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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Biosynthesis of Arsenic by E. coli

callahan, marissa k 01 January 2007 (has links)
A method was developed for pre-concentration, speciation and determination of arsenic species (As(III), As(V), MMA and DMA) in various water samples by solid phase extraction flow injection hydride generation atomic absorption spectrometry (SPE-FI-HG-AAS). The packing materials used for SPE included strong cation-exchange and strong anion-exchange silica beads. The devised method was successfully applied to the quantification of arsenic species in the University of Massachusetts campus pond water. A new method was developed for the determination of methylation and reduction of arsenic species (As(III), As(V) and DMA) in Mueller-Hinton growth media by E. coli based on anion-exchange chromatography with post column hydride generation and inductively coupled plasma optical emission spectrometry (HPLC-HG-ICP-OES). The method was successfully applied to the determination of metabolism of arsenic by E. coli by analyzing the growth media and the cell extracts. The investigations suggested that E. coli did not methylate any of the arsenic species but simply reduced As(V) to As(III). The media created a “split peak” effect for DMA, resulting in shorter retention time for the majority of the bulk and longer retention time for the rest of the species. This effect is most likely due to the reaction of DMA with the protein present in the media, generating a positive complex, which resulted in the shifts in retention times. Although the presence of hydride generation help enhances the arsenic signal by almost 30 times, it also affects the intensities of each arsenic species differently, some, such as As(III), benefit from the reaction than others, such as As(V). The studies revealed that when measuring different arsenic species in the absence of hydride generation, the ICP-OES sensitivity is not the same for all. Results from t- and F-tests suggested that AsB, DMA and As(V) are statistically the same, whereas As(III) and MMA, which are statistically indistinguishable, are from a different distribution.


Vanderpuije, Benjamin P. K. N. Y 25 September 2007 (has links)
USE OF FUNCTIONALIZED GOLD NANOPARTICLES TO EFFICIENTLY EXTRACT AND CONCENTRATE PEPTIDES FOR MALDI-TOF-MS DETECTION MAY 2007 BENJAMIN PAPA KWESI NII YANKOS VANDERPUIJE, B.Sc, KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY, GHANA M.S., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Richard W. Vachet We have developed a straight forward method that uses monolayer protected clusters (MPCs) and mixed monolayer protected clusters (MMPCs) as selective extraction and concentration probes for peptides. After extraction with these nanoparticles (NPs), the peptides are analyzed by MALDI-TOF-MS to obtain their mass fingerprints. Application of the method to a test library of 146 tryptic peptides showed that cationic MPCs/MMPCs target negatively charged peptides while the anionic MPCs/MMPCs target positively charged peptides. The extraction with these NPs is also accompanied by high concentration factors such they can be used to extract and concentrate microcystin-LR at levels below the WHO guideline of 1μg/L.


