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Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2015. / Solvatomorphism of an active pharmaceutical ingredient (API) is one of the most studied areas in pharmaceutical science. Since APIs are exposed to solvents during many stages of their production, knowledge of the consequences from such exposure is essential. Salt formation has been known to improve some physicochemical properties of an API. Amongst these properties, API solubility is one of the most important characteristics as their use in the market is determined by this feature. Research presented here investigated the solvates and salts of mefenamic acid (MA) and tolfenamic acid (TFA); both representing fenamic acids belonging to a class of non-steroidal anti-inflammatory drugs (NSAIDs). Solvates were obtained by reactions of TFA and MA with the solvents 2-picoline, 3-picoline, 4-picoline, 3-bromopyridine and 3-chloropyridine. A solvate polymorph of MA and 2-picoline was isolated. The salts were obtained by using diethanolamine, ethylenediamine, 1-methylpiperazine, and triethylamine in combination with the fenamic acids. Morpholine formed a salt with TFA, but not with MA. Instead a zwitterionic form of MA was synthesised when the latter was mixed with morpholine. The resulting compounds were characterised and their crystal structures analysed. It was found that the conformation of the acids in the solvate and the salt compounds differed. Moreover, within the solvates, the conformation of the fenamate backbone varied depending on the acid and the solvent used for crystallisation. Although similar solvents were utilized, the structural packing arrangements of TFA solvates were very different from the arrangements associated with MA. The thermal analyses of the salts/solvates were determined by using both thermogravimetry and differential scanning calorimetry. The compounds were further investigated after manual grinding and the preparation of slurries. These preparation methods were successful for most compounds but not for MA•2PIC and (MA-)(EDM+). Instead, the recrystallization, grinding and slurry investigations of MA•2PIC yielded a polymorph of this particular solvate. In the case of (MA-)(EDM+), the PXRD results obtained from both the pulverised and slurry samples were completely different from one another and also from those determined for the starting materials. Generally, the desolvation studies of the MA salts and solvates produced the same crystal form as occurred in the starting material. The exception was (MA-)(TA+) wherein desolvation produced a mixture of two polymorphs of MA.

<p> New complexes formed between U(VI), Th(IV) and Sc(III) and tropolone have been prepared. These include the solvates UO2T2⋅X and ThT4⋅X (T = the tropolone anion; X =H2O and CH3OH), and the unsolvated chelate Sc3⋅. Some U(VI), Th(IV) and Sc(III) tropolonates reported in the literature have been re-examined and found to be incorrectly formulated.</p> <p> The adduct chelates UO2T2⋅HT, ScT3⋅HT and the previously unreported ThT4⋅HT have been prepared. Evidence has been presented for hydrogen-bonding in the additional monodentate tropolone ligand.</p> <p> The thermal conversion of the above solvates and adducts to yield UO2T2, ThT4 and ScT3 has been described.</p> <p> The ability of tropolone and other bidentate ligands to displace the water molecule in UO2T2⋅H2O and ThT4⋅H2O, and the addition of such ligands to ScT3, has been studied.</p> / Thesis / Master of Science (MSc)

6,6’-Dimethoxygossypol (DMG) is a natural product of the cotton variety Gossypium barbadense and a derivative of gossypol. Gossypol has been shown to form an abundant number of clathrates with a large variety of compounds. One of the primary reasons why gossypol can form clathrates has been because of its ability to from extensive hydrogen bonding networks due to its hydroxyl and aldehyde functional groups. Prior to this work, the only known solvate that DMG formed was with acetic acid. DMG has methoxy groups substituted at two hydroxyl positions, and consequently there is a decrease in its ability to form hydrogen bonds. Crystallization experiments were set up to see whether, like gossypol, DMG could form clathrates. The following results presented prove that DMG is capable of forming clathrates (S1 and S2) and two new polymorphs (P1 and P2) of DMG have been reported.

This thesis has been divided into five sections. The first chapter introduces the main themes of this thesis, including the description of the concepts of supramolecular chemistry, crystal engineering, hydrogen bonding and graph set analysis. The final section of chapter one describes a typical X-ray experiment used to determine the structures of the compounds presented in this thesis. Chapter two describes the synthesis and single crystal structures of copper(I) complexes with pyridine- and pyrazine-carboxylic acids. A series of novel solvent inclusion compounds of copper(I) complexes with pyridine- and pyrazine-carboxylic acids and the hydrogen bonding patterns adopted are also discussed. Chapter three reports the potential uses of boronic acids as building blocks for the design of novel solid-state architectures utilising hydrogen bonds. Novel copper(I) pyridine-/pyrazine-carboxylate complexes with boronic acid co-crystals are presented in which the heterodimeric boronic carboxylate R22(8) ring motif is present in all cases. Chapter four discusses the synthesis of novel ditertiary phosphines bearing functional groups with hydrogen bonding potential either via a three-step or single step synthetic route which involves a well known method of reductive amination followed by an efficient Mannich-based condensation. Complexation studies of these P,P-bidentate ligands with various transition metal centres such as Pt(II), Mo(0), Ru(II) and Au(I) are also presented. The effect on the structural motifs observed in these series of compounds by the regioselective incorporation of functional groups with potential hydrogen bonding capability such as hydroxyl and amide is also given. Finally, chapter five contains the synthesis and coordination studies of new phosphorus donor ligands leading to ideas for further work.

We present an experimental study on the formation and dissociation characteristics of carbon dioxide (CO2) gas hydrates using Raman spectroscopy. The CO2 hydrates were formed from sodium chloride/water solutions with salinities of 0–10 wt %, which were pressurized with liquid CO2 in a stirred vessel at 6 MPa and a subcooling of 9.5 K. The formation of the CO2 hydrate resulted in a hydrate gel where the solid hydrate can be considered as the continuous phase that includes small amounts of a dispersed liquid water-rich phase that has not been converted to hydrate. During the hydrate formation process we quantified the fraction of solid hydrate, xH, and the fraction of the dispersed liquid water-rich phase, xL, from the signature of the hydroxyl (OH)-stretching vibration of the hydrate gel. We found that the fraction of hydrate xH contained in the hydrate gel linearly depends on the salinity of the initial liquid water-rich phase. In addition, the ratio of CO2 and water was analyzed in the liquid water-rich phase before hydrate formation, in the hydrate gel during growth and dissociation, and after its complete dissociation again in the liquid water-rich phase. We observed a supersaturation of CO2 in the water-rich phase after complete dissociation of the hydrate gel and were able to show that the excess CO2 exists as dispersed micro- or nanoscale liquid droplets in the liquid water-rich phase. These residual nano- and microdroplets could be a possible explanation for the so-called memory effect.