Distribution Pattern, Emission Characteristics and Environmental Impact of Polycyclic Aromatic Hydrocarbons (PAHs) in Download Ash and Dust from Iron and Steel Enterprise.

Download ash and emission dust samples were collected from sintering, coking, ironmaking and steelmaking processes of iron and steel enterprises in Laiwu. Sixteen kinds of polycyclic aromatic hydrocarbons (PAHs) in the United States Environmental Protection Agency (USEPA) priority controlled lists were quantitatively analyzed using Gas Chromatography-Mass Spectrometer (GC-MS). Laser particle size analyzer was used to obtain the distribution pattern of download ash. It was found that the diameter distribution pattern from four production processes was quite different. The proportion of fine particulate (0-2.5 µm) was the highest (72.62%) in the steelmaking refining process, and was 28.962% in the ironmaking process. Moreover, the particle size in download ash from steelmaking refining is all less than 10 µm and that from the ironmaking process was 52.92%. The medium-sized particles (10-100 µm) were dominant in sinter and coking download ashes. The total PAHs (∑16PAHs) mass concentration ranged from 0.49 ± 0.06 to 69.63 ± 5.57 µg·g-1 in download ash samples, and varied from 2.815 ± 0.253 to 19.429 ± 2.545 µg·m-3 in emission dust samples. The ∑16PAHs values were both largest in download ash and dust emission from the coking process (69.63 ± 5.57 µg·g-1 and 19.429 ± 2.545 µg·m-3, respectively). The most abundant individual PAHs were benzo[b]fluoranthene, benzo[k]fluoranthene, phenanthrene, benzo[a]anthracene in ash samples, and benzo[a]anthracene, benzo[k]fluoranthene, benzo[b]fluoranthene and indeno[1,2,3-cd]pyrene in emission dust samples. Dominant compounds were high-molecular weight (four- to six-ring) PAHs in both ash and dust samples. The concentration order of individual compounds in PM10 and PM2.5 in ambient air around the steel plant was completely consistent with each other, and the concentration of ∑16PAHs was the highest in the steel plant and lowest in Daqin village because of upwind of the steel plant. The concentrations of benzo[b]fluoranthene and fluoranthene in ambient air were comparatively high, and were in accordance with the higher concentration of the two monomers in the download ash samples, which suggested that the effect of the emission flue gas from the steel plant on ambient air was necessary to concern.

New insights into the electroreduction of ethylene sulfite as an electrolyte additive for facilitating solid electrolyte interphase formation in lithium ion batteries.

To help understand the solid electrolyte interphase (SEI) formation facilitated by electrolyte additives of lithium-ion batteries (LIBs) the supermolecular clusters [(ES)Li+(PC)m](PC)n (m = 1-2; n = 0, 6 and 9) were used to investigate the electroreductive decompositions of the electrolyte additive ethylene sulfite (ES) as well as the solvent propylene carbonate (PC) with density functional theory. The results show that ES can be reduced prior to PC, resulting in a reduction precursor that will then undergo a ring opening decomposition to yield a radical anion. A new concerted pathway (path B) was located for the ring opening of the reduced ES, which has a much lower energy barrier than the previously reported stepwise pathway (path A). The transition state for the ring opening of PC induced by the reduced ES (path C, indirect path) is closer to that of path A than path B in energy. The direct ring opening of the reduced PC (path D) has a lower energy barrier than paths A, B and C, yet it is less favorable than the latter paths in terms of thermodynamics (vertical electron affinity or reduction potential and dissociation energy). The overall rate constant including the initial reduction and the subsequent ring opening for path B is the largest among the four paths, followed by paths A > C > D, which further signifies the importance of the concerted new path in facilitating the SEI formation. The hybrid models, the supermolecular clusters augmented by a polarized continuum model, PCM-[(ES)Li+(PC)2](PC)n (n = 0, 6 and 9), were used to further estimate the reduction potential by taking into account both explicit and implicit solvent effects. The second solvation shell of Li+ in [(ES)Li+(PC)2](PC)n (n = 6 and 9) partially compensates the overestimation of solvent effects arising from the PCM for the naked (ES)Li+(PC)2, and the theoretical reduction potential of PCM-[(ES)Li+(PC)2](PC)6 (1.90-1.93 V) agrees very well with the experimental one (1.8-2.0 V).

