Metal-catalyzed Oxidation Research Articles

Sulfate formation is dominated by manganese-catalyzed oxidation of SO2 on aerosol surfaces during haze events

The formation mechanism of aerosol sulfate during wintertime haze events in China is still largely unknown. As companions, SO2 and transition metals are mainly emitted from coal combustion. Here, we argue that the transition metal-catalyzed oxidation of SO2 on aerosol surfaces could be the dominant sulfate formation pathway and investigate this hypothesis by integrating chamber experiments, numerical simulations and in-field observations. Our analysis shows that the contribution of the manganese-catalyzed oxidation of SO2 on aerosol surfaces is approximately one to two orders of magnitude larger than previously known routes, and contributes 69.2% ± 5.0% of the particulate sulfur production during haze events. This formation pathway could explain the missing source of sulfate and improve the understanding of atmospheric chemistry and climate change.

Oxidative Stress Conditions Result in Trapping of PHF-Core Tau (297-391) Intermediates.

The self-assembly of tau into paired helical filaments (PHFs) in neurofibrillary tangles (NFTs) is a significant event in Alzheimer’s disease (AD) pathogenesis. Numerous post-translational modifications enhance or inhibit tau assembly into NFTs. Oxidative stress, which accompanies AD, induces multiple post-translational modifications in proteins, including the formation of dityrosine (DiY) cross-links. Previous studies have revealed that metal-catalysed oxidation (MCO) using Cu2+ and H2O2 leads to the formation of DiY cross-links in two misfolding proteins, Aβ and α-synuclein, associated with AD and Parkinson’s disease respectively. The effect of MCO on tau remains unknown. Here, we examined the effect of MCO and ultra-violet oxidation to study the influence of DiY cross-linking on the self-assembly of the PHF-core tau fragment. We report that DiY cross-linking facilitates tau assembly into tau oligomers that fail to bind thioflavin S, lack β-sheet structure and prevents their elongation into filaments. At a higher concentration, Cu2+ (without H2O2) also facilitates the formation of these tau oligomers. The DiY cross-linked tau oligomers do not cause cell death. Our findings suggest that DiY cross-linking of pre-assembled tau promotes the formation of soluble tau oligomers that show no acute impact on cell viability.

Insight into the formation of organosulfur compounds from the reaction of methyl vinyl ketone with sulfite radical in atmospheric aqueous phase

The formation of organosulfur compounds through the reaction of organic species with sulfoxy radicals produced from the metal-catalyzed oxidation of S(IV) has become of recent concern, but the detailed formation mechanism still remains unanswered. In this work, we studied the mechanism of the initial reaction of methyl vinyl ketone (MVK) by SO3− radical and the subsequent sulfonate formation processes using DFT calculation. The results show that dissolved O2 addition to the initial product is more favorable than the addition of MVK to the initial product due to its lower activation free energy (6.19 kcal mol−1). The produced peroxyl radical can undergo bimolecular self-reactions, unimolecular decay and bimolecular reaction with other species (HSO3− and H2O) to form alcohols and ketones. Among them, two pathways are most likely to occur: one belongs to bimolecular self-reactions, whose activation free energy is 16.20 kcal mol−1; the other is derived from bimolecular reaction of peroxyl radical with HSO3−, which needs to overcome the activation free energy of 18.47 kcal mol−1. This work displays a complete description of the formation process of sulfonates and thus can provide some insights into the further study on the formation of organosulfur compounds.

Computational exploration of copper catalyzed vinylogous aerobic oxidation of unsaturated compounds

Selective oxidation is one of the most important and challenging transformations in both academic research and chemical industry. Recently, a highly selective and efficient way to synthesize biologically active γ-hydroxy-α,β-unsaturated molecules from Cu-catalyzed vinylogous aerobic oxidation of α,β- and β,γ-unsaturated compounds has been developed. However, the detailed reaction mechanism remains elusive. Herein, we report a density functional theory study on this Cu-catalyzed vinylogous aerobic oxidation of γ,γ-disubstituted α,β- and β,γ-unsaturated isomers. Our computational study unveils detailed mechanism for each elementary step, i.e. deprotonation, O2 activation, and reduction. Besides, the origin of regioselectivity, divergent reactivities of substrates as well as reducing agents, and the byproduct generation have also been investigated. Notably, the copper catalyst retains the + 2 oxidation state through the whole catalytic cycle and plays essential roles in multiple steps. These findings would provide hints on mechanistic studies and future development of transition metal-catalyzed aerobic oxidation reactions.

