Superoxide Radical Formation Research Articles

N-CQDs act as electronic warehouse in N-CQDs/CdS regulate adsorption energy to promote photocatalytic selective oxidation of aromatic alcohols

The benzaldehyde (BAD) produced by the benzyl alcohol (BA) oxidation method is comprehensively applied to food and pharmaceutical fields. However, the selectivity and conversion of photocatalytic selective oxidation of BA in aqueous solution are still far from expectation. Herein, N-CQDs/CdS composites were synthesized by the in-situ precipitation method. N-CQDs served as an "Electronic Warehouse" to boost the separation efficiency of the carrier. The electron transferred from CdS to N-CQDs made electron on the N-CQDs surface enrich, which was conducive to the formation of superoxide radicals (·O2-).·O2- and h+ could efficiently oxidize BA to BAD. In addition, according to density functional theory (DFT), the adsorption energies of BA and BAD on N-CQDs/CdS were distinctly greater than that of CdS. BAD tended to desorb from the 7.5 N-CQDs/CdS surface, and BA preferred to adsorb on the CdS surface. However, BAD was difficult to desorb from the CdS surface, resulting in the poisoning of CdS. 7.5 N-CQDs/CdS exhibited the BA conversion of 60.4% and BAD selectivity of 99%, which was 2.2 times higher than that of original CdS. This work was expected to provide a theoretical basis for improving photocatalyst carrier separation efficiency and alcohol selective oxidation performance.

Synergistic Effects of Redox Couples and Oxygen Vacancies Improve the Tetracycline Degradation Property of La2NiMnO6.

Improving the e- and h+ separation efficiency and promoting the production of more radicals is the key to improving the degradation efficiency of catalytic degradation of antibiotics. On the other hand, intermediate analysis of antibiotics in the dark adsorption and light irradiation process is very important to clarify the entire antibiotic degradation pathway. Here, the La2NiMnO6 (LNMO) catalyst was prepared by the sol-gel method and the calcination method. By changing the calcination temperature (800, 900, and 1000 °C), the LNMO-based catalysts were successfully formed, abbreviated as L-800, L-900, and L-1000. XPS measurements demonstrated the presence of Mn4+, Mn3+, Mn2+, and oxygen vacancies (OVs) in the LNMO-based catalysts. Analysis of PL, PC, EIS, and TR-PL demonstrated that L-900 had the highest separation efficiency and fastest carrier mobility. The LNMO-based catalysts were used to degrade tetracycline (TC). With the optimized catalyst L-900, the decomposition rate of TC reached 99.57% in 120 min. The entire TC degradation pathway was analyzed according to LC-MS measurements. Radical trap experiments and ESR technology revealed that the synergistic effect of Mn4+/Mn3+, Mn4+/Mn2+, and OVs not only effectively separated e- and h+ but also facilitated the formation of superoxide radicals (•O2-) to accelerate TC degradation. Radicals •OH, h+, and •O2- all contributed to TC deterioration in increasing order of importance. In addition, XPS measurements of the L-900 catalyst before and after use indicated that Mn4+/Mn3+, Mn4+/Mn2+, and OVs were not reactants but mediators of e- and h+. Finally, the mechanism of TC degradation with the LNMO-based catalysts was discussed. This work provided new material for TC degradation in the wastewater.

Rapid oxidation of 4-cholorphenol in the iron-based Metal–Organic frameworks (MOFs)/H2O2 system: The ignored two-steps interfacial single-electron transfer

Fe-based metal–organic frameworks (MOFs) are popular in activating oxidants e.g·H2O2 and persulfate (PS) for degrading recalcitrant organic substances, generally regarded with a simple interfacial efficient iron cycle. This study has revealed that a novel two-steps single-electron transfer mechanism would occur initially to activate the rapid degradation 4-chlorophenol (4-CP) in the MIL-88B(Fe)/H2O2 system (88B/H2O2 system). The degradation of 4-CP was acidic favorable (pH0 ≤ 6.0) and could be divided into two reaction stages, i.e., initial lag phase (0–10 min) and following rapid decay phase (10–50 min). In the first stage, H2O2 was slowly activated on the surface of 88B to form superoxide radical (O2•–), which would lead to the accumulation of the key intermediate hydroquinone (HQ) through reducing 4-CP. Afterwards, HQ could reductively dissolve iron ions which would lead to the subsequent efficient homogeneous Fenton reaction for the rapid oxidation of 4-CP by hydroxyl radical (•OH) in the following rapid decay phase. It was interesting to note that specific aromatic compounds, which would form reductive benzenediols intermediates by O2•–, could be efficiently degraded in the 88B/H2O2 system. The result of this study is expected to provide a new insight for understanding the catalytic oxidation process based on MOFs, and its application if possible.

