Drug Exposure and Risk of Microscopic Colitis: A Systematic Review and Meta-Analysis.

BACKGROUND AND OBJECTIVES: Microscopic colitis (MC) is a chronic inflammatory bowel disease characterized by watery diarrhoea and a normal radiological and endoscopic appearance. Concern regarding a potential association between drug exposure and MC has recently emerged. We sought to systematically review and summarize the evidence for the potential association. METHODS: A systematic review and meta-analysis were performed to evaluate the incidence of MC associated with exposure to drug. The PubMed and Embase databases were searched to identify potential studies for inclusion. RESULTS: Twelve case-control studies were included in the meta-analysis. The results showed exposure to NSAID (OR, 1.64; 95% CI: 1.14-2.37; p < 0.001), PPI (OR, 2.36; 95% CI: 1.59-3.52; p < 0.001), SSRI (OR, 2.16; 95% CI: 1.5-3.13; p < 0.001), or aspirin (OR, 2.84; 95% CI: 1.4-5.76; p < 0.001) was related to the incidence of MC; however, such relationships in PPI and SSRI may be modulated by the selection of controls. Furthermore, we did not found a positive association with other drug exposure and MC. CONCLUSION: This meta-analysis indicated that NSAID, PPI, SSRI, or aspirin consumption may increase the risk for MC. Further studies exploring drug-induced microscopic colitis should include control groups with diarrhoea and not only healthy controls.

Culturable Endophytes Diversity Isolated from Paeonia ostii and the Genetic Basis for Their Bioactivity.

Paeonia ostii is known for its excellent medicinal values as Chinese traditional plant. To date, the diversity of culturable endophytes associated with P. ostii is in its initial phase of exploration. In this study, 56 endophytic bacteria and 51 endophytic fungi were isolated from P. ostii roots in China. Subsequent characterization of 56 bacterial strains by 16S rDNA gene sequence analysis revealed that nine families and 13 different genera were represented. All the fungal strains were classed into six families and 12 genera based on ITS gene sequence. The biosynthetic potential of all the endophytes was further investigated by the detection of putative polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) genes. The PCR screens were successful in targeting thirteen bacterial PKS, five bacterial NRPS, ten fungal PKS and nine fungal NRPS gene fragments. Bioinformatic analysis of these detected endophyte gene fragments facilitated inference of the potential bioactivity of endophyte bioactive products, suggesting that the isolated endophytes are capable of producing a plethora of secondary metabolites. These results suggest that endophytes isolated from P. ostii had abundant population diversity and biosynthetic potential, which further proved that endophytes are valuable reservoirs of novel bioactive compounds.Paeonia ostii is known for its excellent medicinal values as Chinese traditional plant. To date, the diversity of culturable endophytes associated with P. ostii is in its initial phase of exploration. In this study, 56 endophytic bacteria and 51 endophytic fungi were isolated from P. ostii roots in China. Subsequent characterization of 56 bacterial strains by 16S rDNA gene sequence analysis revealed that nine families and 13 different genera were represented. All the fungal strains were classed into six families and 12 genera based on ITS gene sequence. The biosynthetic potential of all the endophytes was further investigated by the detection of putative polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) genes. The PCR screens were successful in targeting thirteen bacterial PKS, five bacterial NRPS, ten fungal PKS and nine fungal NRPS gene fragments. Bioinformatic analysis of these detected endophyte gene fragments facilitated inference of the potential bioactivity of endophyte bioactive products, suggesting that the isolated endophytes are capable of producing a plethora of secondary metabolites. These results suggest that endophytes isolated from P. ostii had abundant population diversity and biosynthetic potential, which further proved that endophytes are valuable reservoirs of novel bioactive compounds.

[Determination of components in chromium-containing refractory with X-ray fluorescence spectrometry].

