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Environmental persistent free radicals (EPFRs) derived from chlorophenols, triggered by light or heat exposure, pose significant ecological concerns, yet the impact of chlorine substituents on EPFRs formation and reactivity remains inadequately understood. Through an intentional synthesis of chlorophenol-derived EPFRs with varying chlorine contents and positioning, we elucidated the role of chlorine in the photoactivation of molecular oxygen. Our combined experimental and theoretical analysis reveals that these EPFRs are primarily oxygen-centered phenoxy radicals, establishing a direct link between chlorine substitution patterns and their ability to activate molecular oxygen under visible light. Increased chlorine content enhances EPFRs formation by elevating the positive charge on the phenolic hydroxyl group's hydrogen atom, facilitating its removal. Moreover, the capability of EPFRs to activate molecular oxygen was directly correlated with chlorine content, with 2,3,5,6-tetrachlorophenol-derived EPFRs showcasing the highest activity. This activity is attributed to their structural propensity for TCSQ·- species generation. Furthermore, our study established a significant correlation between the toxicity and activity of EPFRs, emphasizing the critical role of halogen substituents in determining the reactivity of EPFRs. These insights contribute to our understanding of their environmental and toxicological ramifications, underscoring the imperative for continued research aimed at mitigating their detrimental impacts.

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Our bodies are constantly exposed to or producing free radicals nearly on a daily basis. These highly reactive molecules are generated through a variety of internal and external processes and pathways within the body. If these free radicals are not neutralized by antioxidants, they can lead to a state of oxidative stress, which has been linked to a wide range of severe and debilitating disorders affecting various systems in the human body. This involves neurodegenerative diseases, diabetes, atherosclerosis, fatty liver, inflammation, and aging. Thankfully, the human body is armed with a repertoire of powerful antioxidants with different natures and modes of action. The recent decades witnessed the publication of enormous papers proving antioxidant activity of a novel synthesized compound, plant extract, or a purified drug in vitro, in vivo, and even on human beings. However, the efficacy of antioxidant therapies in clinical trials, including selenium, vitamin C, vitamin E, and vitamin A, has been notably inconsistent. This inconsistency can be primarily ascribed to different factors related to the nature of free radical generation, purpose and the specific type of therapy employed, and the intricate oxidative stress connected network, among others. Collectively, these factors will be explored in this review article to decipher the observed shortcomings in the application of antioxidant therapies within clinical settings.

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Tetrabromobisphenol A bis (allyl ether) (TBBPA-BAE) represents an extensively used brominated flame retardant (BFRs) in the production of many fields and their phototransformation in natural water is still unclear. The environmentally persistent free radicals (EPFRs) with preserved activities could exist in the environment for a long time and involve in the phototransformation of many organic pollutants. Here, the photodegradation of TBBPA-BAE with the degradation rate constant (k= 0.060 h-1) under simulate sunlight and the promoting effect of EPFRs on TBBPA-BAE photodegradation (k = 0.135 h-1) were investigated. According to the detected photogenerated electrons (e-) and singlet oxygen (1O2) rather than hydroxyl radicals (•OH) by the electron paramagnetic resonance (EPR), the effect mechanism may not be related to the typical •OH induced by EPFRs. The possible transformation pathways of the ether cleavage, hydrolysis and hydroxylation of propenyl bond and the debromination were proposed by the primary byproducts identified by UPLC-Q-Exactive Orbitrap MS. EPFRs caused a further debromination and ether cleavage and probably be due to EPFRs directly providing electrons to TBBPA-BAE which promoted the photodegradation of TBBPA-BAE, and their reaction mechanism needed further attention. Overall, this study provided useful information to understand the role of EPFRs on phototransformation of TBBPA-BAE in water.

