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1.
Anal Bioanal Chem ; 412(2): 377-388, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31773226

RESUMO

Insulin oligosaccharide conjugates hold promise as potential glucose-responsive insulins (GRIs), which can improve the therapeutic index of insulins and mitigate the risk of hypoglycemia. A key challenge for the analytical development of such molecules is finding an efficient method to characterize the purity and impurities of conjugated insulins. Using the S-Matrix Fusion QbD-ultrahigh performance liquid chromatography (UHPLC) integrated system, we were able to quickly screen and develop two short UHPLC methods. These methods were used to support process development, clinical batch drug substance (DS) release, and stability studies of MK-2640, an insulin oligosaccharide conjugate. Both methods used a Waters CSH C18 column, with a shallow gradient of acetonitrile to aqueous mobile phase containing 25 mM sodium perchlorate and 0.05% perchloric acid. The 10-min run time method was well suited for process development and monitoring as it was able to separate the main product, MK-2640, six oligosaccharide-substituted recombinant human insulin (RHI) impurities, A21 deamidated MK-2640, and the starting material RHI. The 13-min run time method provided improved separation of the major impurities and demonstrated good chromatographic reproducibility on different instruments or using columns from different lots of stationary phase, which made it ideal for the final DS release. Validation of the 13-min method demonstrated great linearity for both the MK-2640 main peak and its related impurities, low limit of detection (0.02%), and limit of quantitation (0.05%). The high specificity of the method allowed the separation of the degradation products from main peak, thus makes it suitable for stability monitoring. The major impurities in the DS were characterized by two-dimensional liquid chromatography-mass spectrometry (2D-LC-MS).

2.
J Cell Biochem ; 120(12): 19422-19431, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31452264

RESUMO

Osteoporosis (OP), a common metabolic bone disease, is accompanied by reduced bone mass, bone mineral density (BMD), as well as microstructure destruction of bone. Previously, microRNA-196a-2 (miR-196a-2) and miR-196a-3p were reported for its involvement in BMD. Herein, this study set out to identify the functional relevance of miR-196a in osteogenic differentiation in osteoporotic mice and explore the associated mechanism by establishing an OP mouse model. Guanine nucleotide binding protein, alpha stimulating (GNAS) was verified as a target gene of miR-196a, which was decreased in OP mice. Furthermore, the bone marrow stromal cells (BMSCs) were then extracted from OP mice and treated with miR-196 mimic/inhibitor or small interfering RNA against GNAS to investigate miR-196a interaction with GNAS and the Hedgehog signaling pathway. BMSCs in OP mice transfected with miR-196a mimic or si-GNAS displayed the elevated expression of Smo, ALP, Runx2, and OPN, as well as bone gla protein and tartrate-resistant acid phosphatase, elevated ALP vitality and bone formation ability as well as reduced expression of GNAS and PTCH. Taken conjointly, overexpression of miR-196a repressed GNAS expression by activating the Hedgehog signaling pathway, thus promoting osteogenic differentiation in mice with OP.

3.
J Pharm Sci ; 108(11): 3609-3615, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31348935

RESUMO

Research on pharmaceutical pediatric powder-for-suspension formulations mainly focuses on chemical and physical stability of the active pharmaceutical ingredient. However, the chemical stability of excipients could also play a key role in governing the quality and performance of the product. The suspending agents that are added into formulations to suspend the active pharmaceutical ingredient particles are critical to ensure the suspension dose accuracy. In this article, we investigate the chemical stability of the suspending agent-xanthan gum-in the presence of other excipients, particularly commonly used acid modifiers (i.e., citric acid, malic acid, succinic acid, and fumaric acid) in pediatric powder-for-suspension formulations. We observed that some of the acid modifiers catalyze cross-linking of xanthan gum during accelerated stability studies in powder blends, which significantly decreases the viscosity of the corresponding constituted suspension, resulting in poor suspendability and dose inaccuracy. Furthermore, we found that the cross-linking of xanthan gum is acid-dependent and that a careful selection of acid modifiers can mitigate the degradation issues of xanthan gum. Finally, we characterized the cross-linked xanthan gum using Fourier transform infrared spectroscopy and solid-state nuclear magnetic resonance and discussed the possible degradation mechanisms.

