Gas cells make up a significant proportion of bread’s volume and are responsible for a number of bread’s characteristics, making their size distribution throughout bread an important quality parameter. The number and size of cells affect the texture and volume of bread, the quantity of sauce mopped up, and how bright the bread appears. Gas cells are incorporated into bread dough during mixing and manipulated throughout the breadmaking process to obtain the desired cellular structure. Due to the fragile nature of bread dough, obtaining accurate quantitative data on its cellular structure is challenging. This thesis investigates the cellular structure of bread, as well as assessing the effect of sugar during breadmaking. Magnetic resonance imaging (MRI), microscopy and X-ray computerised tomography (X-ray CT) have been used throughout research in bread dough to visualise dough’s cellular structure. A non-destructive and non-invasive method giving a high resolution is X-ray CT, in particular when using a synchrotron light source. However, time on a synchrotron beamline is highly competitive, and can require applications more than two years in advance. Running costs of experiments from a synchrotron beamline are also high. This thesis details an alternative X-ray set-up to accurately visualise dough’s cellular structure using a conventional and therefore more easily accessible X-ray source. Three X-ray CT experiments were conducted to investigate dough’s cellular structure throughout mixing, during proving and in different sugar content doughs. The resolution of the scans varied from 7-11 µm. Industrial bread dough mixing is often conducted at a high pressure initially to improve oxygen availability, followed by a period of partial vacuum to favourably manipulate the cell size distribution. Using X-ray CT, dough cell size distribution was measured at different points throughout pressure-vacuum and constant pressure mixing. A simplified population balance model was fitted to the measured cell size distributions and the validity of the assumptions within the simplified model explored. It was shown that the dynamic changes in the cell size distribution within bread dough could be accurately measured during pressure step change mixing with a non-synchrotron X-ray source. Pressure-vacuum mixing was shown to give a finer cell distribution than constant pressure mixing and the observed decrease in cell number density was found to be much more short lived than the decrease in cell size. The model was found to provide a reasonably accurate characterisation of pressure-vacuum mixing. X-ray CT was also used to monitor dough’s changing cellular structure during proving by taking scans every 5 minutes over 145 minutes. Dough voidage increased from 3% to 66%, resulting in a volume increase from 544 mm3 to 1293 mm3. Cell growth was quickest between 40 and 140 minutes, where a steady increase in volume and significant changes in the cell structure occurred. A change in voidage distribution was observed, with greater proportions of gas located in larger cells over time. In addition, over the course of proving cell numbers dropped, a 156-fold increase in mean cell volume occurred, and mean cell Feret shape increased from 1.59 to 1.91. This in-situ method of X-ray imaging of bread dough provides higher resolution images than comparable data from conventional X-ray sources. In addition, the method has proved to be effective in obtaining high resolution and high contrast 3D images of the cellular structure of dough. This technique will help those wanting to investigate cellular changes in the dough dynamically, but without the waiting time and applications that are required with synchrotron X-rays. On investigating the effect of sugar during breadmaking, sugar was found to increase the gas free dough density and dough voidage, change the dough’s rheology, increase its proving time and produce denser bread. Application of a population balance model on the experimental results indicate that the decrease in steady state voidage as the sugar content increases is a result of an increase in disentrainment. This was reflected in the X-ray CT of sugared vs. non-sugared doughs through fewer and smaller cells present in sugared doughs. This is likely to be a result of a weaker dough structure, making cell rupture more likely. The Chorleywood Bread Process (CBP) is used industrially worldwide for the production of bread in less time and using inferior ingredients compared to the traditional bulk fermentation process, making it more cost effective. These results show that simply extending the pressure vacuum mixing used for the production of standard bread loaves in the CBP to sugared doughs should be avoided as aeration of sugared doughs differs to non-sugared doughs. The results suggest that to do so would be detrimental to the product quality.

