Chlorine Activation Research Articles

Influence of NH4Cl treatment on physical properties of CdTe thin films for absorber layer applications

Abstract The physical properties of electron beam evaporated and chlorine-passivated CdTe thin films are investigated and the influence of NH4Cl treatment on these properties is studied. X-ray diffraction, UV–Vis spectrophotometry, energy-dispersive spectroscopy, atomic force microscopy, and a source meter were used to investigate the physical properties, which were optimized by varying the temperature of the treatment after NH4Cl activation. Structural analysis reveals that the crystallinity is increased at lower annealing temperature while a partial phase transition and oxidation are observed at higher annealing temperature. The absorbance is high in the visible region, and a red shift is observed at higher wavelength, while the direct bandgap is tuned by chlorine activation. The deposition of thin films and chlorine treatment were confirmed by elemental analysis. Surface topographical study reveals that the average roughness is increased with an annealing temperature up to 320 °C, while the I-V characteristics indicated ohmic nature of the contacts. The optimized results show that the NH4Cl-treated CdTe films annealed at 320 °C may be applicable as an absorber layer in solar cells.

On the discrepancy of HCl processing in the core of the wintertime polar vortices

Abstract. More than 3 decades after the discovery of the ozone hole, the processes involved in its formation are believed to be understood in great detail. Current state-of-the-art models can reproduce the observed chemical composition in the springtime polar stratosphere, especially regarding the quantification of halogen-catalysed ozone loss. However, we report here on a discrepancy between simulations and observations during the less-well-studied period of the onset of chlorine activation. During this period, which in the Antarctic is between May and July, model simulations significantly overestimate HCl, one of the key chemical species, inside the polar vortex during polar night. This HCl discrepancy is also observed in the Arctic. The discrepancy exists in different models to varying extents; here, we discuss three independent ones, the Chemical Lagrangian Model of the Stratosphere (CLaMS) as well as the Eulerian models SD-WACCM (the specified dynamics version of the Whole Atmosphere Community Climate Model) and TOMCAT/SLIMCAT. The HCl discrepancy points to some unknown process in the formulation of stratospheric chemistry that is currently not represented in the models. We characterise the HCl discrepancy in space and time for the Lagrangian chemistry–transport model CLaMS, in which HCl in the polar vortex core stays about constant from June to August in the Antarctic, while the observations indicate a continuous HCl decrease over this period. The somewhat smaller discrepancies in the Eulerian models SD-WACCM and TOMCAT/SLIMCAT are also presented. Numerical diffusion in the transport scheme of the Eulerian models is identified to be a likely cause for the inter-model differences. Although the missing process has not yet been identified, we investigate different hypotheses on the basis of the characteristics of the discrepancy. An underestimated HCl uptake into the polar stratospheric cloud (PSC) particles that consist mainly of H2O and HNO3 cannot explain it due to the temperature correlation of the discrepancy. Also, a direct photolysis of particulate HNO3 does not resolve the discrepancy since it would also cause changes in chlorine chemistry in late winter which are not observed. The ionisation caused by galactic cosmic rays provides an additional NOx and HOx source that can explain only about 20 % of the discrepancy. However, the model simulations show that a hypothetical decomposition of particulate HNO3 by some other process not dependent on the solar elevation, e.g. involving galactic cosmic rays, may be a possible mechanism to resolve the HCl discrepancy. Since the discrepancy reported here occurs during the beginning of the chlorine activation period, where the ozone loss rates are small, there is only a minor impact of about 2 % on the overall ozone column loss over the course of Antarctic winter and spring.

