Browsing by Author "Bourne, Susan"

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    Encapsulation of iron(III) protoporphyrin IX and tetraphenylporphyrin in metal-organic frameworks for application as heterogeneous oxidation catalysts
    (2018) Dare, Nicola A; Egan, Timothy John; Bourne, Susan
    Two MOFs, [H2N(CH3)2][Zn3(TATB2(HCOO)]·HN(CH3)2·DMF·6H2O (1) and ZnHKUST-1 (2) (TATB = 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoate) were investigated as potential hosts to encapsulate Fe(III) protoporphyrin IX (ferrihaem = Fe(III)PPIX) and Fe(III) tetraphenylporphyrin (Fe(III)TPP). Methyl orange (MO) adsorption was used as an initial model for substrate uptake in MOFs 1 and 2. MOF 1 showed good adsorption of MO (10.3 ± 0.8 mg.g-1 ) which could undergo in situ protonation upon exposure to aqueous HCl vapour. By contrast MO uptake by 2 was much lower (2 ± 1 mg.g-1 ) and PXRD indicated structural instability on exposure to water was the likely cause. Two methods for Fe(III)PPIX incorporation into 1 were investigated: soaking and encapsulation. Encapsulation was verified by SEM-EDS and showed comparable concentrations of Fe(III)PPIX on exposed interior surfaces and on the original surface of fractured crystals. SEM EDS results were consistent with ICP-OES data on bulk material (1.2 ± 0.1 mass % Fe). PXRD data showed that the framework in 1 was unchanged after encapsulation of Fe(III)PPIX. MO adsorption (6 ± 1 mg.g1 ) by Fe(III)PPIX-1 confirmed there is space for substrate diffusion into the framework, while the UV-visible spectrum of solubilized crystals confirmed that Fe(III)PPIX retained its integrity. A solid-state UV-visible spectrum of Fe(III)PPIX-1 indicated that Fe(III)PPIX was not in a µ-oxo dimeric form. Although single-crystal XRD data did not allow for full refinement of the encapsulated Fe(III)PPIX molecule owing to disorder of the metalloporphyrin, the Fe atom and pyrrole N atoms were located, enabling rigid-body modelling of the porphine core. For comparison, Fe(III)PPIX was further encapsulated in 2, forming Fe(III)PPIX-2. Reaction ABSTRACT of 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) with H2O2, catalysed by Fe(III)PPIX-1 and -2 showed that Fe(III)PPIX-1 is significantly more efficient than Fe(III)PPIX-2 and is superior to solid Fe(III)PPIX-Cl due to the faster initial rate of reaction as well as the greater conversion of ABTS to ABTS●+ . Both frameworks 1 and 2 were also investigated as potential hosts to encapsulate Fe(III) tetraphenylporphyrin (Fe(III)TPP). Attempts to encapsulate Fe(III)TPP into 1 were unsuccessful, but Fe(III)TPP was successfully encapsulated into 2, forming Fe(III)TPP-2. The framework was characterised by PXRD and SEM-EDS confirmed uniform distribution of Fe(III)TPP through the framework. The loading of Fe(III)TPP determined using ICP-OES (0.604 ± 0.008 Fe mass %) agreed well with SEM-EDS data. Single crystals of Fe(III)TPP-2 were obtained and structure determination showed that the Fe(III) porphyrin was positionally disordered over three positions. The instability of Fe(III)TPP-2 in the presence of H2O resulted in it being an inappropriate choice as an oxidation catalyst. The kinetics of ABTS oxidation by H2O2 catalysed by Fe(III)PPIX-1 were further investigated. The peroxidatic activity of this heterogeneous system conforms to a rate law identical to that observed in solution with no discernible influence of particle size, suggesting that the MOF system closely mimics the solution state. The proposed rate law indicates a reaction mechanism with two possible pathways, as suggested for the same reaction in solution. The major pathway describes the coordination of H2O2 to the Fe(III) centre and subsequent formation of a high valent intermediate, while the minor pathway describes the same process preceded by ABTS coordination to the Fe(III) centre forming a six-coordinate complex. The further application of Fe(III)PPIX-1 as an oxidation catalyst was probed by investigating the catalytic oxidation of hydroquinone, thymol, benzyl alcohol and phenyl ethanol by tert-butyl-hydroperoxide ( tBuOOH). Reactions were successful and showed t1/2 values that increase with increasing substrate molecular volume.