Determination of hexabromocyclododecane enantiomers in chicken whole blood by a modified quick, easy, cheap, effective, rugged, and safe method with liquid chromatography and tandem mass spectrometry.

A rapid and simple analytical method has been developed for the determination of hexabromocyclododecane enantiomers in chicken whole blood, based on a modified quick, easy, cheap, effective, rugged, and safe approach before liquid chromatography coupled with tandem mass spectrometry. The factors influencing performance of method were investigated by single factor experiment, and further optimized by the response surface methodology based on Box-Behnken design. The matrix effects were also evaluated by the isotopic dilution method. Under the optimal conditions, the proposed method showed good linearity within the range of 1-500 µg/L and good repeatability with relative standard deviation less than 9.5% (n = 5). The limits of detection (S/N = 3) were 0.03-0.19 µg/L. The developed method was successfully applied for the analysis of hexabromocyclododecane enantiomers in real chicken blood samples. The satisfactory recoveries ranging of 83.6-115.0% were obtained (at spiked levels of 5, 20, and 100 µg/L). The results demonstrated that the proposed method would be a practical value method for the determination of hexabromocyclododecane enantiomers in animal blood. It would be further developed with confidence to analyze other lipophilic organic pollutants in blood sample.

Elucidating pharmacological mechanisms of natural medicines by biclustering analysis of the gene expression profile: a case study on curcumin and Si-Wu-Tang.

Natural medicines have attracted wide attention in recent years. It is of great significance to clarify the pharmacological mechanisms of natural medicines. In prior studies, we established a method for elucidating pharmacological mechanisms of natural products contained in connectivity map (cMap), in terms of module profiles of gene expression in chemical treatments. In this study, we explore whether this methodology is applicable to dissecting the pharmacological mechanisms of natural medicines beyond the agents contained in cMap. First, the gene expression profiles of curcumin (a typical isolated natural medicine) and Si-Wu-Tang (a classic traditional Chinese medicine formula) treatments were merged with those of cMap-derived 1309 agents, respectively. Then, a biclustering analysis was performed using FABIA method to identify gene modules. The biological functions of gene modules provide preliminary insights into pharmacological mechanisms of both natural medicines. The module profile can be characterized by a binary vector, which allowed us to compare the expression profiles of natural medicines with those of cMap-derived agents. Accordingly, we predicted a series of pharmacological effects for curcumin and Si-Wu-Tang by the indications of cMap-covered drugs. Most predictions were supported by experimental observations, suggesting the potential use of this method in natural medicine dissection.

Simultaneous determination of 13 sulfonamides at trace levels in soil by modified QuEChERS with HPLC-MS/MS.

The pretreatment of samples was vital for enhancing the sensitivity and accuracy of analytical methods. An efficient and sensitive method, based on modified QuEChERS with high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) for the simultaneous determination of the 13 sulfonamides (SAs) in soil, was developed. After extraction by sonication with methanol, the clean-up procedure was achieved using QuEChERS with a primary secondary amine (PSA). The quantification of the 13 SAs was performed by HPLC-MS/MS in electrospray ionization (ESI) and multiple reaction monitoring (MRM) modes. Under optimized conditions, the standard solution exhibited good linearity within the range of 0.01-0.5 µg mL-1. The limits of detection and the limits of quantification of the developed method were 0.007-0.030 µg kg-1 and 0.022-0.101 µg kg-1, respectively. The spiked recoveries for the 13 SAs were in the range of 74.5-111.7% with RSD less than 15%. Furthermore, the developed method was successfully applied for the determination of SAs in real soil samples. The above results showed that the proposed method would be an ideal analytical method for SAs in environmental ecological research.