Components like SiO2, Al2 O3, Fe2O3, CaO, MgO and Cr2 O3 dominate the performance of chromium-containing amorphous refractory. That's still a hard task for product evaluation and quality control for amorphous refractory due to various component content, less available standard product and difficulty in fusion bead preparation. In the present study, series calibration standards were made from reagents and marked standards depend upon the content of components in real samples. The fusion bead was prepared with lithium tetraborate-lithium metaborate (67 : 33 by weight) as mixed flux and ammonium iodide as release agent, which was added during fusion process. The calibration curve derivated from the relationship between light intensity and components concentration and calibrated by theoretical alpha coefficient. The results of measurement were consistent with standard by this newly developed method. And good precision was also achieved in determination of real amorphous samples. It is easy in operation with less time spent, and practical in application.

ADHD, stimulant medication use, and the risk of fracture: a systematic review and meta-analysis.

We performed a meta-analysis to quantify the relationships among a diagnosis of attention-deficit/hyperactivity disorder (ADHD), the use of stimulant medication, and the risk of fracture. There was a significant positive association between ADHD and the risk of fracture. However, stimulant ADHD medication therapy appears to be associated with a reduced risk of fracture in patients with ADHD. INTRODUCTION: ADHD is associated with an increased fracture risk due to a lack of impulse control. ADHD medication may have a protective effect via behavior modification. However, previous research found an adverse effect of stimulant use on bone mass. Therefore, this meta-analysis study assessed the relationships among ADHD, the use of stimulant medication, and fracture risk. METHODS: A literature search was conducted using PubMed and EMBASE from inception through December 2020. Random-effects models were used to determine overall pooled estimates and 95% confidence intervals (CIs). RESULTS: The meta-analysis included 10 observational studies. Our results showed that ADHD diagnosis is associated with an increased risk of fracture (OR = 1.17; 1.01-1.35, p = 0.035). Notably, a higher risk of fracture (OR = 1.37, 95% CI 1.2-1.58, p < 0.001) was observed in non-stimulant-treated ADHD. However, no significant association, but a trend toward a lower risk, was observed for stimulant-treated ADHD patients compared with non-stimulant-treated ADHD patients (OR = 0.7, 95% CI 0.47-1.03, p = 0.073). In terms of fracture type, non-stimulant-treated ADHD was associated with traumatic fracture (OR = 1.79, 95% CI 1.54-2.08, p < 0.001) or stress fracture (OR = 1.12, 95% CI 1.04-1.2, p = 0.004) compared to healthy control (HC). In addition, further findings from our systematic review showed that the risk of traumatic (OR = 1, 95% CI 0.88-1.13, p = 0.954) or stress (OR = 0.84, 95% CI 0.62-1.14, p = 0.256) fracture was comparable between treated stimulant-ADHD patients and HC. CONCLUSIONS: Individuals with ADHD are at higher risk of fracture than the general population. Stimulant ADHD medication appears to be associated with a lower risk of traumatic fracture but not with a higher risk of stress fracture.

Molecularly imprinted monolith in-tube solid-phase microextraction coupled with HPLC/UV detection for determination of 8-hydroxy-2'-deoxyguanosine in urine.

Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) has been widely used as a biomarker of oxidative DNA damage. Measurements of 8-OHdG in urinary samples are challenging owing to the low level of 8-OHdG and the complex matrix. In this study, a novel molecularly imprinted polymer (MIP) monolithic column was synthesized with guanosine as a dummy template which was used as the medium for in-tube solid-phase microextraction (SPME). In-tube SPME coupled with HPLC/UV detection for extraction and determination of urinary 8-OHdG was developed. The synthesized MIP monolithic column exhibited high extraction efficiency owing to its greater phase ratio with convective mass transfer and inherent selectivity. The enrichment factor for 8-OHdG was found to be 76 and the limits of detection and quantification of the method for urinary samples were 3.2 nmol/L (signal-to-noise ratio 3) and 11 nmol/L (signal-to-noise ratio 10), respectively. The MIP(')s selectivity also made the sample preparation procedure and chromatographic separation much easier. The linear range of the proposed method was from 0.010 to 5.30 micromol/L (r = 0.9997), with a relative standard deviation of 1.1-6.8%, and the recovery for spiked urine samples was 84 +/- 3%. The newly developed method was successfully applied to determine urinary samples of healthy volunteers, coking plant workers, and cancer patients. The 8-OHdG level in cancer patients was significantly higher than that in healthy people.