BIOFLAVONOIDS AS AGENTS FOR CORRECTING NITRO-OXIDATIVE STRESS AND SALIVARY GLAND FUNCTIONS IN RATS EXPOSED TO ALCOHOL DURING MODELED LIPOPOLYSACCHARIDE-INDUCED SYSTEMIC INFLAMMATORY RESPONSE

The aim: To investigate the effects of bioflavonoids (curcumin, epigallocatechin-3-gallate and quercetin) on nitro-oxidative stress and the functions of submandibular SGs in rats under alcohol exposure during SIR. Materials and methods: The studies were conducted on 35 rats of the Wistar line weighing 205-220 g, divided into 5 groups of seven animals in each: the 1st group, control group I, included animals receiving isotonic sodium chloride solution intragastrically twice a day; the 2nd group, control group II, included rats exposed to alcohol (in a dose of 24 mg/kg intragastrically through gavage a twice a day) for last 2 weeks during lipopolysaccharide (LPS)-induced SIR; the rats of the 3rd, 4th and 5th groups exposed to alcohol during LPS-induced SIR, which also received bioflavonoids. The bioflavonoids (“Sigma-Aldrich, Inc.”, USA) were as following: curcumin (in a daily dose of 200 mg/kg), epigallocatechin-3-gallate (in a daily dose of 40 mg/kg), and quercetin (in a daily dose of 200 mg/kg), respectively. SIR was induced by intraperitoneal administration of Salmonella typhi LPS (during the first week a dose of 0.4 μg/kg of body weight was administered 3 times a week; during the next 7 weeks of the experiment rats received 0.4 μg/kg of body weight once a week. The formation of superoxide anion radical (О2 -), activity of NO-synthase – total (NOS), its constitutive and inducible isoforms (cNOS, iNOS), and concentration of peroxynitrites and S-nitrosothiols were evaluated spectrophotometrically. To assess the functional status of submandibular SGs in their homogenate we determined α-amylase activity (spectrophotometrically) and the aquaporin-5 concentration (by enzyme-linked immunosorbent assay). through gav-age with orogastric cannul. Results: When applying bioflavonoids under the conditions of alcohol administration during SIR, NADH-induced .О2 - production decreased and yielded to the result in the control group II by 36.8% under administering curcumin, by 34.5% under administering epigallocatechin-3-gallate, and by 41.3% under administering quercetin. The total NOS activity in SGs tissues was inferior by 42.8% to the relevant data in the control group II (under curcumin administration), by 33.7% (under epigallocatechin-3-gallate administration) and by 46.6% (under quercetin administration); and the iNOS activity decreased by 47.0, 38.3 and 52.0%, respectively. Under the administration of bioflavonoids peroxynitrites concentration in the submandibular SGs tissues was inferior to the control group II by 35.6% (under curcumin administration), by 37.4% (under epigallocatechin-3-gallate administration), and by 39.3% (under quercetin administration); the content of S-nitrosothiols was lower by 34.5, 31.1 and 35.3%, respectively. The administration of bioflavonoids led to the changes in α-amylase activity in the submandibular SGs tissues: its values exceeded the relevant data in the control group II by 40.4% (under curcumin administration), by 38.2% (under epigallocatechin-3-gallate administration), and by 34.1% (under quercetin administration); under those conditions aquaporin-5 concentration grew in 2.66, 2.61 and 2.55 times, respectively. Conclusions: The use of bioflavonoids (curcumin, epigallocatechin-3-gallate, and quercetin) under the combined administration of 40% ethanol solution and LPS considerably limits the development of nitro-oxidative stress in the tissues of the submandibular SGs. The administration of the bioflavonoids increases the level of cNOS coupling, and improves the functional status of the submandibular SGs under the combined administration of alcohol and LPS enhancing the activity of α-amylase and concentration of aquaporin-5.

