Generation Of Superoxide Radical Anion Research Articles

Revisiting the role of H2O2 in periodate electro-activation system: The non-dependence in Bisphenol A (BPA) removal

The existence of hydrogen peroxide (H2O2) within the electro-activation of periodate (PI) system is conventionally considered as conducive to the removal of pollutants. However, this study discovered an unusual phenomenon: the contaminants removal efficiency and the yield of strong oxidizing species such as hydroxyl radical (OH) and iodate radical (IO3) were improved when H2O2 in the solution was quenched. The study deeply explored the role of H2O2 in graphite felt-based electro-activated PI system (GF-PI), particularly in the mechanism of active species generation and contaminants removal. Bisphenol A (BPA), as the model contaminant, achieves a degradation efficiency of 82.1% and 83.9% within 40 min in w/wo H2O2 system, respectively. Meanwhile, multiple probing techniques clearly identify the variety of active species and generation pathway such as Electron paramagnetic resonance (EPR), LC-QTOF-MS, and quenching experiment. There exist two distinct pathways for PI activation, including direct cathodic electroreduction and indirect in-situ generated H2O2 catalysis. The GF-PI system incorporated both of two pathways, while the GF-PI-catalase system only had the direct activation pathway. Electrogenerated H2O2 serves as a precursor for the generation of superoxide radical anions (O2−) and singlet oxygen (1O2), yet it diminishes the efficiency of direct cathode activation due to the consumption of PI. Furthermore, the system demonstrated excellent stability, applicability, and cleanliness, effectively removing contaminations without the accumulation of iodine byproducts. The degradation intermediates products of BPA are monitored and the toxicities are evaluated. The study provides novel insights into the regulation of active species for contaminant elimination, holding significant implications for specialized sewage treatment.

Strategic Insertion of Heavy Atom to Tailor TADF OLED Material for the Development of Type I Photosensitizing Catalytic Red Emissive Assemblies.

The work presented in the manuscript describes a simple strategy for transforming thermally activated delayed fluorescent organic light-emitting diodes (TADF OLEDs) compound 10-(dibenzo[a,c]phenazin-11-yl)-10H-phenoxazine (DPZ-PXZ) into type I photosensitizer 10-(dibenzo[a,c]phenazin-11-yl)-10H-phenothiazine (DPZ-PHZ) by strategically introducing sulfur atom in the photosensitizing core. The synthesized compound DPZ-PHZ exhibits aggregation-induced enhancement (AIE) and through-space charge transfer (TSCT) characteristics and generates red emissive assemblies in mixed aqueous media. The original compound DPZ-PXZ exhibits well-separated HOMO and LUMO levels and is reported to have highly efficient reverse intersystem crossing (RISC). In comparison, the incorporation of sulfur atom in the phenothiazine donor regulates the electronic communication between donor and acceptor units and promotes the intersystem crossing (ISC) in DPZ-PHZ molecules. Interestingly, compound DPZ-PHZ exhibits rapid activation of aerial oxygen for instant generation of superoxide radical anion. Backed by excellent type I photosensitizing activity, DPZ-PHZ assemblies have high catalytic potential for the synthesis of benzimidazoles, benzothiazoles and quinazolines derivatives under mild reaction conditions. The work presented in the manuscript provides an insight into the combination of heavy atom approach and TSCT for achieving adequate electronic communication between donor and acceptor units, balanced RISC/ISC, and stabilized-charge separated state for the development of efficient type I photosensitizing assemblies.

