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1.
Int J Mol Sci ; 20(21)2019 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-31683506

RESUMO

Benzofuran (BF), benzothiophene (BT), indole (IN), dibenzofuran (DBF), dibenzothiophene (DBT), and carbazole (CA) are typical heterocyclic aromatic compounds (NSO-HETs), which can coexist with polycyclic aromatic hydrocarbons (PAHs) in combustion and pyrolysis conditions. In this work, quantum chemical calculations were carried out to investigate the formation of DBF, DBT, and CA from the reactions of BF, BT, and IN with a cyclopentadienyl radical (CPDyl) by using the hybrid density functional theory (DFT) at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants of crucial elementary steps were deduced over 600-1200 K, using canonical variational transition state theory with a small-curvature tunneling contribution (CVT/SCT). This paper showed that the production of DBF, DBT, and CA from the reactions of BF, BT, and IN with CPDyl involved six elementary steps: the addition reaction, ring closure, the first H shift, C-C cleavage, the second H shift, and elimination of CH3 or H. The cleavage of the C-C bond was regarded as the rate-determining step for each pathway due to the extremely high barrier. The 1-methyl substituted products were more easily formed than the 4-methyl substituted products. The main products were DBF and 1-methyl-DBF, DBT and 1-methyl-DBT, and CA and 1-methyl-CA for reactions of BF, BT, and IN with CPDyl, respectively. The ranking of DBF, DBT, and CA formation potential was as follows: DBT and methyl-DBT formation > DBF and methyl-DBF formation > CA, and methyl-CA formation. Comparison with the reaction of naphthalene with CPDyl indicated that the reactions of CPDyl attacking a benzene ring and a furan/thiophene/pyrrole ring could be inferred to be comparable under high temperature conditions.

2.
Environ Res ; 179(Pt A): 108709, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31479872

RESUMO

Nitrated phenols are receiving increasing attention due to their adverse impacts on the environment and human health. Previous measurements have revealed the non-ignorable contribution of vehicle exhaust to atmospheric nitrated phenols in urban areas. However, there is a lack of comprehensive understanding of the emission characteristics and the total emission of nitrated phenols from current on-road traffic. This study investigated the emissions from eight passenger vehicles, eight trucks, and two taxis, with fuel types including diesel, gasoline, and compressed natural gas. Exhaust emissions were collected and measured using a mobile measurement system on two testing routes. Twelve nitrated phenols in the collected fine particulate matter were detected using ultrahigh performance liquid chromatography-mass spectrometry. Overall, the emission profiles of fine particulate nitrated phenols varied with vehicle load and fuel type. The 4-nitrophenol and its methyl derivatives were dominant nitrated phenol species emitted by the vehicles with proportions of 38.4%-68.0%, which is significantly different from the proportions of nitrated phenols emitted from biomass burning and coal combustion. The emission factors also exhibited large variations across vehicle type, fuel type, and emission standards, with relatively low values for gasoline vehicles and taxis fueled by compressed natural gas and high values for diesel vehicles. Based on the emission factors of nitrated phenols from different vehicles, the estimated total emission of nitrated phenols from on-road vehicles in China was 58.9 Mg (-86%-85% within 95% confidence interval), with diesel trucks contributing the most substantial fractions. This work highlights the very high level of emissions of nitrated phenols from diesel vehicles and provides an essential basis for atmospheric modeling and effective pollution control.

3.
Phys Chem Chem Phys ; 21(39): 21856-21866, 2019 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-31553018

RESUMO

Methoxyphenols, as the main products and tracers of biomass burning, have been demonstrated to play an important role in the formation of secondary organic aerosols. However, their chemical transformation and migration in the atmosphere haven't been well characterized. In this study, detailed gas-phase reaction mechanisms and kinetics of three representative methoxyphenols (guaiacol, creosol and syringol) with OH radicals were investigated by using density functional theory (DFT). The initial reactions of methoxyphenols with OH radicals proceed via two different patterns, including OH-addition and H-atom abstraction. Subsequent reaction schemes of the active intermediates in the presence of O2/NOx are thoughtfully modeled. Catechol, methyl glyoxylate, malealdehyde and carbonyl or carboxyl compounds were confirmed as the dominant oxidation products for guaiacol. As a supplementary study, the formation pathways for the expected products nitroguaiacol and nitrocatechol were presented in high-NO2 conditions. Total and individual rate coefficients are calculated using the MESMER program at 294 K and 1 atm. The lifetimes of guaiacol, creosol and syringol were estimated to be 4.27, 3.56 and 2.98 hours, respectively, which are strongly competitive with the solar photolysis of methoxyphenols.

