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Applied and Environmental Microbiology Aug 2023An important role of nitric oxide (NO) as either a free intermediate in the NH oxidation pathway or a potential oxidant for NH or NHOH has been proposed for...
An important role of nitric oxide (NO) as either a free intermediate in the NH oxidation pathway or a potential oxidant for NH or NHOH has been proposed for ammonia-oxidizing bacteria (AOB) and archaea (AOA), respectively. However, tracing NO metabolism at low concentrations remains notoriously difficult. Here, we use electrochemical sensors and the mild NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) to trace apparent NO concentration and determine production rates at low micromolar concentrations in the model AOB strain Nitrosomonas europaea. In agreement with previous studies, we found that PTIO does not affect NH oxidation instantaneously in both Nitrosospira briensis and Nitrosomonas europaea, unlike inhibitors for ammonia oxidation such as allylthiourea and acetylene, although it effectively scavenged NO from the cell suspensions. Quantitative analysis showed that NO production by amounted to 3.15% to 6.23% of NO production, whereas grown under O limitation produced NO equivalent to up to 40% of NO production at high substrate concentrations. In addition, we found that PTIO addition to grown under O limitation abolished NO production. These results indicate different turnover rates of NO during NH oxidation under O-replete and O-limited growth conditions in AOB. The results suggest that NO may not be a free intermediate or remain tightly bound to iron centers of enzymes during hydroxylamine oxidation and that only NH saturation and adaptation to O limitation may lead to significant dissociation of NO from hydroxylamine dehydrogenase. Ammonia oxidation by chemolithoautotrophic ammonia-oxidizing bacteria (AOB) is thought to contribute significantly to global nitrous oxide (NO) emissions and leaching of oxidized nitrogen, particularly through their activity in nitrogen (N)-fertilized agricultural production systems. Although substantial efforts have been made to characterize the N metabolism in AOB, recent findings suggest that nitric oxide (NO) may play an important mechanistic role as a free intermediate of hydroxylamine oxidation in AOB, further implying that besides hydroxylamine dehydrogenase (HAO), additional enzymes may be required to complete the ammonia oxidation pathway. However, the NO spin trap PTIO was found to not inhibit ammonia oxidation in AOB. This study provides a combination of physiological and spectroscopic evidence that PTIO indeed scavenges only free NO in AOB and that significant amounts of free NO are produced only during incomplete hydroxylamine oxidation or nitrifier denitrification under O-limited growth conditions.
Topics: Nitric Oxide; Ammonia; Hydroxylamine; Nitrogen Dioxide; Oxidation-Reduction; Nitrous Oxide; Archaea; Betaproteobacteria; Nitrogen; Hydroxylamines; Nitrification
PubMed: 37439697
DOI: 10.1128/aem.02173-22 -
Revista Portuguesa de Cardiologia :... Oct 2022Hyperhomocysteinemia (HHcy) can induce vascular inflammatory and oxidative damage and accelerate intimal hyperplasia. This study investigated the protective effect of...
OBJECTIVES
Hyperhomocysteinemia (HHcy) can induce vascular inflammatory and oxidative damage and accelerate intimal hyperplasia. This study investigated the protective effect of pirfenidone (PFD) on the recovery process of injured endothelial arteries during HHcy.
MATERIALS AND METHODS
Thirty rabbits were randomly separated into three groups: A control group (n=10, standard rabbit chow), a model group (n=10, control diet plus 30 g methionine/kg food), and a PFD group (n=10, model diet plus oral administration of 90 mg/day of PFD). After 14 weeks of arterial injury, histopathological changes were determined. Plasma homocysteine (Hcy) concentrations, lipid profiles and oxidant and antioxidant status were evaluated. Macrophage infiltration was assessed using immunohistochemical staining.
RESULTS
PFD supplementation decreased macrophage infiltration of iliac artery significantly without changes in blood lipids and Hcy concentrations. Compared with the model group, PFD restored superoxide dismutase and glutathione peroxidase activities and reduced malondialdehyde and reactive oxygen species levels. A high-methionine diet significantly increased neointimal area and the ratio between neointimal and media area. Systemic administration of PFD inhibited neointimal formation.