4.
J Cosmet Dermatol ; 18(6): 1938-1946, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30980594

RESUMO

BACKGROUND: Limited cutaneous systemic sclerosis is one subtype of systemic sclerosis which is characterized by a prototypic multisystem fibrotic disorder. OBJECTIVE: This study aimed to further investigate the pathological mechanism of limited cutaneous systemic sclerosis (lcSSc). METHODS: The dataset GSE76807 generated from 10 lcSSc patients and five healthy controls was used. After the preprocessing of the original data, differentially expressed genes (DEGs) were identified and then performed functional analysis, protein-protein interaction (PPI) network and module analysis. Additionally, the transcription factors (TFs) and miRNAs which potentially regulating DEGs were identified and the co-regulatory network was constructed. Finally, DEGs targeted by current drugs were identified. Real-time quantitative PCR analyses of some DEGs in mice with lcSSc were performed. RESULTS: Total 203 up-regulated and 189 down-regulated DEGs were obtained. The up-regulated genes were enriched in protein interactions at the synapses neuronal system, NCAM1 interactions, and CREB phosphorylation through the activation of CaMKII, while, cilium assembly, and endothelial form of nitric oxide synthase (eNOS) activation were enriched by down-regulated genes. SCRT2 and RABEP1 regulated by miR-218 were hub nodes in the network. DRD4 and GRIN2D were the main drug targets. RABEP1 and SSB were found lowly expressed in mice model with lcSSc. CONCLUSION: Endothelial form of NOS activation would be suppressed, and the process of neuronal migration and outgrowth would be activated to participant in the pathological mechanism of lcSSc.

5.
Nat Prod Res ; 32(5): 536-543, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-28553725

RESUMO

Microbial transformation of ursolic acid (1) was carried out by Alternaria longipes AS 3.2875. Six transformed products (2-7) from 1 were isolated and their structures were identified as 3-carbonyl ursolic acid 28-O-ß-D-glucopyranosyl ester (2), ursolic acid 3-O-ß-D-glucopyranoside (3), ursolic acid 28-O-ß-D-glucopyranosyl ester (4), 2α, 3ß-dihydroxy ursolic acid 28-O-ß-D-glucopyranosyl ester (5), 3ß, 21ß dihydroxy ursolic acid 28-O-ß-D-glucopyranosyl ester (6), and 3-O-(ß-D-glucopyranosyl)- ursolic acid 28-O-(ß-D-glucopyranosyl) ester (7) based on the analysis of 1D NMR, 2DNMR and MS data. The product 2 was a new compound among them and showed stronger antibacterial activity against S. aureu, MRSA and MRCA than substrate. In this study, we modified structure of ursolic acid through biotransformation to enhance its activities and preliminarily discussed the transformation way of the products.


Assuntos
Alternaria/metabolismo , Antibacterianos/farmacologia , Triterpenos/farmacologia , Antibacterianos/química , Biotransformação , Candida albicans/efeitos dos fármacos , Ésteres/metabolismo , Espectroscopia de Ressonância Magnética , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Estrutura Molecular , Triterpenos/metabolismo
6.
BMC Complement Altern Med ; 17(1): 310, 2017 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-28610566

RESUMO

BACKGROUND: Apoptosis plays a critical role in the progression of diabetic cardiomyopathy (DC). Astragalus polysaccharides (APS), an extract of astragalus membranaceus (AM), is an effective cardioprotectant. Currently, little is known about the detailed mechanisms underlying cardioprotective effects of APS. The aims of this study were to investigate the potential effects and mechanisms of APS on apoptosis employing a model of high glucose induction of apoptosis in H9C2 cells. METHODS: A model of high glucose induction of H9C2 cell apoptosis was adopted in this research. The cell viabilities were analyzed by MTT assay, and the apoptotic response was quantified by flow cytometry. The expression levels of the apoptosis related proteins were determined by Real-time PCR and western blotting. RESULTS: Incubation of H9C2 cells with various concentrations of glucose (i.e., 5.5, 12.5, 25, 33 and 44 mmol/L) for 24 h revealed that cell viability was reduced by high glucose dose-dependently. Pretreatment of cells with APS could inhibit high glucose-induced H9C2 cell apoptosis by decreasing the expressions of caspases and the release of cytochrome C from mitochondria to cytoplasm. Further experiments also showed that APS could modulate the ratio of Bcl-2 to Bax in mitochondria. CONCLUSIONS: APS decreases high glucose-induced H9C2 cell apoptosis by inhibiting the expression of pro-apoptotic proteins of both the extrinsic and intrinsic pathways and modulating the ratio of Bcl-2 to Bax in mitochondria.


