Department of Chemistry (Fredericton)

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1,2-asymmetric induction in carbonyl compounds: a computational study
1,2-asymmetric induction in carbonyl compounds: a computational study
by Jeffrey Retallick, In asymmetric synthesis, it is important to reliably predict the major stereoisomeric product of a reaction. One such reaction is the nucleophilic addition to a carbonyl compound featuring an adjacent chiral carbon. Several reaction models exist in literature to predict the facial selectivity of these reactions. These models provide simple visual drawings to quickly predict the major product of such a reaction without requiring exhaustive quantum mechanical calculations. These models are used on a daily basis, and some models perform better than others, making it valuable to investigate which ones are the most effective. For the first time in this thesis, high-level computations have been performed on all of the literature models to verify their efficacy. The results of this thesis offers a definitive answer that the Felkin-Anh and Wintner models are the most effective, and that bent bond theory offers an interesting insight on the mechanics of these reactions., Electronic Only.
A hyperfine analysis of the [4th power]Π–X[4th power]Σˉ transition of rhenium monocarbide
A hyperfine analysis of the [4th power]Π–X[4th power]Σˉ transition of rhenium monocarbide
by Ryan Hall, In this thesis, the first spectroscopic study of rhenium monocarbide, ReC, is presented. ReC molecules were produced via a supersonic molecular jet apparatus. The ReC spectrum was studied utilizing both high and low-resolution spectroscopic techniques, including laser induced fluorescence (LIF) and dispersed fluorescence (DF). The low-resolution survey scan was performed and four bands from this system were identified, and studied using high-resolution. This clearly revealed the [superscript 187]ReC and [superscript 185]ReC isotopologues, and extensive hyperfine structure, which resulted in a complex spectrum. This experimental data appears to be consistent with a [4th power]Π–X[4th power]Σˉ transition, which agrees with Dr. Grein’s [1] calculations. A program has been written using the Hamiltonian matrix for a [4th power]Π–X[4th power]Σˉ transition, as reported in the literature [2]. After performing a fit using assigned transitions in our spectrum, molecular constants were extracted to describe the molecular system. Dispersed fluorescence spectra were used to extract vibrational information.
A positively charged, diffusion resistant, bispyridinylidene derivative as an anolyte for organic redox flow batteries
A positively charged, diffusion resistant, bispyridinylidene derivative as an anolyte for organic redox flow batteries
by Hillary Wheeler, Redox flow batteries represent a leading technology for large scale energy storage, which is necessary as the use of renewable energy becomes more important. Organic redox flow batteries are a new class of redox flow batteries that have the potential to provide higher cell voltages and improved energy densities. Organic materials with high redox potentials are suitable for applications as cathode materials and are readily available. Research in our group has focused on developing anode materials, which are much less common. Previously, the Dyker group has evaluated non-flowing cells with bispyridinylidene as an anolyte material and TEMPO as a catholyte material separated by an anion exchange membrane (AEM). Cyclic voltammetry (CV) studies showed that the battery degrades due to diffusion of the neutral active materials across the AEM. This thesis describes the preparation and evaluation of a new anolyte couple which lessened the problem of diffusion through the anion exchange membrane owing to the permanent positive charge in both charged and discharged states. Cells exhibited high coulombic, voltage, and energy efficiencies, though also exhibited a drop in capacity after the first charge, thought to perhaps be associated with the impurity present in the electrolyte or crossover of catholyte materials. In order to determine the relative diffusion rates, cells were assembled with active material on one side of the cell and blank electrolyte on the other side. These cells were left to allow for possible diffusion after which CV was carried out on the disassembled cell to determine the extent of active material diffusion. These results led to the belief that the amount of positive charge affects the extent to which the species cross the AEM. Therefore, as a tetracation / dication redox couple, the new anolyte was successful in reducing the amount of active material diffusion across the AEM.
