfish (initial weight of 1.20 ± 0.01 g) were stocked in circular tanks at a rate of 30 fish per tank. The results showed that 20% of the FM in the control diet could be replaced with BSF without significantly reducing weight gain, feed conversion ratio, or whole body and muscle proximate composition. Apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude lipids, gross energy, or amino acids were not affected by 10% FM replacement. 30% FM replacement in the BSF30 diet significantly increased the concentration of cholesterol (CHO) and nitric oxide (NO) in the plasma, and significantly reduced the inhibition of superoxide radical anion formation. In conclusion, it appears that up to 20% of the FM in conventional yellow catfish diets can be replaced with BSF, and thus account for up to 8.9% of the total protein in the diet without causing a significant reduction in growth performance.

The extravascular penetration of tirapazamine into tumours: a predictive model of the transport and efficacy of hypoxia specific cytotoxic analogues and the potential use of cucurbiturils to facilitate delivery

A multiparameter model of the diffusion, antiproliferative assays IC50 and aerobic and hypoxic clonogenic assays for a wide range of neutral and radical anion forms of tirapazamine (TPZ) analogues has found: a) extravascular diffusion is governed by the desolvation, lipophilicity, dipole moment and molecular volume; b) hypoxic assay properties of the TPZ analogues show dependencies on the electron affinity, lipophilicity and dipole moment and desolvation; c) aerobic properties are mainly dependent on the electron affinity, involving free radicals in the extracellular matrix. The model shows that ligand water desolvation and lipophilicity are the dominant processes governing the DNA intercalation of TPZ analogues, consistent with DFT modelling of the complexes formed by TPZ analogues with neutral and N-protonated acridine moieties which intercalate with the guanine DNA nucleobases. It is shown that TPZ can form stable complexes with cucurbit[7]uril as a precursor to proof of principle of improved TPZ delivery to tumours.

The extravascular penetration of tirapazamine into tumours: a predictive model of the transport and efficacy of hypoxia specific cytotoxic analogues and the potential use of cucurbiturils to facilitate delivery

A multiparameter model of the diffusion, antiproliferative assays IC50 and aerobic and hypoxic clonogenic assays for a wide range of neutral and radical anion forms of tirapazamine (TPZ) analogues has found: a) extravascular diffusion is governed by the desolvation, lipophilicity, dipole moment and molecular volume; b) hypoxic assay properties of the TPZ analogues show dependencies on the electron affinity, lipophilicity and dipole moment and desolvation; c) aerobic properties are mainly dependent on the electron affinity, involving free radicals in the extracellular matrix. The model shows that ligand water desolvation and lipophilicity are the dominant processes governing the DNA intercalation of TPZ analogues, consistent with DFT modelling of the complexes formed by TPZ analogues with neutral and N-protonated acridine moieties which intercalate with the guanine DNA nucleobases. It is shown that TPZ can form stable complexes with cucurbit[7]uril as a precursor to proof of principle of improved TPZ delivery to tumours.