Rapid determination of hexabromocyclododecane enantiomers in animal meat by matrix solid phase dispersion coupled with LC-MS/MS.

A rapid and sensitive method was developed based on matrix solid phase dispersion (MSPD) for the determination of hexabromocyclododecane enantiomers (±α, ±ß and ± Î³-HBCD) in animal meat. The instrumental analysis was employed with liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) at trace level (ng g-1). To obtain excellent efficiency, the key parameters, including the type of dispersive adsorbent and elution solvent, were investigated by single-factor experiments. The volume of elution solvent and amount of dispersive adsorbent were optimized by the Box-Behnken design through response surface methodology. Under optimized conditions, the developed method exhibited excellent methodologic characteristics and was applied to the determination of HBCD enantiomers in real chicken and pork meat. Experimental results indicated that the proposed method would be an efficient, rapid and application method for the determination of lipophilic organic pollutants in animal meat.

Environment impact and probabilistic health risks of PAHs in dusts surrounding an iron and steel enterprise.

Dust can be regarded as environmental medium that indicates the level and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) coming from different pollution sources. In this study, samples including road dust, roof dust, and bare soil near an iron and steel enterprise (ISE) in Laiwu city of North China were collected. To assess the environment impact, atmosphere particulates and one flue dust from a coking plant were simultaneously sampled. Sixteen USEPA PAHs were detected quantitatively by Gas Chromatography Mass Spectrometry (GC-MS). A laser particle size analyzer was used to obtain the grain size of the dust particle samples. The results showed that PAH concentrations displayed great variability in the dust samples. The ∑16PAHs concentration was found to be between 0.460 and 46.970 µg/g (avg ± sd 10.892 ± 1.185 µg/g) in road dust, between 0.670 and 17.140 µg/g (avg ± sd 6.751 ± 0.692 µg/g) in roof dust, and 13.990 ± 1.203 µg/g in bare soil. In the environment atmosphere sites, the ∑16 PAHs value in PM2.5 constituted a very large proportion of PM10, indicating that PAHs in finer particle sizes should be given greater emphasis. The ∑16PAHs concentration was relatively high in the area close to the ISE because of the great impact of the ISE industrial activities. PAH concentration curves were similar, and the most abundant individual PAHs in the atmosphere sites were BbF, BkF, and Flu, and BbF, BkF, and Chry in dusts. Toxicity analysis revealed that PAHs with four rings, including carcinogenic PAHs, were the dominant pollutants in the studied area. The toxic equivalency value (TEQBaP), the carcinogenic health risk assessment value recommended by the US EPA, was calculated for seven carcinogenic PAHs, revealing that they account for more than 93.0% of the total TEQBap of the 16 PAHs and indicating the major toxic equivalent concentration contributor. Incremental lifetime cancer risk (ILCR) estimation results showed that PAHs tended to bring about great health risks through skin contact, followed by ingestion and inhalation. By comparison, road dust exhibited greater carcinogenic risks than roof dust, and bare soil may undergo heavier pollution. Therefore, the results of this study would be helpful in the effort to understand the PAHs pollution from the steel industry, which will provide some guidance for the probabilistic assessment of local health risks.

Chemical Compositions and Sources Contribution of Atmospheric Particles at a Typical Steel Industrial Urban Site.