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Carbon dots (CDs) are an emerging type of fluorescent carbon nanomaterial with broad application prospects. Among them, photochromic CDs have been widely used in the field of optoelectronic devices but rarely in ultraviolet (UV) detection. In this work, we successfully developed photochromic CDs that exhibit reversible emission under light stimulation in an amine solvent system. Notably, the CDs showed ultrafast photochromic behavior in diethylamine solvent, shifting the fluorescence color from cyan-green to orange-red after 2 s of irradiation, with the solution color changing from pale yellow to pale purple. Furthermore, this performance could recover without additional stimuli, simply by standing for several tens of seconds. Structural analysis indicated that rapid photochromism arises from changes in the surface functional group radicals of the CDs, with the reversibility attributed to fluctuation in these radicals. Leveraging the excellent photochromic properties of CDs, we further developed a device for detecting UV indices in sunlight. This opens up broad prospects for developing high-performance UV detection devices based on CDs.

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Cladosporium cladosporioides are the pigmented soil fungi containing melanin. The aim of this work was to determine the influence of amphotericin B on free radicals in the natural melanin isolated from pigmented fungi Cladosporium cladosporioides and to compare it with the effect in synthetic DOPA-melanin. Electron paramagnetic resonance (EPR) spectra were measured at X-band (9.3 GHz) with microwave power in the range of 2.2-70 mW. Amplitudes, integral intensities, linewidths of the EPR spectra, and g factors, were analyzed. The concentrations of free radicals in the tested melanin samples were determined. Microwave saturation of EPR lines indicates the presence of pheomelanin in addition to eumelanin in Cladosporium cladosporioides. o-Semiquinone free radicals in concentrations ~1020 [spin/g] exist in the tested melanin samples and in their complexes with amphotericin B. Changes in concentrations of free radicals in the examined synthetic and natural melanin point out their participation in the formation of amphotericin B binding to melanin. A different influence of amphotericin B on free radical concentration in Cladosporium cladosporioides melanin and in DOPA-melanin may be caused by the occurrence of pheomelanin in addition to eumelanin in Cladosporium cladosporioides. The advanced spectral analysis in the wide range of microwave powers made it possible to compare changes in the free radical systems of different melanin polymers. This study is important for knowledge about the role of free radicals in the interactions of melanin with drugs.

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This study systematically investigated the photo-aging of polyvinyl chloride (PVC) in deionized water, estuary water, and seawater. As the concentration of Cl- increases, the carbonyl index (CI) of PVC during photo aging also increases, indicating that Cl- plays a dominant role in PVC photoaging in the environment, which enhance carbonyl index and •OH radical accumulation. Unlike previous studies, this study discovered that halogen radicals were also generated during PVC aging. Compared to •OH radicals, halogen radicals exhibit stronger selectivity and are more conducive to the photo aging of PVC. Additionally, it was found that PVC shows specific toxicity to Paramecia caudatum at various concentrations both before and after aging, affecting the reproduction process of Paramecia caudatum. This study elucidates the mechanism by which anions in natural water bodies affect the rate of PVC aging, providing a scientific basis for understanding the photodegradation of MPs in the ocean.

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The efficient elimination of bacteria within the dentinal tubules has been hindered by the poor deposition and short residence of disinfecting agents. Meanwhile, the current irrigant (e.g., NaClO, 5.25 %) shows severe adverse effects on the surrounding soft tissues because of its inherent high irritancy. To address this issue, this work reports an in situ generated sonosensitizer to handle the biofilm in dentinal tubules with minimal adverse effects. The production of nanoscale sonosensitizer involves the concurrent delivery of H2O2 (0.01 %), ferrocene derivative (Fc), and indocyanine green (ICG). With ultrasound treatment, the reaction between H2O2 and Fc liberated Fe3+ that was further complexed with ICG to generate the nanoscale sonosensitizer in situ, followed by singlet oxygen production for potent disinfecting action. Because the above cascade reactions occur within the confined dentinal tubules, the generated ICG-Fe3+ nanosensitizer would show prolonged retention therein. The anti-bacterial potency of nanosensitizer was demonstrated in petrodish and ex vivo biofilm models. Meanwhile, the transmission electron microscope imaging of biofilm and cytotoxicity assay in L929 fibroblast cells proved the superiority of nanosensitizer against NaClO regarding adverse effects. The current work opens new avenues of biofilm elimination in dentinal tubules, showing a high translation potential.

