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中文学位

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  • [学位] Investigation of fluorescent conjugated polymer chemosensors for the detection and differentiation of iron cations
    摘要:Fluorescent conjugated polymers (FCP) have received interest due to their ability to act as chemosensors to detect metal cations in environmental and biological systems with sensitivity and selectivity. Two polymers containing N,N,N'-trimethylethylenediamino (tmeda) receptors were synthesized and characterized to investigate the role of conjugation in chemosensor response. The two polymer backbones used: poly[2,5-thiophenediyl-1,2-ethynediyl-1,4-phenylenediyl-1,2-ethynediyl] (PPETE) and poly[2,5-thiophenediyl-1,2-ethynediyl-1,4-naphthalenediyl-1,2-ethynediyl] (PNETE), differ in extent of π conjugation. Modifying the energy gap of the polymer backbone could alter sensitivity and selectivity. Absorption and emission spectra of tmeda-PNETE showed blue shifting from tmeda-PPETE, suggesting possible twisting of tmeda-PNETE. The polymers detected most metals with small fluorescence increases, but showed significant quenching upon Cu 2+ addition in aqueous solution. Inorganic/organic hybrid systems, polymer preloaded with Cu2+, were shown to be highly selective and sensitive fluorescence "turn-on" chemosensors for iron cations. To investigate the iron selectivity of the amino receptor, tmpda-PPETE containing N,N,N'-trimethylpropylenediamino (tmpda) receptors was synthesized. This allowed studies of longer alkyl chains between the nitrogen atoms. The absorption and emission wavelength maxima for tmpda-PPETE were analogous to tmeda-PPETE, with higher fluorescence quantum yield for tmpda-PPETE. The metal cation selectivity for tmpda-PPETE in solution was drastically altered from tmeda-PPETE, showing significant quenching for Fe3+ ions. Titration of a variety of other metal cations resulted in little to no emission spectra variation. This work demonstrates that tmpda-PPETE has the ability to distinguish Fe2+ from Fe3+ both of which play major roles in biological environments. In order to take advantage of greater portability and quicker at-source screening, tmeda FCPs were transitioned to solid-state materials. Thin films of have been fabricated through dispersion of each FCP into poly(methyl methacrylate) (PMMA) and polyvinyl alcohol (PVA) matrices. Electropsun tmeda polymer fibers have also been prepared using a blended matrix of PMMA and polyethylene oxide (PEO). Photophysical studies of all solid-state materials were conducted to determine the fluorescent response toward copper and iron cations, showing a time-dependent response. Red shifted absorption and emission spectra were observed, which is consistent with aggregation and increased interchain interactions in the solid-state, with less shifting present with the electrospun fibers. The greatest iron sensitivity was achieved with tmeda polymer Cu2+ preloaded electrospun fibers.
  • [学位] Molecular Monolayers for Hybrid n-Si / organic Inversion Layer Solar Cells
    摘要:In this thesis I show how self-assembled monolayers (SAMs) control the surface energetics and passivation of the oxide-freSi surface, and of semiconductor surfaces in general. The Metal-Insulator-Semiconductor (MIS) structure, suggested for cheap yet efficient solar cells, demands high quality, homogeneous passivation over macroscopic areas. Placing a molecular SAM between the semiconductor absorber and the metal top electrode, helps to probe the basic physics of those structures, as well as the qualities of SAMs as interfacial layers, and define some of their limitations as well. One of the key features of a good MIS cell is that the semiconductor (near)surface is inverted, i.e., effectively is of different doping type than the bulk of the material, due to sufficiently strong band bending. According to our current understanding the interfacial layer in MIS and other inversion layer solar cells has 4 different roles: 1. passivation of surface states by saturating the surface atoms' dangling bonds, 2. preventing direct metal-semiconductor chemical interaction, 3. introducing a surface dipole that can increase the initial potential difference between the metal and semiconductor, 4. as a medium for fixed charges (that will affect the interface electrostatics as -3-). Among these, the first two are necessary conditions and have to be fulfilled for the cell’s VOC to exceed that of its metal-semiconductor analogue, while the last two are