Search

Dielectric barrier discharge (DBD) reactor at non-thermal plasma (NTP) in combination with catalysts was used to remove toluene in air. Several manganese oxides catalysts with ZSM-5 zeolite as the carrier have been prepared for plasma-catalytic degradation of toluene. The prepared catalysts were characterized utilizing the scanning electron microscopy (SEM), transmission electron microscope (TEM), H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD), and N2 adsorption–desorption. And the residence time, plasma power, toluene concentration and specific input energy, which are critical operating factors in this process, were investigated. The experiment proved that the catalysts significantly improved the degradation effect of NTP, the conversion increased from 58 to 91.5% after loading MnOx/ZSM-5-300 at 750 ppm, and the improving trend became more obvious with the increase of concentration. The degradation of toluene can reach 92.4% at the optimal process parameters of residence time 5.8 s, initial concentration 1000 ppm, input power 30 W, SIE 6000 J/L. The results of the evaluation indicate that it is very effective to use MnOx/ZSM-5 catalyst combined with DBD-plasma for synergistic degradation of toluene at room temperature and a relatively low energy consumption.

The hydrolysis of CH2OO is not only a dominant sink for the CH2OO intermediate in the atmosphere but also a key process in the formation of aerosols. Herein, the reaction mechanism and kinetics for the hydrolysis of CH2OO catalyzed by the precursors of atmospheric aerosols, including H2SO4, H2SO4···H2O, and (H2SO4)2, have been studied theoretically at the CCSD(T)-F12a/cc-pVDZ-F12//B3LYP/6-311+G(2df,2pd) level. The calculated results show that the three catalysts decrease the energy barrier by over 10.3 kcal·mol-1; at the same time, the product formation of HOCH2OOH is more strongly bonded to the three catalysts than to the reactants CH2OO and H2O, revealing that small clusters of sulfuric acid promote the hydrolysis of CH2OO both kinetically and thermodynamically. Kinetic simulations show that the H2SO4-assisted reaction is more favorable than the H2SO4···H2O- (the pseudo-first-order rate constant being 27.9-11.5 times larger) and (H2SO4)2- (between 2.8 × 104 and 3.4 × 105 times larger) catalyzed reactions. Additionally, due to relatively lower concentration of H2SO4, the hydrolysis of CH2OO with H2SO4 cannot compete with the CH2OO + H2O or (H2O)2 reaction within the temperature range of 280-320 K, since its pseudo-first-order rate ratio is smaller by 4-7 or 6-8 orders of magnitude, respectively. However, the present results provide a good example of how small clusters of sulfuric acid catalyze the hydrolysis of an important atmospheric species.

The hydrolysis reaction of CH2OO with water and water clusters is believed to be a dominant sink for the CH2OO intermediate in the atmosphere. However, the favorable route for the hydrolysis of CH2OO with water clusters is still unclear. Here global minimum searching using the Tsinghua Global Minimum program has been introduced to find the most stable geometry of the CH2OO⋯(H2O)n (n = 1–4) complex firstly. Then, based on these stable complexes, favorable hydrolysis of CH2OO with (H2O)n (n = 1–4) has been investigated using the quantum chemical method of CCSD(T)-F12a/cc-pVDZ-F12//B3LYP/6-311+G(2d,2p) and canonical variational transition state theory with small curvature tunneling. The calculated results have revealed that, although the contribution of CH2OO + (H2O)2 is the most obvious in the hydrolysis of CH2OO with (H2O)n (n = 1–4), the hydrolysis of CH2OO with (H2O)3 is not negligible in atmospheric gas-phase chemistry as its rate is close to the rate of the CH2OO + H2O reaction. The calculated results also show that, in a clean atmosphere, the CH2OO + (H2O)n (n = 1–2) reaction competes well with the CH2OO + SO2 reaction at 298 K when the concentrations of (H2O)n (n = 1–2) range from 20% relative humidity (RH) to 100% RH, and SO2 is 2.46 × 1011 molecules per cm3. Meanwhile, when the RH is higher than 40%, it is a new prediction that the CH2OO + (H2O)3 reaction can also compete well with the CH2OO + SO2 reaction at 298 K. Besides, Born–Oppenheimer molecular dynamics simulation results show that all the favorable channels of the CH2OO + (H2O)n (n = 1–3) reaction cannot react on a time scale of 100 ps in the NVT simulation. However, the NVE simulation results show that the CH2OO + (H2O)3 reaction can be finished well at 8.5 ps, indicating that the gas phase reaction of CH2OO + (H2O)3 is not negligible in the atmosphere. Overall, the present results have provided a definitive example of how the favorable hydrolysis of important atmospheric species with (H2O)n (n = 1–4) takes place, which will stimulate one to consider the favorable hydrolysis of water and water clusters with other Criegee intermediates and other important atmospheric species.