Varma, Deepti January 2012 (has links)
Chemistry / Ph.D. / Inflammation is implicated in diseases such as hypertension and rheumatoid arthritis (RA). A mechanistic understanding of inflammatory processes as it relates to the disease state and injury needs to be developed. Specifically, the role and modulation of inflammation needs to be assessed, as well as the mechanism that produces arachidonic acid (AA) metabolites (eicosanoids). Eicosanoids are specific biomarkers of inflammation. Their biosynthesis from arachidonic acid can be catalyzed by either free radicals or enzymes such as lipoxygenases (LOX), cyclooxygenase-2 (COX-2) and cytochrome P450. Depending on the pathway or parent molecule, different distributions of eicosanoids are found. The oxidation of AA gives hydroxyeicosatetraenoic acids (HETEs), dihydroxyeicosatetraenoic acids (DHETEs), epoxyeicosatetraenoic acids (EETs), prostaglandins (PGs), isoprostanes (Isops) and thromboxanes (TXs). It is our hypothesis that AA metabolites will help in understanding the progression of inflammatory diseases. To confirm this hypothesis, analytical methods including HPLC-UV and LC-MS were developed. The developed and validated HPLC method was applied to study the effect of acute exercise on prostanoids in hypertensive African American subjects. It was our theory that urinary 6-keto PGF1&alpha and 11-dehydro TXB2 can be used to assess the role of exercise in hypertension. Moreover, we assume that 8-iso PGF2 levels can be used as an indicator to determine the relationship of oxidative stress and endothelial dysfunction in hypertension. The HPLC method involved separating urinary 8-iso PGF2, PGE2, PGD2, PGF2, 6-keto PGF1&alpha and 11-dehydro TXB2 on a SymmetryShield Rp18 column (250mm ¡Á 4.6mm) by an isocratic elution of 17 mM phosphoric acid and acetonitrile in the ratio of 65:35 and at a flow rate of 1.3 ml/min. The wavelength used for detection was 196 nm. Specificity was confirmed by LC-MS. The method was fully validated and was found to be having sufficient sensitivity (limit of quantification - 7.5 ng - 30 ng) for many biological matrices and applications. The accuracy and precision were within bioanalytical method validation limits (90.3 to 112.8 % and RSD < 10%, respectively) and the method was linear over three orders of magnitude. In addition, a HPLC-UV method for the simultaneous determination of urinary creatinine and prostanoids was also developed and validated as it is necessary to monitor creatinine levels in addition to biomarkers when the measurement is done in urine. The method was found to be linear over three orders of magnitude and is sensitive enough for the analysis of creatinine and prostanoids in urine. The advantage of this method was that one can determine the levels of these prostanoids normalized by urinary creatinine in a single analysis and in less than 17 min. The LC- ESI (electrospray ionization) MS method, on the other hand was used to determine the role of HETEs in the initiation, progression and resolution phases of inflammation in RA. It is our assumption that 12/15 HETE can be used as novel targets for the treatment of RA. The separation was performed on a C18 column using a gradient elution of 0.1% formic acid in water and 0.1% formic acid in acetonitrile. The flow rate was 1 ml/min and the run time was 75 mins. The method was found to be specific, sensitive and precise. This LCMS method was also used to develop a retention model for complex regioisomers. Quantitative structure- (chromatographic) retention relationship (QSRR) was used to develop a predictive retention model for fatty acid metabolites. Retention behaviors of the lipid biomarkers were characterized by application of QSRR analysis utilizing Austin Model 1 mode semi-empirical computations. The retention data of these fatty acids were obtained from an RP-HPLC method utilizing a Symmetry C18 column under gradient elution. Molecular descriptors that take into account the polarity; chemical reactivity and hydrophobicity of the analytes were calculated using the semi-empirical AM1 mode. It is our hypothesis that QSRR will give insight into molecular mechanism of separation of lipid biomarkers operating in a given chromatographic system and can predict retention of a new analyte and/or to identify unknown analytes. / Temple University--Theses

Novel Nanomaterials and Chromatographic System for Enhanced Separation and Characterization of Biomacromolecules and Nanoparticles

Wang, Yanhui January 2018 (has links)
No description available.


