The acid-catalyzed inversion of sucrose is often taken as an example of a first order reaction. It is, however, influenced by many factors such as temperature, type of acid used, concentration of sucrose, and the concentration of acid. What has received little attention so far is the influence of addition, in particular, other salts to the reacting solution. In this study, the influence of different salt solutions on the kinetics of sucrose inversion rate was studied at 29 °C by use of optical rotation measurements. The salts chosen for this study are readily soluble in sucrose solution and they provide an opportunity to study the interaction of electrolytes in aqueous solution of sucrose as well as their effects on the inversion of sucrose kinetics. The rates are found to be influenced by the concentration of the salts. No significant differences was measured when the salt were dissolved either in the sucrose or in the acid solutions. The influence of added salts to saccharide solutions was determined by evaluating the difference between the rotation of pure saccharides solutions and the rotation of pure saccharide solutions with salts. The changes in optical rotation were compared to the Hofmeister series. The saccharide-salt systems containing acidic salts (Na2HPO4 or NaH2PO4) were found to be dependent on the pH. Changing the molar ratio of sucrose and salt added also had an influence of the change in optical rotation. / Chemistry / M. Sc. (Chemistry)

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

When solutions of various metal 8-quinolinolates or beta-diketonates in an organic solvent were contacted with an aqueous phase and vigorously stirred to generate a large interfacial area, a reversible decrease in the organic phase concentration of the complex was observed. The magnitude of this decrease varied with interfacial area, solvent, temperature, and the nature and concentration of the complex. Analysis of the phenomenon using the Langmuir isotherm showed that the concentration change may be explained by adsorption of significant quantities of the complexes at the increased liquid-liquid interface generated by stirring. Such adsorption was found to complicate extraction kinetics measurements using the high-speed stirring technique when the product chelate is interfacially active, distorting the absorbance/time profile from which rate constants are derived, altering the interfacial area in the reaction vessel, and displacing reactant molecules from the interface. Neutral surfactants were observed to have similar effects. Chelate adsorption was also demonstrated to affect metal ion extraction equilibria, shifting the pH 1/2 value associated with a given metal ion. The magnitude of this shift was found to depend on the concentration of the chelate, its interfacial adsorption constant, and interfacial area. Differences in the pH 1/2 shift were shown to serve as a means of separating metal ions. Studies of the rate of nickel extraction by 8-quinolinols showed that the distribution constant and interfacial activity of the ligand are important factors governing the balance between bulk and interfacial pathways in the extraction. The interfacial rate constant for a given ligand was independent of organic solvent and was typically 10 times larger than the corresponding bulk value, indicating that the interface, although essentially aqueous in character, is a more conducive medium for the reaction of the metal ion and ligand.

The kinetics of reduction by free flavin semiquinones of the individual components of 1:1 complexes of yeast cytochrome c peroxidase and the cytochrome c from horse, tuna, and yeast, including several site-specific mutants of either the cytochrome c or cytochrome c peroxidase, have been studied. The orientations of the various cytochromes c within electrostatically-stabilized complexes with the peroxidase are not equivalent. This is shown by differential decreases in the rate constants for cytochrome reduction by neutral flavin semiquinones upon complexation which are in the order: tuna ≫ horse > yeast iso-2 > yeast iso-1. We have also directly measured the physiologically-significant intracomplex one-electron transfer rate constants from the ferrous cytochromes c to the peroxide-oxidized species of the peroxidase at several ionic strengths. The rate constants at low ionic strength are highly species dependent, again consistent with the contention that the orientations of the various cytochromes within the complex with CcP are not the same. Increasing the ionic strength in all cases resulted in an increase in the rate constant for the first-order process which controls electron transfer from cytochrome c to the peroxidase Compound I species of the peroxidase. When the two proteins are immobilized by covalent cross-linking, no such rate enhancement is observed, suggesting that the ionic strength effect is manifested by an increase in the number of geometric orientations between the two proteins which results in more rapid electron transfer. Similar rate enhancing effects are observed when positively charged residues on the surface of cytochrome c are converted to electrostatically neutral amino acids by site-specific mutagenesis. The effect of site-specific mutagenesis of two residues of cytochrome c peroxidase have also been studied. His-181, when converted to a glycine has little effect on the electron transfer rate constant, whereas when Trp-191 is converted to a phenylalanine no intracomplex electron transfer could be observed, indicating an obligatory role of this residue in the electron transfer process.

