Radical Adduct Formation Research Articles

Nitrogen-doped CNTs enhance heterogeneous Fenton reaction for IOH removal by FeOCl: Role of NCNTs and mechanism

Heterogeneous Fenton has already been usedextensively to remove emerging contaminants, however, sluggish Fe(III)/Fe(II) circulation and high mass-transport resistance are its two major limitations. In this study, a novel heterogeneous N-doped carbon nanotubes loaded nano-FeOCl (NCF) catalyst was synthesized by partial thermal decomposition to enhance its catalytic performance. By incorporating NCNTs, the specific surface area of NCF was significantly increased in comparisontoFeOCl, which promotes the accumulation of contaminants on the catalyst surface. Similarly, the degradation rate constant (k) of IOH in the NCF/H2O2 system was observed 114 times greater than that of the FeOCl/H2O2 system. Besides not significantly increased k, excessive H2O2 substantially reduced H2O2 utilization. Electron paramagnetic resonance and electrochemical analysis reflected that the NCNTs facilitated the Fe(III)/Fe(II) circulation by improving electron transfer and enhanced •OH, O2•− and 1O2 availability by exerting a confinement effect. The major reactions assumed in IOH degradation include hydrogen atom abstract, amide hydrolysis, deiodination reaction, •OH radical adduct formation, and oxidation of C-OH. This study elucidates the degradation mechanism of IOH in the heterogeneous Fenton system with carbon-based co-catalysts and provides an efficient measure for removing emerging contaminants from the environment.

Antioxidant Chimeric Molecules: Are Chemical Motifs Additive? The Case of a Selenium-Based Ligand.

We set up an in silico experiment and designed a chimeric compound integrating molecular features from different efficient ROS (Reactive Oxygen Species) scavengers, with the purpose of investigating potential relationships between molecular structure and antioxidant activity. Furthermore, a selenium centre was inserted due to its known capacity to reduce hydroperoxides, acting as a molecular mimic of glutathione peroxidase; finally, since this organoselenide is a precursor of a N-heterocyclic carbene ligand, its Au(I) carbene complex was designed and examined. A validated protocol based on DFT (Density Functional Theory) was employed to investigate the radical scavenging activity of available sites on the organoselenide precursor ((SMD)-M06-2X/6-311+G(d,p)//M06-2X/6-31G(d)), as well as on the organometallic complex ((SMD)-M06-2X/SDD (Au), 6-311+G(d,p)//ZORA-BLYP-D3(BJ)/TZ2P), considering HAT (Hydrogen Atom Transfer) and RAF (Radical Adduct Formation) regarding five different radicals. The results of this case study suggest that the antioxidant potential of chemical motifs should not be considered as an additive property when designing a chimeric compound, but rather that the relevance of a molecular topology is derived from a chemical motif combined with an opportune chemical space of the molecule. Thus, the direct contributions of single functional groups which are generally thought of as antioxidants per se do not guarantee the efficient radical scavenging potential of a molecular species.

Degradation behaviors of Nabumetone and its metabolite during UV/monochloramine process: Experimental and theoretical study

This study investigated degradation behaviors of a nonsteroidal anti-inflammatory drug Nabumetone (NMT) and its major metabolite 6-methoxy-2-naphthylacetic acid (MNA) in the coupling process of ultraviolet and monochloramine (UV/NH2Cl). The second-order rate constants of the contaminants reacting with reactive radicals (HO•, Cl•, Cl2•⁻, and CO3•⁻) were determined by laser flash photolysis experiments. HO• and Cl• contributed predominantly with 52.3% and 21.7% for NMT degradation and 60.8% and 22.3% for MNA degradation. The presence of chlorides retarded the degradation of NMT, while promoted the destruction of MNA, which was ascribed to the photosensitization effects of MNA under UV irradiation. Density functional theory (DFT) calculations revealed that radical adduct formation (RAF) was dominant pathway for both HO• and Cl• reacting with the contaminants, and hydrogen atom transfer (HAT) preferred to occur on side chains of NMT and MNA. NMT reacted with NO2• through single electron transfer (SET) with the second-order rate constant calculated to be 5.35 × 107 (mol/L)−1 sec−1, and the contribution of NO2• was predicted to be 13.0% of the total rate constant of NMT in pure water, which indicated that NO2• played a non-negligible role in the degradation of NMT. The acute toxicity and developmental toxicity of NMT were enhanced after UV/NH2Cl treatment, while those of MNA were alleviated. The transformation products of both NMT and MNA exhibited higher mutagenicity than their parent compounds. This study provides a deep understanding of the mechanism of radical degradation of NMT and MNA in the treatment of UV/NH2Cl.