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    Physicochemical study of solid Cyclodextrin inclusion complexes of the antithrombotic Ajoene
    (2004) Smith, Vincent Joseph; Caira, Mino R; Hunter, Roger; Bourne, Susan
    This study describes the preparation and physicochemical characterization of inclusion complexes formed between selected cyclodextrins (CDs) and ajoene, an antlthrombotlc found in garlic. The E and Z isomers of ajoene (4,5,9,-trithiadodeca-1,6,11-triene-9-oxide) were reacted with α, β, γ-CD heptakis(2,6-di-O-methyl )-β-CD (DIMEB) and heptakls(2, 3, 6-tri-O-methyl )-β-CD (TRIMEB) to yield inclusion compounds α-CD·(E)-ajoene (1), α-CD·(Z)ajoene (2), β-CD·(E)-ajoene (3), β-CD·(Z)-ajoene (4), y-CD·(E)-ajoene (5), y-CD·(Z)-ajoene (6), DIMEB·(E)-ajoene (7), DIMEB·(Z)-ajoene (6), TRIMEB·(E)-ajoene·05H20 (9) and TRIMEB·(Z)-ajoene (10).
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    Polymorphs, cyclodextrin inclusion complexes and salts of the bronchodilator tulobuterol
    (2004) Oliver, Clive Lloyd; Caira, Mino R; Bourne, Susan
    The aim of this thesis was to prepare polymorphs, cyclodextrin inclusion complexes and salts of tulobuterol, a drug with bronchodilating properties. Polymorphic drugs are of interest to the pharmaceutical industry because of their varied physical properties, whilst the increase in aqueous solubilities of drugs by their inclusion within cyclodextrins or by salt formation is also an important pharmaceutical consideration. Two polymorphs, four cyclodextrin inclusion complexes and three salts of tulobuterol free base were successfully generated in this study.
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    Porous metal-organic frameworks for sorption of volatile organic compounds
    (2021) Ndamyabera, Christophe Adrien; Bourne, Susan
    Metal-organic frameworks (MOFs) present potential for various applications such as gas sorption, gas storage, sensing, drug delivery, and catalysis. This attracts researchers to design and synthesize MOFs that can respond to a specific application. In this thesis, mixed ligands 34pba and 44pba ligands (34pba = 3-(4-pyridyl)benzoate, and 44pba = 4-(4-pyridyl)benzoate) and Co2+ metal salts were used to synthesize porous MOFs {[Co(34pba)(44pba)]·DMF}n (1) and {[Co(34pba)(44pba)]·(C3H6O)}n (2), with DMF = N,N'-dimethylformamide and C3H6O = acetone through solvothermal reaction. These two relate to each other through hinge-like expansion or contraction of the guest-accessible void. The use of Zn2+ as a metal ion led to an isostructural MOFs [Zn(34pba)(44pba)]·DMF}n (3) of 1. Using 34pba as a single ligand and Cu2+ as the metal ion led to the formation of a 2D [(Cu(34pba)2]·DMF) (4) while a little variation of solvent mixture resulted in a 3D {[CuCl2(34pba)2]∙solvent}n (7) structures. The functionalized ligands 44paba and 34paba (34paba = 3-(pyridyn-4-ylmethyl)aminobenzoate, 44paba = 4-(pyridyn-4- ylmethyl)aminobenzoate) were used with Cu2+ centre to prepare [Cu(44paba)·(H2O)·(DMF)]n (5) and {[Cu3(34paba)5(H2O)2]·(DMF)2}n (6), both of which are 1D structures. The activated MOFs 1d and 3d from (1 and 2) were used for the adsorption of volatile organic compounds (VOCs) and gases. In all tested guest molecules, there was higher sorption capacity in 1d which could be attributed to some gate opening process occurring which does not occur in 3d. Some effects responding to the sorption such as the change of colour in 1d were characterized. This colour change may be associated with the d-d, metal to ligand charge transfer, or π to π* transitions in coordination complex. Crystal structures and their stability, sorption properties and selectivity were characterized by single crystal X-ray diffraction, thermogravimetric analysis, differential scanning, hot stage microscopy, powder X-ray diffraction, infrared spectroscopy, and proton viii nuclear magnetic resonance (1H NMR) analysis. This thesis also reports the effect of methanol on discrete complexes of cis-dichloro-bis(ethylenediamine)cobalt(III) chloride (Coen) that led to the formation of a new crystal structure upon the removal of the water of hydration. The lattice energies calculated prove that Coen is more stable to allow a quick reversible sorption.