CONCLUSIONS
PFD can partly alleviate intimal hyperplasia by inhibiting inflammatory and oxidative stress response induced by HHcy during endothelial injury. It may be a potential therapeutic agent for the prevention and treatment of endothelial injury-associated diseases such as atherosclerosis.
Topics: Animals; Antioxidants; Glutathione Peroxidase; Homocysteine; Hyperhomocysteinemia; Hyperplasia; Lipids; Malondialdehyde; Methionine; Oxidants; Pyridones; Rabbits; Reactive Oxygen Species; Superoxide Dismutase; Tunica Intima
PubMed: 36210587
DOI: 10.1016/j.repc.2021.12.011 -
Scientific Reports Jun 2023As a basic building block of graphene-based materials, graphene oxide (GO) plays an important role in scientific research and industrial applications. At present,...
As a basic building block of graphene-based materials, graphene oxide (GO) plays an important role in scientific research and industrial applications. At present, numerous methods have been employed to synthesize GO, there are still some issues that need to be solved, thus it is of importance to develop a green, safe and low-cost GO preparation method. Herein, a green, safe and fast method was designed to prepare GO, namely, graphite powder was firstly oxidized in a dilute sulfuric acid solution (HSO, 6 mol/L) with hydrogen peroxide (HO, 30 wt%) as oxidant, and then exfoliated to GO by ultrasonic treatment in water. In this process, HO was the only oxidant, and no other oxidants were used, thus the explosive nature of GO preparation reaction in the conventional methods could be completely eliminated. This method has other advantages such as green, fast, low-cost and no Mn-based residues. The experimental results confirm that obtained GO with oxygen-containing groups has better adsorption property compared to the graphite powder. As adsorbent, GO can remove methylene blue (50 mg/L) and Cd (56.2 mg/L) from water with removal capacity of 23.8 mg/g and 24.7 mg/g, respectively. It provides a green, fast and low-cost method to prepare GO for some applications such as adsorbent.
Topics: Graphite; Hydrogen Peroxide; Powders; Water; Oxidants; Adsorption; Water Pollutants, Chemical; Kinetics
PubMed: 37291198
DOI: 10.1038/s41598-023-36595-2 -
The Science of the Total Environment Feb 2021Lead is a toxic environmental contaminant associated with current and historic mine sites. Here we studied the natural attenuation of Pb in a limestone cave system that...
Lead is a toxic environmental contaminant associated with current and historic mine sites. Here we studied the natural attenuation of Pb in a limestone cave system that receives drainage from the ancient Priddy Mineries, UK. Extensive deposits of manganese oxides were observed to be forming on the cave walls and as coatings in the stream beds. Analysis of these deposits identified them as birnessite (δ-MnO), with some extremely high concentrations of sorbed Pb (up to 56 wt%) also present. We hypothesised that these cave crusts were actively being formed by microbial Mn(II)-oxidation, and to investigate this the microbial communities were characterised by DNA sequencing, enrichment and isolation experiments. The birnessite deposits contained abundant and diverse prokaryotes and fungi, with ~5% of prokaryotes and ~ 10% of fungi closely related to known heterotrophic Mn(II)-oxidisers. A substantial proportion (up to 17%) of prokaryote sequences were assigned to groups known as autotrophic ammonia and nitrite oxidisers, suggesting that nitrogen cycling may play an important role in contributing energy and carbon to the cave crust microbial communities and consequently the formation of Mn(IV) oxides and Pb attenuation. Enrichment and isolation experiments showed that the birnessite deposits contained Mn(II)-oxidising microorganisms, and two isolates (Streptomyces sp. and Phyllobacterium sp.) could oxidise Mn(II) in the presence of 0.1 mM Pb. Supplying the enrichment cultures with acetate as a source of energy and carbon stimulated Mn(II)-oxidation, but excess organics in the form of glucose generated aqueous Mn(II), likely via microbial Mn(IV)-reduction. In this karst cave, microbial Mn(II)-oxidation contributes to the active sequestration and natural attenuation of Pb from contaminated waters, and therefore may be considered a natural analogue for the design of wastewater remediation systems and for understanding the geochemical controls on karst groundwater quality, a resource relied upon by billions of people across the globe.
