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| Registros recuperados: 68 | |
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| Sierra Rayne; Kaya Forest. |
| New experimental data is available in the literature regarding the octanol-water distribution behavior of representative straight chain perfluoroalkyl carboxylate (PFCA) and sulfonate (PFSA) congeners. The current study provides the first investigation into the predictive ability of various software programs for estimating the corresponding octanol-water partitioning (log P) and distribution (log D) constants of PFCAs and PFSAs. Wide predictive variation was found within and between the various methods. Several programs were able to accurately estimate the log P/D fragmental contributions of a -CF~2~- group for PFCAs, as well as the associated Gibbs free energies for partitioning into octanol from water due to the hydrophobic character of the... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3282/version/1 |
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| Sierra Rayne; Kaya Forest. |
| New experimental data is available in the literature regarding the octanol-water distribution behavior of representative straight chain perfluoroalkyl carboxylate (PFCA) and sulfonate (PFSA) congeners. The current study provides the first investigation into the predictive ability of various software programs for estimating the corresponding octanol-water partitioning (log P) and distribution (log D) constants of PFCAs and PFSAs. Wide predictive variation was found within and between the various methods. Several programs were able to accurately estimate the log P/D fragmental contributions of a -CF~2~- group for PFCAs, as well as the associated Gibbs free energies for partitioning into octanol from water due to the hydrophobic character of the... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3282/version/2 |
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| Sierra Rayne; Kaya Forest. |
| Gas phase enthalpies of formation at 298.15 and 1 atm (Δ~f~H~(g),298K~) were calculated using the atomization approach at the G4MP2 composite method level of theory for 86 polyaromatic hydrocarbons (PAHs) and other C~10~ through C~20~ unsaturated hydrocarbons. Where available, good agreement with prior experimental data and/or high level theoretical estimates was obtained. Linear regressions between semiempirical MNDO, MNDO-d, AM1, PM3, RM1, and PM6 estimated Δ~f~H~(g),298K~ and the corresponding G4MP2 values were employed to obtain G4MP2 corrected semiempirical Δ~f~H~(g),298K~ for a suite of 156 C~11~ through C~42~ unsaturated hydrocarbons and PAHs. |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6450/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Enthalpies of formation (Δ~f~H~(g)~) at 298.15 K and 0 K were calculated for various potential high energy materials (HEMs) using the high-level Gaussian-4 (G4) and W1BD methods with the atomization approach. Where prior high level estimates are available in the literature, the G4 and W1BD Δ~f~H~(g)~ are in good agreement. The results presented herein represent the highest level calculations performed to date on this suite of HEMs. These G4/W1BD enthalpies of formation should provide utility among the research community as a benchmark set of values against which to assess future experimental and/or theoretical data. |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6461/version/1 |
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| Sierra Rayne; Kaya Forest. |
| A hydrometric analysis over the available historical record (1973-2010) was conducted for the Moose Jaw River station near Burdick in south-central Saskatchewan, Canada. Frequency analyses on mean monthly, average annual, monthly minimum/maximum, and annual minimum flows generally yielded poor fits, and problems with negative flow predictions for mid- to long-term return periods regardless of distribution type. The annual maximum streamflow time series is reasonably well-described by linear and log Pearson Type III distributions, although both distribution types underestimate extreme maximum flows. Mann-Kendall linear time series analysis on mean monthly and annual streamflows reveals no trend in annual water yields, nor in mean monthly flows between March... |
| Tipo: Poster |
Palavras-chave: Earth & Environment. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6697/version/1 |
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| Sierra Rayne; Kaya Forest. |
| A long-term analysis of temporal trends and frequency analyses for temperatures (1913-2010), precipitation (1909-2010), and wind speed (1954-1996) was conducted on the Moose Jaw climate station in south-central Saskatchewan, Canada. Average annual and springtime temperatures are increasing over time, as are daily mean temperatures during March. Mean daily maximum temperatures are increasing on an annual basis and during the spring period, whereas mean daily minimum temperatures are increasing during February, March, August, and September, as well as on an annual basis and during spring and summer. There are significant positive time trends for growing degree days base 8C (GDD~8~) and 10C (GDD~10~). Rainfall has been increasing during March as well as... |
| Tipo: Poster |
Palavras-chave: Earth & Environment. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6703/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Potential historical temporal trends in monthly, seasonal, and annual mean, minimum, and maximum streamflows and date of the spring freshet runoff peak were investigated for the Okanagan and Similkameen Rivers in south-central British Columbia, Canada. There appears to be no compelling evidence that streamflow patterns in the Okanagan and Similkameen Rivers have changed over the available hydrometric record, nor does there appear to be evidence that future changes in streamflow patterns are imminent or likely. |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6584/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Gas to aqueous phase standard state (1 atm to 1 mol/L; 298.15 K) free energies of solvation ([DELTA]G^o^~solv~) were calculated for a range of neutral and ionic inorganic and organic compounds using various levels and combinations of Hartree-Fock and density functional theory (DFT) and composite methods (CBS-Q//B3, G4MP2, and G4) with the IEFPCM-UFF, CPCM, and SMD solvation models in Gaussian 09 (G09). For a subset of highly polar and generally polyfunctional neutral organic compounds previously identified as problematic for prior solvation models, we find significantly reduced [DELTA]G^o^~solv~ errors using the revised solvent models in G09. The use of composite methods for these compounds also substantially reduces their apparent [DELTA]G^o^~solv~... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/4864/version/1 |
