Moose Jaw, Canada
Moose Jaw, Canada

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Rayne S.,Chemologica Research | Forest K.,Saskatchewan Institute of Applied Science and Technology
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2014

A high-level gas and aqueous phase theoretical thermodynamic study was conducted on the primary and related chemical reactions which occur during chloramination for water treatment using the G4MP2, G4, and W1BD composite methods with the SMD, PCM, and CPCM solvation models. The standard state (298.15 K, 1 atm or 1M) formation of mono-, di-, and tri-chloramines from their precursors via hypochlorous acid chlorination is substantially exothermic and exergonic in both the gas and aqueous phases. The excellent agreement between experimental and theoretical values for a range of structural and thermodynamic calculations on a suite of calibration compounds suggests that the G4MP2, G4, and W1BD calculations meet or exceed criteria for thermochemical accuracy. The temperature influence on the thermodynamics of chloramine formation is projected to be negligible regardless of phase between 0 and 100°C. Additional thermodynamic calculations were undertaken on associated chloramination reactions involving the disproportionation of monochloramine, the decomposition of di- and tri-chloramine, and the reactions of trichloramine with ammonia and dichloramine. The results from these investigations not only provide a better understanding of the reaction thermodynamics, they also allow for a more rigorous interpretation of proposed chloramination mechanisms. © 2014 Copyright Taylor & Francis Group, LLC.


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Institute of Applied Science and Technology
Computational and Theoretical Chemistry | Year: 2011

Singlet-triplet (S0→T1) well-to-well (WWES-T) and vertical (VES-T) excitation energies of the [4×n] rectangular graphene nanoribbon series (n=2-6) were estimated using various semiempirical, Hartree-Fock (HF), density functional (DFT), and second order Moller-Plesset perturbation theory methods with the assumption of a closed-shell singlet state. Significant model chemistry dependent variability in theoretically obtained WWES-T/VES-T is evident for the rectangular graphene nanoribbons. With the exception of the B2PLYP density functional (which, along with the mPW2PLYP functional, combines exact HF exchange with an MP2-like correlation to the DFT calculation), all DFT, semiempirical, and HF methods investigated predict the onset of a negative WWES-T/VES-T (ground state triplet) starting somewhere between the [4×3] through [4×6] derivatives, with most functionals predicting a transition from a singlet to triplet ground state between the [4×4] and [4×5] rectangular graphene nanoribbons. Consistent with previous work on the n-acene series, MP2 WWES-T/VES-T estimates have a significant positive systematic bias and HF estimates have substantial negative systematic biases. Extrapolation of the B2PLYP results, which are in excellent agreement with prior FPA-QZ VES-T estimates, for any [m×n] rectangular graphene nanoribbon derivatives predicts a vanishingly small singlet-triplet gap at the polymeric limit (m→∞ and/or n→∞). © 2011 Elsevier B.V.


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Institute of Applied Science and Technology
Computational and Theoretical Chemistry | Year: 2012

The gas phase (298.15K, 1atm) isomerization energies (ΔisomE(g)) of various tetra-substituted (hydro, chloro, bromo, methyl, ethynyl, cyano, tert-butyl, and tetrakis(trimethylsilyl)) tetrahedranes to their corresponding 1,3-cyclobutadienes were investigated with a broad range of model chemistries (Hartree-Fock, density functional, Moller-Plesset perturbation, composite, coupled cluster, and quadratic configuration interaction methods) and Pople-/Ahlrichs-/Dunning-type basis sets. Substantial model chemistry dependent ΔisomE(g) variability was found for all tetrahedrane/1,3-cyclobutadiene derivatives. Basis set influences on ΔisomE(g) variability were modest and less influential than the choice of model chemistry. Several density functionals previously found to provide excellent ΔisomE(g) prediction performance for a broad range of small and large organic compounds demonstrated poor capability when applied to the tetrahedrane/1,3-cyclobutadiene isomerizations. © 2011 Elsevier B.V..