Metabolomics has been used as a promising strategy to evaluate the efficacy of and potential targets for natural products. Alcoholic liver disease (ALD) as a result of chronic ethanol consumption has high morbidity and mortality. Geniposide possesses a hepatoprotective activity against ALD, but its mechanism of action is still not clear. In this study, serum metabolomics based on ultra-performance liquid chromatography-quadrupole time of flight-tandem mass spectrometry (UPLC-Q/TOF-MS) combined with ingenuity pathway analysis was used to explore the therapeutic mechanisms of geniposide. We found that the levels of AST, ALT, MDA, TG, and γ-GT in the geniposide-treated group were significantly decreased, and the level of GSH was significantly increased, compared with the model group. Meanwhile, geniposide effectively inhibits apoptosis and caspase-3 activity in liver tissue. A total of 33 metabolites were identified and related with the model group to illuminate the pathogenesis of ALD, 21 of which are regulated by geniposide, involving the relevant metabolic pathways, such as amino acid metabolism, arachidonic acid metabolism, pyruvate metabolism, TCA cycle, etc. Furthermore, a significant change in amino acid metabolism suggested that it might be a promising mechanism-related target for geniposide against ALD. It also showed that a metabolomic strategy using UPLC-Q/TOF-MS combined with ingenuity pathway analysis is a potentially powerful tool for providing a comprehensive understanding of the therapeutic mechanisms of natural products, but it also offers a theoretical basis for the prevention or treatment of disease.

Quantum chemical calculations at M06-2X and CCSD(T) levels of theory have been performed to investigate the effects of H2O, NH3, and HCOOH on the HO2 + Cl → HCl + O2 reaction. The results show that catalyzed reactions with three catalysts could proceed through two different mechanisms, namely a stepwise route and one elementary step, where the former reaction is more favorable than the latter. Meanwhile, for the stepwise route, a single hydrogen atom transfer pathway in the presence of all catalysts has more advantages than the respective double hydrogen atom transfer pathway. Then, the relative impacts of catalysts under tropospheric conditions were investigated by considering the temperature dependence of the rate constants and the altitude dependence of catalyst concentrations. The calculated results show that at 0 km altitude, the HO2 + Cl → HCl + O2 reaction with catalysts, such as H2O, NH3, or HCOOH, cannot compete with the reaction without a catalyst, as the effective rate constant with a catalyst is smaller by 2–6 orders of magnitude than the naked reaction within the temperature range 280–320 K. The calculated results also show that at altitudes of 5, 10 and 15 km, the effective rate constant of the HCOOH-catalyzed reaction increases obviously with an increase in altitude. At 15 km altitude, its value is up to 9.63 × 10−11 cm3 per molecule per s, which is close to the corresponding value of the reaction without a catalyst, showing that the contribution of HCOOH to the HO2 + Cl → HCl + O2 reaction cannot be neglected at high altitudes. The new findings in this investigation are not only of great necessity and importance for elucidating the gas-phase reaction of HO2 with Cl in the presence of acidic, neutral and basic catalysts, but are also of great interest for understanding the importance of other types of hydrogen abstraction in the atmosphere.

In this article, we report a theoretical investigation on the role of several catalysts in the isomerisation mechanisms of HON(O)NNO2 to ON(OH)NNO2 by theoretical method of CBS-QB3. The isomerisati...

CBS-QB3 method has been employed to determine the geometries, the vibrational frequencies of the reactants, the products and the transition states involved in intramolecular hydrogen-transfer and decomposition reactions of the free gas-phase H3N···HN(NO2)2 (ADN*). The results show that the intramolecular hydrogen-transfer reaction of ADN* is more feasible than that of HDN. ADN* and its hydrogen-transfer isomers ADN*-IIa,b,c decompose along four channels to form NH3 + HONO + 2NO (PI), ȮH + ṄO3 + N2 + NH3 (PII), ȮH + ṄO2 + N2O + NH3 (PIII), and HNO3 + N2O + NH3 (PIV), respectively. It has been found that the dominant decomposition channels are PI and PIII. The hydrogen-transfer reaction can reduce the barrier of elimination of NO2 and forming N2O reactions in ADN* and HDN. The decomposition of ADN*-IIc to form NO2 and N2O is more feasible than that of the gas-phase HDN. The rate constants (k) of rate-determining step of ADN* show that kPI and kPIII are higher than kPIV and kPII. Compared with HDN-II...

