EVALUATION OF REDOX POTENTIAL AS A NOVEL BIOMARKER OF OXIDATIVE STRESS, INFLAMMATORY RESPONSE, AND SHOCK USING NANOPOROUS GOLD ELECTRODES Background: Redox potential is a chemical species’ affinity for electrons. Increased oxidant concentration is associated with disease1,2, yet there is not a way to measure systemic redox status.3 Redox potentiometry uses metal electrodes that do not work in blood because protein molecules adhere on the metal surface, blocking electron exchange. Methods: Nanoporous gold electrodes have large surface areas that allowed electron exchange to continue in blood.4 Redox potential was measured in blood with ascorbic acid, in cardiac bypass patients and pigs undergoing hemorrhagic shock and resuscitation. Results: Blood redox decreased with ascorbic acid addition, both in vitro and in vivo. It was more positive in patients undergoing cardiac surgery compared to healthy volunteers. Conclusions: Preliminary studies were limited, but appear to show correlation to disease processes and medical therapies. More work needs to be done to further examine the relation of redox to disease and treatment.

Thesis advisor: Chia-Kuang Tsung / In order to enhance the selectivity of metal nanoparticle heterogeneous catalysts, a method for the encapsulation of metal nanoparticles by crystalline nanoporous materials was designed and implemented through a wet-chemical, capping-agent-mediated encapsulation strategy. Two thermally and chemically stable metal organic frameworks (MOFs) with different aperture sizes were chosen as the crystalline nanoporous layers for metal nanoparticle (NP) encapsulation. Successful encapsulation and good catalytic performance depended on understanding and engineering the interface between the metal catalyst core and the nanoporous shell. After the synthesis of the NPs-MOF composite, their catalytic activity and selectivity were studied. Two kinds of capping agents (polymer and surfactant) were used to demonstrate different mechanisms for NP encapsulation. The polymer (polyvinylpyrrolidone, PVP) induced interaction between the NP surface and MOF precursors while the surfactant (cetyltrimethylammonium bromide, CTAB) controlled the alignment between the metal nanoparticles and MOFs. Furthermore, the capping-agent-directed overgrowth could be a general method of not only loading various inorganic nanoparticles into MOF single crystals but also bridging two porous materials with totally different structures. MOF shells were further functionalized by postsynthetic linker exchange. By applying the process, a new concept was introduced for the formation of enlarged pore apertures by linker dissociation during MOF linker exchange, as demonstrated by the postsynthetic encapsulation of species much larger than the pore aperture of the MOF structure. Kinetic studies of linker exchange rely on the competition between associative and dissociative linker exchange mechanisms. It was found that guest encapsulation was enhanced under conditions that favored the dissociative pathway. Through kinetics studies, linker exchange rate was also found to vary in different solvents. The different exchange rates were then used to create hierarchical porosity in MOF structure, and a double-solvent-mediated overgrowth strategy was designed to form hollow and mesoporous MOF. The results help to provide new ideas for nanopores related heterogeneous catalysis. The discussion of active metal NP cores with a nanoporous shell, as a frontier core-shell material, may benefit further study in developing highly selective catalysts. / Thesis (PhD) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

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Compliant nanoporous gold is investigated with regards to its elastic modulus and deformation mechanisms. Samples are fabricated by dealloying AgAu alloys at elevated temperature and reduced dealloying potential compared with conventional methods in the literature. This procedure minimizes cracking and shrinkage that is typical from other dealloying methods. Furthermore, samples are found to be more compliant while immersed in water. Samples were tested in cyclic compression using a piezoelectric compression rig. Testing showed that the wet samples become stiffer upon drying and the effect is reversible with short drying times. This is attributed to microstructural effects as the ligament network becomes more connected as a result of drying, effectively shifting the dominant deformation mode from three-point bending to cantilever bending. At longer dry times, the effect is irreversible due to contact weld formation. Preliminary results on sputter deposited AgAuPt alloys show altered dealloying kinetics and crack formation.

