Theses
Permanent URI for this collectionhttps://hdl.handle.net/1969.6/1140
Browse
Browsing Theses by Author "Abdulla, Hussain"
Now showing 1 - 8 of 8
- Results Per Page
- Sort Options
Item Characterization of the dipeptide based micellar systems undecanoic alanine-alanine and undecanoic alanine-glycine(2018-12) Maldonado, Savanna; Billiot, Fereshteh; Billiot, Eugene; Abdulla, HussainSurfactant are surface-active-agents, meaning surfactants have the ability to lower surface tension. In this research, two dipeptide surfactants undecanoic alanine-alanine and undecanoic alanine-glycine were studied to better understand their micellar systems. Variations of pH, temperature, surfactant concentration, and counterion type were examined to determine what effect, if any, changing these variables would have on micelle formation and chiral recognition. The counter ions examined in this study were di-amine alkanes with a different number of methyl groups separating the amines. These counter ions are pH dependent and preliminary results have shown that pH effects the interaction of these counter ions with the amino acid polar head, and in turn effects the physical properties of the surfactants and their micellar behavior. Some of the properties examined include: the critical micelle concentration, Krafft temperature, enantiomeric separation of chiral compounds, hydrodynamic radius of the micelles as well as fraction bound of the surfactant and counterions to the micelles. These systems were studied using proton Nuclear Magnetic Resonance (NMR), Diffusion Order Spectroscopy (DOSY), Capillary Electrophoresis (CE) and a LabQuest 2 with attached conductivity and temperature probes. The results here provide a better insight on the behavior of these dipeptide micellar systems which will aid in future research.Item Chemistry at the glass transition: Fluorescence-detected proton transfer reactions(2019-05) Granfor, Keegan; Causgrove, Timothy P.; Larkin, Patrick; Abdulla, HussainMany liquids when cooled to cryogenic temperatures have the ability to take the form of a glassy substance; these are referred to as amorphous solids. As they are supercooled they do not form crystalline substances but rather an amorphous glass lacking in long-range structure. While the knowledge of these amorphous solids has been around for many years not much is known regarding the simplest physical and chemical processes that are allowed to occur within this glassy state. We introduce a new fluorescence-based temperature derivative spectroscopy methodology with the aim of discerning some of these physical and chemical attributes such as proton transfer in the glassy state. Proton transfer in a cryogenic sample is accomplished by exploiting the photolytic capabilities of o-nitrobenzaldehyde. When exposed to ultraviolet light, o-nitrobenzaldehyde is transformed to o-nitrosobenzoic acid which has a relatively large acid dissociation constant. Fluorescein, a simple fluorescent molecule, and o-nitrobenzaldehyde were dissolved in a glycerol/water mixture and cryogenically supercooled below the glass transition temperature. The sample was then exposed to ultraviolet light and measured fluorometrically for alterations in the spectra. This experiment was repeated at varying viscosities and with deuterated solvents for measuring isotopic effects. The spectra were fit to first-order rate kinetic Arrhenius style equations to determine the energy barriers associated with the proton transfer. Currently there is no documented use of temperature derivative spectroscopy using fluorometric based measurements to study dynamic processes and little if any information regarding simple chemical processes occurring within a supercooled glass sample. This research provides a more detailed picture of these processes as well as describe a new methodology for temperature derivative spectroscopic experimentsItem Development and use of a tissue-destruction method to extract microplastics in blue crabs (callinectes sapidus)(2018-05) Waddell, Elijah Nathaniel; Conkle, Jeremy; Abdulla, Hussain; Smee, LeePlastic materials are nearly ubiquitous throughout the marine environment and are often ingested by marine organisms. Assessing this contamination requires extraction and identification of consumed microplastics, which can be challenging due to their small size and the complexity of the tissues in which they accumulate. Existing methods often favor tissue destruction techniques that use corrosive chemicals to break down organismal tissue to assess microplastic contamination. However, extensive validation of these methods is required because the chemical interactions between the digestants