A thermodynamic and kinetic HO radical scavenging study and protein binding of baicalein

Baicalein (BOH) is an essential flavone molecule with proven significant scavenging activity towards various reactive species, although the actual mechanism has not been fully elucidated. Three common mechanisms: Hydrogen Atom Abstraction (HAA), Radical Adduct Formation (RAF), and Electron Transfer (EA), for the reaction between BOH and HO• have been investigated thermodynamically and kinetically in water and penthylethanoate. Based on the pKa values of BOH, the percentages of various acid-base species were estimated and subsequently incorporated into the described procedures. Changes in Gibbs free energy of HAA reactions demonstrated the spontaneity of hydrogen transfer from each OH group of BOH with reaction rates of 1.8 × 107 and 7.5 × 104 M−1 s−1. This process occurred through Proton Coupled-Electron Transfer (PCET) mechanism. Reactions involving RAF processes were operable in six places, with rate constants ranging from 4.8 × 104 to 3.0 × 108 M−1 s−1. Reaction rates calculated for electron transfer from anionic species (BO-) were the kinetically most favorable reaction pathway of the order of 109 M−1 s−1, which unequivocally shows that these reactions are diffusion controlled. These results shed new light on BOH chemistry and its possible medical use. The molecular docking analysis was performed to identify the inhibition potency of the baicalein-anion against Glyoxalase I (GLOI) receptor. This study demonstrated that molecular docking analysis is an important tool for evaluating the interactions of biologically significant compounds, particularly their many acid-base forms.

Radical adducts formation mechanism of CH3CO2∙ and CH3CO3∙ realized decomposition of chitosan by plasma catalyzed peracetic acid

High-molecular-weight chitosan has limited applications due to unsatisfactory solubility and hydrophilicity. Discharge plasma coupled with peracetic acid (PAA) oxidation (“plasma+PAA”) realized fast depolymerization of high-molecular-weight chitosan in this study. The molecular weight of chitosan rapidly declined to 81.1 kDa from initial 682.5 kDa within 60 s of “plasma+PAA” treatment, and its reaction rate constant was 12-fold higher than single plasma oxidation. Compared with 1O2, ∙CH3, CH3O2·, and O2∙−, CH3CO2∙ and CH3CO3∙ played decisive roles in the chitosan depolymerization in the plasma+PAA system through mechanisms of radical adduct formation. The attacks of CH3CO2∙ and CH3CO3∙ destroyed the β-(1,4) glycosidic bonds and hydrogen bonds of chitosan, leading to generation of low-molecular-weight chitosan; the main chain structure of chitosan was not changed during the depolymerization process. Furthermore, the generated low-molecular-weight chitosan exhibited greater antioxidant activities than original chitosan. Overall, this study revealed the radical adduct formation mechanisms of CH3CO2∙ and CH3CO3∙ for chitosan decomposition, providing an alternative for fast depolymerization of high-molecular-weight chitosan.

