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The effects of water on radical–radical reactions are of great importance for the elucidation of the atmospheric oxidation process of free radicals. In the present work, the HO2 + HO2 reactions with (H2O)n (n = 1–3) have been investigated using quantum chemical methods and canonical variational transition state theory with small curvature tunneling. We have explored both one-step and stepwise mechanisms, in particular the stepwise mechanism initiated by ring enlargement. The calculated results have revealed that the stepwise mechanism is the dominant one in the HO2 + HO2 reaction that is catalyzed by one water molecule. This is because its pseudo-first-order rate constant (kRWM1′) is 3 orders of magnitude larger than that of the corresponding one-step mechanism. Additionally, the value of kRWM1′ at 298 K has been found to be 4.3 times larger than that of the rate constant of the HO2 + HO2 reaction (kR1) without catalysts, which is in good agreement with the experimental findings. The calculated results also showed that the stepwise mechanism is still dominant in the (H2O)2 catalyzed reaction due to its higher pseudo-first-order rate constant, which is 3 orders of magnitude larger than that of the corresponding one-step mechanism. On the other hand, the one-step process is much faster than the stepwise mechanism by a factor of 105–106 in the (H2O)3 catalyzed reaction. However, the pseudo-first-order rate constants for the (H2O)2 and (H2O)3-catalyzed reactions are lower than that of the H2O-catalyzed reaction by 3–4 orders of magnitude, which indicates that the water monomer is the most efficient one among all the catalysts of (H2O)n (n = 1–3). The present results have provided a definitive example that water and water clusters have important influences on atmospheric reactions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effects of (H 2 O) n ( n = 1–2) on hydrogen abstraction reaction (H 2 O 2 + HS → H 2 S + HO 2 ) 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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of a single water molecule on the HO2 + NO2 hydrogen abstraction reaction has been investigated by employing B3LYP and CCSD(T) theoretical approaches with the aug-cc-pVTZ basis set. The reaction without water has three types of reaction channels on both singlet and triplet potential energy surfaces, depending on how the HO2 radical approaches NO2. These correspond to the formation of trans-HONO + O2, cis-HONO + O2 and HNO2 + O2. Our calculated results show that triplet reaction channels are favorable and their total rate constant, at 298 K, is 2.01 × 10−15 cm3 molecule−1 s−1, which is in good agreement with experimental values. A single water molecule affects each one of these triplet reaction channels in the three different reactions of H2O…HO2 + NO2, HO2…H2O + NO2 and NO2…H2O + HO2, depending on the way the water interacts. Interestingly, the water molecule in these reactions not only acts as a catalyst giving the same products as the naked reaction, but also as a reactant giving the product of HONO2 + H2O2. The total rate constant of the H2O…HO2 + NO2 reaction is estimated to be slower than the naked reaction by 6 orders of magnitude at 298 K. However, the total rate constants of the HO2…H2O + NO2 and NO2…H2O + HO2 reactions are faster than the naked reaction by 4 and 3 orders of magnitude at 298 K, respectively. Their total effective rate constant is predicted to be 1.2 times that of the corresponding total rate constant without water at 298 K, which is in agreement with the prediction reported by Li et al. (science, 2014, 344, 292–296). [ABSTRACT FROM AUTHOR]