Molecular profiling and functional delineation of peroxiredoxin 3 (HaPrx3) from the big-belly seahorses (Hippocampus abdominalis) and understanding their immunological responses.

Peroxiredoxins (Prxs) are ubiquitously expressed antioxidant proteins that can protect aerobic organisms from oxidative stress. Here, we characterized the HaPrx3 homolog at the molecular level from big-belly seahorse (Hippocampus abdominalis) and analyzed its functional activities. The coding sequence of HaPrx3 consists of 726bp, which encodes 241 amino acids. The predicted molecular weight and theoretical isoelectric point (pI) of HaPrx3 was 26.20kDa and 7.04, respectively. Multiple sequence alignments revealed that the arrangements of domains, catalytic triads, dimers, and decamer interfaces of HaPrx3 were conserved among Prx sequences of other organisms. According to the phylogenetic analysis, HaPrx3 is clustered with the teleost Prx3 subclade. The highest transcript level of HaPrx3 was detected in the ovary tissue among fourteen healthy fish tissues. The mRNA levels of HaPrx3 in blood and liver tissues were significantly (P<0.05) upregulated in response to lipopolysaccharide (LPS), polyinosinic-polycytidylic (poly I:C), Edwardsiella tarda, and Streptococcus iniae, suggesting its involvement in immune responses. Under functional properties, insulin disulfide reduction assay confirmed the oxidoreductase activity of recombinant HaPrx3. A cell viability assay and Hoechst staining indicated cell survival ability and reduction of apoptotic activity, respectively. Moreover, a peroxidase activity assay verified peroxidase activity, while a metal-catalyzed oxidation (MCO) assay indicated the DNA protection ability of HaPrx3. Collectively, it is concluded that HaPrx3 may play a significant role in oxidative stress and immune responses against pathogenic infections in big-belly seahorses.

On the propagation of the OH radical produced by Cu-amyloid beta peptide model complexes. Insight from molecular modelling.

Oxidative stress and metal dyshomeostasis are considered as crucial factors in the pathogenesis of Alzheimer's disease (AD). Indeed, transition metal ions such as Cu(ii) can generate Reactive Oxygen Species (ROS) via O2 Fenton-like reduction, catalyzed by Cu(ii) coordinated to the Amyloid beta (Aβ) peptide. Despite intensive effort, the mechanisms of ROS-induced molecular damage remain poorly understood. In the present paper, we investigate on the basis of molecular modelling computations the mechanism of OH radical propagation toward the Aβ peptide, starting from the end-product of OH radical generation by Cu(ii)·Aβ. We evaluate (i) the OH oxidative capacity, as well as the energetics of the possible Aβ oxidation target residues, by quantum chemistry Density Functional Theory (DFT) on coordination models of Cu(ii)/OH/Aβ and (ii) the motion of the OH˙ approaching the Aβ target residues by classical Molecular Dynamics (MD) on the full peptide Cu(ii)/OH/Aβ(1-16). The results show that the oxidative capacity of OH coordinated Cu(ii)Aβ is significantly lower than that of the free OH radical and that propagation toward Aβ Asp and His residues is favoured over Tyr residues. These results are discussed on the basis of the recent literature on in vitro Aβ metal-catalyzed oxidation and on the possible implications for the AD oxidative stress mechanism.

Detoxification of toxin A and toxin B by copper ion-catalyzed oxidation in production of a toxoid-based vaccine against Clostridioides difficile