Theoretical study on the reactions of the cyclic trinitrogen radical toward oxygen and water.

Recently, the detection of the neutral simplest all-nitrogen ring, cyclic-N(3) radical, has been realized via various techniques, which has led to numerous studies on its structures, energetics, and spectroscopy. In particular, it has been postulated as a possible building block of high energy density materials. Yet, its intermolecular reactivity is poorly understood. In this paper, we for the first time studied the reactions of cyclic-N(3) with the widespread oxygen and water at the CCSD(T)/aug-cc-pVTZ //B3LYP/6-311++G(d,p)+ZPVE and G3B3//B3LYP/6-311++G(d,p) (italics) levels. An addition-elimination mechanism was revealed for the cyclic-N(3) + O(2) reaction that results in the elementary product N(2) + NO + (3)O with an overall barrier as high as 11.8 (11.0) kcal/mol. The calculated low rate constants (even at high temperatures) show that the cyclic-N(3) radical is stable against oxygen. The cyclic-N(3) + H(2)O reaction is associated with a quasi H-abstraction mechanism forming the product cyclic-N(3)H + OH with the rather high barrier of 35.7 (36.2) kcal/mol. This indicates that cyclic-N(3) is chemically inert toward H(2)O. Chemical implications of the present work are discussed.

Theoretical study on reaction mechanism of fulminic acid HCNO with CN radical.

The HCNO + CN reaction is one potentially important process during the NO-reburning process for the reduction of NOx pollutants from fossil fuel combustion emissions. To compare with the recent experimental study, we performed the first theoretical potential energy surface investigation on the mechanism of HCNO + CN at the G3B3 and CCSD(T)/aug-cc-pVTZ levels based on the B3LYP/6-311++G(d,p) structures, covering various entrance, isomerization, and decomposition channels. The results indicate that the most favorable channel is to barrierlessly form the entrance isomer L1c NCCHNO followed by successive ring closure and concerted CC and NO bond rupture to generate the product P1 HCN + NCO. However, the formation of P4 (3)HCCN + NO, predicted as the only major product in the recent experiment, is kinetically much less competitive. This conclusion is further supported by the master equation rate constant calculation. Future experimental reinvestigations are strongly desired to test the newly predicted mechanism for the CN + HCNO reaction. Implications of the present results are discussed.

[Construction of the recQ double mutants and analysis of adversity in Deinococcus radiodurans].

As a subfamily member of SF1 superfamily, the RecO helicases are highly conserved in evolution and are required for maintaining genome stability in all organisms. Loss of RecO helicase function leads to a breakdown in the maintenance of genome integrity, in particular hyper-recombination. Named after the recQ gene of Escherichia coli, lower eukaryotic species generally only contain a single RecQ family representative; for example, Sgsl in the budding yeast, Saccharomyces cerevisiae, and Rqhl in the fission yeast, Schizosaccharomyces pombe. There are, however, multiple members in most higher organisms, with five being present in humans. Defects in three of these human RecQ helicases give rise to defined clinical disorders associated with cancer predisposition and variable aspects of premature aging. Deinococcus radiodurans encodes two recQ genes with unusual domain: DR1289 and DR2444, whose functions, however, remain obscure currently. DR1289 contains three tandem copies of the C-terminal helicase-RNase D (HRDC) domain, instead of the single copy present in all other bacteria except Neisseria that similarly possesses three copies. DR2444 contains a HRDC domain and a domain homologous to cystathionine gamma-lyase; this is the first example of an HRDC domain that is not associated with either a helicase or a nuclease. In this study, a fusion DNA fragment carrying kanamycin resistance gene with the D. radiodurans groEL promoter, chloramphenicol resistance gene with KAT promoter was cloned by PCR amplification and reversely inserted into the recQ locus in the genome of the wild-type strain RI. Three resulting recQ-deficient strains, designated deltaDR1289, deltaDR2444 and deltarecQ (double mutation), were constructed. Results show that deltaDR1289 and delta recQ were very sensitive to ionizing radiation and H2O2, while delta DR2444 and wild strain R1 were not. The phenotype of delta DR1289 was similar to many RecQ helicase mutants. Therefore, it was presumed that DR1289 was the necessary gene in maintaining the extreme resistance to DNA damaging agents, whereas DR2444 was not. Further research based on genetic and biochemical approaches should help to gain a better understanding of the genes involved in DNA repair.