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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. |
| 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. |
| Perfluoroalkyl aldehydes (PFAlds) and n:2 fluorotelomer aldehydes (FTAlds) are degradation products of precursor compounds that include fluorotelomer alcohols, iodides, acrylates, phosphate esters, and other derivatives, as well as hydrofluorocarbons and hydrochlorofluorocarbons. The SPARC software program and comparative density functional theory (DFT) calculations were used to investigate the aqueous phase hydration equilibrium constants (K~hyd~) of PFAlds and FTAlds. DFT studies suggest that all PFAlds will be dominantly present as the hydrated form in aqueous solution. While SPARC correctly estimates the K~hyd~ for the C~1~ PFAld, it appears to incorrectly predict a large decline in K~hyd~ (particularly between C~1~ and C~2~) with increasing... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/4520/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. |
| Gas phase standard state (298.15 K, 1 atmosphere) relative enthalpies and free energies of formation were calculated for all mono- through hepta-halogenated (X=F, Cl, Br) anthraquinone congeners using the B3LYP, BHandHLYP, M062X, PBE0, and B97D density functionals with the 6-311++G(d,p) basis set. All levels of theory yielded similar results with strong intra- and inter-method correlations for both the relative enthalpy and free energy values and the corresponding thermodynamic stability rank. Within each homolog group, the most thermodynamically stable isomers are those which maximize substitution at the lateral positions (2, 3, 7, and 8) versus the less stabilizing peri positions (1, 4, 6, and 9), while also minimizing destabilizing adjacent substitution... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5153/version/1 |
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| Sierra Rayne; Kaya Forest. |
| A systematic and comprehensive semiempirical, Hartree-Fock (HF) ab initio, and B3LYP density functional theory (DFT) study was conducted on the relative thermodynamic properties of various linear and branched perfluorinated and perhydrogenated alkyl compounds. The semiempirical AM1, PM3, and PM6 methods all consistently and accurately predict that branched alkyl compounds will generally be more thermodynamically stable than their linear counterparts. In contrast, HF and B3LYP calculations with the 6-31G(d,p), 6-31++G(d,p), and 6-311++G(d,p) basis sets predict that linear isomers will be more stable than branched analogs. These different linear versus branched perfluoroalkyl/perhydroalkyl thermodynamic property trends between semiempirical and ab initio/DFT... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3928/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Gas to solution phase Gibbs free energies of solvation at 298.15 K for transfer of six representative combustion flue gas compounds (N~2~, O~2~, CO~2~, H~2~O, SO~2~, and CO) were calculated at the Gaussian-4 (G4) level of theory using the IEFPCM-UFF, CPCM, and SMD implicit solvent models for 178 organic solvents. The IEFPCM-UFF and CPCM models yield similar free energies of solvation for all six compounds in each of the solvents considered, having maximum absolute intra-solvent deviations <1.6 kJ mol^-1^. Substantial free energy of solvation differences were observed between the IEFPCM-UFF/CPCM and SMD models, with maximum absolute intra-solvent deviations up to 45.5 kJ mol^-1^. The IEFPCM-UFF and CPCM models displayed strong free energy of... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5227/version/1 |
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| Sierra Rayne; Kaya Forest. |
| The gas and solution phase relative thermodynamic stabilities of the 89 perfluorooctane sulfonic acid (PFOS) congeners play an important role in assessing whether synthetic conditions for commercial mixtures are under thermodynamic or kinetic control, and in calculating various physico-chemical properties for these important industrial compounds and environmental contaminants. In the present study, 4,272 gas and solvent phase (water and n-octanol) calculations were conducted at various levels of semiempirical (PM6), density functional (B3LYP, B97D, PBE1PBE [PBE0], 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 and the SMD, IEFPCM-UFF, and CPCM implicit... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5353/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. |
| Organic carbon normalized soil and sediment-water partitioning (Koc) coefficients were estimated for all C1 through C8 perfluorinated alkylsulfonic acid (PFSA) and alkylcarboxylic acids (PFCA) congeners. The limited experimental Koc dataset for the straight chain C7 through C10 PFCAs and C8 and C10 PFSAs was correlated to SPARC and ALOGPS computationally estimated octanol-water partitioning constants and used to predict Koc values for both branched and linear C1 through C8 isomers. All branched and linear congeners in this homologue range are expected to have Koc values>1, leading to their accumulation in organic matter on sediments and soils, retardation during ground and pore water flow, and the preferential association with dissolved organic... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3011/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; 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: 68 | |
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