and plastic polymers are not fully understood. For this study, the chemical compatibility between four digestants (hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), and hydrogen peroxide (H2O2)) and three polymers (low-density polyethylene (LDPE), polystyrene (PS), and nylon) was assessed. All three acids (HCl, HNO3, H2SO4) readily attacked nylon upon contact. Because of this, a microplastic recovery method involving low-temperature tissue destruction with 30% H2O2 as a digestant was developed. This method was then validated on blue crabs by spiking known quantities of green nylon fibers, clear nylon fibers, white polyvinyl chloride (PVC) fragments, blue polyethylene (PE) fragments, and black PS fragments into collected stomach tissue before processing them using the developed method. High recovery rates were achieved for PS, PE, and green nylon fibers (>95%) while clear nylon fibers (84%) and white PVC fragments (63%) yielded sub-optimal recoveries. Once validated, the developed method was then used to assess microplastic contamination in 39 blue crabs collected near Corpus Christi Bay, TX. From these blue crabs, 0.44 synthetic fragments/fibers per crab were recovered, with 25.6% of collected blue crabs observed to contain synthetic fragments and fibers within their stomach. The developed method provides a less destructive alternative for assessing microplastic contamination in marine organisms when compared to published acid-based methods. Additionally, this study provides initial evidence of microplastic contamination in blue crabs, with approximately 25% of sampled blue crabs found to have microplastics or synthetic fibers within their stomachs.Item Estuarine CO2 gas transfer kinetics (Corpus Christi Bay, Texas)(2019-05) Clark, Corrie; Hu, Xinping; Abdulla, Hussain; Felix, Joseph D.Carbon dioxide (CO2) flux across the air-water interface at a location (27.724˚N, 97.341˚W) in Corpus Christi Bay, a subtropical estuary in northwestern Gulf of Mexico, was studied over the course of five weeks from November 16th to December 13th, 2018. CO2 flux was measured using the eddy covariance technique. In addition, CO2 concentration in both the atmosphere and sea surface was obtained. Gas transfer velocities were then mathematically derived from combination of CO2 flux measurements and concentration differences. Gas transfer velocity was modeled as a function of wind speed. Corpus Christi Bay was found to be a net sink of CO2 from the atmosphere for the period of study. Average flux was -0.27 μmol m-2 s-1. Small differences in estuarine and atmospheric CO2 concentrations (<100 ppm) were observed during the study period. Due to limited temporal data coverage, it was not possible to make long-term statements about CO2 movement into and out of Corpus Christi Bay from this study. Gas transfer velocity was modeled as a function of wind speed (3.6 m s-1 < U10 < 12.5 m s−1), where k660 = 0.36U103 (R2 = 0.64). At wind speeds below 3.6 m s-1, wind-induced turbulence contributed only 15% to gas transfer as other factors e.g., surfactant contribution and tidal motion, played a dominant role. Overall gas velocity was high (with a mean k660 of 146 cm hr-1), with average values approximately 10 times those found in other estuarine studies. Bottom-driven turbulence caused by low water depth at the study site in addition to high average wind speeds may have caused the large gas transfer velocities.Item Orbitrap and IRMS petroleomics(2021-08) Xu, Derry; Coffin, Richard B.; Abdulla, Hussain; Prakash, JaiPetroleum compounds from crude oil are deceptively complex; aside from the wealth of hydrocarbon compounds, crude oil may also contain other heteroatom compounds, inorganic compounds, and metals. It has been theorized that crude oil contains more compounds than genes in the human genome. Current petroleomic methods, such as the use of stable isotopes (δ13C, δD) as tracers for identification in an environment, would become superannuated. Advancements in analytical techniques such as Orbitrap mass spectrometry allow for the characterization of samples at resolutions at higher resolving powers and mass accuracies than conventional methods. As an initial proof of concept, 13 unique oil samples were retrieved from different processing stages and drilling environments. After these samples were processed via liquid liquid extraction, they were analyzed using ultrahigh high-performance liquid chromatography (UPLC) coupled with Orbitrap Fusion mass spectrometer (OT-FTMS) by both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). I identified 19,000 compounds from the water extract fraction, most of these compounds detected in the