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Ficus auriculata Lour. (Moraceae) is an underutilized wild edible fruit widely consumed for its nutritional properties. The present study aimed to determine the phytochemical composition and in vitro antioxidant, enzyme inhibitory, anti-inflammatory and anti-cancerous properties of the F. auriculata fruit extracts through in vitro digestion (oral, gastric and intestinal phases). The extracts were obtained by hot extraction and cold maceration methods using aqueous and methanolic solvents. Major phytoconstituents identified through LC-MS was subjected to molecular docking against the target proteins. The elemental analysis shows the presence of major elements; high levels of total phenolics (124.61 ± 0.82 mg gallic acid equivalent/g), flavonoids (76.38 ± 0.82 mg quercetin equivalent/g), vitamin E (32.48 ± 0.09 mg alpha-tocopherol equivalent/g), and carbohydrate (34.59 ± 0.45 mg glucose equivalent/g) in hot extracted methanolic undigested extract (HEM UD) and high level of total protein (124.71 ± 0.34 mg bovine serum albumin equivalent/g) in cold extracted methanolic undigested fruit extract were found. HEM UD showed high antioxidant activity in 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), 2,2-diphenyl-1-picryl-hydrazyl, and superoxide radical scavenging assays with IC50 of 53.30 ± 0.57, 80.69 ± 0.12, and 65.47 ± 1.13 µg/mL, respectively. The HEM UD extract also potentially inhibited the enzyme activity of α-amylase, α-glucosidase, tyrosinase, and protein denaturation (IC50 of 67.76 ± 1.22, 83.18 ± 1.23, 87.24 ± 1.15, and 65.76 ± 0.60 µg/mL). The most potent extract (HEM UD) was studied for its anticancer effects by MTT assay against the MCF-7 and HeLa cell lines and showed the IC50 of 89.80 ± 0.56 and 60.76 ± 0.04 µg/mL, respectively. The LC-MS analysis elucidated ten phytoconstituents. Based on the molecular docking study, querciturone could potentially be an effective constituent in treating diabetes and inflammation-related issues. The findings indicated the ability of F. auriculata fruits as a promising functional food.

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Lead is one of the major environmental pollutants which is highly toxic to plants and living beings. The current investigation thoroughly evaluated the synergistic effects of oxalic acid (OA) and salicylic acid (SA) on Zea mays L. plants subjected to varying durations (15, 30, 30, and 45 days) of lead (Pb) stress. Besides, the effects of oxalic acid (OA) combined with salicylic acid (SA) for different amino acids at various periods of Pb stress were also investigated on Zea mays L. The soil was treated with lead nitrate Pb (NO3)2 (0.5 mM) to induce Pb stress while the stressed plants were further treated using oxalic acid (25 mg/L), salicylic acid (25 mg/L), and their combination OA + SA (25 mg/L each). Measurements of protein content, malondialdehyde (MDA) levels, guaiacol peroxidase (GPOX) activity, catalase (CAT) activity, GSH content, and Pb concentration in maize leaves were done during this study. MDA levels increased by 71% under Pb stress, while protein content decreased by 56%, GSH content by 35%, and CAT activity by 46%. After treatment with SA, OA, and OA+SA, there was a significant reversal of these damages, with the OA+SA combination showing the highest improvement. Specifically, OA+SA treatment led to a 45% increase in protein content and a 39% reduction in MDA levels compared to Pb treatment alone. Moreover, amino acid concentrations increased by 68% under the Pb+OA+SA treatment, reflecting the most significant recovery (p < 0.0001).