4.
Environ Int ; 131: 104999, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31319293

RESUMO

Widely distributed fluorocarboxylic acids have aroused worldwide environmental concerns due to its toxicity, persistence, and bioaccumulation. Enzyme-based eco-friendly biodegradation techniques have become increasingly important in treating fluorocarboxylic acids. Here we utilized in silico and in vitro approaches to investigate the defluorination mechanism of fluoroacetate dehalogenase (FAcD) toward monofluoropropionic acids at atomic-level. The experimentally determined kcat and kM for defluorination of 2-fluoropropionic acid are 330 ±â€¯60 min-1 and 6.12 ±â€¯0.13 mM. The in silico results demonstrated positive/negative correlations between activation barriers and structural parameters (e.g. distance and angle) under different enzymatic conformations. We also screened computationally and tested in vitro (enzyme assay and kinetic study) the catalytic proficiency of FAcD toward polyfluoropropionic acids and perfluoropropionic acids which are known to be challenging for enzymatic degradation. The results revealed potential degradation activity of FAcD enzyme toward 2,3,3,3-tetrafluoropropionic acids. Our work will initiate the development of a new "integrated approach" for enzyme engineering to degrade environmentally persistent fluorocarboxylic acids.

5.
Artigo em Inglês | MEDLINE | ID: mdl-31215383

RESUMO

Plant development is different from the animal by many fundamental aspects, immobilized cell, rigid cell wall, and the large central vacuole. The plant growth and cell division activities are restricted to the specific area of the shoot and root called meristems, and the plants have highly totipotency ability of differentiation, dedifferentiation and redifferentiation. Growth is one of the primary and conspicuous characteristics of living organisms. Growth is generally defining the irreversible permanent increase in the size of the organ or even single cell, due to both cell division and expansion. The plants pass through different stages e.g. embryonic, vegetative and reproductive, and in each stage, they produce different organs on the same stem. The height and girth of the plants grow continuously but leaves and flowers have definite dimensional size and fall down periodically. Where and how the structures like shoots, roots, leave and the flower is differentiated from same mother cell (zygote)? All the plant's organs are made of different tissues dermal, vascular and ground tissue and each tissue have precious role in plant survival and development. How the plant organs arrange spatial around the stem axis clock or anti clock wise direction (phyllotaxis)? The plant hormone is one of the important factors which control the plant development; the development is the combine process of growth and differentiation. So the differentiation is the process in which the cell are organized into different shape and functions according to the genetically and environmental signal. In this chapter, we will study both the intrinsic and extrinsic factors which govern the growth and differentiation. Briefly study some basic genetic modification occur in the cell, cell signaling during growth and differentiation. We need to know generally about the three basic structures of the plant organs root, shoot, and leaves.

6.
Chemosphere ; 231: 126-133, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31128347

RESUMO

Massively used plastics have caused worldwide environmental concerns. Polyesters like polylactic acid (PLA) are one of the mostly used plastics due to its excellent physical and chemical properties and low-cost advantages. It is critical to develop the elimination and recycle techniques for polyesters. Experimental studies have shown that a hydrolase RPA1511 isolated from Rhodopseudomonas palustris can efficiently depolymerize polylactic acid (PLA) into oligomers and monomers. It was also active against emulsified aliphatic polymers as well as multipurpose soluble ester monomers (α-naphthyl ester and p-nitrophenyl ester). In the present study, molecular dynamics simulations and molecular mechanics Poisson-Boltzmann surface area method were applied to screen all amino acids from hydrolase RPA1511 and identify the most important amino acids during substrate binding. Seven substrates were considered: PLA (dimer and tetramer), polycaprolactone, butylene succinate, 1-naphthyl acetate, 2-naphthyl formate, p-nitrophenyl acetate. The results highlighted the importance of amino acids like Tyr139, Tyr213, Arg259, Thr46. Subsequent quantum mechanics/molecular mechanics calculations were also performed to determine the detailed degradation mechanism of hydrolase RPA1511 toward PLA and explore the role of the active site residues during catalysis. The results demonstrated that degradation involves two elementary steps: enzyme acylation and PLA hydrolysis. The corresponding Boltzmann average barriers are 20.40 kcal/mol and 14.45 kcal/mol. The electrostatic influence analysis of 15 amino acids on the rate-determining step indicated that amino acids His114, Trp219 and Ala273 facilitate the reaction while the Arg244 suppresses the reaction which may serve as future mutation studies to enhance the enzymatic efficiency.