Ultrasound assisted fabrication of InVO4/In2S3 heterostructure for enhanced sonophotocatalytic degradation of pesticides

A cost effective and environmentally benign ultrasonic method has been developed for the synthesis of InVO4 (InV), In2S3 (InS) and the InVO4/In2S3 heterostructure (InV/InS). All the designed materials were evaluated for their structural, morphological, spectroscopic, and electrochemical characterizations. Materials were examined for photocatalytic, sonocatalytic, and sonophotocatalytic degradation of carbofuran (CBF) and diazinon (DZN) pesticides under visible light. InV/InS showed enhanced degradation of CBF and DZN when compared to InV and InS. Photocatalytic degradation was accelerated by ultrasonication and found to degrade 97 and 98 % of CBF and DZN in 60 and 70 min, respectively. The reaction conditions, like pH, catalyst dosage, acoustic intensity, and ultrasound power, were carefully optimized. Electron spin resonance (ESR) spectroscopy shows the generation of superoxide radical anion and hydroxyl radicals as reactive species during photoredox reaction. The CBF and DZN degradation intermediates were analyzed using liquid chromatography mass spectroscopy (LC-MS) that shows the mineralization of the CBF and DZN to CO2 and H2O. The effect of Cl−, and PO43− were examined towards degradation of CBF and DZN under optimal conditions in the presence of InV/InS. The degradation of CBF and DZN is decreased in presence of Cl−, CO32– and NO3– but PO43− ions does not show any effect on degradation. The bandgap and Mott-Schottky results suggest the existence of type-II heterostructure between InV and InS through the interface. The synthesis of heterostructure and degradation of pesticides utilizes ultrasonic waves, which prove their multiple applications and attract researchers towards the effective use of sonication.

Interface engineered Ca–Co mixed oxide heterostructures for boosting the aerobic and solvent-free selective oxidation of ethybenzene

Exploration of a high-performance, low-cost and easy-to-prepare solid catalyst is a permanent goal to advance the selective oxidation of hydrocarbons to high-value-added oxygenated products. Herein, we demonstrated for the first time that Ca–Co mixed oxide with abundant strongly interacting heterointerfaces for advanced ethylbenzene oxidation performance under solvent-free conditions and using molecular oxygen as the only oxidant. The interface engineering strategy contributes to the formation of weakened Co–O bonds, enhanced oxygen vacancy concentration and boosted reactivity of lattice oxygen, facilitating the generation of superoxide radical anions for driving the ethylbenzene (EB) oxidation catalysis. In addition, the CaxCoyOz catalyst exhibits good recyclability and high stability. This study provides a paradigm for the rational construction of metal oxides with hybrid interfaces towards a lab as well as a large-scale green oxidation of EB and beyond.

Straightforward synthesis of a porous chromium-based porphyrinic metal-organic framework for visible-light triggered selective aerobic oxidation of benzyl alcohol to benzaldehyde

Among MOFs, chromium-based metal–organic frameworks (Cr-MOFs) represent attractive scaffolds for variety of potential applications due to their high porosity and stability. Nevertheless, Cr-MOFs are not very common due to complicate synthesis. Cr-MOFs of large linkers are one clear example of synthetic limitations, since their preparation takes place by post-synthetic routes, commonly starting from Fe-MOFs as precursors. Hence, in this work, the direct synthesis of a phorphyrinic chromium-based MOF, Cr-PCN-600 (PCN stands for Porous Coordination Network) under solvothermal conditions is reported. The resulting Cr-MOF exhibits high surface area, permanent porosity, and broad light absorption wavelength range. Interestingly, this Cr-MOF is a highly effective heterogeneous photocatalyst for the selective aerobic oxidation of benzyl alcohol to benzaldehyde under visible light irradiation without any additive. Importantly, the Cr-MOF showed good recyclability maintaining its activity for three runs. The present results lay the foundation for both synthesis and applications of Cr-MOFs as robust photocatalysts in advanced organic transformations. Notably, quenching studies confirmed the generation of superoxide radical anion (O2−) and singlet oxygen (1O2) (mostly) as reactive species under the reaction conditions.