Clostridioides difficile infections (CDI) has emerged worldwide as a serious antimicrobial-resistant healthcare-associated disease resulting in diarrhea and pseudomembranous colitis. The two cytotoxic proteins, toxin A (TcdA) and toxin B (TcdB) are the major virulence factor responsible for the disease symptoms. We examined time-dependent oxidative detoxification of TcdA and TcdB using different molar ratios of protein:Cu2+:H2O2. The metal-catalyzed oxidation (MCO) reaction in molar ratios of 1:60:1000 for protein:Cu2+:H2O2 at pH 4.5 resulted in a significant 6 log10 fold reduction in cytotoxicity after 120-min incubation at 37 °C. Circular dichroism revealed that MCO-detoxified TcdA and TcdB had secondary and tertiary structural folds similar to the native proteins. The conservation of immunogenic epitopes of both proteins was tested using monoclonal antibodies in an ELISA, comparing our MCO-detoxification approach to a conventional formaldehyde-detoxification method. The oxidative detoxification of TcdA and TcdB led to an average 2-fold reduction in antibody binding relative to native proteins, whereas formaldehyde cross-linking resulted in 3-fold and 5-fold reductions, respectively. Finally, we show that mice immunized with a vaccine consisting of MCO-detoxified TcdA and TcdB were fully protected against disease symptoms and death following a C. difficile infection and elicited substantial serum IgG responses against both TcdA and TcdB. The results of this study present copper ion-catalyzed oxidative detoxification of toxic proteins as a method highly suitable for the rapid production of safe, immunogenic and irreversible toxoid antigens for future vaccine development and may have the potential for replacing cross-linking reagents like formaldehyde.

When Oxygen Can Be Toxic? A Mini Review

No one within the past later a long time had in intellect that the oxygen we breathe that contributes to sparing the lives of millions of patients and the most component of life has no harmful impacts on the body. Oxygen and water are the soul of living beings in common but beneath certain conditions such as weak immune status and lack of the body's ability to excrete natural antioxidants happens that the oxygen atom responds as a receptor for electrons, since its structure within the case of electronic soundness has two electrons that are not bound and as a result of progressive responses that create a few intermediate compounds. (Such as hydroxyl radical (•OH), hydrogen peroxide (H2O2) and superoxide anion (•O-2) that are hurtful to human’ organs and influence the extraordinary degree of cell division process and the physiological activities that it performs since it could be a capable oxidizer. These reactive atoms and free radicals inferred from atomic oxygen are called Reactive Oxygen Species (ROS). In spite of the fact that ROS play a key part as a flag-bearer in ordinary cell flag transduction and cell cycling, they have long been known to be a component of the immune reaction of safe cells to microbial invasion. ROS are created as byproducts during the mitochondrial electron transport of aerobic respiration or by oxido/reductase proteins and metal-catalyzed oxidation. The primary step in ROS generation is the reduction of atomic oxygen (O2) to anion superoxide (•O-2), is the antecedent of other responsive species. For this reason, the significance of normal cancer prevention agents has gotten to be vital to urge freed of the poisonous quality of ROS and particular antioxidant supplement ought to be given to improve the diet. Among the well-known antioxidants and cancer prevention agents are glutathione, vitamins C and D as well as enzymes such as, superoxide dismutase, catalase and peroxidase which contribute successfully to the disposal of these oxidizing substances.

Effects of Oxidation of Human Serum Albumin on the Binding of Aripiprazole.

Aripiprazole (ARP) is one of antipsychotics and binds to human serum albumin (HSA) with a high affinity. In this study, we investigated the binding characteristics of ARP to oxidized HSA as observed in chronic disease conditions. Oxidized HSAs were prepared using chloramine-T (CT-HSA) or metal-catalyzed oxidation system (MCO-HSA) in vitro, respectively. An increase in the carbonyl content was confirmed in oxidized HSAs. From the results of circular dichroism (CD) and tryptophan fluorescence spectra, no significant structural change of oxidized HSAs was observed. These results indicate that prepared HSAs are mildly oxidized and well reflects the status of HSA during chronic diseases. However, oxidized HSAs were observed to have a significant decrease in binding to ARP. The results of the induced CD spectrum suggested that ARP bound to oxidized HSAs with a similar orientation. These results suggest that oxidation of HSA during chronic disease state significantly affected the microenvironment of the binding site for ARP and binding capacity of HSA to ARP.

Protein Formulations Containing Polysorbates: Are Metal Chelators Needed at All?