Efficacy of Chlorine, Chlorine Dioxide, and Peroxyacetic Acid in Reducing Salmonella Contamination in Wash Water and on Mangoes Under Simulated Mango Packinghouse Washing Operations

Salmonellosis associated with consumption of mangoes have been traced back to the use of contaminated wash water. This highlights the critical role of wash water disinfection in mango processing, affecting its quality, and safety. Moreover, steps unique to the post-harvest handling of mangoes also create a conducive environment for internalization of pathogens into the fruit pulp. Currently, no effective treatment exists to eliminate internalized pathogens from mangoes. Therefore, it is critical to prevent contamination on the fruit to avert pathogen internalization. So the present study evaluated the efficacy of chlorine (200 ppm), peroxyacetic acid (80 ppm) and chlorine dioxide (5 ppm) for reducing Salmonella populations on mangoes and in wash water under simulated mango packing house conditions. Nalidixic-acid resistant isolates of Salmonella Montevideo, S. Newport, S. Baildon, S. Braenderup and S. Poona were used in this study. Disinfectants were added to inoculated wash water (ca.7 log CFU/ml) and mangoes (var. Atualfo and Tommy Atkins) were washed under simulated dump tank wash (24°C for 2 min), hot water treatment (46°C for 75 and 110 min) and hydrocooling conditions (21°C for 30 min). Wash water and mangoes were collected at different times for microbiological analysis. Additionally, residual disinfectant concentration was monitored throughout the study. All the three disinfectant tested were effective in significantly reducing Salmonella populations in wash water and on mangoes during dump tank wash, hot water treatment and hydrocooling (p≤0.05). Specifically, no Salmonella was detected from samples treated with 200 ppm chlorine and 80 ppm PAA. On the other hand, Salmonella was consistently recovered from mango and water samples treated with chlorine dioxide (5 ppm). This reduced antimicrobial efficacy can be attributed to the sharp decline in residual chlorine dioxide concentrations in wash water. Further, reductions in residual chlorine and PAA concentrations were also observed over time. Therefore, to ensure the sustained antimicrobial activity of chlorine and PAA, it is critical to regularly monitor and replenish the disinfectant in wash water. However, given the laboratory scale of these experiments, further validation of these results on a commercial scale are warranted.

Elevated Humidity in the Stratosphere as a Gain Factor of Ozone Depletion in the Arctic According to Aura MLS Observations

The analysis of Aura MLS data showed that the temperature in the Arctic stratosphere was much lower than normal throughout the period from January to March 2011 in the altitude range 20–35 km. That led to a considerable spread of polar stratospheric clouds (PSCs), which were formed most intensely in periods and at altitudes of minimal temperatures (maximal temperature drop below PSC formation threshold). The main ozone losses were observed in March. They were due to a photochemical release of chlorine that avoided deactivation in view of the nitrogen deficit caused by denitrification in the course of frequent dehydration events indicated by oscillations of the altitude of maximal humidity distortion. Elevated humidity in the stratosphere had raised the threshold temperature of formation of PSCs that persisted until late March; this promoted the chlorine activation and, thereby, delayed the chlorine deactivation, resulting in an even higher level of overall ozone losses during March 2011.

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null cycles

Abstract. The Antarctic ozone hole arises from ozone destruction driven by elevated levels of ozone destroying (active) chlorine in Antarctic spring. These elevated levels of active chlorine have to be formed first and then maintained throughout the period of ozone destruction. It is a matter of debate how this maintenance of active chlorine is brought about in Antarctic spring, when the rate of formation of HCl (considered to be the main chlorine deactivation mechanism in Antarctica) is extremely high. Here we show that in the heart of the ozone hole (16–18 km or 85–55 hPa, in the core of the vortex), high levels of active chlorine are maintained by effective chemical cycles (referred to as HCl null cycles hereafter). In these cycles, the formation of HCl is balanced by immediate reactivation, i.e. by immediate reformation of active chlorine. Under these conditions, polar stratospheric clouds sequester HNO3 and thereby cause NO2 concentrations to be low. These HCl null cycles allow active chlorine levels to be maintained in the Antarctic lower stratosphere and thus rapid ozone destruction to occur. For the observed almost complete activation of stratospheric chlorine in the lower stratosphere, the heterogeneous reaction HCl + HOCl is essential; the production of HOCl occurs via HO2 + ClO, with the HO2 resulting from CH2O photolysis. These results are important for assessing the impact of changes of the future stratospheric composition on the recovery of the ozone hole. Our simulations indicate that, in the lower stratosphere, future increased methane concentrations will not lead to enhanced chlorine deactivation (through the reaction CH4 + Cl ⟶ HCl + CH3) and that extreme ozone destruction to levels below ≈ 0.1 ppm will occur until mid-century.

