Theses and Dissertations - Department of Chemical & Biological Engineering

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    Engineering Approaches to Study and Target Breast Cancer Brain Metastasis
    (University of Alabama Libraries, 2020) Narkhede, Akshay; Rao, Shreyas S; University of Alabama Tuscaloosa
    Breast cancer brain metastasis marks the most advanced stage of the disease with the median survival period of only 4-16 months. A major hurdle in developing therapeutic strategies to tackle breast cancer brain metastasis is our limited understanding of mechanisms involved in metastatic progression of breast cancer to the brain. This is, in part, due to lack of biomimetic in vitro models to study the interactions between metastatic breast cancer cells and the brain microenvironment. In addition, challenges associated with ineffectiveness of current diagnostic as well as therapeutic techniques in crossing the blood-brain barrier, and specifically labeling and targeting cancer cells pose further difficulties in treating metastatic brain malignancies. To address this issue, this dissertation focuses on engineering an in vitro hyaluronic acid (HA) hydrogel-based platform to investigate the microenvironmental regulation of breast cancer brain metastasis. HA hydrogel was chosen as it recapitulates key bio-physical and bio-chemical aspects of the native brain microenvironment. Specifically, this in vitro HA hydrogel-based platform was utilized to elucidate the mechanobiology underlying breast cancer brain metastasis. Further, the HA hydrogel-based platform was also adapted to model dormancy associated with brain metastatic breast cancer cells. Taken together, the in vitro biomimetic HA hydrogel-based platform for studying microenvironmental regulation of breast cancer brain metastasis, as presented in this dissertation, is a promising first step towards development of robust biomimetic strategies for studying breast cancer brain metastasis in a controlled setting. Finally, this dissertation also focuses on investigating the potential of ultrasmall iron oxide nanoparticles (< 4 nm) for labeling primary and metastatic brain cancer cells in vitro; to be utilized as a platform for tumor-targeted drug delivery and in imaging and early detection. Ultimately, such engineering approaches could provide mechanistic insight into the progression of breast cancer brain metastasis and enable the development of targeted therapeutics for the metastatic disease.
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    Electrodeposition of Cobalt for Advanced Interconnect Applications
    (University of Alabama Libraries, 2021) Hu, Yang; Huang, Qiang; University of Alabama Tuscaloosa
    Copper (Cu) damascene processes have been used to produce back end of line (BEOL) interconnect structures in integrated circuits (IC). As the critical dimension of BEOL structures approaches the electron mean free path of Cu or below, the Cu resistivity exponentially increases, posing significant challenges on further scaling. Metals with shorter electron mean free path, for example cobalt (Co), have been explored as the alternative material to replace Cu in the finest metal levels.The Co electrodeposition process for interconnect applications must produce Co films that can reproducibly fill deep vias or trenches without any defects. It is can be achieved by adding small amounts of organic additives to the plating bath, which lead to the Co electrodeposition preferentially at the bottom of trench, known as bottom-up filling, or super conformal filling, or simply “super-filling”. As the size of interconnect continues to shrink, additives are becoming the key to the successful application of Co electrodeposition in IC manufacture. In this dissertation, a new class of organic additives, dioximes (dimethylglyoxime, cyclohexane dioxime, and furil dioxime), have been investigated for their effects on the electrochemical deposition process of cobalt. In Chapter 2, the nucleation and growth behavior of Co deposition with the addition of dimethylglyoxime and cyclohexane dioxime are studied. Double-peak nucleation curves are observed during Co deposition for the first time. In Chapter 3, a descriptive model is established for the Co nucleation process using furil dioxime, where the suppression effect on Co deposition and the catalytic effect on hydrogen evolution are both more pronounced among the dioxime molecules. Mercaptopropanesulfonate, or MPS, a well-known accelerator used in Cu damascene process, is investigated during the Co deposition in Chapter 4. A potential oscillation is observed during galvanostatic deposition for the first time and a kinetically controlled mechanism is proposed. In Chapter 5, Co films are electrodeposited with different additives including dimethylglyoxime, sodium chloride, and 3-mercapto-1-propanesulfonate. It is found that the addition of 3-mercapto-1-propanesulfonate into the electrolyte significantly increases the S incorporation level and decreases the grain size, both contributing to a higher sheet resistance of film.
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    Atomic Layer Deposition for Surface Modifications and Solid Film Fabrication
    (University of Alabama Libraries, 2021) Yan, Haoming; Peng, Qing; University of Alabama Tuscaloosa
    Along with the unceasing development of the surface and material science, modification of substrates surfaces in nanoscale, to fabricate the functional materials with precisely controlled dimensions, refined composition and desired properties becomes crucial. In this report, atomic layer deposition (ALD), a vapor phase, sequential and self-limiting deposition process, has been used as an alternative strategy to modify the surface of materials and fabricates nanometer or micrometer level of functional materials with precise control. In the first part of this dissertation, ALD was used to modify the surface of the shape-engineered nanocrystals (SENCs), which enhanced the thermal stability of the SENCs from 300˚C to 700˚C and enhanced the catalytic activities of the nanocrystals as well. We also proposed a new reaction mechanism of metal-organic precursor with oxide surface, in which the conventional layered ALD growth does not happen but the oxide surface was modified via controlled metal doping. In the second part of this dissertation, ALD precursors were used to reacting with liquid substrates to fabricate freestanding solid thin films. Benefits from the unique reaction mechanism of the ALD metal-organic precursors, the thickness and the compositions of the fabricated films can be controlled. The fundamental of gas-liquid reaction has been discussed in this study. In the third part of this dissertation, area-selective ALD (AS-ALD) has been reported using carboxylic acid self-assembled monolayer as a growth inhibitor. Excellent selectivity of AS-ALD has been achieved by using this method, which could potentially be used in microfabrication as a substitution step for photolithography.