[Effects of PprI and RecX on antioxidant activity of Deinococcus radiodurans].

Effects of mutations of Pprl (Dr0167) and RecX (Dr1310), which are relative to radioresistance, on reactive oxygen species scavenging activities in Deinococcus radiodurans were investigated using gene mutation, chemiluminescence measurement and enzyme activity analysis. Their possible regulating functions on the activities of antioxidant enzymes was evaluated. Results show that mutant that lacks PprI is remarkably sensitive to reactive oxygen species and its enzyme activities of catalase and superoxide dismutase decrease significantly. On the other hand, RecX has a "negative" effect on reactive oxygen species scavenging activities of this bacterium, i.e., mutation of recX enhances the scavenging activities on reactive oxygen species, and the enzyme activities of catalase and superoxide dismutase in mutant that lacks RecX are significantly increased. These results indicate that these two genes are relative to the regulation of antioxidant system of this bacterium. It presents some idea to the further investigation on the antioxidant mechanism of this bacterium.

[Geometric active contour model with color and intensity priors for medical image segmentation].

A new algorithm using the geometric active contour model with the fusion of color and intensity priors to segment medical images is presented in this paper. The prior knowledge used here are firstly defined in different color spaces and represented as thresholds searched by the genetic algorithm. Then the prior knowledge is merged into active contour model with its contour evolution by the level set technique. The experiments on clinical marrow images and mammograms have successfully demonstrated its superiority of the proposed algorithm over the existing active contour models which deal with image gradient information.

Theoretical study on the tautomerization of 1,5-diaminotetrazole (DAT).

The tautomerization pathways and kinetics of 1,5-diaminotetrazole (DAT) have been investigated by means of second-order Møller-Plesset perturbation theory (MP2) and coupled-cluster theory, with single and double excitations including perturbative corrections for triple excitations (CCSD(T)). Five possible tautomers, namely 4-hydro-1-amino-5-imino-tetrazole (a), 2,5-diamino-tetrazole (b), 1,5-diamino-tetrazole (c), 2-hydro-1-imino-5-amino-tetrazole (d), and 2,4-dihydro-1,5-diimino-tetrazole (e) were identified. The structures of the reactants, transition states, and products along with the tautomerism pathways were optimized by the MP2 method using the 6-311G** basis set, and the energies were refined using CCSD(T)/6-311G**. The minimum-energy path (MEP) information for DAT was obtained at the CCSD(T)/6-311G**//MP2/6-311G** level of theory. Therein, reaction 2 (c → b) is an amino-shift reaction, while reaction 1 (c → a), reaction 3 (c → d), reaction 4 (a → e), and reaction 5 (d → e) are reactions of hydrogen-shift tautomerization. The calculated results show that 2,5-diaminotetrazole (b) with the minimum energy (taking c as a standard) among five tautomers, is the energetically preferred tautomer of DAT in the gas phase. In addition, the energy barrier of reaction 2 is 71.65 kcal · mol(-1) in the gas phase, while reaction 1 takes place more easily with an activation barrier of 61.53 kcal · mol(-1) also as compared to 63.71 kcal · mol(-1) in reaction 3. Moreover, the tautomerization of reaction 4 requires the largest energy barrier of 83.29 kcal · mol(-1), which is obviously bigger than reaction 5 with a value of 73.78 kcal · mol(-1). Thus, the hydrogen-shift of c to a is the easiest transformation, while the tautomerization of a to e is the hardest one. Again, the rate constants of tautomerization have been obtained by TST, TST/Eckart, CVT, CVT/SCT, and CVT/ZCT methods in the range 200-2500 K, and analysis indicated that variational effects are small over the whole temperature range, while tunneling effects are significant in the lower temperature range.