Photocatalytic hydrogen evolution over surface-modified titanate nanotubes by 5-aminosalicylic acid decorated with silver nanoparticles

The efficiency of titanate-nanotubes-based photocatalysts towards hydrogen production was studied in the presence of the sacrificial agent, 2-propanol. The highest hydrogen production rate (~120 μmol h−1 g−1) was observed over surface-modified titanate nanotubes by 5-amino salicylic acid decorated with nanometer-sized silver nanoparticles. The X-ray diffraction analysis, transmission electron microscopy, nitrogen adsorption–desorption isotherms, and diffuse reflection spectroscopy were applied to characterize the prepared photocatalytic materials. The better photocatalytic performance of inorganic–organic hybrid materials in comparison to the pristine titanate nanotubes is a consequence of their improved light-harvesting ability due to the formation of interfacial charge transfer (ICT) complex, as well as the presence of metallic silver nanoparticles that suppress the recombination of photo-generated charge carriers. The spin trapping EPR experiments under irradiation of prepared photocatalysts with either UV or visible light were used to monitor the appearance of hydroxyl radicals and superoxide radical anions. The generation of superoxide radical anions under visible light irradiation was detected for hybrid materials, but not for the pristine titanate nanotubes. These results are a consequence of enhanced promotion of electrons to the conduction band due to extended absorption in visible spectral range in hybrids and support the higher efficiency of hydrogen generation observed for surface-modified titanate nanotubes by 5-amino salicylic acid decorated with silver nanoparticles.

Two-Photon Fluorescence Probe for Selective Monitoring of Superoxide in Live Cells and Tissues.

The abnormal location or generation of superoxide radical anion (O2•-) are implicated in many diseases, including cancers; thus, development of an efficient method to detect O2•- is of great importance. Inspired by the fluorophore-governed selective manner to O2•- and peroxynitrite (ONOO-) of previously reported phosphinate-based fluorescence probes, in this contribution, a phosphinothioate-containing probe, TPP, was designed. The probe exhibited easy accessibility through a one-step sequence and good photostability and biocompatibility. Interestingly, TPP showed high specificity and sensitivity to O2•- over other reactive oxygen species/nitrogen species including ONOO-. Furthermore, with the assistance of two-photon microscopy, TPP was successfully applied for imaging endogenous O2•- in live cells and tissues.

Metal‐Free and Heterogeneous Photocatalytic Reduction of 4‐Nitroaniline by a Poly(Ethylene Glycol)‐Supported Eosin Dye under Visible‐Light Exposure

AbstractA new feasible approach for the photoreduction of a chemical pollutant, 4‐nitroaniline, to p‐phenylenediamine was developed. We highlighted the crucial roles of a polymer backbone and the atmosphere for the efficient heterogeneous reduction of 4‐nitroaniline. The novel synthesized poly(ethylene glycol)‐derived film containing immobilized eosin dye revealed a high photoreduction rate of 4‐nitroaniline. According to laser flash photolysis results the first step of this photoinduced process represents a single electron transfer from eosin radical anion to the 4‐nitroaniline to form a nitroaniline radical anion. The in‐situ electron paramagnetic resonance spin‐trapping experiments evidenced the generation of superoxide radical anion serving as catalyst in the p‐phenylenediamine production according to a photoreduction process. The main roles play by poly(ethylene glycol) matrix as efficient reducing agent and hydrogen‐donor molecule was also pointed out. A mechanism was proposed to explain the heterogeneous photoreduction of 4‐nitroaniline to p‐phenylenediamine in the presence of eosin dye‐based poly(ethylene glycol) system under air.

Repurposing the Electron Transfer Reactant Phenazine Methosulfate (PMS) for the Apoptotic Elimination of Malignant Melanoma Cells through Induction of Lethal Oxidative and Mitochondriotoxic Stress.