Catalytic degradation of bisphenol A by heterogeneous bimetal composite carbon in the PMS and H2O2 systems: Performance and mechanism

Bisphenol A (BPA) has caused adverse effects on human health and natural environment as a poisonous endocrine disrupting chemical. In this study, the bimetal composite carbon material (Co&Ni/C) with carbon nanotubes was fabricated for BPA degradation by the catalytic pyrolysis method. The dense carbon nanotubes were observed on the carbon surface with a specific surface area of up to 265.68 m2/g. The cobalt oxide and nickel oxide were distributed evenly causing more catalytic sites. The factors affecting catalytic efficiency for degrading BPA by the peroxymonosulfate (PMS) and hydrogen peroxide (H2O2) systems were investigated and compared systematically. The Co&Ni/C showed better catalytic performance with a BPA degradation rate of nearly 80%–100% in the Co&Ni/C-PMS process. However, BPA was difficult to be removed completely by H2O2 with a mineralization efficiency below 40% under most reaction conditions. The different degradation pathways and mechanisms under the oxidation of SO4•− and HO• were also discussed respectively, and the intermediate reactions included radical adduct formation, hydroxylation, skeleton oxidation rearrangement, dehydration and ring cleavage. It was proved that the stable Co&Ni/C possessed good reusability for remaining 77% removal rate of BPA after a 4-stage adsorption-degradation reaction. This paper revealed that the synthetic Co&Ni/C was hopeful as the adsorption material with efficient catalytic activity to provide new insight into BPA in-situ degradation.

Radical Scavenging Mechanisms of 1-Arylhydrazone Benzimidazole Hybrids with Neuroprotective Activity.

Benzimidazole-arylhydrazone hybrids showed promising potential as multifunctional drugs for the treatment of neurodegenerative disorders. The neuroprotection studies conducted using an in vitro model of H2O2-induced oxidative stress on the SH-SY5Y cell line revealed a remarkable activity of the compound possessing a vanilloid structural fragment. The cell viability was preserved up to 84% and this effect was significantly higher than the one exerted by the reference compounds melatonin and rasagiline. Another compound with a catecholic moiety demonstrated the second-best neuroprotective activity. Computational studies were further conducted to characterize in depth the antioxidant properties of both compounds. The possible radical scavenging mechanisms were estimated as well as the most reactive sites through which the compounds may deactivate a variety of free radicals. Both of the compounds are able to deactivate not only the highly reactive hydroxyl radicals but also alkoxyl and hydroperoxyl radicals, following hydrogen atom transfer or radical adduct formation mechanism. In nonpolar medium, 3e is predicted to react slightly faster than 3a with alkoxyl radicals and around two orders of magnitude faster than 3a with hydroperoxyl radicals. The most reactive sites for formal hydrogen atom transfer in 3a are the meta-hydroxy group in the phenyl ring in water and the amide N-H group in benzene; in 3e, the amide N-H group is more reactive in both solvents. The radical adduct formation can occur at several positions in 3a and 3e, the most active being C4, C6, and C14. The stability of the formed radicals was estimated by NBO calculations. The NBO calculations indicated that the spin density in the radicals formed by the abstraction of a hydrogen atom from the amide groups of both compounds is delocalized over the phenyl ring and the hydrazone chain. The obtained theoretical data for the better radical scavenging ability of the vanilloid hybrid corroborate its experimentally established better neuroprotective activity.

Theoretical investigation on the degradation of sulfadiazine in water environments: Oxidation of •OH, SO4•−and CO3•− and reactivity of (TiO2)n clusters (n = 1–6)