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Alginate is a natural polysaccharide obtained from brown seaweeds and having advantageous health usefulness, was employed extensively in nutraceutical sectors and the pharmaceutical industry. This research was devoted for optimization of alginate extraction from different brown seaweeds. A Box-Behnken Design (BBD) was used for the optimization of alginate extraction from Padina pavonica by analyzing the influence of temperature (30, 40, and 50 °C), time (60, 120, and 180 min), and alkaline concentration (1 %, 2 %, and 3 %) on extraction yield and uronic acid content. The optimal conditions recorded to maximize the alginate yield and its uronic content were an alkali concentration of 2.5 % and a temperature of 39.95 °C for 102.5 min. The optimized parameters achieved from BBD were used to compare alginate extraction from P. pavonica, Sargassum cinereum, Turbinaria turbinata, and Dictyota dichotoma. FTIR, 1H NMR, and HPLC were used to characterize the extracted alginate. The bioactivity of alginate against free radicals, breast cancer cells (MCF-7), some pathogenic microbes, and SARS-CoV-2 viruses was tested. Under the optimized conditions, alginate was extracted from P. pavonica at a rate of 21.13 ± 2.47 % DW, S. cinereum at 24.08 ± 0.33 % DW g/L, T. turbinata at 17.47 ± 0.26 % DW, and D. dichotoma at a rate of 19.57 ± 3.60 % DW. The alginate extracted from D. dichotoma showed the highest antioxidant, anticancer, and antiviral activity.

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Bee-derived pharmaceutical products, including propolis (PRO) and royal jelly (ROJ), possess outstanding pharmacological properties. However, their efficiency in counteracting the deleterious influences of cadmium (Cd) in testes and the relevant mechanisms entail further investigations. Therefore, this study sheds light on the therapeutic efficacy of PRO and ROJ against testicular dysfunction and infertility induced by Cd. Toward this end, 30 mature male Wistar albino rats were randomly divided into six groups (5 animals/group), including (I) control, (II) Cd, (III) PRO, (IV) ROJ, (V) PRO + Cd, and (VI) ROJ + Cd groups. Furthermore, antioxidant factors, semen quality, hormonal levels, steroidogenic enzymes, and genotoxicity were assessed. Moreover, histopathological and ultrastructural attributes and offspring rates were investigated. The Cd-treated group revealed marked reductions in reduced glutathione (GSH), total antioxidant capacity (TAC), and superoxide dismutase (SOD) with an amplification of lipid peroxidation in testes, indicating disruption of the antioxidant defense system. Furthermore, myeloperoxidase (MPO) activity and DNA damage were significantly heightened, implying inflammation and genotoxicity, respectively. Moreover, steroidogenic enzymes, including 17ß-Hydroxy Steroid Dehydrogenase 3 (HSD17b3), 3ß-Hydroxy Steroid Dehydrogenase 2 (HSD3b2), 17α-hydroxylase/17,20-lyase (CYP17A1), and steroid 5α-reductase 2 (SRD5A2) were markedly diminished accompanied with disorders in luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone. Besides, spermatozoa quality was reduced, associated with a diminution in the diameter of seminiferous tubules. By contrast, PRO or ROJ significantly protected and/or counteracted the Cd-induced pathophysiological consequences, ameliorating antioxidant and inflammatory biomarkers, steroidogenic enzymes, hormonal levels, and sperm properties, along with lessening DNA impairments. Critically, histological and ultrastructural analyses manifested several anomalies in the testicular tissues of the Cd-administered group, including the Leydig and Sertoli cells and spermatozoa. Conversely, PRO or ROJ sustained testicular tissues' structure, enhancing spermatozoa integrity and productivity. Interestingly, treatment with PRO or ROJ improved fertility indices through offspring rates compared to the Cd-animal group. Our data suggest that PRO is a more effective countermeasure than ROJ against Cd toxicity for securing the delicate testicular microenvironment for spermatogenesis and steroidogenesis.

