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A G4/W1BD theoretical study into the gas phase enthalpies of formation for potential high energy materials
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Enthalpies of formation (&amp;#x394;~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 &amp;#x394;~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

Aqueous phase hydration and hydrate acidity of perfluoroalkyl and n:2 fluorotelomer aldehydes
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/4520/version/1

Temporal trends in groundwater levels from Saskatchewan, Canada
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Groundwater resources play a key role in supplying water for domestic, industrial, agricultural, and ecological functions on the Canadian prairies. The current study investigates potential temporal trends in groundwater levels for the Canadian province of Saskatchewan over the past several decades. Overall, the large majority of areally distributed stations throughout Saskatchewan with increasing groundwater level time trends suggests that this hydrogeological resource is growing in quantity and is not under current threat from depletion.
Tipo: Manuscript
Palavras-chave: Earth &amp; Environment.
Ano: 2011
URL: http://precedings.nature.com/documents/6696/version/1

Theoretical study on the gas and solution phase enthalpies, free energies, and equilibrium constants for the isomerization of [1.1]paracyclophane derivatives as potential molecular switches
Provedor de dados: Nature Precedings
Autores: 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

Potential Impacts of Tailings and Tailings Cover Fertilization on Arsenic Mobility in Surface and Ground Waters
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
A number of mining sites worldwide, particularly gold mines, have tailings management facilities (TMFs) that contain high levels of arsenic. Current closed mine site regulatory agencies tend to prefer revegetation of TMFs as part of the mandated reclamation activities. At many sites, often in polar regions, vegetation is difficult to establish either directly on the tailings or on the coarse-rock covers due to nutrient poor soils, phytotoxicity problems, and/or a less than optimum climate. Addition of phosphorus-based fertilizers to the tailings and/or cover material is commonly considered in order to promote the revegetation process and &amp;#x2013; ideally &amp;#x2013; allow the site owners to discharge their closure duties as rapidly as possible....
Tipo: Manuscript
Palavras-chave: Chemistry; Earth &amp; Environment.
Ano: 2008
URL: http://precedings.nature.com/documents/1740/version/1

A Long-Term Analysis of the Moose Jaw Climate Station (4015322/4015320): Temporal Trends and Frequency Analyses for Temperatures, Precipitation, and Wind Speed
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2011
URL: http://precedings.nature.com/documents/6703/version/1

Gas phase bond dissociation enthalpies and enthalpies of isomerization/reaction for small hydrocarbon combustion related compounds between 300 and 1500 K: A comparison of Gaussian-4 (G4) theoretical values against experimental data
Provedor de dados: Nature Precedings
Autores: 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

Historical temporal trends in monthly, seasonal, and annual mean, minimum, and maximum streamflows from the Okanagan River watershed in south-central British Columbia, Canada
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Historical trends in monthly, seasonal, and annual mean streamflows, as well as minimum and maximum monthly streamflows, were investigated at nine hydrometric stations in the Okanagan River watershed from south-central British Columbia, Canada. Overall, mean annual streamflows in the Okanagan River watershed are not exhibiting any significant time trends. No consistent declines in monthly minimum streamflows are evident at any point during the hydrologic year. Mean monthly and monthly maximum streamflows in tributary streams to the mainstem system appear to be significantly increasing over time during the spring snowmelt period of March and April. Any temporal changes in flow patterns at the mainstem Okanagan River stations likely reflect alterations in...
Tipo: Manuscript
Palavras-chave: Earth &amp; Environment.
Ano: 2011
URL: http://precedings.nature.com/documents/6662/version/1

Historical Trends in Annual Water Yields for the Okanagan Basin, British Columbia, Canada
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/4946/version/1

Congener specific organic carbon normalized soil and sediment-water partitioning coefficients for the C~1~ through C~8~ perfluoroalkyl carboxylic and sulfonic acids
Provedor de dados: Nature Precedings
Autores: 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 &amp;#x3e;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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3011/version/2

