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The hydrogen-donor solvent (H-donor) used in direct coal liquefaction (DCL) plays a critical role in both the oil yield and distribution of the products. However, the mechanism of the reaction between H-donor and coal in the DCL is unclear. In this study, the reaction of H-donor and coal in the DCL was investigated using the model compounds tetralin (H-donor) and diphenylmethane (DPM, coal). Density functional theory calculations were employed to examine both pyrolytic radical and solvent-mediated hydrogenolysis mechanisms. Based on the computed results, a modified solvent-mediated hydrogenolysis mechanism was proposed, namely the synergistic double-hydrogen-transfer mechanism, in which the β- and α-hydrogen atoms simultaneously transfer from tetralin to the ipso- and meta-carbon atoms of DPM. The calculated energy barriers of hydrogen transfer were lower than most of the bond dissociation enthalpies for coal. The energy barriers range of the synergistic double-hydrogen-transfer reaction did not correlate with the dissociation enthalpies of Caryl−Calkyl bond, although they were consistent with the order of the hydrogen-donating abilities of different solvents. This study may provide a theoretical guidance to improve the efficiency of H-donor in the DCL.

The low-temperature coal tar contains a considerable number of oxygen-containing compounds, which results in poor quality. The catalytic hydrodeoxygenation of oxygen-containing compound to an added-value chemical compound is one of the most efficient methods to upgrade coal tar. In this study, density functional theory calculations are employed to assess and analyze in detail the hydrodeoxygenation of dibenzofuran, as a model compound of coal tar, on the Ni (1 1 1) surface. The obtained results indicate that dibenzofuran can be firstly hydrogenated to tetrahydrodibenzofuran and hexahydrodibenzofuran. The five-membered-ring opening reaction of tetrahydrodibenzofuran is more straightforward than that of hexahydrodibenzofuran (Ea = 0.71 eV vs. 1.66 eV). Then, both pathways generate an intermediate 2-cyclohexylphenoxy compound. One part of 2-cyclohexylphenoxy is hydrogenated to 2-cyclohexylphenol and consecutively hydrogenated to cyclohexylcyclohexanol, and another part is directly hydrogenated to cyclohexylcyclohexanone. The hydrogenated intermediates of 2-cyclohexylphenol have higher deoxygenation barriers than 2-cyclohexylphenol and cyclohexylcyclohexanol. During the hydrogenation process of cyclohexylcyclohexanone to cyclohexylcyclohexanol, the intermediate 26, formed by adding H to O atom of cyclohexylcyclohexanone, exhibits the lowest deoxygenation barrier of 1.08 eV. High hydrogen coverage may promote the hydrogenation of tetrahydrodibenzofuran, hexahydrodibenzofuran, and intermediate 26 to generate dodecahydrodibenzofuran and cyclohexylcyclohexanol. This dibenzofuran hydrodeoxygenation reaction mechanism corroborates well with previous experimental results and provides a theoretical basis for further optimization of the design of nickel-based catalysts.

Catalytic hydrodeoxygenation is an efficient method to upgrade the quality of low-temperature coal tar and coal liquefied oil. However, only limited researches are performed on the mechanism of hydrodeoxygenation and, therefore, innovation of more efficient and stable catalysts is less progressed and still remains a challenging subject. In this study, density functional theory calculations are carried out to get a deeper insight in the mechanism of dibenzofuran hydrodeoxygenation on the Pt(111) surface. Calculated energies and activation barriers indicate that five-membered-ring opening of tetrahydrodibenzofuran is easier than that of hexahydrodibenzofuran. Then, the generated intermediate can be preferentially hydrogenated through a non-consecutive pathway to 2-cyclohexylphenol, and would result in multiple radical species. The dehydroxylation of that intermediate formed by adding five hydrogen atoms to the phenyl ring of 2-cyclohexylphenol shows a moderate reaction barrier of 1.07 eV; whereas, dehydroxylation of cyclohexylcyclohexanol needs a higher energy barrier of 2.04 eV. For the hydrodeoxygenation of dibenzofuran on the Pt(111) surface, the target product bicyclohexane is most likely to be formed through a radical intermediate. This investigation may provide a potent theoretical guidance to design new catalyst for hydrodeoxygenation of coal to liquid.

By adding different proportions of N-butylimidazole and carboxyethylthiosuccinic acid (CETSA), three hybrid systems of ionic liquids were synthesized and named ILHS1, ILHS2 and ILHS3. Using the weight loss method, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and contact angle test, it was determined that ILHS2 had the best corrosion inhibition among the three ionic liquid systems, and that the inhibition efficiency reached up to 90.63% when the concentration was 10 mM in 1 M HCl at 308 K. The adsorption isotherm was consistent with Langmuir adsorption, and combined with molecular dynamics simulation (MD), it was proved that mixed adsorption occurred on the metal interface. Polarization curves showed that the ionic liquid mixture systems could inhibit the corrosion of both poles, meaning that the anions and cations could act synergistically, and that the anions played a major role. The elemental and molecular structures of ILHS1, ILHS2 and ILHS3 were investigated using 1H NMR, which indicated that the three carboxyl groups on CETSA were regionally selective and combined with imidazole cations to form ionic liquid mixture systems.