Capture of sulfur dioxide using sulfur oxydianions: synthesis and characterization of two novel compounds
Capture of sulfur dioxide using sulfur oxydianions: synthesis and characterization of two novel compounds
by Stephanie Richardson, One mole equivalent of SO2 reversibly reacts with [N(CH3)4]2SO4(s) to give [N(CH3)4]2S2O6(s) (1) containing the [O3SOSO2]2- ion, shown by Raman and IR to be an isomer of the [O3SSO3]2- dianion. The experimental and calculated (B3PW91/6-311+G(3df)) vibrational spectra are in excellent agreement and the IR spectrum is similar to that of the isoelectronic O3ClOClO2. Crystals of [N(CH3)4]2(O2SO)2SO2•SO2 were isolated from a solution of [N(CH3)4]2SO4 in liquid SO2. The X-ray structure showed that it contained the [(O2SO)2SO2]2- dianion (2). The characterized N(CH3)4 + salts 1 and 2 are the first two members of the (SO4)(SO2)x 2- sulfur oxydianions analogous to the well-known small cation salts of the SO4(SO3)x 2- polysulfates., (UNB thesis number) Thesis 9245. (OCoLC)924148057. Electronic only., M.Sc. University of New Brunswick, Department of Chemistry, 2013.
Carbon-based polymeric materials for stretchable supercapacitors
Carbon-based polymeric materials for stretchable supercapacitors
by Mariusz Radtke, The urgent need for the development of efficient and environmentally-friendly energy storage devices has led to the exploration of new materials with chemically tailored properties. More specifically, the field of super- and ultracapacitors is currently moving forward to incorporate carefully modified carbon allotropes in the modern capacitor design. The main goal for previous research in designing capacitive materials has been to maximize their efficiency, without sacrificing environmental safety. This thesis presents a preparation of highly stretchable and heavy-metal-free electrodes based on polyacrylamide/ poly (N, N’- methylenebis(acrylamide)) hydrogels, which contained nanostructured carbons (e.g., graphene, multi-walled carbon nanotubes; MWCNTs, single-walled carbon nanohorns; SWCNHs) covalently bonded to conjugated polymer (polypyrrole; PPy). Carbon cores provided a large electrochemical double layer capacitance, whereas a conjugated polymer was the source of pseudocapacitance. The approach of joining two capacitance mechanisms within one molecule was completed by utilizing nanostructured carbons as polymerization initiators, while the pyrrole or 2-(1H-pyrrol-1-yl) ethyl methacrylate were used as monomers. Polymers were uniformly distributed around the carbon cores via oxidative radical polymerization, electrochemically aided atom transfer polymerization (e-ATRP), and reversible addition-fragmentation chain transfer polymerization (RAFT). The highest specific gravimetric capacitance of active nanocomposite was 456.86 F g[superscript -1], and was found to be highly dependent on the nature of the operating electrolyte. The detailed mechanistic computations, electrochemical quartz microbalance, and electrochemical studies have revealed that potassium chloride is the most suitable electrolyte for maximizing the electrochemical output of obtained nanocomposites. A series of stretchable (up to 1475 %) electrodes were prepared with emphasis on their conductivity, elasticity, and translucent properties. The task of dispersion of nanocomposites within the solid-state electrolyte, based on pAAm/pMBAA hydrogels containing KCl, was addressed by enhancing the zeta potential of active materials through the incorporation of perfluorated long aliphatic molecules (i.e., Nafion 117®). Electrochemical analysis by alternating the current electrochemical admittance spectroscopy, cyclic voltammetry, and the theoretical modeling of an equivalent circuit based on impedance spectroscopy have revealed a large interfacial specific gravimetric capacitance of the stretchable electrodes (up to 516.86 F g[superscript -1]). Prepared materials are stable up to 7500 charge/discharge cycles in liquid electrolytes and up to 717 cycles in hydrogels. Obtained products are market-grade materials for modern supercapacitors.
Cost efficient, scalable asymmetric synthesis of bronze birch borer kairomone (5s,7s)-7-Methyl-1,6-dioxaspiro[4.5]decane
Cost efficient, scalable asymmetric synthesis of bronze birch borer kairomone (5s,7s)-7-Methyl-1,6-dioxaspiro[4.5]decane
by Graham Andrew Atwood, With the increased use of birch trees, specifically non-native birches in parks, and beautification projects, an increase of infestations by the bronze birch borer (Agrilus anxius) has occurred. While reactive measures are available to try to remediate infested trees, a proactive strategy is not as widely available. (5S,7S)-7-Methyl-1,6-dioxaspiro[4.5]decane (5S,7S-conophthorin) has been identified as a possible kairomone that attracts bronze birch borers to susceptible trees. These susceptible trees include Eurasian varieties and stressed native North American species. While synthesized in the past, a scalable, cost efficient synthesis of this kairomone will likely enable its production industrially, and help allow for mass detection/trapping strategies of the pest to be implemented before infestations occur.