The adsorption of O2 on the Cu2O(111) surface at different coverages has been studied by spin-polarized density functional theory (DFT+U) calculations and atomic thermodynamics. It has been found that the dissociative O2 prefers to adsorb on the reconstructed Cu2O(111) surface at low coverages (1/4 to 1 monolayer), while totally dissociative and mixed molecular and dissociative O2 prefers to adsorb on the reconstructed Cu2O(111) surface thermodynamically at higher coverages (5/4 to 7/4 monolayers). More interesting is that the CuO film can be automatically formed on the Cu2O(111) surface that was induced by the surface reconstruction of the Cu2O(111) surface and adsorption of four dissociative O2 molecules (1 monolayer), which agrees well with the recent experimental results. Along higher coverages of O2 adsorption (5/4 to 7/4 monolayers), much stronger surface reconstruction and relaxation was found. The probability distribution of different single-O2 adsorbed states on the Cu2O(111) surface as a function of temperature was analyzed using a Boltzmann model. The adsorption mechanism of O2 on the Cu2O(111) surface was analyzed using the phase diagram and compared with other metal oxides.

The effects of (H2O)n (n = 1–3) clusters on the HO2 + NH2 → NH3 + 3O2 reaction have been investigated by employing high-level quantum chemical calculations with M06-2X and CCSD(T) theoretical methods, and canonical variational transition (CVT) state theory with small curvature tunneling (SCT) correction. The calculated results show that two kinds of reaction, HO2⋯(H2O)n (n = 1–3) + NH2 and H2N⋯(H2O)n (n = 1–3) + HO2, are involved in the (H2O)n (n = 1–3) catalyzed HO2 + NH2 → NH3 + 3O2 reaction. Due to the fact that HO2⋯(H2O)n (n = 1–3) complexes have much larger stabilization energies and much higher concentrations than the corresponding complexes of H2N⋯(H2O)n (n = 1–3), the atmospheric relevance of the former reaction is more obvious with its effective rate constant of about 1–11 orders of magnitude faster than the corresponding latter reaction at 298 K. Meanwhile, due to the effective rate constant of the H2O⋯HO2 + NH2 reaction being respectively larger by 5–6 and 6–7 orders of magnitude than the corresponding reactions of HO2⋯(H2O)2 + NH2 and HO2⋯(H2O)3 + NH2, the catalytic effect of (H2O)n (n = 1–3) is mainly taken from the contribution of the water monomer. In addition, the enhancement factor of the water monomer is 10.06–13.30% within the temperature range of 275–320 K, which shows that at whole calculated temperatures, a positive water effect is obvious under atmospheric conditions.

To study the catalytic effects of (H2O)n (n = 1–3), the mechanisms of the reaction HO2 + HO → 3O2 + H2O without and with (H2O)n (n = 1–3) have been investigated theoretically at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ level of theory, coupled with rate constant calculations using the conventional transition state theory. Our results show that upon incorporation of (H2O)n (n = 1–3) into the channel of H2O + 3O2 formation, two different reactions, i.e. HO + HO2⋯(H2O)n (n = 1–3) and HO2 + HO⋯(H2O)n (n = 1–3), have been observed, and these two reactions are competitive with each other. The catalytic effects of (H2O)n (n = 1–3) mainly arise from the contribution of a single water vapor molecule; this is because the effective rate constants with water are respectively larger by 2–3 and 3–4 orders of magnitude than those of the reactions with (H2O)2 and (H2O)3. Furthermore, the catalytic effects of the water monomer mainly arise from the H2O⋯HO2 + HO reaction, and the enhancement factor of this reaction is obvious within the temperature range of 240.0–425.0 K, with the branching ratio (k′(RW)/ktot) of 17.27–80.77%. Overall, the present results provide a new example of how water and water clusters catalyze gas phase reactions under atmospheric conditions.