Online monitoring concentrations of PM at five sites were obtained from 01/01/2016 to 31/12/2016 in Laiwu, China, and PM2.5 filters were manually sampled for total 34 days at the same sites in four seasons in 2016. PM pollution sources, including soil dust, urban dust, construction dust, coal-fired power plants dust, steel plant dust and motor vehicle exhaust dust were sampled, respectively. The overall mean PM2.5/PM10 ratio (0.57) in Laiwu was at a relatively lower level compared with that in other Chinese cities, which was higher in winter, indicating fine particulate was the main contributor of atmospheric pollution in this period. NH4+ mainly existed in the form of NH4NO3 and (NH4)2SO4 during the sampling periods. Higher sulfate and NH4+ concentrations were in summer while higher nitrate concentrations prevailed in winter. The annual value of OC/EC was (5.38 ± 1.70), higher in summer and lower in winter, and the calculated SOC/OC value (%) was (43.68 ± 12.98)%. The characteristic components were Si, Fe and Ca in urban dust and soil dust; Ca, Mg, and NH4+ in construction dust; Fe, Ca and SO42- in steel dust; OC, EC and Si in motor vehicle exhaust dust; SO42-, Al and NH4+ in power plant dust. Compared with other cities at home and abroad, it was found that the concentrations of metal elements in Laiwu were significantly higher than those in foreign cities, and at a medium level in China. With the improved CRAESCMB model, the urban dust was regarded as the receptor and the source of PM2.5 and apportioned its secondary sources contributions to PM2.5. The CMB results showed the contributions of secondary sources including sulfate (17%), nitrate (17%) and SOC (13%) to PM2.5 accounted for nearly half of all sources. Therefore, more attentions should be paid on secondary sources from the primary emission sources of the motor vehicle exhaust, coal combustion sources especially.

Theoretical investigation on triagonal symmetry copper trimers: magneto-structural correlation and spin frustration.

The mechanisms of the magnetic coupling interactions for two trigonal-bipyramid trinuclear Cu(II) complexes Cu3(mu3-X)2(mu-pz)3X3 (X = Cl and Br, respectively) and three trigonal trinuclear Cu(II) complexes Cu3(mu3-X)(mu-pz)3Cl3 (X = Cl, Br, and O) are investigated by the calculations based on density functional theory combined with broken-symmetry approach (DFT-BS). The research on the magneto-structural correlation reveals that the magnetic coupling interaction is sensitive to the Cu-(mu3-X)-Cu angle. With the Cu-(mu3-X)-Cu angle changing from 76 to 120 degrees, the magnetic coupling interaction is switched from ferromagnetic to antiferromagnetic. According to the analysis of the molecular orbitals and the variation of the spin-state energies versus the ratio of the magnetic coupling constants, it is found that there exists spin frustration phenomenon in these complexes.

Particle morphomics by high-throughput dynamic image analysis.

A novel omics-like method referred to as "particle morphomics" has been proposed in the present study. The dynamic images of >2,000,000 particles per sample in sediments, soils and dusts were collected by a Sympatec GmbH QICPIC particle size and shape analyzer, and the morphological descriptors of each particle including equivalent diameter, sphericity, aspect ratio and convexity were extracted as the "particle morphome". Various multivariate analyses were adopted to process the high-throughput data of particle morphome including analyses of alpha and beta diversities, similarity, correlation, network, redundancy, discretion and principal coordinate. The outcome of particle morphomics could estimate the morphological diversity and sketch the profile of morphological structure, which aided to develop a morphological fingerprint for specific particle samples. The distribution and properties of particle assemblages of specific morphology could also be evaluated by selecting particles with respect to filter criteria. More importantly, the particle morphomics may be extended to investigate and explain the biogeochemical and environmental processes involved with particle morphology if linked with external variables.

Silver nanoparticles inhibit beige fat function and promote adiposity.