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As a result of their unique and novel properties, nanocomposites have found applications in a wide variety of fields. The purpose of this study is to demonstrate the ability to synthesize nanoparticles consisting of zinc oxide (ZnO) and graphene oxide (GO) via sol-gel techniques. An x-ray diffractometer (XRD) as well as a UV-visible spectrometer were used to determine the crystalline and optical characteristics of the prepared samples. A hexagonal wurtzite crystal structure was observed in both pure ZnO nanoparticles and those that contain GO based on XRD results. It was estimated that the average crystallite size is based on the broadening of x-ray lines. In comparison with pure ZnO, the antimicrobial properties were enhanced when GO was incorporated with ZnO. In addition, experiments on the absorption edge indicated the presence of a red shift as a result of the incorporation of GO. When GO is incorporated in quantitative amounts, the bandgap value of pure ZnO decreased. FTIR spectra exhibit a band of absorption at 486 cm-1, which confirms Zn-O stretching in both samples. SEM images reveal a random pattern of structural features on the surface of the prepared samples. According to the EDX spectrum, pure GO nanoparticles and those doped with ZnO contain 61%-64% zinc and 32%-34% oxygen, respectively. When annealed at a higher temperature, ZnO NPs produced more H2 with a narrower bandgap than before annealing. In addition, methyl blue (MB) was used as an example of an organic compound in order to investigate the potential photocatalytic properties of nanoparticles with ZnO doped GO. In addition to DPPH assays, ZnO nanoparticles and ZnO doped GO nanoparticles were tested for their ability to scavenge free radicals. Comparing ZnO doped GO NPs with pure ZnO, these nanoparticles showed increased antioxidant activity. Based on the increased zone of inhibition observed for pure ZnO and ZnO doped GO (5, 10, 50, and 100 mg/mL), the antibacterial activity of pure ZnO and ZnO doped GO is concentration dependent. A detailed discussion of the results of the study demonstrated that ZnO doped GO and pure ZnO are toxic in different ways depending on how long they survive in degreased Zebrafish embryos and how fast they decompose. RESEARCH HIGHLIGHTS: The scope of the manuscript was under the results of the study confirmed that both nanoparticles exhibited concentration dependent antioxidative activity. Determined that 89% of methyl orange dye can be degraded photocatalytically. ZnO nanoparticles were found to be 74.86% antioxidant at a concentration of 50 g/mL in the present study. At a concentration of 50 g/mL, ZnO doped GO NPs showed 79.1% antioxidant activity. Photocatalytic degradation mechanism scheme is implicit in the photoexcited charge carrier transportation path is observed for all the samples. Survival rate of zebrafish embryos was shown to decrease with increasing concentrations of ZnO and zinc oxide plus GO nanoparticles.

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A comparative study explored how photoaging, ozonation aging, and Fenton aging affect tire wear particles (TWPs) and their phosphorus (P) removal in activated sludge. Aging altered TWPs' properties, increasing surface roughness, porosity, and generating more small particles, especially environmental persistent free radicals (EPFRs) in ozonation and Fenton aging. Post-aging TWPs (50 mg/L) inhibited sludge P removal significantly (p < 0.05), with rates of 44.3% and 59.6% for ozonation and Fenton aging, respectively. In addition, the metabolites involved in P cycling (poly-ß-hydroxyalkanoates: PHA and glycogen) and essential enzymes (Exopolyphosphatase: PPX and Polyphosphate kinase: PPK) were significantly inhibited (p < 0.05). Moreover, TWPs led to a decrease in microbial cells within the sludge and altered the community structure, a situation exacerbated by the aging of TWPs. P-removing bacteria decreased (e.g., Burkholderia, Candidatus), while extracellular polymeric substance-secreting bacteria increased (e.g., Pseudomonas, Novosphingobium). Pearson correlation analysis highlighted EPFRs' role in TWPs' acute toxicity to microbial cells, yet, emphasizing particle size's impact on the sludge system's purification and community structure.

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Biochar is commonly utilized as an electrode material in supercapacitors. However, the conventional carbonization process often results in macromolecular compounds, which obstruct the porous structure of carbon materials, thereby reducing their capacitance. Dielectric barrier discharge low-temperature plasma (DLTP) is a technology that transforms gases into highly excited states, utilizing high-energy particles for enhanced energy applications. This study investigated the effects of DLTP on the electrochemical performance of bamboo charcoal (BC), utilizing bamboo shavings (BS) as the carbon source. The results indicated that the specific capacitance of BC varied under different atmospheric conditions, input voltages, and treatment durations, thereby achieving a maximum increase of 144 F/g. Furthermore, when combined with KOH activation, DLTP modification further enhanced the specific capacitance of BC to 237 F/g. The DLTP treatment enhanced the specific surface area and the types of functional groups in BC, thereby leading to a significant enhancement of its electrochemical properties.