The electron-rich nature of vinyl ethers (CH2═CHOR) enables their versatile reactivity patterns with transition metal catalysts. Furthermore, they are highly attractive monomers for the synthesis o...

The structure of transition state is very significant to further understand the related reaction system auxiliary N N bond cleavage process. Here, in order to sort out some DFT functionals in searching the transition states in a N N bond cleavage reaction mediated by the diiron complexes, we compared 49 density functionals with benchmark data of MP2 and DLPNO-CCSD(T) methods. By analyzing the structures and relative energies, we have found two HGGA functionals (B1B95, mPW1PBE) that are more consistently reliable ones. Among them, the B1B95 functional provides the most reliable energetic properties within 8.6 kcal/mol compared with the data of DLPNO-CCSD(T) method. And six HGGA functionals (B1B95, PBE0, mPW1PBE, mPW1PW91, HSEh1PBE, HSE1PBE) and two functionals (B2PLYP-D3, PBE0-D3) with D3 empirical dispersion well optimize the structure of Fe2S2 clusters and evaluate the reaction thermodynamic energy of N N bond cleave process. The functionals with long range correction and D3 empirical dispersion underestimate easily the energy barrier of N N bond cleavage of Fe2S2 clusters.

To induce double-proton transfer (DPT) with guanine in a biological environment, 12 cytosine analogues (Ca) were formed by atomic substitution. The DPT reactions in the Watson–Crick cytosine–guanine model complex (Ca0G) and 12 modified cytosine–guanine complexes (Ca1-12G) were investigated using density functional theory methods at the M06-2X/def2svp level. The intramolecular proton transfers within the analogues are not facile due to high energy barriers. The hydrogen bond lengths of the Ca1-12G complexes are shorter than those in the Ca0G complex, which are conducive to DPT reactions. The DPT energy barriers of Ca1-12G complexes are also lower than that of the Ca0G complex, in particular, the barriers in the Ca7G and Ca11G complexes were reduced to −1.33 and −2.02 kcal/mol, respectively, indicating they are significantly more prone to DPT reactions. The DPT equilibrium constants of Ca1-12G complexes range from 1.60 × 100 to 1.28 × 107, among which the equilibrium constants of Ca7G and Ca11G are over 1.0 × 105, so their DPT reactions may be adequate. The results demonstrate that those cytosine analogues, especially Ca7 and Ca11, are capable of inducing DPT with guanine, and then the guanine tautomer will form mismatches with thymine during DNA replication, which may provide new strategies for gene therapy.

Developing efficient, inexpensive, in situ tar reforming technologies under mild conditions is an important practical aspect of biomass gasification. In this study, a series of biochar-supported Ni...

The polymerization mechanism of functionalized styrene derivatives, viz., p-NMe2 (pMNS)-, o-/p-OCH3 (o/pMOS)-, and p-SCH3 (pMTS)-substituted styrene, catalyzed by cationic rare-earth-metal catalysts has been comparatively studied through density functional theory (DFT) calculations. Having achieved an agreement between theory and experiment, it is found that large steric hindrance as a main factor prevents oMOS from undergoing o-C–H activation relevant to step-growth polymerization, while the nonoccurrence of C–H activation of pMNS and pMTS can be explained by the relatively less dispersion of charge distribution in the four-center transition states. In addition, the electron-donating pyridine side arm weakened the interaction between pMOS and the metal center and meanwhile increased the steric hindrance, preventing the C–H activation. Therefore, the simultaneous occurrence of C–H activation (step-growth polymerization) and C═C insertion (chain-growth polymerization) are affected by multiple factors such ...

A full account of theoretical analyses at the DFT level has been reported, focusing on the formation and reactivity of a family of cationic [R-(CH2)n-Py-Sc(CH2SiMe3)]+ catalysts and the effects of counterion and solvation. Two sets of model systems have been considered: (a) structures having identical bridging unit (n = 1) but having varying cyclopentadienyl groups (R = Cp′ (1), R = Ind (2), and R = Flu (3)) and (b) systems with the identical cyclopentadienyl moiety (Flu) but with varying bridging groups (n = 1 (3), n = 0 (4), and n = 2 (5)). For complex 3, various metal ions (Sc, Y, La, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, and Lu) were considered to investigate the effect of central metals on the contact ion pairs (CIP). The formation and separation of CIP were found to be influenced by the steric hindrance of the ligand, the electron-donating ability of the cyclopentadienyl group, and the rare-earth-metal ion radius. The separation enthalpy of the CIPs decreases with increasing dielectronic constant of the s...

