Chemistry & Biochemistry Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2752

Browse

Search Results

Now showing 1 - 10 of 30

A Novel Pre-fluorescent Nitroxide Probe for the Highly Sensitive Determination of Peroxyl and Other Radical Oxidants
(2009) Jia, Min; Blough, Neil V; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
ABSTRACT Peroxyl and other radical oxidants react with stable cyclic nitroxides, such as the piperidinyl and pyrrolidinyl nitroxides to form initially the one electron oxidation product, the oxoammonium cation. For most of the nitroxides studied thus far, the oxoammonium cation can in part be regenerated to the nitroxide through reduction by solution constituents. The reaction mechanisms, however, remain a matter of debate. Further, the highly-sensitive, quantitative determination of peroxyl and other radical oxidants has yet to be achieved, posing a major hurdle to a further understanding of the impact of peroxyl radicals in many biological and environmental processes. A unique, amino-pyrrolidinyl nitroxide, 3-amino-2,2,5,5,-tetramethyl-1-pyrrolidinyloxy (3-ap) is shown to undergo an irreversible reaction with peroxyl radicals and other radical oxidants to generate a diamagnetic product. When a fluorophore, fluorescamine is covalently linked through the amino group on the nitroxide, the resulting compound (3-apf, or I) has very low fluorescence quantum yield. Upon reaction with peroxyl and other radical oxidants, the quantum yield of the product increases dramatically (~100 fold), and thus 3-ap or 3-apf can be used as a highly sensitive and versatile probe to determine oxidant production optically, either by monitoring the changes in fluorescence intensity using a spectrofluorometer, by HPLC analysis with fluorescence detection, or by a combination of both approaches. By changing the [O2]/[nitroxide] ratio, it is shown that peroxyl radicals can be detected and quantified preferentially in the presence of other radical oxidants, such as *NO2 and CO3*-. When decreasing the [O2]/[nitroxide] ratio, the oxidation product decreases, with a concomitant increase of the alkoxylamine product resulting from reaction of 3-ap (3-apf) with carbon centered radicals. Preliminary studies suggest that the reactions of 3-ap and 3-apf with peroxyl radical produce different final products. High resolution mass spectrometry and NMR studies indicate that 3-ap is oxidized to form a cyclic peroxide structure, while 3-apf is oxidized to form a cyclic -NH-O- structure, with this difference resulting possibly from the presence of the fluorescamine moiety in 3-apf. Detection of photochemically produced peroxyl radicals is achieved by employing 3-amino-2,2,5,5,-tetramethyl-1-pyrrolidinyloxy (3-ap) alone, followed by derivatization with fluorescamine, while detection of thermally-generated peroxyl radicals employs 3-apf. Preliminary applications include the detection of peroxyl radicals generated thermally in soybean phosphatidylcholine liposomes by 3-apf and produced photochemically in tap water by 3-ap.
AN IMPROVED PSEUDO-DETERMINISTIC RECEPTOR MODEL (iPDRM) TO APPORTION AMBIENT PM CONSTITUENTS TO SOURCES IN TAMPA, FL
(2009) Beachley, Gregory Marcus; Ondov, John M; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In 2005, Park et al., developed a new Pseudo-Deterministic Receptor Model (PDRM) to apportion SO2 and ambient particulate matter (PM) constituents to local sources near Tampa Bay. Ambient pollutant measurements were fit to products of emission rates and dispersion factors constrained with a Gaussian plume model for individual sources. In our study, the original samples were reanalyzed by ICPMS for 10 additional elements to improve the resolving power. Chemical mass balance (CMB) terms were added to PDRM to allow fitting of background aerosol sources. More accurate, curvilinear plume trajectories were computed to predict arrival times in both surface and aloft layers. This allowed application of the PDRM complicated meteorological conditions, e.g. wind shifts. Predicted emission rates for particle-bound elements were constrained using chemical compositional information obtained from published source profiles for generic source types. Constraints applied to source emissions of known tracer species allowed the "conditioning" of predicted dispersion factors for those sources to tracer species concentration profiles to better determine the dispersion factor temporal profiles. This enabled the model to apportion pollutants to individual sources with intermittent emissions the omission of which in Park et al. lead to significant residuals. Excellent fits were obtained for all modeled pollutants: 14 of 22 species have Normalized Mean Square Error (NMSE) values of < 2.5% and 21 of 22 have values < 8%. These were improved for SO2 and 8 of 10 elements (by 7-35% for Al, Cu, Ni, Pb, and Zn) modeled by Park et al. Our predicted emission rates are in much better agreement with chemical compositions for generic source types. Key results include: (1) predicted SO2 contributions to ambient levels from a small, lead battery recycling plant that were reduced from 50-59% at its peak influence to a more reasonable 2-4%, (2) Pb/Zn ratios from that plant increased from 1.0 to 734 and better agree with published