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| Registros recuperados: 68 | |
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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. |
| 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. |
| 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. |
| 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; Kaya Forest. |
| Gas phase standard state (298.15 K, 1 atm) structures, enthalpies of formation, and ionization energies (IEs) were calculated at the G4MP2 composite method level of theory for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives. Increasing nitrogen content increases the enthalpies of formation for the carbon-nitrogen, nitrogen-phosphorus, and silicon-nitrogen binary cubanes, with the opposite enthalpies of formation trend for increasing phosphorus content within the carbon-phosphorus, nitrogen-phosphorus, and silicon-phosphorus derivatives. Varying carbon/silicon content in the carbon-silicon cubanes results in no general trends for enthalpies of formation. Isomerization enthalpies within the homolog groups having more... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5154/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Adiabatic ionization energy (AIE) calculations were performed at the AM1, PM3, PM6, PDDG, HF/QZVP, and B3LYP/QZVP levels of theory on 722 atmospherically relevant organic compounds with available experimental rate constants for atmospheric reactions with hydroxyl radicals (k~OH~). From the starting set of molecules, a final suite of 114 mono- and polyfunctionalized compounds provided converged neutral and cationic geometries without imaginary frequencies for all six levels of theory. NIST evaluated AIEs were available for 54 compounds, providing mean absolute AIE prediction errors of 0.31 (AM1), 0.28 (PM3), 0.50 (PM6), 0.36 (PDDG), 1.22 (HF/QZVP), and 0.20 eV (B3LYP/QZVP). Modest correlations were found between the experimental (r=-0.68, SE=0.81) and... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5447/version/1 |
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| Sierra Rayne; Kaya Forest. |
| SPARC, KOWWIN, and ALOGPS octanol-water partitioning (log K~ow~) and distribution (log D) constants were calculated for all C~1~ through C~8~ and the straight chain C~9~ through C~15~ perfluoroalkyl sulfonic acids (PFSAs) and carboxylic acids (PFCAs). Application of five established models for estimating bioconcentration factors (BCFs) were applied to the PFSA and PFCA log K~ow~ and log D data and compared to available field and laboratory BCF data. Wide variability was observed between the methods for estimating log K~ow~ and log D values, ranging up to several log units for particular congeners, and which was further compounded by additional variability introduced by the different BCF equations applied. With the exception of n-perfluorooctanecarboxylic... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3256/version/1 |
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| Sierra Rayne; Kaya Forest. |
| The gas and solution phase relative thermodynamic stabilities of the 39 linear and branched perfluorooctanoic acid (PFOA) congeners in both their acid and anionic forms were calculated at various levels of density functional (B3LYP, wB97XD, and M062X functionals with the 6-311++G(d,p) basis set) and second order Moller-Plesset perturbation (MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p)) theory using the SMD implicit solvation model. The B3LYP functional does not accurately model the expected trends in thermodynamic stability of PFOA isomers with linear versus branched perfluoroalkyl chains. Calculations obtained with the M062X and MP2 model chemistries suggest these theoretical methods may be more appropriate for relative thermodynamic stability studies on... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/5528/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Historical trends in streamflow and climate were investigated for the Coldwater River watershed in south-central British Columbia, Canada. Temporal increases in rainfall and total precipitation during the spring, summer, and autumn periods, as well as on an annual basis, at the city of Merritt near the mouth of the watershed, and year-round temperature increases at this site, compare with declining summertime and annual streamflows at the nearby Merritt hydrometric station on the Coldwater River. Declining summer flows at this site could reflect the dominance of temporally increasing evaporation that is offsetting increased precipitation over the same periods of the hydrologic year. Alternatively, increased water abstractions, altered regulation regimes,... |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2012 |
URL: http://precedings.nature.com/documents/6785/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/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/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. |
