Chemistry - Doctoral Theses

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    Synthesis of novel cycloperoxides
    (University College Cork, 2023) Hennessy, Mary C.; O'Sullivan, Tim; Irish Research Council
    Cycloperoxides represent an important class of compounds for synthetic chemists. Their asymmetric synthesis will be the focus of this thesis, specifically using organocatalysis. Chapter 1 contains a review of organocatalysed peroxidations from the literature and within the research group to date. The key aims and objectives of this project are also outlined. Chapter 2 describes the generation of a diverse library of trans-γ,δ-unsaturated β-keto esters. The preparation of these compounds involves both Wittig chemistry and Lewis acid-catalysed C-H insertion strategies. The synthesis of a cis-γ,δ-unsaturated β-keto ester and a non-enolisable α,α-disubstituted β-keto ester are also outlined. The optimisation of the organocatalysed peroxidation of γ,δ-unsaturated β-keto esters in terms of enantioselectivity and yields is described in Chapter 3. To determine the enantioselectivity of the peroxidation reaction, a robust chiral HPLC methodology is required. The development of a suitable separation methodology is outlined in this chapter. Chapter 4 describes a novel synthetic route to 3,5-substituted 1,2-dioxolane ethyl esters through the chemoselective reduction of a δ-peroxy-β-keto ester to the corresponding δ-peroxy-β-hydroxy ester, and subsequent phosphorus pentoxide-mediated cyclisation. Chapter 5 outlines our preparation of several novel 1,2-dioxolane carboxylic acids and various attempts at subsequently introducing an N-acyl sulfonamide to the 1,2-dioxolane core. Chapter 6 details the main conclusions of this work and proposes several avenues of research to investigate in future. Chapter 7 contains all relevant experimental procedures, including spectroscopic and analytical data.
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    Electrodeposited macroporous vanadium oxide Li-ion battery materials
    (University College Cork, 2022) O'Hanlon, Sally; O'Dwyer, Colm; Science Foundation Ireland
    Enhanced battery materials are an important area of research due to the broad range of applications and the need for high capacity and high cycling stability batteries for enable the future electric vehicles and consumer electronics. This work reports on the electrodeposition of 3D macroporous vanadium oxide inverse opals and binary inverse opals on transparent conducting oxide substrates and stainless steel and thermally oxidized stainless-steel substrates. The electrodeposition follows a diffusion limited growth mode to form 3D porous crystalline V2O5 after removal of a colloid photonic crystal template of self-assembled polystyrene spheres. We show that at high charge and discharge rates, charge storage in macroporous electrode materials can be completely suppressed, and then entirely recovered at low rates. Using a model system of inverse opal V2O5 in a flooded Li-battery three-electrode cell electrodes we show how the IO material is modified under lithiation using X-ray diffraction, Raman scattering and electron microscopy. The data show that electrodes with nanoscale dimensions and macroscale porosity are fundamentally limited for high-rate performance if the intrinsic electronic conductivity is poor, even when fully soaked with electrolyte. We also show that conductive additive-impregnated polylactic acid electrodes formed by 3D printing can be coated with V2O5 by electrodeposition. The surface coating was analysed using Raman scattering spectroscopy, X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy, and details the relationship between diffusion-controlled electrodeposition parameters and the quality of the deposit on the 3D printed PLA electrode.