Leptospira interrogans outer membrane protein LipL21 is a potent inhibitor of neutrophil myeloperoxidase

ABSTRACT Leptospirosis is a widespread zoonotic and neglected infectious disease of human and veterinary concern that is caused by pathogenic Leptospira species. After entrance in the host, pathogenic leptospires evade the host natural defense mechanisms in order to propagate and disseminate to multiple organs. Myeloperoxidase is an enzyme stored in neutrophils azurophilic granules, and is released upon neutrophil activation to produce mainly hypochlorous acid, a strong oxidant and potent antimicrobial agent. In the present investigation, we studied the modulation of myeloperoxidase activity by L. interrogans serovar Copenhageni. We show that leptospires and their culture supernatants are able to inhibit both peroxidase and chlorination activities of myeloperoxidase, without interfering with neutrophil degranulation. By leptospiral outer membrane protein extraction and fractionation, we identified the proteins LipL21 and LipL45 as myeloperoxidase inhibitors, constituting new Leptospira virulence factors. Accordingly, we propose a function for the protein LipL21, one of the most expressed leptospiral outer membrane proteins. Our results show a novel innate immune evasion mechanism by which leptospires interfere with the host response in order to cope with the host oxidative stress and efficiently achieve dissemination and colonization.

Enzymatic and bactericidal activity of myeloperoxidase in conditions of halogenative stress.

Myeloperoxidase (MPO), found mainly in neutrophils, is released in inflammation. MPO produces reactive halogen species (RHS), which are bactericidal agents. However, RHS overproduction, i.e., halogenative stress, can also damage host biomolecules, and MPO itself may be targeted by RHS. Therefore, we examined the susceptibility of MPO to inactivation by its primary products (HOCl, HOBr, HOSCN) and secondary products such as taurine monochloramine (TauCl) and taurine monobromamine (TauBr). MPO was dose-dependently inhibited up to complete inactivity by treatment with HOCl or HOBr. TauBr diminished the activity but did not eliminate it. TauCl had no effect. MPO became inactivated when producing HOCl or HOBr but not HOSCN. Taurine protected MPO against inactivation when MPO was catalyzing oxidation of Cl- to HOCl, whereas taurine failed to prevent inactivation when MPO was working with Br-, either alone or in combination with Cl-. SCN- interfered with HOCl-mediated MPO inhibition. UV-vis spectra showed that heme degradation is involved in HOCl- and HOBr-mediated MPO inactivation. A negative linear correlation between the remaining chlorinating activity of HOCl- or HOBr-modified MPO and Escherichia coli survival upon incubation with MPO/H2O2/Cl- was found. This study elucidated the possibility of MPO downregulation by MPO-derived RHS, which could counteract halogenative stress.

Partial secretome analysis of Caldariomyces fumago reveals extracellular production of the CPO co-substrate H2O2 and provides a coproduction concept for CPO and glucose oxidase.

The culture supernatant of Caldariomyces fumago strains grown in a minimal medium with fructose contains mainly the biotechnologically relevant enzyme chloroperoxidase (CPO) and only minor amounts of other proteins. Our approach to identify the nature of these proteins via peptide mass fingerprinting and transcriptome analysis demonstrated the presence of putative glycosyl hydrolase and glucose oxidase (GOx) enzymes. These activities had been described earlier as parts of the fungus´ halogenation machinery, as they provide CPO with the co-substrate H2O2. The GOx activity was found to have a pH optimum of 5. Compared to the wild type values, GOx activity and glucose-driven MCD chlorination activity in the culture of a white mutant were found to be strongly increased to values of 1-2UmL-1. As most CPO-catalyzed peroxidation reactions also show pH optima at around 5, the C. fumago culture supernatant can provide a highly convenient CPO/GOx source for many reactions with in situ H2O2 production.