The initial aim of the work presented in this thesis was to examine smectic layer compressibility with a view to improving our understanding of the stability of intermediate phases. A natural starting point was to investigate the smectic-A phase, as it is the most basic of the smectic phases. The response of the layered structure to external fields is also a focus of this thesis as electric and magnetic fields enable the layer properties to be probed. Investigations into the reorientation dynamics of smectic-A layers in magnetic fields were performed using geometries and cell thicknesses (>50 μm) that are not feasible using electric fields. Data presented in this thesis show that three distinct reorientation mechanisms can occur, one of which is previously unreported and bridges the gap between the previously known mechanisms. The new mechanism observed in 270 μm and 340 μm thickness cells exhibits multiple stage reorientation on a timescale between tens and hundreds of seconds. Using conventional electro-optic techniques combined with a theoretical approach developed by others, this thesis presents a new technique to provide measurement of relative smectic layer compressibility of eight smectic-A liquid crystalline materials. The method presented here combines data on cell thickness, dielectric anisotropy and the measurement of the voltage threshold of the toroidal to stripe domain transition. As expected, the experimental data indicated that materials with shorter molecular lengths had the largest relative layer compressibility. Finally, direct measurement of smectic layer compressibility was investigated and the design of an apparatus capable of such measurements was undertaken. Preliminary results from such an apparatus are presented along with a discussion on the steps taken to develop the design.

The M-shell x-ray production cross section for thorium and uranium have been determined for protons of energy 0.4 - 4.0 MeV, helium ions of energy 0.4 - 6.0 MeV, carbon ions of energy 4.5 - 11.3 MeV and oxygen ions of energy 4.5 - 13.5 MeV. The total cross sections and the cross sections for individual x-ray peaks in the spectrum, consisting of the following transitions Mz (M4-N2, M5-N3, M4-N3), Ma (M5-N6,7), Mb (M4-N6, M5-O3, M4- O2), and Mg (M4-O3, M5-P3, M3-N4, M3-N5), were compared to the theoretical values determined from the PWBA + OBKN and ECUSAR. The theoretical values for the carbon and oxygen ions were also modified to take into account the effects of multiple ionizations of the target atom by the heavier ions. It is shown that the results of the ECUSAR theory tend to provide better agreement with the experimental data.

Experiments were designed for an undergraduate instrumental analysis laboratory course, two in X-ray diffraction and two in electrochemistry. Those techniques were chosen due their underrepresentation in the Journal of Chemical Education. Paint samples (experiment 1) and pennies (experiment 2) were characterized using x-ray diffraction to teach students how to identify different metals and compounds in a sample. in the third experiment, copper from a penny was used to perform stripping analyses at different deposition times. As the deposition time increases, the current of the stripping peak also increases. the area under the stripping peak gives the number of coulombs passed, which allows students to calculate the mass of copper deposited on the electrode surface. the fourth experiment was on the effects of variable scan rates on a chemical system. This type of experiment gives valuable mechanistic information about the chemical system being studied.

