Physical Sciences and Mathematics Commons^™

Novel Electrochemical Detections Of Biologically And Environmentally Relevant Substances, Clarissa E. Tatum

Doctoral Dissertations

Development and studies of new electrochemical methods for the detection of various biologically and environmentally relevant substances are the focus of this dissertation. A dual amperometric sensor, capable of the simultaneous, real-time determination of NO and O,2, has been developed and optimized. Many tests were performed in order to reduce cross-talking between the two sensors, and an electro-deposited polymer, poly-5-amino-1-naphthol, was shown to reduce the cross-talking to insignificant levels. The use of bismuth-based electrodes in the detection of various metals has been explored. A bismuth bulk electrode has been developed, optimized, and used for the individual and simultaneous determination of …

Tantalum Carbene And Imide Complexes. Synthesis, Characterization, And Pathways Of Formation, Julia Kathryn Covington Abbott

Doctoral Dissertations

This dissertation focuses on two different types of organometallic compounds, carbenes and imides. The first project deals with the archetypal Schrock carbene, and the second project studies complexes that contain metal-nitrogen bonds, both amides and imides.

A summary of the research in this dissertation is discussed in Chapter 1. Chapter 2 begins the studies of the archetypal Schrock carbene (Bu^tCH₂)₃Ta=CHBu^t. The studies include the synthesis of deuterated compounds (Bu^tCD₂)₃TaCl₂ and Bu^tCD₂Li, observation and identification of the intermediate, Ta(CD₂Bu^{t …}

The Importance Of Chain Connectivity In The Formation Of Non-Covalent Interactions Between Polymers And Single-Walled Carbon Nanotubes And Its Impact On Dispersion, Dias Linton

Doctoral Dissertations

Polymer nanocomposites have garnered incredible promise in the field of material science due to the excellent mechanical strength, thermal and electrical conductivities of the nanoparticles and the extension of these properties to the processing flexibility inherent to plastics. However, practical realization of these nanoparticle-based materials has been hindered by the tendency of these nanoparticles to aggregate as a result of strong inter-particle forces. In this dissertation, we investigate the formation of non-covalent charge transfer interactions between polymers and single-walled carbon nanotubes (SWNTs) with the goal of optimizing interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface.

Nanocomposites …

Polymeric Loop Formation At Hard And Soft Interfaces, Earl Ashcraft

Doctoral Dissertations

Copolymers are used to increase the interfacial strength of immiscible components and suppress recombination of the minor phase by steric hindrance. The experiments conducted in these studies are designed to investigate in situ polymer loop formation at soft interfaces and functionalized nanotube surfaces. Block copolymers are the most effective type of copolymer for compatibilization because they extend perpendicular to the interface, allowing good entanglement with the homopolymer chains. Multiblock copolymers are more effective than diblock copolymers for strengthening the interface because they can cross the interface multiple times, forming “loops” in each phase that provide entanglement points for the homopolymer. …

Density Functional Calculation Of X-Ray Absorption Spectra Within The Core Hole Approximation: An Implementation In Nwchem, William Ben Carlen

Doctoral Dissertations

Density functional theory is used to calculate the core excitation spectra of titanium structures. Specifically, the core-hole approximation is used. In this scenario, the excitation energies of core electrons are calculated using the approximation that the core energy level be frozen throughout the relaxation process of the orbitals. This allows a more acurate determination of the resulting X-ray spectra. The method described has been implemented in an NWChem module.

