2017
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Item Regioselective Substituent Effects upon the Synthesis of Dipyrrins from 2-Formyl Pyrroles(Canadian Science Publishing, 2017-12-19) Beh, Michael; Figliola, Carlotta; Lund, Kate-Lyn; Kajetanowicz, Aleksandra; Johnsen, Ann; Aronitz, Elise; Thompson, AlisonThe synthesis of symmetric Îą-free meso-H-dipyrrin hydrobromides from 5-H-2-formyl pyrroles was investigated. The self-condensation produces regioisomeric dipyrrins through adoption of two mechanistic pathways. The key difference between the two pathways lies in which position of the pyrrole directs nucleophilic attack. Through a systematic study involving various substituted and/or isotopically labelled 5-H-2-formyl pyrroles, we herein provide evidence to suggest that not only do two mechanistic pathways exist, but that the steric bulk of the substituent adjacent to the 5-unsubstituted position influences which pathway dominates.Item Theoretical study on electronic and absorption characters of p-type D-A-π-A triaryamine sensitizer(Canadian Science Publishing, 2017-12-04) Yan, Wen; Sun, Zhi-Dan; Ju, Xue-HaiThe structural and electronic properties of well known 4,4'-(4-(5-(2,2-dicyanovinyl)thiophen-2-yl)phenylazanediyl)dibenzoic acid (O2) and its hypothetical dyes O3-O7 were investigated by computational techniques. The absorption properties were probed. By replacing the 2-methylidenepropanedinitrile acceptor with 1,3-diethyl-5-methylene-2-thioxo-dihydropyrimidine-4,6(1H,5H)-dione, the molecular orbital energy levels were well tuned. The modified dyes meet the basic requirements of both ‒ΔGinj and ‒ΔGreg being over 0.2 eV for an efficient hole injection and dye regeneration, respectively. All the designed p-type dyes O3-O7 have smaller energy gap and significant red shift in absorption spectra than that of the reference O2. Finally, our results suggested that O3-O7 have larger light-harvesting efficiencies (LHE) in the visible spectral regions of 400 nm to 700 nm than O2. Among all the dyes, O5 is expected to have excellent performance as a p-type sensitized dye in solar cells due to its great LHE and sufficient hole injection efficiency.Item Theoretical study on the reactions of a series of polybromobenzenes with OH radicals：mechanism, kinetics and QSAR(Canadian Science Publishing, 2017-12-04) Jian, Zheng; Qin, Zhou; Chao, Chen; Xinhui, Jin; Wanyong, Ma; Chenxi, Zhang; Zhou, JianhuaPolybromobenzenes are a kind of monocyclic aromatic flame retardants which are used as a substitute for polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCE). In this paper, the reaction mechanism and rate constants for the reaction of OH radicals with a series of polybromobenenes such as hexabromobenzene (HBB), 1,2,4,5-tetrabromobenzenes (1,2,4,5-TeBB), pentabromobenzene (PEBB), pentabromoethylbenzene (PBEB), pentabromotoluene (PBT) and 2,4,5-tribromotoluene (2,4,5-TrBT) have been investigated by quantum chemical method. The reaction mechanism was obtained at the MPWB1K/6-311+g(3df,2p)//MPWB1K/6-31+g(d,p) level of theory and the rate constants were deduced over the temperature range of 200–370 K using canonical variational transition state (CVT) theory with the small curvature tunneling (SCT) method. The rate constants of OH radicals with HBB, 1,2,4,5-TeBB, PEBB, PBEB, PBT and 2,4,5-TrBT are determined to be 5.72 ×10Item Novel diaminopropyl substituted organotin compounds(Canadian Science Publishing, 2017-12-15) Pichler, Johann; Müller, Philipp; Torvisco, Ana; Uhlig, FrankA novel synthetic pathway involving the desilylation of a tin trimethylsilyl species (Ph2Sn(SiMe3)2) towards non-protected di(3-aminopropyl)tin dichloride (Cl2Sn(CH2)3NH2) is described. Di(3-aminopropyl)tin dichloride is then converted to the respective dicarboxylates species (RCOO)2Sn(CH2)3NH2)2 employing carboxylic acids of different lengths (R = -CH3, -(CH2)10CH3). Depending on the nature of R, discrete packing effects are observed in the solid state of di(3-aminopropyl)tin dicarboxylate derivatives. All the synthesized substances were characterized byItem pH-Related