optional and can increase even further the inversion induced by the metal, i.e., by the difference between the metal and semiconductor work functions. In one system I used self-assembled monolayers of alkyl chains, bound to oxide-free n-Si through Si-O-C bonds to saturate the surface bonds of the Si. The second of the necessary requirements was met by using a semi-transparent Au film that was chemically bound to the terminal thiol group of the monolayer, with a 10 carbon alkyl chain as buffer between metal and semiconductor. Indeed the 480 mV VOC, measured under illumination for this bottom-up constructed cell, is higher than for any n-Si/Au junction before. In another, related system, I used the hydroquinone-methanol treatment to Si(100), which was earlier shown to be the best chemical passivation for Si surfaces. Obviously, the surface bonds in this molecular treatment are well taken care of, but my measurements also demonstrate an impressively large negative surface dipole introduced by the monolayer, effectively reducing the electron affinity of the Si by as much as 500 meV. I combined this molecular treatment with a Hg top electrode, which is chemically inert to Si, to fulfill the first three of the above requirements. Indeed, with the aid of the surface dipole the junction was pushed into strong inversion, despite the rather small work function of the Hg. Using a primary alcohol with alkyl chains of different lengths, instead of methanol, enabled me to tune the magnitude of the dipole, while preserving the excellent surface passivation. In contact with Hg, the junctions followed the Schottky-Mott model for metal-semiconductor contact almost ideally in a way never even approached before for Si-based junctions. One chapter of this work is also dedicated to the chemical mechanism by which the hydroquinone-methanol treatment passivates the Si surface so efficiently, as this was not analyzed before. For large area solar cells, the Hg top electrode was replaced by a conducting polymer - PEDOT:PSS. The polymer was chosen, because it can be deposited in a gentle manner by spin-coating, so as not to damage the molecular surface passivation, and for its high work function, so as to induce inversion in the Si. As it is a degenerate p-type semiconductor, the polymer should also block majority carrier electrons from the Si from moving into the top electrode, thus forcing the junction to rely on minority carrier transport alone - a property favorable for photovoltaics (reduces probability for recombination
  • [学位] Non-covalent Interactions in Peptide Hydrogels: A Mechanism for Mechanical and Structural Control
    摘要:Hydrogels are a unique class of materials lying at the interface of biology and engineering. In the development of this class of materials, understanding the underlying molecular mechanisms that dictate mechanical and structural properties is critical. Non-covalent interactions have been shown here to specifically modulate the properties of peptide hydrogels. A pair of oppositely charged peptides, that when mixed together self-assemble in to a hydrogel network were used in these studies. It was demonstrated using NMR signal decay, that electrostatic interactions are the primary contributions to peptide assembly into a hydrogel network. A decrease of electrostatic interactions results in a decrease in mechanical strength. Also, the ability for hydrogels to form elongated fibrous networks was prevented with the decrease in electrostatic interactions. We further investigated the role of peptide terminal chemistries in hydrogel design. With simple chemical modifications (N-termini acetyl- (COCH3) and amino- (NH2 ); C-terminal -carboxyl (COOH) and -amide (NH2)) regulation of the mechanical and structural properties was demonstrated. Generally the mechanical strength and fiber structure did not vary, however gelation kinetics and fiber characteristics were directly related to changes in peptide terminal chemistries. These results show the utility of non-covalent interactions in modulating peptide hydrogel structural and mechanical properties in the development of biomedical materials. We additionally examined the chromatographic analysis and separation involved in the development of peptide-based biomaterials through comparison of fluorocarbon and hydrocarbon columns and eluents in the retention and separation of non-fluorinated analytes. The results from these studies showed that fluorocarbon columns displayed the best separation and have a significant potential for use in development.