ratios of 67-440, (3) predicted Ni emission rates for one of the oil-fired power plants (OFPP) was increased by 100-fold (larger than Park's), and now better agrees with its published National Emissions Inventory (NEI) emission rate and with X/Ni ratios for generic OFPP emissions derived from EPA's SPECIATE database, and (4) our predicted emission rates for hazardous air pollutants and toxics from power plants agree with ~75% of those reported annual emission rates from NEI and Toxic Release Inventories (TRI) to within a factor of 5. This suggests that these reported data provide a good qualitative estimate of emissions, but should not be treated as accurate in a predictive model to quantify source emissions. It was also observed that the TRI values for As emission rates from coal-fired power plants are more accurate that their NEI values.
TEMPLATE SYNTHESIZED NANOTUBES, NANOWIRES AND HETEROGENEOUS COAXIAL NANOWIRES FOR ELECTROCHEMICAL ENERGY STORAGE
(2009) Liu, Ran; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Template synthesized nanomaterials have been successfully applied in electrochemical energy storage systems such as supercapacitors and lithium ion batteries. The first part of present study will list examples of applying various nanomaterials such as nanowires, nanotubes and heterostructured nanowires in different electrochemical energy storage systems for enhancing their charge/discharge rates, energy densities and power densities, etc. The following of the thesis will describe the template synthesis of nanomaterials in details. The experimental part of this thesis will concentrate on the fabrication of alumina template and the detailed experimental setups for aluminum anodization and template synthesis of nanomaterials. The rest of the thesis analyzes four cases of using template synthesized nanomaterials in electrochemical energy storage, which include my major work during my PhD studies. The first one is utilizing poly(3,4- ethylenedioxythiophene) (PEDOT) nanotubes as electrode materials for highpowered supercapacitor. The thin-walled nanotubes allow fast charge/discharge of the PEDOT to achieve high power. The second one is related to synthesis and characterization of RuO2/PEDOT composite nanotubes for supercapacitors. Loading appropriate amount of RuO2 can effectively enhance the specific capacitance of PEDOT nanotube. The third case illustrates the synthesis of MnO2/PEDOT coaxial nanowires by one step coelectrodeposition for electrochemical energy storage. The combined properties of MnO2 and PEDOT enable the coaxial nanowires to have very high specific capacitances at high current densities. Their formation mechanism will be explored and their nanostructures are tuned for optimized electrochemical properties. The final case reports the MnO2-Nanoparticles enriched PEDOT nanowires for enhanced electrochemical energy storage capacity. Large amount of the MnO2 nanoparticles can be loaded into PEDOT nanowires after they are soaked in KMnO4 solution. Thus loaded MnO2 nanoparticles effective enhance the energy densities of PEDOT nanowires without causing too much volume expansion to them.
Synthesis, Characterization and Catalytic Properties of Bimetallic Nanoparticles
(2009) Dylla, Anthony Greg; Walker, Robert A; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Due to the ever-increasing desire for catalysts that possess high activities and selectivities for industrially relevant reactions, much effort is being spent on the synthesis of mono and bimetallic nanoparticles with tunable characteristics such as size, shape and bimetallic composition. Understanding how these characteristics influence catalytic performance is the key to rationally designing catalysts for a specific reaction. While significant breakthroughs have been made, particularly in the area of monometallic nanoparticles with regard to shape and size, relating the bimetallic structure, i.e., core@shell or alloy to a specific reactivity remains a difficult task. Work presented in this thesis describes the synthesis, characterization and catalytic properties of mono and bimetallic nanoparticles. Our efforts were motivated by the desire to understand the relationships that exist between metallic nanoparticle structure and their function as catalysts. This work also seeks to better understand the dynamic changes a nanoparticle's structure undergoes during typical catalytic operating conditions. Our approach is to use a wide array of analytical tools including optical methods, electron microscopy, XRD and mass spectrometry to provide an interlocking description of nanoparticle structure, function and durability. We show how the polymer coatings and degraded carbonaceous deposits affect propene hydrogenation catalytic activity of Pt nanoparticles. We also present a unique view of the interplay between thermodynamic and kinetic variables that control bimetallic nanoparticle alloy structures by looking at ordered and disordered PdCu alloy nanoparticles as a function of particle size. In another study we show that Ru@Pt and PtRu alloy nanoparticle catalysts have similar surface structures under oxidizing conditions but completely different surface structures under reducing conditions as probed by vibrational spectroscopy. These differences and similarities in surface composition correlate very well to their catalytic activity for CO oxidation under oxidizing and reducing environments, respectively. Finally, we present the synthesis and characterization of Cu@Pt nanoparticles with a particular focus on the core@shell formation mechanism. We also show how dramatic changes in the surface electronic structure of Cu versus Cu@Pt nanoparticles can affect their ability to transform light into heat by using Raman spectroscopy to observe graphite formation on the surface of these nanoparticles.