This study reported the degradation of micro pollutants through reactive radicals like •OH, SO4•−and CO3•−. Sulfadiazine (SDZ) is widely used antibiotic and emerging water pollutant. The synergistic degradation of sulfadiazine by •OH, SO4•−and CO3•− was investigated through quantum chemistry methods. The degradation of SDZ by •OH radicals was dependent on radical adduct formation (RAF) reactions while degradation of SDZ by SO4•− radical was caused by RAF, hydrogen atom transfer (HAT) and also single electron transfer (SET). The degradation of SDZ by CO3•− radical mainly caused by RAF and HAT. The degradation rate constants of SDZ initiated through •OH, SO4•−and CO3•− radicals were calculated separately: kSDZ-SO4•− (5.29 × 1010 M−1 s−1) > kSDZ-•OH (1.38 × 1010 M−1 s−1) > kSDZ-CO3•− (1.28 × 108 M−1 s−1). The degradation mechanism of SDZ by (TiO2)n (n = 1–6) cluster was investigated. The conformation between benzene ring and heterocyclic ring of SDZ has a lower adsorption energy and the (TiO2)n cluster (n = 5) is the most stable adsorption conformation with SDZ. The toxicity assessment showed that most of the degradation products were less toxic and eco-friendly. However, O-P1, P4 and P9 exhibited more severe aquatic toxicity.

Theoretical insights into the oxidation of quinmerac herbicide initiated by HO• radical in aqueous media: Mechanism, kinetics, and ecotoxicity

In this study, the oxidation of quinmerac herbicide initiated by HO• radical was investigated using quantum chemistry and kinetic calculations. Three oxidation processes, namely radical adduct formation (RAF), formal hydrogen transfer (FHT), and single electron transfer (SET), were studied in aqueous media at the M06–2X/6–311 + +G(3df,3pd)//M06–2X/6–31 +G(d,p) level of theory. The results illustrated that the RAF reactions were more likely to occur during the oxidation process, followed by FHT, and SET was found to be a negligible pathway. Branching ratio calculations showed that the HO•-addition to C7 of the benzyl ring was the predominant pathway, followed by the H-abstraction at the methyl group. The rate constant was evaluated as a function of temperature (283−333 K) and pH (0−14). The highest reaction rates were obtained at low pH (0−1) and high temperature (333 K) conditions (i.e., 9.36 × 108 M−1s−1). Quinmerac can exist in the environment from a few seconds to several years, depending on conditions. The ecotoxicity prediction illustrated that quinmerac and its degradation products are not harmful and non-bioaccumulative substances to aquatic organisms. However, they have developmental toxicity but no mutagenic toxicity.

Experimental and theoretical insights into free radical capturing activity of 1,5-diaminonaphthalene and 1,5-dihydroxynaphthalene

The radical scavenging activity of two naphthalene derivatives, 1,5-diaminonaphthalene (DAN) and 1,5-diaminonaphthalene (DAN) and 1,5-dihydroxynaphthalene (DHN), was investigated through both experimental and density functional theory methods. Experimentally, the antioxidant capacity of these compounds was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH·) assay and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS·+) assay and compared to the standard antioxidant Trolox. DHN demonstrated a superior ability to capture DPPH· free radicals, with an IC50DPPH value of 3.62 ± 0.01 µM, while DAN was more effective at neutralizing ABTS·+ radical cations, with an IC50ABTS value of 17.36 ± 0.02 µM. Theoretically, density functional theory (DFT) calculations using the theory level of ωb97xd/6–311++g(d,p) were employed to determine the thermodynamic parameters of DHN and DAN in the gas phase and ethanol solvent. Furthermore, the mechanisms and kinetics of capturing reaction between both naphthalene derivatives and HOO· radical were also investigated. Based on the potential energy surfaces (PES) via hydrogen atom transfer (HAT) and radical adduct formation (RAF) paths, HAT was determined to be the favored mechanism, with the product amount accounting for more than 99% in the gas phase and 92% in ethanol.