Bandegi, Sanaz January 2019 (has links)
Chemistry / Ph.D. / Lipophilic dye probes are widely used for labelling of cells, organelles, liposomes, viruses and lipoproteins. The lipophilic dye diffuses in the membrane and stains the cell and cells even tolerate the lipophilic dye in high concentration. The fluorescence of styryl dyes increases after insertion into the hydrophobic environment of the lipid membrane compared their fluorescence in the aqueous phase solution. The alkyl chains of the fluorescent styryl dye probe insert into membranes and are used to understand their biophysical properties and their behavior in lipid bilayers. The mechanism of incorporation of the dyes into cell membranes, or vesicle model systems, is not resolved. In this study we used a modified dialkylaminostyryl fluorescent lipid, 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (DiA), replacing the I- counterion with the Cl- anion to make DiA-Cl increase hydration of the polar head and to enable self-assembling in water and formation of vesicles. Vesicles composed of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine)/DiA, DPPC (1,2-dipalmitoyl-sn-glycero-3- phosphatidylcholine) /DiA, DSPC (1,2-distearoyl-sn-glycero-3- phosphatidylcholine) /DiA, DMPE (1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine)/DiA, DPPE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine)/DiA and DSPE (1,2-distearoyl-sn-glycero-3-phosphoethanolamine)/DiA have been prepared in mole ratios between 100/0 to 0/100, in order to investigate the effects of chain length and headgroup type on chain packing and phase separation in these mixed amphiphilic systems, using nanocalorimetry, dynamic light scattering and fluorescence data, as well as confocal laser scanning microscopy (CLSM) and cryo-transmission electron microscopy (Cryo-TEM). In addition, we report the self-assembly of DiA-Cl, to form H-aggregates of lipid bilayers in aqueous solution, beyond a critical vesicle concentration. Lipid bilayers can be fused onto silica nanoparticles (NPs) to form supported lipid bilayer (SLB)-NPs. (SLB)-NPs have a varous interdisciplinary applications from medicine to environmental fields and agriculture sciences. Here, the lipids on the nanoparticles were used for two applications. One was to adsorb polycyclic aromatic hydrocarbons (PAHs) from the environment and the other was as vehicles for foliar delivery of nutrients to plants. Silica SLB nanoparticles can increase the solubility of Benzo[a]Pyrene (BaP) in order to extract the BaP from soil for in situ biodegradation. Initial studies were begun on the effect of foliar application of silica SLBs nanoparticles on plants. The SLBs to be used were prepared using both 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and DiA, in order to determine whether the lipid increased the entry of the silica into the plant leaves and whether the lipids also entered. / Temple University--Theses

Detection of drugs of abuse within electronic cigarette liquids using gas chromatography-mass spectrometry and ultra fast liquid chromatography tandem mass spectrometry

Walsh, Erin 03 November 2015 (has links)
As electronic cigarettes become more prevalent in society, their use as a delivery mechanism for drugs of abuse has increased. Electronic cigarette liquids present a complex matrix due to the lack of regulation, and therefore standardization, in their manufacturing. Due to the lack of published data, development of new analytical methods to accommodate this complexity was deemed necessary. Gas chromatography-mass spectrometry (GC/MS) and liquid chromatography-tandem mass spectrometry (LC/MS/MS) methods were developed to identify the flavorants of the electronic cigarette liquids as well as identify and quantify nicotine and common drugs of abuse used with these devices. Seven drugs of abuse were investigated: methamphetamine, heroin, cocaine, fentanyl, JWH-081, JWH-018, and AM-2201. Electronic cigarette liquids from five manufacturers were sampled. From each manufacturer five "flavors" of liquids were chosen. Each liquid "flavor" was tested at the manufactures reported nicotine concentrations of 0 mg/mL, 12 mg/mL, and 24 mg/mL to give a total of 75 electronic cigarette liquid samples. Liquid-liquid extraction was performed on all samples prior to analysis by GC/MS and LC/MS/MS. Analysis was performed in replicates of five to identify the electronic cigarette liquid components as well as quantify nicotine and the four analytes of interest. For any electronic cigarette liquid labeled as containing 0 mg/mL of nicotine in which nicotine was identified, the sample was analyzed by GC/MS to quantify the nicotine level. These concentrations were compared to the naturally occurring levels of nicotine found in certain food products. Identification of the flavorants of the electronic cigarette liquids as well as the quantitation of nicotine and the four commonly abused drugs was accomplished using GC/MS and LC/MS/MS. Samples of e-liquids labeled by the manufacturer as containing 0 mg/mL of nicotine may contain detectable and quantifiable levels of nicotine. Quantitation of drugs of abuse may be affected by matrix components and was found to be dependent on both the specific e-liquid being used with the electronic cigarette as well as the analyte being investigated.