Genetic information is encoded in the long sequence of bases which form DNA, which is replicated during cell division by enzymes known as DNA Polymerases. Polymerases replicate DNA extremely accurately to avoid errors which can cause cell death and diseases such as cancer, although the mechanisms behind these extraordinary fidelities are not well understood. A large conformational change in the protein, in which the “fingers" subdomain closes around an incoming nucleotide, is thought to be implicated in these fidelity mechanisms. Here we present an assay to monitor this conformational change in single polymerase molecules, in real-time. We achieve this using total-internal-reflection-fluorescence (TIRF) microscopy to monitor the fluorescence resonance energy transfer (FRET) of an intra-protein dye labelled DNA Polymerase I (KF) as it binds to surface-immobilised DNA. Initially, we investigated the polymerase fingers-conformations during the pre-chemistry polymerisation reaction, resolving forward and backward rates which would be challenging to observe using ensemble techniques. These observations confirmed that KF closes rapidly around complementary nucleotide, but we discovered that the reverse step, fingers-opening, is particularly slow relative to chemistry. These finger kinetics act to remove the influence of the reaction rate-limiting step on fidelity, surprising given decades of investigations have focused on the rate-limiting step as the key determinant of fidelity. We also use our kinetic measurements to quantify contributions of different reaction steps to the macroscopic error rate of the polymerase. Subsequently, we developed our assay to investigate the fingers-conformations across the entire DNA polymerisation reaction. We observed single-nucleotide incorporations, and processive DNA polymerisation at high and low nucleotide concentrations, which suggested heterogeneous nucleotide incorporation rates. The observations demonstrated that the post-chemistry slow step that limits processive polymerisation occurs before post-chemistry fingers-opening, or is accounted for by post-chemistry fingers-opening. We observe a correlation in turn-over kinetics and binary complex kinetics, suggesting that turn-over rates could be limited by the intrinsic dynamics of the binary complex, as seen in other protein systems, although more work is needed on this.

From a review of the published work in the field of cycloadditions, it is evident that further research is needed to establish the mechanism of ketene cycloadditions. This work was initiated with the intent of obtaining kinetic data which will contribute to the elucidation of the mechanism of ketene cycloadditions.

The kinetic mechanism of activation of the NAD-malic enzyme by fumarate and the transition state structure for the oxidation malate for the NAD-malic enzyme reaction have been studied. Fumarate exerts its activating effect by decreasing the off-rate for malate from the E:Mg:malate and E:Mg:NAD:malate complexes. The activation by fumarate results in a decrease in K_imalate and an increase in V/K_malate by about 2-fold, while the maximum velocity remains constant. A discrimination exists between active and activator sites for the binding of dicarboxylic acids. Activation by fumarate is proposed to have physiologic importance in the parasite. The hydride transfer transition state for the NAD-malic enzyme reaction is concerted with respect to solvent isotope sensitive and hydride transfer steps. Two protons are involved in the solvent isotope sensitive step, one with a normal fractionation factor, another with an inverse fractionation factor. A structure for the transition state for hydride transfer in the NAD-malic enzyme reaction is proposed.