  • [学位] Maternal and child health disparities among Native American women in Oklahoma: A secondary analysis of health behaviors, prior well-being, and adverse pregnancy outcomes, 2004-2011
    摘要:Utilizing data from the Oklahoma Department of Health Pregnancy Risk Assessment Monitoring System (PRAMS) for the years 2004 through 2011, this study examines racial and ethnic differences in unhealthy maternal behaviors and the consequences of those actions on the health of both mother and child. The maternal behavior variables include smoking cigarettes, drinking alcohol, multivitamin use, and prenatal care utilization. The maternal health variables include gestational diabetes and hypertension. The labor and delivery outcome variables include placental issues, premature rupture of membranes (PROM), low birth weight, and child placement in an intensive care unit. This researcher hypothesized that minorities would engage in risky and unhealthy behaviors while pregnant more often than whites due to social disadvantages in the economic and educational realms. Furthermore, minorities would be more likely than whites to have unfavorable outcomes regarding labor, delivery, and health of the child due to lower socioeconomic status, poor maternal health, and underutilization of preventative care. The researcher finds that minority women seem to adhere to proper maternal health recommendations associated with personal choice, including smoking and drinking, though disparities are evident when compared to whites regarding behaviors associated with socioeconomic status, including prenatal care utilization and multivitamin use. African American women are more likely than whites to experience premature rupture of the membranes, have an underweight baby, and to place their baby in ICU, though less likely to experience placental issues. Native American women are less likely than whites to experience premature rupture of the membranes, have an underweight baby, and to place their baby in ICU, but more likely to experience placental issues. As expected, substantial changes have occurred in the maternal health and well-being of Oklahoma mothers over the course of the two PRAMS data collection phases.
  • [学位] Altered cholesterol metabolism in human cancers unraveled by label-free spectroscopic imaging
    摘要:Despite tremendous scientific achievements, cancer remains the second leading cause of death in the United States. Metabolic reprogramming has been increasingly recognized as a core hallmark of cancer. My dissertation work identified novel diagnostic markers and therapeutic targets for human cancers through the study of cholesterol in cancer cells. Enabled by label-free Raman spectromicroscopy, we performed the first quantitative analysis of lipogenesis at single cell level in human patient cancerous tissues. Our imaging data revealed an unexpected, aberrant accumulation of esterified cholesterol in lipid droplets of high-grade prostate cancer and metastases, but not in normal prostate, benign prostatic hyperplasia, or prostatitis. Biochemical and molecular biological studies showed that such cholesteryl ester accumulation was a consequence of loss of tumor suppressor PTEN and subsequent activation of PI3K/AKT pathway in prostate cancer cells. Furthermore, we found that such accumulation arose from significantly enhanced uptake of exogenous lipoproteins and required cholesterol esterification. Depletion of cholesteryl ester storage using pharmacological inhibitors or RNA interference significantly reduced cancer proliferation, impaired cancer invasion capability, and suppressed tumor growth in mouse xenograft models with negligible toxicity. These findings open new opportunities for diagnosing and treating late-stage prostate cancer by targeting the altered cholesterol metabolism. My thesis work also found that cholesterol-rich domains on plasma membranes can be used as a marker for the loss of basoapical polarity, one of the earliest changes observed in breast neoplasia. Raman microspectroscopy revealed that in polarized acini lipids were more ordered at the apical membranes compared to basal membranes, and that an inverse situation occurred in acini that lost apical polarity upon treatment with Ca2+-chelator EGTA. This method allowed us to detect the disruption of apical polarity by dietary breast cancer risk factor, &ohgr;6 fatty acid, even when the effect was too moderate to permit a conclusive assessment by traditional immunostaining method. Collectively, label-free Raman analysis of cholesterol-rich membrane domains in mammary acini provides an effective screening platform to identify risk factors that initiate breast cancer.
  • [学位] Predicting the initial lapse using a mobile health application after alcohol detoxification
    摘要:The prediction and prevention of the initial lapse--which is defined as the first lapse after a period of abstinence--is important because the initial lapse often leads to subsequent lapses (within the same lapse episode) or relapse. The prediction of the initial lapse may allow preemptive intervention to be possible. This dissertation reports on a predictive modeling study of the initial alcohol lapse after patient left residential care. The data were collected via a mobile health application, Addiction-Comprehensive Health Enhancement Support System (A-CHESS). A-CHESS was designed to offer ongoing support to alcohol addiction patients who have returned to their own community after completing inpatient treatment programs. Patients may access A-CHESS services at any time anywhere to help them cope with the recovery. In addition to the first chapter as the introduction of the problems and context, this dissertation consists of the other three chapters; each chapter presents a study to address different challenges faced in the development of such a predictive model in A-CHESS. The first challenge is the validation of a survey instrument used in the A-CHESS Weekly Check-in; the second challenge is the study of A-CHESS use behavior before the initial lapse; and the third challenge is to develop a comprehensive predictive model of the initial lapse. The steps taken in this dissertation to address these challenges have been fruitful. The major findings are practical and can be implemented in A-CHESS.
