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Dissertation made openly available per email from author, 6-2-2016.

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Proteins containing selenocysteine (selenoproteins) have been found to exist in organisms from all domains of life. Selenoproteins are important for many in vivo processes such as the removal of reactive oxygen containing species (ROS), redox disulfide shuffling reactions, and pro-hormone activation. Structurally and functionally analogous to cysteine, selenocysteine's lower pKa appears to be the defining chemical difference between these two amino acids. Using a single-molecule electrical recording technique, rate constants for the reaction of selenocysteine with small molecule disulfides were obtained over a pH range of 6 - 10. Analogous single molecule ~riments carried out ~ .. - using cysteine, revealed that, after correcting for the ratio of selenolate to selenol and thiolate to thiol based on the pKa of each amino acid, the nuc1eophilicity of selenocysteine was comparable to that of cysteine. The selenium atom of the selenylsulfide bond was found to be substantially more electrophilic than a sui fur atom of the analogous disulfide bond and the leaving group ability of the selenolate of selenocysteine compared to the thiolate of cysteine were found to be comparable. Another biologically relavant interaction that occurs in vivo is the reaction between selenocysteine and organoarsenic (Ill) molecules. It is known that arsenic (Ill) compounds are toxic to organisms, and that this toxicity stems from the ability to coordinate to the thiol and selenol groups of the cysteine and selenocysteine residues within proteins. The reaction of selenocysteine with an organoarsenic species was investigated at the single molecule level over the pH range 6.5 - 8.5. By carrying out an analogous reaction between cysteine and the organoarsenic (Ill) species, it was found that selenocysteine and cysteine exhibit similar reaction rates. The organoarsenic reagent could exist in a range of different protonation states in solution and it was concluded that the rate of reaction was governed by the equilibrium of the arsenic molecule, where only some of the forms were reactive towards the selenocysteine and cysteine groups.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 252-265. / Ph.D.

Fe-B熔體可鑄造成網絡狀合金的微觀結構。研究顯示，熔融狀態的Fe₈₄B₁₆在275 K 過冷時將發生形態轉變。實驗結果指出熔融狀態的Fe-B合金存在一亞穏液態互溶區。該互溶區範圍為Fe₈₄B₁₄.到Fe₈₂B₁₈.。Fe-B網絡狀合金的微觀結構，由一個易碎的Fe₃B子網絡和一個具延展性的αFe子網絡組成。因此Fe-B網絡狀合金擁有具吸引性的物理性能。 / 由於Fe₈₄B₁₆網絡狀合金並不存在任何微孔，因此我們可推斷合金在結晶的過程中，兩個子網絡的固體/液體界面將一起生長。而且，在固體/液體界面前並不具有硼原子的濃度梯度。因此我們提出了一個生長模型來分析Fe-B網絡狀合金來自掃瞄電子顯微鏡和透射電子顯微鏡的檢測結果。Fe-B網絡狀合金的結晶動力學和微觀結構均得到解釋。研究顯示，合金中的兩個子網絡均擁有特定的生長方向，並且以樹枝晶的方式來生長。 / Molten Fe₁₀₀-{U+2093}B{U+2093} melts, where x = 14 to 18, can be cast into ingots of network morphology. It was found that there is a morphological transition in molten Fe₈₄B₁₆.with undercooling of 275 K. The experimental results indicate that there is a metastable liquid miscibility gap in undercooled Fe-B melts. The network morphology consists of two interconnected subnetworks, which are αFe subnetwork and Fe₃B subnetwork respectively. The Fe-B network alloys have attractive mechanical properties. / As micropore does not exist in the Fe₈₄B₁₆ network ingot, it is proposed that the solid/liquid interfaces of the two subnetworks advance together during solidification. In addition, there is no composition gradient of boron atoms at the growth front. A growth model is proposed to explain the results by scanning electron microscopy and transmission electron microscopy. It was found that there is special crystallinity in Fe₈₄B₁₆ network ingots. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wong, Tak Cheung = 鐵硼網狀合金的形成和結晶動力學 / 黃德彰. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / Wong, Tak Cheung = Tie peng wang zhuang he jin de xing cheng he jie jing dong li xue / Huang Dezhang. / Abstract --- p.ii / Acknowledge --- p.iv / List of Table --- p.vii / List of Figures --- p.viii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Phase diagram --- p.1 / Chapter 1.1.1 --- Undercooling --- p.1 / Chapter 1.2 --- Nucleation and Growth --- p.2 / Chapter 1.2.1 --- Homogeneous Nucleation --- p.3 / Chapter 1.2.2 --- Heterogeneous Nucleation --- p.3 / Chapter 1.2.3 --- Growth --- p.6 / Chapter 1.2.3.1 --- Growth of Pure Metal --- p.6 / Chapter 1.2.3.2 --- Solid/Liquid interface stability --- p.7 / Chapter 1.2.3.3 --- Solidification of Single Phase Binary Alloys --- p.8 / Chapter 1.2.3.3.1 --- Equilibrium Solidification --- p.8 / Chapter 1.2.3.3.2 --- Non-Equilibrium Solidification --- p.8 / Chapter 1.2.3.3.3 --- Morphology Change --- p.9 / Chapter 1.2.3.4 --- Solidification of the Binary Eutectic Alloy --- p.10 / Chapter 1.2.3.4.1 --- Growth of Lamellar Eutectics --- p.10 / Chapter 1.2.3.4.2 --- Off-Eutectic Alloys --- p.11 / Chapter 1.3 --- Binary Systems with a Solid Miscibility Gap --- p.11 / Chapter 1.4 --- Phase Separation Mechanisms in a Solid Miscibility Gap --- p.12 / Chapter 1.4.1 --- Nucleation and Growth --- p.12 / Chapter 1.4.2 --- Spinodal Decomposition --- p.13 / Chapter 1.4.4.1 --- The initiation of Spinodal Decomposition --- p.13 / Chapter 1.4.4.2 --- Diffusion Equation of Spinodal Decomposition --- p.14 / Chapter 1.4.4.3 --- Solution to the Modified Diffusion Equation --- p.17 / Figures --- p.18 / References / Chapter Chapter 2 --- Experimental --- p.29 / Chapter 2.1 --- Preparation of fused silica tube --- p.29 / Chapter 2.2 --- Alloying and fluxing --- p.29 / Chapter 2.3 --- Undercooling --- p.30 / Chapter 2.4 --- Sample Preparation --- p.31 / Chapter 2.4.1 --- Cutting, Grinding and Polishing --- p.31 / Chapter 2.4.2 --- Sample preparation for Scanning Electron Microscopy (SEM) --- p.32 / Chapter 2.4.3 --- Sample preparation for Transmission Electron Microscopy (TEM) --- p.32 / Chapter 2.5 --- Microhardness Test --- p.33 / Chapter 2.6 --- Compression Test --- p.33 / Chapter 2.7 --- Microstructure Analysis --- p.34 / Chapter 2.7.1 --- Scanning Electron Microscopy Analysis --- p.34 / Chapter 2.7.2 --- Transmission Electron Microscopy Analysis --- p.34 / Chapter 2.7.3 --- Indexing Diffraction Patterns --- p.34 / Figures --- p.36 / Chapter Chapter 3 --- Formation of Fe-B network alloys --- p.38 / Chapter 3.1 --- Abstract --- p.38 / Chapter 3.2 --- Introduction --- p.39 / Chapter 3.3 --- Experimental --- p.40 / Chapter 3.4 --- Results --- p.42 / Chapter 3.5 --- Discussion --- p.47 / Chapter 3.6 --- Conclusions --- p.48 / Figures --- p.50 / References --- p.69 / Chapter Chapter 4 --- SEM and TEM studies of Fe84B16 70 alloys of network morphology --- p.70 / Chapter 4.1 --- Abstract --- p.70 / Chapter 4.2 --- Introduction --- p.71 / Chapter 4.3 --- Background --- p.71 / Chapter 4.4 --- Experimental --- p.73 / Chapter 4.5 --- Results --- p.74 / Chapter 4.6 --- Discussions --- p.81 / Chapter 4.7 --- Conclusions --- p.85 / Figures --- p.87 / References --- p.106