Assuntos
Biodegradação Ambiental , Poliésteres/metabolismo , Rodopseudomonas/metabolismo , Catálise , Simulação por Computador , Hidrolases , Hidrólise , Plásticos/metabolismo , Polímeros/química , Succinatos/metabolismo
7.
Int J Mol Sci ; 20(11)2019 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-31141990

RESUMO

Chlorothiophenols (CTPs) are known to be key and direct precursors of polychlorinated thianthrene/dibenzothiophenes (PCTA/DTs). Self/cross-coupling of the chlorothiophenoxy radicals (CTPRs), sulfydryl-substituted phenyl radicals and thiophenoxyl diradicals evolving from CTPs are initial and important steps for PCTA/DT formation. In this study, quantum chemical calculations were carried out to investigate the homogenous gas-phase formation of PCTA/DTs from self/cross-coupling of 2,4-dichlorothiophenoxy radical (R1), 2-sulfydryl-3,5-dichlorophenyl radical (R2) and 3,5-dichlorothiophenoxyl diradical (DR) at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants of crucial elementary steps were deduced over 600-1200 K, using canonical variational transition state theory with a small curvature tunneling contribution. For the formation of PCTAs, the S•/σ-C• condensation with both thiophenolic sulfur in one radical and ortho carbon in the other radical bonded to single electron is the most efficient sulfur-carbon coupling mode, and the ranking of the PCTA formation potential is DR + DR > R2 + DR > R1 + DR > R1 + R2 > R1 + R1. For the formation of PCDTs, the σ-C•/σ-C• coupling with both ortho carbon in the two radicals bonded to single electron is the energetically favored carbon-carbon coupling mode, and the ranking of the PCDT formation potential is: R2 + DR > R2 + R2 > R1 + DR > R1 + R2 > R1 + R1. The PCTA/DTs could be produced from R1, R2 and DR much more readily than PCDD/DFs from corresponding oxygen substituted radicals.


Assuntos
Compostos Heterocíclicos/síntese química , Compostos de Sulfidrila/síntese química , Tiofenos/síntese química , Simulação por Computador , Cinética
8.
Sci Total Environ ; 674: 234-241, 2019 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-31005830

RESUMO

cis-Pinonic acid (CPA), one of the major photooxidation products of α-pinene, is believed to contribute to the formation of aerosols formed over forested areas. In the current study, we implement quantum chemical calculation to investigate the interaction between sulfuric acid (SA) and CPA as well as the hydrolysate of CPA (HCPA) in the presence of water or ammonia in the atmosphere. The lowest free energy configurations, reactants, transition states, intermediates, and products were optimized at 298/278K and 1atm at the M06-2X/6-311+G(3df,3pd) level. Our results show that one CPA molecule might initially nucleate with SA molecules and subsequently participate in the formation and growth of the new particle in the form of HCPA. More than one HCPA molecule may be involved in the critical nuclei. Furthermore, the hydrolysis reaction of CPA can be effectively catalyzed by SA and nitric acid (NA) in presence of water, which significantly increases the HCPA content in the atmosphere and subsequently promotes the particle nucleation. Overall, the current study elucidates a new mechanism of atmospheric nucleation driven by CPA and its hydrolysate.