Preparation of spherical silver and tin dioxide nanocomposites with the high photocatalytic performance by laser-induced deposition in liquid medium

Nanospheres were widely utilized as atomic clusters for the self-assembly and modification of functional nanomaterials. In this study, by using the laser-induced deposition in a liquid medium, the spherical Silver (Ag) and Tin dioxide (SnO2) nanocomposites were successfully prepared. The characteristics of the product, such as morphologies, components, structures and optical properties were obtained by STEM, EDS, ICP-OES, XPS, XRD, UV-Vis and PL instruments, respectively. During the laser-induced liquid deposition, the pristine Ag nanoparticles were melted to be spheres with the average particle size decreased and welded with the SnO2 nanomaterials under the laser heating and liquid quenching. The photocatalytic performance of the synthesized nanocomposites was evaluated by the degradation of methylene blue aqueous solution as a model organic pollutant. The results indicated that, for the spherical Ag and SnO2 nanocomposites, the reaction rate constant was enhanced 3.1 times than the pure-SnO2 nanomaterials and 13.3 times than the pure-Ag nanoparticles, respectively, with a high value of 0.08 min−1. Where 99.1% methylene blue can be removed in 60 min by using Ag and SnO2 nanocomposites as catalysts under ultraviolet lamp irradiation. This performance performed better than the previous reports in similar physical conditions. The possible enhanced mechanism was analyzed, where the spherical Ag anchoring on the surface of SnO2 induced the perturbation of SnO2 bandgap, the free electrons transfer of spherical Ag promoted the separation of photogenerated electron-hole pairs, increased the formation of superoxide and hydroxyl radicals for methylene blue effectively removal via a redox reaction.

Plasma-catalytic NO x production in a three-level coupled rotating electrodes air plasma combined with nano-sized TiO2

A novel three-level coupled rotating electrodes air plasma with nano-sized TiO2 photocatalysts is developed for plasma-catalytic NO x production. The effects of plasma catalysis on NO x production with different air flow rates, different N2 fractions and different humidity levels are evaluated. Final results show the exceptional synergistic effect between TiO2 and three-level coupled rotating electrodes air plasma significantly increases the NO x concentration by 68.32% (from 4952 to 8335 ppm) and reduces the energy cost by 40.55% (from 2.91 to 1.73 MJ mol−1) at an air flow rate of 12 l min−1 and relative humidity level of 12%, which beats the ideal thermodynamic energy limit ∼2.5 MJ mol−1 for the thermal gas-phase process. A possible mechanism for enhanced NO x production with TiO2 is discussed: Highly energetic electrons in plasma contribute to the formations of the electron–hole pairs and oxygen vacancy (Vo) on the TiO2 catalyst surface, which may facilitate the dissociative adsorption of O2 molecules to form superoxide radical groups (like O2 −), and H2O molecules to form surface hydroxyl groups (like OH·), and thus, improving energy efficiency.

Nitrogen defects/boron dopants engineered tubular carbon nitride for efficient tetracycline hydrochloride photodegradation and hydrogen evolution

Polymeric carbon nitride (g-C3N4) exhibits only mediocre catalytic activity in photocatalytic environmental remediation and energy conversion because of its limited light absorption and sluggish charge transfer. Herein, we assembled novel, tubular carbon nitride (D-TCN450) with nitrogen defects/boron dopants via a self-supramolecular reaction and NaBH4 thermal reduction approach. Advanced characterization results suggested that introducing the nitrogen defects/boron dopants can effectively promote light trapping, charge separation, and valance-band downshift. Density functional theory and electron spin resonance results further proved that the fusion of cyano groups (nitrogen defects) into the framework of D-TCN450 can facilitate oxygen adsorption to form superoxide radicals. As a result, D-TCN450 exhibited dramatically improved photocatalytic hydrogen evolution and photodegradation of tetracycline hydrochloride at a 4- and 9-fold enhancement compared to pristine g-C3N4, respectively. This integrated engineering strategy might provide a unique paradigm for the rational design of novel photocatalysts for sustainable remediation and energy innovation.

