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The relationships between molecular parameters and microdomain formation of a variety of block- and graft-copolymers were studied by Transmission Electron Microscopy (TEM). Molecular variables included chemical composition: dimethyl-, fluoropropyl and diphenyl-siloxane , sulfone styrene, paramethylstyrene, t-butylstyrene, arylester and methyl methacrylate, as well as molecular weight and distribution. Effects of the kinetics of phase-separation were also determined . Thick (approximately lmm) films cast from solvent showed more complete phase separation than either thin (about 10nm) cast films or compression-molded specimens. Spherical domains formed in alternating poly(ester/siloxanes), and phase mixing seemed to correlate with the solubility parameters of the three siloxane types. Shear-stresses during molding changed domain shapes and eliminated short-range ordering. In the PMMA-graft-dimethyl siloxane system, SK, 10K and 20K <M_n> siloxanes were incorporated at 16% and 45% by weight. At 16%, spherical siloxane domains formed in both thick- and thin-cast films. The domain sizes and interdomain distances scaled with siloxane molecular weight and total block molecular weight respectively to a 2/3 power law in excellent agreement with theoretical predictions for di- and triblock copolymers. Thin films cast from the 45% siloxane graft copolymers also showed spherical domains with sizes dependent on molecular weight. However, the thick films showed phase transitions from disordered bicontinuous (M_n = 5K) to lamellar (M_n = 10K) to cylindrical <M_n = 20K). Qualitative TEM/EDX analysis of other systems was used to identify oligomers, homopolymers, and contaminants, thus monitoring the effects of novel reaction conditions and work-up procedures. / Master of Science

The research presented in this thesis aims to uncover the intricate manner in which BRCA1 interacts with RNAP II during mRNA production utilizing a unique microchip system developed in our lab. We were first able to prove the effectiveness of our tunable system using a breast cancer model of patient derived triple negative breast cancer (TNBC) cells. Here we switched out different mammalian antibodies and collected images of the same structure from different angles. This served many purposes: (1) it proved the system could be tuned for specific uses; (2) it demonstrated that all subunits were present in the complex; (3) it eliminated the need for the tilt function allowing for a less intensive computational procedure. In the BRCA1 wild type cell line we were able to incorporate into our 3D reconstruction, atomic models of the BRCA1-BARD1 heterodimer and the RNAP II core in regions of major unoccupied density. Other areas of minor missing density were overlaid with a short strand of DNA and ubiquitin moieties, which proved agreement with Co-IPs. Next we sought to compare the wild type structure with a BRCA1 mutant variety. Using these techniques, we determined the 3D structure of the mutated complex. After further analysis slight differences were detected between the two complexes, especially in the placement of the atomic models. Overall we were able to determine structural abnormalities that occur when a mutation is present in BRCA1 that may have future applications for targetable therapy in TNBC patients. Moreover, by using TNBC as the disease model, we have created a platform that can be used to evaluate other human diseases due to the tunable nature of our microchip system. / Master of Science

Yes / Understanding the effect of physical parameters (e.g., temperature) on crystallisation dynamics is of paramount importance for the synthesis of nanocrystals of well‐defined sizes and geometries. However, imaging nucleation and growth is an experimental challenge owing to the resolution required and the kinetics involved. Here, by using an aberration‐corrected transmission electron microscope, we report the fabrication of precious metal nanocrystals from nuclei and the identification of the dynamics of their nucleation at three different temperatures (20, 50, and 100 °C). A fast, and apparently linear, acceleration of the growth rate is observed against increasing temperature (78.8, 117.7, and 176.5 pm min−1, respectively). This work appears to be the first direct observation of the effect of temperature on the nucleation and growth of metal nanocrystals. / The Royal Society. Grant Number: UF150295 Leverhulme Trust. Grant Number: ECF-2013-414 The Academy of Medical Sciences. Grant Number: SBF003\1170

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No description available.

This project concerns the non-classical crystal growth of various porous and non-porous materials. In order to determine their crystal growth mechanism, the reaction was stopped at several different reaction times with the size, morphology, crystal structure and orientation of the particles analysed using scanning electron microscopy and high resolution transmission electron microscopy as the principal characterisation techniques. Other techniques used include X-ray diffraction, energy dispersive X-ray spectroscopy, selected area electron diffraction and thermal gravimetric analysis. Selected biomimetic systems include the early stage crystal growth of ZnO/gelatin composite twin-crystals and the time dependent microstructural evolution of CaCO₃/gelatin composite particles from spherulites into rods. Further investigations of the role of gelatin molecules were carried out by replacing gelatin by gum arabic. Using knowledge gained from synthetic systems, several travertine crust specimens collected from hot springs were investigated to gain an insight into the possible formation mechanisms of naturally occurring biominerals. Another form of ZnO investigated was the formation of core-shell ZnO hexagonal microdisks and selective dissolution of their core to form microstadiums followed by the selective growth of nanorods and nanocones onto the columnar surfaces of the microstadiums to generate branched-microstadiums. The formation mechanism of ultrasonically prepared BiOBr displaying a flower-like architecture was investigated. These BiOBr assemblies are found to exhibit excellent photocatalytic activity and stability during the photodegradation of Rh.B under visible-light irradiation. Finally mesoporous silicate plates displaying a single crystal-like property were re-investigated to clarify whether the previously reported mesoporous silicate plates exhibiting a single crystalline property were one-phase materials or a composite of non-crystalline mesoporous silicate and crystalline zeolite.