Proteins are prone to post-translational modifications at specific sites, which can affect their physicochemical properties, and consequently also their safety and efficacy. Sources of post-translational modifications include oxygen and reactive oxygen species. Additionally, catalytic amounts of Fe(II) or Cu(I) can promote increased activities of reactive oxygen species, and thus catalyse the production of particularly reactive hydroxyl radicals. When oxidative post-translational modifications are detected in the biopharmaceutical industry, it is common practice to add chelators to the formulation. However, the resultant complexes with metals can be even more damaging. Indeed, this is supported here using an ascorbate redox system assay and peptide mapping. Ethylenediaminetetraacetic acid (EDTA) addition strongly accelerated the formation of hydroxyl radicals in an iron-ascorbate system, while diethylenetriaminepentaacetic acid (DTPA) addition did not. When Fe(III) was substituted with Cu(II), EDTA addition almost stopped hydroxyl radical production, whereas DTPA addition showed continued production, but at a reduced rate. Further, EDTA accelerated metal-catalysed oxidation of proteins, and thus did not protect them from Fe-mediated oxidative damage. As every formulation is unique, justification for EDTA or DTPA addition should be based on experimental data and not common practice.

Purification, biochemical characterization and DNA protection against oxidative damage of a novel recombinant superoxide dismutase from psychrophilic bacterium Halomonas sp. ANT108

A novel superoxide dismutase (referred hereafter to as HsSOD) from the psychrophilic bacterium Halomonas sp. ANT108 was purified and characterized. Escherichia coli (E. coli) was selected as the expression host. After recombinant HsSOD (rHsSOD) was purified, the specific activity was determined to be 213.47 U/mg with a purification ratio of approximately 3.61-fold. SDS-PAGE results demonstrated that rHsSOD has the molecular weight of 31.3 kDa, and type identification revealed that it belongs to Cu/Zn SOD. The optimum activity of rHsSOD was at 35 °C and 28% of its maximum activity remained at 0 °C. Further enzymatic assays indicated that rHsSOD exhibited thermal instability with a half-life of 20 min at 60 °C. Moreover, Cu2+ and Zn2+ significantly promoted rHsSOD activity. The values of Km and Vmax were 0.33 mM and 476.19 U/mg, respectively. Interestingly, rHsSOD could avoid DNA strand breakage formed by metal-catalyzed oxidation, demonstrating its antioxidant capacity. To summarize, the results suggested that rHsSOD has relatively high catalytic efficiency and oxidation resistance at low temperatures.

Catalytic oxidations by dehydrogenation of alkanes, alcohols and amines with defined (non)-noble metal pincer complexes

The present review highlights the latest developments in the field of transition metal-catalysed oxidations, in particular C–C–, C–O– and C–N-bond dehydrogenations.

Microfluidic investigation of the coalescence susceptibility of pea protein-stabilised emulsions: Effect of protein oxidation level

Proteins are used to stabilise oil-in-water (O/W) emulsions, and plant proteins are gaining interest as functional ingredients due to their higher sustainability potential compared to e.g., dairy proteins. However, their emulsifying properties are not that well understood, and depend on how their production process affects their physicochemical status. In the present work, we use the soluble fraction of commercial pea protein isolate to stabilise O/W emulsion droplets formed in a microfluidic device, and record coalescence stability after droplet formation (11–173 ms) for different protein concentrations (0.1–1 g/L). For the shortest adsorption times (11–65 ms) droplets were unstable, whereas for longer adsorption times differences in coalescence stability could be charted. Metal-catalysed oxidation of pea proteins performed for up to 24-h, prior to emulsion formation and analysis, increased the coalescence stability of the droplets, compared to fresh pea proteins. This may be explained by oxidation-induced protein fragmentation, leading to low molecular weight products. The Langmuir-Blodgett films looked highly heterogeneous for films prepared with fresh or mildly oxidised (3-h) proteins, and was more homogenous for 24-h oxidised proteins. This could be the cause for the observed differences in emulsion coalescence stability, structurally heterogeneous films being more prone to rupture.From this work, it is clear that the emulsifying properties of pea are strongly dependent on their chemical status, and associated structural properties at the molecular and supramolecular levels. The present microfluidic device is an efficient tool to capture such effects, at time scales that are relevant to industrial emulsification.

Impact of pyridine-2-carboxaldehyde-derived aroylhydrazones on the copper-catalyzed oxidation of the M112A PrP103-112 mutant fragment.