Oxygen vacancy/Ti3+ engineered TiO2 nanotube arrays prepared by in-situ exfoliation with H2 bubbles: A visible-light-driven self-supporting photocatalyst for detoxfication of chloraphenicol

Oxygen vacancy/Ti3+ engineered TiO2 nanotube arrays were prepared through electrochemical strategy at high potential (−6 V). The electrons surging from DC power initiate the valance decline of Ti4+, and countless H2 bubbles released from TiO2 surface lead to the in-situ exfoliation of some TiO2 tiny debris, generating point defects containing Ti3+ inside the TiO2 and oxygen vacancy (OV) embedded on TiO2. The generated Ti3+/ OV help TiO2 to increase the harvest toward visible light and serve as active sites for activating molecular oxygen to form superoxide radical (·O2-). Besides, as improved separation of electron-hole pairs endowed by the defects, the yield of hydroxyl radicals (·OH) is enhanced compared with the pristine TiO2. Chloramphenicol (CAP, an antibiotic) molecules can be efficiently degraded with the reduced TiO2 under the visible light with its degradation and evolution pathway expounded in detail. Fukui index is employed to anticipate the probable sites that are subjected to oxidation by·OH and the MS spectra evidence that the·OH governs the decomposition routes of CAP molecules. ECOSAR simulation evaluates the toxicity of CAP and the intermediates, demonstrating that the final products from the photocatalysis do not post any hazardous risk on ecosystem.

Construction of 2D/2D Bi2WO6/BN heterojunction for effective improvement on photocatalytic degradation of tetracycline

Bi2WO6/BN heterojunction photocatalyst with high catalytic activity has been successfully constructed by the solvothermal synthesis. It is worth noting that the formation of superoxide radicals (·O2-) and hydroxyl free radicals (·OH) benefit from the formation of heterojunctions, which effectively degrade pollutants. The photocatalytic activities of the optimal sample for tetracycline (TC) and ofloxacin (OFL) degradation efficiency reached almost 99.1% and 94.66% under visible-light irradiation, respectively. It is mainly because the addition of BN not only provided more active sites for the catalyst but also improved the separation efficiency of electron-hole pairs. It can be found that h+ and·O2- played a major role in the degradation process through the active species quenching experiment. Furthermore, the possible photocatalytic degradation pathways of TC were revealed by analyzing intermediates and a reasonable photocatalytic mechanism was proposed. Moreover, Bi2WO6/BN heterojunctions were endowed with excellent recycling and stability. Therefore, this research illustrated that two dimensions/two dimensions (2D/2D) Bi2WO6/BN heterojunction may hold a great prospect for the degradation of antibiotics in wastewater.

The effect of Luteolin on DNA damage mediated by a copper catalyzed Fenton reaction

Luteolin has been reviewed as a flavonoid possessing potential cardioprotective, anti-inflammatory, anti-cancer activities. Having multiple biological effects, luteolin may act as either an antioxidant or a pro-oxidant. In this work, the protective role of copper(II)-chelation by luteolin on DNA damage via the Cu-Fenton reaction was studied. EPR and UV–vis spectroscopic data demonstrated that the luteolin, lacking 3-OH group, chelates to Cu(II) via the 5-OH and 4-CO groups, respectively. EPR spin trapping experiments using DMPO spin trap confirmed that the coordination of luteolin to Cu(II) significantly suppressed formation of hydroxyl and superoxide radicals (by 80%) in a Cu-Fenton system. Absorption titrations showed that the chelation of Cu(II) by luteolin slightly increased the mild intercalation strength of its interaction with DNA, as compared with free luteolin. Comparison with kaempferol and quercetin revealed, that the strength of the interaction between the free flavonoids/Cu-flavonoid complexes with DNA is only mildly affected by the presence/absence of 3-OH group. Due to the differences in the sensitivities of absorption titrations and viscometry, the latter confirmed weaker DNA intercalating efficiency of Cu-luteolin complex than does free luteolin. A dose dependent protective effect of luteolin against ROS-induced DNA damage was observed using gel electrophoresis. This effect was more pronounced compared to quercetin and kaempferol. In conclusion, the administration of luteolin to patients suffering from oxidative stress-related diseases with disturbed Cu-metabolism such as Alzheimer's diseases (antioxidant effect) and certain cancers (prooxidant effect) may have several health benefits.

Pt-Fe3O4, Pd-Fe3O4, and Au-Fe3O4 Nanoheterodimers and Their Efficacy as Radiosensitizers in Cancer Therapy.