Gas phase enthalpies of formation for potential nitro-substituted borazine high energy materials: A G4MP2 and G4 theoretical study
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Gas phase (298.15 K, 1 atm) enthalpies of formation ([DELTA]~f~H~(g)~) were calculated at the G4MP2 and G4 levels of theory using the atomization energy approach for various nitro-substituted borazines proposed as high energy materials (HEMs). Modest general agreement was obtained between the G4MP2/G4 atomization energy [DELTA]~f~H~(g)~ estimates and those previously reported using density functional theory methods and homodesmic reaction approaches, with deviations ranging between +9.7 to -56.5 kJ/mol. The results should help constrain the actual enthalpies of formation for these potential HEMs, and suggest the nitroborazines are a particularly challenging case for [DELTA]~f~H~(g)~ calculations using theoretical approaches, requiring high-level composite...
Tipo: Manuscript
Palavras-chave: Chemistry.
Ano: 2011
URL: http://precedings.nature.com/documents/5580/version/1

A comparative assessment of octanol-water partitioning and distribution constant estimation methods for perfluoroalkyl carboxylates and sulfonates
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3282/version/1

Performance of the ALOGPS 2.1 program for octanol-water partition coefficient prediction with organic chemicals on the Canadian Domestic Substances List
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
The KOWWIN and ALOGPS octanol-water partition coefficient (K~ow~) estimation software programs were compared for their capacity to accurately predict log K~ow~ values of 1596 organic compounds on the publicly available Domestic Substances List (DSL) from Environment Canada for which experimental data is available. KOWWIN contained a significantly lower number and magnitude of prediction errors compared to ALOGPS, particularly at experimental log K~ow~ values &amp;#x3c;2. Substantial predictive differences were observed between the two programs for 9093 compounds not having experimental K~ow~ data on the Canadian DSL. Predictive differences of up to 40 log K~ow~ units were found between KOWWIN and ALOGPS, and in some cases, the discrepancies were...
Tipo: Manuscript
Palavras-chave: Chemistry; Pharmacology; Earth &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3882/version/1

Temporal trends in annual water yields from the Mackenzie, Saskatchewan-Nelson, Churchill, and Missouri-Mississippi River watersheds in western and northern Canada
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/5342/version/1

Gas phase enthalpies of formation for aminonitroacetylene, aminonitromethane, and diaminodinitromethane: A Gaussian-4 (G4) theoretical study
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Gas phase (298.15 K, 1 atm) enthalpies of formation were calculated at the Gaussian-4 (G4) level of theory using the atomization energy approach for the proposed high energy materials aminonitroacetylene (284.0 to 285.7 kJ/mol), aminonitromethane (-66.4 to -65.0 kJ/mol), and diaminodinitromethane (-84.0 to -81.6 kJ/mol). The results are in good agreement with prior G2 and G3 level estimates, and should help constrain the actual enthalpies of formation for these potential HEMs.
Tipo: Manuscript
Palavras-chave: Chemistry.
Ano: 2010
URL: http://precedings.nature.com/documents/5467/version/1

Comparative theoretical investigation on the isomerization energies of long-chain perfluoroalkanes: A case study with perfluorooctane sulfonic acid congeners
Provedor de dados: Nature Precedings
Autores: 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

A G4MP2 theoretical study on the gas phase enthalpies of formation for various polycyclic aromatic hydrocarbons (PAHs) and other C~10~ through C~20~ unsaturated hydrocarbons
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Gas phase enthalpies of formation at 298.15 and 1 atm (&amp;#x394;~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 &amp;#x394;~f~H~(g),298K~ and the corresponding G4MP2 values were employed to obtain G4MP2 corrected semiempirical &amp;#x394;~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

Accuracy of computational solvation free energies for neutral and ionic compounds: Dependence on level of theory and solvent model
Provedor de dados: Nature Precedings
Autores: 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

Semiempirical, Hartree-Fock, density functional, and second order Moller-Plesset perturbation theory methods do not accurately predict ionization energies and electron affinities of short- through long-chain [n]acenes
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Vertical, well-to-well, and adiabatic ionization energies (IEs) and electron affinities (EAs) were calculated for the n=1-10 [n]acenes using a wide range of semiempirical, Hartree-Fock, density functional, and second order Moller-Plesset perturbation theory model chemistries. None of the model chemistries examined were able to accurately predict the IEs or EAs for both short- through mid-length [n]acenes, as well as for extrapolations to the polymeric limit, when compared to available experimental and benchmark theoretical data. Provided a minimal basis set size is employed, basis set effects on predicted IEs and EAs are not significant relative to the choice of model chemistry. The poor IE/EA prediction performance for the parent [n]acenes likely extends...
Tipo: Manuscript
Palavras-chave: Chemistry.
Ano: 2011
URL: http://precedings.nature.com/documents/6578/version/1