Density functional theory studies have been conducted for isoprene polymerization catalyzed by the cationic half-sandwich scandium alkyl species containing a methoxy side arm [(C5Me4C6H4OMe-o)Sc(CH2SiMe3)]+ (1) and that containing a phosphine oxide side arm [{C5Me4SiMe2CH2P(O)Ph2}Sc(CH2SiMe3)]+ (2). It has been found that trans-1,4-polymerization of isoprene by species 1 prefers an insertion–isomerization mechanism: (i) an insertion of cis-isoprene into the metal–alkyl bond to give η3-π-anti-form, (ii) anti-syn isomerization of the resulting 1,2-disubstituted allyl complex to yield a syn-allyl form, (iii) repetitive insertion of cis-isoprene into the metal–syn-allyl bond and subsequent anti–syn isomerization. The resulting η3-π-syn-allyl species is suitable for more kinetically favorable cis-monomer insertion. The stability of the key transition state involved in the most feasible pathway could be ascribed to the smaller deformation of cis-isoprene and stronger interaction between the cis-isoprene moiety ...

The flow and heat transfer characteristics in slip flow regime at low pressure state are numerically investigated by using CFD solver. The complete boundary conditions of first-order velocity slip are considered by User Defined Functions (UDFs), which include effects of thermal creep and wall curvature, as well as temperature jump. Based on the dimensionless continuity, momentum and energy equations along with these boundary conditions, the numerical simulation for flow and heat transfer behaviors over a circular cylinder is conducted in a wide range of Re = 0.001 to 20 and Kn = 0.01 to 0.1. It is found that the prediction results without considering the slip boundary conditions obviously deviate from the experimental values with the increase of Knudsen number, while the one by the developed model is in good agreement with the experimental results. Meanwhile, the variation of physical fields under different Reynolds and Knudsen numbers is discussed in detail. The empirical correlations in the slip flow regime for predicting average drag coefficient and average Nusselt number are proposed on the basis of simulation data, which makes the traditional method used for continuous flow regime be successfully applied into the prediction of flow and heat transfer performances in the slip flow regime.

The mechanisms of H–H and N–H bond cleavages of dihydrogen and ammonia mediated by the diiridium μ2-imido complex [(Cp*Ir)2(μ2-H)(μ2-NH)]+ (A; Cp* = η5-C5Me5) were theoretically investigated with the density functional theory (DFT) method. Both oxidative addition and metal–ligand cooperation modes have been studied for H–H and N–H bond cleavages, respectively. The H–H bond cleavage most likely occurs through competitive oxidative addition and metal–ligand cooperation, and both cleavage modes have similar overall free energy barriers (24.3 and 25.7 kcal/mol, respectively). The ligand-assisted N–H bond heterolytic cleavage mechanism is proposed for the NH3 reaction, and the general oxidative addition pathway can be reasonably ruled out, as it is kinetically unfavorable.

The isoprene/ethylene copolymerization catalyzed by cationic rare earth metal complexes [(η5-C5Me5)Sc(CH2SiMe3)]+ (A) had afforded alternating isoprene-ethylene copolymer with rich 3,4-polyisoprene microstructures, whereas no isoprene-ethylene copolymer was observed by using analogous [(PNPPh)Sc(CH2SiMe3)]+ (B) under the same conditions. Theoretical calculations in this work have revealed that, in the case of A, successive 3,4-insertion of isoprene resulted in a noncovalent interaction between the C = C double bond of penultimate unit and the metal center, suppressing the further insertion of monomers due to higher energy barrier and endergonic character. On the other hand, the ethylene pre-inserted species with alkyl active site is more suitable for the subsequent kinetically and thermodynamically favorable isoprene insertion and copolymerization is therefore realized. In the case of B, the experimentally observed cis-1,4-specific homopolymerization of isoprene was the outcome of both kinetic and thermodynamic control. And, the unfavorable ethylene insertion into the isoprene pre-inserted species with allyl active site could account for the experimental finding that no isoprene-ethylene copolymer was obtained. These computational results are expected to provide some hints for the design of rare earth copolymerization catalysts.

Contamination by herbicides such as clopyralid (CLP) poses a significant threat to human health and ecological systems. In the present study, efficient removal of CLP was achieved by thermo activated persulfate, among which sulfate radical was identified as the predominant oxidizing species responsible for the decontamination. Based on high resolution LC-MS, derivatization method and density functional theory (DFT) computation, the detailed oxidation pathways and mechanisms were proposed. The primary oxidation pathways included dechlorination-hydroxylation, decarboxylation and the formation of quinone-like moieties. Afterwards, numerous intermediate byproducts ranging from high molecular to very small ones were identified, suggesting the pyridine ring was damaged during the thermo activated persulfate process. The detected products containing six and five carbons indicated the pyridine ring cleavage would take place on the quinone-structure intermediate. Further oxidation could continue by breaking each bond on the ring-cleavage product, yielding a series of short-chain carbonyl chemicals, carboxylic acids and inorganic ions. In addition, the presence of dissolved oxygen (DO) was favorable to CLP degradation, indicating DO played an important role in applying such technology. The degradation rate constants of CLP increased appreciably with increasing temperature, and acidic pH facilitated the CLP degradation. The results obtained in this work would increase our understanding on the environmental fates of nitrogen heterocyclic compounds during sulfate radical (SO4•-)-based advanced oxidation processes (SR-AOPs).