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    Cocrystallization of organic compounds
    (University College Cork, 2023) Huang, Shan; Lawrence, Simon; Science Foundation Ireland
    This thesis discusses the synthesis, characterization, and properties of multi-component crystalline materials of active pharmaceutical ingredients. A special emphasis is placed on cocrystallization, which is the supramolecular phenomenon of aggregation of two or more different chemical entities in a crystalline lattice through non-covalent interactions. This research has been divided into seven chapters. Chapter 1 gives an overview of the concept of multi-component crystalline materials and cocrystallization, where the design, methodology, characterization and application of cocrystals are also included. Chapter 2 discusses the synthesis of multi-component crystal forms of a sulfonamide compound, sulfasalazine, through cocrystallization and explores the crystal structure landscape of sulfasalazine. Furthermore, the differences are illustrated between cocrystals and salts of sulfasalazine via structural analysis, Hirshfeld surface analysis and frontier molecular orbitals analysis. Chapter 3 investigates the hydrogen bonding interactions in cocrystals of a frequently used sulfonamide compound, sulfaguanidine, by both experimental methods and theoretical calculations including the analysis of Hirshfeld surface, molecular electrostatic potential surfaces and quantum theory of atoms in molecules. Chapter 4 focuses on pharmaceutical salts of piroxicam and meloxicam with three basic organic counterions, respectively. The solubility of six salts and two parent drugs in sodium phosphate solution were conducted. Furthermore, piroxicam and its salts exhibited different luminescent properties, thus, the different luminescent mechanisms were discussed. Chapter 5 explores cocrystallization of 19 natural L-amino acids and both enantiomers of four pharmaceutically relevant chiral compounds. The formation of diastereomeric or enantiospecific systems were explored using an examination of their hydrogen bonding motifs. Chapter 6 investigates the formation of diastereomeric cocrystal pairs of S mandelamide with both enantiomers of mandelic acid and proline, respectively. In addition, the crystal structures of (±)-mandelamide, S-mandelamide and enantio-enriched mandelamide (94 S:6 R) were determined. Detailed crystal structural analyses together with Hirshfeld surface analysis were carried out. Chapter 7 summarizes the main findings of the entire work and examines future work, such as the use of ternary phase diagrams to assist in developing chiral separation processes.
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    Development of silica materials of different particle and pore morphology for the application in cannabinoid research and in separation of biomolecules by HPLC
    (University College Cork, 2023) Analakkattillam, Sandhyarani; Moore, Eric; Hanrahan, John P.; Irish Research Council for Science, Engineering and Technology
    Currently, pharmaceutical companies have focused their development to large molecule biotherapeutics for the treatment of diseases such as cancer and neurodegenerative diseases. These new protein biopharmaceuticals have large molecular weights and have intricate structures. The complexity of these biopharmaceuticals requires new analysis methodology as compared to those of small molecule drugs. To enable this characterization, new liquid chromatographic stationary phase particle technologies are required. In this project, we developed novel large pore (≥ 1000 Å) and non-porous silica based stationary phases for the separation of biomolecules such as proteins. Both fully porous and superficially porous silica materials were utilized in an alkali hydrothermal pore expansion process. The experimental conditions were optimised for type and concentration of mineralising agent and the treatment temperature. The selection of mineralising agent and the treatment temperature depends on the particle and pore size of silica precursor molecule and the optimum concentration was found to be 0.5% w/v. These silica materials were subsequently chemically bonded with monofunctional alkyl ligands of different chain lengths under optimised reflux conditions. These materials were then packed into stainless steel columns of varying column dimensions and subjected to performance evaluation studies using in-house as well as Tanaka and Walters test methods. The suitability of these silica materials in biomolecular separation was tested using a test mixture containing six proteins of molecular weight ranging from 12 to 97 kDa. The non-porous stationary phases 2 µm C18 columns shows the ability to separate all the protein molecules with lower recovery for larger proteins. Both fully porous and superficially porous ultra-wide pore stationary phases of short and longer alkyl groups (C4, C8 and C18) displayed the ability to separate proteins where the superficially porous materials leads faster separation with low column backpressure. Moreover, the C8 stationary phases achieved to recover the larger proteins as compared to C18 and C4 stationary phases. The use of amorphous silica as drug carrier system in cannabinoid research was also studied. The main focus was made on two cannabinoids namely cannabidiol (CBD) and tetrahydrocannabinol (THC). Hemp Oil Supplements-mainly CBD rich products-have grown in popularity worldwide and have received much positive (due to non-psychoactive CBD) and negative press (because of psychoactive THC), however little is known about the actual strength of CBD and THC in these products. This demands a uniform method to quantify CBD and THC in these products. Hence, a simple and reliable assay test method was developed and validated simultaneous determination of CBD and THC in hemp oil products by high performance liquid chromatography. The assay test method was validated as per International council for harmonisation quality guidelines allowing hemp oil/CBD manufactures to utilize this method for quality control checks for their products. Moreover, for the first time in-vitro dissolution studies were conducted to quantify the CBD release in hemp oil products. Additionally, for the first time stability studies were conducted for quantifying CBD in hemp oil and hemp oil infused silica materials to identify the correct storage and labelling conditions to be followed while handling hemp oil products in market.
