Physical Sciences and Mathematics Commons^™

Syntheses And Reactions Of Early Transition Metal Amidinate Compounds, Adam Christopher Lamb

Doctoral Dissertations

Homoleptic Groups 4 and 5 metal amide compounds have been used as precursors in CVD/ALD processes to make microelectronic metal oxide thin films. These compounds are often very air sensitive. Ancillary ligands such as amidinates have been used to reduce their air sensitivity and to make their handling easier. Reactions of amidinates with dioxygen and water have thus been used to make metal oxide thin films. Studies of these reactions are important in order to make better precursors and purer thin films. This dissertation focuses on the following areas: (a) Syntheses of zirconium and Group 5 amidinate amides; (b) Studies …

Design And Synthesis Of Novel Sultams As Non-Nucleoside Inhibitors Of Hiv Reverse Transcriptase, Brian Chadwick Lecroix

Doctoral Dissertations

The compound 2-methyl-3-phenyl-2,3-dihydro-1,2-benzisothiazole 1,1-dioxide (NSC 108406) was identified as an HIV-1 reverse transcriptase inhibitor by the National Cancer Institute. Using this lead, the Baker group has developed a series of analogues with various groups at the 3-position that show a spectrum of biological activities. In the end, the substituents used could not compare to the biological activity of the inhibitor efavirenz (Sustiva^® [trademark]), and so it was decided to synthesize sultams with alkylethynyl substituents at the 3-position of the sultams in an attempt to mimic the activity of efavirenz.

Previous research analyzed the proposed novel sultams in the modeling …

Synthesis And Characterization Of Fullerene-Based Hydrogen Storage Materials, Patrick Alan Ward

Doctoral Dissertations

Storing hydrogen safely and efficiently is an area of great interest for the utilization of hydrogen as an energy carrier in transportation applications. The feasibility of using fullerenes in hydrogen storage materials was investigated. Alkali decorated fullerenes Li_xC₆₀ [LixC60] and Na_xC₆₀ [NaxC60] were found to enhance the hydrogen chemisorption and physisorption properties of fullerenes. Although the overall hydrogen physisorption uptake in these materials is low due to the crystalline nature of the material, the isosteric heats of adsorption of fullerenes were increased by lithium doping. C₆₀ [C60] is also capable of acting as …

Magneto-Optical Properties Of Complex Oxides, Peng Chen

Doctoral Dissertations

Complex oxides give rise to rich physics and exotic cross-coupled electronic and magnetic properties. This is because of the competing interaction between charge, structure, and magnetism in the materials. In this dissertation I present a spectroscopic investigation of several model complex oxides under external stimuli of magnetic field and temperature. The compounds of interest include BiFeO₃ [bismuth ferrite] nanoparticles and tetragonal film, Bi_1-xNd_xFeO₃ [neodymium doped bismuth ferrite], α-Fe₂O₃ [hematite], Ni₃V₂O₈ [nickel vanadate], and RIn_1-xMn_xO₃ [manganese doped rare earth indium oxide]. …

Characterization Techniques And Electrolyte Separator Performance Investigation For All Vanadium Redox Flow Battery, Zhijiang Tang

Doctoral Dissertations

The all-vanadium redox flow battery (VRFB) is an excellent prospect for large scale energy storage in an electricity grid level application. High battery performance has lately been achieved by using a novel cell configuration with advanced materials. However, more work is still required to better understand the reaction kinetics and transport behaviors in the battery to guide battery system optimization and new battery material development. The first part of my work is the characterization of the battery systems with flow-through or flow-by cell configurations. The configuration difference between two cell structures exhibit significantly different polarization behavior. The battery output can …

The Development Of Lithium Tetraborate Compounds For Thermal Neutron Detection, John David Auxier Ii

Doctoral Dissertations

Due to the shortage of ³He [helium-3], the goal of this project was to develop replacement materials for slow neutron detection in mixed radiation fields. The U.S. Department of Homeland Security (DHS) indicated that replacement materials should have an absolute neutron efficiency of 2.5 cps/ng of ²⁵²Cf (Californium-252) and a neutron/gamma discrimination intrinsic efficiency of 1 x 10^-6 [one gamma-ray response in a million counts]. In this work, the use of amorphous lithium tetraborate (Li₂B₄O₇:Ce) is analyzed as a thermal neutron detector. Also discussed is the synthesis of the lithium tetraborate, …

Developing 16- And 18-Atom Ringed Macrocyclic Tetracarbene Complexes, Heather Marie Bass