The presence of inorganic ions and organic matter in natural water would cause unpredictable consequence on the oxidation efficiency and pathways of sulfate radical (SO4 −) based advanced oxidation process (SR-AOPs). In this study, the impacts of water constituents, namely, halides (including chloride (Cl−) and bromide (Br−)), bicarbonate (HCO3−) and natural organic matter (NOM) on SO4 − induced degradation of salbutamol (SAL) and terbutaline (TBL) were evaluated systematically. Our results indicated that chloride exhibited no effect on oxidation efficiencies of SAL and TBL, while Br−, HCO3− and NOM all showed inhibitory effects. Specifically, the detrimental effect of bromide was mainly attributed to the scavenging of SO4 − to form the less reactive species, Br2 −. By using laser flash photolysis (LFP), the second-order rate constants of Br2 − with SAL and TBL were estimated to be 2.1 and 3.9 × 108 M−1 s−1, respectively, much smaller than those with SO4 − (3.7 × 109 M−1 s−1 for SAL and 4.2 × 109 M−1 s−1 for TBL). Moreover, bromine addition products of SAL and TBL were detected in the presence of Br−, which were believed to be more toxic than the parent compounds. Similar to bromide, HCO3− could also quench SO4 − to generate carbonate radical (CO3 −), also less reactive than sulfate radical with SAL (4.8 × 107 M−1 s−1) and TBL (3.2 × 108 M−1 s−1). In the case of NOM, a light screening effect was regarded as the major factor responsible to the decrease of reaction rates, while sulfate radical scavenging played a very limited role. The present work would increase the awareness of secondary reactions during SR-AOPs, as more toxic products were generated in the case of bromide.

Xylene and its derivatives are known to be neurotoxic to the central nervous system of animals. Our previous work has shown that para-xylene (PX) can cause an increase in apoptotic cells and abnormal avoidance behavior in Xenopus laevis. However, the mechanism underlying the impact of PX on neuronal structural and functional plasticity is less clear. Here, we examined the effects of PX on neuronal development and plasticity in the developing optic tectum. We found that HuC/D-positive neurons were more vulnerable than SOX2-positive progenitor cells or BLBP-positive radial glial cells after exposure to PX at 1 mM for 48 h. The further measurement of postsynaptic receptors and synaptic vesicle proteins showed that the expression levels of GluA1 and GluA2, but not Rab3a and SNAP25, were significantly decreased in the tectal brain. In vivo time-lapse images and electrophysiological recordings showed that PX exposure resulted in significant deficits in neuronal structure, particularly in the total dendritic branch length (TDBL), and visual stimulation-induced excitatory compound synaptic currents (eCSCs) without altering neurotransmitter release probability. Strikingly, coexposure to d-glucuronolactone (GA) and PX rescued the structural and functional deficits caused by PX exposure alone. Furthermore, we found that visual experience-induced structural, functional and behavioral plasticity was blocked by PX exposure, which was also rescued by the simultaneous administration of GA and PX . Thus, our findings indicate that PX is neurotoxic to brain development and plasticity and that GA may be considered a promising candidate to treat PX-induced defects in neural circuits.

Biochar-supported nickel (Ni/BC) catalysts have potential applications in steam reforming of tar during biomass gasification. However, the industrial application of Ni/BC catalysts is restricted by their rapid deactivation caused by the gasification of biochar support and deposition of carbon on the active Ni metal. In this study, the effect of boron doping was explored on the performance of Ni/BC catalysts in steam reforming of toluene as a tar model compound. A series of Ni/BC and boron-doped Ni/BC catalysts were prepared by impregnating Ni salts on raw and acid-washed biomass as the starting materials and used in steam reforming of toluene as the tar model compound. It was found that boron doping significantly prolonged the lifetime of Ni/BC catalysts by interacting with Ni and the biochar support simultaneously. It is believed that boron doping lowered the gasification consumption rate of the biochar support in three ways: transforming the inherent K into more stable borates, inhibiting the desorption of CO and CO2, and forming B2O3 as the active site blocker. Furthermore, boron doping also reduced coke deposition on the Ni particles.

Acorus tatarinowii Schott is a traditional Chinese medicine used to treat memory and cognitive dysfunction. Because of their efficacy and lower toxic effects, research on α- and β-asarone, the phytoconstituents, has attracted attention owing to their remarkable pharmacological activities. Silver ion coordination complexation high-speed counter-current chromatography was used to separate these isomers from A. tatarinowii extract, coupled with accelerated solvent extraction. Accelerated solvent extraction parameters were investigated with single-factor and orthogonal testing. A two-phase solvent system composed of n-hexane-ethyl acetate-ethanol-water (2:1:2:1, v/v) with 0.50 mol/L silver ions was selected for separation. From 2.0 g crude extract, 1.4 g of β-asarone and 0.09 g of α-asarone were obtained with purities over 98% by sequential sample loading in 20 h. The isolated compounds were identified by electrospray ionization mass spectrometry, 1H and 13C NMR. Silver ions significantly increased the separation factor and retention of the stationary phase. The chromatographic behavior indicated that cis-configuration was more strongly complexed with the silver ion. This was further demonstrated with the help of computational analysis. In conclusion, the established method could be employed to separate other cis-trans or E/Z isomers that form coordination complexes.