  • [学位] Mechanical Characterization of Coating-Interconnect Interfaces and Anode-Electrolyte Interfaces for Solid Oxide Fuel Cells
    摘要:A planar solid oxide fuel cell (SOFC) consists of multiple layers of dissimilar materials with distinct physical, mechanical, and thermal properties. High operating temperatures and mechanical loadings during service can significantly weaken the interfaces of different components in an SOFC. The strength and integrity of various interfaces, for example, coating-interconnect interfaces and electrode-electrolyte interfaces play an important role in increased power density of an SOFC. In the first part of the present investigation, the interfaces between oxide coatings and interconnects are characterized. The repeating anode-electrolyte-cathode units in a planar SOFC stack are physically separated by electrically conductive interconnects. With the reduction of operating temperature to 800°C, it is possible to replace lanthanum based ceramics with less expensive, more readily available chromium alloyed iron metals as interconnects. However, when incorporating chromium-alloyed interconnects, steps must be taken to inhibit chromium poisoning of cathodes. To prevent the chromium poisoning, a dense manganese cobalt spinel oxide (MCO) coating is applied on the cathode side surface of interconnect prior to its installation in the fuel cell. But highly ceramic brittle nature of MCO coatings makes them susceptible to damage under mechanical loads and thermal stresses developed during cooling down the fuel cell from operating temperature to room temperature. A room temperature four-point bend experiment is designed to assess the quality of coatings and coating adhesion. Resulting tensile cracking patterns on the coatings on the convex side of the bend specimen are used to quantify the interfacial shear strength from a shear lag model. In addition, the onset strain of coating spallation is incorporated in an energy based fracture mechanics model to obtain the interfacial fracture energy. Images from scanning electron microscopy (SEM) of the tested coating surfaces are processed to analyze the interface failure mechanisms, the crack spacing, and the spalled areas at higher strains. The analysis obtained from the present investigation is able show distinct differences between coatings processed with different parameters. In addition, based on the results obtained from the bend experiments, coating lifetime is predicted. Lifetime prediction of coatings will greatly assist in optimizing the coating process parameters and assessing the reliability of coated interconnects. In the second part of this dissertation, anode-electrolyte interfaces at which the important electro-chemical hydrocarbon fuel reactions take place are investigated. Frequent anticipated and unanticipated shut down and startup of fuel cells can cause delamination and failure of the anode-electrolyte interfaces. Room temperature four-point bend experiments are performed to obtain the interfacial fracture energy of the anode-electrolyte interfaces. The notched bend test specimens consist of NiO-YSZ anode and ScSZ electrolyte bi-layers are sandwiched between two steel stiffeners. A stable crack is forced to propagate along the interfaces and is monitored with a long distance camera lens. The constant load at which the stable crack propagates is recorded and utilized to obtain the critical strain energy release rate of the interfaces. The cracked surfaces are studied with SEM and energy dispersive spectroscopy (EDS).
  • [学位] Antifouling and Antithrombogenic Ultrathin Surface Chemistry for Bioanalytical and Biomedical Applications
    摘要:Whether the aim is to merely prevent the adsorption and accumulation of biological species, or to inhibit the surface-mediated activation of potentially harmful biological processes, biomaterial research invariably faces the need for man-made, foreign surfaces intimately contacting bodily fluids/tissues to be 'bioinert'. A popular strategy to address this technological constraint consists in passivating substrate materials with an antifouling (respectively a biocompatible) organic coating. Yet, despite tremendous research activity and progress in recent times, efficient adlayers are scarce, and endowing artificial surfaces with such properties remains, in essence, a difficult task. This PhD Thesis describes recent research contributions in the development of original and versatile stealth coatings, based on novel oligoethylene glycol trichlorosilane surface chemistry, for bioanalytical and biomedical healthcare applications. Surface modification also has the advantage of being straightforward, rapid and inexpensive. One primary objective was to engineer biosensors capable of selectively and sensitively detecting target analytes in real-world biofluids – exploiting the transducing technology of the ultra-high frequency electromagnetic piezoelectric acoustic sensor (EMPAS) system – as potential clinical assay alternatives to current screening/diagnostic tests. Biosensing platforms featured dual-functional, binary organosilane surface chemistry on quartz combining high analyte binding capability (for biorecognition) with pronounced antifouling properties (to minimize the otherwise overwhelming interference signal from the biological matrix). Clinical testing performance was successfully demonstrated through the detection of bacterial endotoxin – a potent pathogen associated with the highly-incident, deadly condition of sepsis. EMPAS measurements performed in full human blood plasma (and in a real-time and label-free advanced fashion compared to modern clinical assays that rely on chromogenic reporter molecules) showed that samples at abnormally high concentration (1000 pg/mL) can be readily differentiated from those presenting basal endotoxin level (< 10 pg/mL).