Detecting spoilage of tomatoes by ultrasound spectroscopy
Detecting spoilage of tomatoes by ultrasound spectroscopy
by Alison Kathleen Power, Food spoilage caused by bacterial or fungal contamination can lead to cases of food poisoning and even death. Current techniques for spoilage detection cannot routinely measure packaged products. We present how ultrasound spectroscopy can be used to classify spoiled and non-spoiled samples of tomato juice. Spoilage was induced with a bacterium (Lactobacillus rhamnosus) and mold (Geotrichum candidum) commonly found in spoiled tomatoes and samples analyzed using ultrasound spectroscopy. Frequency profiles of the inoculated samples showed changes with spoilage when compared to control samples. Cross-validated multivariate models separated fresh and spoiled samples with 100% accuracy. A global model was created using the combined inoculation data resulting in a sensitivity and specificity each of 94% with an independent validation set resulting in 100% accuracy of separation. Overall, ultrasound spectroscopy shows promise in the detection of food spoilage. The potential for measuring food samples non-invasively could benefit both the food industry and consumers.
Developing new supramolecular tools for biomedical and environmental applications
Developing new supramolecular tools for biomedical and environmental applications
by Christopher Jennings, Supramolecular chemistry has quickly developed from simple host-guest chemistry to the self-assembly of molecular building blocks to form large aggregates, both in solution and the solid state. Currently, supramolecular structures are being developed for several applications, including gas storage technologies, heterogeneous catalysis, chemical sensors and drug delivery systems. Among these structures are metal-organic frameworks (MOFs), metal-organic polyhedra (MOPs) and vesicles. Here, we assess the ability of MOFs to remove cholesterol from the bloodstream. A diverse series of MOFs were first selected from the literature and then synthesised, characterised and their ability to uptake cholesterol quantified by liquid phase ¹H NMR analysis. Further work was undertaken where different methodologies to encapsulate MOF particles within a vesicle - a lipid bilayer cell model - were explored. This process is designed to improve the biostability and bioavailability of the MOF candidates in their role as cholesterol-removal agents. This study led to the serendipitous finding that micron-sized MOF particles can be used to immobilise vesicles, which may provide an alternative strategy to the study of their biophysical and mechanical properties. Finally, two novel, fluorine-rich MOPs have been designed for the selective uptake of chlorofluorocarbons (CFCs), and for eventual use within the environmental chemistry domain. The molecular building blocks that comprise these MOPs have been synthesised and characterised, and the final steps of MOP synthesis and characterisation are currently ongoing.
Development of electrochemical biosensors for the direct detection of infectious disease
Development of electrochemical biosensors for the direct detection of infectious disease
by Connor Flynn, Infectious disease detection is an extremely important field, as clinicians and scientists around the world continue to seek improved diagnostics. Electrochemical biosensors represent an emerging class of diagnostic techniques that are rapid, inexpensive, and easily scalable. By combining the intricate interactions of biological molecules with the sensitive techniques of electrochemistry, these biosensors hold great promise in the future of infectious disease sensing. The current thesis explores the development of two such devices, for Lyme disease and hepatitis B, by describing their design, assembly, and effectiveness. The Lyme sensor exploits a known protein-protein interaction between bacterial and human cells to produce a biomimetic sensor capable of binding individual bacteria. This biosensor proves effective at capturing the Lyme bacteria and producing a significant electrochemical response. Likewise, the hepatitis B sensor employs highly specialized surface chemistry to detect hepatitis-specific antigens. Through the development of these sensors, we hope to provide insight into potential devices that can combat these dangerous diseases.