Theoretical studies on the all-anti zigzag geometries of perfluoro-n-alkyl chains
Provedor de dados: Nature Precedings
Autores: 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 &amp;#x3e;=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

Projected Climate Change Impacts on Grape Growing in the Okanagan Valley, British Columbia, Canada
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3162/version/1

Structures, enthalpies of formation, and ionization energies for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives: A G4MP2 theoretical study
Provedor de dados: Nature Precedings
Autores: 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

A hydrometric analysis of the Moose Jaw River near Burdick (05JE006): Temporal trends and frequency analyses for mean, minimum, and maximum flows
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2011
URL: http://precedings.nature.com/documents/6697/version/1

Historical temporal trends in groundwater levels from British Columbia, Canada
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
A time trend study of groundwater monitoring well levels was conducted in British Columbia, Canada. Trend data was available for a total of 210 groundwater monitoring well stations throughout the province with end-of-month water levels over the period of record. Significant temporal trends in groundwater levels were found at 67 stations (40.4% of all stations amenable to statistical examination, and 31.9% of all available stations). Of these 67 stations, 10 had increasing groundwater level trends and the remaining 57 had declining groundwater level trends. Thus, 34.3% of stations with a sufficiently long time series for analysis displayed declining groundwater level trends, while 6.0% have increasing trends, and 59.6% of these stations appear to have no...
Tipo: Manuscript
Palavras-chave: Earth &amp; Environment.
Ano: 2012
URL: http://precedings.nature.com/documents/6844/version/1

Hydrologic and climate trends for the Coldwater River watershed in south-central British Columbia, Canada
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2012
URL: http://precedings.nature.com/documents/6785/version/1

Comparative density functional theory study on the relative gas phase enthalpies and free energies of formation for the mono- through hepta-halogenated (X=F, Cl, Br) anthraquinones
Provedor de dados: Nature Precedings
Autores: 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

Theoretical studies on the pK~a~ values of perfluoroalkyl carboxylic acids: Non-helical conformation acidity constants for n-perfluorooctanoic acid (n-PFOA)
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3837/version/1

Estimated carboxylic acid ester hydrolysis rate constants for food and beverage aroma compounds
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Aroma compounds in the Flavornet database were screened for potentially hydrolyzable carboxylic acid ester functionalities. Of the 738 aroma compounds listed in this database, 140 molecules contain carboxylic acid ester groups that may be amenable to hydrolysis in various food and beverage products.  Acid- (k~A~) and base- (k~B~) catalyzed and neutral (k~N~) hydrolysis rate constants in pure water at 25&amp;#xb0;C were estimated for these aroma compounds. Where available, good agreement between theoretical and experimental hydrolytic half-lives was obtained at various pH values. Wide ranges and broad frequency distributions for k~A~, k~B~, and k~N~ are expected among the various hydrolyzable aroma compounds, with estimated k~A~ ranging from...
Tipo: Manuscript
Palavras-chave: Chemistry; Plant Biology.
Ano: 2011
URL: http://precedings.nature.com/documents/6471/version/1

Theoretical studies on the pK~a~ values of perfluoroalkyl carboxylic acids: Chain helicity
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Semiempirical, ab initio, and density functional theory (DFT) studies were conducted on a homologous series of straight chain perfluoroalkyl carboxylic acids (PFCAs) ranging in chain length from C~1~ (trifluoroacetic acid; TFA) to C~9~ (perfluorodecanoic acid). Regardless of perfluoroalkyl chain length and computational method and level employed, no significant change in the electrostatic or steric characteristics of the carboxylate head group was found between C~2~ and C~9~. Application of a thermodynamic cycle to calculations at the B3LYP/6-311++G(3df,2p) level provided an accurate prediction of the experimental monomeric pK~a~ for TFA. At this &amp;#x2013; and similar &amp;#x2013; levels of theory, monomeric pK~a~ values of longer straight chain PFCAs...
Tipo: Manuscript
Palavras-chave: Chemistry; Earth &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3829/version/1