Redox-directed pharmacophores have shown potential for the apoptotic elimination of cancer cells through chemotherapeutic induction of oxidative stress. Phenazine methosulfate (PMS), a N-alkylphenazinium cation-based redox cycler, is used widely as an electron transfer reactant coupling NAD(P)H generation to the reduction of tetrazolium salts in biochemical cell viability assays. Here, we have explored feasibility of repurposing the redox cycler PMS as a superoxide generating chemotherapeutic for the pro-oxidant induction of cancer cell apoptosis. In a panel of malignant human melanoma cells (A375, G361, LOX), low micromolar concentrations of PMS (1–10 μM, 24 h) displayed pronounced apoptogenicity as detected by annexin V-ITC/propidium iodide flow cytometry, and PMS-induced cell death was suppressed by antioxidant (NAC) or pan-caspase inhibitor (zVAD-fmk) cotreatment. Gene expression array analysis in A375 melanoma cells (PMS, 10 µM; 6 h) revealed transcriptional upregulation of heat shock (HSPA6, HSPA1A), oxidative (HMOX1) and genotoxic (EGR1, GADD45A) stress responses, confirmed by immunoblot detection demonstrating upregulation of redox regulators (NRF2, HO-1, HSP70) and modulation of pro- (BAX, PUMA) and anti-apoptotic factors (Bcl-2, Mcl-1). PMS-induced oxidative stress and glutathione depletion preceded induction of apoptotic cell death. Furthermore, the mitochondrial origin of PMS-induced superoxide production was substantiated by MitoSOX-Red live cell fluorescence imaging, and PMS-induced mitochondriotoxicity (as evidenced by diminished transmembrane potential and oxygen consumption rate) was observable at early time points. After demonstrating NADPH-driven (SOD-suppressible) superoxide radical anion generation by PMS employing a chemical NBT reduction assay, PMS-induction of oxidative genotoxic stress was substantiated by quantitative Comet analysis that confirmed the introduction of formamido-pyrimidine DNA glycosylase (Fpg)-sensitive oxidative DNA lesions in A375 melanoma cells. Taken together, these data suggest feasibility of repurposing the biochemical reactant PMS as an experimental pro-oxidant targeting mitochondrial integrity and redox homeostasis for the apoptotic elimination of malignant melanoma cells.

Synthesis of ZnO–SnO2 nanocomposites: impact of polyethylene glycol on morphological, luminescence and photocatalytic properties

Zinc oxide-doped tin dioxide (ZnO–SnO2) nanomaterials were prepared by a sol–gel method with and without different amounts (0.5, 1.0 and 2.0 g) of polyethylene glycol (PEG). The prepared nanocomposites were characterized for structural, surface and optical properties. The effect of a PEG on the prepared ZnO–SnO2 nanocomposites was investigated. The photocatalytic activities of the synthesized nanocomposites were evaluated by methylene blue dye degradation under UV illumination. The ZnO–SnO2 nanocomposites prepared with 2.0 g of PEG showed the highest degradation efficiency of 87.30%, suggesting that adding PEG enhances the photocatalytic performance of ZnO–SnO2 nanocomposites due to increased inhibition of e−/h+ pair recombination and efficient generation of superoxide radical anions and hydroxyl radicals.

Facet-dependent generation of superoxide radical anions by ZnO nanomaterials under simulated solar light

The capability of ZnO nanomaterials to generate reactive oxygen species under solar light, which is critical for their photocatalytic applications and may affect their environmental implications, can be substantially influenced by exposed facets.

Degradation of PFOA by hydrogen peroxide and persulfate activated by iron-modified diatomite

Perfluorooctanoic acid (PFOA) is one of the most problematic perfluoroalkyl compounds widely used to make fluoropolymers. The exceptional strength of the carbon–fluorine (CF) bond in PFOA makes it extremely resistant to oxidative attack even by hydroxyl radicals, resulting in its persistence in the environment. As a result, this study investigated generation of superoxide radical anions to reductively decompose such a highly oxidized chemical, PFOA. Catalyzed hydrogen peroxide (CHP) propagations and activated persulfate systems for generating reductive species such as superoxide radical anions along with oxidizing hydroxyl and sulfate radicals were examined. Improved activation mechanism for hydrogen peroxide and persulfate by using iron-modified diatomite (MD), which favorably leads the reaction to generation of the reductive radicals, was proposed. Three comparative systems were efficient in order of CHP>hydrogen peroxide-activated persulfate>alkaline-activated persulfate at PFOA decomposition of 83%, 69% and 48%, respectively, under given conditions. The heterogeneous system employing MD was also compared with a homogeneous system employing dissolved Fe ions to evaluate the effectiveness of MD. All the results supported that MD has significant catalytic activity for the degradation of PFOA when used to activate hydrogen peroxide and persulfate for the generation of superoxide radical anions. The reductive systems coupled with MD exhibited high decompose efficiency for the most recalcitrant chemical, PFOA and thus high potential for the decomposition of other problematic halogenated compounds.