Pulse-Laser Infrared Photothermal Spectrometry of Condensed-Phase Aerosols Based on Photothermal Deflection Spectroscopy

Dada, Oluwatosin Olubunmi 01 December 2008 (has links)
The research reported in this dissertation is aimed at development of photothermal deflection detector that is consistent with constraints imposed by aerosols sampling and analysis. The main objectives of this project are: 1) the design and evaluation of initial apparatus prototypes and 2) a test of the prototype apparatus with surrogate substances using conventional mid-infrared gas lasers. Experimental evaluation of reduced size photothermal apparatus is first performed with gaseous samples. Analysis of trichlorofluoromethane (CFC-11) and ethanol vapors is performed with both conventional large apparatus and the prototype small apparatus. Comparison studies in terms of photothermal signal from both apparatuses are carried out to examine how apparatus downscaling affects photothermal signal. The main result indicates that the small apparatus performs about the same as the conventional laboratory-size apparatus. For better understanding of heat transport from aerosols collect on a flat substrate and its surrounding media, a numerical methodology based on finite element analysis is used to investigate the heat transfer between aerosol, substrate, and air. The numerical modeling is extended to prediction of photothermal signals from laser excited optical beam deflection due to temperature gradient inside the air above aerosols. The modeling results help to understand how aerosol properties such as size, shape, thermo-optical properties, and particles arrangement affect photothermal signal. The model is also used to investigate the influence of substrate properties on photothermal signal. A photothermal deflection apparatus is then used to examine the potential of mid-infrared photothermal spectroscopy for aerosol analysis. Laboratory-generated ammonium nitrate aerosols are deposited on germanium substrate by using Micro-Orifice Uniform Deposits Impactor (MOUDI). Photothermal spectroscopy, based on optical beam deflection (mirage effect), is used to analyze the collected aerosols. The measurements are carried out in terms of aerosol number concentration and aerosol mass concentration. Based on standard 30 minutes sampling time and 30 L/min flow rate, the limit of detection obtained for our instrument are 18 particles, equivalence of 0.2 μg m-3 mass concentrations for 3 μm particles diameter) for aerosol number concentration measurement and 0.65 μg m-3 for aerosol mass concentration measurement. Out of curiosity on whether standard materials could be used to calibrate a photothermal lens apparatus without having to make up liquid samples, it was thought that colored glass filters would serve as such standards. Photothermal lens measurements and finite element modeling are used to examine the physical changes taking place in optical filter glasses. Colored-glass and neutral density filters are found to have a strong positive temperature-dependent refractive index change.

Complex Mixtures: Identifying and Characterizing Secondary Organic Aerosols

Walhout, Emma Quinn 01 January 2019 (has links)
Complex organic mixtures in the environment can contain hundreds to thousands of different organic molecules, and their composition and reactivity can have important environmental implications. In addition to gases, the atmosphere is made of a variety of small liquids and solids called aerosols. These aerosols have large impacts on human health, climate, and atmospheric chemical reactions. Here, secondary organic aerosol (SOA) from the ozonolysis of α-pinene is characterized. The atmospheric lifetime of SOA is very uncertain, but recent laboratory and modeling studies have demonstrated that photolysis is potentially an important process for organic mass loss from aerosol particles.1-5 Photolysis modifies the molecular composition and properties of aerosols through photolytic cleaving and repartitioning of volatile products. Characterization of dry, irradiated SOA can provide insights into photolysis driven changes in absorption properties and chemical composition. These results illuminate aging mechanisms and chemical and physical properties of organic aerosols in order to improve atmospheric modeling and the understanding of atmospheric chemical reactions. However, the high chemical complexity and low atmospheric abundance presents a difficult analytical challenge. Milligrams, or more, of material may be needed for speciated spectroscopic analysis.6 This study used a suite of advanced analytical techniques, including a novel combination of action spectroscopy and mass spectrometry that provides more structural information on organic mixtures than mass spectrometry alone. This study also used tunable light from a free electron laser, infrared and UV/Vis absorption, and computational chemistry to characterize molecules in α-pinene SOA. In addition, complex organic mixtures are also found in particulate matter that has deposited onto Earth’s surface. The preliminary results of dew analysis, including a foundation method of analysis for future study, gives the first look at organic material deposited into dew water on natural surfaces. This offers insight into atmospheric organic deposition to better understand chemical transport, air quality, and carbon cycling in the atmosphere.

Interpretation of GC-MS data by reverse search and relative retention indices

Hein, Christopher 01 January 1981 (has links)
No description available.

Automated Data Acquisition for Analysis of Fly Ash by Graphite Furnace Atomic Absorption Spectrophotometry

Dowds, Eileen 01 January 1989 (has links)
No description available.

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