OBJECTIVE: Obesity is a complex chronic disease of high prevalence worldwide. Multiple factors play integral roles in obesity development, with rising interest focusing on the contribution of environmental pollutants frequent in modern society. Silver nanoparticles (AgNPs) are widely used for bactericidal purpose in various applications in daily life. However, their potential toxicity and contribution to the obesity epidemic are not clear. METHODS: Beige adipocytes are newly discovered adipocytes characterized by high thermogenic and energy dissipating capacity upon activation and the "browning" process. In the present study, we assess the impact of AgNPs exposure on beige adipocytes differentiation and functionality both in vitro and in vivo. We also systematically investigate the influence of AgNPs on adiposity and metabolic performance in mice, as well as the possible underlying molecular mechanism. RESULTS: The results showed that, independent of particle size, AgNPs inhibit the adipogenic, mitochondrial, and thermogenic gene programs of beige adipocytes, thus suppressing their differentiation ability, mitochondrial activity, and thermogenic response. Importantly, exposure to AgNPs in mice suppresses browning gene programs in subcutaneous fat, leading to decreased energy expenditure and increased adiposity in mice. Mechanistically, we found that AgNPs increase reactive oxidative species (ROS) levels and specifically activate MAPK-ERK signaling in beige adipocytes. The negative impacts of AgNPs on beige adipocytes can be ameliorated by antioxidant or ERK inhibitor FR180204 treatment. CONCLUSIONS: Taken together, these results revealed an unexpected role of AgNPs in promoting adiposity through the inhibition of beige adipocyte differentiation and functionality, possibly by disrupting ROS homeostasis and ERK phosphorylation. Future assessments on the health risk of AgNPs applications and their safe dosages are warranted.

Magnetic interactions in two heterobridged dinuclear copper(II) complexes: orbital complementarity or countercomplementarity?

The mechanisms of magnetic exchange interactions in two heterobridged mu-hydroxyl-mu-X dicopper complexes A and B (X = azaindole for A and X = pyrazole for B) are investigated by the calculations based on density functional theory combined with the broken-symmetry approach (DFT-BS). It is found that although the coordination circumstances of the copper centers in the two complexes are very similar, the magnetic magnitudes and signs are diametrically opposed. By the theoretical analyses of magnetic orbital interaction and spin distribution, it is indicated that the difference between the magnetic properties of the two complexes is due to the distinction of orbital interaction of two bridge ligands. Namely, the weak ferromagnetic coupling for complex A arises from the orbital countercomplementarity of the hydroxo and azaindole bridges while the strong antiferromagnetic coupling for complex B arises from the orbital complementarity of the hydroxo and pyrazolato bridges.

Pilot investigation on formation of 2,4,6-trichloroanisole via microbial O-methylation of 2,4,6-trichlorophenol in drinking water distribution system: An insight into microbial mechanism.

Taste & odor (T&O) problems in drinking water are always complained by customers. Recent studies have indicated biofilms in drinking water distribution system (DWDS) are always ignored as potential sources of T&O compounds. In this paper, the formation of 2,4,6-trichloroanisole (2,4,6-TCA), one of the dominant T&O compounds, was investigated in a pilot-scale DWDS. The addition of precursor 2,4,6-trichlorophenol (2,4,6-TCP) of 0.2 mg/L induced the formation of 2,4,6-TCA with a maximum yield of ∼400 ng/L, and the formation kinetics can be described by a pseudo-first-order kinetic model. Effects of water distribution factors such as pipe material, temperature, flow velocity, and residual chlorine on the formation of 2,4,6-TCA were evaluated, and the pipe material was found to have the most remarkable effect. Ductile iron and stainless steel pipes produced much more 2,4,6-TCA than polyethylene (PE) pipe. The biofilm microbial communities on the three types of pipe walls were then comprehensively analyzed by heterotrophic plate count and 16S rRNA/ITS1 genes high throughput sequencing. The links between the 2,4,6-TCA formation potential and the microbial activity in genus and enzymatic levels in DWDS have been revealed for the first time. According to the characteristics of microbial assemblages of producing 2,4,6-TCA, quorum-sensing (QS) bacterial signaling system and extracellular DNA (eDNA) may be two promising targets for biofilm treatment and 2,4,6-TCA control in DWDS.

