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| Registros recuperados: 83 | |
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| Sierra Rayne; Kaya Forest. |
| Perfluoroalkyl carboxylates are contaminants whose environmental fate and toxicological effects are of broad interest within the academic, industrial, and governmental science and regulatory communities. In addition, coupled perfluoroalkyl and carboxylate moieties are often used in medicinal chemistry as part of the drug design process. However, to date there has been a notable absence of reliable acidity constant estimation programs for these compounds. Here we report that the ADME/Tox WEB method for in silico pKa value predictions is more accurate than the PM6, SPARC, and COSMOtherm methods for the longer chain perfluoroalkyl carboxylic acids, suggesting this may be a good general acidity constant estimation approach for these compounds. |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Pharmacology; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/2936/version/1 |
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| Sierra Rayne; Kaya Forest; Ken J. Friesen. |
| A statistical analysis was conducted on long-term climate records in the Okanagan Valley wine grape growing region of British Columbia, Canada. No observable trends for average annual temperatures were found in the region. Analyses of monthly mean and extreme temperatures show wide spatial and temporal heterogeneity, indicating that future studies using downscaling of global climate models for this region will require resolutions on the order of several kilometers. Mean winter temperatures are increasing throughout the valley, and extreme minimum temperatures are also increasing during the winter at the central and northern sites which have historically presented the most risk of winter damage to grapevines. Only the most southern and northern sub-regions... |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/3162/version/2 |
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| Sierra Rayne; Kaya Forest. |
| The large number of historical and current organic chemicals in commerce, and the ability of these compounds to make their way from industrial to remote regions, has resulted in concerted efforts to predict which chemicals have the capacity to migrate from where they are used/disposed to areas such as the Arctic. A suite of 120 high production volume chemicals has been recently screened from an initial dataset of >100,000 compounds and listed as potential Arctic contaminants. In the current work, we critically assess members of this proposed list for their possible rapid reactivity in environmental systems that would prevent substantial accumulation or transport in the environment and accumulation in vivo, as well as whether the investigated... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/4436/version/1 |
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| Sierra Rayne; Kaya Forest. |
| The SPARC software program was benchmarked for calculating the solubilities of two representative polyaromatic hydrocarbons (PAHs), naphthalene and anthracene, in a range of organic solvents at various temperatures. Although SPARC was able to reasonably approximate the solubilities of naphthalene in some organic solvents, gross errors were obtained for other solvents. For anthracene, poor prediction performance was observed in all solvents considered. Overall, the results suggest that SPARC is currently not suitable for accurately predicting the solubilities of representative PAHs relevant for the petroleum sector in various organic solvents. |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6648/version/1 |
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| Sierra Rayne; Kaya Forest. |
| The gas phase standard state (298.15 K, 1 atm) isomerization enthalpy prediction performance of the major semiempirical, ab initio, and density functional levels of theory was investigated using the linear to branched heptanes. The M062X density functional, MP2 (and higher) levels of Moller-Plesset perturbation theory, and the CBS and Gaussian-n composite methods are best suited for thermodynamic studies of alkane derivative isomerizations expected during the processing of petroleum, biomass, coal, or other fuels. Where large molecular systems prohibit the use of higher levels of theory, the PM6 and PDDG semiempirical methods may offer an appropriate computational cost-accuracy compromise. Non-M062X density functionals are not recommended for theoretical... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/4865/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Well-to-well (WWE~S-T~) and adiabatic (AE~S-T~) singlet-triplet excitation energies were calculated at the Gaussian-4 (G4) and W1BD levels of theory for a suite of mono- and disubstituted R~1~R~2~Si=Si silylene derivatives (where R~1~/R~2~=H, CH~3~, NH~2~, OH, and F), as well as H~2~C=Si and HN=Si. Reasonable agreement was obtained with prior E~S-T~ estimates at the CCSD(T)/6-311++G(d,p)//QCISD/6-31G(d) and B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G(d) levels of theory. The G4/W1BD E~S-T~ are systematically higher than these prior estimates by between 1 to 5 kcal/mol, averaging positive deviations of about 1-2 and 3-4 kcal/mol from the CCSD(T) and B3LYP estimates, respectively. Qualitative ground state multiplicity agreement between the four levels of theory was... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6465/version/1 |
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| Sierra Rayne. |