Fluorescence Quenching Mechanism of Pterin Derivatives and the Effects of 6-Substituents(Canadian Science Publishing, 2017-12-06) Liu, Lei; Sun, Bingqing2-amino-4-hydroxypteridine (pterin) and its derivatives serve as photo-oxidants and exhibit strong fluorescence. When they interact with hydrogen acceptors such as acetate and phosphate, their fluorescence are significantly quenched in acidic condition (pH 4.9-5.5) whereas retained in basic condition (pH 10.0-10.5). This pH-related fluorescence quenching mechanism of pterin and its derivatives are fully investigated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Pterin and its derivatives are demonstrated to show favorable excited state proton transfer (ESPT) abilities in acidic conditions which induce the experimentally observed fluorescence quenching. In contrast, the ESPT processes are found to be retarded due to the lack of strong hydrogen-bonding interactions in basic environments which sustain their fluorescence. Interestingly, these ESPT processes are found to show different site specificities depending on the 6-site substituents. The introduction of electron-donating substituent activates the N1 site, making it the preferable ESPT site. By contrast, the introduction of electron-withdrawing substituent activates the N5 site, making it the favorable ESPT site. The substitutions of different functional groups are found to affect the locations of acidic centers during the excitation and relaxation processes. This further affects the hydrogen-bonding patterns and ultimately brings site specificity to the ESPT process.Item Pyridine, Thiophosphine and Selenophosphine Complexes of the Phenylphosphine Dication(Canadian Science Publishing, 2017-11-26) Sinclair, Hannah; Suter, Riccardo; Burford, Neil; McDonald, Robert; Ferguson, Michael J.Compounds of the generic formula [PhPL][OTf]2 with L = bipyridine (bipy) and 4,4'-di(tert-butyl)-2,2'-bipyridine (Bbipy), and [PhPL2][OTf]2 with L = dimethyl-amminopyridine (dmap), tricyclohexyl-thiophosphine and tricyclohexyl-selenophosphine have been prepared by the reaction of dichlorophenylphosphine with two equivalents of trimethylsilyl triflate and the respective ligand. The new complexes of the phenylphosphine dication with this variety of ligands expands the scope of coordination complexes involving phosphorus as an acceptor.Item A Water Soluble Fluorescent Chemosensor Based on Asp Functionalized Naphthalimide for Successive Detection Fe3+ and H2PO4-(Canadian Science Publishing, 2017-11-06) Zhang, You-Ming; Chen, Xiao-Peng; Liang, Guo-Yan; Zhong, Kai-Peng; Yao, Hong; Wei, Tai-Bao; Lin, QiThe selective recognition of target ions in water is very important and the development of novel water soluble chemosensor is still an intriguing challenge. Herein, a novel water soluble fluorescent sensor based on aspartic acid (Asp) functionalized 1,8-naphthalimide derivative (Asp-NI) has been designed and synthesized. The sensor Asp-NI could dissolve in water and successively detect Fe3+ and H2PO4- in water solution with high selectivity and sensitivity. The detection limits are 4.97 × 10-7 M for Fe3+ and 5.27 × 10-6 M for H2PO4-. Other coexistent competitive metal ions (Hg2+, Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+ and Mg2+) showed no interference in the Fe3+ detection process. The sensor Asp-NI could act as a Fe3+ and H2PO4- controlled “On-Off-On” fluorescent switch. More interestingly, the Fe3+ induced fluorescence quenching process could be totally reversed by the addition of H2PO4-, this “On-Off-On” switching process could be repeated several times with little fluorescence loss. Notably, the actual usage of sensor Asp-NI was further demonstrated by test kits.Item Exploiting the Full Quantum Crystallography(Canadian Science Publishing, 2017-11-15) Massa, Lou; Matta, CherifAbstract Quantum crystallography (QCr) is a branch of crystallography aimed at obtaining the complete quantum mechanics of a crystal given its X-ray scattering data. The fundamental value of obtaining an electron density matrix that is N-representable is that it ensures consistency