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The Effect Of Mobile Phase Composition And Temperature On The Adsorption Behavior Of Tryptophan, Tarab Jamil Ahmad

Doctoral Dissertations

Single-component adsorption isotherm data were acquired by frontal analysis for tryptophan on a C₁₈-Kromasil packed column, using acetonitrile-water solutions of various compositions (2.5, 5, and 7.5% ACN + 1% ACOH). These isotherms have a complex behavior, exhibiting at least one clear inflection point at an intermediate concentration and, possibly, another such point, close to the origin. The isotherm for 2.5 % ACN has the strongest curvature. At high concentrations, all these isotherms tend toward a limit, showing that the adsorbent has a finite saturation capacity. At low concentrations, these isotherms seem to exhibit langmuirian behavior. The isotherm model …

Thermodynamic And Neutron Structural Studies Of Hydrocarbon Adsorption On Mgo Nanocubes, Richard E. Cook

Doctoral Dissertations

Presented is a series of thermodynamic and neutron scattering experiments used to probe the nature of the hydrocarbon - MgO (100) interaction. High-resolution volumetric isotherms are used to probe the wetting, layer transitions, heats of adsorption, two-dimensional compressibilities, and identify possible phase transitions of thin films of benzene, ethane, and n - pentane on MgO powders. Neutron diffraction experiments were used to probe the structure and identify any phase transitions within monolayer films of ethane, butane and n -pentane.

Benzene adsorption, while showing no visible layering steps, shows a shift in the shape of the isotherm for p/p_o > 0.7. …

Characterization Of Aβ Aggregates Using Hydrogen/Deuterium Exchange Mass Spectrometry, Maolian Chen

Doctoral Dissertations

The work presented in this dissertation aimed to localize the hydrogen-bonding interaction sites within Aβ aggregates associated with Alzheimer’s disease using hydrogen/deuterium exchange mass spectrometry (HDX-MS) coupled with proteolysis. Toward this end, an on-line digestion system utilizing a triaxial electrospray probe as the front end to MS was developed. Using this approach, regions of Aβ(1-40) fibrils and protofibrils that are protected from HDX have been identified. The HDX data show that the C-terminal segment 35-40 and the N-terminal segment 1-19 are highly exposed to exchange in both fibrils and protofibrils, while the internal fragment 20-34 is highly protected from exchange …

Direct Integration Of Surface Enhanced Raman Spectroscopy As A Detection Mode For Microfluidic Separations And Fluid Handling: Μfluidic-Sers, Raynella Magdalene Connatser

Doctoral Dissertations

The arena of microfluidics (µfluidics) has grown over the past decade to encompass myriad separation techniques and exploit copious detection modes. The direct integration of a vibrational spectroscopic detection technique, rich with structural information, onto a platform that is portable and potentially highly controllable such as µfluidics, could offer redress for some of the problems inherent in many of the electrophoretically driven separations carried out on said devices. Herein, this direct integration is explored, and methods of device fabrication, spectroscopic data collection conditions, analytical figures of merit of the detection technique, and separations method development results are discussed. The creation …

The Reaction Of Telechelic Polymers At Multicomponent Interfaces: A Molecular Loop Study, James Kevin Rice

Doctoral Dissertations

The work presented in this dissertation attempts to form an understanding of the reaction parameters that govern the reaction of telechelic polymers to form multiply bound polymer chains, resulting in polymer loop formation, at both soft and hard polymeric interfaces. Both theoretical and experimental studies offer evidence that blocky copolymers, as opposed to random or alternating morphologies, are the best compatibilizers of a given polymer blend system. This has been attributed to the fact that blocky copolymers spread across the interface, with each block lying in or near the homopolymer region in which it is miscible, effectively “stitching” the interface …

Multiple Approaches To The Separation Of Amino Acids And Biologically-Relevant Compounds, Lance Andrew Riddle

Doctoral Dissertations

The branch of analytical chemistry known as separations has continued to grow and expand ever since its beginnings a century ago. With all the technological advances occurring to make separations a more powerful technique, the main goal continues to be the desired separation of the compounds of interest in a mixture. Although a desired separation may be achieved, there can always be room for improvement with regards to the time necessary for the separation as well as better resolution of closely-related species as well as enantiomers of the same analyte.