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    Computational Predictions for the Interactions of Lewis Acid Gases with Each Other and with Materials of Interest
    (University of Alabama Libraries, 2021) Lee, Zachary Ryan; Dixon, David A.; University of Alabama Tuscaloosa
    This dissertation focuses on the computational chemistry predictions of the mechanisms and products of Lewis acid gases with materials of interest to understand the chemistry of these systems and to aid in the design of practical sorbents for acid gas separations and conversions. A detailed computational investigation of the species present prior to the introduction of a sorbent was performed. The barriers and overall thermodynamics of H2SO4, H2SO3, H2S2O3, and H2S2O2 formation from the reactions of SOx (x = 2 or 3) with H2O and H2S in both gas phase and in aqueous solution as well as the resulting acidities of these Brønsted acids were predicted. These calculations were performed using the Feller-Peterson-Dixon (FPD) methodology with implicit MP2/aug-cc-pVTZ/COSMO corrections included for predicting energies in aqueous solution and predict favorable formation of strongly acidic H2SO4 and the experimentally elusive H2S2O3. The thermodynamics of a novel type of NO2 adsorption to Groups IV and VI transition metal oxide clusters, calculated at the CCSD(T)//B3LYP level, are compared directly to the previously predicted binding energies of CO2, SO2, and H2O to these oxides and correlated with the M-O bond dissociation enthalpy, vertical excitation energy, electron affinity, and ionization potential trends of the bare metal oxides themselves. The results provide key insight into the importance of band gaps and M-O bond strengths for the selection of metal oxides for NOx separations. The role of 4f electrons and the surrounding ligand environment on the acid gas interactions of H2O, NO2, and SO2 with a promising class of metal-organic frameworks (MOFs), the rare-earth 2,5-dihydroxyterephthalic acid frameworks, was studied using DFT for both a cluster model which explicitly treats the lanthanide 4f electrons and a periodic model to predict bulk interactions without the inclusion of active 4f electrons. Insight into the reaction mechanisms of the promising post-combustion capture of CO2 by aqueous and solid-state amines was studied primarily using the composite G3(MP2) methodology. As a whole, these studies provide a detailed understanding of the chemical thermodynamics and kinetics relevant to acid gas capture by promising materials of interest.
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    Transition Metal Dichalcogenides for Use in Hydrogen Evolution Reaction, CO2 Reduction and Their Photoluminescence Spectroelectrochemistry
    (University of Alabama Libraries, 2021) Strange, Lyndi Elizabeth; Pan, Shanlin; University of Alabama Tuscaloosa
    Transition metal dichalcogenides (TMDs) are semiconductors of the form MX2, where M is a transition metal (Mo, W, etc.) and X is a chalcogen atom. They are structured in layers of M atoms sandwiched between two layers of X atoms. Two-dimensional TMDs (2D-TMDs) consist of a single layer of atoms that have the structure X-M-X and have electronic properties that differ from the bulk material. In the search for efficient and low-cost catalysts for renewable energy harvesting and conversion and storage, TMDs have emerged as promising catalysts for alternative energy such as photovoltaic water splitting anodes, hydrogen evolution reaction, CO2 reduction, photovoltaic absorber layers, and protective layers for photovoltaic devices. The structure of the TMDs can also be tuned at the monolayer level to increase catalytic activity by doping and introducing defects to enhance electrocatalytic hydrogen reduction. The highly tunable structure also leads to tunable optical properties that are useful in next-generation optoelectronics such as light-emitting diodes (LEDs), field-effect transistors (FETs), and ultra-sensitive molecular sensing due to their unique surface-sensitive optical properties. Learning how the structure affects the catalytic and optical properties serves as an important area of research to tune TMDs to produce more efficient catalysts and serve in various optical applications. This dissertation will focus on developing and understanding TMD catalysts for proton reduction, CO2 reduction, and also their spectroelectrochemical properties. Chapter 1 of this dissertation provides an overview of recent progress made in the field of TMDs and the goals of this doctoral research work. Chapter 2 summarizes the operation principles of the critical instrumental and experimental methods of this research work. Chapter 3 describes proton reduction characteristics of electrodeposited TMD thin-film electrodes and structural confirmation with advanced characterization techniques such as XPS depth profiling to understand the synthesized structure. Chapter 4 is devoted to the investigation of the photophysical properties and spectroelectrochemistry performance of 2D TMDs using SECM, SECCM, and spectroelectrochemical techniques. Chapter 5 describes the electrocatalytic CO2 reduction characterization of liquid exfoliated MoS2 film and an extensive literature overview of the field of photocatalytic CO2 reduction with TMD heterostructures. Finally, Chapter 6 summarizes the entire research work and challenges and proposed plans to address these challenges.