The effects of (H2O)n (n = 1–2) on hydrogen abstraction reaction (H2O2 + HS → H2S + HO2) have been investigated at the level of theories of B3LYP and CCSD(T). The aug-cc-pVTZ basis set has been used in the present treatment. The catalytic effect has been found to be small for water dimer and is significant for water, because the effective rate constant for the water-catalyzed reaction being 3–4 orders of magnitude larger than the corresponding water-dimer assisted reaction. Compared to the un-catalyzed reaction, the rate enhancement due to water catalysis at lower temperature (e.g., 240 K) was only 0.17%, which was increased to 72.7% at higher temperature (e.g., 325 K).

In the current work, time-dependent density functional theory calculations coupled with a set of multidimensional visualization techniques have been used to investigate the photovoltaic properties (the band gap, optical absorption, reorganization energy, charge transfer integrals, and rates of exciton dissociation and charge recombination.) of PC 61 BM-PTDPPTFT4 system with a simplified molecular model. Calculations reveal that TDPPTFT4 oligomers possess the narrow electronic band gap (1.792–1.903 eV), strong and wide optical absorption ( λ max = 792 nm, f max = 4.962 for TDPPTFT4 trimer) in UV–Vis region, and small internal reorganization energy (0.118 eV) in charge transfer process. In addition, the calculation also shows that the exciton-dissociation rate is very fast (10 10 –10 13 s −1 ) in the interface of PC 61 BM-TDPPTFT4 n=1,2,3 complexes, while the charge-recombination one is relatively slow (10 6 –10 8 s −1 ) under the same condition, which denotes that the exciton dissociation efficiency in the studied donor–acceptor interface is very high. Combining the large mobility (0.47–2.10 cm 2 V −1 s −1 ), we consider that PTDPPTFT4 is a very promising electron donor material of polymer-based solar cells, and worthy of being investigated further in experiments. Our theoretical investigation can promote deeper understanding of the connection between the chemical structure and the optical and electronic properties of the donor–acceptor, and provide some valuable references to the rational design of novel donor–acceptor systems.

The oxidation of CO over Au3− cluster was investigated using the DFT by selecting peroxo-like adsorbate intermediate, Au3CO(O2)−, of CO and O2 over the Au3− cluster, as the reactant model. Based on the transition state investigation at UB3LYP/LANL2DZ, the energies at the UB3LYP/aug-cc-pVTZ-PP//LANL2DZ level theory and corresponding relativistic effective core potential (RECP) for Au, 6-311 + G∗ for carbon and oxygen atoms, the reaction potential energy diagrams and pathways were analyzed. For the selecting Au3CO(O2)− as the initial intermediated proceeded through a typical LH mechanism and forming a complex of CO2 and Au3O−, and the subsequent intermediate, Au3OCO−, formed by the reaction of CO with Au3O− were also analyzed. The results indicated that the CO oxidation followed the LH or ER mechanism, and their rate constants increased with increasing temperature. For the main reason of CO oxidation over Au3− cluster with no perceptible catalytic activity, it should be the no sufficient peroxo-like complex (Au3COO2−, 1A) formation due to the very low content of low-spin O2 under normal conditions, and that the peroxo-like compound also showed a low oxidation rate at low temperature.

Described herein is a novel palladium-catalyzed C–N bond-formation reaction employing aryltrimethylgermanes as the new arylating reagents. Primary/secondary amines or even amides could be smoothly arylated to provide the corresponding N-arylation products in moderate to excellent yields.

The mechanism for the biradical reaction of HS with HO2 is investigated at the CCSD(T)/6-311++ G(3df,2pd)//B3LYP/6-311+G(2df,2p) level on both the singlet and triplet potential energy surfaces, along with rate constant calculations of the major channel. The results show that there are eight reaction channels involved in the HS + HO2 reaction system. The major channel R1 of the title reaction occurs on the triplet potential energy surfaces, and includes two pathways: Path 1 (R → IM1 → TS1 → P1(O2 + H2S)) and Path 1a 701 Acta Phys. -Chim. Sin. 2016 Vol.32