with an underlying properly antisymmetrized wavefunction, a requirement of quantum mechanical validity. But mostly X-ray crystallography has progressed in an impressive way for decades based only upon the electron density obtained from the X-ray scattering data without the imposition of the mathematical structure of quantum mechanics. Therefore, one may perhaps ask regarding N-representability “why bother?” It is the purpose of this article to answer such a question by succinctly describing the advantage that is opened by quantum crystallography. Résumé français La cristallographie quantique (QCr) est une branche de la cristallographie visant à obtenir la description quantique complète d'un cristal compte tenu de ses facteurs de structure obtenus à partir de la diffraction des rayons X. La valeur fondamentale de l'obtention d'une matrice de densité électronique qui est N-représentable est l'assurance de sa cohérence avec une fonction d'onde sous-jacente correctement anti-symétrisée comme l'exige la mécanique quantique. Mais la cristallographie aux rayons X a, pour la plupart, progressé de façon impressionnante pendant des décennies en se basant uniquement sur la densité électronique obtenue à partir des facteurs de structure expérimentaux sans l’imposition de la structure mathématique de la mécanique quantique. Par conséquent, on peut peut-être se demander à propos de la N-représentabilité «pourquoi s'en soucier?» Le but de cet article est d’adresser cette question en décrivant brièvement l'avantage que présente la cristallographie quantique.Item Linear dicoordinate beryllium: a 9Be solid-state NMR study of a discrete zero-valent s-block beryllium complex(Canadian Science Publishing, 2017-12-21) Leroy, C.; Schuster, J.K.; Schaefer, T.; Müller-Buschbaum, K.; Braunschweig, H.; Bryce, D.L.Beryllium-9 quadrupolar coupling and chemical shift tensor data are reported for bis(1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidine-2-ylidene)beryllium (Be(CAAC)2). These are the first such data for beryllium in a linear dicoordinate environment. TheItem Inverted P3HT:PC61BM organic solar cells incorporating a pi-extended squaraine dye with H- and/or J -aggregation.(Canadian Science Publishing, 2017-12-14) Dayneko, Sergey V.; Payne, Abby-Jo; Welch, Gregory C.In this report, we investigated the impact of adding a large pi-extended squaraine dye to the classic bulk heterojunction P3HT:PC61BM system. The compound SQIQ-A is a squaraine dye appended with acetylene-indoloquinoxaline end-capping units that exhibits strong optical absorption in the film from 650-750 nm, beyond the absorption wavelength cut-off for P3HT:PC61BM films (ca. ~650 nm). The dye SQIQ-A can form H or J-aggregates (blue or red shifting the optical absorption profiles) via solvent vapour annealing with CHCl3 or THF, respectively, thus providing a simple method to control the morphology and optical properties of the molecule. Ternary blended films comprised of a P3HT:PC61BM:SQIQ-A materials composition (1:1:0.3 mass ratio) were investigated as-cast, after solvent vapour annealing and after thermal annealing. Films were characterized using optical absorption spectroscopy, X-ray diffraction, atomic force microscopy, polarized light optical microscopy. Solar cells were fabricated using an inverted architecture in air and analysed using current-voltage and external quantum efficiency measurements. It was found that solar cells thermally annealed at 130째C for 10 minutes gave good power conversion efficiencies of 3%, like the control P3HT:PC61BM, but with improved fill factors and noticeable photo-current generation from 650-760 nm where the SQIQ-A molecule absorbs. Exposure to solvent vapour (CHCl3 or THF) results in aggregation of all components, but specifically lead to the formation of micron sized domains, lowering the overall photovoltaic performance.Item Investigation of the push-pull effects on β-functionalized zinc porphyrin coordinated to C60 donor-acceptor conjugates(Canadian Science Publishing, 2017-10-05) Thomas, Michael B.; Jinadasa, R.G. Waruna; Hu, Yi; Schmitz, Benjamin; Wang, Hong; D'Souza, FrancisTwo