Misfolded prion protein (PrPSc) is known for its role in fatal neurodegenerative conditions, such as Creutzfeldt-Jakob disease. PrP fragments and their mutants represent important tools in the investigation of the neurotoxic mechanisms and in the evaluation of new compounds that can interfere with the processes involved in neuronal death. Metal-catalyzed oxidation of PrP has been implicated as a trigger for the conformational changes in protein structure, which, in turn, lead to misfolding. Targeting redox-active biometals copper and iron is relevant in the context of protection against the oxidation of biomolecules and the generation of oxidative stress, observed in several conditions and considered an event that might promote sporadic prion diseases as well as other neurodegenerative disorders. In this context, ortho-pyridine aroylhydrazones are of interest, as they can act as moderate tridentate ligands towards divalent metal ions such as copper(II). In the present work, we explore the potentiality of this chemical class as peptide protecting agents against the deleterious metal-catalyzed oxidation in the M112A mutant fragment of human PrP, which mimics relevant structural features that may play an important role in the neurotoxicity observed in prion pathologies. The compounds inhere studied, especially HPCFur, showed an improved stability in aqueous solution compared to our patented lead hydrazone INHHQ, displaying a very interesting protective effect toward the oxidation of methionine and histidine, processes that are related to both physiological and pathological aging.

Catalytic Water Oxidation Reaction with Use of Triarylaminium Radicals as Single-electron Oxidants and Pyridines as Bases

Transition metal-catalyzed water oxidation reaction is widely studied as an oxidation half reaction of artificial photosynthesis. To date, various investigations of model reaction systems under the...

Impacts of epicatechin on the formation of advanced lipid oxidation end products (ALEs) in a fish oil oxidation model

The purpose of present study is to investigate the inhibitory effects of epicatechin (EC) on the formation of ALEs. A chemical model containing bovine serum albumin (BSA, 1 mg/mL) and fish oil (0.5 mg/mL) under accelerated metal-catalyzed oxidation (37 °C, 72 h) was established to mimic the generation of ALEs. The incorporation of EC (0.25, 0.5, 1, and 2 mmol/L) significantly reduced TBARS content in a dose-dependent manner (P < 0.05). The enhanced protein fluorescence associated with the formation of ALEs was also attenuated by EC. Visualization of the inhibitory effects of EC on the formation of protein carbonyls and MDA-related ALEs was achieved by Western blot analysis which showed the fading of signal intensity in the native BSA monomer and protein cross-linking and aggregation at higher molecular weights. However, EC could not restore the protein total sulfhydryl, surface hydrophobicity and microstructure to their original state due to the complicated interaction between proteins and natural phenolic compounds in the presence of lipid oxidation products. Findings of the present study highlight EC as a promising inhibitor on the formation of dietary ALEs.

Differentiating the Effects of Oxidative Stress Tests on Biopharmaceuticals.

A rapid and broadly applicable method to assess relevant oxidative damage in biopharmaceuticals is important for lifecycle management of product quality. Multiple methods are currently employed as stress tests to induce oxidative damage for assessment of stability, safety, and efficacy. We compared two common methods for inducing oxidative damage to assess differences in impact on bioactivity and structure of the biopharmaceuticals. Biopharmaceuticals were treated with either metal-catalyzed oxidation (MCO) conditions or the reactive-oxygen species (ROS) inducer 2,2'-Azobis(2-amidinopropane) dihydrochloride (AAPH), then analyzed for changes in structure and bioactivity. We demonstrate that commonly used chemical methods for assessing oxidation yield distinct oxidation profiles for each of the biotechnology products analyzed, including monoclonal antibodies. We further report oxidant- and product-specific changes in bioactivity under oxidizing conditions, along with differential oxidation on the molecular subunits of monoclonal antibodies. Our results highlight the need for product-specific optimization and selection of orthogonal, relevant oxidizers when characterizing stress responses in biopharmaceuticals.