The hydroxyl radical may attack the new cytosine derivative 5-hydroxymethylcytosine (5-hmCyt) causing DNA oxidative damage, but the study of the related mechanism is still in its infancy. In the present work, two distinct mechanisms have been explored by means of the CBS-QB3 and CBS-QB3/PCM methods, the addition of ˙OH to the nucleophilic C5 (R1) and C6 (R2) atoms and H-abstraction from the N4 (R3 and R4), C7 (R5 and R6), C6 (R7) and O3 (R8) atoms of 5-hmCyt, respectively. The solvent effects of water do not significantly alter the energetics of the addition and abstraction paths compared to those in the gas phase. The ˙OH addition to the C5 and C6 sites of 5-hmCyt is energetically more favorable than to the N3, C4 or O2 sites, and the ΔGs‡ value of the C5 channel is a little lower than that of the C6 route, indicating some amount of regioselectivity, which is in agreement with the conclusions of ˙OH-mediated cytosine reactions reported experimentally and theoretically. The H5 and H6 abstraction reactions are more favorable than other abstractions, which have almost the same energy barriers as those of ˙OH addition to the C5 and C6 sites. Moreover, the energies of the H5 and H6 dehydrogenation products, which formed benzyl-radical-like complexes, are about 62–101 kJ mol−1 higher than those of the adduct radicals, indicating that the H5 and H6 abstractions have a relatively high probability of happening. Accordingly, the proportions of the H5 and H6 dehydrogenation products are large and may be detectable experimentally. These findings hint that the new DNA base (5-hmCyt) is easily damaged when exposed to the surroundings of a hydroxyl radicals environment. Therefore the reduction of free radical production or the addition of some antioxidants should be done in mammalian brain tissues to resist DNA damage. Our results provide some evidence between 5-hmCyt and tumor development for experimental scientists.

Two type routes of HCl···H2SO4-(trans, cis and cage) + HO and HO···H2SO4-(trans, cis and cage) + HCl in H2SO4-catalyzed HCl + HO reaction have been investigated by using CCSD(T)-F12a/cc-pVDZ-F12 //M06-2X/6–311++G(2d,2p) methods, and canonical variational transition state theory with small curvature tunneling. It is shown that the process of HCl···H2SO4-trans + HO is the most favorable in all H2SO4-assisted routes. Within the temperature range of 280–320 K, H2SO4 not only is more effective than HCOOH (0.01 ppbv) and NH3 (0.1 ppbv), but also are competitive with NH3 (10 ppbv) and HCOOH (2 ppbv). However, H2SO4 would not be able to compete with H2O (20–100% RH), NH3 (2900 ppbv), HCOOH (10 ppbv) and the naked reaction of HCl + HO due to its relatively lower concentration.

The MIL-88/PVB nanofibers were prepared by hydrothermal synthesis and subsequent electrostatic spinning. The composite was used as a high efficiency heterogeneous catalyst for photocatalysis coupling of Fenton process to remove tetracycline hydrochloride (TC-HCl) under visible light irradiation. The results indicated that 99% of TC-HCl (500 mg·L−1) was degraded in 90 min. The MIL-88/PVB nanofibers were easy to separate from solution. The results of scavenging experiments and ESR analysis demonstrated that OH and O2− were the predominant radicals for the TC-HCl degradation. Moreover, the possible mechanism for enhanced degradation performance of TC-HCl in the heterogeneous catalytic oxidation system was proposed.

A comprehensive investigation of the roles of H2O and NH3 on the HO + NH3 → NH2 + H2O reaction in the troposphere has been carried out by CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/6–311+G(2d,2p) method, and the canonical variational transition state theory with small curvature tunneling correction. The results show that both H2O and NH3 catalyzed reactions prefer the single hydrogen atom transfers (HAT) pathways than the double HAT routes. Meanwhile, the catalytic effect of H2O is more obvious as compared with NH3 with its effective rate constant (k'(WM)) larger by 2–5 orders of magnitude. However, within the temperature range of 213–320 K, the calculated value of k'(WM) is smaller by 5–9 orders of magnitude than the corresponding rate constant of the naked reaction. This result is in agreement with H2O catalyzed OH + CH2CH2, OH + CH2O and OH + CH2NH reactions, where water-assisted reaction cannot accelerate the reaction.