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    Computational Studies of Transition Metals and Small Molecules
    (University of Alabama Libraries, 2021) Persaud, Rudradatt Randy; Dixon, David A.; University of Alabama Tuscaloosa
    The chemistry that transition metals can access due to their d orbitals has expanded the horizons of many fields in chemistry. The work covered in this dissertation focuses on designing a computer system for performing computational studies, and a wide range of computational chemical studies of transition metals in various applications including predictions of bulk properties, homogenous/heterogenous catalysis, and the acidity of solvated transition metals for use in proteomics. Utilizing high-performance computers allows chemists to explore the d-block elements to aid in the analysis of experimental results or to explore new chemistry cheaply, safely, and ‘greenly’. Although a handful of high-performance computer cluster building recipes are available for general use, a free-open source recipe geared towards computational chemistry with compatibility for a broad range of computer hardware is provided. High level MO theory studies of coinage-metal trimers were done to study their potential energy surfaces. While exploring these potential energy surfaces, a novel, vibrationally bound, local minimum for the gold trimer was discovered, one of the first examples of bond angle isomerism. The normalized clustering energies of small metal clusters (n = 2-20) of the coinage metals were extrapolated to predict the cohesive energy of the bulk metal. The importance of spin orbit coupling for the binding energies of gold clusters was found. Density functional theory was used to calculate the binding energies of organic molecules including cyclohexane and benzene on a model of the rutile TiO2(110) surface, an important first step in heterogeneous catalysis of these species on a transition metal oxide. The calculated vibrational frequencies were used to predict reliable prefactors for analysis of temperature programmed desorption experiments. Mechanisms for the homogenous catalysis of the reduction of CO2 to formate using a triphosphine-ligated Cu(I) catalyst were developed. A mechanism of enhanced protonation involving transition metals in an electrospray ionization source in mass spectrometry for proteomic applications was developed.
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    Pyridine Modified Gold Nanoparticles for Electrocatalytic Carbon Dioxide Reduction and Methanol Oxidation Reactions
    (University of Alabama Libraries, 2021) Kang, Xin; Pan, Shanlin; University of Alabama Tuscaloosa
    The global consumption of fossil fuels produces an enormous amount of carbon dioxide, causing a series of environmental problems such as glacial melting, food production reduction, and sea-level rise. Because it can potentially help address the global energy challenges and environmental issues from fossil fuels, CO2 harvesting, storage, and conversion to chemical fuels are of great research interest. CO2 can be transformed into chemical fuels (e.g., CO, CH4, and methanol) by electrochemical reduction reaction. Catalysts play critical roles in enhancing the selectivity and lowering the overpotential of the CO2 reduction reaction. For example, the main product of the carbon dioxide reduction reaction with the gold electrode is CO due to its low adsorption on the gold surface. Pyridine has been used to promote CO2 reduction by controlling the local pH of an electrode to enhance catalytic efficiency and selectivity. This research project primarily focuses on developing pyridine-modified Au nanoparticles for catalyzing electrochemical CO2 reduction and methanol Oxidation. The effects of the gold-pyridine conjugate formula, reduction potential with a rotating ring disc electrode (RRDE) and RRDE rotation speed on CO2 reduction current density and product collection efficiency, and electrode stability are investigated. Pyridine-modified nanoparticles improve the CO2 reduction catalytic reaction. Au/Cu nanoparticles are supposed to have better catalytic performance CO2 reduction than pure Pt nanoparticles due to the synergistic effect of Au and Cu promoting efficient reduction and desorption of CO from its surface. This study also investigated the MOR activities of pyridine-modified Au nanostructures. Au/Pt nanoparticles are supposed to have better catalytic performance for methanol oxidation than pure Au nanoparticles.
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    Bioengineering of Heterogenous Glioblastoma Multiforme Microenvironment
    (University of Alabama Libraries, 2021) Park, Seungjo; Kim, Yonghyun; University of Alabama Tuscaloosa
    Glioblastoma (GBM) is the most aggressive brain tumor that originates from glioblastoma stem cells (GSCs). In the brain, GSCs are supported by a tumor microenvironment (TME) wherein the perivascular niche and hypoxic region are present. The glioblastoma microenvironment (GBME) exhibits high heterogeneity, vast cell-to-cell interactions, and stiff mechanical properties. To produce in vitro models mimicking the GBME features, GBM organoid (GBO) models have been developed. Conventional organoid studies rely on growing them in serum-free media, resulting in sphere formation. However, this conventional method is not scalable and often fails in recapitulating inter- and intratumor heterogeneity. Also, the conventional method is not ideal to produce adequate quantities of GBOs to screen drugs for personalized medicine. Therefore, development of a reproducible and scalable GBO culture method can provide a better platform to simulate novel treatments.First, the bioreactor design was optimized by using different diameters of impellers and bioreactor vessels. Even with similar shear stresses, cell proliferation was inhibited or promoted depending on the ratio of the impeller diameters to the vessel diameters. With the optimized vessel geometry, shear stress and media supplements were optimized for GBO production. The bioreactor GBOs (bGBOs) were produced in uniform size, not by clonal aggregations, but by cell proliferation. With the optimal agitation rate, bGBOs displayed upregulation of genes involved in stemness, hypoxia, angiogenesis, proliferation, and migration. The statistical analysis revealed the synergetic effects of the high agitation rate and the size of the bGBOs. Next, bGBO models were characterized by their morphologies and transcriptional and translational profiles. The bGBOs exhibited high and strong cell-to-cell contact. Multivariate gene analysis found a significant correlation between gene expression and the size of the bGBOs. GBME was established and spatially organized in bGBOs greater than 800 µm in diameter. Hypoxic TME was developed in bGBOs greater than 400 µm in diameter. Inside the bGBOs, spatially separated features of the hypoxic niche and the perivascular niche were demonstrated. Also, the large bGBOs displayed angiogenesis features. Self-established GBME was organized by transdifferentiated GBM into endothelial cells, pericytes, and astrocytes. GBME containing necrotic regions displayed more spatially distinctive and hierarchically organized GSC niches. The GSCs in the niche were regulated by transcription factors involved in dedifferentiation. Hydrogels have been employed to further understand underlying mechanisms of the transformation of GBM in the bGBO model. Mechanical properties of GBME was engineered using hyaluronic acid (HA)-based hydrogels. Cell behavior in response to the hydrogel stiffness was examined. Transcription factors dedifferentiating GBM into GSCs were translocated to the nucleus in response to stiffer substrates. Collectively, these studies provided a small-scale model for a high-throughput production of GBOs that recapitulate in vivo GBM features, including high heterogeneity and high cell-to-cell interactions. Hydrogel model and the bioreactor culture conditions described here suggest that GBOs can be biomanufactured by modulating mechanical stress.