The Sonogashira cross-coupling reaction is one of the most important and widely used sp2–sp carbon–carbon bond formation reactions in organic synthesis. Up to now, the exact mechanism of the palladium/copper-catalyzed Sonogashira reaction is far from being fully understood, mainly due to the difficulties in clarifying the combination behavior of the two metal catalysts. In this study, DFT calculations have been performed to elucidate the mechanism of the copper-cocatalyzed Sonogashira cross-coupling reaction, where bis(triphenylphosphino)palladium was used as a catalyst and Cs2CO3 was applied as a base. In an agreement between theory and experiment, the Cu cycle could favorably generate an I–-coordinated copper acetylide as the catalytically active species rather than the generally considered neutral copper acetylide. In addition, the transmetalation is calculated to be the rate-determining step. The results reported herein are expected to have broad mechanistic implications for other bimetal-catalyzed re...

This study provides a quantitative forecast method for predicting the potential maximum wind gust at certain automatic weather stations (AWSs) in South China through the investigation of the relationship between the wind gusts observed at the stations and tropical cyclones’ (TCs) main characteristics: TC intensity, TC distance to the station, TC azimuth relative to the station, and TC size. Historical TC data from 1968 to June 2014 within a distance of 700 km to several AWSs in South China are analyzed. The wind gust data available for the same period taken from six coastal AWSs: Yantian International Container Terminal (YICT), Mawan Port (MWP), and Shekou Ferry Terminal (SFT) in Shenzhen, and Hong Kong Observatory (HKO), Cheung Chau Island (CCH), and Waglan Island (WGL) in Hong Kong, are used to build the statistical relationship. The probability of gust gale occurrence (wind gust ≥ 17 m s−1) at these six stations is also computed. Results show that the wind induced by offshore TCs is strongly affected by the surrounding terrain conditions of the stations. Coastal stations open to the wind direction suffer a greater wind influence than do stations with obstructions located in the wind direction. When TCs are approaching the coast in South China, the most dangerous area is the northeast quadrant of TCs. In this quadrant, typhoons might incur gust gales at coastal stations in South China even at a distance of more than 400 km from the stations.

The mechanism of styrene polymerization catalyzed by five analogous cationic rare-earth-metal complexes [(RCH2–Py)Y(CH2SiMe3)]+ (R = C5Me4 (Cp′), 1+; R = C9H6 (Ind), 2+; R = C13H8 (Flu), 3+), [(Flu–Py)Y(CH2SiMe3)]+ (4+), and [(Flu–CH2CH2–NHC)Y(CH2SiMe3)]+ (5+) has been studied through DFT calculations. Having achieved an agreement between theory and experiment in the activity discrepancy and selectivity, it is found that styrene polymerization kinetically prefers 2,1-insertion to 1,2-insertion. The free energy profiles for the insertion of a second monomer molecule have been computed for both migratory and stationary insertion manners, and the former resulting in a syndiotactic enchainment indicates obvious kinetic preference. The current results suggest that the coordination of styrene to the active metal center could play an important role in the observed activity difference. Interestingly, the charge on central metal of the cationic species accounts for the activities of 1+, 2+, and 3+: the higher the ...

Predicting metabolism of chemicals and potential toxicities of relevant metabolites remains a vital and difficult task in risk assessment. Recent findings suggested that polybrominated diphenyl ethers (PBDEs) can be transformed into dihydroxylated and dioxin metabolites catalyzed by cytochrome P450 enzymes (CYPs), whereas the mechanisms pertinent to these transformations remain largely unknown. Here, by means of density functional theory (DFT) calculations, we probed the metabolic pathways of 2,2',4,4'-tetraBDE (BDE-47) using the active center model of CYPs (Compound I). Results show that BDE-47 is first oxidized to monohydroxylated products (HO-BDEs), wherein a keto-enol tautomerism is identified for rearrangement of the cyclohexenone intermediate. Dihydroxylation with HO-BDEs as precursors, has a unique phenolic H-abstraction and hydroxyl rebound pathway that is distinct from that for monohydroxylation, which accounts for the absence of epoxides in in vitro studies. Furthermore, we found only dihydroxylated PBDEs with heterophenyl -OH substituents ortho- and meta- to the ether bond serve as precursors for dioxins, which are evolved from aryl biradical coupling of diketone intermediates that are produced from dehydrogenation of the dihydroxylated PBDEs by Compound I. This study may enlighten the development of computational models that afford mechanism-based prediction of the xenobiotic biotransformation catalyzed by CYPs.

The effect of alkyls on the chain initiation efficiency of ethylene, propene, 1-hexene, styrene, butadiene, and isoprene polymerizations catalyzed by the half-sandwich cationic rare-earth-metal alkyl complexes [(η5-C5Me5)ScR]+ (R = CH2SiMe3, 1; R = o-CH2C6H4NMe2, 2; R = η3-C3H5, 3) has been studied by using a DFT approach. It has been found that 2 with the largest sterically demanding aminobenzyl group results in the lowest initiation efficiency and thus longest induction period among the three catalysts investigated. In contrast, 1 with CH2SiMe3 displays the best chain initiation ability, and 3 with η3-allyl gives moderate chain initiation activity, mainly due to the most stable resulting coordination complex. Species 1 and 3 have better regioselectivity in the chain initiation of styrene polymerization than species 2. In addition, species 1′ ([(η5-C5Me5)Sc(CH2SiMe3)THF]+) with a THF ligand has better chain initiation efficiency in styrene and isoprene polymerizations than species 2 but is reasonably wor...