Octanol/water distribution coefficients of the C~1~ through C~7~ perfluoro-n-alkyl sulfonates: Comparison of the IEFPCM-UFF, CPCM, and SMD solvation models
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
The octanol/water distribution coefficients (log D~ow~) of the C~1~ through C~7~ perfluoro-n-alkyl sulfonates (PFSAs) were calculated using the M062X/6-311++G(d,p) and MP2/6-311++G(d,p)//M062X/6-311++G(d,p) levels of theory and the IEFPCM-UFF, CPCM, and SMD solvation models. At both levels of theory with all solvation models, absolute log D~ow~ calculated for the straight chain C~1~ through C~7~ PFSAs display a substantial negative bias against available experimental data and expected trends by several log units. However, the SMD solvation model achieves accurate relative log D~ow~ accuracy, yielding fragmental contributions of a -CF~2~- group towards the log D~ow~ of 0.51+/-0.02 to 0.54+/-0.01 units (-3.0+/-0.1 to -3.1+/-0.1 kJ/mol), in good agreement...
Tipo: Manuscript
Palavras-chave: Chemistry.
Ano: 2010
URL: http://precedings.nature.com/documents/5103/version/1

Performance of the ALOGPS 2.1 program for octanol-water partition coefficient prediction with organic chemicals on the Canadian Domestic Substances List
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
The KOWWIN and ALOGPS octanol-water partition coefficient (K~ow~) estimation software programs were compared for their capacity to accurately predict log K~ow~ values of 1545 organic compounds on the publicly available Domestic Substances List (DSL) from Environment Canada for which experimental data is available. Approximately equivalent log K~ow~ error statistics were observed between KOWWIN and ALOGPS against available experimental data. Substantial predictive differences were observed between the two programs for 6529 compounds not having experimental K~ow~ data on the Canadian DSL. Predictive differences of up to 40 log K~ow~ units were found between KOWWIN and ALOGPS, and in some cases, the discrepancies were sufficiently large that strongly opposing...
Tipo: Manuscript
Palavras-chave: Chemistry; Pharmacology; Earth &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/3882/version/2

Gas phase hydration, bond dissociation enthalpies, and acidity of aldehydes: A CBS-Q//B3, G4MP2, and G4 theoretical study of substituent effects
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
CBS-Q//B3, G4MP2, and G4 composite method calculations were used to estimate gas phase standard state (298.15 K, 1 atm) free energies of hydration (&amp;#x394;~hydr~G&amp;#xb0;~(g)~), hydration equilibrium constants (log K~hydr,(g)~), bond dissociation enthalpies (BDEs), and enthalpies (&amp;#x394;~d~H&amp;#xb0;~(g)~) and free energies (&amp;#x394;~d~G&amp;#xb0;~(g)~) of aldehydic proton acid dissociation for various substituted aldehydes with electron withdrawing and electron releasing groups. Good quality log K~hydr,(g)~ correlations with the Swain-Lupton resonance effect parameters R and R^+^ were found, allowing extension of the model to predict log K~hydr,(g)~ values for 487 substituted aldehydes having available R-values and 108 substituted aldehydes...
Tipo: Manuscript
Palavras-chave: Chemistry; Earth &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/5084/version/1

Modeling the hydrolysis of perfluorinated compounds containing carboxylic and phosphoric acid ester functions, alkyl iodides, and sulfonamide groups
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Temperature dependent rate constants were estimated for the acid- and base-catalyzed and neutral hydrolysis reactions of perfluorinated telomer acrylates (FTAcrs) and phosphate esters (FTPEs), and the SN1 and SN2 hydrolysis reactions of fluorotelomer iodides (FTIs). Under some environmental conditions, hydrolysis of monomeric FTAcrs could be rapid (half-lives of several years in marine systems and as low as several days in some landfills) and represent a dominant portion of their overall degradation. Abiotic hydrolysis of monomeric FTAcrs may be a significant contributor to current environmental loadings of fluorotelomer alcohols (FTOHs) and perfluoroalkyl carboxylic acids (PFCAs). Polymeric FTAcrs are expected to be hydrolyzed more slowly, with estimated...
Tipo: Manuscript
Palavras-chave: Chemistry; Earth &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3728/version/1