Efficient elimination of phenazone by an electro-assisted Fe3+-EDDS/PS process at neutral pH: Kinetics, mechanistic insights and toxicity evaluation

The feasibility of the degradation of phenazone (PNZ), a common anti-inflammatory drug used for reducing pain and fever, in water at neutral pH by an electrochemically assisted Fe3+-ethylenediamine disuccinate-activated persulfate process (EC/Fe3+-EDDS/PS) was investigated. The efficient removal of PNZ at neutral pH condition was mainly attributed to the continuous activation of PS via electrochemically driven regenerated Fe2+ from a Fe3+-EDDS complex at the cathode. The influence of several critical parameters, including current density, Fe3+ concentration, EDDS to Fe3+ molar ratio, and PS dosage, on PNZ degradation was evaluated and optimized. Both hydroxyl radicals (•OH) and sulfate radicals (SO4●–) were considered major reactive species responsible for PNZ degradation. To understand the mechanistic model of action at the molecular level, the thermodynamic and kinetic behaviors of the reactions between PNZ with •OH and SO4●– were theoretically calculated using a density functional theory (DFT) method. The results revealed that radical adduct formation (RAF) is the most favorable pathway for the •OH-driven oxidation of PNZ, while single electron transfer (SET) appears to be the dominant pathway for the reaction of SO4●– with PNZ. In total, thirteen oxidation intermediates were identified, and hydroxylation, pyrazole ring opening, dephenylization, and demethylation were speculated to be the major degradation pathways. Furthermore, predicted toxicity to aquatic organisms indicated that PNZ degradation resulted in products that were less harmful. However, the developmental toxicity of PNZ and its intermediate products should be further investigated in the environment. The findings of this work demonstrate the viability of effectively removing organic contaminants in water at near-neutral pH by using EDDS chelation combined with electrochemistry in a Fe3+/persulfate system.

Hydroxylation of some emerging disinfection byproducts (DBPs) in water environment: Halogenation induced strong pH-dependency

In this work, the hydroxylation mechanisms and kinetics of some emerging disinfection byproducts (DBPs) have been systematically investigated through theoretical calculation methods. Five chlorophenols and eleven halogenated pyridinols were chosen as the model compounds to study their pH-dependent reaction laws in UV/H2O2 system. For the reactions of HO• with 37 different dissociation forms, radical adduct formation (RAF) was the main reaction pathway, and the reactivity decreased with the increase of halogenation degree. The kapp values (at 298 K) increased with the increase of pH from 0 to 10, and decreased with the increase of pH from 10 to 14. Compared with phenol, the larger the chlorination degree in chlorophenols was, the stronger the pH sensitivity of the kapp values; compared with chlorophenols, the pH sensitivity in halogenated pyridinols was further enhanced. As the pH increased from 2 to 10.5, the degradation efficiency increased at first and then decreased. With the increase of halogenation degree, the degradation efficiency range increased, the pH sensitivity increased, the optimal degradation efficiency slightly increased, and the optimal degradation pH value decreased. The ecotoxicity and bioaccumulation of most hydroxylated products were lower than their parental compounds. These findings provided meaningful insights into the strong pH-dependent hydroxylation of emerging DBPs on molecular level.

Capturing Hydrogen Radicals by Neutral Metal Hydroxides.

Capturing the hydrogen radical is of central importance in various systems ranging from catalysis to biology to astronomy, but it has been proven to be challenging experimentally because of its high reactivity and short lifetime. Here, neutral MO3H4 (M = Sc, Y, La) complexes were characterized by size-specific infrared-vacuum ultraviolet spectroscopy. All these products were determined to be the hydrogen radical adducts in the form of H•M(OH)3. The results indicate that the addition of the hydrogen radical to the M(OH)3 complex is both thermodynamically exothermic and kinetically facile in the gas phase. Moreover, the soft collisions in the cluster growth channel with the helium expansion were found to be demanded for the formation of H•M(OH)3. This work highlights the pivotal roles played by the soft collisions in the formation of hydrogen radical adducts and also opens new avenues toward the design and chemical control of compounds.

A DFT study on the scavenging activity of curcumin toward methyl and ethyl radicals

The curcumin is a well-known antioxidant that can scavenge free radicals efficiently. The methyl free radicals, generated by the metabolism of various genotoxic compounds such as hydrazines and peroxides, can methylate various sites in DNA. Herein, we have carried out density functional theory calculations to investigate the scavenging activity of curcumin toward the methyl and ethyl radicals through radical adduct formation (RAF), hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms. The SET mechanism is found to be highly endergonic and so not viable. Our calculations show that the curcumin can scavenge methyl radicals through both RAF and HAT mechanisms but RAF would be preferred over the HAT. Further, it is found that the curcumin can scavenge methyl radicals more efficiently as compared to ethyl radicals through RAF mechanism.