Modern spark ignition engines are downsized and boosted to meet stringent emission standards and growing customer demands on performance and fuel economy. They operate under high intake pressures and close to their limits to engine knock. As the intake pressure is increased knock becomes the major barrier that prevents further improvement on downsized boosted spark ignition engines. It is generally accepted that knock is caused by end gas autoignition ahead of the propagating flame. The propagating flame front has been identified as one of the most influential factors that promote the occurrence of autoignition. Systematic understanding and numerical relation between the propagating flame front and the occurrence of knock are still lacking. Additionally, knock mitigation strategy that minimizes compromise on engine performance needs further researching. Therefore the objectives of the current research consist of two steps: 1). study of turbulent flame propagation in both naturally aspirated SI engine. 2) study of the relationship between flame propagation and the occurrence of engine knock for downsized and boosted SI engine. The aim of the current research is, firstly, to find out how turbulent flames propagate in naturally aspirated and boosted S.I. engines, and their interaction with the occurrence of knock; secondly, to develop a mitigation method that depresses knock intensity at higher intake pressure. Autoignition of hydrocarbon fuels as used in spark ignition engines is a complex chemical process involving large numbers of intermediate species and elementary reactions. Chemical kinetics models have been widely used to study combustion and autoignition of hydrocarbon fuels. Zero-dimensional multi-zone models provide an optimal compromise between computational accuracy and costs for engine simulation. Integration of reduced chemical kinetics model and zero-dimensional three-zone engine model is potentially a effective and efficient method to investigate the physical, chemical, thermodynamic and fluid dynamic processes involved in in-cylinder turbulence flame propagation and knock. The major contributions of the current work are made to new knowledge of quantitative relations between intake pressure, turbulent flame speed, and knock onset timing and intensity. Additionally, contributions have also been made to the development of a knock mitigation strategy that effectively depresses knock intensity under higher intake pressure while minimizes the compromise on cylinder pressure, which can be directive to future engine design.