Enzymatic and bactericidal activity of monomeric and dimeric forms of myeloperoxidase

This study was carried out to compare the enzymatic and bactericidal activity of mature, dimeric myeloperoxidase (MPO) and its monomeric form. Dimeric MPO was isolated from HL-60 cells. Hemi-MPO obtained from dimeric MPO by reductive cleavage of a disulfide bond between protomeric subunits was used as the monomeric form. Both peroxidase and halogenating (chlorinating) activities of MPO were assayed, each of them by two methods. Bactericidal activity of the MPO/Н2О2/Cl- system was tested using the Escherichia coli laboratory strain DH5a. No difference in the enzymatic and bactericidal activity between dimeric MPO and hemi-MPO was found. Both forms of the enzyme also did not differ in the resistance to HOCl, the main product of MPO. HOCl caused a dose-dependent decrease in peroxidase and chlorinating activity, and the pattern of this decrease was identical for dimeric MPO and hemi-MPO. At equal heme concentration, a somewhat higher bactericidal effect was observed for the hemi-MPO/Н2О2/Cl- system compared with the dimeric MPO/Н2О2/Cl- system. However, this is most likely not related to some specific property of hemi-MPO and can be accounted for by the higher probability of contacting between bacterial surface and hemi-MPO molecules due to their two-fold greater number relative to that of dimeric MPO molecules at the same heme concentration. By using Western-blotting with antibodies to MPO, we showed, for the first time, that the dimeric molecule of MPO could be cleaved into two monomeric subunits by HOCl, most probably due to oxidation of the disulfide bond between these subunits. This finding suggests that appearance in blood of MPO corresponding in mass to its monomer may result from the damage of dimeric MPO by reactive halogen species, especially upon their overproduction underlying oxidative/halogenative stress in inflammatory diseases.

Entire Peroxidation Reaction System of Myeloperoxidase Correlates with Progressive Low-Density Lipoprotein Modifications via Reactive Aldehydes in Atherosclerotic Patients with Hypertension

Background/Aims: Reactive oxygen species (ROS) contribute to the dysfunction of serum lipoproteins, which triggers lipid metabolism abnormalities in the development of atherosclerosis and hypertension. Myeloperoxidase (MPO) is involved in ROS modifications, triggering lipid peroxidation and aldehyde formation. However, the relationship between the entirety of the MPO reaction system and oxidative modification of serum lipoproteins in atherosclerotic patients with hypertension remains unclear. Methods: We measured MPO activity (peroxidation and chlorination), 4-hydroxynonenal-modified low-density lipoprotein (HNE-LDL), malondialdehyde-modified low-density lipoprotein (MDA-LDL), H₂O₂, reduced glutathione (GSH), and oxidized glutathione (GSSG) using a corresponding commercial kit in atherosclerotic patients with hypertension and healthy participants. We used Spearman’s correlation analysis to investigate the correlation between MPO activity and the levels of these oxidative and anti-oxidative stress-related indices and performed response surface regression to investigate the relationship between the MPO reaction system and the levels of HNE-LDL, MDA-LDL, and the GSH/GSSG ratio. Results: Our results showed no association between the levels of MPO peroxidation activity, MPO chlorination activity, H₂O₂, and Cl^- and those of HNE-LDL, MDA-LDL, GSH, and GSSG, and the GSH/GSSG ratio in healthy participants. In addition, no effects of the peroxidation reaction system of MPO (PRSM) and the chlorination reaction system of MPO (CRSM) on GSH/GSSG were found in this investigation. However, we found that the PRSM rather than the CRSM correlated with progressive low-density lipoprotein (LDL) modifications by HNE-LDL and MDA-LDL in atherosclerotic patients with hypertension. Conclusion: The PRSM rather than the CRSM correlated with progressive LDL modifications via reactive aldehydes in atherosclerotic patients with hypertension. Further investigation is warranted to evaluate whether the PRSM may serve as a potential index for monitoring LDL function in atherosclerosis and hypertension.