Prostate cancer is known as a common malignant tumor in clinics and moreover, traditional chemotherapeutic drugs have great toxic side effects and drug resistance. Therefore, the searching the highly efficient and low toxicity antitumor drugs from natural drugs has become an important approach for the treatment of prostate cancer. Many studies showed that Cortex Phellodendri has important therapeutic significance for prostate cancer. Magnoline is the main component of Cortex Phellodendri Amurensis, and it is of great significance to evaluate the effect of magnoline on prostate cancer. By using metabolomics, we established a comprehensive analysis strategy based on cell metabolic analysis to study the inhibitory effect of magnoline on the proliferation of prostate cancer cell line 22RV1, and finally conducted an analysis on the cell metabolism footprint samples. Results showed that magnoline had a significant inhibitory effect on the proliferation of the prostate cancer cell line 22RV1. According to the established cell metabolomics methods, we found that 12 metabolic biomarkers of the cell metabolic footprint samples, respectively, could inhibit the proliferation of prostate cancer cells. Magnoline could significantly affect these metabolic biomarkers to disrupt the growth and proliferation of the prostate cancer cell line 22RV1. Additionally, through MetPA analysis indicated that these biomarkers were closely correlated with a variety of metabolic pathways in tumor cells, including the energy metabolism, amino acid metabolism and fatty acid metabolism, most of which were associated with nutrition and energy metabolism. Therefore, we speculated that because of the disturbance of nutrition metabolism and energy metabolism of the prostate cancer cell line 22RV1, cells could not provide the material basis for rapid proliferation, eventually resulting in the inhibition effect.

Effects of (H2O)n (n = 1–3) on the H2O2 + HO → HO2 + H2O reaction have been investigated by the reactions of H2O2L(H2O)n (n = 1–3) + HO and H2O2 + HOL(H2O)n (n = 1–3) at the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level of theory, coupled with rate constant calculations by using canonical variational transition state theory. Interestingly, for the former reactions, one-step process and stepwise mechanism are involved, where one-step processes occurring though cage-like hydrogen bonding network complexes and the transition states are favourable. Due to larger effective rate constants, these favourable processes are also favourable than the corresponding latter reactions. Meanwhile, the catalytic effect of (H2O)n (n = 1–3) is mainly taken from water monomer, because the effective rate constant (k'(R_WM2)) of H2O2···H2O + HO reaction is, respectively, larger by 3, 6–10 orders of magnitude than that of H2O2···(H2O)2 + HO (k'(R_WD1)) and H2O2···(H2O)3 + HO (k'(R_WT1)) reactions. Furthermore, the enhancement factor of water molecular (k'(R_WM2)/ktot) is only 0.28% at 240 K, while at high temperature (such as at 425 K), the positive water vapour effect enhances up to 27.13%. This shows that at high temperatures the positive water effect is obvious under atmospheric conditions.

The addition reaction of CH2OO + H2O → CH2(OH)OOH without and with X (X = H2CO3, CH3COOH and HCOOH) and H2O was studied at CCSD(T)/6-311+ G(3df,2dp)//B3LYP/6-311+G(2d,2p) level of theory. Our results show that X can catalyse CH2OO + H2O → CH2(OH)OOH reaction both by increasing the number of rings, and by adding the size of the ring in which ring enlargement by COOH moiety of X inserting into CH2OO···H2O is favourable one. Water-assisted CH2OO + H2O → CH2(OH)OOH can occur by H2O moiety of (H2O)2 or the whole (H2O)2 forming cyclic structure with CH2OO, where the latter form is more favourable. Because the concentration of H2CO3 is unknown, the influence of CH3COOH, HCOOH and H2O were calculated within 0–30 km altitude of the Earth's atmosphere. The results calculated within 0–5 km altitude show that H2O and HCOOH have obvious effect on enhancing the rate with the enhancement factors are, respectively, 62.47%–77.26% and 0.04%–1.76%. Within 5–30 km altitude, HCOOH has obvious effect on enhancing the title rate with the enhancement factor of 2.69%–98.28%. However, compared with the reaction of CH2OO + HCOOH, the rate of CH2OO···H2O + HCOOH is much slower.

The advancement of omics technology has vigorously promoted the development of the life sciences; metabolomics in particular has emerged as a powerful tool that has a promising future in scientific research and clinical practice. As terminal products of complex biochemical networks, endogenous low-molecular-weight metabolites contain rich information about the physiological status of an individual or group of people. Also, this information has more practical significance in that we know "what happened" instead of "what might happen" to some degree. Rapid and accurate screening of metabolites on a large scale was beyond imagining in the past; however, benefiting from high-throughput technical means, the overall disturbance of metabolites induced by environmental stimulus or treatments can now be well analyzed. After appropriate bioinformatic analysis, clinically relevant biomarkers of a disease can be found, and an accurate and dynamic picture of metabolic disturbance that contributes to a phenotype of a certain organism can be constructed. Biomarkers can also reveal the general metabolic condition by pathways that correlate with disease progression, or even with the risk of certain diseases. Thus, as an indispensable part of the framework of systems biology, metabolomics has been widely used in, but not limited to, the fields of medical science, pharmaceuticals, botany, and microbiology. In this article, we focus on metabolomics' mainstream research content and technical innovations such as determination methods for biologically active compounds; further, we pay more attention to the future trends and various possibilities for metabolomics study.