The isomerization of CH3S(OH)CH2 to CH3S(O)CH3 in the absence and presence of water has been investigated at the G3XMP2//B3LYP/6-311+G(2df,p) level. The naked isomerization, the reaction without water, gives the high barrier height (21.56 kcal·mol−1). Three models are constructed to describe the water influence on the isomerization, that is, water molecules are the catalyst and the microsolvation, and water molecules act as the catalyst and microsolvation simultaneously. Our results show that the isomerization barrier heights of CH3S(OH)CH2 to CH3S(O)CH3 are reduced by 12.32, 11.04, and 7.80 kcal·mol−1, respectively, when one, two, and three water molecules are performed as catalyst, in contrast to the naked isomerization. Moreover, the rate constants of the isomerization are calculated using the transition state theory with the Wigner tunneling correction over the temperature range of 240-425 K. We find that the rate constant of a single water molecule as the catalyst is 1.58 times larger than the naked isomerization at 325 K, whereas it is slower by 6 orders of magnitude when water molecule serves as the microsolvation at 325 K, compared to naked reaction. So the water-catalyzed isomerization of CH3S(OH)CH2 to CH3S(O)CH3 is predicted to be the key role in lowering the activation energy. The isomerization involving water molecules acting as microsolvation is unfavorable under atmospheric conditions. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of the reaction of the radical C2H5S with the radical HO2 has been investigated theoretically by means of the density functional theory (DFT) and coupled cluster theory (CC). The geometries of all the stationary points and the selected points along the potential energy surfaces for the reaction of C2H5S with HO2 were optimized at the B3LYP/6-311G(2d,p) level of theory. The harmonic vibrational frequencies of all the stationary points were calculated at the above same level of theory. The single point energies were further refined at the CCSD(T)/aug-cc-pVDZ level of theory based on the B3LYP/6-311G(2d,p) optimized geometries. Eight possible reaction pathways including eleven reaction channels on both the singlet and triplet potential energy profiles for the title reaction were explored. The calculated results indicated that Path R4, the formation of the products C2H5SO+OH on the singlet potential energy profile, is likely to be the most favorable channel among Path R1∼4, and Path R5, hydrogen abstraction of HO2 by the S atom of CH3CH2S, is the most favorable among Path R5∼8 on the triplet potential energy profile. The major products of the reaction may be C2H5SH, 3O2, C2H5SO and OH. [Copyright &y& Elsevier]

The gas-phase hydrogen abstraction reactions of CH3O2and HO2with HO2in the presence and absence of a single water molecule have been studied at the CCSD(T)/6-311++G(3d,2p)//B3LYP/6-311G(2d,2p) level of theory. The calculated results show that the process for O3formation is much faster than that for 1O2and 3O2formation in the water-catalyzed CH3O2+ HO2reaction. This is different from the results for the non-catalytic reaction of CH3O2+ HO2, in which almost only the process for 3O2formation takes place. Unlike CH3O2+ HO2reaction in which the preferred process is different in the catalytic and non-catalytic conditions, the channel for 3O2formation is the dominant in both catalytic and non-catalytic HO2+ HO2reactions. Furthermore, the calculated total CVT/SCT rate constants for water-catalyzed and non-catalytic title reactions show that the water molecule doesn't contribute to the rate of CH3O2+ HO2reaction though the channel for O3formation in this water-catalyzed reaction is more kinetically favorable than its non-catalytic process. Meanwhile, the water molecule plays an important positive role in increasing the rate of HO2+ HO2reaction. These results are in good agreement with available experiments. [ABSTRACT FROM AUTHOR]

A theoretical study of the mechanism and the kinetics for the hydrogen abstraction reaction of the biradical hydroperoxy radical has been presented at the CCSD(T)/6‐311++G(3d,2p)//CCSD/6‐31+G(d,p) level of theory. Our theoretical calculations suppose a stepwise mechanism involving the formation of a postreactant complex in the triplet and singlet entrance channels. Four transition states of the six‐membered chain complexes (3TS1 and 1TS1) and six‐membered ring complexes (3TS2 and 1TS2) are located at the high dual level CCSD(T)/6‐311++G(3d,2p)//CCSD/6‐31+G(d,p) method. The rate constants of Path 1 ∼ Path 4 at the CCSD(T)/6‐311++G(3d,2p)//CCSD/6‐31+G (d,p) level are calculated by means of the conventional transition state theory (TST) and canonical variational TST without and with small‐curvature tunneling (SCT) correction within the temperature range of 200–2,500 K. The calculated results show that the triplet channel is the dominating reaction channel and Path 2 is found to be the most favorable pathway. The rate constants of Path 2 are in good agreement with the experimental values at the experimentally measured temperatures. Moreover, the variational effect is not obvious in the low temperature range but is not neglectable in the high temperature range. The SCT plays an important role particularly in the low temperature range. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]