Assuntos
Astrágalo (Planta)/química , Cardiomiopatias Diabéticas/fisiopatologia , Extratos Vegetais/farmacologia , Polissacarídeos/farmacologia , Apoptose/efeitos dos fármacos , Caspases/metabolismo , Linhagem Celular , Citocromos c/metabolismo , Cardiomiopatias Diabéticas/tratamento farmacológico , Cardiomiopatias Diabéticas/metabolismo , Glucose/metabolismo , Humanos , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Transdução de Sinais/efeitos dos fármacos
7.
Biochem Biophys Res Commun ; 490(2): 217-224, 2017 08 19.
Artigo em Inglês | MEDLINE | ID: mdl-28602700

RESUMO

Cancer cells usually utilize glucose as a carbon source for aerobic glycolysis, a phenomenon known as the Warburg effect. Increasing studies have shown that PVT1 (a long non-coding RNA, lncRNA) functions as critical regulator of multiple cancers. However, it remains totally unknown whether and how PVT1 regulates glucose metabolism in OS cells. In this study, we found that the expression of PVT1 were specifically increased in OS cells and tissues, and the upregulated PVT1 indicated poor prognosis. Glucose uptake, lactate production, and the expression of HK2 in OS cells were increased by overexpression of PVT1, while decreased by PVT1 knockdown. We further fund that PVT1 acted as molecular sponge to repress miR-497. Inhibition of miR-497 promoted glucose consumption and lactate production, phenomenon could be reversed by PVT1 silencing. Moreover, HK2 was a direct target of miR-497 and overexpression of HK2 attenuated the suppressive effect of miR-497 on glycolysis. Functionally, knockdown of PVT1 exerted tumor-suppressive effect by suppressing cell proliferation, cell cycle progression, and invasion in vitro, whereas miR-497 inhibitor partially abolished the inhibition effect of si-PVT1. Overexpression of HK2 attenuated the miR-497 induced inhibition of cell growth and motility. Taken together, these findings suggested that PVT1 contributes to OS cell glucose metabolism, cell proliferation, and motility through the miR-497/HK2 pathway, and revealed a novel relation between lncRNA and the alteration of glycolysis in OS cells.


Assuntos
Progressão da Doença , Glicólise , Hexoquinase/metabolismo , MicroRNAs/metabolismo , Osteossarcoma/metabolismo , RNA Longo não Codificante/metabolismo , Linhagem Celular Tumoral , Hexoquinase/genética , Humanos , MicroRNAs/antagonistas & inibidores , Osteossarcoma/enzimologia , Osteossarcoma/genética
8.
Sci Rep ; 7: 40264, 2017 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-28067283

RESUMO

In this study, the mechanistic and kinetic analysis for reactions of CF3OCH(CF3)2 and CF3OCF2CF2H with OH radicals and Cl atoms have been performed at the CCSD(T)//B3LYP/6-311++G(d,p) level. Kinetic isotope effects for reactions CF3OCH(CF3)2/CF3OCD(CF3)2 and CF3OCF2CF2H/CF3OCF2CF2D with OH and Cl were estimated so as to provide the theoretical estimation for future laboratory investigation. All rate constants, computed by canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT), are in reasonable agreement with the limited experimental data. Standard enthalpies of formation for the species were also calculated. Atmospheric lifetime and global warming potentials (GWPs) of the reaction species were estimated, the large lifetimes and GWPs show that the environmental impact of them cannot be ignored. The organic nitrates can be produced by the further oxidation of CF3OC(•)(CF3)2 and CF3OCF2CF2• in the presence of O2 and NO. The subsequent decomposition pathways of CF3OC(O•)(CF3)2 and CF3OCF2CF2O• radicals were studied in detail. The derived Arrhenius expressions for the rate coefficients over 230-350 K are: k T(1) = 5.00 × 10-24T3.57 exp(-849.73/T), k T(2) = 1.79 × 10-24T4.84 exp(-4262.65/T), kT(3) = 1.94 × 10-24 T4.18 exp(-884.26/T), and k T(4) = 9.44 × 10-28T5.25 exp(-913.45/T) cm3 molecule-1 s-1.