    Unimolecular, subnanometric silane adlayers featuring a single type of ultrashort monoethylene glycol-terminated chains (MEG-OH) also displayed pronounced antifouling behaviour, against full serum. Further experimental and computational studies collectively corroborated the mechanistic hypothesis according to which water would play a critical role in this respect – through the formation of a permeant, tightly coordinated hydration network, whose disturbance by foulants was rationalized to constitute a penalty in terms of energy and generate repulsive forces. Another major finding was the key participation of the single, internal ether atom of oxygen in the MEG chains in maintaining such a stable, nanoscale zone of hydration. The scope of derivatizable substrate materials of biotechnological importance was also readily expanded to gold (with adapted thiol anchoring chemistry) and polycarbonate polymer. In the latter work with plastic, the unique MEG-OH 'nanogel' ultrathin surface chemistry was also shown to display remarkable antithrombogenic properties, far exceeding those of the bare plastic substrate. More importantly, thrombus growth was nearly non-existent. Such performance was quite outstanding considering the fact that whole human blood did not require any anticoagulant treatment to prevent clotting (besides its standard collection and storage in heparinized tubes) despite being exposed to a foreign surface, in vitro.

  • [学位] A molecular picture of biofuel decomposition: Pyrolysis of furan and select furanics
    摘要:Limited fossil fuel resources and climate impacts due to carbon dioxide emissions have made it critical that we use renewable, carbon-neutral fuels. Biomass, in the form of crop waste or the inedible portion of plants, has the potential to be a renewable and economical source of energy. Recent developments in the conversion of lignocellulosic biomass have sparked an interest in the production of biofuels and valuable platform chemicals, synthesizing molecules such as alkylated furans, furanic ethers, and various lactones. Early studies indicate that many of these potential furanic and lactonic fuels have similar properties to gasoline or diesel, however, little is known about their pyrolytic and combustion behavior. In order to establish a molecular picture of the first thermal products formed from the pyrolysis and oxidation of furanic biofuels, a microtubular flow reactor was used to thermally decompose furan, 2-methoxyfuran, and select lactones. Dilute samples of these molecules were entrained in He or Ar and thermally cracked in a heated silicon carbide microreactor. Products, including radicals and metastables formed at early pyrolysis times (50-200 μs), were detected by 118.2 nm (10.487 eV) photoionization mass spectrometry (PIMS), tunable synchrotron vacuum ultraviolet PIMS and Ar matrix infrared spectroscopy. As most initiation rates need to be calculated because they are too difficult to measure, the experimental results presented in this thesis demonstrate progress towards validating these calculations, aiding in the development of accurate initiation chemistry for kinetic mechanisms. The published mechanism for pyrolysis of furan (C4H4 O), the parent compound of the more complicated furans described above, involves decomposition via a pair of carbenes. The product branching ratio of this reaction was measured over a range of temperatures and compared to predictions of three published furan kinetic mechanisms. A higher-energy radical channel that produces propargyl radical (HCCCH 2) and H-atom was also detected and quantified. The unimolecular and low-pressure bimolecular decomposition mechanisms of the simplest furanic ether, 2-methoxyfuran, were also studied. Recent electronic structure calculations indicate this substituted furan has an unusually weak O-CH3 bond, which results in bond scission and the production of CH3 and 2-furanyloxy radicals. The final products detected from the ring opening of 2-furanyloxy radical include 2 CO, HCCH and H. Secondary products resulting from H or CH3 addition to the parent and radical reactions with 2-furanyloxy were also detected and include CH2=CH-CHO, CH3-CH=CH-CHO, CH3-CO-CH=CH2 and furanones. In addition to detection and quantification of the primary pyrolysis products, this work also includes the first experimental characterization of 2-furanyloxy radical by the assignment of several vibrational bands in an Ar matrix and a low-resolution estimate of the ionization threshold of this allylic lactone. Finally, the pyrolysis products of the lactones 2(5H)-furanone, 2(3H)-furanone and α-angelica lactone (5-methyl-2(3H)-furanone) were identified by 118.2 nm PIMS and Ar matrix IR spectroscopy as these species were also shown to be relevant to the decomposition of 2-methoxyfuran. Furans and lactones are among a variety of molecules derived from non-edible biomass that offer a renewable path to biofuels. Since the pyrolytic behavior of these oxygenated fuels are not well-known this work contributes to the field by identifying the first thermal products, helping to elucidate possible chemical mechanisms for emission formation from these biofuels.