International audience; Application of activated peroxymonosulfate (PMS) to generate sulfate radical or hydroxyl radical is a promising strategy for wastewater treatment, while our knowledge on the background reaction, namely, the direct interaction between PMS and target contaminants is quite limited. In this contribution, the degradation kinetics, stoichiometry, products and mechanism of the reaction between unactivated PMS and trimethoprim (TMP), one of the most commonly detected micro-pollutants in the aquatic system were investigated systematically. The results indicated that TMP was susceptible to degradation by direct PMS oxidation via a non-radical process. By recording the decay of two reactants simultaneously, the stoichiometric ratio between PMS and TMP was estimated to be approximately 1. Higher PMS levels exhibited a promotion effect on PMS decay. And the degradation was pH-dependent, basic conditions were favorable for TMP degradation, which could be well modeled based on the species-specific reactions. The two amine groups on the pyrimidine ring were identified as the reactive sites. After direct attacks by PMS, they would be oxidized to form hydroxylamine-products, namely, N8–OH-TMP and N9–OH-TMP. These two hydroxylamine-products were quite stable and resistant to further oxidation by PMS, preventing the formation of more toxic nitroso- and nitro-products. The new findings in the present work would provide beneficial information on the strategy choice for the elimination of specific pollutants, like TMP, as PMS also exhibits relatively high reactivity towards them.

DFT calculations have been conducted for investigating the relation between the electronic states and catalytic properties of iminopyridine-ligated cationic iron complexes in the stereoselective polymerization of isoprene. Iminopyridine ligand is found to be redox-inert in this catalytic system. The neutral pre-catalyst and active cationic species present as a high spin quintet and the open-shell unpaired 3d-electrons reside on Fe center. The trans and cis polymerization of isoprene catalyzed by the complexes [(octyl-iminopyridine)FeII(Me)]+ (A1) and [(supermesityl-iminopyridine)FeII(Me)]+ (A2) could be attributed to the electronic and steric effects in the transition states, respectively.

Because of the steric bulkiness and the η5/κ1-constrained-geometry-configuration (CGC) geometry, the entire range of pyridyl-methylene-fluorenyl-stabilized rare earth metal bisalkyl complexes, (Flu-CH2-Py)Ln(CH2SiMe3)2(THF)x (Flu = fluorenyl; Py = pyridyl; for 1, Ln = Sc and x = 0; for 2–11, Ln = Lu, Tm, Er, Ho, Y, Dy, Tb, Gd, Nd, or Pr and x = 1), and monoalkyl complex, (Flu-CH2-Py)2La(CH2SiMe3) (THF) (12), has been successfully achieved for the first time via the sequential salt metathesis reactions. Activated by [Ph3C][B(C6F5)4] and AliBu3, complexes 1–9 showed high activity and perfect syndioselectivity for styrene polymerization, while the large Nd- and Pr-attached precursors 10 and 11 exhibited slightly decreased syndioselectivity but rather low activity; the monoalkyl La precursor 12 was completely inert. The activity increased with the decrease in the rare earth metal size, in striking contrast to the literature that has shown that a large metal facilitates a high activity, which was also not a re...

Recent in vivo and in vitro experiments indicated that methoxylated polybrominated diphenyl ethers (MeO-PBDEs) can be biotransformed into hydroxylated PBDEs (HO-PBDEs) that are more toxic than PBDEs and MeO-PBDEs. Nevertheless, the enzymatic transformation mechanism is not clear. We hypothesized that cytochrome P450 enzymes (CYPs) play a key role in the transformation and employed the density functional theory calculations to unveil the mechanism. The transformation of a model compound, 6-MeO-BDE-47, catalyzed by the active center of CYPs (Compound I), was computed. For the first time, our results show that the energy barriers for the addition of Compound I to the C atoms on the phenyl of 6-MeO-BDE-47 are much higher than that for hydroxylation of the methoxyl, indicating that O-demethylation is a dominating metabolic pathway. This is in line with experimental observations performed by others. The pathways for the transformation of 6-MeO-BDE-47 catalyzed by Compound I were clarified. A C-H bond of the methoxyl is activated by Compound I, followed by radical rebound to form carbinol intermediates, then the carbinols decompose to form 6-HO-BDE-47 with the assistance of water molecules. The computational method can be potentially employed to develop models that predict biotransformation of xenobiotics catalyzed by CYPs.