9.
Prim Care Diabetes ; 10(4): 272-80, 2016 08.
Artigo em Inglês | MEDLINE | ID: mdl-26778708

RESUMO

BACKGROUND: Observational studies and meta-analyses suggested that increased total fruits and vegetables consumption have a protective role in incidence of type 2 diabetes mellitus (T2DM). However, we still don't know whether the subtypes, such as citrus fruits and cruciferous vegetables (CV), have a preventive role. METHODS: We systematically searched the MEDLINE and EMBASE databases up to December 31, 2014. Summary relative risks (SRRs) and 95% confidence intervals (CIs) were calculated using random-effects models. RESULTS: Seven distinct prospective cohort studies (five articles) were identified for this study. A total of 16,544 incident cases of type 2 diabetes were ascertained among 306,723 participants with follow-up periods ranging from 4.6 to 24 years. Based on four prospective cohort studies, we found that overall, consumption of CV had a protective role in the T2DM incidence (highest vs. lowest analysis: SRR=0.84, 95% CI: 0.73 to 0.96), with evidence of significant heterogeneity (P=0.09, I(2)=54.4%). This association was independent of the main risk factors for cardiovascular disease: smoking, alcohol use, BMI, and physical activity etc. Consumption of citrus fruits did not have a protective role in the T2DM development (highest vs. lowest analysis: SRR=1.02, 95% CI: 0.96 to 1.08), with no evidence of significant heterogeneity (P=0.49, I(2)=0). CONCLUSIONS: Higher consumption of CV, but not citrus fruits, is associated with a significantly decreased risk of type 2 diabetes. Further large prospective studies are needed to elucidate both relationships.


Assuntos
Brassicaceae , Citrus , Diabetes Mellitus Tipo 2/epidemiologia , Diabetes Mellitus Tipo 2/prevenção & controle , Frutas , Verduras , Diabetes Mellitus Tipo 2/diagnóstico , Humanos , Incidência , Razão de Chances , Prognóstico , Estudos Prospectivos , Fatores de Proteção , Recomendações Nutricionais , Medição de Risco , Fatores de Risco , Fatores de Tempo
10.
Mol Neurobiol ; 53(4): 2679-84, 2016 May.
Artigo em Inglês | MEDLINE | ID: mdl-26154489

RESUMO

Sex steroids can positively affect the brain function, and low levels of sex steroids may be associated with worse cognitive function in the elderly men. However, previous studies reported contrary findings on the relationship between testosterone level and risk of Alzheimer's disease in the elderly men. The objective of this study was to comprehensively assess the relationship between low testosterone level and Alzheimer's disease risk in the elderly men using a meta-analysis. Only prospective cohort studies assessing the influence of low testosterone level on Alzheimer's disease risk in elderly men were considered eligible. Relative risks (RRs) with 95% confidence intervals (95% CI) were pooled to assess the risk of Alzheimer's disease in elderly men with low testosterone level. Seven prospective cohort studies with a total of 5251 elderly men and 240 cases of Alzheimer's disease were included into the meta-analysis. There was moderate degree of heterogeneity among those included studies (I(2) = 47.2%). Meta-analysis using random effect model showed that low plasma testosterone level was significantly associated with an increased risk of Alzheimer's disease in elderly men (random RR = 1.48, 95% CI 1.12-1.96, P = 0.006). Sensitivity analysis by omitting one study by turns showed that there was no obvious change in the pooled risk estimates, and all pooled RRs were statistically significant. This meta-analysis supports that low plasma testosterone level is significantly associated with increased risk of Alzheimer's disease in the elderly men. Low testosterone level is a risk factor of worse cognitive function in the elderly men.