Gas phase carbon acidity and correlations with aqueous pK~a~ values: A comparison of B3LYP/6-311++G(d,p), Gaussian-4 (G4), and experimental approaches
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Gas phase standard state (298.15 K, 1 atm) calculations were conducted at the B3LYP/6-311++G(d,p) density functional and the Gaussian-4 (G4) composite method levels of theory to estimate the acidity of various carbon acids. Excellent agreement was found between the G4 gas phase enthalpies and free energies of carbon acid dissociation and corresponding experimental values. The B3LYP/6-311++G(d,p) level of theory displayed a significantly lower accuracy for gas phase acidity prediction, but with similar qualitative trends as the G4 calculations. Good correlations using both theoretical methods were found with corresponding carbon acid aqueous pK~a~ values. However, the pK~a~ prediction accuracy of carbon acids based on correlations with theoretical gas phase...
Tipo: Manuscript
Palavras-chave: Chemistry.
Ano: 2010
URL: http://precedings.nature.com/documents/4381/version/1

Examining the PM6 semiempirical method for pKa prediction across a wide range of oxyacids
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest; Ken J. Friesen.
The pK~a~ estimation ability of the semiempirical PM6 method was evaluated across a broad range of oxyacids and compared to results obtained using the SPARC software program. Compound classes under consideration included acetic acids, alicyclic and aromatic heterocyclic acids, benzoic acids, boronic acids, hydroxamic acids, oximes, peroxides, peroxyacids, phenols, &amp;#x3b1;-saturated acids, &amp;#x3b1;-saturated alcohols, sulfinic acids, &amp;#x3b1;-unsaturated acids, and &amp;#x3b1;-unsaturated alcohols. PM6 accurately predicts the acidity of acetic and benzoic acids and their derivatives, but is less reliable for alicyclic and aromatic heterocyclic acids and phenols. &amp;#x3b1;-Saturated acids are reliably modeled by PM6 except for polyacid...
Tipo: Manuscript
Palavras-chave: Chemistry; Pharmacology; Earth &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/2981/version/1

Congener specific organic carbon normalized soil and sediment-water partitioning coefficients for the C1 through C8 perfluorinated alkylsulfonic and alkylcarboxylic acids
Provedor de dados: Nature Precedings
Autores: 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&amp;#x3e;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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3011/version/1

Time Trends for Agricultural Crop Production in Saskatchewan, Canada: 1905-2011
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Saskatchewan, Canada, with a total land area of 651,900 km^2^, is one of the world&amp;#x2019;s most productive agricultural cropping regions. Approximately 44% of Canada&amp;#x27;s total cultivated farmland is in the province. In 2008, the total export value of crops was CAD$8.34 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 crops produced. The current work examines time trends for agricultural crop production since Saskatchewan was created in 1905. While yields of all crops have generally increased over time, total production trends vary widely by crop, warranting more detailed investigations into the socio-economical and...
Tipo: Poster
Palavras-chave: Earth &amp; Environment; Plant Biology.
Ano: 2011
URL: http://precedings.nature.com/documents/6712/version/1

Absence of historical temporal trends in monthly, seasonal, and annual streamflows for the Okanagan and Similkameen Rivers in south-central British Columbia, Canada
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2011
URL: http://precedings.nature.com/documents/6584/version/1

An assessment of organic solvent based equilibrium partitioning methods for predicting the bioconcentration behavior of perfluorinated sulfonic acids, carboxylic acids, and sulfonamides
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3256/version/1

Comparative theoretical investigation on the isomerization energies of long-chain perfluoroalkanes: A case study with perfluorooctanoic acid congeners
Provedor de dados: Nature Precedings
Autores: 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

Theoretical studies on the pK~a~ values of perfluoroalkyl carboxylic acids: Non-helical conformation acidity constants for n-perfluorooctanoic acid (n-PFOA)
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3837/version/2

Correlations between experimental and theoretical adiabatic ionization energies for organic compounds and rate constants for atmospheric reactions with hydroxyl radicals
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/5447/version/1