  • [学位] Development and applications in computational chemistry for inorganic catalysis
    摘要:A robust metadata database called the Collaborative Chemistry Database Tool (CCDBT) for massive amounts of computational chemistry raw data has been designed and implemented. It performs data synchronization and simultaneously extracts the meta data. The indexed meta data can be used for data analysis and data mining. A novel tree growth – hybrid genetic algorithm (TG-HGA) was developed to search the global minimum of small clusters. In the TG algorithm, the clusters grow from a small seed to the size of interest stepwise. New atoms are added to the smaller cluster from the previous step, by analogy to new leaves grown by a tree. The initial structures for the search for the global minimum of TiO2 nanoclusters were generated by TG-HGA, and new low energy structures that have not been previously reported were found. Low energy isomers of Agn, n = 2 – 99, were studied at different computational level depending on the size of Agn. The geometries of Agn, n = 2 – 8, were optimized using density functional theory (DFT), and the energies were calculated at the CCSD(T)/CBS level. The Agn, n = 9 – 20, were initially generated by the TG-HGA builder with an EAM potential, and optimized using the DFT method. The relative energies and normalized atomization energies for the optimized structures were calculated at the CCSD(T) level with a small basis set. For larger Agn, 20 < n < 100, the low energy structures were generated using TG-HGA with an EAM potential, and the energies were calculated at the DFT level with a small basis set. A range of DFT functionals were benchmarked with the normalized atomization energies at the CCSD(T) level for the small Agn clusters. PW91 and &ohgr;-B97XD provided best results for predicting the normalized atomization energies. The normalized atomization energies for Agn start to converge slowly to the bulk at n = 55. At n = 99, the normalized atomization energy is predicted to be ~50 kcal/mol. The low energy isomers of the Irn(CO)m complexes (n=1, 2, 3, 4, and 6) were investigated using electronic structure methods at the density functional theory and coupled cluster (CCSD(T) theory levels. Ir4(CO)12 is predicted to be the most favored complex for reactions of Irn(CO)m with CO at low temperature, and Ir6(CO)16 is predicted to be formed above room temperature. Smaller Irn(CO)m clusters will nucleate to form Ir 4(CO)12 spontaneously. Low-lying structures of the small iridum clusters Irn (n = 2 – 8) were optimized using DFT methods. Ir2 and Ir 3 were also optimized using the CASSCF method. MRCI-SD (for Ir 2) energies and CCSD(T) (for Ir2 and Ir3) energies of the leading configurations from the CASSCF calculations were done to predict the low-lying states. The normalized atomization energies for Irn (n = 2 - 8) were calculated at the CCSD(T) level up to the complete basis set (CBS) limit in some cases using the B3LYP optimized geometries. Inclusion of the spin orbit corrections in the normalized atomization energies for Ir n is critical and will decrease the normalized atomization energies by ~ 15 kcal/mol for n ≥ 4. Several molecular models were used to characterize various binding sites of the metal complexes in the zeolites. The calculated structures and energies indicate a metal–oxygen (M(I)–O) coordination number of two for most of the supported complexes but a value of three when the ligands include C2H5 or H. The results characterizing various isomers of supported metal complexes incorporating hydrocarbon ligands indicate that some carbene and carbyne ligands could form. A set of ligand bond dissociation energies is reported to explain reactivity trends. (Abstract shortened by UMI.)

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