Doctor of Philosophy / Department of Chemistry / Christer B. Aakeroy / The impact of the molecular electrostatic potential values (MEPs) in halogen and hydrogen bond interactions were explored using two acceptors with multiple acceptor sites with twelve hydrogen-bond donors, five halogen bond donors and four mixed halogen and hydrogen bond donors. The results suggested if the difference between the two acceptor sites is above 38 kJ/mol both hydrogen and halogen bond donors prefer the acceptor site with the highest MEP value and this selectivity was lost if the difference is below 26 kJ/mol. To examine the potential of halogen-bond donors in organocatalysis, a halogen-bond donor molecule was synthesized and the catalytic activity was measured using a benchmark Ritter type solvolysis reaction. Results suggested the catalytic activity of the halogen-bond donor molecule with > 90 % conversion of the product with the use of a stoichiometric amount of the catalyst for 96 hrs. Successful use of the control molecules confirm that the catalytic activity is an outcome of having halogen-bond donors in the molecule. The benefit of using a structural mimic in landscaping the structural outcomes of poorly soluble molecules was explored using an anticancer drug erlotinib. A structural mimic was synthesized by maintaining all binding sites that are important to design a structural landscape and the structural outcomes were analyzed using five FDA approved dicarboxylic acids. The results suggested that the structural outcomes of the mimic can be related to the actual drug erlotinib. Solubility and thermal behavior analysis of the co-crystals also suggested that with the systematic changes of the co-crystallization agent, it is possible to make predictable changes to the physical properties. To observe the effect of co-crystallization technology in reducing the chemical reactivity and sensitivity of an energetic compound dinitrobenzotriazole, a series of co-crystallization experiments was carried out using fourteen nitrogen and oxygen based acceptors. Four co-crystals were obtained and the acceptors were identified as supramolecular protecting groups which led to successful diminish of chemical instability and decreased impact sensitivity. Hygroscopicity and chemical reactivity of tetranitrobisimidazole, a potential RDX replacement, was successfully decreased by protecting the acidic N-H protons in the molecule by introducing suitable co-formers. Introduction of the N-oxide based acceptors into the system enhanced the stability while retaining most of the desirable energetic properties.

Finding materials with high stability, high yield, and excellent catalytic performance has been an outstanding research challenge. Thiol-stabilized atomically precise metal nanoclusters (NCs) have attracted a lot of interest in recent years due to their unique properties and industrial applications, including catalysis, toxic metal-ion sensing, and magnetism. Unlike classical nanoparticles (NPs) which have larger sizes ranging between 10-100 nm, the size of nanoclusters typically ranges from 1 to 3 nm. Thus, nanoclusters represent good candidates to gain fundamental insights into optical and catalytic properties from the atomic to the molecular level. The majority of nanoclusters are based on Ag, Au, and more recently Cu. The major goal of this dissertation is the synthesis and structure determination of silver and copper nanoclusters. The first part of this dissertation addresses a shape-controlled synthesis strategy based on an isomeric dithiol ligand to yield the smallest crystallized silver nanocluster to date, formulated as Ag9. The second part discusses the preparation of different sizes of copper nanoclusters using a one-pot synthesis method and attempted to understand the structure-dependent catalytic pathways at the atomic level. Moreover, three novel Cu nanoclusters were developed: Cu29, Cu45, and Cu67. In terms of size, Cu67 represents a milestone towards high-nuclearity nanoclusters with interesting optical and structural properties. In terms of catalytic properties, Cu45 was found to be promising catalyst in hydroboration reactions of alkynes/alkenes and B2pin2, which affords hydroborated products with good to excellent yield. Mechanistic studies showed single-electron oxidation of an in-situ formed ate complex ([B2pin2]OH-) by the Cu45 catalyst, enabling hydroboration of unsaturated double bonds via a boryl-centred radical. These findings motivate us to extend the library of ligand-protected nanoclusters and focus deeply on exploiting metal nanoclusters based on Cu for catalysis.