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Rayne S.,Ecologica Research | Forest K.,Okanagan College
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2010

A set of 543 ionizable commercial organic compounds with various acid/base functionalities and experimental octanol-water partitioning coefficients (log Kow) were obtained from the Canadian Domestic Substances List. Corresponding pH-dependent octanol-water distribution coefficients (log D ow) and air-water partitioning coeffients (log Kaw,eff ) were estimated using the SPARC software program, as were log Kow and log K aw values for the neutral forms of each chemical. Significant ionization dependent effects on chemical screening results at various pH values were obtained using established criteria for bioaccumulation potential (BAP) in aquatic organisms, terrestrial animals, and humans, as well as for atmospheric long range transport potential (LRTP). Future modelling efforts for environmental and toxicological screening of commercial chemicals should therefore explicitly include the influence of ionization for both weak and strong organic acids and bases on bioavailability and air-water mobility within the respective regulatory frameworks. Functional group specific sorption of both ionizable and neutral compounds to particulate and dissolved inorganic and organic matter will also affect chemical screening results for BAP and LRTP. More complex sorption related modelling in various types of representative aquatic systems also appears necessary to achieve reliable chemical screening results for commercial organic compounds. Copyright © Taylor & Francis Group, LLC.


Rayne S.,Ecologica Research | Forest K.,Okanagan College
Journal of Chemical and Engineering Data | Year: 2011

Gas phase (298.15 K, 101.325 kPa) adiabatic ionization energies (AIEs) were calculated for 236 organic compounds with the Gaussian-4 (G4) composite method and for 17 molecules at the W1BD level of theory. Functional group types considered span a range of mono- and polyfunctionalized halogenated, saturated and unsaturated, cyclic and acyclic, and heteroatom (N, O, S) substituted moieties without substantial conformational complexity. Excellent agreement was found using both computational methods against available experimental data. Approximately equivalent AIE prediction accuracy was observed between the G4 and the W1BD methods. For compounds with well-constrained experimental AIEs, both levels of theory provide effective chemical accuracy. © 2010 American Chemical Society.


Rayne S.,Ecologica Research | Forest K.,Okanagan College
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2010

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 half-lives in soil and natural waters ranging between several centuries to several millenia absent additional surface area limitations on reactivity. Poor agreement was found between the limited experimental data on FTPE hydrolysis and computational estimates, requiring more detailed experimental data before any further modeling can occur on these compounds or their perfluoroalkyl sulfonamidoethanol phosphate ester (PFSamPE) analogs. FTIs are expected to have hydrolytic half-lives of about 130 days in most natural waters, suggesting they may be contributing to substantial FTOH and PFCA inputs in aquatic systems. Perfluoroalkyl sulfonamides (PFSams) appear unlikely to undergo abiotic hydrolysis at the S-N, C-S, or N-C linkages under environmentally relevant conditions, although potentially facile S-N hydrolysis via intramolecular catalysis by ethanol and acetic acid amide substituents warrants further investigation. Copyright © Taylor & Francis Group, LLC.


Rayne S.,Ecologica Research | Forest K.,Okanagan College
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2010

The SPARC software program aqueous pKa prediction module was validated against corresponding experimental acidity constants for chlorinated and brominated phenols and the limited experimental aqueous pKa data sets for monohydroxylated polychlorinated biphenyls (OH-PCBs), polychlorinated diphenyl ethers (OH-PCDEs), and polybrominated diphenyl ethers (OH-PBDEs). pKa values were then estimated for all 837 monohydroxylated mono- through nona-halogenated congeners in each of the OH-PCB, OH-PCDE, and OH-PBDE classes, as well as for the monohydroxylated polybrominated biphenyls (OH-PBBs), giving a total of 3348 compounds. Large intrahomolog pKa variation by up to six units is expected within each contaminant class, with pKa values ranging from about 4 to 11 dependent on the degree and pattern of halogenation. Increasing halogenation generally decreased the average pKa within each homolog group. Significant intrahomolog differences in pKa values exist between OH-PCB, OH-PBB, OH-PCDE, and OH-PBDE congeners, including large acidity constant variation between isomers with equivalent halogenation patterns but varying location of the hydroxy moiety. Congener specific pH dependent investigations into the partitioning and degradation behaviors of these compounds are necessary, including greater consideration of analyte ionization effects during their extraction and analysis. Copyright © Taylor & Francis Group, LLC.


Rayne S.,Ecologica Research | Forest K.,Okanagan College
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2010

A quantitative structure-activity relationship (QSAR) was developed to predict the congener specific ryanodine receptor type RyR1 activity of all 209 polychlorinated biphenyl (PCB) congeners. A three-variable QSAR equation was obtained via stepwise forward linear regression on an unsupervised forward selection reduced data set from an initial database. Application of the QSAR towards predicting EC2x values for all 209 PCB congeners indicated good agreement in substitution pattern trends between the experimental and estimated data sets. The QSAR model predicts a less than two-fold increase in maximal potency among all congeners outside the experimental database, and it appears that no high-potency PCB congeners with EC2x values much less than 0.2 μM exist. Increasing RyR1-neuro toxicity equivalents with increasing homologue number and Aroclor chlorination likely reflect indirect molecular controls on toxicity, since congeners with multiple ortho substituentsthe primary structural feature controlling a lack of coplanarity and resulting neurotoxicityare more likely to be found in higher homologues.