9.
Int J Mol Sci ; 20(7)2019 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-30934774

RESUMO

Polychlorinated phenoxathiins (PCPTs), polychlorinated dibenzothiophenes (PCDTs), and polychlorinated thianthrenes (PCTAs) are sulfur analogues of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/DFs). Chlorothiophenols (CTPs) and chlorophenols (CPs) are key precursors for the formation of PCTA/PT/DTs, which can react with H or OH to form chloro(thio)phenoxy radical, sulfydryl/hydroxyl-substituted phenyl radicals, and (thio)phenoxyl diradicals. However, previous radical/radical PCTA/DT formation mechanisms in the literature failed to explain the higher concentration of PCDTs than that of PCTAs under the pyrolysis or combustion conditions. In this work, a detailed thermodynamics and kinetic calculations were carried out to investigate the pre-intermediate formation for PCTA/PT/DTs from radical/molecule coupling of the 2-C(T)P with their key radical species. Our study showed that the radical/molecule coupling mechanism explains the gas-phase formation of PCTA/PT/DTs in both thermodynamic and kinetic perspectives. The S/C coupling modes to form thioether-(thio)enol intermediates are preferable over the O/C coupling modes to form ether-(thio)enol intermediates. Thus, although the radical/molecule coupling of chlorophenoxy radical with 2-C(T)P has no effect on the PCDD/PT formation, the radical/molecule coupling of chlorothiophenoxy radical with 2-C(T)P plays an important role in the PCTA/PT formation. Most importantly, the pre-PCDT intermediates formation pathways from the couplings of sulfydryl/hydroxyl-substituted phenyl radical with 2-C(T)P and (thio)phenoxyl diradicals with 2-C(T)P are more favorable than pre-PCTA/PT intermediates formation pathways from the coupling of chlorothiophenoxy radical with 2-C(T)P, which provides reasonable explanation for the high PCDT-to-PCTA ratio in the environment.


Assuntos
Clorofenóis/química , Dibenzofuranos/química , Compostos Heterocíclicos/química , Teoria Quântica , Tiofenos/química , Radicais Livres/química , Cinética , Conformação Molecular
10.
Sci Total Environ ; 673: 414-423, 2019 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-30991331

RESUMO

The various applications of iron oxide nanoparticles (NPs) in clinical care and wastewater treatment are rapidly developing, thus their biological safety is worth attention. The electrostatic interaction between cell membranes and NPs is the key mechanism behind membrane damage and membrane penetration. Cell membranes are generally negatively charged with a few positively charged domains. The role of the positively charged sites in the NP-membrane interaction needs further investigation. In this study, the ratio of the positively charged sites was adjusted in two model cell membranes: giant and small unilamellar vesicles (GUVs and SUVs). After exposure to negatively charged γ-Fe2O3 NPs, the adhesion of NPs on the membranes and the induced membrane disruption were studied by microscopic observation and quartz crystal microbalance (QCM) monitoring. γ-Fe2O3 NPs adhered to and disrupted the membranes containing even few positively charged sites, although the whole membrane exhibited a negative zeta potential and hence electrostatically repels the NPs. The number of adhered γ-Fe2O3 NPs increased remarkably on membranes with overall positive zeta potential, but more serious disruption happened to membranes with higher ratios of positively charged sites. Therefore, the membrane rupture was more correlated to the number of positively charged sites than to the zeta potential of the whole membrane. In addition, exposure to γ-Fe2O3 NPs decreased the order of the lipid molecules and hence increased the fluidity of the membrane phase, and the most significant phase change occurred in the negatively charged membrane with the highest ratio of positively charged sites. Infrared spectra indicated that γ-Fe2O3 NPs probably interact with the membranes via the phosphodiester and trimethylamine groups in the lipid head groups. Our research furthers our knowledge of the electrostatic interaction between NPs and cell membranes, which should help to predict the biological effects of γ-Fe2O3 NPs.