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeroy / Tailoring the properties of a bulk material such as a pharmaceutical compound, through non-covalent interactions, could lead to the enhancement of its physical properties without chemically modifying the individual molecules themselves. In order to obtain a degree of control and reliability of these non-covalent interactions, we must develop a series of synthons - patterns of non-covalent interactions between molecules. A family a N-heterocyclic amides were synthesised and an assessment of their binding selectivities was made, by evaluation of the supramolecular yield, (the frequency of occurrence of the desired connectivities). It was found that the supramolecular yield increased with increasing basicity of the heterocyclic nitrogen atom. However, there is a point where the heterocycle becomes basic enough to produce salts, which often leads to unpredictable connectivity and stoichiometry. Once the effectiveness of the N-heterocyclic amides as supramolecular reagents was established, a series of more closely-related ditopic hydrogen-bond acceptor molecules were synthesized. The supramolecular reagents contained imidazole and pyridine binding sites, so that the two sites differ in terms of their basicity and geometry. An assessment of the ability of these molecules to induce selectivity when a hydrogen bond donor such as a cyanoxime or a carboxylic acid is introduced was made. A total of nineteen crystal structures were obtained, of which one yielded a salt with unpredictable connectivity, and eighteen were cocrystals. Ten of these were 2:1 co-crystals, which shows that the two sites are accessible for binding. Eight were 1:1 stoichiometry, with five out of eight (63%) forming a hydrogen bond to the best acceptor. In addition, a series of molecular electrostatic potential calculations were employed to investigate the binding preferences and probe the best donor/best acceptor hypothesis. A ternary supermolecule was also constructed from a central, asymmetric hydrogen-bond acceptor and two different hydrogen-bond donor molecules. It was found that the best donor, the cyanoxime, bound to the best acceptor, the imidazole nitrogen atom, while the second best donor, a carboxylic acid, bound to the second best acceptor. The calculated molecular electrostatic potential values were used to rationalize this event. A series of substituted cyanophenyloxime, hydrogen bond donor molecules were synthesized and their effectiveness at forming co-crystals was examined. It was found that simple R group substitution could have a significant effect upon the co-crystal forming ability of the hydrogen bond donors, having improved the yield from 4% and 7% in a series of co-crystallizations with closely-related oximes, to 96% with the cyanoximes. A series of di- and tritopic cyanoximes were synthesized and an assessment of their co-crystal-forming ability was made. They were found to be equally effective at producing co-crystals as the monotopic cyanoximes, having done so in 23 out of 24 cases. In contrast to their carboxylic acid counterparts, the polycyanoximes also exhibited excellent solubility. Finally, a series of ditopic ligands (N-heterocyclic amide and pyridyl cyanoximes) were employed in the synthesis of metal complexes. The amide-based ligands were found to be very effective at organizing the metal architectures with coordination through the heterocyclic nitrogen atom and propagation of one-dimensional chains through carboxamidecarboxamide interactions. These interactions prevailed even in the presence of potentially disruptive species such as solvent molecules, (in Ag(I) complexes) counterions, or other hydrogen bond acceptors. The self-complementarity of the oxime moiety was found not to prevail in any of the cases, but the pyridyl cyanoximes were consistent in their behaviour, forming an O-H…O (oxime-oxygen) hydrogen bond to a carboxylate or acac moiety.

Magister Pharmaceuticae - MPharm / Many active pharmaceutical ingredients (APIs) have poor physicochemical properties such as solubility, dissolution and chemical stability. Several strategies are used to enhance and improve these properties of the API. Co-crystallization and polymorphism studies are possible strategy used in pre-formulation studies to optimize these properties of the drug without modifying its pharmacological effect. The purpose of this research was to investigate the polymorphism and co-crystallization effects of the penicillin-type antibiotic, amoxicillin tri-hydrate. Several techniques such as: slow evaporation, slow cooling, vapour diffusion, sublimation, grinding and solvent assisted grinding was employed. In producing co-crystals, the API was non-covalently bound to selected co-formers such as: saccharin, nicotinamide, salicylic acid, L-tartaric acid, D-tartaric acid, L-aspartic acid, stearic acid, benzoic anhydride, oxalic acid di-hydrate, cinnamic acid, succinic acid and citric acid monohydrate. Nine co-crystals of amoxicillin tri-hydrate had been formed. Differential scanning calorimetry (DSC), hot stage microscopy (HSM) and thermal gravimetric analysis (TGA) was conducted to analyse the thermal behaviour of the co-crystals. Powder X-ray diffraction (PXRD) and spectroscopic techniques [infra-red (FTIR) and H1-nuclear magnetic resonance (H1MNR)] were employed for screening of the co-crystal forms. Furthermore, dissolution testing was conducted to investigate the application of the newly derivatised forms.