Assuntos
Doença de Alzheimer/sangue , Testosterona/sangue , Idoso , Humanos , Masculino , Viés de Publicação , Fatores de Risco
11.
Lipids Health Dis ; 14: 22, 2015 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-25889773

RESUMO

BACKGROUND: Low serum cholesterol levels are related to an increased risk of depression and its serious consequences. However, the effect of central cholesterol on depressive disorder and its potential regulatory mechanism is poorly understood. Therefore, brain cholesterol in patients with depression may not only decrease the risk for developing this disease but also increase the beneficial effects of treatment for depression. METHODS: In current study, rats were exposed to chronic mild stress (CMS) for consecutive 28 days, and the depressive-like behavior was tested by sucrose preference test, immobility in the forced swim test, locomotor activity in the open field test, decreased bodyweight and food intake. Additionally, the total cholesterol levels in the medial prefrontal cortex (mPFC) and the hippocampus of rats were measured by gas chromatograph mass spectrometer. Finally, 5-HT1A receptor antagonist WAY100635 was used to determine the potential role of serotonin system in the interaction between central cholesterol and depression. RESULTS: CMS significantly reduced total cholesterol levels in the mPFC but not in the hippocampus and resulted in depressive-like behavior. Chronic supplementation of cholesterol by food reversed the depressive-like behavior induced by CMS. Furthermore, pre-injection of 5-HT1A receptor antagonist WAY100635 into the mPFC blocked the treatment effects of cholesterol on the reversal of behavioral response. CONCLUSION: This finding suggested that cholesterol in the mPFC may have an impact on the sensitivity of the 5-HT1A receptor in the development and treatment of depression. The treatment benefits of cholesterol could be through modulation of the brain 5-HT1A receptor.


Assuntos
Colesterol/análise , Depressão/metabolismo , Hipocampo/química , Córtex Pré-Frontal/química , Receptor 5-HT1A de Serotonina/fisiologia , Animais , Modelos Animais de Doenças , Cromatografia Gasosa-Espectrometria de Massas , Masculino , Piperazinas/farmacologia , Piridinas/farmacologia , Ratos , Ratos Sprague-Dawley , Antagonistas do Receptor 5-HT1 de Serotonina/farmacologia , Estresse Psicológico/complicações
12.
J Comput Chem ; 32(6): 987-97, 2011 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-20949511

RESUMO

The mechanisms and kinetics studies of the OH radical with alkyl hydroperoxides CH(3)OOH and CH(3)CH(2)OOH reactions have been carried out theoretically. The geometries and frequencies of all the stationary points are calculated at the UBHandHLYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies method at the MC-QCISD level of theory. For two reactions, five H-abstraction channels are found and five products (CH(3)OO, CH(2)OOH, CH(3)CH(2)OO, CH(2)CH(2)OOH, and CH(3)CHOOH) are produced during the above processes. The rate constants for the CH(3)OOH/CH(3)CH(2)OOH + OH reactions are corrected by canonical variational transition state theory within 250-1500 K, and the small-curvature tunneling is included. The total rate constants are evaluated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental data. The Arrhenius expressions for the reactions are obtained.


Assuntos
Peróxido de Hidrogênio/química , Radical Hidroxila/química , Teoria Quântica , Cinética
13.
J Phys Chem A ; 114(34): 9057-68, 2010 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-20669929

RESUMO

The mechanisms and dynamics studies of the multichannel reactions of CH(2)FCF(2)OCHF(2) + OH (R1) and CH(2)FOCH(2)F + OH (R2) have been carried out theoretically. Three hydrogen abstraction channels and two displacement processes are found for reaction R1, whereas there are two hydrogen abstraction channels and one displacement process for reaction R2. The minimum energy paths are optimized at the B3LYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies (ISPE) method at the BMC-QCISD level of theory. By means of canonical variational transition state theory with small-curvature tunneling correction, the rate constants of reactions R1 and R2 are obtained over the temperature range of 220-2000 K. The rate constants are in good agreement with the experimental data for reaction R1 and estimated data for reaction R2. The Arrhenius expression k(1) = 1.62 x 10(-20) T(2.75) exp(-1011/T) for reaction R1 and k(2) = 3.40 x 10(-21) T(3.04) exp(-384/T) for reaction R2 over 220-2000 K are obtained. Furthermore, to further reveal the thermodynamics properties, the enthalpies of formation of reactants CH(2)FCF(2)OCHF(2), CH(2)FOCH(2)F, and the product radicals CHFCF(2)OCHF(2), CH(2)FCF(2)OCF(2), and CHFOCH(2)F are calculated by using isodesmic reactions.