Assuntos
Membrana Celular/química , Nanopartículas/química , Compostos Férricos/química , Eletricidade Estática
11.
Sci Total Environ ; 669: 920-929, 2019 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-30897445

RESUMO

Atmospheric oxidation of fluorene and its derivatives initiated by OH radicals was investigated theoretically with quantum chemical calculation methods [M06-2X/6-311++G(3df,2p)//M06-2X/6-311+G(d,p)]. It revealed that the OH addition pathways form hydroxyfluorene and ring-opening product dialdehyde while the H abstraction pathways lead to the formation of 9-fluorenone. Subsequent oxidation of 9-fluorenone has considerable potential to form dibenzo-p-dioxin and nitrofluorenone according to the present calculation results. The atmospheric lifetime of fluorene relative to the reactions with OH radicals is deduced to be 12.51 h based on the calculated overall rate constant (2.29 × 10-11 cm3 molecule-1 s-1) at 298 K and 1 atm. The oxidation products of fluorene in the atmosphere are generally more toxic and persistent. This work provides a comprehensive explanation for atmospheric oxidation processes of fluorene and facilitates clarifying its environmental risks.

12.
J Mol Model ; 25(2): 53, 2019 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-30712174

RESUMO

The original version of this article unfortunately contained a mistake. The sequence of the author affiliations was incorrect. The correct information is given below.

13.
J Phys Chem B ; 123(10): 2244-2253, 2019 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-30776233

RESUMO

An extradiol-cleaving catecholic dioxygenase, 2,3-dihydroxybiphenyl dioxygenase, plays important roles in the catabolism of biphenyl/polychlorinated biphenyl aromatic contaminants in the environment. To better elucidate the biodegradable pathway, a theoretical investigation of the ring-opening degradation of 2,3-dihydroxybiphenyl (DHBP) was performed with the aid of quantum mechanical/molecular mechanical calculations. A quintet state of the DHBP-iron-dioxygen group adducts was found to be the reactive state with a substrate radical-FeII-superoxo (DHBP•↑-FeII-O2•-↓) character. The HOO• species was the reactive oxygen species responsible for the subsequent attack of DHBP. Among the whole reaction energy profile, the first step in proton-coupled electron transfer was determined to be the rate-determining step with a potential energy barrier of 17.2 kcal/mol, which is close to the experimental value (14.7 kcal/mol). Importantly, the residue His194 shows distinct roles in the catalytic cycle, where it acts as an acid-base catalyst to deprotonate the hydroxyl group of DHBP at an early stage, then stabilizes the negative charge on the dioxygen group, and, at the final stage, promotes the semialdehyde product formation as a proton donor.

14.
Chem Res Toxicol ; 32(4): 603-612, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30794404

RESUMO

The metabolic activation and transformation of naphthalene by the cytochrome P450 enzyme (CYP 1B1) plays an important role in its potential carcinogenicity. The process has been explored by a quantum mechanics/molecular mechanics (QM/MM) computational method. Molecular dynamic simulations were performed to explore the interaction between naphthalene and CYP 1B1. Naphthalene involves α- and ß-carbon, the electrophilic addition of which would result in different reaction pathways. Our computational results show that both additions on α- and ß-carbon can generate naphthalene 1,2-oxide. The activation barrier for the addition on ß-carbon is higher than that for the α-carbon by 2.6 kcal·mol-1, which is possibly caused by the proximity between ß-carbon and the iron-oxo group of Cpd I in the system. We also found that naphthalene 1,2-oxide is unstable and the O-C bond cleavage easily occurs via cellular hydronium ion, hydroxyl radical/anion; then it will convert to the potential ultimate carcinogen 1,2-naphthoquinone. The results demonstrate and inform a detailed process of generating naphthalene 1,2-oxide and new predictions for its conversion.

15.
Chemosphere ; 221: 11-20, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30634144

RESUMO

Interactions between metals and anaerobic ammonium oxidizing consortia substantially affect the quality of wastewater treatment plant effluent. In this study, we conducted acid-base titrations to ascertain the surface reactivity and proton adsorptive capacity of anammox consortia. A combination of titration data modeling and infrared spectroscopy suggested the presence of carboxyl, amine, and hydroxyl groups. Cd adsorption experiments demonstrate that 1 g of dry biomass could bind an equivalent of 7.12 × 10-6 mol/L of Cd. Density functional theory calculations further reveal that carboxyl and hydroxyl groups are able to form stable Cd complexes. Furthermore, considerable carboxyl and hydroxyl groups promote bacterial aggregation, and thus solid-liquid separation. The results of this study highlight the potential role of anammox consortia in adsorbing metal cations, and thus help to improve the understanding of the universally significant contribution of anammox consortia at the detoxification of metal cations in wastewater treatment systems.