Characterization and Biochemical Assays of Streptomyces Vanadium-Dependent Chloroperoxidases.

Vanadium-dependent haloperoxidases (VHPOs) are fascinating enzymes that facilitate electrophilic halogen incorporation into electron-rich substrates, simply requiring vanadate, a halide source, and cosubstrate hydrogen peroxide for activity. Initially characterized in fungi and red algae, VHPOs were long believed to have limited regio-, chemo-, and enantioselectivity in the production of halogenated metabolites. However, the recent discovery of homologues in the biosynthetic gene clusters of the stereoselectively halogenated meroterpenoids from marine-derived Streptomyces bacteria has revised this paradigm. Their intriguing transformations have both enhanced and contributed to the fields of synthetic organic and natural product chemistry. We, herein, describe the expression, purification, and chemical assays of two characterized vanadium-dependent chloroperoxidase enzymes (NapH1 and Mcl24), and one homologue devoid of chlorination activity (NapH3), involved in the biosyntheses of halogenated meroterpenoid products.

The relevance of reactions of the methyl peroxy radical (CH3O2) and methylhypochlorite (CH3OCl) for Antarctic chlorine activation and ozone loss

The maintenance of large concentrations of active chlorine in Antarctic spring allows strong chemical ozone destruction to occur. In the lower stratosphere (approximately 16–18 km, 85–55 hPa, 390–430 K) in the core of the polar vortex, high levels of active chlorine are maintained, although rapid gas-phase production of HCl occurs. The maintenance is achieved through HCl null cycles in which the HCl production is balanced by immediate reactivation. The chemistry of the methyl peroxy radical (CH3O2) is essential for these HCl null cycles and thus for Antarctic chlorine and ozone loss chemistry in the lower stratosphere in the core of the polar vortex. The key reaction here is the reaction ; this reaction should not be neglected in simulations of polar ozone loss. Here we investigate the full chemistry of CH3O2 in box-model simulations representative for the conditions in the core of the polar vortex in the lower stratosphere. These simulations include the reaction CH3O2 + Cl, the product methylhypochlorite (CH3OCl) of the reaction CH3O2 + ClO, and the subsequent chemical decomposition of CH3OCl. We find that when the formation of CH3OCl is taken into account, it is important that also the main loss channels for CH3OCl, namely photolysis and reaction with Cl are considered. Provided that this is the case, there is only a moderate impact of the formation of CH3OCl in the reaction CH3O2 + ClO on polar chlorine chemistry in our simulations. Simulated peak mixing ratios of CH3OCl ( ppb) occur at the time of the lowest ozone mixing ratios. Further, our model simulations indicate that the reaction CH3O2 + Cl does not have a strong impact on polar chlorine chemistry. During the period of the lowest ozone concentrations in late September, enhanced values of CH3O2 are simulated and, as a consequence, also enhanced values of formaldehyde (about 100 ppt) and methanol (about 5 ppt).

Denitrification, dehydration and ozone loss during the 2015/2016 Arctic winter

Abstract. The 2015/2016 Arctic winter was one of the coldest stratospheric winters in recent years. A stable vortex formed by early December and the early winter was exceptionally cold. Cold pool temperatures dropped below the nitric acid trihydrate (NAT) existence temperature of about 195 K, thus allowing polar stratospheric clouds (PSCs) to form. The low temperatures in the polar stratosphere persisted until early March, allowing chlorine activation and catalytic ozone destruction. Satellite observations indicate that sedimentation of PSC particles led to denitrification as well as dehydration of stratospheric layers. Model simulations of the 2015/2016 Arctic winter nudged toward European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data were performed with the atmospheric chemistry–climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC) for the Polar Stratosphere in a Changing Climate (POLSTRACC) campaign. POLSTRACC is a High Altitude and Long Range Research Aircraft (HALO) mission aimed at the investigation of the structure, composition and evolution of the Arctic upper troposphere and lower stratosphere (UTLS). The chemical and physical processes involved in Arctic stratospheric ozone depletion, transport and mixing processes in the UTLS at high latitudes, PSCs and cirrus clouds are investigated. In this study, an overview of the chemistry and dynamics of the 2015/2016 Arctic winter as simulated with EMAC is given. Further, chemical–dynamical processes such as denitrification, dehydration and ozone loss during the 2015/2016 Arctic winter are investigated. Comparisons to satellite observations by the Aura Microwave Limb Sounder (Aura/MLS) as well as to airborne measurements with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) performed aboard HALO during the POLSTRACC campaign show that the EMAC simulations nudged toward ECMWF analysis generally agree well with observations. We derive a maximum polar stratospheric O3 loss of ∼ 2 ppmv or 117 DU in terms of column ozone in mid-March. The stratosphere was denitrified by about 4–8 ppbv HNO3 and dehydrated by about 0.6–1 ppmv H2O from the middle to the end of February. While ozone loss was quite strong, but not as strong as in 2010/2011, denitrification and dehydration were so far the strongest observed in the Arctic stratosphere in at least the past 10 years.