Limonene: A scented and versatile tropospheric free radical deactivator

AbstractThe reactions of limonene with various free radicals (•OCH3, •OBr, •SH, •OOH, and •OOCH3) were investigated along the 273.15–312.15 K temperature range. To that purpose the density functional theory was used, at the M06‐2X/6–311+g(d,p) level. Two reaction mechanisms, hydrogen atom transfer (HAT) and radical adduct formation (RAF) were considered. It was found that the relative reactivity of the studied radicals toward limonene is: •SH > •OBr > •OCH3 > •OOH > •OOCH3. HAT was identified as the dominant mechanism for •OOH and •OOCH3, while RAF contributes the most to the reactions involving •OCH3, •OBr, and •SH. The obtained Arrhenius expressions are: k(•OCH3) = 1.58 × 10−13 e−1.59/RT, k(•OBr) = 3.55 × 10−12 e+1.82/RT, k(•SH) = 3.30 × 10−11 e+0.79/RT, k(•OOH) = 1.33 × 10−15 e−5.99/RT, and k(•OOCH3) = 5.88 × 10−17 e−6.26/RT. According to them, the reactions of •OBr and •SH become slower as temperature rises from 273.15 to 312.15 K, while for the other radicals the reactions rate increases with temperature. The subsequent tropospheric fate of the most abundant •OBr adduct was also investigated in the same temperature range, considering O2 addition to this radical (step 2) and the reaction of the peroxyl radical yielded in this step 2 with NO. The latter is predicted to take place in two steps: the NO addition (3a) and the NO2 elimination (3b). The corresponding Arrhenius expression are k2 = 3.56 × 10−15 e+1.43/RT and k3b = 1.35 × 1014 e−31.65/RT. Step 3a was found to be barrierless. To our best knowledge, all the data provided here is reported for the first time. Thus, it would hopefully contribute to enhance the knowledge necessary for the full understanding (and accurate modeling) of the troposphere.

Alizarin as a potential protector of proteins against damage caused by hydroperoxyl radical

Alizarin is a natural anthraquinone molecule with moderate antioxidative capacity. Some earlier investigations indicated that it can inhibit osteosarcoma and breast carcinoma cell proliferation by inhibiting of phosphorylation process of ERK protein (extracellular signal-regulated kinases). Several mechanisms of deactivation of one of the most reactive oxygen species, hydroperoxyl radical, by alizarin are estimated: hydrogen atom abstraction (HAA), radical adduct formation (RAF), and single electron transfer (SET). The plausibility of those mechanisms is estimated using density functional theory. The obtained results indicated HAA as the only thermodynamically plausible mechanism. For that purpose, two possible mechanistic pathways for hydrogen atom abstraction are studied in detail: hydrogen atom transfer (HAT) and proton-coupled electron transfer (PCET). Water and benzene are used as models of solvents with opposite polarity. To examine the difference between HAT and PCET is used kinetical approach based on the Transition state theory (TST) and determined rate constants (k). Important data used for a distinction between HAT and PCET mechanisms are obtained by applying the Quantum Theory of Atoms in Molecules (QTAIM), and by the analysis of single occupied molecular orbitals (SOMOs) in transition states for two examined mechanisms. The molecular docking analysis and molecular dynamic are used to predict the most probable positions of binding of alizarin to the sequence of ApoB-100 protein, a protein component of plasma low-density lipoproteins (LDL). It is found that alizarin links the nitrated polypeptide forming the π-π interactions with the amino acids Phenylalanine and Nitrotyrosine. The ability of alizarin to scavenge hydroperoxyl radical when it is in a sandwich structure between the polypeptide and radical species, as the operative reaction mechanism, is not significantly changed concerning its antioxidant capacity in the absence of polypeptide. Therefore, alizarin can protect the polypeptide from harmful hydroperoxyl radical attack, positioning itself between the polypeptide chain and the reactive oxygen species.

