Masters Degrees (Chemistry and Polymer Science)
Permanent URI for this collection
Browse
Recent Submissions
Now showing 1 - 5 of 345
- ItemGuest inclusion in porous metal-organic crystals and high-pressure single-crystal X-ray diffraction analysis at low temperatures(Stellenbosch : Stellenbosch University, 2024-03) Kutama, Aluwani; Barbour, Leonard James; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Porous metal-organic materials are an intriguing class of compounds that are capable of adsorbing guest molecules, such as gases, into their cavities. This ability of these materials has stimulated research across various domains, including purification, gas storage, separation, and drug delivery. In this study, we analyzed two well-known porous metal-organic compounds namely, [Zn2(L1)(OBA)2] and [Cu2(L2)2(Cl)4]. The metal-organic framework (MOF), [Zn2(L1)(OBA)2], was successfully synthesized and fully characterized in preparation for gas sorption studies. This characterization included single crystal Xray diffraction (SCXRD), thermogravimetric analysis (TGA), and Fourier-transform infrared (FT-IR) spectroscopy. Gas sorption studies were thereafter carried out using volumetric sorption analysis and pressure-ramped differential scanning calorimetry (P-DSC) up to 50 bar using CO2 and C2H4. The sorption profiles with CO2 indicated the presence of shape memory, while the sorption profiles with C2H4 were indicative of Type 1 isotherms. In addition, the metallocycle [Cu2(L2)2(Cl)4], was synthesized using a layering methodology that required the use of three solvents (namely EtOAc, DMF and EtOH), and further studies revealed that EtOAc was the solvent that was included in the crystal structure and hence responsible for the structural channel formation. The characterization of [Cu2(L2)2(Cl)4] involved using powder X-ray diffraction, SCXRD, TGA, FT-IR, and thereafter the activated crystals were pressurized up to 20 bar with CO2 and characterized using, gravimetric sorption analysis and P-DSC. In this work a novel method for obtaining high-pressure SCXRD data at low temperatures is also described for the first time and utilized primarily to reduce the thermal motion of the included guest molecules for structural modelling purposes. This was carried out with CO2 (20 bar) and Xe (10 bar). The results revealed acceptable molecular geometrical parameters for the included CO2 guest molecule, and that the cavity of [Cu2(L2)2(Cl)4] increased in volume to accommodate the large Xe molecule, indicating the flexible nature of this metallocycle.
- ItemExpansion of a porous organic molecular material induced by gas pressure(Stellenbosch : Stellenbosch University, 2024-03) Mathada, Gundo; Barbour, Leonard James; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The interplay between external stimuli and the structural properties of crystalline materials holds immerse potential for the design of novel functional materials. In this study, the intriguing phenomenon of reversible elongation of an organic crystal in response to gas pressure (carbon dioxide and ethylene) was investigated. Through a comprehensive experimental approach combining series in situ crystallography, gas sorption isotherm measurements, and photomicroscopy, we elucidate the molecular-level mechanisms underlying this behaviour. The findings of this study reveal that gas molecules infiltrate the intricate 0D cavities within the crystal lattice, prompting subtle adjustments in molecular arrangement to accommodate the guest species. The molecular rearrangement (with no phase changes), manifested as an elongation of the crystallographic c axis, is observed across varying gas pressures and molecular environments. Notably, the empirical modelling of gas-induced elongation using the Sips equation provides valuable insights into the relationship between gas pressure and crystal expansion. The in-house instruments were utilized throughout this study to investigate the observed phenomena in the crystals