In this article, the isomerisation mechanisms of HN(NO2)2 to O2NNN(O)OH without and with catalyst X (X = H2O, (H2O)2, (H2O)3, HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2) have been investigated theoretically at the CBS-QB3 level of theory. Our results show that the catalyst X (X = H2O, (H2O)2, (H2O)3, HCOOH, H2SO4 and CH3CH2COOH) shows different positive catalytic effects on reducing the apparent activation energy of the isomerisation reaction processes. Such different catalytic effects are mainly related to the number of hydrogen bonds and the size of the ring structure in X (X = H2O, (H2O)2 and (H2O)3)-assisted transition states, as well as different values of pKa for H2SO4, HCOOH and CH3CH2COOH. Very interesting is also the fact that H2SO4-assisted reaction is the most favourable for the hydrogen transfer from HN(NO2)2 to O2NNN(O)OH, due to the smallest pKa (−3.0) value of H2SO4 than H2O, HCOOH, H2SO4 and CH3CH2COOH, and also because of the largest ∠X•••H•••Y (the angle between the hydrogen bond donor and acceptor) involved in H2SO4-assisted transition state. Compared to the self-catalysis of the isomerisation mechanisms of HN(NO2)2 to O2NNN(O)OH, the apparent activation energy of H2SO4-assisted channel also reduces by 9.6 kcal⋅mol−1, indicating that H2SO4 can affect the isomerisation of HN(NO2)2 to O2NNN(O)OH, most obvious among all the catalysts H2O, (H2O)2, (H2O)3, HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2.

The reaction mechanism of HCHO with HO2 radical has been studied at CBS-QB3 level of theory. Three direct hydrogen abstraction processes, one double hydrogen transfer mechanism, three cooperative hydrogen abstraction processes, and one additional channel have been identified for HCHO + HO2 reaction. The calculated results indicate that the additional mechanism of HOCH2OO formation as well as the direct hydrogen abstraction process of HOC + H2O2 formations is dominant. Other channels may be negligible due to the high barrier heights. Rate constants and branching ratios have been estimated by means of the conventional transition state theory with zero-curvature tunnelling over the temperature range of 275–1800 K. The calculation shows that the overall rate constant in the temperature of 275–1800 K is mainly dependent on the channel of HOCH2OO formation. The three-parameter expression for the total rate constant is fitted to be cm3 molecule−1 s−1 between 275 and 1800 K.

A detailed effects of catalyst X (X = H2O, (H2O)2, NH3, NH3···H2O, H2O···NH3, HCOOH and H2SO4) on the HO4H → O3 + H2O reaction have been investigated by using quantum chemical calculations and canonical vibrational transition state theory with small curvature tunnelling. The calculated results show that (H2O)2-catalysed reactions much faster than H2O-catalysed one because of the former bimolecular rate constant larger by 2.6–25.9 times than that of the latter one. In addition, the basic H2O···NH3 catalyst was found to be a better than the neutral catalyst of (H2O)2. However it is marginally less efficient than the acidic catalysts of HCOOH, and H2SO4. The effective rate constant (k't) in the presence of catalyst X have been assessed. It was found from k't that H2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K at 0 km altitude. However, compared with the rate constant of HO4H → H2O + O3 reaction, the k eff values for H2O catalysed reaction are smaller by 1–2 orders of magnitude, indicating that the catalytic effect of H2O makes a negligible contribution to the gas phase reaction of HO4H → O3 + H2O. Highlights A detailed effects of catalyst of H2O, (H2O)2, NH3, NH3···H2O, H2O···NH3, HCOOH and H2SO4 on the HO4H → O3 + H2O reaction has been performed.From energetic viewpoint, H2SO4 exerts the strongest catalytic role in HO4H → O3 + H2O reaction as compared with the other catalysts.At 0 km altitude H2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K.HO4H → H2O + O3 reaction with H2O cannot be compete with the reaction without catalyst, due to the fact that the effective rate constants in the presence of H2O are smaller. A detailed effects of catalyst of H2O, (H2O)2, NH3, NH3···H2O, H2O···NH3, HCOOH and H2SO4 on the HO4H → O3 + H2O reaction has been performed. From energetic viewpoint, H2SO4 exerts the strongest catalytic role in HO4H → O3 + H2O reaction as compared with the other catalysts. At 0 km altitude H2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K. HO4H → H2O + O3 reaction with H2O cannot be compete with the reaction without catalyst, due to the fact that the effective rate constants in the presence of H2O are smaller.