The X-radiation enhancing effect of caffeic acid-functionalized Au-Fe3O4, Pt-Fe3O4, and Pd-Fe3O4 nanoheterodimers (NHDs) on 2D and 3D breast tumor (MCF-7) and healthy breast epithelial (MCF-10A) cells was comprehensively examined by performing cell viability, reactive oxygen species (ROS) detection, enzyme activity, and clonogenic assays. Intracellular NHDs were observed to cause DNA fragmentation and to enhance superoxide and hydroxyl radical formation in MCF-7 cells when exposed to a single dose of 1 Gy. MCF-7-derived multicellular tumor spheroids (MCF-7 MCTS) and MCF-10A-derived multicellular spheroids (MCF-10A MCS) were incubated with the NHDs and irradiated with five daily doses of 2 Gy. The Au-Fe3O4 and Pt-Fe3O4 NHD-loaded MCF-7 MCTS significantly decreased in volume after being exposed to fractionated irradiation, whereas intracellular Au-Fe3O4 and Pt-Fe3O4 NHDs promoted the growth of the irradiated MCF-10A MCS. Moreover, Au-Fe3O4 and Pt-Fe3O4 NHDs were shown to impede ROS formation and inhibit DNA strand breakage in the noncancerous MCF-10A cells. On the other hand, the Pd-Fe3O4 NHDs boosted X-radiation-induced damage of MCF-10 A cells, which was ascribed to impairment of the ROS scavenging enzyme activities. In summary, caffeic acid-functionalized Au-Fe3O4 and Pt-Fe3O4 NHDs performed as excellent X-radiation enhancing agents in breast tumor cells, while they protect healthy breast epithelial cells against X-radiation.

Nanoscale Covalent Organic Frameworks with Donor-Acceptor Structures as Highly Efficient Light-Responsive Oxidase-like Mimics for Colorimetric Detection of Glutathione.

Although organic artificial enzymes have been reported as biomimetic oxidation catalysts and are widely used for colorimetric biosensors, developing organic artificial enzymes with high enzymatic activity is still a challenge. Two-dimensional (2D) covalent organic frameworks (COFs) have shown superior potential in biocatalysts because of their periodic π-π arrays, tunable pore size and structure, large surface area, and thermal stability. The interconnection of electron acceptor and donor building blocks in the 2D conjugated COF skeleton can lead to narrower band gaps and efficient charge separation and transportation and thus is helpful to improve catalytic activity. Herein, a donor-acceptor 2D COF was synthesized using tetrakis(4-aminophenyl)pyrene (Py) as an electron donor and thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT) as an electron acceptor. Under visible light irradiation, the donor-acceptor 2D COF exhibited superior enzymatic catalytic activity, which could catalyze the oxidation of chromogenic substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) by the formation of superoxide radicals and holes. Based on the above property, the photoactivated donor-acceptor 2D COF with enzyme-like catalytic properties was designed as a robust colorimetric probe for cheap, highly sensitive, and rapid colorimetric detection of glutathione (GSH); the corresponding linear range of GSH was 0.4-60 μM, and the limit of detection was 0.225 μM. This study not only presents the construction of COF-based light-activated nanozymes for environmentally friendly colorimetric detection of GSH but also provides a smart strategy for improving nanozyme activity.

Assembly of Cobalt Layered Double Hydroxide on Cuprous Phosphide Nanowire with Strong Built-In Potential for Accelerated Overall Water Splitting.

Heterostructure plays an important role in boosting the overall water splitting (OWS) performance of nonprecious metal electrocatalysts. However, rational design and synthesis of semiconductor heterojunctions especially for Cu-based ones as efficient bifunctional electrocatalysts toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) still face challenges, and the in-depth study of catalytic mechanisms is urgently needed. Herein, n-type cobalt layered double hydroxide nanosheets are assembled on p-type cuprous phosphide nanowire to form p-n junction. This heterostructure with a strong built-in potential (EBI ) of 1.78V provides enlarged electrochemical active surface area, enhanced active site, facilitated electron separation and transfer, and accelerated formation of superoxide radical. As expected, the heterogeneous electrocatalyst exhibits significantly improved activities for OWS, achieving an overpotential of 111mV for HER and 221mV for OER and an applied voltage of 1.575V for OWS at 10mAcm-2 in 1 m KOH. Moreover, the overpotentials are further decreased under visible light irradiation. This work represents a new insight into Cu-based catalysts toward OWS and an approach based on EBI to design semiconductor heterostructure promising for renewable energy applications.