Theoretical study on novel nitrogen-rich energetic compounds of bis(amino)-azobis(azoles) with tetrazene unit.

Six stereoisomers of 5,5'-bis(amino)-1,1'-azobis(tetrazoles) and 30 other structures, including all possible bis(amino)-azobis(azoles) with an N-N=N-N unit, were designed. The molecular geometries were fully optimized at the DFT-B3LYP level with the 6-31++g (d, p) basis set. From the absence of any imaginary frequency in the infrared vibration frequency spectrum, it is predicted that all these studied structures may exist in stable forms. The results of the total energies of the stereoisomers of 5,5'-bis(amino)-1,1'-azobis(tetrazoles) indicate that the two symmetric trans-form structures are more likely to exist than the other four. The pyrolysis process, chemical stability and molecular electrostatic potential were studied via the investigation of their electronic structure. Heats of formation (HOFs) were calculated using the atomization energy method based on the results of the harmonic vibration frequencies, and a linear relationship was found between the HOF and nitrogen chain or nitrogen content. Densities of the title compounds were predicted with the Monte Carlo method. Finally, according to the results of the calculated HOFs and densities, the explosive parameters of these compounds were calculated using the Kamlet-Jacobs formula. 5,5'-Bis(amino)-1,1'-azobis(tetrazoles) and its isomer 5,5'-bis(amino)-2,2'-azobis(tetrazoles) may have potential for use as energetic compounds.

Theoretical study of the decomposition mechanisms and kinetics of the ingredients RDX in composition B.

RDX as a component in composition B (TNT + RDX) was first studied by us on its mechanism and kinetics of decomposition reactions in this paper. We have pointed out three possible pathways and found a new low-energy process of its decomposition. The N-N bond cleavage in composition B has higher dissociation energies than the monomer, but it is also the initial step. The optimized structures and the frequencies of all the stationary points were calculated at the B3LYP/6-31G(d) level. The minimum-energy paths were obtained by using the intrinsic reaction coordinate (IRC) theory, and the reaction potential energy curve was corrected with zero-point energy. Finally, the rate constants were calculated in a wide temperature region from 200 to 2500 K using TST, TST/Eckart theories. The obtained results also indicate that the tunneling effects are remarkable at low temperature (200 K

First-principles study of energetic complexes (II): (5-cyanotetrazolato-N2) pentaammine cobalt (III) perchlorate (CP) and Ni, Fe and Zn analogues.

First-principles methods using the TPSS density functional level of theory with the basis set 6-31G** were applied to study (5-cyanotetrazolato-N(2)) pentaammine cobalt (III) perchlorate (CP) and Ni, Fe and Zn analogues in the gas phase. The optimized lowest-energy geometry of CP was calculated from reported experimental structural data using the TPSS method. The calculated values are in good agreement with those measured by X-ray diffraction. Ni, Fe and Zn analogues were constructed and calculated on the same basis. NBO results showed that the metal-ligand interactions have covalent character. Donor-acceptor analyses predicted that the delocalization energy E(2) decreases from Co to Zn, so the covalent nature of the complexes increases in the order Co>Fe>Ni>Zn. In addition, HOMO-LUMO composition was investigated to determine the stability of the title compounds.

Gaseous reaction mechanism between two H(2)CN radicals.

The self-recombination of the methylene amidogen radical (H(2)CN) is known to be fast and should play an important role in determining the concentration of H(2)CN radicals in both combustion and astrophysical processes. The rate constants of H(2)CN + H(2)CN have been determined by previous experiments, whereas its detailed evolution process and product distribution are still unclear. In this work, by means of quantum chemical and master equation calculations, we for the first time explored theoretically the potential energy surface and kinetics of the H(2)CN + H(2)CN reaction. At the CCSD(T)/6-311++G(2df,p), CCSD(T)/aug-cc-pVTZ and Gaussian-3 single-point levels based on the B3LYP/6-31++G(d,p) structures, the dominant channel was found to be () H(2)CN + H(2)CN --> H(2)CNNCH(2) () --> r-CH(2)NNCH(2) () --> N(2) + C(2)H(4) () with a zero overall barrier. The calculated rate constants are in agreement with available experiments. Of particular interest, since the formed product involves molecular nitrogen, the H(2)CN + H(2)CN reaction might have important contribution to the nitrogen-recycling in a number of conflagrant and astrophysical processes.