water fraction are higher polarity heteroatom compounds than the hexane fraction. I identified a unique set of compounds (from 30 to 100s compounds) in each crude oil sample by applying volcano plot and principal component analyses. Identifying these unique compounds allows for the distinctive characterization of oil wells, spills, and processing methods. Our future goal is to apply these techniques to a wide variety of crude oil samples and form a global fuel library, using our research to protect oil companies (counterfeiting, spill responsibility) and the environment (complete spill cleanup, environmental interactions with crude oil).Item Quantification and transformation of water soluble organic nitrogen in a coastal urban airshed(2021-05) Apacible, Scilyn; Apacible, Scilyn; Felix, Joseph; Felix, Joseph; Coffin, Richard; Abdulla, Hussain; Coffin, Richard; Abdulla, HussainAtmospheric organic nitrogen (ON) is poorly quantified due to its complexity, measurement difficulty and historical consensus that it was less significant than inorganic nitrogen. Studies that have measured ON are not evenly spread across various environments or geographic regions further contributing to a general lack of knowledge about global atmospheric ON deposition and transformations. In this study, PM2.5 and PM10 samples were collected in an urban coastal airshed, Corpus Christi, TX, USA between November 2019, and October 2020. The organic and inorganic forms of nitrogen were analyzed and the factors controlling their concentrations were examined. The mean concentrations of water soluble organic nitrogen (WSON) in PM2.5 and PM10 were 0.081 ± 0.12 and 0.12 ± 0.11 µg m-3, respectively. The observed WSON concentrations were similar to those observed in remote and marine sites. The WSON concentrations showed significant correlation with NO3⁻ and NH4⁺ during spring season in PM10 indicating that marine source (e.g., sea salt) and biogenic emission are contributing factor for NO3⁻, while agricultural sources are contributing factor for NH4⁺. On average, ON contributed 15% and 10% to total nitrogen in PM2.5 and PM10 at the coastal urban airshed. The average annual dry deposition fluxes for PM2.5 NO3⁻, NH4⁺, and WSON were 0.217, 0.027, and 0.68 kg ha−1 y −1, respectively. The annual dry deposition fluxes for PM10 NO3⁻, NH4⁺, and WSON were 0.55, 0.031, and 2.48 kg ha−1 y −1. The EPA CASTNET network’s closet monitoring site reports annual dry N deposition flux of 3.67 kg ha−1 y −1 , but does not account for ON thus potentially overlooking ~40% of N deposition. Furthermore, the photochemical transformation of ON into IN was investigated and results from these experiments revealed alternating photoproduction and degradation of IN (NO3⁻, NH4⁺). These WSON photochemical transformation will contribute to the increase or decrease of nitrogen bioavailability after deposition in this coastal region. This study highlights the significance of the ON component of atmospheric deposition in this northern Gulf of Mexico region and the need to for ON inclusion when determining coastal N loading and N mitigation strategies.Item Quantifying the water-atmosphere flux of ammonia for the estuaries of the Texas coastal bend(2020-05) Dunegan, Warren; Felix, Joseph; Abdulla, Hussain; Hu, XingpingIn the United States urbanization and agricultural activities within coastal watersheds have greatly contributed to excessive nutrient loading in downstream waters. As a result, a gross majority of U.S. estuaries are now considered to be ecologically impaired. Nitrogen (N) is often a limiting nutrient to primary production in estuarine waters and as such, excessive contributions have been linked to eutrophication, hypoxic events, and the emergence of harmful algal blooms (HABs). Such indicators of nutrient pollution have occurred in the surface waters of the Texas Coastal Bend, a coastal region of southeastern Texas, USA that borders the northwest Gulf of Mexico. Within that region, hypoxic episodes in areas of Corpus Christi Bay and persistent HABs in Baffin Bay have both been observed. Ammonium (NH4+) is an inorganic N species that in great enough concentrations, can directly influence such conditions as it is immediately bioavailable to primary producers. Total ammonia (NHx) refers to the combined concentration of both NH4+ and its complementary gaseous compound, ammonia (NH3). In water, NHx is partitioned between NH4+ and NH3 by the chemical and physical conditions which are present there. Further, when such aqueous concentrations of NH3 are great enough and favorable water quality and meteorological conditions exist, NH3 may be emitted from surface waters into the lower