研究證實，助焊劑能將溶融合冷卻至其溶點之下，仍保持溶液態，亦即達到過冷態。這些溶液因而能夠進液態調幅分。它們凝固之後，會有種互相接的相。在這篇文，這種結構的合簡稱為網絡合。近期研究顯示，白鑄鐵Fe₈₀C₂₀ 亦可憑上述方法，冶成網絡合。其網絡合由種相構成。它們分別是αFe 子網絡及Fe₃C 子網絡，前者柔韌後者堅硬，因此這種網絡合有很優越的機械性能。 / 久之前，有報告研究Fe₇₉.₅B₆.₅C₁₄ 及Fe₈₄B₁₆ 網絡合的結晶過程。這篇文中，研究會集中在過冷Fe₈₀C₂₀ 的結晶過程。其微觀結構分為三區：區由無序網絡構成，十分細小。區之外遍佈高碳的Fe₃(C,B)，由於成份上與Fe₇₉.₅B₆.₅C₁₄的C區相，因此Fe₈₀C₂₀A區外的區稱作C₁ 區及C₂ 區，以相對照。C₁ 區的種子網絡成棒。C₂ 區與Fe₇₉.₅B₆.₅C₁₄ 的C 區一樣，網絡有明顯方向性，且長成樹幹圖案，其Fe₃(C,B) 子網絡屬多晶結構。 / 我們認為合的碳含是引致Fe₈₄B₁₆，Fe₇₉.₅B₆.₅C₁₄，Fe₈₀C₂₀ 三種網絡合，於微觀結構上有差別的原因。高碳的Fe₃(C,B)比低碳的Fe₃(C,B)難生長。以此，我們解釋上述三個合的結晶過程。在Fe₈₀C₂₀ 系統，大碳原子堆積於生長中的固體/液體界面前，這引致細小的A區､C₁ 區的高碳Fe₃(C,B)枝晶出現。 / By employing a fluxing technique, molten alloys can be undercooledsubstantially below its liquidus. The melts carry out phase separation by liquid state spinodal decomposition. After crystallization, solids with interconnected phases are obtained. They are called network alloy in this work. Recently, it is reported that a Fe₈₀C₂₀ eutectic ingot can be cast into a network alloy. The network alloy has two constituent phases. One of which is a ductile αFe subnetwork and the other one is a strong Fe₃C subnetwork. Therefore the network alloy has attractive mechanical properties. / The kinetics of crystallization in undercooled Fe₇₉.₅B₆.₅C₁₄ and Fe₈₄B₁₆ are latelyreported. In this thesis, the kinetics of crystallization in undercooled Fe₈₀C₂₀ alloy was studied. The microstructure can be classified into three zones. Zone A is a small random network. Outside zone A, the microstructure contains high-carbon Fe₃(C,B). In terms of the composition of Fe₃(C,B), they are analogous to the zone C inFe₇₉.₅B₆.₅C₁₄ system. Therefore the two zones outside zone A are named zone C₁ and C₂. Zone C₁ contains dendrites of the two subnetworks. Zone C₂ is the same as thezone C in Fe₇₉.₅B₆.₅C₁₄ systems, which is an aligned network structure showing patterns. The structure of Fe₃(C,B) subnetwork is polycrystalline. / The difference in microstructures between Fe₈₄B₁₆, Fe₇₉.₅B₆.₅C₁₄ and Fe₈₀C₂₀ isattributed to the carbon concentration. The formation of high carbon Fe₃(C,B) is less favoured than low carbon Fe₃(C,B). By this, the kinetics of crystallization in the 3 systems is explained. In Fe₈₀C₂₀, a high concentration of carbon atoms is established in front of the growing solid/liquid interface. This results in the presence of a small zone A and high carbon Fe₃(C,B) dendrites (zone C₁). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Yip, Kai Hou = 因過冷引致相分離的網絡結構Fe₈₀C₂₀合金的結晶動力學 / 葉繼豪. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / Yip, Kai Hou = Yin guo leng yin zhi xiang fen li de wang luo jie gou Fe₈₀C₂₀ he jin de jie jing dong li xue / Ye Jihao. / Abstract --- p.i / Acknowledgements --- p.v / List of Figures --- p.ix / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Composites --- p.1 / Chapter 1.2.1 --- Different Types of Composites --- p.1 / Chapter 1.2.2 --- Fabrication of Composites --- p.3 / Chapter 1.3 --- Phase Transformation --- p.3 / Chapter 1.4 --- Nucleation --- p.5 / Chapter 1.4.1 --- Homogeneous Nucleation --- p.5 / Chapter 1.4.2 --- Heterogeneous Nucleation --- p.6 / Chapter 1.5 --- Growth --- p.7 / Chapter 1.5.1 --- Solidification in Pure Metals --- p.8 / Chapter 1.5.2 --- Solidification in Alloys --- p.9 / Chapter 1.5.2.1 --- Growth of Single-Phase Alloys --- p.9 / Chapter 1.5.2.2 --- Solidification in Eutectic Binary Alloys --- p.11 / Chapter 1.6 --- Phase Separation by Spinodal Decomposition --- p.12 / Chapter 1.6.1 --- Spontaneous Phase Separation --- p.12 / Chapter 1.6.2 --- Uphill Diffusion --- p.13 / Chapter 1.6.3 --- Modified Diffusion Equation --- p.14 / Chapter 1.6.4 --- Solution to the Equation --- p.16 / Chapter 1.6.5 --- Morphology Resulted from Spinodal Decomposition --- p.17 / Chapter 1.7 --- Aim of This Project --- p.18 / Figures --- p.20 / References --- p.28 / Chapter Chapter 2: --- Experiment --- p.30 / Chapter 2.1 --- Introduction --- p.30 / Chapter 2.2 --- Preparation of Fused Silica Tube --- p.30 / Chapter 2.3 --- Sample Preparation --- p.31 / Chapter 2.3.1 --- Preparation of Eutectic Fe₈₀C₂₀ ingots --- p.31 / Chapter 2.3.2 --- Fluxing with Dehydrated B₂O₃ --- p.32 / Chapter 2.4 --- Optical Microscopy Analysis --- p.33 / Chapter 2.5 --- Scanning Electron Microscopy (SEM) Analysis --- p.34 / Chapter 2.6 --- Transmission Electron Microscopy (TEM) Analysis --- p.34 / Chapter 2.6.1 --- TEM Specimen Preparation --- p.34 / Chapter 2.6.1.1 --- Polishing --- p.35 / Chapter 2.6.1.2 --- Ion Milling --- p.35 / Chapter 2.6.2 --- TEM Characterization: Indexing Diffraction Patterns --- p.36 / Chapter 2.6.3 --- TEM Characterization: Electron Energy Loss Spectrum (EELS) --- p.37 / Figures --- p.39 / References --- p.43 / Chapter Chapter 3: --- Kinetics of crystallization in undercooled phase-separated molten Fe₈₀C₂₀ alloys --- p.44 / Chapter 3.1 --- Introduction --- p.45 / Chapter 3.2 --- Experimental --- p.45 / Chapter 3.3 --- Results --- p.46 / Chapter 3.3.1 --- SEM studies --- p.47 / Chapter 3.3.2 --- TEM studies --- p.49 / Chapter 3.4 --- Discussion --- p.55 / Chapter 3.5 --- Conclusion --- p.61 / Figures --- p.62 / References --- p.92 / Bibliography --- p.93