Total Synthesis of (3R,3'R,6'R)-Lutein, (3R,3'R)-Zeaxanthin and Their Stereoisomers
(2008) Chang, An-Ni; Khachik, Frederick; DeShong, Philip; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
(3R,3'R,6'R)-Lutein (1) and (3R,3'R)-zeaxanthin (5) are dietary carotenoids that are found in most fruits and vegetables. Numerous studies have shown that 1 and 5 play an important role in the prevention of age-related macular degeneration (AMD) that is the leading cause of blindness. To date, the metabolic pathways of 1 and 5 in ocular tissues of an animal model in relation to AMD have not been explored. This is primarily because of the lack of a viable method for the synthesis of 1 and 5 that can be labeled with a stable isotope. Among the eight possible stereoisomers of lutein, only 1 has been previously prepared by total synthesis in 14 steps in an overall yield of 0.5%. The total synthesis of lutein, zeaxanthin, and their stereoisomers from (rac)-alpha-ionone has been accomplished by a C15+C10+C15 coupling strategy. Therefore, (3R,3'R,6'R)-lutein (1, 8%), (3R,3'S,6'S)-lutein (2, 7%), (3R,3'S,6'R)-lutein (3, 6%), and (3R,3'R,6'S)-lutein (4, 7%) were each prepared in a high optical purity in 7 steps. 3-Hydroxy-alpha-ionylideneacetaldehyde served as a common precursor to afford luteins 1 - 4 by a much shorter synthetic sequence and a higher overall yield than that of a published method for 1. The other four stereoisomers of lutein can be similarly prepared. (3R,3'R)-Zeaxanthin (5, 12%) and (3S,3'S)-zeaxanthin (6, 11%) were prepared in 8 steps from (rac)-alpha-ionone via 3-hydroxy-alpha-ionone which was transformed into 3-hydroxy-beta-ionone (3R-42, 22%) and its enantiomer (3S-42, 21%), respectively. The key intermediates, 3R-42 and 3S-42 were converted into the corresponding C15-Wittig salts 3R-16 and 3S-16 that were used in a double Wittig reaction with the C10-dialdehyde 17 to afford 5 (98% ee) and 6 (98% ee). Utilizing Wittig salts 3R-16 and 3S-16, (3R)-beta-cryptoxanthin (135, 8%) and (3S)-beta-cryptoxanthin (136, 9%) were each prepared in optical purity of 98%. The most important feature of the strategies presented here is its application to the total synthesis of isotopically labeled and optically pure lutein, zeaxanthin, and their stereoisomers for metabolic studies. This synthesis also provides access to the C15-precursors of optically active carotenoids with 3-hydroxy-alpha- and 3-hydroxy-beta-end groups that are otherwise difficult to synthesize.
Synthesis of Magnetic Nanotubes as Magnetic Resonance Contrast Agents and Drug Carriers and the Study of Their Cytotoxicity
(2008-11-20) Bai, Xia; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The increasing interest in the medical application of nanotechnology has heightened the need for synthesizing nanoparticles with well-defined dimensions and multifunctionalities. Studies on template synthesis demonstrate relatively reliable reproducibility of the nanostructures. Moreover, differential modification can be achieved with template synthesis method. Based on template synthesis method, magnetic nanotubes (MNT), silica nanotubes (SNT) loaded with superparamagnetic iron oxide nanoparticles (SPION), were successfully prepared. The magnetic properties of MNTs including saturation magnetization (Msat) and magnetic resonance (MR) relaxivities were investigated. Results revealed that Msat of MNTs is as high as 95 emu/gFe, which is on the highest side of reported value for magnetite nanoparticles. The MR study showed that MNTs enhanced proton MR relaxation considerably, especially transverse relaxation T2 (*). The transverse relaxivities (r2(*)) of MNTs are higher than that of Feridex, a FDA approved MR contrast agent, indicating that MNTs could potentially act as efficacious T2(*)-weighted MR contrast agents. MNTs were also studied as drug carriers to control the loading and release of Doxorubicin (Dox: a cancer drug model). The inner surfaces of MNTs were modified with C18- and pyridine-silane with various ratios. The results showed that Dox molecules held in the MNTs were stable at pH 7.2, and released at pH 4.5. With proper modification, MNTs can be used to control drug release profiles. The magnetic nanoparticles in MNTs helped in loading drug molecules due to barrier effect. Cytotoxicity and cellular uptake of SNTs with two different sizes and surface charges were investigated for two cell models, primary (non-malignant) and cancer cells. The nanotubes showed limited toxicity which was concentration-, surface charge-, and length- dependent. The internalization was confirmed with both confocal microscopy and TEM studies. Confocal microscopic images demonstrated that endocytosis was one of the main mechanisms for internalization of nanotubes. A novel method was developed in this thesis to improve multifunctionality of SNT as a drug delivery system by modifying the nanotubes segmentedly between the entrance and the remainder. Ideally, we can make a universal delivery vehicle with SNTs as the constitute structure which can be filled with therapeutic and imaging payloads and have biological surface modifiers for targeting.