- ItemPro–apoptotic iron oxide nanosystems as selective anti – TB drugs(Stellenbosch : Stellenbosch University, 2024-03) Jaffer, Shaakirah; Malgas-Enus, Rehana; Mavumengwana, Vuyo; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Tuberculosis (TB) is reportedly the biggest airborne disease, after covid-19, and amongst the top 10 causes of death worldwide. The disease is mainly prevalent in low- and middle-income countries and has financial and social impacts that negatively affect development in these countries. Consequently, addressing the implications of this disease is highly important. According to the World Health Organization (WHO), approximately a third of the world’s population is infected with TB. TB is transmitted by inhaling a droplet of Mycobacterium tuberculosis (M. tuberculosis), it remains within the body as its latent form. However, it takes a weak immune system to activate the latent form to become active TB. With current treatments showing a moderate to high success rate, the duration of treatment which causes toxicity, and drug resistance are issues that are faced TB treatment. Treatment spans between 6 to 24 months depending on case severity, with accompanying acute side effects. Therefore, the purpose of this study was to investigate functionalized iron oxide nanoparticles and their efficacy as antimycobacterial agents. The synthesized bare iron oxide nanoparticles include magnetite (Fe3O4), ferrous oxide (FeO) and ferric oxide (Fe2O3) nanoparticles and were modified using compounds that are known to activate apoptosis including, 1,3,5-triaza-7-phosphaadamantane (PTA), 3,3′,3″-phosphanetriyltris (benzenesulfonic acid) trisodium salt (TPPTS), 9-β-D-arabinofuranosyl guanine hydrate (ara-g hydrate), 2,3-diphenylbenzo[g]quinoxaline-5,10-dione (DPBQ) and 4,5,6,7- tetrahydro-5,5,7,7-tetramethyl-2-[[(5-nitro-2-thienyl) carbonyl]amino]-thieno[2,3-c]pyridine-3- carboxylic acid ethyl ester (NPC -26). Characterization techniques included, fourier transform infrared spectroscopy (FT–IR), ultraviolet – visible spectroscopy (UV-Vis) and high-resolution transmission electron microscopy (HR-TEM) on the synthesized and modified nanoparticles. The selected bare nanoparticles and modified nanoparticles were tested for antimycobacterial activity against Mycobacterium smegmatis (M. smegmatis), frequently used to emulate M. tuberculosis due to its non-infectious attributes. Interestingly, both the bare and modified nanoparticles noticeably promoted growth of M. smegmatis in a dose dependent manner at all concentrations tested ranging from 250 to 1,95 µg/mL. A rapid uptake effect on iron oxide nanoparticles by M. smegmatis caused an exponential increase in bacterial growth, indicating that the bacterium itself was able to metabolize both the bare and modified nanoparticles synthesized in this study. The dose dependant results indicated a notable affinity of mycobacteria for the bare iron oxide nanoparticles, suggesting a high binding capability and implicating a potential role of iron acquisition mechanisms in the pathogenesis or survival strategies of mycobacteria. The iron oxide nano system that piqued interest was magnetite + NPC-26 which showed a degree of potential at the lowest concentration of 1,95 µg/mL. The dosage effect of this concentration showed a more progressive growth curve showing inhibition of the bacterial growth over the 5-day test period. Thus, the cells uptake of the magnetite was due to an affinity for iron and the NPC-26 inhibiting cell growth to some extent. The study set out to synthesize three variations of iron oxide nanoparticles with the intent to capitalize on the distinctive properties of iron oxide nanoparticles to allow for precise drug delivery to the site of infection. Further modifying the nanoparticles with apoptotic-inducing drugs to enhance the efficacy of treatment by promoting programmed cell death in infected cells and accelerating the clearance of the pathogen. The utilization of magnetite loaded with NPC-26 demonstrated a noteworthy inhibitory effect on the growth of mycobacteria, as indicated by the dosage effect experimental results. Therefore, the utilization of the iron oxide nanoparticles modified with apoptotic-inducing abilities may have significant promise as a novel and targeted approach for the treatment of tuberculosis.