Improving Bispyridinylidene-based organic reducing agents by increasing solubility and reductant strength
Improving Bispyridinylidene-based organic reducing agents by increasing solubility and reductant strength
by Nadine M. Arseneault, Recently, a tetrasubstituted bispyridinylidene (BPY) featuring methyl groups on the pyridyl nitrogens and four triphenyliminophosphorano groups at the para and ortho positions of the pyridine rings was reported. This compound is a powerful electron donor but isolated only in low yield because of low solubility. One goal of this work was to improve solubility and isolated yield by modification of the N-alkyl substituents. An N-propyl derivative was synthesized, as evidenced by [superscript 31]P NMR spectroscopy; however, this BPY derivative could not be isolated. The reduction potential, determined by cyclic voltammetry of the oxidized BPY, was -1.67 V vs SCE, which is a slight decrease in reduction strength compared to the N-methyl derivative (-1.70 V vs SCE). Because of challenges in isolating the compound, it was concluded that the N-propyl derivative gave no benefits over the N-methyl derivative. In order to develop new BPYs with increased reductive strength, the four triphenyliminophosphorano groups of the tetrasubstituted BPY were systematically changed to tricyclohexyliminophosphorano groups in pairs. Tricyclohexyliminophosphorano groups are stronger π-donors than triphenyliminophosphorano groups as shown by their Hammett constants (σ[subscript p][superscript +]) of -1.82 and -2.21, respectively. The primary target was a BPY featuring four tricyclohexyliminophosphorano groups, which was prepared in four steps, and characterized by [superscript 31]P, [superscript 1]H, [superscript 13]C and ROESY 2D NMR spectroscopy as well as cyclic voltammetry. Cyclic voltammetry showed a reduction potential of -1.87 V vs SCE, which surpasses the tetrasubstituted triphenyliminophosphorano BPY derivative in reductive strength by 170 mV vs SCE, and makes the new compound the most powerful neutral organic electron donor ever reported. In addition, a BPY featuring triphenyliminophosphorano groups at the two para positions and tricyclohexyliminophosphorano groups at the two ortho positions was prepared in situ as evidenced by [superscript 31]P NMR spectroscopy; however, was not isolated. Cyclic voltammetry analysis is pending, therefore reductive strength is unknown, but should fall between tetrakis(triphenyliminophosphorano) BPY and the tetrakis(tricyclohexyliminophosphorano) BPY. Lastly, the pyridinium salt precursor to the other targeted BPY, featuring two tricyclohexyliminophosphorano groups at the para positions and two triphenyliminophosphorano groups at the ortho positions, respectively, was prepared as evidenced by [superscript 31]P and [superscript 1]H NMR spectroscopy. Unfortunately, this compound could not be completely purified and the preparation of the new BPY remains to be done.
Intramolecular [4+2] cycloaddition reactions :
Intramolecular [4+2] cycloaddition reactions :
by Narjs Moslem Alnakhli, Natural products have contributed to health care and prevention of diseases for thousands of years. One family of bioactive compounds that is of particular interest to the MaGee group is the manzamine alkaloids and their derivatives. During their studies on the synthesis of the ABC-tricyclic core targeted for manzamine A and B, an intramolecular Diels-Alder reaction was used that resulted in a 25:1 ratio of endo to exo selectivity. This contrasted other results where a similar substrate resulted in a 2:1 ratio of endo to exo stereoisomers. Therefore a study was initiated to look at the influence of the ring size, where the dienonphile is contained, on endo/exo ratio’s in the intramolecular Diels-Alder reaction. The intramolecular Diels-Alder reaction was examined where the dienophile was embedded in 5, 7, 9 and 11-membered C-rings. While the 5- and 7-membered keto-acids were known compounds, synthetic routes had to be designed to make the other homologues. Once these were made and coupled with dieneamine, it was discovered that depending on ring size different endo/exo ratio’s were obtained. The five and sevenmembered C-rings produced a ratio of 2:1 endo:exo, in contrast to the nine-membered C-ring, which produced an 18:1 endo:exo. The eleven-membered C-ring produced a ratio of only 5.4:1 endo:exo. Although the exact reasons for the differences are not completely known, it is clear that the conformational flexibility of the rings plays a major role., Electronic Only., M.Sc. University of New Brunswick, Department of Chemistry, 2016.
Investigating the use of a thioketene methodology for heterocyclic ring formation
Investigating the use of a thioketene methodology for heterocyclic ring formation
by Fayza A. Aljohany, Thioamides are important and useful functional groups in organic synthesis, especially as building blocks for the construction of compounds containing N and S that possess pharmacological properties. A convenient and general method for the preparation of thiolactams using a thioketene strategy as an alternative route for heterocyclic formation has been examined. Amino-alkynes, which were easily synthesized in two steps, acted as bifunctional substrates for intramolecular reactions. Thioketenes were generated at low temperature by protonation, silylation or alkylation of amino-alkynyl thiolates. The in situ generated thioketenes were then trapped with different amines through intramolecular reactions to produce thiolactams in various yields. This is the first report of the intramolecular trapping of thioketenes with amines to produce thiolactams., Electronic Only., M.Sc. University of New Brunswick, Department of Chemistry, 2017.

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