Comparative study on the gas to solution phase solvation free energies of model combustion flue gas compounds (N~2~, O~2~, CO~2~, H~2~O, SO~2~, and CO) in 178 organic solvents using the IEFPCM-UFF, CPCM, and SMD implicit solvent models at the Gaussian-4 (G4) level of theory
Provedor de dados: Nature Precedings
Autores: 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 &amp;#x3c;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

Comparative semiempirical, ab initio, and DFT study on the thermodynamic properties of linear and branched PFSA/Fs, PFCA/Fs, and perhydroalkyl sulfonic acids, alkanes, and alcohols
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3928/version/1

Singlet-triplet excitation energies of substituted benzenes: A G4 theoretical study
Provedor de dados: Nature Precedings
Autores: 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

Theoretical studies in the molecular Platonic solids: Pure and mixed carbon, nitrogen, phosphorus, and silicon tetrahedranes
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Calculations were conducted at the G4MP2 and G4 composite method levels of theory on the 35 potential carbon, nitrogen, silicon, and phosphorus tetrahedrane derivatives with the general form C~a~N~b~Si~c~P~d~H~(4-b-d)~ (where a+b+c+d=4). At both levels of theory, optimized electronic ground state neutral singlet gas phase (298.15 K, 1 atm) geometries were obtained for 24 of the 35 possible C/N/Si/P tetrahedrane derivatives. Corresponding enthalpies of formation were calculated using the atomization method. Triplet state neutral tetrahedron starting geometries for all compounds either resulted in cage opening or failed to converge. Only 9 cationic and 3 anionic forms converged to stable geometries that retained the tetrahedron cage and were absent imaginary...
Tipo: Manuscript
Palavras-chave: Chemistry.
Ano: 2011
URL: http://precedings.nature.com/documents/6299/version/1

ADME/Tox WEB in silico predictions of longer chain perfluoroalkyl carboxylic acid pKa values are more accurate than other computational methods
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/2936/version/1

Projected Climate Change Impacts on Grape Growing in the Okanagan Valley, British Columbia, Canada
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2011
URL: http://precedings.nature.com/documents/3162/version/2

Re-evaluating the list of high-production chemicals predicted to become Arctic contaminants
Provedor de dados: Nature Precedings
Autores: 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 &amp;#x3e;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 &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/4436/version/1

Benchmarking the SPARC software program for estimating solubilities of naphthalene and anthracene in organic solvents
Provedor de dados: Nature Precedings
Autores: 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

Performance of the major semiempirical, ab initio, and density functional theory methods in evaluating isomerization enthalpies for linear to branched heptanes
Provedor de dados: Nature Precedings
Autores: 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

Singlet-triplet excitation energies of R~1~R~2~Si=Si silylene derivatives: A G4/W1BD theoretical study
Provedor de dados: Nature Precedings
Autores: 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

Extending the semi-empirical PM6 method for carbon oxyacid pKa prediction to sulfonic acids: Application towards congener-specific estimates for the environmentally and toxicologically relevant C1 through C8 perfluoroalkyl derivatives
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest; Ken J. Friesen.
A positive bias in the semi-empirical PM6 method for estimating pKa values of sulfonic acids was corrected by a correlation developed between non-adjusted PM6 pKa values and the corresponding experimentally obtained/estimated acidity constants for a range of representative alkyl, aryl, and halogen substituted sulfonic acids. Application of this correction to PM6 values allows for extension of this computational method to a new acid functional group.
Tipo: Manuscript
Palavras-chave: Chemistry; Earth &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/2922/version/1

Predicting the Congener-Specific Environmental Behaviour of Perfluorinated Acid Contaminants Using Semi-Empirical Computational Methods
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2008
URL: http://precedings.nature.com/documents/1956/version/1

Historical temporal trends in overwinter and spring snowpack for the Okanagan and Similkameen River watersheds in south-central British Columbia, Canada
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2011
URL: http://precedings.nature.com/documents/6590/version/1

Ionization effects on the partitioning behavior of food and beverage aroma compounds between aqueous phases and air and organic matrices
Provedor de dados: Nature Precedings
Autores: 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&amp;#xd7;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

Geometries of the perchlorinated and perbrominated C~3~ through C~6~ n-alkanes: A comparative density functional theory study
Provedor de dados: Nature Precedings
Autores: 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