Compliant nanoporous gold is investigated with regards to its elastic modulus and deformation mechanisms. Samples are fabricated by dealloying AgAu alloys at elevated temperature and reduced dealloying potential compared with conventional methods in the literature. This procedure minimizes cracking and shrinkage that is typical from other dealloying methods. Furthermore, samples are found to be more compliant while immersed in water. Samples were tested in cyclic compression using a piezoelectric compression rig. Testing showed that the wet samples become stiffer upon drying and the effect is reversible with short drying times. This is attributed to microstructural effects as the ligament network becomes more connected as a result of drying, effectively shifting the dominant deformation mode from three-point bending to cantilever bending. At longer dry times, the effect is irreversible due to contact weld formation. Preliminary results on sputter deposited AgAuPt alloys show altered dealloying kinetics and crack formation.

¡@¡@In this thesis, the formation of m-plane (10-10) Gallium nitride (GaN) on the surface of a-plane (100) lithium gallate (LiGaO2, LGO) substrates via nitridation with ammonia (NH3) at high temperature. The parameters in this research were mainly focus on temperature, ammonia flow rate, reaction pressure, and growth time. ¡@¡@Specimens were analyzed with various instruments. X-ray Diffraction patterns showed that the nitridation process on LGO substrate resulted in the formation of the GaN single crystalline films. The crystalline quality of the GaN film could be improved by changing parameters of nitridation process. Scanning electron microscope image showed that the structure of GaN films was nanoporous. A red shift in the E2(high) phonon peak of GaN from micro-Raman indicates a compressive stress in the porous GaN with respect to the single crystalline epitaxial GaN. PL intensity ratio (INBE/IYL) of the porous GaN was found to be increased as changing parameters of nitridation process, namely the optical and crystalline quality of porous GaN was improved. Hall measurement showed that the porous GaN was p-type, and it had high hole concentration, good mobility, and low resistivity. Analyses of the elements depth profile by Auger electron spectroscopy. Transmission electron microscopy was used to observe the high resolution cross-section of porous GaN. From the selected area electron diffraction patterns, the orientation relationship between porous and LGO was determined as [100]LGO//[10-10]GaN and [0-10]LGO//[11-20]GaN when zone axis was [0001].

With increased worries of our Nations’ reliance on fossil fuels and their deleterious effects on the environment, researchers are concentrating on developing sustainable alternative sources for energy and chemicals. One potential starting resource that is worldwide distributed and renewable is biomass. Cellulose, the most plentiful source of biomass on earth, can be hydrolyzed into biofuel precursors such as 5-hydroxymethylfurfural (HMF). However, due to the poor solubility of cellulose and its robust crystalline structure, current methods available to degrade cellulose into these biofuel precursors are costly, result in low yields along with a large amount of waste. Generally, fructose is the preferred feedstock for the synthesis of HMF with high efficiency and selectivity. However, the large-scale production of HMF from fructose is limited due to the scarcity and the high cost of fructose. Therefore, it is desirable to use a cheaper renewable starting material for the synthesis of HMF such as sucrose. This study is conducted to develop an efficient one-pot process to synthesize HMF from biomass, particularly sucrose, using various sulfonated heterogeneous catalysts such as ordered mesoporous silica, bridged periodic mesoporous organosilicas (PMO) and carbon materials. The HMF yields in the presence of such acidic nanoporous materials were comparable to those using much less environmentally-friendly metal-based catalysts.