Doctoral Dissertations

Stabilizing metal-ligand multiple bonds is important for the understanding of biological intermediates, as well as, for their use in group transfer reactions. Two considerations to make when developing a ligand system to support metal-ligand multiple bonds are the strength of the ligand and the symmetry of the ligand. Herein, our group has proposed a class of four-coordinate, strong σ-donor ligands by synthesizing macrocyclic tetraimidazoliums that form tetracarbenes upon deprotonation. By examining group theory, these systems should allow for the formation of complexes with metal-ligand multiple bonds in a bent square pyramidal geometry that exhibit high oxidation states and novel spin …

Syntheses, Characterization And Reactions Of Early Transition Metal Guanidinate And Imide Compounds, Bhavna Sharma

Doctoral Dissertations

Early transition metal compounds and their reactions have been widely used in catalysis and preparation of advanced materials such as metal oxides in microelectronic devices. Studies of the compounds and their reactions provide a fundamental understanding of chemistry of the compounds and are critical to their applications. This dissertation focuses on the following areas: (a) Reactions of Group 4 amide guanidinates with dioxygen or water; (b) Formation of a tantalum imide complex through an unusual α [alpha]-SiMe₃ [trimethylsilyl] abstraction. Reactions of the amide guanidinates with either dioxygen or water yield products that are identified to be dimers and polymers …

Copper Mediated, Transmetallation Coupling Reactions Using High Intensity Ultrasound, Bryan J. Musolino

Doctoral Dissertations

This dissertation summarizes research efforts focused on the use of boron and copper acetate to form new carbon-carbon and carbon-heteroatom bonds. Two new methods were developed using high intensity ultrasound as the reaction energy source. The first focused on the homocoupling of various aryl compounds using a commercially available polymer support. The use of this polymer support allows the reaction to proceed in an aqueous solvent system with only minimal preparation. The product yields were better than values reported in the literature using traditional reaction conditions and reaction times were decreased from 24-72 hours to 6 hours. The second method …

Neutron Scintillation Detectors Based On Polymers Containing Lithium-6 For Radiation Portal Monitor Applications, Andrew Neil Mabe

Doctoral Dissertations

The work presented herein describes an investigation of four main types of thin film polymer scintillators containing ⁶Li [lithium-6] for neutron detection: polystyrene containing ⁶LiF [lithium-6 fluoride] and a preblended fluor mixture comprising 2,5-diphenyloxazole and 1,4-bis(5-phenyloxazol-2-yl)benzene; poly(styrene-co-lithium maleate) containing salicylic acid; poly[styrene-co-lithium maleate-co-2-phenyl-5-(4-vinylphenyl)oxazole]; and poly(styrene-co-lithium 4-vinylbenzoate). A variety of chemical and physical characterizations as well as optical and scintillation characterizations were performed to guide the development of optimized compositions of each type of polymer film. The scintillation performances of optimized compositions of each type of polymer film were calibrated using …

Exploration Of Aqueous Interfaces And Their Effect On Ion Behavior, Oneka T. Cummings

Doctoral Dissertations

An in-depth understanding of a wide range of physical, chemical, atmospheric and biological processes can only be achieved after the structure and dynamics of interfaces and the interfacial behavior of aqueous species, such as ions, are thoroughly studied and understood. This dissertation describes computational studies conducted to gain a more comprehensive understanding of such interfaces and the behavior of ions in the bulk and interfacial regions of the (1) air/water interface, and (2) alkane/water interfaces.

At the air/water interface the effect of counterion (sodium cations) charge and the influence of ion pairing on anion (chloride) propensity for the air/water interface …

New Applications Of Boron Dihalides And Organotrifluoroborates In Organic Synthesis, Kelly Elizabeth Hall

Doctoral Dissertations

This dissertation summarizes research focused on the use of boron dihalides and organotrifluoroborates in organic synthesis. The boron dihalide mediated aryl propargyl ether cleavage reactions to generate the corresponding aryl alcohols were investigated to explain the mechanistic pathway of using boron trihalides and boron dihalides in propargyl ether cleavage reactions. The results of this study strongly support that the mechanistic pathway for these reactions follows the pathway shown in this dissertation. In addition, the use of polymer-supported organotrifluoroborates for radiolabeling reactions was also investigated. The results of these studies support the use of polymer supported organotrifluoroborates in radiolabeling reactions as …

1,2,4-Triazine-Accelerated Azide-Alkyne Cycloaddition And Synthesis Of Metalloenzyme Inhibitors, Belinda Shea Lady

Doctoral Dissertations

The work of this dissertation describes the design and synthesis of 1,2,4-triazine ligands and other N-containing heterocycles and their use in the copper-catalyzed azide-alkyne cycloaddition (CuAAC). A variety of ligands were synthesized to probe the steric and electronic demands required for use in the CuAAC reaction. Substituents on the 1,2,4-triazine were systematically altered and the core 1,2,4-triazine modified to determine the most active ligand. Additional experiments explored the variability in the reaction conditions, such as solvent choice, use of reducing agents, and optimal stoichiometry. Under optimum conditions 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine and copper (II) tetrafluoroborate in the presence of triethylamine was found to …