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    Chromium(III) Interaction with Transferrin and Transferrin Receptor
    (University of Alabama Libraries, 2021) Edwards, Kyle Carter; Vincent, John B.; University of Alabama Tuscaloosa
    Transferrin (Tf), the major iron transport protein in the blood, apparently also transports trivalent chromium via endocytosis. The release of chromium(III) from human serum transferrin has been examined under conditions mimicking an endosome during endocytosis. At pH 4.5 and 5.5, the release of Cr(III) from Tf occurs rapidly from the C-lobe binding site and slowly from the N-lobe binding site. The loss of N-lobe bound Cr(III) under these conditions is accelerated by the presence of a anionic chelating ligand. When Cr(III)-loaded transferrin is added to soluble transferrin receptor (sTfR), the loss of Cr(III) from both binding sites becomes rapid at acidic pH, more rapid than from either site in the absence of the receptor. Loss of Cr(III) from the Tf-sTfR complex is easily sufficiently rapid for Tf to serve as the physiological transporter of Cr(III) from the bloodstream to the tissues. Studies have also found that Cr(III)2-Tf can exist in multiple conformations giving rise to different spectroscopic properties and different rates of Cr(III) release. Time-dependent spectroscopic studies of the binding and release of Cr(III) from human serum Tf have been used to identify three conformations of Cr(III)2-Tf. The conformation formed between 5 and 60 minutes after the addition of Cr(III) to apoTf at pH 7.4 resembles the conformation of Cr(III)2-Tf in its complex with sTfR and loses Cr(III) rapidly at endosomal pH. Loss of Cr(III) from Cr2-Tf and Cr2-Tf-sTfR in the presence of apo-chromodulin (LMWCr) results in accumulation of Cr(III) bound to LMWCr and is rapid when sTfR is present indicating the species can form under endosomal conditions and may be the next carrier in the Cr(III) transport pathway. Techniques used throughout the projects were also applied to Mn(III)2-Tf, and the first parallel mode EPR signal for Mn(III)-Tf is reported, which could prove valuable for future studies.
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    Molecular Design of High-Performance Imidazolium Ionenes as Gas Separation Membranes and 3D Printing Materials
    (University of Alabama Libraries, 2021) O'Harra, Kathryn Elizabeth; Bara, Jason E.; University of Alabama Tuscaloosa
    This dissertation details the development and performance of a library of imidazolium ionenes for advanced engineering applications, with an emphasis on membrane-based gas separations and additive manufacturing. Several distinct sets of high-performance ionenes, polymers which contain ionic groups along the backbone chain rather than as pendants, were methodically designed and synthesized. These materials combine structural features commonly associated with state-of-the-art gas-separation membranes with chemical functionalities associated with high-performance engineering polymers. These functional features are spaced by incorporated ionic groups along the main chain, specifically imidazolium cations paired with fluorinated, delocalized anions. The modular synthetic methods and diverse processability of these new ionenes demonstrate that the rational design of materials can lead to enhanced performance and unique properties and behaviors. Through variation of substituents, connectivity along the backbone, and the sequence of functional and ionic segments, this work demonstrates the expansive opportunities for incorporating, distributing, and alternating structural features. These ionenes possess excellent thermal and mechanical properties, while the tailorability and synthetic modularity ionenes provide access to an array of interesting behaviors and molecular architectures. These ionic polymers materials exhibit self-assembly and local structuring when impregnated with “free” imidazolium-based ionic liquids (IL) or multivalent organic salts, which contributes additional tunability and alters intermolecular interactions in the ionene matrix. These HP-ionenes and IL composites were thoroughly characterized to develop structure-property relationships and to understand the coordination between the dispersed, discrete additives and the polymeric ionene matrix. Using the information gathered from characterization of these ionenes and IL composites, the specific suitability of processing techniques for each series of functional imidazolium ionenes was explored, yielding applied studies of these advanced materials as films/coatings, fibers, 3D printing resins, and self-healing elastomers.