Topics: Groundwater; Humans; Lead; Manganese; Manganese Compounds; Oxidation-Reduction; Oxides
PubMed: 33254903
DOI: 10.1016/j.scitotenv.2020.142312 -
Nature Jan 2020Functionalization of the β-C-H bonds of aliphatic acids is emerging as a valuable synthetic disconnection that complements a wide range of conjugate addition reactions....
Functionalization of the β-C-H bonds of aliphatic acids is emerging as a valuable synthetic disconnection that complements a wide range of conjugate addition reactions. Despite efforts for β-C-H functionalization in carbon-carbon and carbon-heteroatom bond-forming reactions, these have numerous crucial limitations, especially for industrial-scale applications, including lack of mono-selectivity, use of expensive oxidants and limited scope. Notably, the majority of these reactions are incompatible with free aliphatic acids without exogenous directing groups. Considering the challenge of developing C-H activation reactions, it is not surprising that achieving different transformations requires independent catalyst design and directing group optimizations in each case. Here we report a Pd-catalysed β-C(sp)-H lactonization of aliphatic acids enabled by a mono-N-protected β-amino acid ligand. The highly strained and reactive β-lactone products are versatile linchpins for the mono-selective installation of diverse alkyl, alkenyl, aryl, alkynyl, fluoro, hydroxyl and amino groups at the β position of the parent acid, thus providing a route to many carboxylic acids. The use of inexpensive tert-butyl hydrogen peroxide as the oxidant to promote the desired selective reductive elimination from the Pd(IV) centre, as well as the ease of product purification without column chromatography, render this reaction amenable to tonne-scale manufacturing.
Topics: Alkylation; Amino Acids; Carbon; Carboxylic Acids; Catalysis; Chemistry Techniques, Synthetic; Gemfibrozil; Hydrogen; Lactones; Ligands; Oxidants; Oxidation-Reduction; Palladium; tert-Butylhydroperoxide
PubMed: 31825951
DOI: 10.1038/s41586-019-1859-y -
Nature Communications May 2022Removal of organic micropollutants from water through advanced oxidation processes (AOPs) is hampered by the excessive input of energy and/or chemicals as well as the...
Removal of organic micropollutants from water through advanced oxidation processes (AOPs) is hampered by the excessive input of energy and/or chemicals as well as the large amounts of residuals resulting from incomplete mineralization. Herein, we report a new water purification paradigm, the direct oxidative transfer process (DOTP), which enables complete, highly efficient decontamination at very low dosage of oxidants. DOTP differs fundamentally from AOPs and adsorption in its pollutant removal behavior and mechanisms. In DOTP, the nanocatalyst can interact with persulfate to activate the pollutants by lowering their reductive potential energy, which triggers a non-decomposing oxidative transfer of pollutants from the bulk solution to the nanocatalyst surface. By leveraging the activation, stabilization, and accumulation functions of the heterogeneous catalyst, the DOTP can occur spontaneously on the nanocatalyst surface to enable complete removal of pollutants. The process is found to occur for diverse pollutants, oxidants, and nanocatalysts, including various low-cost catalysts. Significantly, DOTP requires no external energy input, has low oxidant consumption, produces no residual byproducts, and performs robustly in real environmental matrices. These favorable features render DOTP an extremely promising nanotechnology platform for water purification.
Topics: Decontamination; Environmental Pollutants; Oxidants; Water; Water Pollutants, Chemical
PubMed: 35637224
DOI: 10.1038/s41467-022-30560-9 -
Molecules (Basel, Switzerland) Jun 2022The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry,... (Review)
Review
The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry, resulting in a broad variety of useful organic molecules. These chemicals have potential uses in various functionalization procedures due to their non-toxic and environmentally friendly properties. As they are also strong electrophiles and potent oxidizing agents, the use of hypervalent iodine reagents in palladium-catalyzed transformations has received a lot of attention in recent years. Extensive research has been conducted on the subject of C-H bond functionalization by Pd catalysis with hypervalent iodine reagents as oxidants. Furthermore, the iodine(III) reagent is now often used as an arylating agent in Pd-catalyzed C-H arylation or Heck-type cross-coupling processes. In this article, the recent advances in palladium-catalyzed oxidative cross-coupling reactions employing hypervalent iodine reagents are reviewed in detail.