>Magister Scientiae - MSc / Efavirenz is a non-nucleoside reverse transcriptase inhibitor used as an anti-retroviral for the treatment of human immunodeficiency virus (HIV) type I. It is classified as a class IΙ drug under the Biopharmaceutical Classification System (BCS) and exhibits a low solubility (aqueous solubility of 9.0 μg/ml) and high permeability (variable oral bioavailability). This study aims to choose a pre-formulation protocol with the best efavirenz derivative in literature between co-crystals and CD inclusion complexes. Upon selection of the efavirenz derivative, the complications of both small scale and large scale laboratory pre-formulation production is highlighted for formulation of a tablet dosage form. Numerous variables were selected for the pre-formulation protocol. Physical, chemical, pharmacological, pharmaceutical and economical variables were investigated. Citric acid monohydrate (CTRC) was chosen as the best co-former for a co-crystal while hydroxypropyl-beta-cyclodextrin (HP-β-CD) was selected as a host for an inclusion complex. Pharmaceutically, the angle of repose, Carr’s index, Hausner’s ratio, moisture content, disintegration time, hardness/resistance to crush, manufacturing process problems and particle size of the CTRC and HP-β-CD were all evaluated. The CTRC was ultimately selected for formulation of a tablet. The preparation of small laboratory scale of EFA/CTRC co-crystal was successfully achieved after several attempts. The large laboratory scale of EFA/CTRC was prepared under various environmental seasons which were indicated as batches 1-6 for purposes of this study. Characterization of the large laboratory scale EFA/CTRC co-crystals was performed by scanning electron microscopy (SEM), hot-stage microscopy (HSM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and by physical inspection (i.e. season, texture, colour, shape and particle size) of the EFA/CTRC product. Batch 1 and 2 were prepared during the summer season. The SEM analysis showed that the particles were needle-like shaped. The thermal analysis values of batch 1 by HSM, DSC and TGA results were 123 °C, 119 °C and 1.68 % of mass loss, respectively. In batch 2, morphology results by SEM revealed spikes of irregular and agglomerated particles. Batch 2 melted at 123 °C and a small unmelted quantity was observed at 143 °C. The DSC and TGA (mass loss) analysis were 118 °C and 0.75 % respectively. The hardness test of EFA/CTRC tablet prepared in batch 2 was extremely hard hence failed the disintegration test. The EFA/CTRC prepared in batches 3, 4 and 5 was during the winter season which is associated with high humidity and wet weather conditions. The SEM, DSC, TGA results were significantly different from the previous batches. The SEM morphology was highly irregular particles for batch 3, clustered and randomly size particle for batch 4 and irregular, needle-like, spikes and spherical shaped particles for batch 5, respectively. The thermal results HSM, DSC and TGA confirmed the presence of moisture in the prepared EFA/CTRC products. The HSM melting point results of batches 3, 4 and 5 were 123 °C, 115 °C and 121 °C, respectively. The DSC results of 110 °C, 105 °C and 118 °C were observed for batches 3, 4 and 5 respectively. The mass loss i.e. TGA results for batches 3, 4 and 5 were 1.178%, 1.5 % and 2.235 % respectively. In batch 6, EFA/CTRC was prepared using a different commercial batch of EFA and CTRC. The SEM results indicated the formation of needle-like and clustered particles. The values obtained from HSM, DSC and TGA results were 124 °C, 114 °C and 0.54 % in mass loss. The physical appearance of EFA/CTRC prepared from batch 1 and 2 were white in colour while batch 3, 4, 5 and 6 of the prepared EFA/CTRC was pink in colour. The physical appearance of the individual batches differed but the identity of the sample remained intact implying the same pharmacological effects with differing pharmaceutical properties impacting the dosage form preparation.