- ItemInvestigating mechanical responses to structural changes in crystalline materials(Stellenbosch : Stellenbosch University, 2023-11) van Rijn, Raymond Michael; Barbour, Leonard James; Loots, Leigh-Anne; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Previous work has established that the compound 2,7-dimethylocta-3,5-diyne-2,7-diol crystallizes to produce a range of inclusion compounds – the crystals of which exhibit elastic flexibility. In an attempt to tailor the Young’s modulus of the system, substitution of guest species, using both polar and apolar compounds, was carried out. Ultimately, little difference in elasticity was observed, regardless of the included guest species. Analysis of crystal structures revealed that little interaction takes place between guest molecules, or between host and guest. Thus, hydrogen bonding in the host framework is concluded to be the determining factor in crystal flexibility. Several other elastically flexible crystals were subsequently investigated to determine how their elastic moduli would change when temperature was varied. A relationship was identified between the change in elasticity and thermal expansion of the crystals. As the bending axis of a crystal expands in length, the Young’s modulus decreases. Thus, for crystals exhibiting positive thermal expansion, elasticity is reduced as temperature is decreased. Conversely, for a material displaying negative thermal expansion, decrease in temperature was found to produce an increase in elasticity. Greater intermolecular spacing likely allows for a greater degree of molecular reorientation that must occur to facilitate mechanical bending of crystals. Two of the compounds subjected to variable-temperature flexibility studies, Pd(acac)2 and Cu(acac)2, are isostructural and isomorphous, yet exhibit opposite thermal expansion characteristics along their crystallographic b axes. As such, they were identified as promising candidates to form solid solutions, whose thermal expansion behaviours could be tuned. A mixed crystal displaying near-zero thermal expansion was successfully produced, demonstrating the applicability of solid solutions in tailoring the thermal properties of molecular compounds. A reaction between 2,7-dimethylocta-3,5-diyne-2,7-diol and iodine was observed to produce a novel cumulene-type compound in high yield. It was established that light is required for the reaction to proceed, and can also be used to isomerize the cumulene in a cis to trans manner. Several other diyne compounds were found to react in analogous ways under the novel reaction conditions, provided they featured hydroxyl functional groups. Thus, it is proposed that formation of hydrogen-bonded adducts is responsible for halting the halogenation reaction upon formation of a cumulene.
- ItemCrystallisation of multicomponent crystals by sublimation: effect of experimental conditions(Stellenbosch : Stellenbosch University, 2023-10) Volkwyn, Alexandra Lemisha; Haynes, Delia Ann; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: This thesis aimed to develop a greater understanding of important principles behind the technique of sublimation and demonstrate how we can gain control over the technique to selectively form multicomponent crystal forms, such as hydrates, co-crystals, and salts. This aim was attained by carrying out two studies. The first study focused on investigating whether hydrates of oxalic acid (1), isonicotinamide (2), theophylline (3), caffeine (4), and 1,4-diazabicyclo[2.2.2]octane (5) can be grown by sublimation. Compounds 1-5 were sublimed in the presence and absence of water. An increase in the quantity of water added to the sublimation vessel resulted in an increase in the water content of sublimed crystals. Hydrates of 1 and 5 were easily crystallised from the gas phase in the presence of water. Competition experiments were carried out by co- subliming an anhydrous material and a hydrate, and water transfer took place from the hydrate to the anhydrous material. This study has shown that materials which have the most favourable interactions between the molecule in question and water within the hydrate crystal structure are more likely to crystallise as the hydrate from sublimation with water. The second study focused on investigating the effect of sublimation time, vacuum pressure, temperature, separation apparatus, mass scale, additives, and co-former polymorph on the co-sublimation of two systems: system 1 = succinic acid + hexamethylenetetramine and system 2 = oxalic acid + 4,4'-bipyridine. A salt formed under higher temperature and lower pressure conditions, and co-crystal was favoured under a reduced temperature and higher pressure. Separating the acid and base components prior to sublimation allowed for more control over the concentration of components in the gas phase. Sublimation conditions under which the concentration of acid and base component in the gas phase is maximised are more likely to result in salt formation. In the presence of additives, co-crystal formation was favoured during co-sublimations of system 1. In system 2, salt formation was favoured in the presence of methanol. Results suggest that the type and quantity of additive added to the sublimation vessel can be used to control the outcome of co-sublimations. These studies have shown that simple experimental conditions can be used to gain control over the method of sublimation, and can be used tomanipulate the concentration of components in the gas phase to selectively form salts or co-crystals. The effect of polymorph used during the co-sublimation of system 1 was studied. Sublimation with the β polymorph of succinic acid favoured the formation of co-crystal. It is clear that the use of a specific co-former polymorph can be used to direct the co-sublimation outcome. Overall, this thesis has provided a good foundational understanding of the important principles of the technique of sublimation, and has successfully demonstrated the importance of simple experimental conditions in multicomponent crystal growth from the gas phase. We believe that this simple approach towards gaining control over a crystallisation technique to form a desired product has broadened the scope of sublimation as a whole and will aid the development and design of new materials.