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    The Deprotonation and Dissociation of Amino Acids and Peptides by Negative Ion Mode Mass Spectrometry
    (University of Alabama Libraries, 2021) Cui, Can; Cassady, Carolyn J.; University of Alabama Tuscaloosa
    Investigation of negative ion mass spectrometry (MS) is important to proteomics due to its superior ability to analyze acidic peptides and provide complementary information to positive ion mode. This dissertation focuses on the deprotonation and dissociation of amino acids and peptides, which provides fundamental knowledge and assists in development of negative ion MS. Gas-phase acidities (GA) of acidic peptides were determined experimentally and compared to computational values. In electrospray ionization (ESI), either one major structure or multiple structures with very similar GAs were formed. Peptides with acidic residues at the C-terminus are more acidic than those at the N-terminus. Replacing glutamic acid residues (E) with aspartic acid (D) can increase the acidities when E is at the C-terminus but has no effect if E is at the N-terminus. Bond dissociation energies of deprotonated amino acids, dipeptides, and their amides were investigated by combining MS and computations. The loss of H2O occurs in collision-induced dissociation (CID) from all amides except glycine amide. Loss of the C-terminus is only seen in CID of deprotonated dipeptides. In addition, an intense y1 ion forms from dipeptides and their corresponding amides. In the comparison among radical-based dissociation techniques, negative ion in-source decay (nISD) has the best performance for peptides. nISD gives the highest sequence coverage and consistently generated singly charged c- and z-ions. Besides, nISD produced the least neutral loss products and is the fastest technique. The disadvantage of nISD is its inability to select precursor ions. For the investigation of nISD with oxidizing matrices on acidic peptides, 4-nitro-1-naphthylamine (4N1NA) was used as a MALDI matrix for the first time and was found to be the most useful matrix. The overall sequence coverage obtained with 4N1NA is higher than with three other matrices. The formation of c- and a-ions indicates that 4N1NA has both reducing and oxidizing characteristics.
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    Pattern-Based Discrimination of Carboxylate Anions in Aqueous Media and on Solid Supports
    (University of Alabama Libraries, 2021) Xu, Yifei; Bonizzoni, Marco; University of Alabama Tuscaloosa
    Carboxylate-containing species play important roles in biosynthesis, energy generation and biological signaling; they are also common functional groups in pharmaceuticals, and potential pollutants in aqueous media. Sensing and discrimination of carboxylates was achieved using non-covalent interactions mediated by poly(amidoamine) (PAMAM) dendrimers, a family of macromolecular polyelectrolytes.Our focus was on fast, sensitive, and inexpensive detection methods based on optical spectroscopy. However, neither the dendrimers nor the analytes have spectroscopic signals in the visible region, so we first designed and tested an indicator displacement assay (IDA), built from PAMAM dendrimers and common organic dyes, whose response was monitored through absorbance, fluorescence emission and fluorescence anisotropy (Chapter 2). We achieved qualitative and quantitative discrimination among structurally similar carboxylates using pattern-based clustering methods applied to the output of the IDA sensing system (Chapter 3). It is noteworthy that we obtained not only qualitative discrimination (where pattern recognition commonly excels) but also quantitative measurements, a much rarer accomplishment. In Chapter 4, the scope was extended to the discrimination of β-lactam antibiotics, a family of environmentally and biologically relevant analytes that contain carboxylate groups and comprise more than half of the world market for antibiotics. A novel partial hydrolysis method, introduced here, significantly increased the affinity of these compounds for the PAMAM hosts; this in turn allowed us to successfully differentiate samples drawn from an analyte panel comprising two penicillins, five cephalosporins, and two references. In Chapter 5 we move these carboxylate sensing methods to solid supports with lower cost and higher stability, on a path towards the construction of a portable, deployable device. Studied support media included cellulose acetate, SiO2 dispersions, regular printing paper, filter paper, and chromatography paper. Chromatography paper, the best performer, yielded excellent differentiation and repeatability, and improved long-term stability over the same system in water. Finally, Chapter 6 describes our efforts to improve the determination of the concentration of chloroform, a halogenated byproduct of water chlorination and a dangerous water pollutant. We attempted to improve upon the common colorimetric Fujiwara test, using the intensely colored Fujiwara product as an optical filter to modulate the fluorescence emission of organic fluorophores.
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    Structure-property relationships in polyimide-ionenes and composites with ionic liquids as gas separation membranes
    (University of Alabama Libraries, 2020-12) Dennis, Grayson Patrick; Bara, Jason E.; University of Alabama Tuscaloosa
    Ionic polymers have capabilities to shape the pathway to new membranes and polymer systems that did not exist before. The imidazolium moiety has shown substantial abilities to integrate into a platform for ionic polymers allowing their growth and formation through imidazolium use as a building block. Addition of this component, both ionic and non-ionic, into a polymer matrix has been developed, but the creation of highly tunable, modular polymer structure that contains imidazolium has the potential to surpass previous iterations of ionic compounds and materials in gas separation. After developing a tailorable approach to high performance ionic polymers, we have formed ionic polyimides and polyamides that have been used for various applications such as gas separation, coatings, and films. The ionic polyimides and polyamides which were formed have the potential to be used as CO2/light gas membranes.The hardest factor to overcome within membrane separation is the flux-selectivity tradeoff which describes the upper limits of permeability, gases ability to flow through a membrane, and selectivity, one gas’s ability over another to permeate. With the addition of these ionic units into the backbone and as “free”-ILs within the polymer matrix, the permeabilities of these materials can be greatly increased. Through systematic design and study of materials, the structure-property relationship of these newly developed ionic polymers can be determined and applied to further the understanding of these unique polymer systems.
