Prediction of hydroxyl radical exposure during ozonation using different machine learning methods with ozone decay kinetic parameters.

The abatement of micropollutants by ozonation can be accurately calculated by measuring the exposures of molecular ozone (O3) and hydroxyl radical (•OH) (i.e., ∫[O3]dt and ∫[•OH]dt). In the actual ozonation process, ∫[O3]dt values can be calculated by monitoring the O3 decay during the process. However, calculating ∫[•OH]dt is challenging in the field, which necessitates developing models to predict ∫[•OH]dt from measurable parameters. This study demonstrates the development of machine learning models to predict ∫[•OH]dt (the output variable) from five basic input variables (pH, dissolved organic carbon concentration, alkalinity, temperature, and O3 dose) and two optional ones (∫[O3]dt and instantaneous ozone demand, IOD). To develop the models, four different machine learning methods (random forest, support vector regression, artificial neural network, and Gaussian process regression) were employed using the input and output variables measured (or determined) in 130 different natural water samples. The results indicated that incorporating ∫[O3]dt as an input variable significantly improved the accuracy of prediction models, increasing overall R2 by 0.01-0.09, depending on the machine learning method. This suggests that ∫[O3]dt plays a crucial role as a key variable reflecting the •OH-yielding characteristics of dissolved organic matter. Conversely, IOD had a minimal impact on the accuracy of the prediction models. Generally, machine-learning-based prediction models outperformed those based on the response surface methodology developed as a control. Notably, models utilizing the Gaussian process regression algorithm demonstrated the highest coefficients of determination (overall R2 = 0.91-0.95) among the prediction models.

Nitrate Upcycling Mediated by Organonickel Catalysis.

Nitrogen oxides (NOx) are major environmental pollutants and to neutralize this long-term environmental threat, new catalytic methods are needed. Although there are biological denitrification processes involving four different enzymatic reactions to convert nitrate (NO3-) to dinitrogen (N2), it is unfortunately difficult to apply in industry due to the complexity of the processes. In particular, nitrate is difficult to functionalize because of its chemical stability. Thus, there is no organometallic catalysis to convert nitrate to useful chemicals. In this article, we present that a nickel pincer complex is effective as a bifunctional catalyst to stepwise deoxygenate NO3- by carbonylation and further to C-N coupling. By using this nickel catalysis, nitrate salts can be selectively transformed into various oximes (>20 substrates) with excellent conversion (>90%). Here, we demonstrate for the first time that the highly inert nitrate ion can be functionalized to produce useful chemicals by a new organonickel catalysis. Our results show that the NOx conversion and utilization (NCU) technology is a successful pathway for environmental restoration coupled with value-added chemical generation.

Reactivity of low-valent nickel carbonyl species supported by acridane based PNP ligands towards iodoalkanes.

Nickel monocarbonyl species with Ni(I) and Ni(0) have been synthesized and fully characterized by employing an acriPNP-Ph pincer ligand having a -C(Ph)2- bridge moiety to tether two aromatic rings. To see the effect of the bridge moiety, these complexes were structurally compared with the previously studied nickel complexes supported by PNP and acriPNP-Me ligands and methylation of the nickel carbonyl species was particularly investigated. Since a Ni(I)-CO species is known to be one of the key intermediates during the C-C coupling reaction to give an acetyl species, according to the paramagnetic mechanism of acetyl coenzyme A synthase (ACS), their reactivity toward MeI has been examined. Methylation of a nickel(I)-CO species reveals enhanced C-C coupling when both acriPNP-Me and acriPNP-Ph ligands were used. According to spin density analysis calculated by density functional theory, all Ni(I)-CO species reveal similar spin density at nickel and the carbon atom of CO. X-ray crystallographic data suggest that the corresponding selectivity may be related to the steric influence. For both (acriPNP-Ph)Ni-CO (2) and (acriPNP-Me)Ni-CO (2'), the nickel(I) site is sterically well protected, leading to selective interaction with a methyl radical to give a nickel acyl product. Steric influence was marginally observed when an anionic {(acriPNP-R)Ni-CO}- (R = Me or Ph) species reacted with MeI. The corresponding C-C coupled product was also observed from the methylation of nickel(0)-CO species.

Occurrence, removal, and prioritization of organic micropollutants in four full-scale wastewater treatment plants in Korea.