| Theoretical investigations were conducted on the gas phase all-anti zigzag geometries of C~3~ through C~7~ perfluoro-n-alkanes and the perfluoro-n-octanoate anion using various semiempirical, density functional theory, and composite method approaches. The major theoretical methods are in agreement that the gas phase zigzag geometry of >=C~3~ perfluoro-n-alkyl chains is a transition state between the left and right handed helical/twisted global minima. For the C~3~ perfluoropropyl group, a slightly twisted (about 1 to 2 degree central F-C-C-F dihedral angle) near zigzag conformation exists as a global minimum, whereas helical global minima are obtained for C~4~ and longer perfluoroalkyl chains. The left to right handed helix inversion activation... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5061/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Theoretical studies were conducted on the predicted gas and solution phase thermodynamic properties for isomerization of various [1.1]paracyclophane derivatives to their corresponding transannular[4+4] adducts at representative levels of density functional and composite method theory. Calculations suggest the [1.1]paracyclophane to transannular[4+4] adduct isomerizations are not likely amenable to thermodynamic solvent tuning for the methylene, ether, and thioether bridged derivatives using a broad range of nonpolar and polar aprotic and polar protic implicit solvation models, but may be receptive towards solvent tuning for the amine bridged analogs. Varying the nature of the cyclophanic bridging atoms and the electron withdrawing/releasing character of... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5332/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. |
| A molecular mechanics force field method (MMFF94) systematic rotor conformational search was conducted on the well known environmental contaminant n-perfluorooctanoic acid (n-PFOA). The MMFF94 conformational search yielded 2915 separate low- through high-energy conformers of n-PFOA. Ranking of these structures gave the 94 lowest MMFF94 energy conformations that were subjected to subsequent density functional theory (DFT) computational investigations at the B3LYP/6-311++G(d,p) level of theory. Application of a thermodynamic cycle approach, coupled with aqueous and gas phase DFT calculations on the molecular and anionic forms for each of the 94 lowest energy n-PFOA conformers, gave estimated acidity constants (pK~a~ values) for a final converged set of... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3837/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Organic carbon normalized soil and sediment-water partitioning coefficients (K~oc~) were estimated for all C~1~ through C~8~ perfluoroalkyl carboxylic (PFCA) and sulfonic (PFSA) acid congeners. The limited experimental K~oc~ dataset for the straight chain C~7~ through C~10~ PFCAs and C~8~ and C~10~ PFSAs was correlated to SPARC and ALOGPS computationally estimated octanol-water partitioning / distribution constants and used to predict K~oc~ values for both branched and linear C~1~ through C~8~ isomers. Branched and linear congeners in this homologue range are generally expected to have K~oc~ values >1, leading to their accumulation in organic matter on sediments and soils, retardation during ground and pore water flow, and the preferential... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3011/version/2 |
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| Sierra Rayne; Kaya Forest. |
| The Okanagan Basin in south-central British Columbia, Canada, includes the Okanagan River watershed upstream from the outlet of Osoyoos Lake, with a total area of 8,046 km^2^. Over the past century, the population of the Basin has grown rapidly, and this trend is expected to continue. Water management issues attract significant attention in the region, given projected declines in supply and increases in demand. Historical streamflow data was obtained for three hydrometric stations on the Okanagan River between the outlet of Okanagan Lake at Penticton and near the U.S. border at Oliver. Collectively, the historical data series indicate no temporal changes in regional annual water yields for the Okanagan Basin over the past century, despite large increases... |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/4946/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Singlet-triplet adiabatic (AE~S-T~) and well-to-well (WWE~S-T~) excitation energies of variously substituted phenyl cations were calculated at the G4 level of theory. The G4 E~S-T~ estimates range from 19 to 40 kJ/mol higher than prior density functional theory based predictions for these cations, and suggest that E~S-T~ and ground state multiplicity structure-property trends for phenyl cations previously proposed in the literature may be incorrect. Among the substituents considered, meta-substituted phenyl cations with electron donating groups have singlet ground states, and are not isoenergetic with the corresponding triplet states as previously claimed. Depending on the functional group, ortho- or para- substituted phenyl cations may also be ground... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6449/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Historical temporal trends in annual water yields were examined at 109 hydrometric monitoring stations in the Mackenzie, Saskatchewan-Nelson, Churchill, and Missouri-Mississippi River watersheds from the western Canadian provinces of Alberta, Saskatchewan, and northeastern British Columbia, as well as the Northwest Territories and the eastern portion of the Yukon territory. Effective drainage areas range in size from 325 to 1,680,000 (mean=65,600; median=9,300) km^2^, with associated hydrometric record lengths ranging between 18 and 97 (mean=41; median=38) years. Approximately three-quarters of the stations have no significant trend in average annual flow, with about equal numbers of stations exhibiting significant temporal increases or decreases in annual... |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5342/version/1 |
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| Registros recuperados: 68 | |
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