novel β-functionalized push-pull zinc porphyrins with amine or phenyl push groups and cyclic imide or carboxylic esters pull-groups have been newly synthesized for light energy harvesting applications. The ethynylphenyl spacers extended the conjugation of the porphyrin π-systems, as reflected by their red-shifted absorbance and fluorescence spectra. Computational studies performed at the B3LYP/6-31G* level indicated no steric hindrance between the porphyrin π-system and the substituents. The calculated HOMO and LUMO orbitals displayed significant delocalization in 1, where the electron density in the HOMO was localized over the push groups while the LUMO was extended over the porphyrin π- and pull groups. On the other hand, 2 did not display significant orbital segregation which is attributed to its weaker push-pull character. Electrochemical studies revealed smaller HOMO-LUMO gaps for the push-pull zinc porphyrins. As a consequence of the push-pull effects, reduction in fluorescence intensity and lifetime was observed. Femtosecond transient absorption spectral studies revealed successful formation of singlet excited state in both of the push-pull porphyrins. Donor-acceptor conjugates were subsequently built and characterized by coordinating an electron acceptor, C60Im, via metal-ligand axial coordination. Efficient photoinduced charge separation in both donor-acceptor conjugates was witnessed wherein the charge separated states persisted tens of nanoseconds prior returning to the ground state.Item Calculated antioxidant activity of selected Phenolic Compounds(Canadian Science Publishing, 2017-11-27) Cotes, Sandra; Cotuá, José; Muñoz, AmnerDetermination of the corresponding bond dissociation enthalpy, ionization potential and proton affinity, dipole moment values, highest occupied molecular orbital eigenvalues, and spin density along with the bioactivity score is central to the antioxidant activity evaluation in this paper. Molecular geometries were optimized with DFT using B3LYP and UB3LYP for parent, ionic, and radical species, and 6-311+G(d,p) basis set. Bioactivity, drug-likeness, and drug-scores were calculated using freely available cheminformatics programs for data visualization and analysis. Overall, the values revealed two structures as promising molecules because of good reaction enthalpies (â Hr). Lipinski rules were fully satisfied for all molecules.Item Submicron Probes for Scanning Electrochemical Microscopy(Canadian Science Publishing, 2017-11-23) Li, Michelle S. M.; Filice, Fraser Patrick; Ding, ZhifengTo improve the spatial resolutions of scanning electrochemical microscopy (SECM) imaging, the laser-pulled submicron electrode fabrication method was explored in this work. Manual polishing of a laser-pulled Pt nanoelectrode exposed a Pt tip diameter of 250 nm with a ratio of the tip glass to exposed Pt disc (RG) 30. This fabricated submicron probe was then utilized to study the electrochemical functionality of an independently addressable microband electrode (IAME) sample using SECM. In the constant imaging mode of SECM, where the probe is scanned linearly across the sample at a fixed z position, SECM demonstrated higher resolution than that of the conventional micrometer electrodes when the feedback currents from the Pt and glass microbands were characterized. In addition, the depth scan imaging mode of SECM was also used to extract experimental horizontal line scans and probe approach curves for analysis. 