Cheng, Lai Fung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaf 79). / Abstracts in English and Chinese. / Cheng, Lai Fung. / Chapter Chapter1 --- Introduction --- p.1 / Chapter 1.1 --- Phase diagram determination --- p.1 / Chapter 1.2 --- Formation of a hump in the free energy curve of L in a eutectic alloy --- p.2 / Chapter 1.3 --- Spinodal decomposition --- p.2 / Chapter 1.4 --- Early experience --- p.3 / Chapter 1.5 --- Bulk metallic glasses (BMG) --- p.5 / Chapter 1.6 --- Metal matrix composites (MMC) --- p.6 / Chapter 1.7 --- Liquid state phase separation and the formation of metal matrix comosites by fluxing --- p.6 / Chapter Chapter2 --- Experimental --- p.15 / Chapter 2.1 --- Introduction --- p.15 / Chapter 2.2 --- Preparation of fused silica tube --- p.15 / Chapter 2.3 --- Sample Preparation --- p.16 / Chapter 2.3.1 --- Alloying --- p.16 / Chapter 2.3.2 --- Fluxing --- p.16 / Chapter 2.4 --- Liquidus of Fe-C-Si specimens --- p.16 / Chapter 2.5 --- Microstructure Analysis --- p.17 / Chapter 2.6 --- Mechanical properties --- p.18 / Chapter 2.6.1 --- Hardness test --- p.18 / Chapter 2.6.2 --- Compressive strength --- p.18 / Chapter Chapter3 --- Formation and mechanical properties of Fe86Si14 network alloys --- p.23 / Chapter 3.1 --- Abstract --- p.23 / Chapter 3.2 --- Introduction --- p.24 / Chapter 3.3 --- Experimental --- p.25 / Chapter 3.4 --- Results --- p.27 / Chapter 3.5 --- Discussion --- p.33 / Chapter Chapter4 --- Dependence of mechanical behavior on C concentration in Fe-C-Si network alloys --- p.63 / Chapter 4.1 --- Abstract --- p.63 / Chapter 4.2 --- Introduction --- p.64 / Chapter 4.3 --- Experimental --- p.66 / Chapter 4.4 --- Results --- p.68 / Chapter 4.5 --- Discussions --- p.76