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    Experimental and computational studies of materials decomposition
    (University of Alabama Libraries, 2020) Confer, Matthew Phelan; Street, Shane C.; Klein, Tonya M.; University of Alabama Tuscaloosa
    Hydrogen enriched fuels offer a broad range of thermo-physical and chemical properties that are desirable for combustion reactions. In this work, a eutectic mixture of ammonia borane and methylamine borane that demonstrates improved solubility in polar solvents compared to the single constituents was prepared and characterized. Ignition and burn of the amine borane eutectic mixture were characterized using high framerate imaging and emission spectroscopy. The solubility of ammonia borane, methylamine borane, dimethylamine borane, trimethylamine borane, and tert-butylamine borane in different solvents was measured and modeled using the COSMO-RS utility in ADF2016 and the self-consistent reaction field (SCRF) method. The enthalpy of solution was experimentally determined for ammonia borane, methylamine borane, dimethylamine borane, and the ammonia borane/methylamine borane eutectic in different solvents.In addition to characterization of known hydrogen storage materials, new high energy hydrogen storage materials were computationally designed. The energetics and decomposition pathways for novel carbon, nitrogen, silicon, and phosphorus centered substituted amine borane hydrogen storage materials were modeled using composite correlated molecular orbital theory at the G3MP2 level, and the amounts of different species as a function of temperature were predicted using Gibbs free energy minimization. Theoretical models of decomposition reactions are also important for perfluorocarbon synthesis and polymer property modification. Safe and effective direct fluorination of compounds can reduce cost of synthesizing fluorinated compounds as well as potentially improving processability. The thermodynamics for direct fluorination of tetrafluoroethylene and the role of hexafluoropropylene oligomers in reducing explosions were predicted. In addition, high energy radiation from γ-rays or lasers can be used to improve the properties and processability of polymers such as a tetrafluoroethylene/perfluoro(methyl vinyl ether) copolymer or poly(vinyl alcohol) potentially leading to reduces bacterial contamination in packaging for pharmaceutical and food. A computational model for decomposition of a tetrafluoroethylene/perfluoro(methyl vinyl ether) copolymer was developed using composite correlated molecule orbital theory corrected density functional theory calculations. The mechanism of infrared laser ablation of γ-irradiated poly(vinyl alcohol) to produce water and ketone species was studied computationally using composite correlated molecular orbital theory.
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    Structural investigations and determination of biocatalyst potential of Pseudomonas putida CBB5
    (University of Alabama Libraries, 2020) Mills, Shelby Brooks; Summers, Ryan M.; University of Alabama Tuscaloosa
    Pseudomonas putida CBB5 has evolved the ability to metabolize caffeine and other methylxanthines to xanthine using a set of five enzymes, NdmABCDE. NdmABC are N1-, N3-, and N7-specific N-demethylases, respectively, that are part of the multicomponent Rieske oxygenase family. Structural investigations of NdmA, NdmB, and NdmD were conducted along with determining the applicability of harnessing this N-demethylation system for the bioproduciton of methylxanthines. Protein co-expression and purification of NdmA and NdmB confirmed the presence of an NdmAB complex that is constructed to perform N-demethylation. The interactions of NdmD and NdmAB were then elucidated because NdmD serves as the sole Rieske reductase for this set of enzymes and transfers electrons to each catalytic site. NdmD is unique amongst Rieske reductases because it contains an extra Rieske [2Fe-2S] cluster at the N-terminal end. The hypothesis is the Rieske [2Fe-2S] cluster on NdmD is used in conjunction with the Rieske-less NdmC enzyme and structural subunit NdmE to carry out the N7-demethylation of 7-methylxanthine to xanthine, but is not required for activity with the NdmA and NdmB enzymes. The results support the hypothesis and expand it by suggesting that the extra Rieske [2Fe-2S] cluster can be used as a secondary electron transport pathway to NdmAB. NdmA converts caffeine to theobromine, which is further N3-demethylated by NdmB, resulting in 7-methylxanthine. However, NdmA exhibits a slight promiscuity toward the N3-methyl group, resulting in 1.5% of caffeine being convertedto paraxanthine. Analysis of the NdmA and NdmB structures identified that only two of the nine amino acids in the binding pocket differ between NdmA and NdmB. Mutation of the two unique amino acids in NdmA to mimic the NdmB active site produced a mutant enzyme with a paraxanthine:theobromine ratio of at least 3:1, over a 100-fold improvement from the wild-type ratio (1:39). Additionally, a peptide loop near the active sites also differs between NdmA and NdmB. Mutation of the NdmA loop sequence to match that of the NdmB loop further increased the yield of paraxanthine. This research confirms that biocatalytic production of paraxanthine from caffeine is achievable and begins to optimize the starting reaction conditions.