Cloning and functional characterization of rockfish peroxiredoxin 4 homolog with its innate immune responses

The fourth member of the typical 2-cysteine peroxiredoxin (Prx4) is a well-known antioxidant enzyme, which reduces different peroxides in their catalytic process. The present study reports the identification of the rockfish Sebastes schlegelii Prx4 (SsPrx4) at a genomic level, as well as the characterization of its structural and functional features. SsPrx4 harbors a complete ORF of 786 bp encoding a polypeptide (29 kDa) of 262 amino acids (aa) with an isoelectric point of 6.2. Thioredoxin 2 domain was prominent in the SsPrx4 sequence, which has a signal peptide (31 bp) at the N-terminus. Hence, the SsPrx4 may be functionally active in the cytoplasm of rockfish cells. Moreover, two VCP motifs and three catalytic triad residues (112T, 115C, 191R) were identified in the SsPrx4 protein sequence. A peroxidatic cysteine (115CP) and resolving cysteines (236CR) were detected at the VCP motifs. The rockfish Prx4 genome consists of seven exons, which are similar to the architecture of other Prx4 orthologs. The deduced amino acid sequence of SsPrx4 shares a relatively high amino acid sequence identity (91.6%) and close evolutionary relationship with Miichthys miiuy and Stegastes partitus Prx4. The potential for scavenging extracellular H2O2 was evidenced by the purified recombinant SsPrx4 protein (rSsPrx4) in vitro system. Moreover, rSsPrx4 may protect the plasmid DNA in a metal-catalyzed oxidation system and catalyze the reduction of an insulin disulfide bond. Quantitative real-time PCR revealed that SsPrx4 mRNA was ubiquitously expressed in fourteen different tissues, with the highest expression observed in the liver followed by the ovary, and kidney tissues. Transcriptional modulations were observed in liver and spleen tissues of rockfish after injecting them with bacterial stimuli, including Streptococcus iniae, LPS, and a viral mimic of poly I:C. Together, the results suggest that SsPrx4 may play an important role in both the antioxidant and innate immune defense of black rockfish. These findings provide structural and functional insights into the SsPrx4 of the teleost.

Dietary ascorbic acid restriction in GNL/SMP30-knockout mice unveils the role of ascorbic acid in regulation of somatic and visceral pain sensitivity

Cav3.2 T-type Ca2+ channels are expressed in the primary afferents and play a pronociceptive role. The activity of Cav3.2 is enhanced by H2S, a gasotransmitter, and suppressed by ascorbic acid (vitamin C) through metal-catalyzed oxidation of the Zn2+-binding His191 in Cav3.2. Since rodents, but not humans, are capable of synthesizing ascorbic acid, the present study examined the role of ascorbic acid in nociceptive processing, using the mice lacking GNL/SMP30, an enzyme essential for ascorbic acid biosynthesis. Intraplantar and intracolonic administration of NaHS, an H2S donor, caused somatic allodynia and referred hyperalgesia, respectively, and repeated treatment with paclitaxel produced neuropathic allodynia in wild-type mice, all of which were suppressed by ascorbic acid or T-type Ca2+ channel blockers. Dietary ascorbic acid restriction caused dramatic decreases in plasma and tissue ascorbic acid levels in GNL/SMP30-knockout, but not wild-type, mice. The ascorbic acid restriction enhanced the somatic and visceral hypersensitivity following intraplantar and intracolonic NaHS, respectively, and paclitaxel-induced neuropathy in GNL/SMP30-knockout mice, while it had no such effect in wild-type mice. Together, our data unveil the critical role of ascorbic acid in regulating somatic and visceral pain sensitivity and support accumulating clinical evidence for the usefulness of ascorbic acid in pain management.

High-throughput Carbonyl Content Method of Therapeutic mAb using size-exclusion chromatography with ultraviolet and fluorescence detection

Monoclonal antibody (mAb), one of the major types of therapeutic proteins in the pharmaceutical industry, is predominantly manufactured using mammalian cell culture [1]. Oxidative stress, potentially present during cell culture process, may increase the protein carbonyl content in the mAb product, which was reported to positively correlate with aggregate burst rate during storage [2]. In order to monitor carbonyl content during mAb process development, we developed a high-throughput screening method for therapeutic mAbs using size-exclusion chromatography followed by ultraviolet and fluorescence detection (SEC-UV/FL), optimized from a fluorescein thiosemicarbazide (FTC) semi-microplate method. The method demonstrated a good correlation with conventional ELISA assay and FTC-based fluorometric semi-microplate method with improved throughput and precision. The method was successfully applied in three case studies to improve our understanding of mAb carbonylation, including the impact of metal-catalyzed oxidation on an IgG4 mAb, comparison of carbonyl content between several mAbs expressed by CHO cell culture with human serum antibody pool, as well as the surface charge property of carbonylated mAb assessed by ion-exchange chromatography.