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Free radicals (FRs), also known as reactive oxygen species (ROS), are usually established in the body when adequate oxygen depletion occurs. Oxidative stress and the establishment of FRs in the body are mainly caused by high metabolic activity, the need for rapid growth, inadequate flock management, exposure to viral and bacterial microorganisms, and adverse environmental conditions. Furthermore, FRs can also be produced during the activity of phagocytes when they depend on the action of ROS to kill the engulfed pathogen. FRs have very adverse effects on all cells, particularly the cells of the immune system. They are extremely erratic and reactive molecules that directly harm DNA, cellular proteins, lipids, and carbohydrates within cells. Antioxidants are substances that can eliminate and neutralize FRs within the body and free the body from the oxidative stress that occurs due to the accumulation of FRs. Many vitamins and minerals support the activity and effect of the immune system in fighting against microbes and cancer, which mostly depend on their antioxidant elements to diminish the negative impact of FRs in the body. Examples are vitamin C, vitamin E, superoxide dismutase, selenium, glycine, cofactors of glutathione peroxidase, manganese, essential oils, and phenolic compounds.

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Environmentally persistent free radicals (EPFRs) play an important role in aerosol effects on air quality and public health, but their atmospheric abundance and sources are poorly understood. We measured EPFRs contained in PM2.5 collected in Fairbanks, Alaska, in winter 2022. We find that EPFR concentrations were enhanced during surface-based inversion and correlate strongly with incomplete combustion markers, including carbon monoxide and elemental carbon (R2 > 0.75). EPFRs exhibit moderately good correlations with PAHs, biomass burning organic aerosols, and potassium (R2 > 0.4). We also observe strong correlations of EPFRs with hydrocarbon-like organic aerosols, Fe and Ti (R2 > 0.6), and single-particle mass spectrometry measurements reveal internal mixing of PAHs, with potassium and iron. These results suggest that residential wood burning and vehicle tailpipes are major sources of EPFRs and nontailpipe emissions, such as brake wear and road dust, may contribute to the stabilization of EPFRs. Exposure to the observed EPFR concentrations (18 ± 12 pmol m-3) would be equivalent to smoking ∼0.4-1 cigarette daily. Very strong correlations (R2 > 0.8) of EPFR with hydroxyl radical formation in surrogate lung fluid indicate that exposure to EPFRs may induce oxidative stress in the human respiratory tract.

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In this paper, we demonstrated the biological effects of acute low-dose neutrons on the whole body of rats and investigated the impact of that level of neutron dose to induce an in vivo radio-adaptive response. To understand the radio-adaptive response, the examined animals were exposed to acute neutron radiation doses of 5 and 10 mSv, followed by a 50 mSv challenge dose after 14 days. After irradiation, all groups receiving single and double doses were kept in cages for one day before sampling. The electron paramagnetic resonance (EPR) method was used to estimate the radiation-induced radicals in the blood, and some hematological parameters and lipid peroxidation (MDA) were determined. A comet assay was performed beside some of the antioxidant enzymes [catalase enzyme (CAT), superoxide dismutase (SOD), and glutathione (GSH)]. Seven groups of adult male rats were classified according to their dose of neutron exposure. Measurements of all studied markers are taken one week after harvesting, except for hematological markers, within 2 h. The results indicated lower production of antioxidant enzymes (CAT by 1.18-5.83%, SOD by 1.47-17.8%, and GSH by 11.3-82.1%). Additionally, there was an increase in red cell distribution width (RDW) (from 4.61 to 25.19%) and in comet assay parameters such as Tail Length, (from 6.16 to 10.81 µm), Tail Moment, (from 1.17 to 2.46 µm), and percentage of DNA in tail length (DNA%) (from 9.58 to 17.32%) in all groups exposed to acute doses of radiation ranging from 5 to 50 mSv, respectively. This emphasizes the ascending harmful effect with the increased acute thermal neutron doses. The values of the introduced factor of radio adaptive response for all markers under study reveal that the lower priming dose promotes a higher adaptation response and vice versa. Ultimately, the results indicate significant variations in DNA%, SOD enzyme levels, EPR intensity, total Hb concentration, and RDWs, suggesting their potential use as biomarkers for acute thermal neutron dosimetry. Further research is necessary to validate these measurements as biodosimetry for radiation exposure, including investigations involving the response impact of RAR with varied challenge doses and post-irradiation behavior.