| Modes of carcinogenicity for the well-known environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have been investigated over the past several decades. However, the mechanisms underlying TCDD carcinogenicity are still unclear. Recent work also suggests TCDD may have anti-cancer activity. Based on established photochemical generation of reactive 2,2'-biphenylquinone intermediates from dioxins, a novel toxicological mechanism for TCDD that may be operative is proposed. 2,2'-Biphenylquinones may be obtained via biochemical activation of dioxins such as TCDD, and these intermediates may play a role in expressing both the carcinogenic and anti-cancer activities of this important contaminant class. The broader research community... |
| Tipo: Manuscript |
Palavras-chave: Cancer; Chemistry. |
| Ano: 2008 |
URL: http://precedings.nature.com/documents/1929/version/1 |
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| Sierra Rayne; Kaya Forest; Ken J. Friesen. |
| Perfluorinated acids (PFAs) are contaminants detected worldwide in a range of abiotic and biotic environmental matrices. The two major classes of PFAs include the perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonic acids (PFSAs), both of which are considered persistent and potentially bioaccumulative. Current research and regulatory efforts are focussed on the straight-chain members of each PFA class and homologue group, primarily because these congeners are the major components of technical mixtures and are also available as pure standards. However, the numerous potential branched congeners in each PFA class represent a poorly understood family of environmental contaminants whose environmental and toxicological properties may be more... |
| Tipo: Poster |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2008 |
URL: http://precedings.nature.com/documents/1956/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Potential historical temporal trends in the overwinter and spring snowpack were investigated for the Canadian portions of the Okanagan and Similkameen Valleys in south-central British Columbia. Significant evidence is available that the Okanagan and Similkameen River watersheds are exhibiting both spatially and temporally heterogeneous declines in snowpacks over the past several decades, but whether the causes are part of a natural cycle or result from longer term climatic changes is not clear. The variability in the magnitude, timing, and location of any significant time trends in snowpack decline also precludes efforts towards developing reliable hydrologic models that reflect a response to potential future changes in snowpack patterns for these regions... |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6590/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Aroma compounds in the Flavornet database were screened for ionizable functional groups such as carboxylic acids, aliphatic and aromatic amines, phenols, alcohols, and thiols. Of the 738 aroma compounds listed in this database, 101 molecules have ionizable moieties with estimated monomeric aqueous pK~a~ values ranging between 1.75 and 10.97. pH dependent effective air/water partitioning coefficients (K~aw,eff~) and n-octanol/water partitioning coefficients (D~ow~) were estimated for all ionizable aroma compounds over the pH range from 0 to 14. The ionizable aroma compounds display a broad range of K~aw,eff~ (1.8×10^-23^ to 6.1 atm M^-1^) and log D~ow~ (-6.2 to +7.2 units) values. For many aroma compounds, pH dependent ionization will have a... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6269/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Gas phase standard state (298.15 K, 1 atm) geometries of the perchlorinated and perbrominated C~3~ through C~6~ n-alkanes were calculated using the B3LYP, B97D, M062X, and PBE0 density functionals with the 6-311++G(d,p) basis set. For both halogen classes and at all levels of theory, the C~3~ compounds adopt a trans conformation analogous to that of perfluoropropane. Similar to their perfluorinated counterparts, the perchlorinated and perbrominated C~4~ through C~6~ n-alkanes are predicted to have helical geometries. In contrast to perfluoroalkyl chains, the central CCCC dihedral angles of the perchlorinated and perbrominated derivatives are expected to decline with increasing chain length. |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5157/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Gas phase (298.15 K, 1 atm) enthalpies of formation (Δ~f~H°~(g)~), enthalpies of disproportionation to two corresponding acetylene molecules (Δ~rxn~H°~(g),Td→acet~), and enthalpies of isomerization from a tetrahedrane geometry to a 1,3-cyclobutadiene structure (Δ~isom~H°~(g),Td→CBD~) were calculated for the mono- through tetra-substituted hydro, fluoro, chloro, bromo, methyl, ethynyl, and cyano carbon tetrahedrane derivatives at the G4MP2 and G4 levels of theory. All derivatives have endothermic Δ~f~H°~(g)~ indicative of the cage strain in these systems. In all cases, Δ~rxn~H°~(g),Td→acet~ and... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6421/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Saskatchewan, Canada, with a total land area of 651,900 km^2^, is one of the world’s most productive agricultural regions. A broad variety of livestock are raised in the province, including cattle, pigs, poultry, sheep/goats, llama, ostrich, elk, deer, and bison. In 2010, the total revenue from the Saskatchewan livestock sector was CAD$1.6 billion. Over the past century, changing industry economics and advances in scientific, technical, and engineering knowledge and practices have affected the amount and type of livestock produced. The current work examines time trends for livestock production since Saskatchewan was created in 1905. While production trends vary widely by livestock type, most sectors display clearly increasing amounts of industry... |