Fast heterogeneous N<sub>2</sub>O<sub>5</sub> uptake and ClNO<sub>2</sub> production in power plant and industrial plumes observed in the nocturnal residual layer over the North China Plain

Abstract. Dinitrogen pentoxide (N2O5) and nitryl chloride (ClNO2) are key species in nocturnal tropospheric chemistry and have significant effects on particulate nitrate formation and the following day's photochemistry through chlorine radical production and NOx recycling upon photolysis of ClNO2. To better understand the roles of N2O5 and ClNO2 in the high-aerosol-loading environment of northern China, an intensive field study was carried out at a high-altitude site (Mt. Tai, 1465 m a.s.l.) in the North China Plain (NCP) during the summer of 2014. Elevated ClNO2 plumes were frequently observed in the nocturnal residual layer with a maximum mixing ratio of 2.1 ppbv (1 min), whilst N2O5 was typically present at very low levels (< 30 pptv), indicating fast heterogeneous N2O5 hydrolysis. Combined analyses of chemical characteristics and backward trajectories indicated that the ClNO2-laden air was caused by the transport of NOx-rich plumes from the coal-fired industry and power plants in the NCP. The heterogeneous N2O5 uptake coefficient (γ) and ClNO2 yield (ϕ) were estimated from steady-state analysis and observed growth rate of ClNO2. The derived γ and ϕ exhibited high variability, with means of 0.061 ± 0.025 and 0.28 ± 0.24, respectively. These values are higher than those derived from previous laboratory and field studies in other regions and cannot be well characterized by model parameterizations. Fast heterogeneous N2O5 reactions dominated the nocturnal NOx loss in the residual layer over this region and contributed to substantial nitrate formation of up to 17 µg m−3. The estimated nocturnal nitrate formation rates ranged from 0.2 to 4.8 µg m−3 h−1 in various plumes, with a mean of 2.2 ± 1.4 µg m−3 h−1. The results demonstrate the significance of heterogeneous N2O5 reactivity and chlorine activation in the NCP, and their unique and universal roles in fine aerosol formation and NOx transformation, and thus their potential impacts on regional haze pollution in northern China.

In vitro efficacy of disinfectants utilised for skin decolonisation and environmental decontamination during a hospital outbreak with Candida auris.

Candida auris has caused nosocomial infections and transmissions within hospital settings. As little is known about the efficacy of skin and environmental decontamination products to kill C. auris, this study investigated the in vitro activity of chlorine, chlorhexidine, iodine povidone and vaporised hydrogen peroxide products against C. auris. H2 O2 vapour showed 96.6%-100% effective killing of C. auris. All isolates were inhibited by chlorhexidine gluconate concentrations at 0.125%-1.5% and for iodinated povidone at 0.07%-1.25%. Other species of Candida were also killed at 1000ppm chlorine except C. parapsilosis which failed to be killed at 3minutes contact time. We conclude that chlorhexidine gluconate, iodinated povidone, chlorine and H2 O2 vapour demonstrate effective killing activity against C. auris at concentrations used in clinical practice.