This study investigated the occurrence, removal rate, and potential risks of 43 organic micropollutants (OMPs) in four municipal wastewater treatment plants (WWTPs) in Korea. Results from two-year intensive monitoring confirmed the presence of various OMPs in the influents, including pharmaceuticals such as acetaminophen (pain relief), caffeine (stimulants), cimetidine (H2-blockers), ibuprofen (non-steroidal anti-inflammatory drugs- NSAIDs), metformin (antidiabetics), and naproxen (NSAIDs) with median concentrations of >1 µg/L. Some pharmaceuticals (carbamazepine-anticonvulsants, diclofenac-NSAIDs, propranolol-ß-blockers), corrosion inhibitors (1H-benzotriazole-BTR, 4-methyl-1H-benzotriazole-4-TTR), and perfluorinated compounds (PFCs) were negligibly removed during WWTP treatment. The OMP concentrations in the influents and effluents were mostly lower in August than those of other months (p-value <0.05) possibly due to wastewater dilution by high precipitation or enhanced biodegradation under high-temperature conditions. The anaerobic-anoxic-oxic process (A2O) with a membrane bioreactor exhibited higher OMP removal than other processes, such as A2O with sedimentation or the conventional activated sludge process (p-value <0.05). Pesticides (DEET and atrazine), corrosion inhibitors (4-TTR and BTR), and metformin were selected as priority OMPs in toxicity-driven prioritization, whereas PFCs were determined as priority OMPs given their persistence and bioaccumulation properties. Overall, our results contribute to an important database on the occurrence, removal, and potential risks of OMPs in Korean WWTPs.

Pleiotropic effects of N-acylhomoserine lactone synthase ExpI on virulence, competition, and transmission in Pectobacterium carotovorum subsp. carotovorum Pcc21.

BACKGROUND: Pectobacterium species are necrotrophic phytopathogenic bacteria that cause soft rot disease in economically important crops. The successful infection of host plants relies on interactions among virulence factors, competition, and transmission within hosts. Pectobacteria primarily produce and secrete plant cell-wall degrading enzymes (PCWDEs) for virulence. The regulation of PCWDEs is controlled by quorum sensing (QS). Thus, the QS system is crucial for disease development in pectobacteria through PCWDEs. RESULTS: In this study, we identified a Tn-insertion mutant, M2, in the expI gene from a transposon mutant library of P. carotovorum subsp. carotovorum Pcc21 (hereafter Pcc21). The mutant exhibited reduced production and secretion of PCWDEs, impaired flagellar motility, and increased sensitivity to hydrogen peroxide, resulting in attenuated soft rot symptoms in cabbage and potato tubers. Transcriptomic analysis revealed the down-regulation of genes involved in the production and secretion in the mutant, consistent with the observed phenotype. Furthermore, the Pcc21 wild-type transiently colonized in the gut of Drosophila melanogaster within 12 h after feeding, while the mutant compromised colonization phenotype. Interestingly, Pcc21 produces a bacteriocin, carocin D, to compete with other bacteria. The mutant exhibited up-regulation of carocin D-encoding genes (caroDK) and inhibited the growth of a closely related bacterium, P. wasabiae. CONCLUSION: Our results demonstrated the significance of ExpI in the overall pathogenic lifestyle of Pcc21, including virulence, competition, and colonization in plant and insect hosts. These findings suggest that disease outcome is a result of complex interactions mediated by ExpI across multiple steps. © 2023 Society of Chemical Industry.

Predicting micropollutant fate during wastewater treatment using refined classical kinetic model based on quantitative monitoring in multi-metropolitan regions of South Korea.