Hydroxylated polyhalodiphenyl ethers (HO-PXDEs) are emerging aquatic pollutants. Previous studies have shown that HO-PXDEs can photogenerate dioxins and phenolic compounds. However, it is unclear which photochemical pathways are responsible for the various photoproducts. This study investigates the direct photolysis and photooxidation initiated by (1)O2 and ˙OH that can be formed by photosensitization, taking 2'-HO-2,3',4,5'-tetrabromodiphenyl ether (2'-HO-BDE-68) as a case study. The results show that 1,3,8-tribromodibenzo-p-dioxin can only be produced during direct photolysis. By mass spectrum analysis, four dihydroxylated polybromodiphenyl ethers, generated from both direct and indirect photodegradation were confirmed. Among them, di-HO-tribromodiphenyl ether (di-HO-TBDE) was the main product generated from direct photohydrolysis. Most probably, the di-HO-TBDE is 2',5'-HO-2,3',4-tribromodiphenyl ether, as was suggested by density functional theory calculations. Ether bond cleavage is a dominant pathway for the direct photolysis and photooxidation reactions leading to 2,4-dibromophenol as the dominant product. The yields of the products, which are irrespective of reaction time and can be employed to compare the ability of different HO-PXDEs to photogenerate a given product, were reported. This study indicates that for accurate ecological risk assessment of HO-PXDEs, their different photodegradation pathways that may lead to different photoproducts should be considered.

Transition-metal-catalyzed copolymerization reactions of olefins with polar-functionalized comonomers are highly important and also highly challenging. A second-coordination-sphere strategy was developed to address some of the difficulties encountered in these copolymerization reactions. A series of α-diimine ligands bearing nitrogen-containing second coordination spheres were prepared and characterized. The properties of the corresponding nickel and palladium catalysts in ethylene polymerizations and copolymerizations were investigated. In the nickel system, significant reduction in polymer branching density was observed, while lower polymer branching densities, as well as a wider range of polar monomer substrates, were achieved in the palladium system. Control experiments and computational results reveal the critical role of the metal-nitrogen interaction in these polymerization and copolymerization reactions.

Precisely controlling the stereochemistry of a copolymerization by single catalyst, and achieving copolymers with predicted sequences, is a challenging project in organometallic and macromolecular sciences. This article reports that the copolymerization of isoprene and butadiene with the 3,4- and cis-1,4 different regioselectivities has been accessed through employing a pyridylmethylene functionalized fluorenyl ligated yttrium cationic species. The thus unprecedented regularity combination is attributed mainly to the backbiting interaction of the penultimate unit of the polymer chain to the active central metal ion according to the DFT calculation. Moreover, the compositions can be adjusted by regulating the monomer feed ratio according to the copolymerization kinetics study.

This paper reports a DFT study on trans-1,4-specific polymerization of isoprene catalyzed by the cationic heterobimetallic half-sandwich complex [(C5Me5)La(AlMe4)]+. The possible structures of the active species, viz., [(C5Me5)La(μ2-Me)3AlMe]+ (A), [(C5Me5)La(μ2-Me)2AlMe2]+ (B), and [(C5Me5)La(Me)(μ2-Me)AlMe2]+ (C), have been investigated. On the basis of the chain initiation and the structure transformations among these three species, C has been proposed to be the true active species smoothly producing trans-1,4-polyisoprene observed experimentally. Both La/Al bimetal-cooperating monomer insertion and La-center-based insertion pathways have been calculated, and the latter is found to be more favorable, where the AlMe3 moiety serves as a ligand coordinating to the La center via a methyl group. In contrast to this, in the Y analogous system, the AlMe3 ligand is proposed to leave away from the Y center during the chain propagation and the cis-1,4-selectivity is preferred, showing a consistence with experime...

Multiple secondary eyewall formations (SEFs) and eyewall replacement cycles (ERCs) are simulated with the fifth-generation Pennsylvania State University (PSU)–National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) at horizontal grid spacing of 0.67 km. The simulated hurricane is initialized from a weak, synthetic vortex in a quiescent environment on an f plane. After spinup and rapid intensification, the hurricane enters a mature phase during which the intensity change is relatively slow. Convective clouds then organize into a ring with a secondary tangential wind maximum at radii beyond the hurricane’s primary eyewall. This secondary eyewall (SE) then contracts and strengthens. The primary eyewall weakens and is eventually replaced by the SE. The hurricane grows in size and the radius of maximum wind (RMW) increases as similar ERCs repeat 5 times during the simulation. Two existing hypotheses on SEF are evaluated using the simulation output. Then, model diagnostics are used to reveal that crucial linked components of SEF are (i) a broadening of the swirling flow, (ii) the structure of the evolving secondary circulation, and (iii) the structure of the net radial force (NRF) in the boundary layer (with largest contributions from the agradient and frictional forces). During SEF, there exists strong positive NRF in the region of the primary eyewall, a secondary positive maximum over the SEF region, and a minimum between the two. As a response of the boundary layer depth–integrated radial flow to the NRF, a secondary maximum convergence zone (SMCZ) in the boundary layer develops at the SEF radii. Eventually moist convection in the SMCZ becomes active as the SEF develops.