Topics: Catalysis; Indicators and Reagents; Iodides; Iodine; Oxidants; Oxidation-Reduction; Palladium
PubMed: 35745020
DOI: 10.3390/molecules27123900 -
Angewandte Chemie (International Ed. in... Aug 2022The development of C(sp )-H functionalization reactions that use common protecting groups and practical oxidants remains a significant challenge. Herein we report a...
The development of C(sp )-H functionalization reactions that use common protecting groups and practical oxidants remains a significant challenge. Herein we report a monoprotected aminoethyl thioether (MPAThio) ligand-enabled β-C(sp )-H lactamization of tosyl-protected aliphatic amides using tert-butyl hydrogen peroxide (TBHP) as the sole oxidant. This protocol features exceedingly mild reaction conditions, reliable scalability, and the use of practical oxidants and protecting groups. Further derivatization of the β-lactam products enables the synthesis of a range of biologically important motifs including β-amino acids, γ-amino alcohols, and azetidines.
Topics: Amides; Catalysis; Ligands; Oxidants; Palladium
PubMed: 35790471
DOI: 10.1002/anie.202207354 -
Antioxidants & Redox Signaling May 2023Coronary artery disease (CAD) is commonly treated using percutaneous coronary interventions (PCI). However, PCI with stent placement damages the endothelium, and... (Review)
Review
Coronary artery disease (CAD) is commonly treated using percutaneous coronary interventions (PCI). However, PCI with stent placement damages the endothelium, and failure to restore endothelial function may result in PCI failure with poor patient outcomes. Oxidative signaling is central to maintaining endothelial function. Potentiation of oxidant production, as observed post-PCI, results in endothelial dysfunction (ED). This review delves into our current understanding of the physiological role that endothelial-derived oxidants play within the vasculature and the effects of altered redox signaling during dysfunction. We then examine the impact of PCI and intracoronary stent placement on oxidant production in the endothelium, which can culminate in stent failure. Finally, we explore how recent advances in PCI and stent technologies aim to mitigate PCI-induced oxidative damage and improve clinical outcomes. Current PCI technologies exacerbate cellular oxidant levels, driving ED. If left uncontrolled, oxidative signaling leads to increased intravascular inflammation, restenosis, and neoatherosclerosis. Through the development of novel biomaterials and therapeutics, we can limit PCI-induced oxidant production, allowing for the restoration of a healthy endothelium and preventing CAD recurrence.
Topics: Humans; Percutaneous Coronary Intervention; Oxidants; Treatment Outcome; Coronary Artery Disease; Oxidation-Reduction
PubMed: 36641638
DOI: 10.1089/ars.2022.0204 -
Nature Communications Nov 2022Biogenic volatile organic compounds (BVOCs) affect climate via changes to aerosols, aerosol-cloud interactions (ACI), ozone and methane. BVOCs exhibit dependence on...
Biogenic volatile organic compounds (BVOCs) affect climate via changes to aerosols, aerosol-cloud interactions (ACI), ozone and methane. BVOCs exhibit dependence on climate (causing a feedback) and land use but there remains uncertainty in their net climatic impact. One factor is the description of BVOC chemistry. Here, using the earth-system model UKESM1, we quantify chemistry's influence by comparing the response to doubling BVOC emissions in the pre-industrial with standard and state-of-science chemistry. The net forcing (feedback) is positive: ozone and methane increases and ACI changes outweigh enhanced aerosol scattering. Contrary to prior studies, the ACI response is driven by cloud droplet number concentration (CDNC) reductions from suppression of gas-phase SO oxidation. With state-of-science chemistry the feedback is 43% smaller as lower oxidant depletion yields smaller methane increases and CDNC decreases. This illustrates chemistry's significant influence on BVOC's climatic impact and the more complex pathways by which BVOCs influence climate than currently recognised.
Topics: Ozone; Earth, Planet; Industry; Methane; Oxidants; Volatile Organic Compounds
PubMed: 36418337
DOI: 10.1038/s41467-022-34944-9