Model simulation of NO3, N2O5 and ClNO2 at a rural site in Beijing during CAREBeijing-2006

Abstract A chemical box model was used to study nitrate radical (NO 3 ), dinitrogen pentoxide (N 2 O 5 ) and nitryl chloride (ClNO 2 ) in a rural site during the Campaign of Air Quality Research in Beijing 2006 (CAREBeijing-2006). The model was based on regional atmospheric chemistry mechanism version 2 (RACM2) with the heterogeneous uptake of N 2 O 5 and the simplified chloride radical (Cl) chemistry mechanism. A high production rate of NO 3 with a mean value of 0.8 ppbv/h and low mixing ratios of NO 3 and N 2 O 5 (peak values of 17 pptv and 480 pptv, respectively) existed in this site. Budget analysis showed that NO emission suppressed the NO 3 chemistry at the surface layer, the reaction of NO 3 with VOCs made a similar contribution to NO 3 loss as N 2 O 5 heterogeneous uptake. The NO 3 chemistry was predominantly controlled by isoprene, and NO 3 oxidation produced organic nitrate with a mean value of 0.06 ppbv/h during nighttime. The organic nitrate production initiated by NO 3 was equal to that initiated by OH, implying the importance of nighttime chemistry for secondary organic aerosol (SOA) formation. We confirmed that the N 2 O 5 heterogeneous reaction accounted for nighttime particle NO 3 − enhancement, with a large day to day variability, and made less of a contribution to NOx loss compared to that of OH reacting with NO 2 . Additionally, abundant ClNO 2 , up to 5.0 ppbv, was formed by N 2 O 5 heterogeneous uptake. ClNO 2 was sustained at a high level until noon in spite of the gradually increasing photolysis of ClNO 2 after sunrise. Chlorine activation caused by N 2 O 5 heterogeneous uptake increased primary ROx formation by 5% and accounted for 8% of the net ozone production enhancement in the morning.

Mesna (2-mercaptoethane sodium sulfonate) functions as a regulator of myeloperoxidase

Myeloperoxidase (MPO), an abundant protein in neutrophils, monocytes, and macrophages, is thought to play a critical role in the pathogenesis of various disorders ranging from cardiovascular diseases to cancer. We show that mesna (2-mercaptoethanesulfonic acid sodium salt), a detoxifying agent, which inhibits side effects of oxazaphosphorine chemotherapy, functions as a potent inhibitor of MPO; modulating its catalytic activity and function. Using rapid kinetic methods, we examined the interactions of mesna with MPO compounds I and II and ferric forms in the presence and absence of chloride (Cl-), the preferred substrate of MPO. Our results suggest that low mesna concentrations dramatically influenced the build-up, duration, and decay of steady-state levels of Compound I and Compound II, which is the rate-limiting intermediate in the classic peroxidase cycle. Whereas, higher mesna concentrations facilitate the porphyrin-to-adjacent amino acid electron transfer allowing the formation of an unstable transient intermediate, Compound I*, that displays a characteristic spectrum similar to Compound I. In the absence of plasma level of chloride, mesna not only accelerated the formation and decay of Compound II but also reduced its stability in a dose depend manner. Mesna competes with Cl-, inhibiting MPO's chlorinating activity with an IC50 of 5µM, and switches the reaction from a 2e- to a 1e- pathway allowing the enzyme to function only with catalase-like activity. A kinetic model which shows the dual regulation through which mesna interacts with MPO and regulates its downstream inflammatory pathways is presented further validating the repurposing of mesna as an anti-inflammatory drug.

Inhibition of Myeloperoxidase- and Neutrophil-Mediated Hypochlorous Acid Formation in Vitro and Endothelial Cell Injury by (-)-Epigallocatechin Gallate.