Theoretical studies on the tautomerism and intramolecular hydrogen shifts of 5-amino-tetrazole in the gas phase.

The tautomerism and intramolecular hydrogen shifts of 5-amino-tetrazole in the gas phase were studied in the present work. The minimum energy path (MEP) information of 5-amino-tetrazole was obtained at the CCSD(T)/6-311G**//MP2/6-311G** level of theory. The six possible tautomers of 1H, 4H-5-imino-tetrazole (a), 1H-5-amino-tetrazole (b), 2H-5-amino-tetrazole (c), 1H, 2H-5-imino-tetrazole (d), the mesoionic form (e) and 2H, 4H-5-imino-tetrazole (f) were investigated. Among these tautomers, there are 2 amino- forms, 3 imino- forms, and 1 mesoionic structure form. In all the tautomers, 2-H form (c) is the energetically preferred one in the gas phase. In the imino- tautomers, the energy value of the compound d is similar as that of the compound f but it is higher than the energy value of the compound a. The potential energetic surface (PES) and kinetics for five reactions have been investigated. Reaction 2 (b-->c) was hydrogen shifts only in which the 1-H and 2-H rearrangement. This means that the reaction 2 (b-->c) is energetically favorable having an activation barrier of 45.66 kcal.mol(-1) and the reaction energies (DeltaE) is only 2.67 kcal.mol(-1). However, the reaction energy barrier for tautomerism of reaction 1 (b-->e) is 54.90 kcal.mol(-1). Reaction 1 (b-->a), reaction 3 (c-->d), and reaction 5 (c-->f) were amino- -->imino- tautomerism reactions. The energy barriers of amino- -->imino- tautomerism reactions required are 59.39, 65.57, 73.61 kcal.mol(-1) respectively in the gas phase. The calculated values of rate constants using TST, TST/Eckart, CVT, CVT/SCT and CVT/ZCT methods using the optimized geometries obtained at the MP2/6-311G** level of theory show the variational effects are small over the whole temperature range, while tunneling effects are big in the lower temperature range for all tautomerism reactions.

The mechanism and kinetics of decomposition of 5-aminotetrazole.

The pathway and ab initio direct kinetics of the decomposition 5-aminotetrazole (5-ATZ) to HN(3) and NH(2)CN was investigated. Reactant, products and transition state were optimized with MP2 and B3LYP methods using 6-311G** and aug-cc-pVDZ basis sets. The intrinsic reaction coordinate curve of the reaction was calculated using the MP2 method with 6-311G** basis set. The energies were refined using CCSD(T)/6-311G**. Rate constants were evaluated by conventional transition-state theory (CVT) and canonical variational transition-state theory (TST), with tunneling effect over 300 to 2,500 K. The results indicated that the tunneling effect and the variational effect are small for the calculated rate constants. The fitted three-parameter expression calculated using the CVT and TST methods are k(T) = 4.07 x 10(11) x T(0.84) x e((-2.42 x 10(4))/T)s(-1) and k(T) = 2.09 x 10(11) x T(0.89) x e((-2.36 x 10(4))/T)s(-1), respectively.

Theoretical study on the methyl radical with chlorinated methyl radicals CH(3-n)Cln (n = 1, 2, 3) and CCl2.