Response of platelets to silver nanoparticles designed with different surface functionalization

Despite increasing use of silver nanoparticles (AgNPs) in different medicinal products, knowledge about their effects on hemostasis and platelets functionality is still scarce. Published scientific reports provide neither data on oxidative stress response of platelets to AgNPs nor information about the effects of AgNPs physicochemical properties on functionality and activation of platelets. This study aimed to explore the role of AgNPs surface functionalization on cell viability, particle uptake, oxidative stress response, and activation of platelets. Small sized, spherical AgNPs were surface functionalized by negatively charged sodium bis(2-ethylhexyl) sulphosuccinate (AOT), neutral polymer polyvinylpyrrolidone (PVP), positively charged polymer poly-l-lysine (PLL) and bovine serum albumin (BSA). Platelet viability, activation and particle uptake were evaluated by flow cytometry. Oxidative stress response was evaluated by measuring the levels of intracellular glutathione (GSH), peroxy and superoxide radicals using assays based on fluorescence dies. Cytotoxicity and uptake of AgNPs to platelets were found to be dose-dependent in a following order PLL-AgNP >> > BSA-AgNP > AOT-AgNP > PVP-AgNP. Particle internalization was further confirmed by transmission electron microscopy. Treatment of platelets with AgNPs induced superoxide radical formation, depletion of GSH and hyperpolarization of the mitochondrial membrane. Small, but statistically significant increase of P-selectin expression in cells treated with all AgNPs compared to non-treated controls evidenced AgNPs-induced activation of platelets. Increased PAC-1 expression was found only in platelets treated with PLL-AgNPs. Obtained results demonstrate that different surface decoration of AgNPs determines their biological effects on platelets highlighting the importance of careful design of AgNPs-based medicinal products regarding their biocompatibility and functionality.

Nox2-derived superoxide radical is crucial to control acute Trypanosoma cruzi infection

Trypanosoma cruzi is a flagellated protozoan that undergoes a complex life cycle between hematophagous insects and mammals. In humans, this parasite causes Chagas disease, which in thirty percent of those infected, would result in serious chronic pathologies and even death. Macrophages participate in the first stages of infection, mounting a cytotoxic response which promotes massive oxidative damage to the parasite. On the other hand, T. cruzi is equipped with a robust antioxidant system to repeal the oxidative attack from macrophages. This work was conceived to explicitly assess the role of mammalian cell-derived superoxide radical in a murine model of acute infection by T. cruzi. Macrophages derived from Nox2-deficient (gp91phox-/-) mice produced marginal amounts of superoxide radical and were more susceptible to parasite infection than those derived from wild type (wt) animals. Also, the lack of superoxide radical led to an impairment of parasite differentiation inside gp91phox-/- macrophages. Biochemical or genetic reconstitution of intraphagosomal superoxide radical formation in gp91phox-/- macrophages reverted the lack of control of infection. Along the same line, gp91phox-/- infected mice died shortly after infection. In spite of the higher lethality, parasitemia did not differ between gp91phox-/- and wt animals, recapitulating an observation that has led to conflicting interpretations about the importance of the mammalian oxidative response against T. cruzi. Importantly, gp91phox-/- mice presented higher and disseminated tissue parasitism, as evaluated by both qPCR- and bioimaging-based methodologies. Thus, this work supports that Nox2-derived superoxide radical plays a crucial role to control T. cruzi infection in the early phase of a murine model of Chagas disease.

The effect of TiO2 coatings on the formation of ozone and nitrogen oxides in non-thermal atmospheric pressure plasma

The use of photocatalytic materials in plasma systems has the potential to enhance the selectivity and yield of desired products. However, the surface interaction between the photocatalyst and plasma is a complex process that is not well understood. This work presents a comprehensive study of the effects of combining titanium dioxide (TiO2) photocatalysts with non-thermal atmospheric pressure nitrogen-oxygen plasmas, which increases the production of ozone and dinitrogen pentoxide (N2O5) while limiting the formation of harmful nitrogen dioxide (NO2) and nitrous oxide (N2O) by products. TiO2 coatings were deposited by magnetron sputtering onto barium titanate (BaTiO3) particulates for use within a packed bed dielectric barrier discharge reactor (DBD). The presence of titanium dioxide can affect the plasma chemistry in the DBD by acting as a sink for atomic oxygen, through photocatalytic formation of superoxide anion radical (O2-), and alteration of the dielectric constant of the BaTiO3 particulates. This work explains the complex interaction of these effects on oxygen and nitrogen plasma chemistry. The effect of the photocatalyst surface properties, gas composition and residence time on the reaction pathways for the formation of ozone and nitrogen oxides (NxOy) were investigated. The photocatalytic activity of titanium dioxide was improved by annealing the coated surface, and was subsequently found to enable the formation of ozone, increase the formation of N2O5 while significantly decreasing the formation of harmful NO2 and N2O with a residence time of 0.011 s