14.
Phys Chem Chem Phys ; 12(36): 10846-56, 2010 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-20657941

RESUMO

Singlet and triplet potential energy surfaces for the reactions of oxygen atoms ((3)P and (1)D) with CF(3)CN have been studied computationally to evaluate the reaction mechanisms, possible products, and rate constants. On the triplet surface, six kinds of pathway are revealed, namely: direct fluorine abstraction, C-addition/elimination, N-addition/elimination, substitution, insertion and F-migration. The results show that the reaction should occur mainly through the C-addition/elimination mechanism involving the chemically activated CF(3)C(O)N* intermediate, and the major products are CF(3) and NCO. The rate constants for C-addition/elimination channel of the reaction of O((3)P) with CF(3)CN have been determined by using RRKM statistical rate theory and compared with the experimental data. On the singlet surface, the atomic oxygen can easily insert into the C-F or C-C bond of CF(3)CN, forming the insertion intermediates FOCF(2)CN and CF(3)OCN, and O((1)D) can add to the carbon or nitrogen atom of the CN group in CF(3)CN, forming the addition intermediates CF(3)C(O)N and CF(3)CNO; both approaches are found to be barrierless. The decomposition and isomerization of some intermediates were also modeled at the QCISD(T)/6-311+G(2df)//B3LYP/6-311+G(d) level for the better understanding of the O((1)D) with CF(3)CN chemistry. The decomposition products CF(3) and NCO arising from CF(3)OCN and CF(3)NCO are the dominant species. Further comparison with similar reactions is also summarized.

15.
J Comput Chem ; 31(12): 2263-72, 2010 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-20575010

RESUMO

The dual-level direct kinetics method has been used to investigate the multichannel reactions of C(2)H(5)I + Cl. Three hydrogen abstraction channels and one displacement process are found for the title reaction. The calculation indicates that the hydrogen abstraction from -CH(2)- group is the dominant reaction channel, and the displacement process may be negligible because of the high barrier. The rate constants for individual reaction channels are calculated by the improved canonical variational transition-state theory with small-curvature tunneling correction over the temperature range of 220-1500 K. Our results show that the tunneling correction plays an important role in the rate constant calculation in the low-temperature range. Agreement between the calculated and experimental data available is good. The Arrhenius expression k(T) = 2.33 x 10(-16) T(1.83) exp(-185.01/T) over a wide temperature range is obtained. Furthermore, the kinetic isotope effects for the reaction C(2)H(5)I + Cl are estimated so as to provide theoretical estimation for future laboratory investigation.

16.
J Chem Phys ; 132(6): 064301, 2010 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-20151737

RESUMO

The low-lying triplet and singlet potential energy surfaces of the O((3)P)+CH(3)CN reaction have been studied at the G3(MP2)//B3LYP/6-311+G(d,p) level. On the triplet surface, six kinds of pathways are revealed, namely, direct hydrogen abstraction, C-addition/elimination, N-addition/elimination, substitution, insertion, and H-migration. Multichannel Rice-Ramsperger-Kassel-Marcus theory and transition-state theory are employed to calculate the overall and individual rate constants over a wide range of temperatures and pressures. It is predicted that the direct hydrogen abstraction and C-addition/elimination on triplet potential energy surface are dominant pathways. Major predicted end products include CH(3)+NCO and CH(2)CN+OH. At atmospheric pressure with Ar and N(2) as bath gases, CH(3)C(O)N (IM1) formed by collisional stabilization is dominated at T<700 K, whereas CH(3) and NCO produced by C-addition/elimination pathway are the major products at the temperatures between 800 and 1500 K; the direct hydrogen abstraction leading to CH(2)CN+OH plays an important role at higher temperatures in hydrocarbon combustion chemistry and flames, with estimated contribution of 64% at 2000 K. Furthermore, the calculated rate constants are in good agreement with available experimental data over the temperature range 300-600 K. The kinetic isotope effect has also been calculated for the triplet O((3)P)+CH(3)CN reaction. On the singlet surface, the atomic oxygen can easily insert into C-H or C-C bonds of CH(3)CN, forming the insertion intermediates s-IM8(HOCH(2)CN) and s-IM5(CH(3)OCN) or add to the carbon atom of CN group in CH(3)CN, forming the addition intermediate s-IM1(CH(3)C(O)N); both approaches were found to be barrierless. It is indicated that the singlet reaction exhibits a marked difference from the triplet reaction. This calculation is useful to simulate experimental investigations of the O((3)P)+CH(3)CN reaction in the singlet state surface.