An experimental in vitro study of antioxidant and antiradical properties of cytoflavin, vinpocetine, actovegin and ethylmethylhydroxypyridine succinate

To investigate experimentally in vitro the antioxidant and anti-radical activity of several drugs. Antioxidant activity was assessed by induced luminol-dependent chemiluminescence (CL). An impact on the generation of reactive oxygen species (O2-, OH, 1D, H2O2, HClO) and their ability to inhibit the auto-oxidation of quercetin combined with the generation of superoxide radical anion were determined. Anti-radical activity was studied by the method of restoring a stable radical α-α-diphenyl-β-picryl hydrazine (DPPH) molecule of the alleged anti-oxidant. The many-sided action of the drugs on the products of free radicals generated in the in vitro experiments has been shown. Only cytoflavin has the highest total antioxidant and antiradical activity. Vinpocetine has demonstrated similar, but somewhat less pronounced, activity. Ethylmethylhydroxypyridine succinate and actovegin have shown only the nonspecific superoxide dismutase activity which was by times lower than that of cytoflavin and vinpocetine.

UVA-induced effects of 2,6-disubstituted 4-anilinoquinazolines on cancer cell lines

Five 2,6-substituted 4-anilinoquinazolines were evaluated for their ability to generate superoxide radical anion and singlet oxygen upon UVA irradiation and to induce cytotoxic/phototoxic effects on cancer cell lines L1210, HeLa and HT-29. The formation of radical intermediates, especially reactive oxygen species, upon UVA photoexcitation of the studied derivatives was monitored by indirect techniques of EPR spectroscopy. For all 4-anilinoquinazolines the photoinduced generation of superoxide radical anion was evidenced using spin trapping agent 5,5-dimethyl-1-pyrroline N-oxide, and the presence of 1O2 was detected by the oxidation of 4-hydroxy-2,2,6,6-tetramethylpiperidine to the paramagnetic species 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl. The confirmed photoinduced activation of molecular oxygen via both Type I and Type II photooxidation mechanisms indicates potential phototoxic responses in cells. Biological results showed that derivatives I–V initiated different cytotoxic/phototoxic effects dependent on their concentration, time of treatment and the character of the cell line. UVA irradiation increased the cytotoxic activity of all tested 4-anilinoquinazoline derivatives. The highest cytotoxicity/phototoxicity on all tested cancer cells was induced by N,2-diphenyl-quinazolin-4-amine (derivative III). This most effective derivative emerged as the potent photosensitizer, which possesses a significant antiproliferative activity and DNA damage in L1210 cells increased by UVA irradiation. In addition derivative III induced programmed cell death in leukemia cells through mitochondrial/caspase 9/caspase 3-dependent pathway.

NOX4-dependent Hydrogen peroxide promotes shear stress-induced SHP2 sulfenylation and eNOS activation