Amphiphilic tricationic Zn(II)phthalocyanine provides effective photodynamic action to eradicate broad-spectrum microorganisms

A novel tricationic Zn(II)phthalocyanine derivative, (NCH3)3ZnPc3+, was synthesized by ring expansion reaction of boron(III) [2,9(10),16(17)-trinitrosubphthalocyaninato]chloride. First, the reaction of this subphthalocyanine with 2,3-naphthalenedicarbonitrile and Zn(CH3COO)2 catalyzed by 8-diazabicyclo[5.4.0]undec-7-ene was used to obtain the A3B-type nitrophthalocyanine. After reduction of nitro groups with Na2S and exhaustive methylation of amino groups, (NCH3)3ZnPc3+ was formed in good yields. In addition, the tetracationic analog (NCH3)4ZnPc4+ was synthesized to compare their properties. The absorption and fluorescence spectra showed the Q-bands and the red emission, respectively, which are characteristic of the Zn(II)phthalocyanine derivatives in N,N-dimethylformamide. Furthermore, photodynamic activity sensitized by these compounds was studied in the presence of different molecular probes to sense the formation of reactive oxygen species. (NCH3)3ZnPc3+ efficiently produced singlet molecular oxygen and also it sensitized the formation of superoxide anion radical in the presence of NADH, while the photodynamic activity of (NCH3)4ZnPc4+ was very poor, possibly due to the partial formation of aggregates. Furthermore, the decomposition of L-tryptophan induced by (NCH3)3ZnPc3+ was mainly mediated by a type II mechanism. Antimicrobial photodynamic inactivation sensitized by these phthalocyanines was evaluated in Staphylococcus aureus, Escherichia coli, and Candida albicans, as representative microbial cells. In cell suspensions, (NCH3)3ZnPc3+ was rapidly bound to microbial cells, showing bioimages with red fluorescence emission. After 5min of irradiation with visible light, (NCH3)3ZnPc3+ was able to completely eliminate S. aureus, E. coli and C. albicans, using 1.0, 2.5 and 5.0μM phthalocyanine, respectively. In contrast, a low photoinactivation activity was found with (NCH3)4ZnPc4+ as a photosensitizer. Therefore, the amphiphilic tricationic phthalocyanine (NCH3)3ZnPc3+ is a promising photosensitizing structure for application as a broad-spectrum antimicrobial phototherapeutic agent.

Enhanced Photocatalytic Degradation of Perfluorooctanoic Acid by Mesoporous Sb2O3/TiO2 Heterojunctions.

Perfluorooctanoic acid (PFOA), a typical perfluorinated carboxylic acid, is an emerging type of permanent organic pollutants that are regulated by the Stockholm Convention. The degradation of PFOA, however, is quite challenging largely due to the ultra-high stability of C-F bonds. Compared with other techniques, photocatalytic degradation offers the potential advantages of simple operation under mild conditions as well as exceptional decomposition and defluorination efficiency. Titanium dioxide (TiO2) is one of the most frequently used photocatalysts, but so far, the pristine nanosized TiO2 (e.g., the commercial P25) has been considered inefficient for PFOA degradation, since the photo-generated hydroxyl radicals from TiO2 are not able to directly attack C-F bonds. Mesoporous Sb2O3/TiO2 heterojunctions were therefore rationally designed in this work, of which the confined Sb2O3 nanoparticles in mesoporous TiO2 framework could not only tune the band structure and also increase the number of active sites for PFOA degradation. It was found that, after loading Sb2O3, the absorption of UV light was enhanced, indicating a higher efficiency of light utilization; while the band gap was reduced, which accelerated the separation of photo-generated charge carriers; and most importantly, the valence band edge of the Sb2O3/TiO2 heterojunction was significantly lifted so as to prevent the occurrence of hydroxyl radical pathway. Under the optimal ratio of Sb2O3–TiO2, the resulting catalysts managed to remove 81.7% PFOA in 2 h, with a degradation kinetics 4.2 times faster than the commercial P25. Scavenger tests and electron spin resonance spectra further revealed that such improvement was mainly attributed to the formation of superoxide radicals and photo-generated holes, in which the former drove the decarboxylation from C7F15COOH–C7F15 •, and the latter promoted the direct electron transfer for the conversion of C7F15COO−–C7F15COO•. The Sb2O3/TiO2 photocatalysts were highly recyclable, with nearly 90% of the initial activity being retained after five consecutive cycles, guaranteeing the feasibility of long-term operation.