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Institute of Applied Science and Technology
Computational and Theoretical Chemistry | Year: 2012

Singlet-triplet excitation energies (E S-T) were calculated for the phenyl, 1-naphthyl, and 2-naphthyl cations using a broad range of model chemistries, including semiempirical, Hartree-Fock, density functional, Moller-Plesset perturbation, composite, coupled cluster, and quadratic configuration interaction methods and various basis sets. Substantial model chemistry dependent E S-T results were obtained for all three cations with correspondingly minimal basis set size effects. G4/G4MP2 composite method well-to-well (and adiabatic) E S-T for the phenyl, 1-naphthyl, and 2-naphthyl cations are 101.9/102.3 (101.7/102.0), 20.4/18.8 (19.3/17.8), and 21.6/21.4 (20.8/20.7)kJ/mol, respectively. All composite methods predict a substantially positive E S-T for the 1- and 2-naphthyl cations, and are in both quantitative and qualitative disagreement with many other model chemistries (particularly density functionals such as B3LYP) in estimating both the magnitude and sign of the singlet-triplet excitation energy for the 1- and 2-naphthyl cations. Composite method approaches suggest both the 1- and 2-naphthyl cations are ground state singlets with sufficiently large E S-T such that the population of the corresponding triplet state should be negligible, and thereby non-observable, where experimental conditions operate under thermodynamic control. © 2012 Elsevier B.V..


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Polytechnic
Science of the Total Environment | Year: 2016

Annual and summertime trends towards increasingly variable values of the Palmer Drought Severity Index (PDSI) over a sub-decadal period (five years) were investigated within the contiguous United States between 1895 and the present. For the contiguous United States as a whole, there is a significant increasing trend in the five-year running minimum-maximum ranges for the annual PDSI (aPDSI5yr(min|max, range)). During this time frame, the average aPDSI5yr(min|max, range) has increased by about one full unit, indicating a substantial increase in drought variability over short time scales across the United States. The end members of the running aPDSI5yr(min|max, range) highlight even more rapid changes in the drought index variability within the past 120years. This increasing variability in the aPDSI5yr(min|max, range) is driven primarily by changes taking place in the Pacific and Atlantic Ocean coastal climate regions, climate regions which collectively comprise one-third the area of the contiguous United States. Similar trends were found for the annual and summertime Palmer Hydrological Drought Index (PHDI), the Palmer Modified Drought Index (PMDI), and the Palmer Z Index (PZI). Overall, interannual drought patterns in the contiguous United States are becoming more extreme and difficult to predict, posing a challenge to agricultural and other water-resource related planning efforts. © 2015 Elsevier B.V.


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Polytechnic
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2016

In order to estimate isomer-specific acidity constants (pKa) for the perfluorinated sulfonic acid (PFSA) environmental contaminants, the parameterization method 6 (PM6) pKa prediction method was extensively validated against a wide range of carbon oxyacids and related sulfonic/sulfinic acids. Excellent pKa prediction performance was observed for the carbon oxyacids using the PM6 method, but this approach was found to have a severe positive bias for sulfonic/sulfinic acids. To overcome this obstacle, a correlation was 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 the PM6 values allows for extension of this computational method to a new acid functional group. When used to estimate isomer-specific pKa values for the C1 through C8 PFSAs, the modified PM6 approach suggests an adjusted pKa range from −5.3 to −9.0, indicating that all members of this class of well-known environmental contaminants will be effectively completely dissociated in aquatic systems. © 2016 Taylor & Francis Group, LLC


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Polytechnic
Computational and Theoretical Chemistry | Year: 2016

Gas phase standard state (298.15K, 1atm) enthalpies of formation (δfH°(g)), enthalpies of disproportionation to two corresponding acetylene molecules (δrxnH°(g),Td→acet), and enthalpies of isomerization from a tetrahedrane geometry to a 1,3-cyclobutadiene structure (δisomH°(g),Td→CBD) were calculated for the mono- through tetra-substituted hydro, fluoro, chloro, bromo, methyl, ethynyl, and cyano carbon tetrahedrane derivatives at the G4(MP2) and G4 levels of theory. All derivatives have endothermic δfH°(g) indicative of the cage strain in these systems. In all cases, δrxnH°(g),Td→acet and δisomH°(g),Td→CBD are predicted to be substantially exothermic. High quality linear regression fits within a homologous series were obtained between the number of substituents and the G4(MP2)/G4 estimated δfH°(g). Via calculations on lower homolog members, this strategy was employed to allow extrapolated G4 and/or G4(MP2) δfH°(g) (as well as some δrxnH°(g),Td→acet and δisomH°(g),Td→CBD) to be obtained for the higher homolog t-butyl, trifluoromethyl, and trimethylsilyl carbon tetrahedrane derivatives. © 2015 Elsevier B.V.