This study aimed to implement an extensive prediction model for the fate of micropollutants (MPs) in wastewater treatment plants (WWTPs). Five WWTPs equipped with seven different biological treatment processes were monitored from 2020 to 2022 with three to four sampling events in each year, and 27 datasets for 20 MPs were collected. Among these datasets, 12 were used to investigate the behavior and fate of MPs in WWTPs in South Korea. Metformin, acetaminophen, caffeine, naproxen, and ibuprofen were the MPs with the highest influent concentrations (ranging from 3,933.3-187,637.0 ng L-1) at all WWTPs. More than 90% of MPs were removed by biological treatment processes in all WWTPs. The Kruskal-Wallis test verified that their efficacy did not differ statistically (p-value > 0.05). Meanwhile, to refine the performance of the prediction model, this study optimized the biodegradation rate constants (kbio) of each MP according to the variation of seasonal water temperature. As a result, compared to the original prediction model, the mean difference between the actual data and predicted results (MEAN) decreased by 6.77%, while the Nash-Sutcliffe efficiency (NSE) increased by 0.226. The final MEAN and NSE for the refined prediction model were calculated to be 5.09% and 0.964, respectively. The prediction model made accurate predictions, even for MPs exhibiting behaviors different from other cases, such as estriol and atrazine. Consequently, the optimization strategy proposed in this study was determined to be effective because the overall removal efficiencies of MPs were successfully predicted even with limited reference datasets.

Evaluation of the prediction of micropollutant elimination during bromide ion-containing industrial wastewater ozonation using the ROH, O3 value.

The composition of the wastewater matrix influences the oxidation potential of ozonation, a technique widely recognized efficient removal of micropollutants. Here, we developed a chemical kinetic model to determine the ozone dose required to minimize bromate production in wastewater containing bromine ions while achieving target removal rates. In wastewater ozonation, ozone decomposition comprises instantaneous ozone consumption and subsequent decomposition at first-order reaction rates. Under the injection condition of 1.5 g O3/g dissolved organic carbon (DOC), the instantaneous ozone demand was 62.7% of the injection concentration, and it increased proportionally with increasing injected ozone concentration. Ozone and hydroxyl radical exposures were proportional to the initial ozone dose, while hydroxyl radical exposure was proportional to ozone exposure, and the deviation was relatively high at 1.0-1.5 g O3/g DOC. The calculated hydroxyl radical exposure was 3.0 × 10-10 to 5.3 × 10-10 M s. Ozone and hydroxyl radicals are highly correlated with the ratio of ozone dose to organic matter concentration. Therefore, a trace substance removal rate evaluation model combined with the ROH, O3 model and a bromate generation model were also considered. For ibuprofen, the ozone dose for achieving the target removal rate of 80% while maintaining the bromate concentration below 50 µg L-1 was suitable in the operating range of 0.86 g O3/g DOC or more. The proposed method provides a practical operation strategy to calculate the appropriate ozone dose condition from the target compound removal rate prediction and bromate generation models considering the ratio of ozone dose to organic matter concentration in the incoming wastewater.

Versatile Post-synthetic Modifications of Helical ß-Peptide Foldamers Derived from a Thioether-Containing Cyclic ß-Amino Acid.

We introduce a novel cyclic ß-amino acid, trans-(3S,4R)-4-aminotetrahydrothiophene-3-carboxylic acid (ATTC), as a versatile building block for designing peptide foldamers with controlled secondary structures. We synthesized and characterized a series of ß-peptide hexamers containing ATTC using various techniques, including X-ray crystallography, circular dichroism, and NMR spectroscopy. Our findings reveal that ATTC-containing foldamers can adopt 12-helical conformations similar to their isosteres and offer the possibility of fine-tuning their properties via post-synthetic modifications. In particular, chemoselective conjugation strategies demonstrate that ATTC provides unique post-synthetic modification opportunities, which expand their potential applications across diverse research areas. Collectively, our study highlights the versatility and utility of ATTC as an alternative to previously reported cyclic ß-amino acid building blocks in both structural and functional aspects, paving the way for future research in the realm of peptide foldamers and beyond.

Efficiency of ozonation and O3/H2O2 as enhanced wastewater treatment processes for micropollutant abatement and disinfection with minimized byproduct formation.