Supported Aqueous-Phase Catalysis For Atom Transfer Radical Polymerization, Ravi Aggarwal

Doctoral Dissertations

Atom transfer radical polymerization (ATRP) which utilizes transition metal based catalysts is a versatile methodology for the synthesis of a wide spectrum of polymers with controlled architectures. However, high concentrations of soluble catalyst required in an ATRP process makes the final polymer colored and toxic. Thus, the catalyst removal/reduction/recycling remains a challenge in the field of ATRP. Supported catalysts on insoluble solids such as silica gel, polystyrene beads, etc. have been used in ATRP to facilitate the catalyst recovery and recycling. However, the ability of the supported catalysts to mediate a polymerization is substantially reduced due to their reduced mobility …

Multidimensional Liquid Chromatography Separations, Jacob N. Fairchild

Doctoral Dissertations

Many mixtures important to research consist of hundreds or even thousands of individual components of interest. These types of mixtures are far too complex to separate by a single chromatographic dimension in any reasonable amount of time. However, if a multidimensional approach is used, where a complex mixture is separated by an initial dimension, simpler fractions of that separation are collected and each of those fractions are analyzed individually, highly complex mixtures can be resolved in relatively short amounts of time. This dissertation serves as a guide to multidimensional chromatography, in particular, two-dimension liquid chromatography. There are many aspects of …

New Electrochemical And Optical Detection Methods For Biological And Environmental Applications, Royce Nicholas Dansby-Sparks

Doctoral Dissertations

Detection of chromium and vanadium is of interest for biomedical and environmental applications. The two metals have narrow limits between being essential and toxic for humans. Ultra-sensitive techniques have been studied to measure Cr and V at low concentrations found in human blood and environmental samples. Bismuth film and mercury-alloy electrodes have been developed as alternatives to traditional Hg-based electrodes for Cr and V detection. While catalytic adsorptive stripping voltammetry (CAdSV) has been used to detect Cr and V, little is known about the process. The mechanisms of CAdSV have been probed to provide a better understanding of its exceptional …

Boron And Titanium(Iv) Halide Mediated Reactions, Michael Patrick Quinn

Doctoral Dissertations

This dissertation summarizes research efforts focused on the use of boron and transition metal halides to form new carbon-carbon and carbon-halide bonds. The boron halide mediated alkyne-aldehyde coupling reaction to generate 1,3,5-triaryl-1,5-dihalo-1,4-dienes was reinvestigated in an attempt to explain the stereochemistry observed during changing of both the mode of addition and the reaction temperature. Either (Z,Z)-1,4-dienes or (Z,E)-1,4-dienes can be the predominant product depending on reaction conditions used. This mechanistic investigation also led to the discovery of several novel reactions. These include the stereoselective preparation of (Z)-3-chloroallylic ethers from the reaction of alkenylboron dichlorides with aryl aldehydes in the presence …

Hairy Particles: Polymer Brush-Supported Organocatalysts And Asymmetric Mixed Homopolymer Brushes, Xiaoming Jiang

Doctoral Dissertations

This dissertation presents the synthesis and studies of polymer brush-supported organocatalysts and asymmetric mixed homopolymer brushes grafted on particles. The brushes were synthesized from initiator-functionalized particles by surface-initiated “living” radical polymerizations.

Polymer brush-supported organocatalysts were designed to combine the advantages of both soluble polymer- (high activity) and crosslinked insoluble polymer-supported catalysts (recyclability). Chapter 1 describes the synthesis of a polymer brush-supported 4-N,N-dialkylaminopyridine (DAAP) catalyst from initiator-functionalized latex particles by surface-initiated nitroxide-mediated radical polymerization (NMRP). The hairy particles efficiently catalyzed the acylation of secondary alcohols and Baylis-Hillman reaction and were recycled  six times with no or negligible decrease in the …

Development Of Nanomechanical Sensors For Environmental Contaminate Screening Using Protein Functionalized Microcantilevers, Kasey L. Hill

Doctoral Dissertations

The development of real time, label-free biosensors based on ligand-induced nanomechanical responses of microcantilevers (MCs) allows for sensitive and selective detection. High sensitivity is afforded by the MCs small dimensions. Immobilizing biomolecular recognition phases imparts selectivity from bioaffinity interactions. Biological sensors on a MC platform utilize various proteins, such as antibodies and nuclear receptors, which can be used to detect and screen for potential environmental contaminants.