In this work, a variety of separation methods and variations …

Synthesis And Radiolabeling Of Potassium Trifluoroborate Benzylidene Anabaseine Derivatives, Aaron Landon Smith

Doctoral Dissertations

Anabaseine has demonstrated a high, non-selective, affinity for the α7- bungarotoxin sensitive neuronal nicotinic acetylcholine receptor binding site found in small cell lung carcinoma. The benzylidene anabaseine derivatives of anabaseine have shown a selective affinity for these binding sites. These studies suggest that radiolabeled benzylidene anabaseine derivatives could act as potential imaging agents to aid in the early detection of lung cancer.

This dissertation outlines the strategy and methods employed in the synthesis of a family of potassium trifluoroborate derivatives of benzylidene anabaseine and their subsequent halogenation. Two of the trifluoroborate salts were converted to their radiolabeled analogues for potential …

Adsorption Of Small Molecules On Mgo And Graphite, Peter Nikolaivich Yaron

Doctoral Dissertations

The physical adsorption of molecules on metal oxide surfaces has direct implications in a number of industrial applications such as; catalysis, electronics, and fuel cells to name a few. Despite the large number of adsorption studies to date, only a small number of systems can be explained with the most advanced ab initio calculations currently available.

One of the simplest metal oxide systems to study is magnesium oxide due to its simple cubic rock-salt structure. Using a patented method, nearly defect-free MgO cubes can be synthesized with a narrow size distribution exposing exclusively the (100) equilibrium crystal face. The use …

Synthesis And Characterization Of Complex Polymer Architectures, Brandon Scott Farmer

Doctoral Dissertations

Anionic polymerization based upon high vacuum technique has been used to synthesize different star polymers using varying linking techniques. In particular chlorosilanes, divinylbenzene, and polyhedral oligomeric silsesquioxane (POSS) chlorosilane derivatives were used in the synthesis of star polymers. These polymers, along with polymers synthesized by others, have been characterized by a range of methods in this work.

A series of polyisoprene (PI) stars were synthesized from dimethylaminopropyllithium (DMAPLi) and subsequently hydrogenated to form poly (ethylene-co-propylene) (PEP) these were characterized by size exclusion chromatography (SEC) coupled with online two angle laser light scattering (TALLS). These polymers were synthesized in an attempt …

The Role Of Specific Interactions On The Dispersion And Properties Of Carbon Nanotube-Polymer Nanocomposites, Asif Rasheed

Doctoral Dissertations

This dissertation presents work that exammes the role of specific chemical interactions in enhancing the dispersion of carbon nanotubes in a polymer matrix. Carbon nanotubes (CNT) possess unique mechanical, electrical and thermal properties hence can have a number of potential applications including high strength, light weight composites. Due to strong interaction among nanotubes, they stay as aggregates and hence their full potential for application is severely limited. Utilization of specific chemical interactions to induce/improve miscibility in polymer blends is well known. In this thesis, this approach is applied to carbon nanotubes polymer composites to enhance the dispersion of nanotubes in …

Spectroscopic Investigations In Chiral Crystalline And Solution Phases, Andrew Thomas Fischer

Doctoral Dissertations

Chirality is an interesting phenomenon that is not completely understood, and the present work broadens the present body of knowledge using various methods. Crystallization experiments of glycine have confirmed the previously reported phenomenon of nonphotochemical laser induced nucleation (NPLIN), and experiments utilizing a geometry with focused lasers may also display NPLIN, though the results indicate that new factors such as pH of the irradiated solution may affect the crystallizing process. Sodium bromate, NaBrO₃, may also crystallize via NPLIN, though the results are not as conclusive as the glycine experiments. For both glycine and sodium bromate, sound waves produced …

Nanodot-Based Organic Memory Devices, Zhengchun Liu

Doctoral Dissertations

In this study, resistor-type, diode-type, and transistor-type organic memory devices were investigated, aiming at the low-cost plastic integrated circuit applications. A series of solution-processing techniques including spin-coating, inkjet printing, and self-assembly were employed to fabricate these devices.

The organic resistive memory device is based on a novel molecular complex film composed of tetracyanoquinodimethane (TCNQ) and a soluble methanofullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM). It has an Al/molecules/Al sandwich structure. The molecular layer was formed by spin-coating technique instead of expensive vacuum deposition method. The current-voltage characteristics show that the device switches from the initial 'low' conduction state to …