New C8-substituted caffeine derivatives as promising antioxidants and cytoprotective agents in human erythrocytes

New structurally diverse groups of C8-substituted caffeine derivatives were synthesized and evaluated for their chemical and biological properties. Mass spectrometry, FT-IR, and NMR characterizations of these derivatives were performed. The cytotoxic activity of the derivatives was estimated in vitro using human red blood cells (RBC) and in silico pharmacokinetic studies. The antioxidant capacity of the compounds was analyzed using a ferrous ion chelating activity assay. The ability of the derivatives to protect RBC from oxidative damage, including the oxidation of hemoglobin to methemoglobin, was assessed using a water-soluble 2,2′-azobis(2-methyl-propionamidine) dihydrochloride (AAPH) as a standard inducer of peroxyl radicals. The level of intracellular oxidative stress was assessed using the fluorescent redox probe 2′,7′-dichlorodihydrofluorescein diacetate (DCF-DA). The results indicate that all derivatives are biocompatible compounds with significant antioxidant and cytoprotective potential dependent on their chemical structure. In order to explain the antioxidant and cytoprotective activity of the derivatives, a mechanism of hydrogen atom transfer (HAT), radical adduct formation (RAF), or single electron transfer (SET), as well as the specific interactions of the derivatives with the lipid bilayer of RBC membrane, have been proposed. The results show that selected modifications of the caffeine molecule enhance its antioxidant properties, which expands our knowledge of the structure–activity relationship of caffeine-based cytoprotective compounds.

A Novel Source of Radicals from UV/Dichloroisocyanurate for Surpassing Abatement of Emerging Contaminants Versus Conventional UV/Chlor(am)ine Processes.

Ultraviolet (UV)/chlor(am)ine processes are emerging advanced oxidation processes (AOPs) for water decontamination and raising continuous attention. However, limitations appear in the UV/hypochlorite and UV/monochloramine for removing specific contaminants ascribed to the differences in the sorts and yields of free radicals. Here, this study reports UV/dichloroisocyanurate (NaDCC) as a novel source of radicals. NaDCC was demonstrated to be a well-balanced compound between hypochlorite and monochloramine, and it had significant UV absorption and a medium intrinsic quantum yield. The UV/NaDCC produced more substantial hydroxyl radicals (·OH) and reactive chlorine species (RCSs, including Cl·, ClO·, and Cl2·-) than conventional UV/chlor(am)ine, thereby generating a higher oxidation efficiency. The reaction mechanisms, environmental applicability, and energy requirements of the UV/NaDCC process for emerging contaminants (ECs) abatement were further investigated. The results showed that ·OH and ·NH2 attacked ECs mostly through hydrogen atom transfer (HAT) and radical adduct formation, whereas Cl· destroyed ECs mainly through HAT and single electron transfer, with ClO· playing a certain role through HAT. Kinetic model analyses revealed that the UV/NaDCC outperformed the conventional UV/chlor(am)ine in a variety of water matrices with superior degradation efficiency, significantly saving up to 96% electrical energy per order. Overall, this study first demonstrates application prospects of a novel AOP using UV/NaDCC, which can compensate for the deficiency of the conventional UV/chlor(am)ine AOPs.

Theoretical and Experimental Investigation of the Antioxidation Mechanism of Loureirin C by Radical Scavenging for Treatment of Stroke.