The interaction between contaminants and immobilized receptors induces an apparent surface stress that leads to static bending of the MC, which is monitored by an optical beam bending technique. Biofunctionalized MCs can provide high …

Radial Heterogeneity And Surface Properties Of Columns Used In High Performance Liquid Chromatography, Jude A. Abia

Doctoral Dissertations

The radial heterogeneity of some columns used in high performance liquid chromatography (HPLC) was investigated using an on-column microelectrochemical amperometric detector. Such a detector allowed the recording of the elution profiles at different spatial positions throughout the column exit cross-section. From this, we obtain information about the radial distribution of the mobile phase velocity, column efficiency, and analyte concentration. In all cases, the results obtained show that the spatial distribution of the mobile phase velocity does not follow a piston-flow behavior but exhibits radial heterogeneity with differences not exceeding 5% between the center and wall regions of any column. The …

Newly-Developed Nanostructured Microcantilever Arrays For Gas-Phase And Liquid-Phase Sensing, Zhou Long

Doctoral Dissertations

The microcantilever (MC) has become a common transducer for chemical and biological sensing in gas phase and liquid phase during recent years. MC sensors provide superior mass sensitivity by converting weak chemical and biological stimuli into high mechanical response. Moreover, other advantages such as small size, low cost and array format have made MCs more attractive than other comparable sensors.

Selectivity in MC sensors can be enhanced by creating a differentially functionalized MC array (MCA) with responsive phases (RPs). A well-designed array should incorporate RPs exhibiting a variety of possible interactions with the analytes, and a specific analyte should induce …

The Stereochemistry Of Selected Supramolecular Complexes Of Cucurbiturils And The Effect Of Homogeneous Equilibria And Electron Transfer Of The Guest, Arumugam Thangavel

Doctoral Dissertations

"From a practical perspective, host-guest complexes are vehicles for understanding and using supramolecular interactions for purposeful function in sensors, molecular machines and switches, while from a fundamental perspective they may lead to novel supramolecular protection schemes in basic organic reactions. This dissertation examines the interactions of cucurbiturils as barrel-shaped hosts, exhibiting a hydrophobic cavity, with substituted benzoylpyrydinium, phenypyrylium, and diazaanthraquinonediium cations as guests. In water, N-methyl-4-(p-substituted benzoyl)pyridinium cations exist in equilibrium with their hydrated forms (gem-diols), whose concentrations depend on the para substituent. In the presence of cucurbit7uril (CB[7]), the benzoyl group shows a preference for the CB[7] cavity, and …

Adsorption And Segmental Dynamics Of Acrylate And Methacrylate Polymers Adsorbed On A Silica Surface, Piyawan Krisanangkura

Doctoral Dissertations

"Poly(isopropyl acrylate)-d₇ (PIPA- d₇) was studied using ²H solid-state NMR and modulated differential scanning calorimetry (MDSC). The polymer was deuterated on the methyl groups and side-chain methine. The PIPA- d₇ was adsorbed onto Cab-O-Sil silica. These two types of deuterons each showed their own characteristic deuterium nuclear magnetic resonance (NMR) spectra for bulk PIPA- d₇. The ²H NMR spectra of adsorbed PIPA- d₇ samples showed the presence of heterogeneity of the segmental dynamics. A residual powder pattern was found in the spectra of the surface samples at higher temperatures, indicating that the segments were tightly attached to the silica. The …

Effect Of Structure And Plasticizer On The Glass Transition Of Adsorbed Polymer, Boonta Hetayothin

Doctoral Dissertations

"The effect of molecular mass on adsorbed poly(methyl methacrylate) (PMMA) on silica was determined using temperature-modulated differential scanning calorimetry (TMDSC). A two-component model, based on loosely-bound polymer (glass transition temperature, T_g, similar to that of bulk) and tightly-bound polymer (T_g higher than that of bulk) was used to interpret the thermograms. Similar amounts of tightly-bound polymer were found for 450 and 85 kDa PMMA (0.78 mg/m²), while the 32 kDa sample had a smaller amount (0.48mg/m²). A comparison of adsorbed PMMA, poly(vinyl acetate) (PVAc), and poly(methyl acrylate) (PMA) on silica was made using the same technique. The …