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    Study of ternary complexes of cucurbit[8]uril and their applications in self diagnostic composites
    (2020) Das, Anjali Devi; Dalcanale, Enrico; Bourne, Susan
    Self-assembly in supramolecular systems has profound implications on creating the next generation of smart materials, with potential applications in self healing, energy storage, stimuli responsive hydrogels and sensors. Macrocyclic receptors that form host guest complexes with organic molecules, provide a unique platform for the formation of tailor made materials with programmable properties for specific applications. The cucurbiturils are one such class of receptors that have garnered increasing interest in the last decade due to their unique guest binding abilities. Cucurbit[8]uril, as one of the larger homologues, is a particularly appealing host molecule for functional materials, capable of forming ternary complexes with suitable guests. The main scope of this thesis is to design and employ host guest systems based on the macrocyclic host cucurbit[8]uril as supramolecular probes to identify early stage damage in carbon fibre reinforced composite materials. Chapter 2 outlines the main project, the development of a novel system for early stage damage detection in a fibre reinforced polymer composite. CB[8] has the ability to form heteroternary complexes of high stability of two different guests in polar environments. In the reported system, CB[8] encapsulates two pendant molecules in the matrix, a donor and a fluorescent acceptor forming a complex by stabilising a charge transfer pair within its cavity. The emission of the probe is suppressed within the ternary complex via photo induced electron transfer. The application of stress causes the weak supramolecular link to break apart, and in turn the fluorescence of the probe is reinstated. Several ternary complexes of the host molecule and fluorescent guest molecules were investigated and a Perylene imide (PER) - Cucurbit[8]uril (CB[8]) based system was found to be best suitable as a strain sensor. Studying the photophysical behaviour of the complex showed that the fluorescence of the PER - CB[8] complex was effectively switched off upon the complexation of a second guest molecule such as dibenzofuran or azobenzene. The supramolecular complex cross-linking the polymer chains was seen to provide a fluorescence response induced by strain even if present in a very low amount of 10−6 mol kg−1 , preserving the mechanical characteristics of the matrix. In addition to uniaxial compressive and tensile testing, the specimens were subjected to fatigue to assess the performance of the material under similar conditions during actual use. The ability to detect fatigue damage is especially important, due to it being one of the major causes of in-service failure of materials. Carbon fibreepoxy composite materials are widely used in the structures of aircraft, robots and other machines because of their high specific strength. Self-diagnosis is potentially an important tool for Non-Destructive Evaluation (NDE) of such composite materials used for purposes where structural integrity is absolutely essential. This work has been recently published in ACS Applied Polymer Materials in 2019 and was recognised by ACS as Editor's Choice. While studied as a versatile host molecule for molecular recognition, cucurbit[8]uril also offers a platform for the development of supramolecular organic frameworks and the formation of porous materials. In this context, the fundamental study of the stoichiometry and geometry of CB[8], its complexes in the solid state and the exploration of new binding motifs is pivotal. Indeed, due to their differential solubility, CB[8] complexes have proved to be difficult to characterise in the solid state, and limited examples are present in literature. Chapter 3 outlines the synthesis of nanotubular CB[8] assemblies. Organic molecular porous materials, in particular materials with a one-dimensional nanochannel structure have found a diverse range of applications in separation, energy storage, and adsorption. Three tubular frameworks of CB[8] were synthesised through chaperone induced methods and metal coordination. Finally, in a bid to develop better probes for self diagnostic composites, different CB[8] complexes with varying stoichiometry were studied in solution and in the solid state. Several CB[8] host guest systems were extensively studied with the aim to improve upon the damage reporting system reported in Chapter 2, by two main approaches. Firstly, there is an interest to move to near IR dyes due to their improved depth-penetration of light, allowing visualisation of damage deeper within the composite material. Secondly, moving from a 1:1:1 heteroternary complex by accommodating two different guests, to a 2:1 homoternary complex by accommodating two identical guests should provide an advantage by reducing the complexity of the system. Chapter 4 describes the study of the interaction of a series of potential dye molecules with CB[8] that fulfil these categories with the aim of developing improved supramolecular probes for self diagnostic composites. In addition, this chapter also reports three novel crystal structures of CB[8] complexes of varying stochiometry, from a 2:1, 1:1 to an unusual 1:2 complex with respect to the host. Overall, this thesis deals with the design and characterisation of CB[8] based host guest complexes, the study of their photo-physical behaviour and binding in solution, and exploits this behaviour in the design and implementation of a novel approach to the technologically relevant field of damage detection in composites.