Fluorescence Spectroscopy With Correlated Atomic Force Microscopy Of Gold Nanoparticles And Meso-Scale Ribbons, Meredith Marie Therrien

Doctoral Dissertations

Studies on the optical properties of gold nanoparticles are of great interest due to the size and shape control and easy adaptability through functionalization to most any application, everything from nanomedicine to nanosensing. Gold nanoparticle optical properties change with size, morphology, and environment. Gold nanospheres were explored to determine the effect of environmental change, from many particles in solution to a single particle immobilized and in air, on fluorescence peak position. A statistical distribution of single gold nanorod fluorescence spectra demonstrate the spectral changes associated with slight variations in size. In solution, gold nanorods self-absorb and only exhibit bulk gold …

Tuning Sol-Gel Phase Diagrams Of Doubly Thermosensitive Hydrophilic Diblock Copolymers In Water, Naixiong Jin

Doctoral Dissertations

This dissertation presents the synthesis of stimuli-responsive hydrophilic diblock copolymers and the study of their behavior in water under various conditions. The polymers were made by “living”/controlled radical polymerization. Chapter 1 presents a background of this dissertation. Chapters 2-4 describe a family of doubly thermosensitive diblock copolymers with a small amount of carboxylic acid groups incorporated into either one or both blocks. The lower critical solution temperature (LCST) of the weak acid-containing block increases with increasing pH due to the ionization of carboxylic acid. Chapter 5 presents the preparation of pH-sensitive diblock copolymer micelle-embedded agarose hydrogels.

Chapter 2 describes the …

Resonance Hyper-Raman Characterization Of Nonlinear Chromophores, Christopher Bennett Milojevich

Doctoral Dissertations

Hyper-Raman spectroscopy is a nonlinear optical probe which can be used to explore the multi-photon properties of molecules. Three studies are presented in this dissertation. The first study is a combined experimental investigation of the surfaceenhanced hyper-Raman scattering with a theoretical study of the electronic states of the Rhodamine 6G molecule. This study demonstrates that hyper-Raman spectroscopy can be used to probe electronic states which are one-photon inaccessible. The second study involves a comparison of experimentally measured resonance hyper-Raman spectra to first-principles calculations of the resonance hyper-Raman scattering. This study shows the utility of coupling hyper-Raman spectroscopy and hyper-Raman calculations …

Alkane Adsorption On Mgo(100): Volumetric Isotherm, Inelastic Neutron Scattering, And Computational Studies, Andrew Spencer Hicks

Doctoral Dissertations

Volumetric adsorption isotherms and computational molecular dynamics (MD) simulations were performed for nonane and decane adfilms on MgO(100) nanocubes. From the isotherms, variety of thermodynamic quantities are calculated. These values, along with visual inspection of the isotherms, indicate a layer by layer trend from 2D to 3D behavior. This is attributed to the increasing importance of vertical adsorbate-adsorbate interactions as distance from the surface increases. Additionally, a 2D phase transition is observed for the first adsorbed layer as indicated by the evolution of the widths of the isotherm first derivative peaks. These experimental results are complemented by the MD calculations, …

Quorum Sensing And Metabolism In Marine Environments, Amanda May

Doctoral Dissertations

Quorum sensing (QS) is a phenomenon that allows bacteria to communicate with each other. Small molecules known as autoinducers are synthesized and released by bacteria, and once enough members of the community are around to ensure survival, i.e. quorum, a phenotype, e.g. bioluminescence, is expressed. There are two types of QS molecules, intra- and inter-species.

S-4,5-Dihydroxy-2,3-pentanedione (DPD) is a byproduct of the activated methyl cycle which recycles methionine. This has led to the discussion as to whether DPD is a metabolic byproduct or is the interspecies signal as proposed previously. The detection and quantitation of DPD however, has not …

Synthesis And Characterization Of Stimuli Responsive Polymer Brushes, Chaitra Vasant Deodhar

Doctoral Dissertations

Polyelectrolytes (PE) are the least understood polymeric systems due to their complex behavior that arises because of the intimate connection between charge and conformation. To address this challenge, my research focuses on understanding the responsive behavior of weak polyelectrolyte brushes to different stimuli such as pH, type of ion and ionic strength. In this work, weak polyelectrolyte brushes made of poly(methacrylic acid) (PMAA) and random copolymer brushes incorporating hydroxyethyl methacrylate (HEMA) as co-monomer were studied. The polymer brushes were synthesized by both “grafting to” and “grafting from” approaches and were characterized mainly by ellipsometry and neutron reflectometry.