Rayne S.,Ecologica Research | Forest K.,Okanagan College
Journal of Molecular Structure: THEOCHEM | Year: 2010

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 C1(trifluoroacetic acid) to C9(n-perfluorodecanoic acid) as well as the monomethyl branched C7(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 pKa values between C1 and C9, all having a relatively constant pKa of about 0 that is in agreement with earlier predictions and recent experimental evidence. Perfluoroalkyl chain helicity does not appear to result in increased monomeric PFCA pKa values at chain lengths greater than 5. Increasing chain length does not substantially influence the structural or electronic character of the carboxylic acid head group. A 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 DFT investigations. Application of a thermodynamic cycle approach, coupled with aqueous and gas phase DFT calculations on the molecular and anionic forms for each of the conformers, gave conformationally averaged pKa values for n-PFOA equal to the global minimum helical conformer pKa. The conformational populations under study occupy ∼100% of the global n-PFOA conformational space, indicating no higher energy/low acidity conformations remain unexamined that could influence the predicted composite aqueous monomeric pKa of zero for this compound. © 2010 Elsevier B.V. All rights reserved.


The Gaussian-3 (G3) and Gaussian-4 (G4) ab initio post-Hartree-Fock composite methods were employed to estimate the gas phase standard state (298.15. K, 1. atm) enthalpies of formation (ΔfH(g)̊) for 38 representative C1(n=15) and C2(n=23) chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Using the atomization approach, good agreement was found between experimental ΔfH(g)̊ and corresponding G3 and G4 estimates. Where significant differences between G3/G4 and experimental ΔfH(g)̊ exist, the errors may be due to problems with the experimental data rather than deficiencies in the theoretical methods. © 2010 Elsevier B.V.


Rayne S.,Ecologica Research | Forest K.,Okanagan College
Journal of Molecular Structure: THEOCHEM | Year: 2010

A database of gas phase standard state isomerization enthalpies was constructed for 562 pure and nitrogen-, oxygen-, sulfur-, and halogen-containing hydrocarbon reactions. The PM6 and PDDG semiempirical methods, B3LYP and M062X hybrid density functionals with the 6-311++G(d,p) and 6-311+G(3df,3p) basis sets, and the CBS-Q//B3 and G4MP2 ab initio post-Hartree-Fock composite methods were examined for prediction accuracy within each class of isomerization reactions. At much lower computational cost, the PM6 and PDDG semiempirical methods offer modest isomerization enthalpy prediction performance approximately comparable to the B3LYP density functional. The M062X density functional provides nearly equivalent accuracy to the higher level CBS-Q//B3 and G4MP2 methods across all hydrocarbon classes. Increasing basis set size from 6-311++G(d,p) to 6-311+G(3df,3p) with the B3LYP and M062X density functionals does not influence their respective isomerization enthalpy prediction accuracies. Using the 6-311+G(3df,3p) basis set, the M062X functional also achieves near CBS-Q//B3 quality accuracy for enthalpies of formation using the atomization approach. © 2010 Elsevier B.V. All rights reserved.


Gas-phase standard state (298.15 K, 1 atm) enthalpies of formation (Δ fH (g) o) and enthalpies (Δ acidH (g) o) and free energies (Δ acidG (g) o) of acid dissociation were calculated for the [m, n]polyprismanes (m ≥ 2; n = 3-8; m × n ≤ 16) using the composite method CBS-Q//B3, G4MP2, and G4 levels of theory. Excellent agreement was obtained between the theoretical estimates and experimental values for [2, 4]polyprismane (cubane), the only member with reliable experimental data. Gas-phase acidities of the [2, 3], [2, 4], and [2, 5]polyprismanes correlate well with percent s-character of the C-H bonds as determined by nuclear magnetic resonance spectroscopy. Based on this correlation, and calculations on the [2, n] (n = 3-8) series, no substantial change in the gas-phase acidity or C-H bond s-character is expected with increasing [2,n]polyprismane ring size at n = 6-8. Where three or more stacked [m, n]polyprismane rings are present (m > 2), geometry optimizations for the deprotonated anions converged on cage-opened non-prismatic geometries, suggesting these compounds may be structurally unstable to gas-phase deprotonation/protonation cycles and potentially preventing reliable experimental measurement or calculation of their acidities. Total strain energies (E str) increase with larger [m, n]polyprismane size, and strain energies per one C-C bond (E str CC) increase with increasing stack height within a given ring size series. Within a given stack height, E str CC reaches a minimum with a ring size of five, increasing with either decreasing or increasing ring size away from this minima. E str and E str CC do not correlate with gas-phase acidity, likely because the deprotonated anionic [2, n]polyprismane geometry retains approximately equal strain as the undissociated species despite substantial geometry changes due to carbon acid dissociation. © 2010 Springer-Verlag.


Rayne S.,Okanagan College | Forest K.,Ecologica Research
Journal of Chemical and Engineering Data | Year: 2010

Gas-phase standard state (298.15 K, 1.01325 bar [1 atm]) enthalpies of formation (Δ fH° (g)) were calculated using the atomization approach for 313 organic compounds with the Gaussian-4 (G4) composite method and for 54 molecules with the W1BD level of theory. The functional group types considered span a range of mono- and polyfunctionalized halogenated, saturated and unsaturated, cyclic and acyclic, and heteroatom (N, O, S) substituted moieties without substantial conformational complexity. Good agreement was found using both computational methods against available experimental data. © 2010 American Chemical Society.

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