TARGETING BIOMARKERS VIA CITP-BASED SELECTIVE PROTEOME ENRICHMENT
(2008-06-30) Fang, Xueping; Lee, Cheng S; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Besides the complexity of protein samples, probably the greatest challenge presently facing comprehensive proteome analysis is related to the large variation of protein relative abundances (>6 orders of magnitude), having potential biological significance in mammalian systems. To achieve comprehensive proteome analysis including the identification of low abundance proteins, this project aims to develop and demonstrate a capillary isotachophoresis (CITP)-based proteome platform, capable of providing selective analyte enrichment and extremely high resolving power toward complex protein mixtures. In contrast to universally enriching all proteins by a similar degree, the result of the CITP stacking process is that major components may be diluted, but trace compounds are concentrated. By employing combined CITP/nano-reversed phase liquid chromatography (nano-RPLC) separations, a total of 6,112 fully tryptic peptides are sequenced by electrospray ionization mass spectrometry (ESI-MS), leading to the identification of 1,479 distinct human SwissProt protein entries from a single proteome sample of whole unstimulated human saliva. By comparing with capillary isoelectric focusing as another electrokinetics-based stacking approach, CITP not only offers a broad field of application, but also is less prone to protein/peptide precipitation during the analysis. The CITP-based proteome platform is further employed for the analysis of protein expression within synaptic mitochondria isolated from mouse brain. The ultrahigh resolving power of CITP separation is evidenced by the large number of distinct peptide identifications measured from each CITP fraction together with the low peptide fraction overlapping among identified peptides. Furthermore, the collective proteome datasets yield the identification of 2,191 distinct mitochondrial protein entries, corresponding to 76% coverage of the MitoP2-database reference set. Comparisons among CITP and multidimensional liquid chromatography techniques are conducted using a single processed protein digest from brain cancer stem cells, identical second dimension separation (nano-RPLC) and ESI-MS conditions, and consistent search parameters and cutoff established by the target-decoy determined false discovery rate. Besides achieving superior overall proteome performance in total peptide, distinct peptide, and distinct protein identifications, analytical reproducibility of the CITP proteome platform is determined by a Pearson R2 value of 0.98 and a coefficient of variation of 15% across all proteins quantified.
PROTEOME ANALYSIS OF FORMALIN-FIXED AND PARAFFIN-EMBEDDED TISSUE
(2008-04-04) Guo, Tong; Lee, Cheng S; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Because of the long history of the use of formalin as the standard fixative for tissue processing in histopathology, these archival formalin-fixed and paraffin-embedded (FFPE) tissues present invaluable resources for conducting retrospective disease investigations. However, the high degree of covalently cross-linked proteins in FFPE tissues hinders efficient extraction of proteins from tissue sections and prevents subsequent proteomics efforts from opening the door to a veritable treasure trove of information sequestered in archival tissues. To this end, a protein extraction methodology has been optimized and demonstrated to achieve effective protein extraction together with combined technological development for enabling comprehensive and comparative proteome studies across archival FFPE tissue collections. An effective discovery-based proteome platform combining capillary isoelectric focusing (CIEF)-based multidimensional separation system with electrospray ionization-mass spectrometry (ESI-MS) has been developed to enable ultrasensitive analysis of minute protein amounts extracted from targeted cells in tissue specimens in this thesis. Based on our initial success in analyzing protein profiles within microdissected FFPE tissues, this project further demonstrates the ability to achieve high confidence and comparative proteomic analysis using tissue blocks stored for as many as 28 years. Vacuolar proton translocating ATPase 116 kDa subunit isoform a3, one of the unique proteins expressed in the ASPS, is further validated by immunohistochemistry (IHC). Although IHC is highly sensitive and provides the subcellular resolution, MS-based proteome profiling enables global identification and quantification of thousands of proteins without a prior knowledge of individual proteins being analyzed or the need of validated antibodies.
Barcoded Silica Nanotubes for Bioanalysis