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    Supramolecular derivatives of selected bioactive compounds : a physicochemical study
    (2010) Samsodien, Halima; Caira, Mino R; Bourne, Susan
    The author’s objective was to prepare new solid phases of three bioactive compounds: the steroidal anticancer agent 2-methoxyestradiol [polymorphs and cyclodextrin (CD) inclusion complexes], its derivative 2-methoxyestradiol-bis-sulfamate (polymorphs), and the antiretroviral agent, nevirapine (co-crystals). The solubility and dissolution profiles of the three compounds and those of selected ‘supramolecularly-derived’ species were also assessed. Three distinct phases of 2-methoxyestradiol (2ME) were successfully isolated, the most stable form (a polymorph) by the recrystallisation method, an amorph by melt studies and a solvated form by recrystallisation. 2-methoxyestradiol-bis-sulfamate (2MES), in the form of a hemihydrate, remained unchanged when recrystallised from various solvents. Several CDs were used for possible 2-methoxyestradiol inclusion; these were α-, β -,γ-CD, and nine derivatised cyclodextrins. Co-precipitation and kneading techniques were employed in attempts to produce inclusion complexes. An inclusion complex of 2ME was isolated with each of the following: -CD, HPBCD, RAMEB, DIMEB and TRIMEB. Co-crystallisation of nevirapine was attempted using twelve potential co-formers with GRAS status. Two co-crystals, one with saccharin and one with rac-tartaric acid, were isolated by the co-precipitation method. Physicochemical characterisation techniques used to assess the thermal behaviour of the products included hot stage microscopy, differential scanning calorimetry and thermogravimetric analysis. UV spectrophotometry and elemental analysis were used for hostguest stoichiometric assay and purity determination respectively. X-ray powder diffraction and single crystal X-ray structure determination were used for structural analysis.
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    Synthesis and inclusion of S-aryl alkylthiosulfinates as stable allicin mimics
    (2007) Stellenboom, Nashia; Hunter, Roger; Caira, Mino; Bourne, Susan; Cele, Khethiwe; Qwebani, Tozama
    S-Aryl alkylthiosulfinates showing aromatic rings with varying electronic demand have been prepared by oxidation of the corresponding disulfide, the latter prepared using new one-pot methodology involving thiol oxidation with 1-chlorobenzotriazole. Whereas thiosulfinates with electron-withdrawing substituents in the aromatic ring were unstable towards isolation, those with a releasing substituent in the para-position have shown good stability as potential allicin mimics and one of them (p-OMe) has been characterised as its inclusion compound in the cyclodextrin, TRIMEB, by X-ray crystallography.
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    Synthesis, structure and properties of novel Cu(II)-based metal-organic frameworks
    (2019) Bardini, Marco; Bacchi, Alessia; Bourne, Susan; Zacharias, Savannah
    Porous crystalline materials are known to be useful for a number of applications, including sensing, 1 drug delivery, 2 solid state catalysis3 and controlled absorption and release of liquids, gases and small molecules in solution. 4,5 Within this general definition, a class of materials that has seen its importance grow exponentially in the past two decades has been that of the Metal-Organic Frameworks, or MOFs. These materials have shown a lot of potential, especially in devices aimed at sequestering greenhouse gases (such as CO2 and CH4) from the atmosphere, 6 as well as in fuel tanks for hydrogen-powered cars. 7 The characteristics that allow MOFs to be used for such purposes are their high internal surface area to volume ratio, their relatively high thermal stability and the possibility to fine-tune their structure to optimize a given MOF for a given application. 8 Another feature of some MOFs, especially those built with semiflexible organic linkers9 between metallic nodes, is that they can change their conformation and therefore their pore size and internal surface area, in response to an external stimulus. 2,10 This behavior is especially interesting for systems which can be engineered to absorb and then release small molecules in a controlled manner. 11,12 This last property is one that I set out to exploit in my thesis work, starting from Cu(II) molecular complexes previously synthesized in the University of Cape Town (UCT) laboratories and varying experimental conditions in order to get MOFs of similar systems. Thus, this work will mainly describe the several novel crystal structures I obtained during my research. Each chapter will also discuss the basic spectroscopic and thermal properties of the material explored therein. Of these crystals, two are novel Cu(II)-based coordination polymers, which were named 1-MBUCT and 2-MBUCT, with seldom-seen coordination characteristics and other interesting features, including solvent-filled cavities within their crystal structure, which makes them promising candidates to be fully considered MOFs. After exploring the synthesis and structure of the materials, this work will mainly focus on determining whether the cavities inside 1-MBUCT and 2-MBUCT are accessible to other guests, without disrupting the overall morphology of the material. This was done through solvent exchange experiments, which were inconclusive but nonetheless suggested that these materials did indeed retain their shape, while allowing guest molecules inside their pores, thus being worthy of being described as MOFs. 6 All other structures are byproducts obtained during various attempts to optimize the synthesis of these MOFs, and are often examples of unusual compound classes in their own right. The first of these compounds is a Cu-based [12]crown-6 cyclical compound in which two monomethyl sulfide anions for every copper ion act as bridging ligands within the ring-like structure of the molecule, while the second is a discrete molecular complex formed by two 2,6- pyridinedicarboxylic acid molecules chelating a Cu(II) ion. The main point of interest of the last byproduct, instead, is not its structure, but rather the fact that all the carboxylic acid groups of the 3,5-pyridinedicarboxylic acid molecules included in the complex were subject to an esterification reaction. Such a reaction was unexpected, as the components of this system did not correspond to those found in any reported esterification reaction performed on 3,5-pyridinedicarboxylic acid.