Ozonation, a viable option for improving wastewater effluent quality, requires process optimization to ensure the organic micropollutants (OMPs) elimination and disinfection under minimized byproduct formation. This study assessed and compared the efficiencies of ozonation (O3) and ozone with hydrogen peroxide (O3/H2O2) for 70 OMPs elimination, inactivation of three bacteria and three viruses, and formation of bromate and biodegradable organics during the bench-scale O3 and O3/H2O2 treatment of municipal wastewater effluent. 39 OMPs were fully eliminated, and 22 OMPs were considerably eliminated (54 ± 14%) at an ozone dosage of 0.5 gO3/gDOC for their high reactivity to ozone or •OH. The chemical kinetics approach accurately predicted the OMP elimination levels based on the rate constants and exposures of ozone and •OH, where the quantum chemical calculation and group contribution method successfully predicted the ozone and •OH rate constants, respectively. Microbial inactivation levels increased with increasing ozone dosage up to ∼3.1 (bacteria) and ∼2.6 (virus) log10 reductions at 0.7 gO3/gDOC. O3/H2O2 minimized bromate formation but significantly decreased bacteria/virus inactivation, whereas its impact on OMP elimination was insignificant. Ozonation produced biodegradable organics that were removed by a post-biodegradation treatment, achieving up to 24% DOM mineralization. These results can be useful for optimizing O3 and O3/H2O2 processes for enhanced wastewater treatment.

Highly Distorted Bismuth-Nickel(II) Complex.

The synthesis and characterization of a series of nickel complexes bearing a bismuth-containing pincer ligand are presented herein. In particular, synthesis of a 4-coordinate Bi-Ni(II) complex allows the influence of bismuth on a d8 Ni(II) ion to be investigated. A trigonal-bipyramidal complex, (BiP2)Ni(PPh) (1), possessing an anionic bismuth donor was prepared via the Bi-C bond cleavage of a BiP3 ligand (BiP3 = Bi(o-PiPr2-C6H4)3) mediated by Ni(0). To remove a PPh moiety, compound 1 was treated with MeI to give a 5-coordinate nickel(II) complex (MeBiP2)Ni(PPh)(I) (2), followed by its exposure to heat or UV irradiation, resulting in the formation of a nickel halide complex, (BiP2)Ni(I) (3). The X-ray crystal structure of 2 revealed that the methyl moiety binds to a bismuth site, providing a neutral MeBiP2 ligand, while the iodide anion is bound to the nickel(II) center, displacing one phosphine donor. Because of the methylation on a Bi site, the Bi-Ni bond in 2 is clearly elongated relative to that of 1, which indicates that the bonding interactions between Bi and Ni are substantially different. Interestingly, compound 3 revealing a sawhorse geometry is significantly distorted away from a square-planar structure compared to the previously reported nickel(II) pincer complexes, (NP2)Ni(Cl) and (PP2)Ni(I). Such difference indicates that a bismuth donor can be a structurally influencing cooperative site for a nickel(II) ion, leading to have a Ni(I)-Bi(II) character. Migratory insertion of CO into a Ni-C bond of 1 gives (BiP2)Ni(COPPh) (4), which further leads to an analogous methylated product (MeBiP2)Ni(COPPh)(I) (5) from reaction with MeI. Due to the structural influence of a carbonyl group in each step, the total reaction time from 1 to 3 was dramatically reduced. The bimetallic cooperativity of the complexes and unusual bonding properties presented here highlight the potential of a bismuth-nickel moiety as a new type of heterobimetallic site for the design of bimetallic complexes to facilitate a variety of chemical transformations.

Disruption of the metC Gene Affects Methionine Biosynthesis in Pectobacterium carotovorum subsp. carotovorum Pcc21 and Reduces Soft-Rot Disease.

Plant pathogenic Pectobacterium species cause severe soft rot/blackleg diseases in many economically important crops worldwide. Pectobacterium utilizes plant cell wall degrading enzymes (PCWDEs) as the main virulence determinants for its pathogenicity. In this study, we screened a random mutant, M29 is a transposon insertion mutation in the metC gene encoding cystathionine ß-lyase that catalyzes cystathionine to homocysteine at the penultimate step in methionine biosynthesis. M29 became a methionine auxotroph and resulted in growth defects in methionine-limited conditions. Impaired growth was restored with exogenous methionine or homocysteine rather than cystathionine. The mutant exhibited reduced soft rot symptoms in Chinese cabbages and potato tubers, maintaining activities of PCWDEs and swimming motility. The mutant was unable to proliferate in both Chinese cabbages and potato tubers. The reduced virulence was partially restored by a complemented strain or 100 µM of methionine, whereas it was fully restored by the extremely high concentration (1 mM). Our transcriptomic analysis showed that genes involved in methionine biosynthesis or transporter were downregulated in the mutant. Our results demonstrate that MetC is important for methionine biosynthesis and transporter and influences its virulence through Pcc21 multiplication in plant hosts.