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    The understanding, control, and application of polycrystalline compound semiconductor thin films
    (University College Cork, 2023) Curran, Anya; Gity, Farzan; Hurley, Paul K.; O'Dwyer, Colm; Irish Research Council
    In this thesis, low-temperature grown polycrystalline III-V materials are investigated for their potential as channel materials for devices located in the back-end-of-line (BEOL) of integrated circuits. The key aims of this thesis are to demonstrate high carrier mobility III-V materials grown at low temperatures on silicon/amorphous substrates, and to fabricate functional transistor devices using these polycrystalline/amorphous III-V films as channel materials. There are very few reports of low temperature grown polycrystalline III-V materials available in the literature and so this thesis is well placed to add substantial knowledge to the field. Both an n-type (InAs) and a p-type (GaSb) material are investigated. The poly III-V films are grown on Si/SiO2, glass, or Semi-Insulating (SI) GaAs substrates. For the intended implementation in the BEOL, it is necessary to stick to a restrained thermal budget, with maximum temperatures generally being <500◦C. Growth of III-V materials on silicon substrates is an important step towards their integration with silicon-based electronics. Growth at these reduced temperatures and on amorphous substrates such as SiO2 are large challenges to overcome while maintaining a reasonable carrier mobility. It is also important to develop n- and p-type options so that these materials can be implemented in low-power Complementary Metal Oxide Semiconductor (CMOS) type architectures. Material properties of the films as grown are explored through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) and Cross-sectional Transmission Electron Microscopy (XTEM), and Hall Effect measurements. The Hall Effect measurements indicate that both of these materials have high carrier concentrations independent of intentional doping or a high-temperature dopant activation step and display high carrier mobilities despite their polycrystalline or amorphous nature. Electron mobility values in polycrystalline InAs are found to be 100 cm2/Vs at room temperature for InAs grown directly on a glass substrate, and values reaching 155 cm2/Vs for a heterostructure including the polycrystalline InAs film. Hole mobilities in the polycrystalline GaSb films are found to be up to 66 cm2/Vs for a film grown directly on SiO2 and 299 cm2/Vs for a film grown directly on SI GaAs. An amorphous GaSb layer which is part of a heterostructure on SiO2 is found to have a hole mobility of 9.1 cm2/Vs. These results are compared against those found in the literature and found to exceed many, while being competitive with those that are grown at higher temperatures, on crystalline substrates, or to greater thicknesses. All of these are self-imposed limits to keep the material growth suitable for devices in the BEOL, so to be competitive with mobilities obtained without these limitations is a very important and positive result. Development of both n- and p-type semiconductor options is a vital component of this field of research and the p-type mobilities reported in this thesis compare particularly well with those reported in the literature. Junctionless transistor devices are fabricated, with full processing steps described. Both n- and p-type functional devices are demonstrated, and analysis of the device characteristics is performed to determine limiting factors and mechanisms at play. Analysis is performed on the devices at different stages of the device processing to understand the effect on the semiconducting material. The highest ION/IOFF values are achieved at -50◦C for both types of devices, with 104 achieved for n-type devices, and 550 achieved for p-type devices. These results are compared against those found in the literature. Recommendations for future implementation of these materials into high-performance devices are made based on the results generated in this thesis. This includes the recommendation to grow thicker films and develop a Chemical Mechanical Polishing (CMP) process to thin them back down, ideally creating a thinner yet more continuous film, and to conduct some systematic studies of the gate stack process for the transistor devices. Low-temperature grown polycrystalline and amorphous materials show great potential as high carrier mobility materials which can be implemented into silicon-based electronics in the BEOL where a low thermal budget is required for device processing.