Recent pharmacological studies have shown that dragon's blood has an anti-cerebral ischemia effect. Loureirin C (LC), a kind of dihydrochalcone compound in dragon's blood, is believed to be play an important role in the treatment of ischemia stroke, but fewer studies for LC have been done. In this paper, we report the first experimental and theoretical studies on the antioxidation mechanism of LC by radical scavenging. The experimental studies show that LC has almost no effect on cell viability under 15 μM for the SH-SY5Y cells without any treatments. For the SH-SY5Y cells with oxygen and glucose deprivation-reperfusion (OGD/R) treatment, LC increased the viability of SH-SY5Y cells. The results of 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) and MitoSox Red experiments indicate that LC is very efficient in inhibiting the generation of the intracellular/mitochondrial reactive oxygen species (ROS) or removing these two kinds of generated ROS. The density functional theory (DFT) calculations allowed us to elucidate the antioxidation mechanisms of LC. Fukui function analysis reveals the radical scavenging of LC by hydrogen abstraction mechanism, the complex formation by e-transfer, and radical adduct formation (RAF) mechanism. Among the H-abstraction, the complex formation by e-transfer, and radical adduct formation (RAF) reactions on LC, the H-abstraction at O-H35 position by OH• is favorable with the smallest energy difference between the product and two reactants of the attack of OH• to LC of -0.0748 Ha. The bond dissociation enthalpies (BDE), proton affinities (PA), ionization potential (IP), proton dissociation enthalpy (PDE), and electron transfer enthalpy (ETE) were calculated to determine thermodynamically preferred reaction pathway for hydrogen abstraction mechanism. In water, IP and the lowest PDE value at O3-H35 position are lower than the lowest BDE value at O3-H35 position; 41.8986 and 34.221 kcal/mol, respectively, indicating that SEPT mechanism is a preferred one in water in comparison with the HAT mechanism. The PA value of O3-H35 of LC in water is -17.8594 kcal/mol, thus the first step of SPLET would occur spontaneously. The minimum value of ETE is higher than the minimum value of PDE at O3-H35 position and IP value, 14.7332 and 22.4108 kcal/mol, respectively, which suggests that the SEPT mechanism is a preferred one in water in comparison with the SPLET mechanism. Thus, we can draw a conclusion that the SEPT mechanism of is the most favorite hydrogen abstraction mechanism in water, and O-H35 hydroxyl group has the greatest ability to donate H-atoms.

New insight into environmental oxidation of phosmet insecticide initiated by HO˙ radicals in gas and water - a theoretical study.

Phosmet is an organophosphorus insecticide widely used in agriculture to control a range of insects; recently, it was banned by the European Union in 2022 due to its harmful effects. However, its environmental degradation and fate have not yet been evident. Thus, phosmet oxidation by HO˙ radicals was theoretically studied in this work using the DFT approach at the M06-2X/6-311++G(3df,3pd)//M06-2X/6-31+G(d,p) level of theory. Three different mechanisms were considered, including formal hydrogen transfer (FHT), radical adduct formation (RAF), and single electron transfer (SET). The mechanisms, kinetics, and lifetime were studied in the gas and aqueous phases, in addition to its ecotoxicity evaluation. The results show that FHT reactions were dominant in the gas phase, while RAF was more favourable in the aqueous phase at 298 K, while SET was negligible. The branching ratio indicated that H-abstractions at the methyl and the methylene groups were the most predominant, while the most favourable HO˙-addition was observed at the phosphorus atom of the dithiophosphate group. The overall rate constant values varied from 1.2 × 109 (at 283 K) to 1.40 × 109 M-1 s-1 (at 323 K) in the aqueous phase and from 6.29 × 1010 (at 253 K) to 1.32 × 1010 M-1 s-1 (at 323 K) in the gas phase. The atmospheric lifetime of phosmet is about 6 hours at 287 K, while it can persist from a few seconds to several years depending on the temperature and [HO˙] concentration in the aqueous environment. The QSAR-based ecotoxicity evaluation indicates that phosmet and its degradation products are all dangerous to aquatic organisms, although the products are less toxic than phosmet. However, they are generally developmental toxicants and mutagenicity-negative compounds.