Electronic Effect on Phenoxide Migration at a Nickel(II) Center Supported by a Tridentate Bis(phosphinophenyl)phosphido Ligand.

A phosphide nickel(II) phenoxide pincer complex (2) reacts with CO(g) to give a pseudo-tetrahedral nickel(0) monocarbonyl complex (3) possessing a phosphinite moiety. This metal-ligand cooperative (MLC) transformation occurs with a (PPP)Ni scaffold (PPP- = P[2-PiPr2-C6H4]2-), which can accommodate both square planar and tetrahedral geometries. The 2-electron reduction of a nickel(II) species induced by CO coordination involves group transfer to generate a P-O bond. For better mechanistic understanding, a series of nickel(II) phenolate complexes (2a-2e, XC6H4O- (X = OMe, Me, H, and CF3) and pentafluorophenolate) were prepared. Kinetic experimental data reveal that a phenolate species with an electron-withdrawing group reacts faster than those with electron-donating groups. The reaction kinetic experiments were conducted in pseudo-first order conditions at room temperature monitored by UV-vis spectroscopy. A pentafluorophenolate nickel(II) complex (2e) reveals instantaneous reactions even at -40 °C to give a nickel(0) monocarbonyl species (3e) and the reverse reaction is also possible. According to kinetic experiments, the rate determining step (RDS) would be the formation of a 5-coordinate intermediate 4 with a negative entropy value (ΔS‡ < 0), and a positive ρ value based on the Hammett plot indicates that the electron-deficient phenolate leads to a faster CO association. Furthermore, scramble experiments suggest that phenolate de-coordinates from the intermediate 4, which gives a (PPP)Ni-CO species 6. The cationic nickel monocarbonyl intermediate can possess a P--Ni(II), P•-Ni(I), or even a P+-Ni(0) character. Such an inner-sphere electron transfer is suggested when a π-acidic ligand such as CO coordinates to a metal ion. Another possible reaction is homolysis of a Ni-O bond to give P--Ni(I) or P•-Ni(0), when a phenoxyl radical is liberated. Considering the P-O bond formation, closed-shell nucleophilic and open-shell radical pathways are suggested. A phenolate pathway reveals a lower energy state for 2e relative to other complexes (2c and 2d), while its radical pathway undergoes via a higher energy state. Therefore, the formation of a P-O bond may occur with the binding of a closed-shell phenolate to the electron-deficient P center.

A conjugate of chlorin e6 and cationic amphipathic peptoid: a dual antimicrobial and anticancer photodynamic therapy agent.

Cationic amphipathic structures are often utilized in natural membrane-active host-defense peptides. Negatively charged surface membranes of rapidly proliferating bacterial and cancer cells have been targeted by various synthetic peptides and peptidomimetics adopting the structural motif. Herein, we synthesized a set of conjugates composed of cationic amphipathic peptoids (i.e., oligo-N-substituted glycines) and a chlorin photosensitizer, named chlorin e6 (Ce6)-peptoid conjugates (CPCs). Among the nine CPCs, CPC 7, composed of Ce6, a PEG linker, and guanidine-rich helical amphipathic peptoids, exhibited a distinct photoresponsive inactivation of Gram-positive and Gram-negative bacteria. Subsequent studies showed that CPC 7 effectively killed various cancer cells after irradiation with red light (655 nm), suggesting the potential of CPC 7 as a dual antimicrobial and anticancer agent. Confocal laser scanning microscopy and flow cytometry data suggested that CPC 7 could induce apoptotic cell death. Our results show the potential of peptoid-based photosensitizer conjugates as a versatile platform for antimicrobial and anticancer photodynamic therapy agents and peptoid therapeutics.

Assessment of the recycling potential of valuable metals by mapping the elemental composition in discarded light-emitting diodes (LEDs).