An overview of nanomaterials applied for removing dyes from wastewater.

Organic dyes are one of the most commonly discharged pollutants in wastewaters; however, many conventional treatment methods cannot treat them effectively. Over the past few decades, we have witnessed rapid development of nanotechnologies, which offered new opportunities for developing innovative methods to treat dye-contaminated wastewater with low price and high efficiency. The large surface area, modified surface properties, unique electron conduction properties, etc. offer nanomaterials with excellent performances in dye-contaminated wastewater treatment. For examples, the agar-modified monometallic/bimetallic nanoparticles have the maximum methylene blue adsorption capacity of 875.0 mg/g, which are several times higher than conventional adsorbents. Among various nanomaterials, the carbonaceous nanomaterials, nano-sized TiO2, and graphitic carbon nitride (g-C3N4) are considered as the most promising nanomaterials for removing dyes from water phase. However, some challenges, such as high cost and poor separation performance, still limit their engineering application. This article reviewed the recent advances in the nanomaterials used for dye removal via adsorption, photocatalytic degradation, and biological treatment. The modification methods for improving the effectiveness of nanomaterials are highlighted. Finally, the current knowledge gaps of developing nanomaterials on the environmental application were discussed, and the possible further research direction is proposed.

Application of magnetic OMS-2 in sequencing batch reactor for treating dye wastewater as a modulator of microbial community.

The potential and mechanism of synthesized magnetic octahedral molecular sieve (Fe3O4@OMS-2) nanoparticles in enhancing the aerobic microbial ability of sequencing batch reactor (SBR) for treating dye wastewater have been revealed in this study. The addition of Fe3O4@OMS-2 of 0.25g/L enhanced the decolorization of SBRs with an operation cycle of 24h by more than 20%. The 16S rRNA gene high-throughput sequencing indicated Fe3O4@OMS-2 increased the microbial richness and diversity of SBRs, and more importantly, promoted the potential dye-degrading bacteria. After a series of enriching and screening, four bacterial strains with the considerable decolorizing ability were isolated from SBRs, designating Alcaligenes faecalis FP-G1, Bacillus aryabhattai FP-F1, Escherichia fergusonii FP-D1 and Rhodococcus ruber FP-E1, respectively. The growth and decolorization of these pure strains were promoted in the presence of Fe3O4@OMS-2, which agrees with the result of high-throughput sequencing. Monitoring dissolved Fe/Mn ions and investigating the change of oxidation states of Fe/Mn species discovered OMS-2 composition played the critical role in modulating the microbial community. The significant enhancement of Mn-oxidizing/-reducing bacteria suggested microbial Mn redox may be the key action mechanism of Fe3O4@OMS-2, which can provide numerous benefits for the microbial community and decolorization of SBRs.

Efficient Pb(II) removal using sodium alginate-carboxymethyl cellulose gel beads: Preparation, characterization, and adsorption mechanism.

Alginate-carboxymethyl cellulose (CMC) gel beads were prepared in this study using sodium alginate (SA) and sodium CMC through blending and cross-linking. The specific surface area and aperture of the prepared SA-CMC gel beads were tested. The SA-CMC structure was characterized and analyzed via infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Static adsorption experiment demonstrated that Pb(II) adsorption of SA-CMC exceeded 99% under the optimized conditions. In addition, experiments conducted under the same experimental conditions showed that the lead ion removal efficiency of SA-CMC was significantly higher than that of conventional adsorbents. The Pb(II) adsorption process of SA-CMC followed the Langmuir adsorption isotherm, and the dynamic adsorption model could be described through a pseudo-second-order rate equation. Pb(II) removal mechanisms of SA-CMC, including physical, chemical, and electrostatic adsorptions, were discussed based on microstructure analysis and adsorption kinetics. Chemical adsorption was the main adsorption method among these mechanisms.

Theoretical elucidation on the antioxidant mechanism of curcumin: a DFT study.

