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Enoch E. Dames 《国际化学动力学杂志》2014,46(3):176-188
The unimolecular decomposition of two radical isomers of C2H5O (CH3CH2O/ethoxy, CH3CHOH/α‐hydroxyethyl) are investigated by means of Rice–Ramsperger–Kassel–Marcus/master equation simulations in helium and nitrogen bath gases on an accurate one‐dimensional potential energy surface. For ethoxy, simulations are carried out between temperatures of 406 and 1200 K and pressures of 0.001 and 100 atm. For CH3CHOH, simulations are carried out between temperatures of 800 and 1500 K and pressures of 0.001 and 100 atm. Results are compared with available experimental data, with good agreement. The dominant product of α‐hydroxyethyl decomposition is CH3CHO + H, with C2H3OH + H and CH3 + CH2O, being minor channels. Rate coefficients are strongly dependent on temperature and pressure and are recommended with attendant uncertainty factor estimates. The relative roles of vinyl alcohol and acetaldehyde in the context of combustion chemistry are also discussed. 相似文献
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This study outlines how results from a glutathione reactivity assay (so-called in chemico data) can be used to define the applicability domain for the nucleophilic aromatic substitution (SNAr) reaction for nitrogen-containing aromatic compounds. SNAr is one of the six mechanistic domains that have been shown to be important in toxicological endpoints in which the ability to bind covalently to a protein is a key molecular initiating event. This study has analysed experimental data (2 h RC50 values), allowing a clear and interpretable structure–activity relationship to be developed for pyridines and pyrimidines which reside within the SNAr domain. The in-ring nitrogen(s) act as activating groups in the SNAr reaction. The position(s) of the in-ring nitrogen(s) as well as other activating groups, especially in relationship to the leaving group, affect reactive potency. The experimentally defined applicability domain has resulted in a series of structural alerts. These results build on early work on the benzene derivatives residing in the SNAr domain. The definition of the applicability domain for the SNAr reaction and the resulting structural alerts are likely to be beneficial in the development of computational tools for category formation and read-across in hazard identification, and the development of adverse outcome pathways. 相似文献
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Skin sensitisation is a key endpoint under REACH as it is costly and its assessment currently has a high dependency on animal testing. In order to reduce both the cost and the numbers of animals tested, it is likely that (quantitative) structure–activity relationships ((Q)SAR) and read-across methods will be utilised as part of intelligent testing strategies. The majority of skin sensitisers elicit their effect via covalent bond formation with skin proteins. These reactions have been understood in terms of well defined nucleophilic–electrophilic reaction chemistry. Thus, a first step in (Q)SAR analysis is the assignment of a chemical's potential mechanism of action enabling it to be placed in an appropriate reactivity domain. The aim of this study was to design a series of SMARTS patterns capable of defining these reactivity domains. This was carried out using a large database of local lymph node assay (LLNA) results that had had potential mechanisms of action assigned to them using expert knowledge. A simple algorithm was written enabling the SMARTS patterns to be used to screen a database of SMILES strings. The SMARTS patterns were then evaluated using a second, smaller, test set of LLNA results which had also had potential mechanisms of action assigned by experts. The results showed that the SMARTS patterns provided an excellent method of identifying potential electrophilic mechanisms. The findings are supported, in part, by molecular orbital calculations which confirm assignment of reactive mechanism of action. The ability to define a chemical's potential reaction mechanism is likely to be of significant benefit to regulators and risk assessors as it enables category formation and subsequent read-across to be performed. 相似文献
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RITVA LINDBERG GORAN SUNDHOLM JOHAN SJö BLOM PETRI AHONEN ESKO I. KAUPPINEN 《Journal of Dispersion Science and Technology》2013,34(1-2):715-722
The zeta-potentials of silica, copper, platinum and gold particles have been measured as a function of pH. The isoelectric points were found to be at pH 3.0, 5.8, 3.0 and 3.5, respectively. In the pH range 3.0 to 5.8 copper and silica particles are oppositely charged and accordingly the coating of silica with copper particles could be demonstrated. In the case of gold and platinum the sign of the charge is such that direct adhesion to silica particles cannot be expected and this was also demonstrated in the case of platinum. 相似文献
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The Effect of Alcohol and Carbonyl Functional Groups on the Competition between Unimolecular Decomposition and Isomerization in C4 and C5 Alkoxy Radicals
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Presented here are computed rates for the thermal unimolecular decomposition of a variety of alkoxy radicals with four‐ and five‐carbon length backbones. Three classes of molecules are examined: alkoxy radicals with saturated hydrocarbon backbones, those with alcohol functional groups, and those with carbonyl functional groups. The chosen species represent many of those found during the combustion of fossil fuels as well as bio‐derived alternatives. Density functional theory calculations were benchmarked against higher level coupled cluster calculations and used to explore the potential energy surfaces of these systems. Transition state theory was used to calculate high‐pressure limit rate coefficients of all radical intermediates in the regimes relevant to atmospheric chemistry and combustion. We show that the assumption that alkoxy radicals quickly decompose via β‐scission to aldehydes and other radicals is not valid for some of the alkoxy radicals investigated in this work. We further illustrate how intra‐H migrations in larger alkoxy radicals with carbonyl and alcohol functional groups can dominate unimolecular decomposition under combustion and atmospheric relevant conditions. Finally, we discuss why carbonyl groups can increase or decrease intra‐H migration barriers depending on their location relative to the transferring H‐atom. 相似文献
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We show that extraordinary light transmission of periodic subwavelength hole arrays, generally attributed to surface-plasmon resonances, is strongly influenced by the hole shape. Both experiments and calculations, based on a Fourier modal method, demonstrate that a shape change from circular to rectangular increases the normalized transmission by an order of magnitude while the hole area decreases. Moreover, the spectra exhibit large redshifts (approximately 2500 cm(-1)). A comparison with the transmission of isolated holes shows that shape resonances of the rectangular holes play a dominant role. 相似文献
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van Enk SJ 《Physical review letters》2000,84(4):789; author reply 790