LaNiO3/g-C3N4 nanocomposite: An efficient Z-scheme photocatalyst for wastewater treatment using direct sunlight

The major findings in this report are (i) development of nanocomposite photocatalyst working through Z-scheme charge transfer pathway across the heterojunction, (ii) utilization of direct sunlight as the photo-source, and (iii) prospect of ligand-hole in photocatalysis through enhanced sub-band gap absorption. The photocatalysts, namely LaNiO3, g-C3N4 and LaNiO3/g-C3N4 nanocomposites were synthesized via facile route and were characterized for their structure, morphology, microstructure, texture, elemental mapping and surface oxidation states by using several physicochemical techniques. The photocatalytic performance of the nanocomposite was tested through the degradation of hazardous azo dye pollutants, namely reactive black 5 and methylene blue as well as the colorless antibiotic-pollutant tetracycline hydrochloride in aqueous solution in presence of natural sunlight with excellent recycling activity. The 10%LaNiO3/g-C3N4 nanocomposite sample shows the best catalytic activity, degrading respectively 94%, 98.6% and 88.1% of reactive black 5, methylene blue and tetracycline hydrochloride in 60, 180 and 120 min. The photocatalytic activity of the nanocomposite phase is several times superior to that of the pure phases. The improvements of photocatalytic activity of g-C3N4 in the nanocomposite have been rationalized through the construction of direct Z-scheme heterojunction and suppression of electron–hole pair recombination efficiency. The enhanced photo-absorption of the nanocomposite can possibly be related to sub-bandgap absorption, which is associated to the midgap state originating from ligand-hole formation or defects in the structure. The photodegradation process is mediated through the formation of super oxide radical (˙O2¯) and hole (h+) as the main responsible species.

Association of NQO2 With UDP-Glucuronosyltransferases Reduces Menadione Toxicity in Neuroblastoma Cells.

The balance between detoxification and toxicity is linked to enzymes of the drug metabolism Phase I (cytochrome P450 or oxidoreductases) and phase II conjugating enzymes (such as the UGTs). After the reduction of quinones, the product of the reaction, the quinols—if not conjugated—re-oxidizes spontaneously to form the substrate quinone with the concomitant production of the toxic reactive oxygen species (ROS). Herein, we documented the modulation of the toxicity of the quinone menadione on a genetically modified neuroblastoma model cell line that expresses both the quinone oxidoreductase 2 (NQO2, E.C. 1.10.5.1) alone or together with the conjugation enzyme UDP-glucuronosyltransferase (UGT1A6, E.C. 2.4.1.17), one of the two UGT isoenzymes capable to conjugate menadione. As previously shown, NQO2 enzymatic activity is concomitant to massive ROS production, as previously shown. The quantification of ROS produced by the menadione metabolism was probed by electron-paramagnetic resonance (EPR) on cell homogenates, while the production of superoxide was measured by liquid chromatography coupled to mass spectrometry (LC-MS) on intact cells. In addition, the dysregulation of the redox homeostasis upon the cell exposure to menadione was studied by fluorescence measurements. Both EPR and LCMS studies confirmed a significant increase in the ROS production in the NQO2 overexpressing cells due to the fast reduction of quinone into quinol that can re-oxidize to form superoxide radicals. However, the effect of NQO2 inhibition was drastically different between cells overexpressing only NQO2 vs. both NQO2 and UGT. Whereas NQO2 inhibition decreases the amount of superoxide in the first case by decreasing the amount of quinol formed, it increased the toxicity of menadione in the cells co-expressing both enzymes. Moreover, for the cells co-expressing QR2 and UGT the homeostasis dysregulation was lower in presence of menadione than for the its counterpart expressing only QR2. Those results confirmed that the cooperation of the two enzymes plays a fundamental role during the cells’ detoxification process. The fluorescence measurements of the variation of redox homeostasis of each cell line and the detection of a glucuronide form of menadiol in the cells co-expressing NQO2 and UGT1A6 enzymes further confirmed our findings.