Gas phase enthalpies of formation, isomerization, and disproportionation of mono- through tetra-substituted tetrahedranes: A G4MP2/G4 theoretical study
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Gas phase (298.15 K, 1 atm) enthalpies of formation (&amp;#x394;~f~H&amp;#xb0;~(g)~), enthalpies of disproportionation to two corresponding acetylene molecules (&amp;#x394;~rxn~H&amp;#xb0;~(g),Td&amp;#x2192;acet~), and enthalpies of isomerization from a tetrahedrane geometry to a 1,3-cyclobutadiene structure (&amp;#x394;~isom~H&amp;#xb0;~(g),Td&amp;#x2192;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 &amp;#x394;~f~H&amp;#xb0;~(g)~ indicative of the cage strain in these systems. In all cases, &amp;#x394;~rxn~H&amp;#xb0;~(g),Td&amp;#x2192;acet~ and...
Tipo: Manuscript
Palavras-chave: Chemistry.
Ano: 2011
URL: http://precedings.nature.com/documents/6421/version/1

Time Trends for Livestock Production in Saskatchewan, Canada: 1905-2011
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Saskatchewan, Canada, with a total land area of 651,900 km^2^, is one of the world&amp;#x2019;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 &amp; Environment.
Ano: 2011
URL: http://precedings.nature.com/documents/6714/version/1

Gas phase bond dissociation enthalpies and enthalpies of isomerization/reaction for small hydrocarbon combustion related compounds between 300 and 1500 K: A comparison of Gaussian-4 (G4) theoretical values against experimental data
Provedor de dados: Nature Precedings
Autores: 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

Gas phase homolytic bond dissociation enthalpies of common laboratory solvents: A G4 theoretical study
Provedor de dados: Nature Precedings
Autores: 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

Performance of the M062X density functional against the ISOL set of benchmark isomerization energies for large organic molecules
Provedor de dados: Nature Precedings
Autores: 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

Theoretical studies on the pK~a~ values of perfluoroalkyl carboxylic acids
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/3829/version/2

Modeling the hydrolysis of the polymeric brominated flame retardants BC-58 and FR-1025
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2010
URL: http://precedings.nature.com/documents/4160/version/1

Congener-Specific Numbering Systems for the Environmentally Relevant C4 through C8 Perfluorinated Homologue Groups of Alkyl Sulfonates, Carboxylates, Telomer Alcohols and Acids, and Their Derivatives
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2008
URL: http://precedings.nature.com/documents/1957/version/2

Congener-Specific Numbering Systems for the Environmentally Relevant C4 through C8 Perfluorinated Homologue Groups of Alkyl Sulfonates, Carboxylates, Telomer Alcohols and Acids, and Their Derivatives
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2008
URL: http://precedings.nature.com/documents/1957/version/1

Gas phase constant pressure heat capacities (C~p,gas~) for the C~1~ through C~10~ straight chain alkanes, isobutane, hydrogen atom, hydroxyl and methyl radicals, and water between 298.15 and 1500 K: A comparison of theoretical values against experimental data
Provedor de dados: Nature Precedings
Autores: Sierra Rayne; Kaya Forest.
Gas phase constant pressure heat capacities (C~p,gas~) for the C~1~ through C~10~ straight chain alkanes, isobutane, hydrogen atom, hydroxyl and methyl radicals, and water were calculated between 298.15 and 1500 K using various low (semiempirical PM6) through high level (CBS-Q//B3 and G4 composite) theoretical methods. All levels of theory provided good agreement with experimental C~p,gas~ data (&amp;#x3c;+/-10% deviation) regardless of molecular size. A modest but progressive loss of C~p,gas~ predictive accuracy occurs with increasing molecular size among the n-alkanes. For most compounds at all levels of theory, the highest C~p,gas~ estimation accuracy occurs at elevated temperatures, with decreasing accuracy as the temperature is lowered or raised about...
Tipo: Manuscript
Palavras-chave: Chemistry.
Ano: 2010
URL: http://precedings.nature.com/documents/5024/version/1

A comparative assessment of octanol-water partitioning and distribution constant estimation methods for perfluoroalkyl carboxylates and sulfonates
Provedor de dados: Nature Precedings
Autores: 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 &amp; Environment.
Ano: 2009
URL: http://precedings.nature.com/documents/3282/version/2