A measurement-driven probability hypothesis density (MD-PHD) filter based on track initiation is proposed in this paper to handle the incapability of PHD filter when dealing with unknown newborn intensity. Measurements are distinguished into two parts by using gating technology. The existing measurements are used to update intensity while the suspicious measurements are utilized to explore new target via track initiation. The sequential Monte Carlo (SMC) implementation of the proposed filter is derived and applied to passive scenario. The simulation results demonstrate that the proposed method not only tracks existing target accurately but also initiates new target duly without any prior knowledge of newborn intensity.

Flower-like tellurium (Te) nanocrystals with uniform branches were successfully prepared in large quantities by a surfactant-assisted method. The product was characterised with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electronic diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS). The characterisation results revealed that the branch of flower-like Te was grown along [001] direction. Furthermore, the Raman spectrum of the flower-like Te with uniform branches was studied. The result shows that the flower-like Te exhibits three typical vibration peaks. This study provides a simple method to prepare three-dimensional Te nanostructures in large scale, which broadens their practical applications.

Rainfall prediction remains one of the most challenging problems in weather forecasting. In order to improve high-resolution quantitative precipitation forecasts (QPF), a new procedure for assimilating rainfall rate derived from radar composite reflectivity has been proposed and tested in a numerical simulation of the Chicago floods of 17–18 July 1996. The methodology is based on the one-dimensional variation scheme (1DVAR) assimilation approach introduced by Fillion and Errico but applied here using the Kain-Fritsch convective parameterization scheme (KF CPS). The novel feature of this work is the continuous assimilation of radar estimated rain rate over a three hour period, rather than a single assimilation at the initial (analysis) time. Most of the characteristics of this precipitation event, including the propagation, regeneration of mesoscale convective systems, the frontal boundary across the Midwest and the evolution of the low-level jet are better captured in the simulation as the radar-estimated precipitation rate is assimilated. The results indicate that precipitation assimilation during the early stage can improve the simulated mesoscale feature of the convection system and shorten the spin-up time significantly. Comparison of precipitation forecasts between the experiments with and without the 1DVAR indicates that the 1DVAR scheme has a positive impact on the QPF up to 36 hours in terms of the bias and bias equalized threat scores.

International audience; The reactions of the charge neutral dinuclear aluminum tetraalkyl complexes of di-Schiff base ligands, i.e. [AlMe2_ON₋R-_ON_AlMe2] (1a, R = 1,3-propylene; 1b, R = 1,3-cyclohexylene) with B(C6F5)3 and [H(Et2O)2]+[H2N_B(C6F5)3₂]- were investigated. When B(C6F5)3 was used as the cationizing agent (1 or 2 equiv. vs. Al), only monocationic dinuclear complexes [2a,b]+[MeB(C6F5)3]- were obtained. In contrast, with [H(Et2O)2]+[H2N_B(C6F5)3₂]-, both mixed-dicationic [3a,b·(OEt2)2]2+[MeB(C6F5)3]-[H2N_B(C6F5)3₂]- and homo-dicationic [3a,b·(OEt2)2]2+[H2N_B(C6F5)3₂]- 2 ion-pairs were prepared. All cationic complexes were characterized by 1H, 13C, 19F and 11B NMR spectroscopy, and an X-ray diffraction study was performed for [3b·(OEt2)2]2+[H2N_B(C6F5)3₂]- 2. © 2016 The Royal Society of Chemistry.

Because of the lack of three-dimensional (3D) high-resolution data and the existence of highly nonelliptic flows, few studies have been conducted to investigate the inner-core quasi-balanced characteristics of hurricanes. In this study, a potential vorticity (PV) inversion system is developed, which includes the nonconservative processes of friction, diabatic heating, and water loading. It requires hurricane flows to be statically and inertially stable but allows for the presence of small negative PV. To facilitate the PV inversion with the nonlinear balance (NLB) equation, hurricane flows are decomposed into an axisymmetric, gradient-balanced reference state and asymmetric perturbations. Meanwhile, the nonellipticity of the NLB equation is circumvented by multiplying a small parameter ɛ and combining it with the PV equation, which effectively reduces the influence of anticyclonic vorticity. A quasi-balanced ω equation in pseudoheight coordinates is derived, which includes the effects of friction and diabatic heating as well as differential vorticity advection and the Laplacians of thermal advection by both nondivergent and divergent winds.This quasi-balanced PV–ω inversion system is tested with an explicit simulation of Hurricane Andrew (1992) with the finest grid size of 6 km. It is shown that (a) the PV–ω inversion system could recover almost all typical features in a hurricane, and (b) a sizeable portion of the 3D hurricane flows are quasi-balanced, such as the intense rotational winds, organized eyewall updrafts and subsidence in the eye, cyclonic inflow in the boundary layer, and upper-level anticyclonic outflow. It is found, however, that the boundary layer cyclonic inflow and upper-level anticyclonic outflow also contain significant unbalanced components. In particular, a low-level outflow jet near the top of the boundary layer is found to be highly unbalanced (and supergradient). These findings are supported by both locally calculated momentum budgets and globally inverted winds. The results indicate that this PV inversion system could be utilized as a tool to separate the unbalanced from quasi-balanced flows for studies of balanced dynamics and propagating inertial gravity waves in hurricane vortices.