[reaction: see text] Bond dissociation enthalpies (BDEs) for the curcumin-related compounds have been calculated using density functional theory (DFT) methods. It was found that the antioxidant mechanism of curcumin was a H-atom abstraction from the phenolic group, not from the central CH2 group in the heptadienone link. Curcumin, methylcurcumin, and half-curcumin had similar O-H BDEs, indicating that the two phenolic groups in curcumin were independent of each other.

Theoretical studies on degradation mechanism for OH-initiated reactions with diuron in water system.

Diuron, a chlorine-substituted dimethyl herbicide, is widely used in agriculture. Though the degradation of diuron in water has been studied much with experiments, little is known about the detailed degradation mechanism from the molecular level. In this work, the degradation mechanisms for OH-induced reactions of diuron in water phase are investigated at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level with polarizable continuum model (PCM) calculation. Three reaction types including H-atom abstraction, addition, and substitution are identified. For H-atom abstraction reactions, the calculation results show that the reaction abstracting H atom from the methyl group has the lowest energy barrier; the potential barrier of ortho- H (H1') abstraction is higher than the meta- H abstraction, and the reason is possibly that part of the potential energy is to overcome the side chain torsion for the H1' abstraction reaction. For addition pathways, the ortho- site (C (2) atom) is the most favorable site that OH may first attack; the potential barriers for OH additions to the ortho- sites (pathways R7 and R8) and the chloro-substituted para- site (R10) are lower than other sites, indicating the ortho- and para- sites are more favorable to be attacked, matching well with the -NHCO- group as an ortho-para directing group.

Structure-activity relationships of tanshinones in activating Nrf2. A DFT study and implications for multifunctional antioxidant discovery.

A series of recent studies reveal that tanshinones, derived from the traditional Chinese herbal medicine Salvia miltiorrhiza Bunge, are promising multifunctional antioxidants by activating nuclear factor (erythroid-derived 2) - like 2 (Nrf2). It is thus of great interest to elucidate their structure-activity relationships (SAR) for Nrf2 activation. In this study, two theoretical parameters characterizing the electron-abstracting potential, namely, electron affinity (EA) and energy level of the lowest unoccupied molecular orbital (ELUMO), are calculated by a density functional theory (DFT) method. By these parameters, we provide a satisfactory explanation to the SAR oftanshinones for activating Nrf2, which is helpful to find new multifunctional antioxidants.

DFT comparison of the OH-initiated degradation mechanisms for five chlorophenoxy herbicides.

To compare the OH-initiated reaction mechanisms of five chlorophenoxy herbicides, density functional theory (DFT) calculations of reactions in which ·OH attacks one of three active positions on each herbicide were carried out at the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) level. For each herbicide, the calculation results show that ·OH addition to the C1 atom, which is the nexus between the benzene ring and the side group, possesses the lowest energy barrier among the three kinds of reactions, indicating that ·OH addition-substitution of the side chain is the most energetically and kinetically favorable reaction mechanism. Comparisons among the herbicides show that the mechanisms are affected by the steric hindrance and the electronegativities of the -CH3 and -Cl groups. When comparing the addition of ·OH to the C1 site among the five herbicides, the activation energy for the reaction of ·OH with DCPP reaction is the lowest (3.61 kcal mol(-1)), while that for the ·OH and 4-CPA reaction was the highest (5.91 kcal mol(-1)). ·OH addition to the C4 site presents the highest energy barriers among the three kinds of reactions, indicating that the para Cl is difficult to break down. When comparing the H-atom abstraction reactions of the five herbicides, the H atoms in the -CH2- group of 2,4-D are the easiest for ·OH to abstract, whereas those of DCPP and MCPP are more difficult to abstract, due to the steric hindrance of the -CH3 group. Additionally, the results obtained from the PCM calculations reveal that most of the reactions occur more easily in water than in gas, though the mechanisms involved are the same as those discussed above.