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    Electrodeposition of materials from novel solvents
    (University of Alabama Libraries, 2019) Sides, William Donald; Huang, Qiang; University of Alabama Tuscaloosa
    The electrodeposition of metals and alloys is explored with a focus on solvents and additives capable of reducing or eliminating hydrogen evolution while operating at highly cathodic potentials. The nucleation and growth behavior of binary codepositing systems are modelled in Chapter 2. Deep eutectic solvents based on choline chloride and urea are demonstrated to be capable of electrodepositing metallic manganese for the first time in Chapter 3. Chapter 4 describes the first time manganese has been incorporated into an electrodeposited magnetic iron-group alloy. Water-in-salt electrolytes are applied to the electrodeposition of metals in Chapters 5 and 6. These electrolytes are shown to suppress the proton reduction reaction and subsequent hydrogen evolution in aqueous systems. The tetrabutylammonium ion is also shown to be capable of suppression of proton reduction. The origins of this suppression are examined in Chapter 6, and it is determined that the additive adsorbs onto the electrode surface, blocking proton access. The suppressing behaviors of tetrabutylammonium and water-in-salt electrolytes are combined to achieve significant suppression of proton reduction and the ability to electrodeposit metals at highly negative cathodic potentials. Chapter 6 describes the use of these solvents to electrodeposit ruthenium for interconnect applications. The origin of enhanced superconductivity in rhenium electrodeposited from water-in-salt electrolytes is explored in Chapter 5. A disordered atomic structure is found to be highly correlated with enhanced superconductivity.
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    Investigation of polymers towards advanced functional materials
    (University of Alabama Libraries, 2019) Lu, Yang; Wujcik, Evan K.; University of Alabama Tuscaloosa
    With the rational design and modification of the fundamental polymers, new polymer complexes and composites can be developed with unique properties as functional materials. These new materials with enhanced and specialized functionality can thus replace the traditional materials and advance new technology. Here, two advanced functional materials are developed and investigated for applications in wearable strain sensing and toxic Cr(VI) removal from aqueous solutions. Chapter 2 & 3 focus on developing a soft electronic polymer material that possesses the properties of skin—compliant, elastic, stretchable, and self-healable—which would be ideal for bioelectronics such as wearable strain sensors. Current materials have limited on stretchability and durability (self-healing ability). A regenerative polymer complex composed of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA), polyaniline (PANI) and phytic acid (PA) that exhibits ultrahigh stretchability (1935 %), repeatable autonomous self-healing ability (repeating healing efficiency > 98 %), quadratic response to strain ( R2 > 0.9998), and linear response to bending ( R2 > 0.9994) is rationally designed. The hydrogen bonds and electrostatic interactions between PAAMPSA, PA and PANI synergistically construct a homogeneous regenerative network, which contribute to the elasticity and soft compliant nature of the as-prepared electronic material, along with extremely high omni-directional stretchability and excellent self-healing ability. Sensitive strain responsive geometric and piezoresistive mechanisms provide excellent linear responses to omnidirectional tensile strain and bending deformations. Furthermore, this material is scalable and simple to process in an environmentally friendly manner. In Chapter 4, the catalytic effects of metallic iron on morphologies, chemical structures, graphitic carbon growth, and thermal behavior of pyrolyzed carbon nanofibers are investigated. Polyacrylonitrile / iron nitrate (PAN/Fe(NO3)3) precursor nanofibers were prepared via electrospinning and subsequently converted into carbon/iron nanocomposite fibers via pyrolysis. It was found that the existence of iron nitrate has significant effects on the morphology of the resulting carbon fibers, as they can direct the initially non-woven nanofiber assembly into aligned nanofibers. The presence of catalytic iron can facilitate the stabilization and carbonization of precursor PAN fibers resulting in an increased carbon fiber yield, being more ordered on the nanoscale, and having larger graphitic crystallites. In Chapter 5, the developed carbon/iron nanocomposite fibers are used as the nanoadsorbent to remove the Cr(VI) in water. The nanoadsorbents show a fast and powerful performance in Cr(VI) removal through reduction and adsorption. CF-50 with abundant surface-bound α-iron nanoparticles performs ~ 1000% of amorphous carbon CF-0 in terms of Cr(VI) removal rate and capacity. The metallic iron on the carbon fiber surface is first oxidized to reduce the Cr(VI). Subsequently, diffusion controlled redox reactions between iron inside of carbon fiber matrix and Cr(VI) achieves a sustained removal for 30 days. Moreover, due to the magnetic nature, the nanoadsorbent can be easily separated from the treated water by a neodymium magnet.
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    Improve the stability of organic-inorganic hybrid perovskite by vapor-solid reaction
    (University of Alabama Libraries, 2019) Yu, Xiaozhou; Peng, Qing; University of Alabama Tuscaloosa
    Abstract Organic-inorganic hybrid perovskites, such as CH3NH3PbI3 and NH2CH=NH2PbI3, emerge as a new class of low-cost semiconductors that have the potential applications in high-efficiency photovoltaic cells, light emitting diodes, lasers, and sensors. However, hybrid perovskites can be easily degraded by H2O, O2, and light in ambient conditions. To improve the stability of hybrid perovskites, we carried out a comprehensive study including the degradation kinetics and surface modification by vapor-solid reactions for encapsulation. The degradation kinetics of perovskites were studied by using in situ methods. We found CH3NH3PbI3 perovskite degrades slowly at 85°C. This result indicates hybrid perovskites alone is not stable in the working conditions. We enhanced the stability of perovskites by surface modification through studying the surface reaction mechanism on perovskites. We found that by increasing the partial pressure of vapor reactants such as pyridine, the vapor-perovskite reactions will change from surface terminated reaction to bulk transformation reactions. A thin pin-hole free oxide barrier layer cannot only block H2O and O2 from meeting perovskites but also encapsulate the gas byproducts from the degradation reactions to stop the reversible degradation reaction. Atomic layer deposition (ALD) is a promising method to deposit a pinhole-free metal oxide barrier film onto perovskites. Although there are numerous reports in applying ALD on hybrid perovskites, the nucleation mechanism of ALD on these perovskites are poorly understood. Herein, we will present our findings about the atomic level surface reaction mechanism during ALD on perovskite-related substrates. Collectively, we are able to create a couple of new pathways to improve the stability of perovskite materials.