Radical-radical reactions involving chlorinated methyl radicals are particularly important in the mechanism of combustion of chlorinated hydrocarbons. Yet, they are usually difficult to study experimentally. In this paper, four chloride-related radical-radical reactions, i.e., CH3+CH(3-n)Cln (n = 1, 2, 3) and CH3+CCl2, are theoretically studied for the first time by means of the Gaussian-3//B3LYP potential energy surface survey combined with the master equation study over a wide range of temperatures and pressures. Our calculated results show that the three CH3+CH(3-n)Cln reactions can barrierlessly generate the former two kinetically allowed products P1 H(2)C=C(H)(3-n)Cl(n-1)+HCl and P2 CH3CH(3-n)Cl(n-1)+Cl with the very high predominance of P1 over P2. For the CH3 reaction with the biradical CCl2, which inevitably takes place during the CH3+CCl3 reaction and yet has never been studied experimentally or theoretically, H(2)C=CCl2+H and H(2)C=C(H)Cl+Cl are predicted to be the respective major and minor products. The results are compared with the recent laser photolysis/photoionization mass spectroscopy study on the CH3+CH(3-n)Cln (n = 1, 2, 3) reactions. The predicted rate constants and product branching ratios of the CH3+CCl2 reaction await future experimental verification.

The reaction of the aminoboranylidene-iminoborane isomerization: a CASSCF direct dynamics study.

The barrier and the potential-energy surface of the isomerization from aminoboranylidene (BNH2) to iminoborane (HBNH) have been studied using complete active space self-consistent field (CASSCF) with the 6-31 + G(d, p) basis set and higher-level energy methods. The rate constants of the isomerization reaction are reported by employing the direct ab initio dynamics method. The geometries of all the stationary points were optimized using the B3LYP and CCSD methods with the cc-pVTZ and cc-pVQZ basis sets. The information along the intrinsic reaction coordinate (IRC) was also calculated at the CASSCF/6-31 + G (d,p) level of theory. The energies were refined at the G3, G3MP2, G3MP2B3, CBS-Q, CBS-QB3, and two high-level (HL) methods based on the geometries optimized using CASSCF/6-31 + G(d,p). The rate constants were evaluated using conventional transition-state theory (TST), canonical variational transition-state theory (CVT), and canonical variational transition-state theory with small curvature tunneling correction (CVT/SCT) and conventional transition-state theory with Eckart tunneling correction (TST/Eckart). According to the calculated results, we conclude that the tunneling effect is very important to this isomerization reaction.

An ignored but most favorable channel for NCO+C2H2 reaction.

The NCO+C(2)H(2) reaction has been considered as a prototype for understanding the chemical reactivity of the isocyanate radical towards unsaturated hydrocarbons in fuel-rich combustion. It has also been proposed to provide an effective route for formation of oxazole-containing compounds in organic synthesis, and might have potential applications in interstellar processes. Unfortunately, this reaction has met mechanistic controversy both between experiments and between experiments and theoretical calculations. In this paper, detailed theoretical investigations at the Becke's three parameter Lee-Yang-Parr-B3LYP6-31G(d), B3LYP6-311++G(d,p), quadratic configuration interaction with single and double excitations QCISD6-31G(d), and Gaussian-3 levels are performed for the NCO+C(2)H(2) reaction, covering various entrance, isomerization, and decomposition channels. Also, the highly cost-expensive coupled-cluster theory including single and double excitations and perturbative inclusion of triple excitations CCSD(T)/aug-cc-pVTZ single-point energy calculation is performed for the geometries obtained at the Becke's three parameter Lee-Yang-Parr-B3LYP6-311++G(d,p) level. A previously ignored yet most favorable channel via a four-membered ring intermediate with allyl radical character is found. However, formation of P(3) H+HCCNCO and the five-membered ring channel predicted by previous experimental and theoretical studies is kinetically much less competitive. With the new channel, master equation rate constant calculations over a wide range of temperatures (298-1500 K) and pressures (10-560 Torr) show that the predicted total rate constants exhibit a positive-temperature dependence and no distinct pressure dependence effect. This is in qualitative agreement with available experimental results. Under the experimental conditions, the predicted values are about 50% lower than the latest experimental results. Also, the branching ratio variations of the fragments P(2) HCN+HCCO and P(5) OCCHCN+H as well as the intermediates L1 HCHCNCO, r4 cCHCHNC-O, and L5 NCHCHCO are discussed with respect to the temperature and pressure. Future experimental reinvestigations are strongly desired to test the newly predicted channel for the model NCO+C(2)H(2) reaction. Implications of the present results in various fields are discussed.