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Polytechnic
Science of the Total Environment | Year: 2016

A statistical analysis was conducted on long-term climate records for sites bordering Okanagan Lake in the Okanagan Valley viticultural region of British Columbia, Canada. Average wine grape growing season temperatures are increasing rapidly in the area over the post-1980 period at rates upwards of 7.0 ± 1.3 °C/century. Similar increases in the average dormant season temperature are evident. These temperature changes are likely some of the most extreme observed among the world's wine producing areas during the past few decades. Growing degree day base 10 °C (GDD10) has increased by nearly 50% at some locations since the 1970s, resulting in major impacts on the corresponding climate classification for viticulture. If current climate trends continue, the southern and central portions of the region will likely enter Winkler region II within the next few decades, placing them in the same category as well-established warmer wine regions from France, Spain, Italy, and Australia. The large dormant season temperature increases over the last several decades have resulted in the area no longer being a cold season outlier when compared to most other cool-climate viticultural areas. Based on average growing season temperatures, the southern end of Okanagan Lake has moved out of the cool-climate viticultural classification and into the intermediate zone, while the central and northern regions are now at the cool/intermediate viticulture interface, similar to the historical positions of the Rhine Valley in Germany, northern Oregon in the United States, and the Loire Valley, Burgundy-Cote, Burgundy-Beaujolais, and Champagne appelations of France. The corresponding suitable grape species for the area have evolved into warmer region varietals during this time frame, having substantial economic impacts on producers. Increased temperatures are also expected to bring greater threats from agricultural pests, notably Pierce's disease from the bacterium Xylella fastidiosa. © 2016 Elsevier B.V.


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Polytechnic
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2016

The SPARC software program and comparative density functional theory (DFT) calculations were used to investigate the aqueous phase hydration equilibrium constants (Khyd) of perfluoroalkyl aldehydes (PFAlds) and n:2 fluorotelomer aldehydes (FTAlds). Both classes are degradation products of known industrial compounds and environmental contaminants such as fluorotelomer alcohols, iodides, acrylates, phosphate esters, and other derivatives, as well as hydrofluorocarbons and hydrochlorofluorocarbons. Prior studies have generally failed to consider the hydration, and subsequent potential hydrate acidity, of these compounds, resulting in incomplete and erroneous predictions as to their environmental behavior. In the current work, DFT calculations suggest that all PFAlds will be dominantly present as the hydrated form in aqueous solution. Both SPARC and DFT calculations suggest that FTAlds will not likely be substantially hydrated in aquatic systems or in vivo. PFAld hydrates are expected to have pKa values in the range of phenols (ca. 9 to 10), whereas n:2 FTAld hydrates are expected to have pKa values ca. 2 to 3 units higher (ca. 12 to 13). In order to avoid spurious modeling predictions and a fundamental misunderstanding of their fate, the molecular and/or dissociated hydrate forms of PFAlds and FTAlds need to be explicitly considered in environmental, toxicological, and waste treatment investigations. The results of the current study will facilitate a more complete examination of the environmental fate of PFAlds and FTAlds. © 2016 Taylor & Francis Group, LLC


Rayne S.,Chemologica Research | Forest K.,Saskatchewan Polytechnic
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2016

The gas phase standard state (298.15 K, 1 atm) isomerization enthalpy (ΔisomH°(g)) prediction performance of the major semiempirical, ab initio, and density functional levels of theory for environmentally relevant transformations was investigated using the linear to branched heptanes as a representative case study. The M062X density functional, MP2 (and higher) levels of Moller-Plesset perturbation theory, and the CBS and Gaussian-n composite methods are well suited for investigating the thermodynamic properties of environmentally interesting isomerizations, although the M062X functional may not be appropriate for all systems. 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. © 2016 Taylor & Francis Group, LLC

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