Laminar shear stress (LSS) triggers signals that ultimately result in atheroprotection and vasodilatation. Early responses are related to the activation of specific signaling cascades. We investigated the participation of redox-mediated modifications and in particular the role of hydrogen peroxide (H2O2) in the sulfenylation of redox-sensitive phosphatases. Exposure of vascular endothelial cells to short periods of LSS (12dyn/cm2) resulted in the generation of superoxide radical anion as detected by the formation of 2-hydroxyethidium by HPLC and its subsequent conversion to H2O2, which was corroborated by the increase in the fluorescence of the specific peroxide sensor HyPer. By using biotinylated dimedone we detected increased total protein sulfenylation in the bovine proteome, which was dependent on NADPH oxidase 4 (NOX4)-mediated generation of peroxide. Mass spectrometry analysis allowed us to identify the phosphatase SHP2 as a protein susceptible to sulfenylation under LSS. Given the dependence of FAK activity on SHP2 function, we explored the role of FAK under LSS conditions. FAK activation and subsequent endothelial NO synthase (eNOS) phosphorylation were promoted by LSS and both processes were dependent on NOX4, as demonstrated in lung endothelial cells isolated from NOX4-null mice. These results support the idea that LSS elicits redox-sensitive signal transduction responses involving NOX4-dependent generation of hydrogen peroxide, SHP2 sulfenylation, and ulterior FAK-mediated eNOS activation.

An ESR study on superoxide radical anion generation and its involvement in the photooxidative degradation of poly-3-hexylthiophene in chlorobenzene solution

The photooxidative degradation of poly-3-hexylthiophene (P3HT) in chlorobenzene solution containing dissolved oxygen was performed at room temperature. The generation of superoxide radical anion (O2−) during the photooxidation of P3HT was verified by ESR measurements using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin trap. The changes in mass spectra determined by MALDI-TOF MS showed that P3HT photodegradation was prevented in the presence of DMPO. Kinetics analysis shows that the prevention of P3HT photodegradation is due to the scavenging of O2− by DMPO. Therefore, the involvement of O2− in the initial step of P3HT photodegradation could be concluded.

Spectroscopic characterization, photoinduced processes and cytotoxic properties of substitutedN-ethyl selenadiazoloquinolones

7-R-9-ethyl-6,9-dihydro-6-oxo-[1,2,5]selenadiazolo[3,4-h]quinolines (R = H, COOC2H5, COOCH3, COOH and COCH3, E1h, E2h, E3h, E4h, E5h) and 6-ethyl-6,9-dihydro-9-oxo-[1,2,5]selenadiazolo[3,4-f]quinoline (E1f) were characterized by UV/vis, FT-IR and fluorescence spectroscopy. The electronic absorption spectra of the derivatives E1h, E2h, E3h and E5h in the aprotic solvents dimethylsulfoxide (DMSO) and acetonitrile (ACN) reveal low-energy absorption maxima with λmax > 400 > nm, shifted hypsochromically in water. In DMSO, N-ethyl selenadiazoloquinolones behave as strong fluorescent agents (λem ≥ 550 nm) with the exception of the carboxylic acid derivative E4h which shows only poor emission. Photoinduced reactions of N-ethyl selenadiazoloquinolones were investigated by means of electron paramagnetic resonance (EPR) spectroscopy. Photoexcitation of N-ethyl selenadiazoloquinolones in aerated DMSO with either 385 nm or 400 nm wavelengths, monitored by EPR spin trapping technique, results in the generation of superoxide radical anions; under an inert atmosphere, the generation of methyl radicals originating from the solvent predominates. Upon exposure at either 365 nm, 385 nm or 400 nm, aerated ACN solutions of selenadiazoloquinolones in the presence of sterically hindered amines produce nitroxide radicals via a reaction with photogenerated singlet oxygen. The 7-substituted derivatives of 9-ethyl-6,9-dihydro-6-oxo-[1,2,5]selenadiazolo[3,4-h]quinoline behave as photosensitizers activating molecular oxygen upon photoexcitation and possess the sufficient photochemical stability under the given experimental conditions. The cytotoxic effects of non-photoactivated and UVA photoactivated N-ethyl substituted selenadiazoloquinolones on cancer (human HeLa and murine L1210) and non-cancer (NIH-3T3) cell lines were monitored by the MTT test. The derivative E2h demonstrates the highest cytotoxic/photocytotoxic activity on the neoplastic cell lines. Copyright © 2013 John Wiley & Sons, Ltd.