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    The effects of physiological fluid shear stress on circulating tumor cells
    (University of Alabama Libraries, 2018) Triantafillu, Ursula Lea; Kim, Yonghyun; University of Alabama Tuscaloosa
    The focus of this dissertation is on the effects of physiological fluid shear stress (FSS) on circulating tumor cells (CTCs). FSS occurs on cells both in vitro and in vivo. FSS is typically considered as a major variable in large scale bioprocessing while FSS is assumed to have a negligible role in bench scale culture. In physiological settings, FSS impacts cells in cancer where local, regional, and distant cancers experience FSS through interstitial, lymphatic, and hematological flow, respectively. CTCs in hematological flow experience the highest FSS and are involved in the transit stage of metastasis. One challenge of metastatic cancer is the lack of secondary tumor detection. Detection of CTCs largely relies on the epithelial cell adhesion molecule (EpCAM). CTC phenotype also includes expression of cancer stem cell (CSC) and epithelial to mesenchymal transition (EMT), which are correlated to increased resistance to chemotherapy. The study of FSS using an in vitro model can provide a better understanding on CTC phenotype expression and drug resistance. FSS was first examined using a baseline study with in vitro cell spheroid culture. Spheroids provide better representation of the stem and tumor cell environment than 2D culture. These cells experience FSS during cell dissociation. Since FSS can detrimentally affect cells, a gentler mechanical platform was developed for dissociation. Furthermore, this method, as well as traditional dissociation methods, was tested to study how FSS affects cell viability and expression. This platform was further used to model breast CTCs as suspension cells under FSS. This metastatic model allowed for testing the effects of FSS on CTC phenotype, and it was found that FSS increased CSC and CTC expression. Since an increase in CSC expression is correlated to increased drug resistance, drug resistance on CTCs under FSS was tested with chemotherapy drugs. It was found that the combination of FSS and drug resistance synergistically increases drug resistance expression in the model CTCs, corroborating clinical reports of CTC drug resistance. Finally, the effects of FSS and drug resistance was tested on estrogen receptor positive (ER+) molecular subtype. Collectively, these studies provide a better understanding on CTC behavior during metastasis.
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    Thermodynamics of ionic liquid solvents in gas purification and exfoliation mechanisms: molecular dynamics simulation and Monte Carlo calculations
    (University of Alabama Libraries, 2018) Abedini, Asghar; Turner, C. Heath; University of Alabama Tuscaloosa
    Demand for green sources of energy is increasing due to the critical need to decrease greenhouse gas emissions. This research involved different approaches for reducing CO2 emission to the atmosphere. In the first study, the exfoliation of bismuth telluride (Bi2Te3) as a well-know thermoelectric (TE) material was investigated. In the literature, it has been experimentally and computationally proven that producing a thinner layer of Bi2Te3 increases the “figure of merit” by reducing the thermal conductivity and enhancing the electrical conductivity. A liquid-phase exfoliation technique is one of the potential approaches to exfoliate Bi2Te3. In my simulation work, different types of imidazolium-based ionic liquids (ILs) were screened to find the most efficient exfoliant, by first considering the value of the solid surface energy and surface tension of the applied liquids. We found that [Tf2N-]-based ionic liquids are relatively effective at enhancing the exfoliation, and this performance can be correlated to the unique molecular-level solvation structures developed at the Bi2Te3 surfaces. In the second study, I modeled CO2 separation during typical pre-combustion and post-combustion condition using a novel IL + polymer membrane material. This work was inspired by recent experimental findings from the Bara group at UA. The new class of materials was generated by adding ionic liquid molecules to the backbone of polymers while using (pyromellitic dianhydride) PMDA as an organic ligand. For the first time, these polymers, “ionic polyimides” (i-IPs), were computationally investigated as a potential membrane for CO2 separation. The presence of the IL significantly displaces the CO2 molecules from the ligand nitrogen sites in the neat i-IP to the imidazolium rings in the i-IP + IL composite. These molecular details can provide critical information for the experimental design of highly selective i-IP materials, as well as provide additional guidance for the interpretation of simulated adsorption systems. It is found that the 50% IL addition can increase CO2/CH4 selectivity by 16% in [BF4-]-based and by 36% in [PF6-]-based structures. While the [BF4-]-based system shows higher CO2/CH4 selectivity, the [Tf2N-]-based system shows higher CO2/N2 gas separation performance. These findings are exemplified by high gas solubility of [PF6-]-based structures, which also compensate to a correlated larger theoretical surface area.