Assuntos
Adsorção , Bactérias Anaeróbias/metabolismo , Consórcios Microbianos , Oligoelementos , Águas Residuárias/química , Compostos de Amônio/metabolismo , Biomassa , Reatores Biológicos/microbiologia , Cádmio/metabolismo , Oxirredução , Purificação da Água/métodos
16.
Sci Total Environ ; 662: 41-47, 2019 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-30684901

RESUMO

Polychlorinated dibenzo­p­dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic, carcinogenic and mutagenic to humans. As precursors of PCDD/Fs, dibenzofuran (DF) and dibenzo­p­dioxin (DD) have received considerable public and scientific attention. To reduce the emission of PCDD/Fs, it is critical to explore the formation mechanisms of DF and DD. The present study delineated the DF and DD formation mechanisms from anthracene partial oxidation with the aid of high-accuracy quantum chemistry calculations. The rate constants of crucial elementary steps were obtained utilizing canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) correction. The results indicate that anthracene could be important precursor of DF and DD, because of the potential barriers for all the major elementary reactions are lower than 33.54kcalmol-1. This work also reveals that water molecule plays an important catalytic effect during the formation of both DF and DD by lowering the barriers of about 27.24kcalmol-1. For the water-assisted formation pathway, DF is the dominate product of anthracene partial oxidation with the highest barrier of 30.45kcalmol-1. For the non-water-assisted formation pathway, DD is the dominate product with the highest barrier of 33.54kcalmol-1.

17.
Chemosphere ; 219: 645-654, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30557720

RESUMO

As an effective organochlorine pesticide, Dicofol has been extensively applied in more than 30 countries for protecting over 60 different crops. Considering its large consumption and potential adverse effect on human health (endocrine disrupting and carcinogenicity), the fate of Dicofol sprayed into the air is of public concern. In this study, we conducted a comprehensive study on the reaction mechanisms of p,p'-Dicofol with OH and NO3 radicals using DFT method. Comparing the abstrations by OH and NO3 radical, OH and NO3 radical addition reactions are predominant due to the lower potential barriers and stronger heat release. The phenolic substances (P1P5), epoxides (P11 and P15), dialdehyde (P13) and other species (P8, P9, P10 and P14) are generated by OH additions and their subsequent reactions while OH abstraction reactions produce DCBP, P7 and chlorphenyl radical. Particularly, NO3 additions and their subsequent reactions yield dialdehydes (P16 and P17) and 2,8-DCDD, which is the first report of the generation of dioxin from atmospheric oxidation of p,p'-Dicofol. Additionally, based on the structure optimization and energy calculation, rate constants and Arrhenius formulas of the elementary reactions of p,p'-Dicofol with OH and NO3 radicals were obtained over the temperature range of 280-380 K and at 1 atm. The rate constants for the reactions of p,p'-Dicofol with OH and NO3 radicals are 1.51 × 10-12 and 8.88 × 10-14 cm3 molecule-1 s-1, respectively. The lifetime (τTotal) of p,p'-Dicofol determined by the reactions of OH and NO3 radical is 5.86 h, indicating a potential long-range transport in the atmosphere.


Assuntos
Poluentes Atmosféricos/química , Atmosfera/química , Dicofol/química , Radicais Livres/química , Radical Hidroxila/química , Inseticidas/química , Cinética , Nitratos/química , Oxirredução , Temperatura Ambiente
18.
Chemosphere ; 214: 781-790, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30296766

RESUMO

Amides, a class of nitrogen-containing organic pollutants in the atmosphere, may affect the formation of atmospheric aerosols by the interactions with sulfuric acid. Here, the molecular interactions of sulfuric acid with formamide, methylformamide, dimethylformamide, acetamide, methylacetamide and dimethylacetamide was investigated by density functional theory. Geometry optimization and Gibbs free energy calculation were carried out at M06-2X/6-311++G(3df,3pd) level. The results indicate that the addition of amides to H2SO4 might have a promoting effect on atmospheric new particle formation at 298.15 K and 1 atm. In the initial stage of new particle formation, the binding capacity of amides and sulfuric acid is stronger than ammonia, but weaker than methylamine. It is worth noting that the trans-methylacetamide could have similar capabilities of stabilizing sulfuric acid as dimethylamine. In the presence of water, amides are found to only have a weak enhancement capability on new particle formation. In addition, we can infer from evaporation rate that the small molecule clusters of formamide and sulfuric acid may be more energetically favorable than macromolecule clusters.