Yes / The present study demonstrates the application of decision tree algorithms to the co-crystallization process. Fifty four (54) batches of carbamazepine-salicylic acid co-crystals embedded in poly(ethylene oxide) were manufactured via hot melt extrusion and characterized by powder X-ray diffraction, differnetial scanning calorimetry, and near-infrared spectroscopy. This dataset was then applied in WEKA, which is an open-sourced machine learning software to study the effect of processing temperature, screw speed, screw configuration, and poly(ethylene oxide) concentration on the percentage of co-crystal conversion. The decision trees obtained provided statistically meaningful and easy-to-interpret rules, demonstrating the potential to use the method to make rational decisions during the development of co-crystallization processes. / Commonwealth Scholarship Commission in the UK (ZMCS-2018-783) and Engineering and Physical Sciences Research Council (EPSRC EP/J003360/1 and EP/L027011/1)

yes / Reproducible control of stoichiometry and difficulties in large scale production have been identified as two of the major challenges to commercial uptake of pharmaceutical co-crystals. The aim of this research was to extend the application of SFCC to control stoichiometry in caffeine: maleic acid co-crystals. Both 1:1 and 2:1 caffeine: maleic acid co-crystals were produced by control of the feedstock composition and process conditions. It was also observed that formation of 2:1 stoichiometry co-crystals involved formation of a 1:1 co-crystal which was subsequently transformed to 2:1 co-crystals. The investigation of stoichiometric transformation revealed that although 1:1 co-crystals could be converted into 2:1 form with addition of excess caffeine, the reverse was not possible in the presence of excess maleic acid. However, conversion from 2:1 into 1:1 was only achieved by melt seeding with the phase pure 1:1 co-crystals. This investigation demonstrates that stoichiometric control can be achieved by SFCC by control of parameters such as extrusion temperature.

Hydrophobic membrane proteins perform a variety of important functions in the cell, but their structures are notoriously difficult to solve. Thus, new strategies to obtain crystals of membrane proteins for structure determination are critical. We aim to develop a toolbox of peptide specific single-chain antibody fragment chaperones engineered for hyper-crystallizability. These peptide sequences can be introduced into various regions of membrane proteins without interfering with protein function. The resulting protein-chaperone complex is expected to form a crystal lattice mediated by chaperone interactions. We have developed candidate scFv chaperone proteins binding hexa-histidine (His6) and EYMPME (EE) tags with improved biophysical features influencing crystallization propensity, including peptide affinity, stability and solubility. The scFv libraries were generated using a novel ligation-free technique, MegAnneal, allowing us to rapidly generate large libraries based on 3D5 scFv. We identified two candidate chaperones, 3D5/His_683, specific for His6 and 3D5/EE_48, specific for EE tags. Variants exhibit high solubility (up to 16.6 mg/ml) and nanomolar peptide affinities; complexes of 3D5/EE_48 with EE-tagged proteins were isolated by gel filtration. We have developed design rules for EE peptide placement at terminal, inter-domain or internal loop regions of the target protein to balance peptide accessibility for chaperone binding while retaining rigid protein-chaperone complexes suitable for crystallization. The 3D5/ His_683 crystallized in four different conditions, utilizing multiple space groups. The 3D5/EE_48 scFv was crystallized (3.1 Å), revealing a ~52 Å channel in the crystal lattice, which may accommodate a small peptide-tagged target protein. Our evolution experiments altered scFv surface residues, resulting in use of different crystallization contacts. Analysis of these crystal contacts and those used by crystallized 14B7 scFv variants, led us to postulate that lattice formation is driven by strong crystal contacts. To test this hypothesis, we introduced amino acid changes expected to reduce the affinity of the 3D5/EE_48 energetically dominant crystal contacts. This approach to crystal contact engineering may allow semi-rational control over lattice networks preferred by scFv chaperones. Co-crystallization trials with model proteins are on-going. These engineered scFvs represent a new class of chaperones that may eliminate the need for de novo identification of candidate chaperones from large antibody libraries. / text