This thesis concerns the experimental application of the technique of optical sectioning in the aberration-corrected scanning transmission electron microscope (STEM). Another aim was to perform optical sectioning experiments on the still relatively new scanning confocal electron microscope (SCEM). To test the feasibility of this technique, experiments were performed on a variety of samples to measure the achievable depth response. Deconvolution methods were explored in an attempt to further improve the depth response. Finally, some of the first optical sectioning experiments were performed in the SCEM using both elastic and inelastically scattered electrons. The results showed a clear need to investigate confocal electron microscopy due to the missing cone problem for incoherent imaging in the STEM. This is particularly evident when imaging objects of greater width than the STEM probe. Confocal electron microscopy using inelastic electrons appeared to be a promising imaging mode for the future with this thesis consisting of early work in the field.

The oligomerisation of protein subunits is an area of much research interest, in particular the relationship to protein function. In the last decade, the potential to control the interactions involved in order to design constructs with tuneable oligomeric properties in vitro has been pursued. The subject of this thesis is the quaternary structure of members of the peroxiredoxin family, which have been seen to assume an intriguing array of organisations. Human Peroxiredoxin 3 (HsPrx3) and Mycobacterium tuberculosis alkyl hydroperoxide reductase (MtAhpE) catalyse the detoxification of reactive species, preferentially hydrogen peroxide and peroxynitrite respectively, and form an essential part of the antioxidant defence system. As well as their biomedical interest, the ability of these proteins to form organised supramolecular assemblies makes them of interest in protein nanotechnology. The work described focusses on the elucidation of the quaternary structure of both proteins, resolving previous debates about their oligomeric state. The factors influencing oligomerisation were examined through biophysical characterisation in different conditions, using solution techniques including chromatography, light and X-ray scattering, and electron microscopy. The insight gained, along with analysis of the protein-protein interfaces, was used to alter the quaternary structure through site-directed mutagenesis. This resulted in a level of control over the protein’s oligomeric state to be achieved, and novel structures with potential applications in nanotechnology to be generated. The activity of the non-native structures was also assessed, to begin to unravel the relationship between peroxiredoxin quaternary structure to enzyme activity. The formation and structure of very high molecular weight complexes of HsPrx3 were explored using electron microscopy. The first high resolution structural data for such a complex is presented, analysis of which allowed the theory of an assembly mechanism to be proposed.

Copper-alumina composites were developed for testing in abrasive wear applications. The composites featured a porous continuous ceramic-preform network infiltrated by a liquid metal to form the final consolidated composite. The liquid metal phase was pure copper. Six different ceramic preform variants were tested. Ceramic volume fractions of 40, 50 and 60% were used, of two preform types; one pure-alumina, and one with additional 2wt% copper(I) oxide (CU20), functioning as an infiltration aid, the effects of which were determined in a previous study; the copper-oxide reduced infiltration pressure and allowed the use of higher ceramic phase volume fraction in the final composite. Abrasive wear tests against two automotive braking system materials were conducted. Grey cast iron of alloy type GG15 was used to establish a baseline for behaviour of the six different composite samples and compare them. Following this, the three volume fraction variants of samples using the copper-oxide infiltration aid were trialled against a commercially-available European passenger vehicle brake pad friction material; ABEX 6091. Wear tests were conducted on a pin-on-disc tribometer. Hemispherical-headed pins were made from the composite and tested against rotating discs of the grey cast iron and the ABEX friction material. Contact velocity was kept constant at Ims-?? at room temperature in air, and contact loads up to 15N were used. Test loads of 1-4N were used against grey cast iron, and 15N against the ABEX friction material. Optical micrography was used to monitor the wear rate of samples tested against grey cast iron. Scanning electron microscopy (SEM) was used to characterise bulk microstructures and evaluate surface wear features. Transmission electron microscopy (TEM) was used for further microstructural investigation of the sintering and interfacial features of the undamaged pin samples, as well as damage zones and tribofilm compositions. Focussed ion beam (FIB) milling was used to create subsurface cross-sections of wear regions and prepare TEM samples. The wear performance of the different sample types was compared by ceramic content and preform additives. It was found that the wear resistance of pure-alumina preform composites was dependent on ceramic volume fraction. Increasing ceramic content lead to increased wear resistance. The lower sinter temperature of the samples with the copper oxide additive led to reduced wear resistance compared with the monolithic alumina preforms and changes in ceramic volume fractions were not discernable in wear resistance against grey cast iron. This could be further supported by qualitative micrographic observations. All tests against grey cast iron were dominated by tribochemical film formation, which was determined to be oxidation of the iron which formed at the composite pin contact surface. Further testing of the copper-oxide containing samples against the ABEX friction material revealed a mixed result; the 50 and 60% ceramic volume samples produced near-identical wear performance, while the 40% sample suffered poor wear resistance. The dominant wear mechanism of composite pins tested against the ABEX friction material was abrasive wear. Sub-surface analysis of wear pins revealed a prominent damage layer forming at the contact surface of all pin samples which progressively grew into the bulk material. This layer was believed to have an important effect on the wear behaviour of the materials.