Myeloperoxidase (MPO) plays important roles in various diseases through its unique chlorinating activity to catalyze excess hypochlorous acid (HOCl) formation. Epidemiological studies indicate an inverse correlation between plant polyphenol consumption and the incidence of cardiovascular diseases. Here we showed that (-)-epigallocatechin gallate (EGCG), the main flavonoid present in green tea, dose-dependently inhibited MPO-mediated HOCl formation in vitro (chlorinating activities of MPO: 50.2 ± 5.7% for 20 μM EGCG versus 100 ± 5.6% for control, P < 0.01). UV-vis spectral and docking studies indicated that EGCG bound to the active site (heme) of MPO and resulted in the accumulation of compound II, which was unable to produce HOCl. This flavonoid also effectively inhibited HOCl generation in activated neutrophils (HOCl formation: 65.0 ± 5.6% for 20 μM EGCG versus 100 ± 6.2% for control, P < 0.01) without influencing MPO and Nox2 release and superoxide formation, suggesting that EGCG specifically inhibited MPO but not NADPH oxidase activity in activated neutrophils. Moreover, EGCG inhibited MPO (or neutrophil)-mediated HOCl formation in human umbilical vein endothelial cells (HUVEC) culture and accordingly protected HUVEC from MPO (or neutrophil)-induced injury (P < 0.05, all cases), although it did not induce cytotoxicity to HUVEC (P > 0.05, all cases). Our results indicate that dietary EGCG is an effective and specific inhibitor of MPO activity and may participate in the regulation of immune responses at inflammatory sites.

Assessment of chlorine tolerance profile of Citrobacter species recovered from wastewater treatment plants in Eastern Cape, South Africa.

This present study assessed the chlorine tolerance of some Citrobacter species recovered from secondary effluents from the clarifiers of two wastewater treatment plants in the Eastern Cape, South Africa. The bacterial survival, chlorine lethal dose and inactivation kinetics at lethal doses were examined. Inactivation of the test bacteria (n=20) at the recommended dose of 0.5mg/l for 30min exposure showed a progressive reduction in bacterial population from 4 to 5 log reduction and residuals ranged between 0.12 and 0.46mg/l. The bactericidal activity of chlorine increased at higher dosages with a substantial reduction in viability of the bacteria and complete inactivation of the bacterial population at a lethal dose of 0.75 and 1.0mg/l in 30min. For the inactivation kinetics, bactericidal activity of chlorine increased with time showing a 3.67-5.4 log reduction in 10min, 4.0-5.6 log reduction in 20min and above 6.3 log reductions to complete sterilization of bacterial population over 30min for all the entire test Citrobacter isolates used in this study. Furthermore, there was a strong correlation (R 2>0.84) between bacteria inactivation and increase in contact time. This study appears to have provided support for laboratory evidence of bacterial tolerance to chlorine disinfection at current recommended dose (0.5mg/l for 30min), and chlorine concentration between 0.75 and 1.0mg/l was found to have a better disinfecting capacity to check tolerance of Citrobacter species.

A fluorescent homogeneous assay for myeloperoxidase measurement in biological samples. A positive correlation between myeloperoxidase-generated HOCl level and oxidative status in STZ-diabetic rats

Myeloperoxidase (MPO) is a key enzyme derived from leukocytes which is associated with the initiation and progression of many inflammatory diseases. Increased levels of MPO may contribute to cellular dysfunction and tissues injury by producing highly reactive oxidants such as hypochlorous acid (HOCl). Myeloperoxidase-generated HOCl is therefore considered as a relevant biomarker of oxidative stress-related damage and its quantitation is of great importance to the study of disease progression. In this context, the current study describes a rapid, sensitive and homogeneous fluorescence-based method for detecting the MPO chlorination activity in biological samples. This assay utilizes 7-hydroxy-2-oxo-2H-chromene-8-carbaldehyde oxime as a selective probe for HOCl detection, and is adapted to 96-well microplates to allow high-throughput quantitation of active MPO. The ability of the method to monitor HOCl release was further investigated in hyperglycemic streptozotocin-treated diabetic rats. The data proved that the present assay has a reliable performance when quantitating the active MPO in the plasma of diabetic animals, a feature of inflammatory disease found concomitant with an elevation of protein carbonyls levels and lipid peroxidation and which was negatively correlated with the ratio of reduced-to-oxidized glutathione.