| Tipo: Poster |
Palavras-chave: Earth & Environment. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6714/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Gas phase calculations at 1 atmosphere pressure between 300 and 1500 K at 200 K intervals were conducted using the Gaussian-4 (G4) composite method level of theory on a representative set of reactions having broad relevance in hydrocarbon combustion chemistry. Reasonable agreement between the experimental and theoretical data was obtained across the temperature range under consideration for all bond dissociation enthalpies, isomerization enthalpies, and enthalpies of reaction. For some reaction schemes, chemical accuracy for the theoretical method was maintained over the complete temperature range, whereas other systems displayed up to several kcal mol^-1^ deviations from experimental data. The direction of signed errors generally increased as the... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5021/version/2 |
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| Sierra Rayne; Kaya Forest. |
| Gas phase standard state (298.15 K, 1 atm) calculations were conducted at the Gaussian-4 (G4) composite method level of theory to estimate the bond dissociation enthalpies (BDEs) of various common laboratory solvents. Excellent agreement was obtained between experimental and G4 estimated BDEs. The current study demonstrates the BDE prediction accuracy of the G4 method, and is also intended to function as a potentially useful resource in any reevaluations of the preferred BDEs for these common laboratory solvents. |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/4425/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Gas phase standard state (298.15 K, 1 atm) isomerization energies were calculated using the M062X functional with the QZVP, 6-311++G(d,p), 6-311++G(2d,2p), and cc-pVTZ basis sets against the 24 reactions in the ISOL set of benchmark isomerization energies for large organic molecules. The M062X functional appears to offer comparable isomerization energy prediction performance to the best performing currently available dispersion corrected functionals against this benchmark dataset. |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5183/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Computational studies were conducted using the major levels of semiempirical, ab initio, density functional theory (DFT), and the CBS-Q//B3 method and various solvation models on a homologous series of straight chain perfluoroalkyl carboxylic acids (PFCAs) ranging in chain length from C~1~ (trifluoroacetic acid) to C~9~ (n-perfluorodecanoic acid) as well as the monomethyl branched C~7~ (n-perfluorooctanoic acid; n-PFOA) isomers. Regardless of perfluoroalkyl chain length and theoretical method employed, application of a computational thermodynamic cycle indicated no significant change in the estimated aqueous monomeric pK~a~ values between C~1~ and C~9~, all having a relatively constant pK~a~ of about 0 that is in agreement with earlier predictions and... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/3829/version/2 |
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| Sierra Rayne; Kaya Forest. |
| The SPARC software program was used to estimate the acid-catalyzed, neutral, and base-catalyzed hydrolysis rate constants for the polymeric brominated flame retardants BC-58 and FR-1025, as well as the hydrolyzable daughter products of BC-58. Relatively rapid hydrolysis of BC-58, producing 2,4,6-tribromophenol and tetrabromobisphenol A as the hydrolytically stable end products from all potential hydrolysis reactions, is expected in both environmental and biological systems with starting material hydrolytic half lives (t~1/2,hydr~) ranging from less than one hour in marine systems, several hours in cellular environments, and up to several weeks in slightly acid fresh waters. Hydrolysis of FR-1025 to give 2,3,4,5,6-pentabromobenzyl alcohol is expected to be... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/4160/version/1 |
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| Sierra Rayne; Kaya Forest; Ken J. Friesen. |
| We introduce a congener-specific numbering system for the C4 through C8 perfluorinated homologue groups of alkyl sulfonates, carboxylates, telomer alcohols and acids, and their derivatives. Increasing length of the carbon chain beyond C3 leads to a corresponding rapid increase in the number of potential isomers (C4 =4, C5 =8, C6 =17, C7 =39, and C8 =89 congeners). There is a need for clear and unambiguous chemical shorthand to ensure accuracy and consistency in the future perfluorinated alkyl substance (PFA) literature, and to correct previous misconceptions that may have restricted research efforts into developing full-congener PFA analysis. If adopted by the research community, introduction of a numbering system at this relatively early stage of... |
| Tipo: Poster |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2008 |
URL: http://precedings.nature.com/documents/1957/version/2 |
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| Registros recuperados: 83 | |
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