abstract: Traditionally nanoporous gold is created by selective dissolution of silver or copper from a binary silver-gold or copper-gold alloy. These alloys serve as prototypical model systems for a phenomenon referred to as stress-corrosion cracking. Stress-corrosion cracking is the brittle failure of a normally ductile material occurring in a corrosive environment under a tensile stress. Silver-gold can experience this type of brittle fracture for a range of compositions. The corrosion process in this alloy results in a bicontinuous nanoscale morphology composed of gold-rich ligaments and voids often referred to as nanoporous gold. Experiments have shown that monolithic nanoporous gold can sustain high speed cracks which can then be injected into parent-phase alloy. This work compares nanoporous gold created from ordered and disordered copper-gold using digital image analysis and electron backscatter diffraction. Nanoporous gold from both disordered copper-gold and silver-gold, and ordered copper-gold show that grain orientation and shape remain largely unchanged by the dealloying process. Comparing the morphology of the nanoporous gold from ordered and disordered copper-gold with digital image analysis, minimal differences are found between the two and it is concluded that they are not statistically significant. This reveals the robust nature of nanoporous gold morphology against small variations in surface diffusion and parent-phase crystal structure. Then the corrosion penetration down the grain boundary is compared to the depth of crack injections in polycrystal silver-gold. Based on statistical comparison, the crack-injections penetrate into the parent-phase grain boundary beyond the corrosion-induced porosity. To compare crack injections to stress-corrosion cracking, single crystal silver-gold samples are employed. Due to the cleavage-like nature of the fracture surfaces, electron backscatter diffraction is possible and employed to compare the crystallography of stress-corrosion crack surfaces and crack-injection surfaces. From the crystallographic similarities of these fracture surfaces, it is concluded that stress-corrosion can occur via a series of crack-injection events. This relationship between crack injections and stress corrosion cracking is further examined using electrochemical data from polycrystal silver-gold samples during stress-corrosion cracking. The results support the idea that crack injection is a mechanism for stress-corrosion cracking. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

Nanoporous alumina is a rather newly characterized material that so far has found limited use in the construction of bioreactors. The material has many advantages compared to conventional immobilization matrices. I have investigated its use in flow-through bioreactors. The rigidity and porous structure of the material makes it an excellent choice for multienzyme reactor construction. The total activity in a reactor is easily controlled by the number of membranes since the porosity makes the material less prone to increase flow system pressure. This bioreactor is suitable for characterization of new enzymes since the amount of immobilized enzyme is standardized and the enzyme may be reused many times. We designed a simple stepwise technique for covalent immobilization on this matrix in a monolayer to minimize mass transfer effects in the reactor function. The kinetic parameters for ten different substrates were investigated for immobilized alcohol oxidase and, as a second step, a two-step reactor was also designed by addition of horseradish peroxidase. This bienzymatic reactor was, in turn, employed for measuring injected alcohol concentrations. The use of the matrix for substrate specificity screening was proven for two new epsilon-class glutathione transferases from Drosophila melanogaster. Immobilized trypsin showed a substantially prolonged lifetime and its potential use as an on-line digestion unit for peptide mass fingerprinting was also demonstrated. Finally, I investigated the immobilization of the model enzyme lactate dehydrogenase by adsorption mediated by metal ion chelation similar to IMAC. Regeneration was here possible multiple times without loss of capacity. In conclusion, immobilization of enzymes on nanoporous alumina is a convenient way to characterize, stabilize and reuse enzymes.

A study is presented on the synthesis and characterization of nanoporous AgPt and AgAu alloys after annealing and dealloying in 5% HClO4. Dealloying removes the less-noble atom from the alloy surface to produce nanoporous, highly-interconnected ligaments. Voltammetry of AgPt and AgAu shows the critical potential, Ec, at various potential scan rates. Potential hold current decay experiments on Ag-23Pt and Ag-23Au further show the intrinsic Ec to be 275 mV and 290 mV, respectively. Ec was governed by thermodynamic clustering in the alloys as opposed to dissolution-diffusion kinetic effects. EDX shows the starting 77Ag-23Pt material changes composition after dealloying to about 12Ag-88Pt. XRD indicates the presence of ordering in AgPt via a superlattice (100)-peak for a specific anneal treatment. EIS measurements done on as-annealed and dealloyed AgPt and AgAu samples show the onset of bulk porosity and show that capacitance increase is equal for both alloys at two different dealloying potentials.