3D simulations of the IAME-SECM probe experiments were explored for the first time to quantify the tip-to-sample distances, tilt angle of the sample (or electrode) and height of the Pt microbands. The experimentally characterized height was found to be similar to manufacturer specification (125 nm vs 110 nm). Furthermore, the more computationally-demanding 3D simulation of the true IAME sample geometry (110 nm height of the Pt microbands) revealed minimal difference in feedback behaviors in comparison to the idealized flat geometry. The removal of this simulation complexity was proved to be sufficient for SECM analysis of the IAME sample by a 250 nm Pt probe, which saves greatly the computation resources.Item Molecular Structure and Melting: Implications for Phase Change Materials(Canadian Science Publishing, 2017-11-09) Noël, John A.; Kahwaji, Samer; White, Mary AnnePhase change materials (PCM) offer a promising technology for thermal energy storage, load leveling, and peak shifting applications. A desirable PCM has a melting temperature within the temperature boundaries of its application, and a high change in enthalpy on melting. Knowledge of the relationships between these thermodynamic properties and molecular structure would advance informed selection of PCM candidates for a given application. In the present investigation, the relationship between structure (length of alkyl chains) and properties has been investigated for isomeric esters, showing that esters containing longer individual alkyl chains have higher melting temperatures, and higher enthalpy changes on melting. The melting entropy changes, however, are relatively independent of the alkyl chain distribution.Item Nanoscale Thin Films of Niobium Oxide on Platinum Surfaces: Creating a Platform for Optimizing Material Composition and Electrochemical Stability(Canadian Science Publishing, 2017-12-11) Eastcott, Jennie; Parakh, Abhinav; Paul, Michael T.Y.; Lee, Austin W.H.; Bilton, Matthew W.; Gates, ByronA nanoscale thin film of niobium oxide on a platinum substrate was evaluated for its influence on the electronic and chemical properties of the underlying platinum towards the oxygen reduction reaction with applications to proton exchange membrane fuel cells. The nanoscale thin film of niobium oxide was deposited using atomic layer deposition onto the platinum substrate. A film of niobium oxide is a chemically stable and electronically insulating material that can be used to prevent corrosion and electrochemical degradation when layers are several nanometers thick. These layers can be insulating if sufficiently thick, and may not be sufficient to protect the platinum from corrosion if too thin. An ~3-nm thin film of niobium oxide was fabricated on the platinum surface to determine its influence on the electronic and chemical properties at the interface of these materials. The atomic layer deposition process enabled a precise control over the material composition, structure, and layer thickness. The niobium oxide film was evaluated using cyclic voltammetry and electrochemical impedance spectroscopy to evaluate whether a balance could be found between the inhibition of platinum degradation and electronic insulation of the platinum for use in proton exchange membrane fuel cells. The 3-nm thin niobium oxide film was found to be sufficiently thin to permit electronic conductivity while reducing the incidence of platinum dissolution.Item Synthesis of carotol using a formal (4 + 1)-cycloaddition of chiral dialkoxycarbenes(Canadian Science Publishing, 2017-11-10) Gund, Machhindra; Déry, Martin; Spino, ClaudeWe report formal intramolecular (4+1)-cycloadditions of dialkoxycarbenes used in the synthesis of the daucane-type sesquiterpene carotol. We found a chiral dialkoxycarbene capable of diastereoselective formation of a key oxabicyclo[3.3.0]octene adduct. Carotol was synthesized in 14 linear steps from simple starting materials.Item A divergent synthesis to generate targeted libraries of inhibitors for endo-N-acetylglucosaminidases.(Canadian Science Publishing, 2017-09-13) Seo, Isaac K; Woo, Esther H; Cecioni, Samy; Vocadlo, David JCell active inhibitors of glycoside processing enzymes are valuable research tools that aid understanding the physiological roles of this diverse class of enzymes. endo-N-Acetylglucosaminidases have emerged as playing important roles in both mammals and human pathogens, however, metabolically stable cell active inhibitors of these enzymes are lacking. Here we describe a divergent synthetic strategy involving elaboration of a thiazoline core scaffold. We illustrate the potential of this approach by using the copper catalysed azide-alkyne click (CuAAC) reaction, in combination with a suitable catalyst to avoid poisoning by the thiazoline moiety, to generate a targeted panel of candidate inhibitors of endo-N-Acetylglucosaminidases and chitinases.Item An Ethylene Glycol-Based New Sol-gel Route to Multiferroic (1-x)LaCrO3−xBiCrO3 Solid Solution(Canadian Science Publishing, 2017-11-06) Abbasi, Bahareh; Guo, Haiyan; Wu, Hua; Tailor, Hamel N.; Ye, Z.