Assuntos
Amidas/química , Teoria da Densidade Funcional , Ácidos Sulfúricos/química , Ligações de Hidrogênio
19.
Nanotechnology ; 30(9): 095202, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30561381

RESUMO

In this paper, a near-ideal subthreshold swing MoS2 back-gate transistor with an optimized ultrathin HfO2 dielectric layer is reported with detailed physical and electrical characteristics analyses. Ultrathin (10 nm) HfO2 films created by atomic-layer deposition (ALD) at a low temperature with rapid-thermal annealing (RTA) at different temperatures from 200 °C to 800 °C have a great effect on the electrical characteristics, such as the subthreshold swing (SS), on-to-off current (I ON/I OFF) ratio, etc, of the MoS2 devices. Physical examinations are performed, including x-ray diffraction, atomic force microscopy, and electrical experiments of metal-oxide-semiconductor capacitance-voltage. The results demonstrate a strong correlation between the HfO2 dielectric RTA temperature and the film characteristics, such as film density, crystallization degree, grain size and surface states, inducing a variation in the electrical parameters, such as the leakage, D it, equivalent oxide thickness, SS, and I ON, as well as I ON/I OFF of the MoS2 field effect transistors with the same channel materials and fabrication methods. With a balance between the crystallization degree and the surface state, the ultrathin (10 nm) HfO2 gate dielectric RTA at 500 °C is demonstrated to have the best performance with a field effect mobility of 40 cm2 V-1 s-1 and the lowest SS of 77.6 mV-1 decade, which are superior to those of the control samples at other temperatures. The excellent transistor results with an optimized industry-based HfO2 ALD and RTA process provide a promising approach for MoS2 applications into the scaling of the nanoscale CMOS process.

20.
Ecotoxicol Environ Saf ; 168: 110-119, 2019 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-30384158

RESUMO

Bacteria are ubiquitous in the near-surface atmosphere where they constitute an important component of aerosols with the potential to affect climate change, ecosystems, atmospheric process and human health. Limitation in tracking bacterial diversity accurately has thus far prevented the knowledge of airborne bacteria and their pathogenic properties. We performed a comprehensive assessment of bacterial abundance and diverse community in PM2.5 collected at Mt. Tai, via high-throughput sequencing and real-time PCR. The samples exhibited a high microbial biodiversity and complex chemical composition. The dominating populations were gram-negative bacteria including Burkholderia, Delftia, Bradyrhizobium, and Methylobacterium. The PM mass concentration, chemical composition, bacterial concentration and community structure varied under the influence of different air-mass trajectories. The highest mass concentration of PM2.5 (61 µg m-3) and major chemical components were recorded during periods when marine southeasterly air masses were dominant. The local terrestrial air masses from Shandong peninsula and its adjacent areas harbored highest bacterial concentration loading (602 cells m-3) and more potential pathogens at the site. In contrast, samples influenced by the long-distance air flow from Siberia and Outer Mongolia were found to have a highest richness and diversity as an average, which was also marked by the increase of dust-associated bacteria (Brevibacillus and Staphylococcus). The primary research may serve as an important reference for the environmental microbiologist, health workers, and city planners.


Assuntos
Microbiologia do Ar , Poluentes Atmosféricos/análise , Monitoramento Ambiental , Material Particulado/análise , Administração por Inalação , Aerossóis/análise , Bactérias/classificação , Bactérias/isolamento & purificação , Biodiversidade , China , Análise por Conglomerados , Variações do Número de Cópias de DNA , Poeira/análise , Biblioteca Gênica , Humanos , RNA Ribossômico 16S/genética , Análise de Sequência de DNA
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