This dissertation has focused on the solid-state characterization of different co-crystal system as well as the effect of co-crystallization of these systems on pharmaceutical dosage form performance. Urea/ 2-MB, caffeine/ malonic acid, caffeine/ oxalic acid and theophylline/ malonic acid co-crystals were prepared using co-grinding- and co-precipitation techniques. In addition, the synthesis of co-crystals through two novel methods has been demonstrated. This includes compaction and convection mixing. The solid-state characterization of the co-crystals has been carried out using XRPD, Raman spectroscopy, DSC, TGA, hot-stage microscopy and SEM. After preparation of co-crystals, tablets have been produced from co-ground-, co-precipitated-, and physical mixtures using Compaction Studies Press (Kaleva), and the data were recorded to compare between the different mixtures, regarding compactibilty, compressibility and deformational properties. The DSC results showed that the physical mixtures of all systems, formed co-crystals during heating process. For systems of urea/ 2-MB, caffeine/ malonic acid and theophylline/ malonic acid, the co-ground mixture produced tablets with higher tensile strength compared with either co-precipitated or physical mixture. However, for caffeine/ oxalic acid system, the tensile strengths of compacts produced from the physical mixture were greater than those obtained from either co-ground or co-precipitated mixtures. The Heckel data suggested that urea/ 2-MB, caffeine/ malonic acid and theophylline/ malonic acid systems are Type 1 materials, as an extensive linearity during compression was indicative of a plastic deformation mechanism, while the caffeine/ oxalic acid system was Type 2 materials. However, the co-precipitated mixture of urea/ 2-MB system was the least compressible, as it possessed the greatest value of yield pressure (85 MPa) and the highest elastic recovery (7.42%). The co-precipitated mixture of both of caffeine/ malonic acid and theophylline/ malonic acid systems was the most compressible with small yield pressure values of (44 & 80 MPa) and elastic recovery of (7.2% & 6.56%), respectively. The co-ground mixture of caffeine/ oxalic acid possessed the highest value of yield pressure (166 MPa) and thus the lowest compressibility among other mixtures. Furthermore, the addition of microcrystalline cellulose and α-lactose monohydrate has affected the crystallinity as well as the tableting properties of the co-crystals. After the addition of excipients, the tensile strength of compacts was about 2 times higher than any other mixture. Finally, urea/ 2-MB and caffeine/ malonic acid co-crystals were successfully synthesized through convection mixing and compaction.

Les co-cristaux représentent une classe de composés offrant de grandes opportunités pour l'industrie pharmaceutique. La plupart des études présentées dans la littérature porte sur le diagramme thermodynamique et sur l'ingénierie cristalline. Ce travail y ajoute l'aspect cinétique qui est essentiel à prendre en compte pour la mise en place d'un procédé de cristallisation à l'échelle industrielle. Différentes techniques d'analyse en ligne ont été mises en oeuvre pour suivre le procédé de co-cristallisation. Le système modèle carbamazépine / nicotinamide a été sélectionné. Dans un premier temps, l'utilisation d'une sonde de visualisation in-situ a permis la construction d'un diagramme de phase pour le système modèle étudié. Par la suite, les chemins cinétiques du procédé de co-cristallisation ont été mesurés en solution grâce au suivi des concentrations en soluté par spectroscopie InfraRouge à Transformée de Fourier. Enfin, la transition entre les phases solides (carbamazépine et cocristaux) a été suivie in-situ par spectroscopie IR et en couplant la sonde de visualisation avec la sonde Lasentec FBRM. Les essais ont permis de vérifier qu'une dérive de procédé conduisant à une autre phase cristalline que les co-cristaux peut être corrigée pour obtenir au final uniquement des co-cristaux / Co-crystals represent a class of compounds, which offers huge opportunities for the pharmaceutical industry. Most studies presented in the literature deals with the thermodynamic diagram and crystal engineering. This work adds the kinetic aspect that must imperatively be taken into account in the establishment of a crystallization process at an industrial case. Different in-line process analytical techniques were carried out to monitor the co-crystallization process. The model system carbamazepine / nicotinamide was selected. The use of an in-situ visualization probe allowed us to build the phase diagram of the model system studied. Afterwards, the kinetic pathways of the co-crystallization process were highlighted thanks to the following of the solute concentrations by Fourier Transform InfraRed spectroscopy. Finally, the phase transition between carbamazepine and co-crystals was monitored by IR spectroscopy, and by using simultaneously the visualization probe with the Lasentec FBRM probe. In order to finally obtain the only co-crystal phase, we subsequently verified that it was possible to correct a situation of process deviation, for which another crystalline phase remained in suspension