-G.Solid solution of multiferroic (1-x)LaCrO3â xBiCrO3 has been synthesized in the perovskite structure via a new sol-gel route using ethylene glycol as solvent. This synthetic process is proved to be superior to the solid state reaction method, with a lower formation temperature, improved reactivity and a higher solubility limit. The complex chemical reactions taking place in the sol and precursor powder upon heating are investigated by simultaneous thermal gravity and differential thermal analysis (TG/DTA). The substitution of BiCrO3 for LaCrO3 results in a higher density for the ceramics and an increased electric conductivity at high temperatures. The sol-gel synthesized La1-xBixCrO3 solid solution (with x=0.3) exhibits a superparaelectric behaviour with a slim and non-linear polarization - electric field hysteresis loop, while a double hysteresis loop of antiferroelectric appearance is displayed in the compound with x=0.4.Item An Improved Two-Rotor Function for Conformational Potential Energy Surfaces of 20 Amino Acid Diamides(Canadian Science Publishing, 2017-10-31) Villar, John Justine S.; Valdez, Adrian Roy L; Setiadi, David H.; Csizmadia, G. Imre; Viskolcz, Béla; Rágyanszki, AnitaPredicting the three-dimensional structure of a protein from its amino acid sequence requires a complete understanding of the molecular forces that influences the protein folding process. Each possible conformation has its corresponding potential energy, which characterizes its thermodynamic stability. This is needed to identify the primary intra- and intermolecular interactions, so that we can reduce the dimensionality of the problem, and create a relatively simple representation of the system. Investigating this problem using quantum chemical methods, albeit produces accurate results, this also entails large computational resources needed. In this study, an improved two-rotor potential energy function is proposed to represent the backbone interactions in amino acids, through a linear combination of a Fourier series and a mixture of Gaussian functions. This function is applied to approximate the 20 amino acid diamide Ramachandran-type PESs, and results yielded an average RMSE of 2.36 kJ路molItem Nitroimidazoles with a halogen-containing side-chain(Canadian Science Publishing, 2017-11-14) Baird, Ian R.; Patrick, Brian O.; Skov, Kirsten A; James, Brian R.Syntheses are reported for: nine 2-nitroimidazoles, the abbreviated names all beginning with E, based on derivation from Etanidazole); five 2-methyl-5-nitroimidazoles (M compounds, derived from Metronidazole); and five 2-methyl-4-nitroimidazoles (labelled 2M4N compounds). The nitroimidazoles all have an amide side-chain at the N1 atom of the imidazole, 17 of them containing one to five halogen atoms. The aim is to study compounds for comparison with EF5 (the number showing the presence of five F-atoms), a previously reported, pentafluoropropylacetamide derivative of 2-nitroimidazole that is currently used as a hypoxia marker drug to detect cancerous tumours. The new compounds are characterized by standard methods, including X-ray structural data for the fluorinated MF5, 2M4NF5, and 2M4NF1(-1) species, the â -1â indicating two C-atoms in an alkylamide chain rather than the three C-atoms in the propylacetamide of EF5. Intra- and inter-molecular H-bonding is seen in the solid state structures, likely an important property in biological use; another key property of the nitroimidazoles is their reduction potentials, and the measured CV data confirm that 2NO2Im compounds with longer side-chains and more F-atoms (like EF5) are worth investigating for possible activity as hypoxia-selective, bioreductive agents.