17.
J Phys Chem A ; 114(10): 3516-22, 2010 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-20175584

RESUMO

Both singlet and triplet potential energy surfaces for the reaction of ground-state formaldehyde (CH(2)O) and ozone (O(3)) are theoretically investigated at the BMC-CCSD//BHandHLYP/6-311+G(d,p) level. Various possible isomerization and dissociation pathways are probed. Hydrogen abstraction, oxygen abstraction, and C-addition/elimination are found on both the singlet and the triplet surfaces. The major products for the total reaction are HCO and HOOO, which are generated via hydrogen abstraction. The transition state theory (TST) and multichannel RRKM calculations have been carried out for the total and individual rate constants for determinant channels over a wide range of temperatures and pressures.

18.
J Comput Chem ; 31(6): 1126-34, 2010 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-19862810

RESUMO

The reaction of H radical with C(2)H(5)CN has been studied using various quantum chemistry methods. The geometries were optimized at the B3LYP/6-311+G(d,p) and B3LYP/6-311++G(2d,2p) levels. The single-point energies were calculated using G3 and BMC-CCSD methods based on B3LYP/6-311++G(2d,2p) geometries. Four mechanisms were investigated, namely, hydrogen abstraction, C-addition/elimination, N-addition/elimination and substitution. The kinetics of this reaction were studied using the transition state theory and multichannel Rice-Ramsperger-Kassel-Marcus methodologies over a wide temperature range of 200-3000 K. The calculated results indicate that C-addition/elimination channel is the most feasible over the whole temperature range. The deactivation of initial adduct C(2)H(5)CHN is dominant at lower temperature with bath gas H(2) of 760 Torr; whereas C(2)H(5)+HCN is the dominant product at higher temperature. Our calculated rate constants are in good agreement with the available experimental data.

19.
J Comput Chem ; 31(7): 1520-7, 2010 May.
Artigo em Inglês | MEDLINE | ID: mdl-19890969

RESUMO

The reaction of N(2)H(4) with OH has been investigated by quantum chemical methods. The results show that hydrogen abstraction mechanism is more feasible than substitution mechanism thermodynamically. The calculated rate constants agree with the available experimental data. The calculated results show that the variational effect is small at lower temperature region, while it becomes significant at higher temperature region. On the other hand, the small-curvature tunneling effect may play an important role in the temperature range 220-3000 K. Moreover, the calculated rate constants show negative temperature dependence at the temperatures below 500 K, which is in accordance with Vaghjiani's report that slightly negative temperature dependence is found over the temperature range of 258-637 K. The mechanism of the major product (N(2)H(3)) with OH has also been investigated theoretically to understand the title reaction thoroughly.

20.
J Phys Chem A ; 114(1): 417-24, 2010 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-19950919

RESUMO

A dual-level direct dynamic method is employed to study the reaction mechanisms of CF(3)CHFOCF(3) (HFE-227 mc) with the OH radical and Cl atom. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the BH&H-LYP/6-311G(d,p) level, and the energetic information along the MEPs is further refined by MC-QCISD theory. The classical energy profile is corrected by the interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunneling effect (SCT) calculated by the variational transition state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k(1) = 2.87 x 10(-21)T(2.80) exp(-1328.60/T) and k(2) = 3.26 x 10(-16)T(1.65) exp(-4642.76/T) cm(3) molecule(-1) s(-1) over the temperature range 220-2000 K. The standard enthalpies of formation for the reactant CF(3)CHFOCF(3) and product radical CF(3)CFOCF(3) are evaluated via group-balanced isodesmic reactions, and the corresponding values are -454.06 +/- 0.2 and -402.74 +/- 0.2 kcal/mol, respectively, evaluated by MC-QCISD theory based on the BH&H-LYP/6-311G(d, p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of formation of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFE-227 mc.

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