Flavonoids are a specialized group of compounds produced by plants that give them greater adaptability to their environment and ultimately enhance their ability to survive. In plants, one function of flavonoids is to attract pollinators by their various flavor and scent profiles. They also protect the photosynthetic machinery from photo-oxidation. In humans, flavonoids have been shown to act as antioxidants, exhibit antimicrobial activity, and have shown potential as cancer treatments. In nature, flavonoids are most often found coupled with a sugar group (glucose, rhamnose, and others) which imparts stability and increases bioactivity. The process of adding a sugar (glycosylation) is catalyzed by a class of enzymes called glycosyltransferases (GT). One such enzyme found in grapefruit only glucosylates the flavonol class of flavonoids at the 3-OH position and is of interest due to its unique substrate and regio-specificity. Called Cp3GT (Citrus paradisi flavonol 3-O glucosyltransferase), this enzyme is similar in structure to other plant GT’s yet differs in the flavonoids it can glucosylate and where the glucose can be added. To date, the literature has not reported a structural mechanism for a flavonol specific 3-O glucosyltransferase’s unique catalytic activity. High-resolution structural imagery of enzymes, elucidated using X-ray crystallography, can be used to direct custom enzyme development to produce bioavailable natural products. Furthermore, structural research on enzymes with high specificity strengthens enzyme-ligand docking simulations, which are commonly used to test the binding affinity of potential pharmaceuticals. This research hypothesizes Cp3GT has structural features that confer its unique substrate and regiospecificity that are not revealed by homology modeling. This hypothesis will be tested using x-ray crystallography of purified Cp3GT protein bound to its preferred flavonol substrates. The gene for Cp3GT was transformed into Pichia pastoris and was recombinantly expressed using methanol induction. Cp3GT was purified to 80% purity using cobalt metal affinity chromatography. Cp3GT was subjected to additional purification measures using anion exchange chromatography with the goal of increasing purity to ≥95% for crystallization experiments. Purity analysis was conducted using SDS-PAGE (Coomassie/silver stain, western blot) and UV-Vis spectrophotometry. While initial results are promising, additional purification steps may be needed to achieve the purity necessary for crystallization.

In prokaryotes, protein glycosylation can be a determinant of pathogenicity as it plays a role in host adherence, invasion, and colonization. Impairment of glycosylation in some organisms, for example N-linked glycosylation in Campylobacter jejuni, leads to decreased pathogenicity; thus, opening new avenues for the development of antivirulence agents. A member of the protein glycosylation (pgl) gene locus in C. jejuni, PglC, is predicted single-pass transmembrane (TM) protein, that catalyzes the phosphoglycosyl transferase (PGT) reaction in the first membrane-committed step of the N-linked glycosylation pathway. The small size of PglC (201 aa) compared to homologous PGTs suggests it may represent the minimal catalytic unit for the monotopic PGT superfamily. Herein, the structure of C. concisus PglC including its putative TM domain has been solved to 2.74 Å resolution to reveal a novel protein fold with a unique alpha-helix-associated beta-hairpin (AHABh) motif and largely solvent-exposed structure. There is noted a parsimony of fold in the form of short-range motifs underpinning the structural basis for critical functions of PglC: membrane association and active-site geometry. Biochemical and bioinformatics studies support structural evidence suggesting the crystallographically-observed, kinked TM helix is re-entrant on the cytoplasmic face of the membrane rather than membrane spanning. Thus, PglC represents a first-in-class structure of a novel membrane interaction mode for monotopic membrane proteins. Additionally, the AHABh-motif and active-site helical geometry establishes co-facial positioning of the catalytic-dyad. Molecular docking of PglC substrates, undecaprenyl phosphate (UndP) and UDP-N,N-diacetylbacillosamine (UDP-diNAcBac), within the active-site reveals co-incident binding sites, consistent with the proposed ping-pong enzymatic mechanism. Loading of PglC into membrane-bilayer nanodiscs (ND) allows for the investigation of PglC structure and function within a native-like membrane environment by small-angle x-ray scattering (SAXS). Observation of PglC in ND via SAXS confirms the application of the method for studying small, integral, monotopic membrane proteins in a membrane environment. Moreover, development of a mathematical approach by which resident-protein: ND stoichiometry can be deduced from measured scattering intensity enables independent confirmation of loading stoichiometry. Overall, the membrane-interaction modality observed for PglC is the first structurally characterized example of a new membrane association mode for monotopic proteins with the membrane. These studies provide insight into the structural determinants of the chemical mechanism and substrate-binding for C. concisus PglC and for the extensive homologous monotopic PGT superfamily, thus allow homology modeling and enabling future inhibitor design. / 2019-06-12T00:00:00Z