(2007-09-25) He, Bo; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Analysis of the chemical/biological species involved in health care is the most important step for diseases diagnosis and new drug screening. Barcoded nano/microparticles are attracting more and more interest for detection and identification of multiplexed chemical/biological species simultaneously. However, the development of barcoded particles is still in an early stage. To solve problems existing in current barcoded particles, such as spectral overlap and degradation of materials, our group has invented barcoded silica nanotubes (SNTs) and applied them to multiplexed immunoassays and cancer marker detection as coding materials. Barcode SNTs are fabricated by a multistep anodization template synthesis method. Each barcoded SNT has several segments with different reflectance values depending on their diameters and wall thicknesses. Therefore, the barcode of each SNT can be "read-out" with a conventional optical microscope. Barcoded SNTs have shown high stability and dispersibility in aqueous buffer media. Suspension arrays with barcoded SNTs have shown high sensitivity and high selectivity for the detection of multianalytes in the multiplexed immunoassays. Magnetic field separation is one promising technique to replace tedious filtration or centrifugation separation for rapid, gentle, and reliable isolation of target analytes. Barcoded SNTs have been coupled with magnetic bead (MB) separation for protein detection and analysis. The species and number of final collected SNTs represent the types and amount of analyte proteins, respectively. By using barcoded SNTs instead of fluorescence as signals, these suspension arrays overcome the problems existing in current MB suspension arrays, such as fluorescence quenching and interference of MBs' autofluorescence. Barcoded magnetic nanotubes (BMNTs) have also been successfully fabricated as dual-functional microcarriers for multiplexed immunoassays and cancer biomarker detection with magnetic separation. BMNTs combine the shape variety of barcoded SNTs and superparamagnetic properties of magnetic nanotubes. BMNTs overcome the problems in the existing dual-functional particles. The iron oxide nanocrystals are evenly dispersed in the inner void of the tubular structures without interference with the optical barcoded patterns. BMNTs have shown high selectivity when applied in multiplexed assays and cancer biomarker detection. The identification of BMNTs with software shows promising results for rapid data analysis. The dual-functional BMNTs provide a promising way for ultrafast, gentle, efficient, and automated detection of target chemical/biochemical molecules for diagnosis and drug screening.
Controlled Electrochemical Synthesis of Conductive Polymer Nanostructures and Electrochromism Property Study
(2007-09-14) Xiao, Rui; Lee, Sang Bok; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Conductive polymers have attracted the attention of many scientists in the whole world since Australians DE Weiss and coworkers reported high conductivity in oxidized iodine-doped polypyrrole, a polyacetylene derivative. In recent years, conductive polymers have served as the basis for many different new technologies such as electrochemical power sources, electrochromic display devices, photovoltaic devices and biosensors. For all of these applications, it is necessary to maintain ultra-fast charge and discharge rates in the conductive polymer layers in order to obtain high energy capacity, fast sensing speed or color change rate. For conductive polymer films there is always a problem for the slow charge/discharge ratio due to the diffusion of counter-ions into and out of the conductive polymer layers. To solve this problem, one-dimensional conductive polymers are ideal choices. We have investigated the electrochemical synthetic mechanism for conductive polymer nanotubes in a porous alumina template using poly(3,4-ethylenedioxythiophene) (PEDOT) as a model compound. As a function of monomer concentration and potential, electropolymerization leads either to solid nanowires or hollow nanotubes and it is the purpose of these investigations to uncover the detailed mechanism underlying this morphological transition between nanowire and nanotube. Electrochemically-synthesized PEDOT nanostructures were characterized using transmission electron microscopy to measure the extent of nanotubular portion in the PEDOT nanostructure. The study on potential dependency of nanotubular portion shows that nanotubes are grown at a low oxidation potential (< 1.2 V vs. Ag/AgCl) regardless of monomer concentration. This phenomenon is explained by the annular base electrode shape at the pore bottom of a template and further supported by an electrochemical study on a flat-top electrode. We investigate the mechanism by taking into account the effect of electrolyte concentration, temperature, and template pore diameter on PEDOT nanostructures. This mechanism is additionally used to control the nanotube dimensions of other conductive polymers such as polypyrrole and poly(3-hexylthiophene). The electrochromic properties and applications of PEDOT nanostructures are also addressed.

Chemistry & Biochemistry Theses and Dissertations

Browse

Filters

Settings

Sort By

Results per page

Search Results