A Highly Efficient and Selective Aerobic Cross‐Dehydrogenative‐Coupling Reaction Photocatalyzed by a Platinum(II) Terpyridyl Complex

Thanks to the superior redox potential of platinum(II) complex compared with that of Ru(bpy)3(2+) in the excited state, an efficient and selective visible-light-induced CDC reaction has been developed by using a catalytic amount (0.25 %) of 1. With the aid of FeSO4 (2 equiv), the corresponding amide could not be detected under visible-light irradiation (λ=450 nm), but the desired cross-coupling product was exclusively obtained under ambient air conditions. A spectroscopic study and product analysis revealed that the CDC reaction is initiated by photoinduced electron-transfer from N-phenyltetrahydroisoquinoline to the complex. An EPR (electron paramagnetic resonance) experiment provides direct evidence on the generation of superoxide radical anion (O2(-·)) rather than singlet oxygen ((1)O2) under irradiation of the reaction system, in contrast to that reported in the literature. Combined, the photoinduced electron-transfer and subsequent formation of superoxide radical anion (O2(-·)) results in a clean and facile transformation.

Aerobic Denitration of 2,4,6-Trinitrotoluene in the Presence of Phenazine Compounds and Reduced Pyridine Nucleotides

Phenazine-containing spent culture supernatants of Pseudomonas aeruginosa concentrated with a C18 solid-phase extraction cartridge initiate NAD(P)H-dependent denitration of 2,4,6-trinitrotoluene (TNT). In this study, TNT denitration was investigated under aerobic conditions using two phenazine secondary metabolites excreted by P. aeruginosa, pyocyanin (Py) and its precursor phenazine-1- carboxylic acid (PCA), and two chemically synthesized pyocyanin analogs, phenazine methosulfate (PMS+) and phenazine ethosulfate (PES+). The biomimetic Py/NAD(P)H/O2 system was characterized and found to extensively denitrate TNT in unbuffered aqueous solution with minor production of toxic amino aromatic derivatives. To a much lesser extent, TNT denitration was also observed with PMS+ and PES+ in the presence of NAD(P)H. No TNT denitration was detected with the biomimetic PCA/NAD(P)H/O2 system. Electron paramagnetic resonance (EPR) spectroscopy analysis of the biomimetic Py/NAD(P)H/O2 system revealed the generation of superoxide radical anions (O2 •−). In vitro TNT degradation experiments in the presence of specific inhibitors of reactive oxygen species suggest a nucleophilic attack of superoxide radical anion followed by TNT denitration through an as yet unknown mechanism. The results of this research confirm the high functional versatility of the redox-active metabolite pyocyanin and the susceptibility of aromatic compounds bearing electron withdrawing substituents, such as nitro groups, to superoxide-driven nucleophilic attack.

Spectroscopic characterization and photoinduced processes of 4-oxoquinoline derivatives

Derivatives of 1,4-dihydro-4-oxoquinoline substituted at 4-pyridone or/and benzene moieties were synthesized ( Q1– Q17), and characterized by UV/vis and FT-IR spectroscopy. In dimethylsulfoxide and acetonitrile solvents a significant influence of the substituent's character and position on the quinolone skeleton was observed on the absorption bands in the UVA region (315–400 nm). Electron-withdrawing substituents (nitro, cyano, acetyl or trifluoroacetyl) caused a red shift, resulting in the effective absorption of UVA light. Photoinduced generation of superoxide radical anion and singlet oxygen upon UVA irradiation was followed by EPR spectroscopy using in situ spin trapping technique; 4-hydroxy-2,2,6,6-piperidine (TMP) served for singlet oxygen ( 1O 2) detection. An efficient generation of superoxide radical anions and singlet oxygen was observed predominantly for nitro-substituted quinolones. The effect of quinolones on proliferation of HL-60 cells was monitored, and the values of IC 50 evidenced the highest inhibition in the presence of ethyl 1,4-dihydro-6-fluoro-8-nitro-4-oxoquinoline-3-carboxylate ( Q17) and ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate ( Q5).