Electronic waste (e-waste) is the world's fastest-growing type of waste, with lighting accounting for 9% of the total. Light-emitting diodes (LEDs) are composed of the most concentrated critical elements (Ag and Au) and recovery of these metals could generate economic benefits and reduce the burdens of environmental pollution; nevertheless, the absence of information about their composition currently presents a challenge in recycling these metals with minimal prospects for recovery. This study assessed the distribution and variation of elemental concentrations of 16 different elements in three generations of LEDs (12 different LED units): sub-mounted-device (SMD #10), chip-on-board (COB #1), and positive-intrinsic-negative (PIN #1). The SMD LEDs contained a considerable amount of Au with a median average concentration of 1204 mg/kg (ranging from 323 - 3687 mg/kg), which was similar to that of COB (1550 mg/kg), but higher than that of PIN LED (175 mg/kg). Based on the total threshold limiting concentration (TTLC), the Cu levels (605,823 mg/kg) in the SMD package exceeded the regulatory limits (2500 mg/kg). Concentrations of the hazardous elements Cr (29 mg/kg), Pb (12 mg/kg), Cd (0.1 mg/kg), and As (1 mg/kg) in the LED packages were within the regulatory limits. To recycle precious metals and other technological metals, a well-organized and dedicated optimized assessment of the value of metals is required especially in accordance with the concept of criticality and recyclability. Two factors, i.e., a high resource index (RI) and technology index (TI), suggest the importance of waste to the economy and has a significant potential for recycling with less processing burdens. Present findings indicated that the COB and a few of the studied SMD LEDs (3020, 4014, 5630, and 7020), exhibit high criticality and recyclability. For the RI and TI index, the contribution of metals such as Cu, Fe, Al, and Au were dominant. These findings can serve as a reference for the development of a viable approach for the recycling and recovery of targeted metals from LED e-waste.

Reaction of Amino Acids with Ferrate(VI): Impact of the Carboxylic Group on the Primary Amine Oxidation Kinetics and Mechanism.

Ferrate (Fe(VI)) is a novel oxidant that can be used to mitigate disinfection byproduct (DBP) precursors. However, the reaction of Fe(VI) with organic nitrogen, which is a potential precursor of potent nitrogenous DBPs, remains largely unexplored. The present work aimed to identify the kinetics and products for the reaction of Fe(VI) with primary amines, notably amino acids. A new kinetic model involving ionizable intermediates was proposed and can describe the unusual pH effect on the Fe(VI) reactivity toward primary amines and amino acids. The Fe(VI) oxidation of phenylalanine produced a mixture of nitrile, nitrite/nitrate, amide, and ammonia, while nitroalkane was an additional product in the case of glycine. The product distribution for amino acids significantly differed from that of uncarboxylated primary amines that mainly generate nitriles. A general reaction pathway for primary amines and amino acids was proposed and notably involved the formation of imines, the degradation of which was affected by the presence of a carboxylic group. In comparison, ozonation led to higher yields of nitroalkanes that could be readily converted to potent halonitroalkanes during chlor(am)ination. Based on this study, Fe(VI) can effectively mitigate primary amine-based, nitrogenous DBP precursors with little formation of toxic halonitroalkanes.

In vitro bioanalytical assessment of the occurrence and removal of bioactive chemicals in municipal wastewater treatment plants in Korea.

Effluents of wastewater treatment plants (WWTPs) contain various organic micropollutants, some of which can exert negative effects on the quality of receiving waters or drinking water sources. This study monitored two full-scale WWTPs in Korea for the occurrence and removal of bioactive chemicals for a one-year period using a battery of in vitro bioassays as a complementary approach to chemical analysis. Bioassays covering different endpoints were employed, such as hormone receptor activation (AR and ERα), xenobiotic metabolism (PAH and PXR), oxidative stress response (Nrf2), and cytotoxicity. The WWTP influents showed AR, ERα, and PAH activities at ng/L - µg/L and PXR and Nrf2 activities at µg/L - mg/L as bioanalytical equivalent concentrations of a reference compound for each bioassay. These bioactivities decreased along with the WWTP treatment train, with significant removals achieved by the secondary biological treatment processes. Cytotoxicity was observed only for some municipal wastewater (M-WWTP) influents but was below the limit of quantification for most cases. The influent and effluent bioactivities observed in this study were mostly comparable to those reported in other WWTPs in the literature. Comparison of the bioactivities with the effect-based trigger (EBT) values indicates that the impact of WWTP effluents on receiving water quality was low for most endpoints. For Nrf2, however, further investigation is required to evaluate the observed high bioactivities compared with the current EBT. The observed ERα activity could partly be explained by the presence of some steroid estrogens. Overall, our results contribute to an important database for the concentrations and removal efficiencies of bioactive chemicals in WWTPs and demonstrate bioassays as a useful tool for urban water quality monitoring.