Analysis And Occurrence Of Disinfection By-Products In Fresh And Salt Water, Honglan Shi

Doctoral Dissertations

"Haloacetic acids, trihalomethanes, and bromate are important toxic water disinfection by-products (DBPs) that the US Environmental Protection Agency (USEPA) regulates in drinking water. Iodoacetic acids and halonitromethanes (HNMs) are the unregulated emerging DBPs that have been recently found in the disinfected drinking waters, and which have much higher toxicity than the regulated DBPs. The purpose of this study was to develop new analytical methods for analysis of these emerging DBPs, to study their occurrence in Missouri drinking water systems, and to investigate the occurrence and formation of these DBPs in saltwater and seawater based marine park aquaria. A new rapid …

Capillary Electrophoresis Of Pteridines In Urine And Plants And Quantification Of Pharmaceutical And Personal Care Products In Missouri Waste Water, Stephen E. Gibbons

Doctoral Dissertations

"Capillary electrophoresis (CE) is a powerful technique that separates molecules based on their respective charge and hydrodynamic size. The major advantages of CE are high separation efficiency, small sample volume requirements, simple to no sample preparation and often organic solvents are not required for the separation.

The work presented in this dissertation utilized capillary electrophoresis for the analysis two different classes of compounds in different matrices. The first project investigated pteridines in urine and plants. The second project investigated pharmaceutical and personal care products (PPCP's) in Missouri waste water.

As cancer continues to be one of the top three causes …

Haart Drugs Induce Oxidative Stress And Mitochondrial Dysfunction In Blood-Brain Barrier, Kalyan Reddy Manda

Doctoral Dissertations

"The era of highly active antiretroviral therapy (HAART) has controlled AIDS and its related disorders considerably; however, the prevalence of HIV-1-associated neurocognitive disorders (HAND) has been on the rise in the post-HAART era. In view of these developments, we investigated whether a HAART drug combination of 3'-Azido-2', 3'-deoxythymidine (AZT) and Indinavir (IDV) can alter the functionality of the blood-brain barrier (BBB) endothelial cells, thereby exacerbating the condition. Viability of hCMEC/D3 cells (in vitro model of BBB) that were exposed to the drugs was significantly reduced after a 72 hr treatment, in a dose-dependent manner. Reactive oxygen species (ROS) were highly …

Chemical Bath Deposition And Electrodeposition Of Epitaxial Semiconductor Materials For Application In Photovoltaic Devices, Guojun Mu

Doctoral Dissertations

"This dissertation investigates the chemical bath deposition of zinc oxide and electrodeposition of cuprous iodide on polycrystalline and single crystal substrates. Paper I describes the chemical bath deposition and characterization of titled epitaxial zinc oxide nanospears on Si(001) single crystal substrate. In Paper II, the chemical bath deposition of zinc oxide nanospears from highly alkaline solutions is discussed in detail, including a thermodynamic calculation of saturation and speciation of Zn(II) in aqueous solution, and a kinetic study of the deposition process. In this paper the epitaxial zinc oxide is reported grown on Au(100), (110), and (111) single crystals. Paper III …

Nmr Investigations Of Biomass-To-Fuel Conversions By Hydrothermal Processes, Wenjia Zhang

Doctoral Dissertations

"Biofuels have gained significant attention as the most promising alternative energy and fuel supply for the near future because of two dominant reasons: first, biofuels are environmentally friendly; and second, they afford a sustainable technology. Biofuels can be synthesized from biomass by several different processes, among which, hydrothermal conversion is considered to be more energy efficient. However, scientific efforts to improve hydrothermal biomass-to-fuel (HT-BTF) conversion efficiencies are severely limited because little is known about the salient reaction mechanisms and intermediates. This study is aimed at a better understanding of the hydrothermal biomass degradation kinetics by advanced NMR spectroscopy and, accordingly, …