In this article, the reaction mechanisms of H2S + 3O2 formation by the HO2 + HS reaction without and with catalyst X (X = H2O, (H2O)2 and (H2O)3) have been investigated theoretically at the CCSD(T)/6-311++G(3df,2pd)//B3LYP/6-311+G(2df,2p) level of theory, coupled with rate constant calculations by using conventional transition state theory. Our results show that in the presence of catalyst X (X = H2O, (H2O)2 and (H2O)3) into the channel of H2S + 3O2 formation, the reactions between the SH radical and HO2⋯(H2O)n (n = 1–3) complexes are more favorable than the corresponding reactions of the HO2 radical with HS⋯(H2O)n (n = 1–3) complexes due to the lower barrier of the former reactions and the higher concentrations of HO2⋯(H2O)n (n = 1–3) complexes. Meanwhile, the catalytic effect of water, water dimers and water trimers is mainly taken from the contribution of a single water vapor molecule, since the total effective rate constant of HO2⋯H2O + HS and H2O⋯HO2 + HS reactions was, respectively, larger by 7–9 and 9–12 orders of magnitude than that of SH + HO2⋯(H2O)2 and SH + HO2⋯(H2O)3 reactions. Besides, the enhancement factor of water vapor is only 0.37% at 240 K, while at high temperatures, such as 425 K, the positive water vapor effect is enhanced up to 38.00%, indicating that at high temperatures the positive water effect is obvious under atmospheric conditions. Overall, these results show how water and water clusters catalyze the gas phase reactions under atmospheric conditions.

In this work, four different channels, represented by H2O•••HO2 + HOCl, HO2•••H2O + HOCl, H2O•••HOCl + HO2 and HOCl•••H2O + HO2 have been analysed for water-catalysed formations of H2O2 + ClO to gain insight into the potential impact of the reaction in the atmosphere. The results at the CCSD(T)/aug-cc-pVTZ//MP2/6-311+G(2df,2p) level show that the H2O•••HO2 + HOCl reaction is kinetically the most favourable channel among the four channels. Compared to the channel of H2O2 + ClO formations without water vapour, the effective rate constant of H2O•••HO2 + HOCl reaction is estimated to be faster than the naked reaction by 2–3 orders of magnitude, indicating that the single water molecule in the H2O•••HO2 + HOCl channel exhibits a positive catalytic effect on enhancing the rate of H2O2 + ClO formations. Meanwhile, it is interesting that the transfer process between H2O•••HOCl + HO2 and H2O•••HO2 + HOCl has an activation energy of 0.6 kcal⋅mol−1 and can occur easily under tropospheric conditions.

Hydroxyl radical (•OH) damages DNA/RNA by attacking pyrimidine nucleobases through the addition reaction and H-atom abstraction. It may attack on the new cytosine derivative (5-formylCytosine [5-fCyt]) causing DNA oxidative damage, whereas the study of the related mechanism is still in its infancy. In the present work, 2 distinct mechanisms of •OH-mediated 5-fCyt at the complete basis set methods (CBS-QB3) and CBS-QB3/polarized continuum model approaches have firstly been explored, the addition reaction (paths R1 ~ R3) and the abstraction reaction (paths R4 ~ R6), respectively, and it shows that the addition of •OH to the C5═C6 double bond of 5-fCyt is more favourable than other reactions, indicating that the •OH addition to the C5 and C6 atoms have relatively high probability to happen. The proportion of the C5 and C6 adducts is large and may be detectable experimentally, which is in agreement with the conclusions of •OH-mediated cytosine reaction reported experimentally and theoretically. These hint that the new DNA base (5-fCyt) is easily damaged when exposed the surrounding of •OH environment. Therefore, the reducing free radical production or the addition of some antioxidants should be taken in embryonic stem cells to resistance DNA damage. Our results provide some evidences between 5-fCyt and tumor development for the experimental scientists.