Effect of Sulfide and Chloride Ions on Pitting Corrosion of Type 316 Austenitic Stainless Steel in Groundwater Conditions Using Response Surface Methodology.

This study investigates the corrosion resistance of Type 316 stainless steel as a candidate material for radioactive waste disposal canisters. The viability of stainless steel is examined under groundwater conditions with variations in pH, bisulfide ions (HS-), and chloride ions (Cl-) concentrations. Utilizing response surface methodology, correlations between corrosion factors and two crucial response variables, passive film breakdown potential and protection potential, are established. Cyclic potentiodynamic polarization tests and advanced analytical techniques provide detailed insights into the material's behavior. This research goes beyond, deriving an equation through response surface methodology that elucidates the relationship between the factors and breakdown potential. HS- weakens the passive film and reduces the pitting corrosion resistance of the stainless steel. However, this study highlights the inhibitory effect of HS- on pitting corrosion when Cl- concentrations are below 0.001 M and at equivalent concentrations of HS-. Under these conditions, immediate re-passivation occurs from the destroyed passive film to metal sulfides such as FeS2, MoS2, and MoS3. As a result, no hysteresis loop occurs in the cyclic polarization curve in these conditions. This research contributes to the understanding of Type 316 stainless-steel corrosion behavior, offering implications for the disposal of radioactive waste in geological repositories.

Pyocyanin and 1-Hydroxyphenazine Promote Anaerobic Killing of Pseudomonas aeruginosa via Single-Electron Transfer with Ferrous Iron.

Previously, it was reported that natural phenazines are able to support the anaerobic survival of Pseudomonas aeruginosa PA14 cells via electron shuttling, with electrodes poised as the terminal oxidants (Y. Wang, S. E. Kern, and D. K. Newman, J Bacteriol 192:365-369, 2010, https://doi.org/10.1128/JB.01188-09). The present study shows that both pyocyanin (PYO) and 1-hydroxyphenazine (1-OHPHZ) promoted the anaerobic killing of PA14 Δphz cells presumably via a single-electron transfer reaction with ferrous iron. However, phenazine-1-carboxylic acid (PCA) did not affect anaerobic survival in the presence of ferrous iron. Anaerobic cell death was alleviated by the addition of antioxidant compounds, which inhibit electron transfer via DNA damage. Neither superoxide dismutase (SOD) nor catalase was able to alleviate P. aeruginosa cell death, ruling out the possibility of reactive oxygen species (ROS)-induced killing. Further, the phenazine degradation profile and the redox state-associated color changes suggested that phenazine radical intermediates are likely generated by single-electron transfer. In this study, we showed that the phenazines 1-OHPHZ and PYO anaerobically killed the cell via single-electron transfer with ferrous iron and that the killing might have resulted from phenazine radicals. IMPORTANCE Pseudomonas aeruginosa is an opportunistic human pathogen which infects patients with burns, immunocompromised individuals, and in particular, the mucus that accumulates on the surface of the lung in cystic fibrosis (CF) patients. Phenazines as redox-active small molecules have been reported as important compounds for the control of cellular functions and virulence as well as anaerobic survival via electron shuttles. We show that both pyocyanin (PYO) and 1-hydroxyphenazine (1-OHPHZ) generate phenazine radical intermediates via presumably single-electron transfer reaction with ferrous iron, leading to the anaerobic killing of Pseudomonas cells. The recA mutant defect in the DNA repair system was more sensitive to anaerobic conditions. Our results collectively suggest that both phenazines anaerobically kill cells via DNA damage during electron transfer with iron.

o-(2-Thienyl)vinylarene as an Alternative Synthetic Motif for Porphyrinoids: o-Arene-Connected Porphyrinoids.

o-Arene-connected porphyrinoids were synthesized with o-(2-thienyl)vinylarene motif as a new building block for porphyrinoids. This motif can replace meso-aryl-substituted dipyrromethene and serve as a command key arranging o-connectivity of porphyrinoid. While 6a (benzene version) is very weak, 6b (pyridine version) shows a substantial amount of diatropic ring current due to reduced steric hindrance (without H23) and rigidified Pd-6a became more aromatic than 6b.