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18073号 / 理博第3951号 / 新制||理||1569(附属図書館) / 30931 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 鶴 剛, 教授 谷森 達, 教授 柴田 大 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Cholesterol is known to affect biophysical quantities in one and two component membranes, overall increasing membrane thickness and orientational order and decreasing membrane fluidity. Although these effects are useful in the plasma membrane of cells where strength is a desired property, there is evidence suggesting that the appearance of cholesterol in other cellular membranes has adverse effects. Indeed, cholesterol is found at elevated levels in the mitochondria membranes of cancer cells and is associated with chemotherapy resistance. At the molecular level, the link between cancer and cholesterol seems to be that cholesterol interferes with apoptosis, or programmed cell death, specifically by inhibiting the insertion of the pro-apoptotic protein Bax in the mitochondria outer membrane. We studied the effects of cholesterol on a five component mitochondria-like membrane, in order to determine which of these are relevant for Bax membrane insertion. As expected we found, using x-ray and neutron scattering, that upon cholesterol addition: (1) the thickness of the mitochondria-like membrane increases, (2) the area per phospholipid decreases, and (3) the orientational order of the membrane increases. Interestingly, our data indicate that the ordering effect of cholesterol is less efficient for the five component mitochondria-like membrane than for a single component membrane. Finally, we determined that in spite of the relatively high degree of unsaturation of the lipids in the mitochondria-like membrane, cholesterol adopts a canonical orientation. At higher cholesterol concentrations, cholesterol's polar hydroxyl group moves outwards and comes in proximity with the phospholipid's carbonyl group, allowing hydrogen bonding between the two types of molecules. Any of the above effects could in principle be responsible for cholesterol's inhibition of Bax insertion, thus follow up studies are required to confirm which, or what combination of them are relevant for apoptosis. / Thesis / Master of Science (MSc)

No description available.

The lead-free tin telluride (SnTe) is considered as a potential candidate to substitute lead telluride (PbTe) for thermoelectric power generation based on their similar crystal and electronic structures. However, the relatively high lattice thermal conductivity and low Seebeck coefficient of pristine SnTe are detrimental for real-life applications. This dissertation explored elements-doping/substituting of SnTe to overcome those shortcomings and improve SnTe thermoelectric performance. A series of the Sn1-xGexTe phases were synthesized and studied. When the Ge amount reaches 50% or higher, Sn1-xGexTe undergoes a phase transition from the rock-salt structure (Fm3̅m) to the rhombohedral one (R3m). The Sn0.5Ge0.5Te phase was explored in more details because it delivers the best thermoelectric performance with the Sn1-xGexTe series. The electron-richer Sb and Bi were substituted on the Sn/Ge site to optimize the charge transport properties, and Cu2Te was added into the matrix to improve the thermoelectric performance further. The In/Sb and In/Bi co-doping on the Sn/Ge sites was employed for Seebeck coefficient optimization. A comparative study of the electronic structure of the Sn0.5Ge0.5Te-based samples was performed. The calculations indicated a band convergence and changes in the valence band, thus providing insight into the co-doping effects. Suppression of the lattice thermal conductivity of SnTe was performed via alloying with AgSnSe2 and PbTe, which introduced strong atomic disorder. Additionally, AgSnSe2 showed a hole donor behavior in SnTe, and the increased carrier concentration compensated for the reduction in the carrier mobility, thus rendering a decent electrical conductivity in alloyed samples. As a result, the alloying effectively improved the samples' thermoelectric performance. / Thesis / Doctor of Philosophy (PhD) / In recent decades, renewable energy has attracted a lot of attention due to an increase in the global energy use and depletion of fossil fuel reserves. Thermoelectric materials are expected to play a vital role as green energy generators to overcome the upcoming energy crisis as they can directly convert waste heat into electricity through the Seebeck effect. In this dissertation, the main goal is optimizing the thermoelectric performance of SnTe for the above room temperature applications. Different doping/ substituting/alloying strategies were applied to improve the performance. The obtained thermoelectric properties of the SnTe-based materials were rationalized in terms of the charge carrier behavior, changes in the electronic structure, and phonon propagation.