Several methods for …

Analysis Of Ecological Change In Marine Ecosystems Via Novel Imaging And Spectroscopic Techniques On Microalgae Cells, Morgan Breonne Mcconico-Lewis

Doctoral Dissertations

With the increase in anthropogenic pollutants such as: atmospheric CO₂ [carbon dioxide], fossil fuel combustion and fertilizer run off, the fate of the environment is of great importance. Through industrialization, the greenhouse gas, CO₂, is a major contributor to global warming; while nitrogen based fertilizer, causes the production of toxins due to harmful algal blooms. Both chemical impacts dissolve into marine ecosystems effecting the chemical composition of organisms such as microalgae. Microalgae remediate these changes by sequestering carbon and nitrogen; thus there is a need to understand how these impacts affect the ecosystem by detecting the change …

Multiscale Modeling Of Enzyme-Catalyzed Methanol Production By Particulate Methane Monooxygenase, Katherine K. Bearden

Doctoral Dissertations

In this work, the conversion of methane to methanol by the particulate Methane Monooxygenase (pMMO) enzyme is investigated using a multi-scale modeling approach. This enzyme participates in carbon cycling and aids in the removal of harmful atmospheric methane, converting it to methanol. The interaction between pMMO and a neighboring enzyme that is present in the same organism is studied, and the unknown pMMO active site is elucidated and tested for methane oxidation towards the production of methanol.

Fundamental knowledge of pMMO's mechanism is not fully understood. Understanding how this enzyme works in nature will provide information towards designing efficient synthetic …

Fundamental Properties Of Colloidal Unimolecular Polymer Particles, Minghang Chen

Doctoral Dissertations

"Colloidal Unimolecular Polymer (CUP) particles are a new genre of material formed by self-assembly into spheroidal particles due to the effect of hydrophilic/hydrophobic interactions of the polymer with a change in the solvent. The particle sizes were characterized by means of Dynamic Light Scattering with corrected viscosities instead of water's viscosity. The distribution of particle size agreed well with the distribution of molecular weight proving that the polymer had undergone unimolecular collapse. The rheology study shows the presence of surface water and its significant effect on the rheology. The primary and secondary electroviscous effects were also found to play roles …

Isocyanate-Derived Organic Aerogels: Polyurethanes, Polyureas, Polyamides And Polyimides, Chakkaravarthy Chidambareswarapattar

Doctoral Dissertations

"Aerogels are 3D assemblies of nanoparticles with high open porosity and high surface area, and are pursued for their low density, low thermal conductivity, low dielectric constant and high acoustic attenuation. The foundation for those exceptional properties is their complex hierarchical solid framework (agglomerates of porous, fractal secondary nanoparticles). On the down side, however, aerogels are also fragile materials. The mechanical strength of silica aerogels has been improved by crosslinking the framework with organic polymers. The crosslinking polymer has been assumed to form a conformal coating on the surface of the skeletal framework bridging covalently the elementary building blocks. However, …

Creating New Superconducting & Semiconducting Nanomaterials And Investingating The Effect Of Reduced Dimensionality On Their Properties, Sukhada Mishra

Doctoral Dissertations

"The field of nanomaterials has continued to attract researchers to understand the fundamentals and to investigate potential applications in the fields of semiconductor physics, microfabrication, nanomedicine, surface sciences etc. One of the most critical aspects of the nanomaterials research is to establish synthetic protocols, which can address the underlying product requirements of reproducibility, homogenous morphology and controlled elemental composition. We have focused our research in exploring synthetic routes for the synthesis of superconducting and semiconducting nanomaterials and analyze their structure--property relationship through detailed characterizations. The first part of dissertation is focused on the synthesis of superconducting FeSe nanostructures using catalyst …

Polybenzoxazine Aerogels: Synthesis, Characterization, Conversion To Porous Carbons, And Energetic Composites, Shruti Mahadik-Khanolkar

Doctoral Dissertations

"Aerogels are nanoporous, low-density bulk objects, consisting of three-dimensional assemblies of nanoparticle. Structured similarly, polymeric aerogels are emerging as a mechanically strong alternative to traditional silica aerogels, which are fragile. Amongst polymeric aerogels, those based on polybenzoxazine (PBO - a type of phenolic resin), are extremely robust and comprise an economic alternative to resorcinol-formaldehyde aerogels, also a class of phenolic resins, as the main source of carbon aerogels. The drawback of the PBO chemistry has been the long (days) processing time at high-temperatures (>130 ºC). Herewith, we have developed an energy- and time-efficient process to PBO aerogels by inducing …