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With the increasing use of vaping devices that deliver high levels of nicotine (NIC) to the lungs, sporadic lung injury has been observed. Commercial vaping solutions can contain high NIC concentrations of 150 mM or more. With high NIC levels, its metabolic products may induce toxicity. NIC is primarily metabolized to form NIC iminium (NICI) which is further metabolized by aldehyde oxidase (AOX) to cotinine. We determine that NICI in the presence of AOX is a potent trigger of superoxide generation. NICI stimulated superoxide generation from AOX with Km = 2.7 µM and Vmax = 794 nmol/min/mg measured by cytochrome-c reduction. EPR spin-trapping confirmed that NICI in the presence of AOX is a potent source of superoxide. AOX is expressed in the lungs and chronic e-cigarette exposure in mice greatly increased AOX expression. NICI or NIC stimulated superoxide production in the lungs of control mice with an even greater increase after chronic e-cigarette exposure. This superoxide production was quenched by AOX inhibition. Furthermore, e-cigarette-mediated NIC delivery triggered oxidative lung damage that was blocked by AOX inhibition. Thus, NIC metabolism triggers AOX-mediated superoxide generation that can cause lung injury. Therefore, high uncontrolled levels of NIC inhalation, as occur with e-cigarette use, can induce oxidative lung damage.

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The formation of environmentally persistent free radicals (EPFRs) is mediated by the particulate matter's surface, especially transition metal oxide surfaces. In the context of current atmospheric complex pollution, various atmospheric components, such as key atmospheric oxidants ·OH and O3, are often absorbed on particulate matter surfaces, forming particulate matter surfaces containing ·OH and O3. This, in turn, influences EPFRs formation. Here, density functional theory (DFT) calculations were used to explore the formation mechanism of EPFRs by C6H5OH on α-Fe2O3(0001) surface containing the ·OH and O3, and compare it with that on clean surface. The results show that, compared to EPFRs formation with an energy barrier on a clean surface, EPFRs can be rapidly formed through a barrierless process on these surfaces. Moreover, during the hydrogen abstraction mechanism leading to EPFRs formation, the hydrogen acceptor shifts from a surface O atom on a clean surface to an O atom of ·OH or O3 on these surfaces. However, the detailed hydrogen abstraction process differs on surfaces containing oxidants: on surfaces containing ·OH, it occurs directly through a one-step mechanism, while, on surfaces containing O3, it occurs through a two-step mechanism. But, in both types of surfaces, the essence of this promotional effect mainly lies in increasing the electron transfer amounts during the reaction process. This research provides new insights into EPFRs formation on particle surfaces within the context of atmospheric composite pollution.

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Hydroxyl (OH) and hydroperoxyl (HO2) radicals, collectively known as HOx radicals, are crucial in removing primary pollutants, controlling atmospheric oxidation capacity, and regulating global air quality and climate. An imbalance between radical observations and simulations has been identified based on radical closure experiments, a valuable tool for accessing the state-of-the-art chemical mechanisms, demonstrating a deviation between the existing and actual tropospheric mechanisms. In the past decades, researchers have attempted to explain this deviation and proposed numerous radical generation mechanisms. However, these newly proposed unclassical radical generation mechanisms have not been systematically reviewed, and previous radical-related reviews dominantly focus on radical measurement instruments and radical observations in extensive field campaigns. Herein, we overview the unclassical generation mechanisms of radicals, mainly focusing on outlining the methodology and results of radical closure experiments worldwide and systematically introducing the mainstream mechanisms of unclassical radical generation, involving the bimolecular reaction of HO2 and organic peroxy radicals (RO2), RO2 isomerization, halogen chemistry, the reaction of H2O with O2 over soot, epoxide formation mechanism, mechanism of electronically excited NO2 and water, and prompt HO2 formation in aromatic oxidation. Finally, we highlight the existing gaps in the current studies and suggest possible directions for future research. This review of unclassical radical generation mechanisms will help promote a comprehensive understanding of the latest radical mechanisms and the development of additional new mechanisms to further explain deviations between the existing and actual mechanisms.

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