atmosphere. This water-atmosphere exchange process is bidirectional, allowing for both NH3 emission to the atmosphere, and atmospheric NH3 invasion into surface waters. Due to the two-way nature of this process, the determination of net NH3 deposition in coastal regions must factor local surface water NH3 emissions as well as ambient air NH3 concentrations to produce accurate estimates. Quantifying water-atmosphere NH3 flux was the primary objective of this study, where ten sites throughout the Coastal Bend were observed regularly during regional and local campaigns of eight and twelve months, respectively. Surface water NH4+ concentrations, atmospheric NH3 concentrations and a collection of supporting surface water and meteorological parameters were obtained to determine resulting rates of water-atmosphere NH3 flux. Across the entire Coastal Bend, a NH3 flux of 2.52 ± 3.57 ng m-2 s-1 was calculated, denoting net NH3 emission during the period of September 2018 - April 2019. Specific to the Corpus Christi area, a similarly upward water-atmosphere NH3 flux of 2.54 ± 1.23 ng m-2 s-1 was determined for the period of May 2018 - April 2019. Seasonal trends in water-atmosphere NH3 flux were evident as generally the late summer and fall months featured NH3 emission events from surface waters while winter and early spring months saw the deposition of atmospheric NH3. Individual locations displayed characteristic water-atmosphere NH3 flux signatures, including a site at San Antonio Bay where it is believed that a host of conditions unique to that estuary resulted in NH3 emission in two months during which all nearby bays displayed deposition. Within the Corpus Christi area, the NH3 fluxes of Corpus Christi Bay, the Upper Laguna Madre and the nearshore Gulf of Mexico appear to have been influenced by a collection of factors including the wet deposition of NH4+, surface water inflow and transport, and the transfer of NH4+ enriched sediment pore water into the overlying water column. Additionally, water-atmosphere NH3 emission events from the Gulf of Mexico periodically coincided with deposition at the Upper Laguna Madre, indicating a potentially important transport pathway for NH3 between coastal marine waters and a neighboring coastal lagoon. Bulk water-atmosphere NH3 estimates derived from the Corpus Christi area fluxes revealed an annual magnitude of NH3 emission that amounted to more than 30% of an earlier quantification of total N deposition to area surface waters. As a potentially substantial contributor to local ambient air NH3 concentrations, the water-atmosphere flux of NH3 requires comprehensive quantification across varying estuary systems to help guide mitigation efforts if NH3 emissions in the U.S. are ever subject to regulations similar to those set forth in European countries.Item Synthetic biomimetic complexes of the oxygen evlolving complex of photosystem ii as water oxidation catalysts for energy applications(2020-05) Kayne, Michael; Prakash, Jai; Larkin, Patrick; Abdulla, HussainFossil fuels are the major source of greenhouse gasses. There is a global effort to find a replacement fuel. Renewable energy is a primary focus and already provides a substantial portion of energy demand. Among them is molecular hydrogen (H2). This is due to its combustion and fuel cell product being water as well as its use as energy storage. Further, H2 can be obtained in a green and renewable way through electrolysis of water. However, Clean H2 production is currently expensive, and catalysts are one solution to help bring the costs down. Development of catalysts for this purpose have the added benefit of elucidating complex redox reactions involved in photosynthesis and the formation of the O-O bond. Direct inspiration from nature has led to the development of proposed water oxidation catalysts. These are synthetic metal-ligand (organometallic) complexes attempting to mimic the structure and functionality of the oxygen evolving complex (OEC) found in photosystem II. The goal is to mimic this unique portion of photosynthesis. This is done by producing ligands capable of binding three to four metal atoms and testing each complexes’ ability to perform the redox reactions associated with splitting water into hydrogen and oxygen. Ligands are designed and produced that utilized terminal pyridine groups to chelate three or four metal atoms. These ligands are complexed with the manganese atom inspired by nature as well as the less expensive and more abundant iron atom. The iron complex is spectroscopically compared to that of the manganese. In the future these organometallic complexes will be reacted with calcium and oxidizing agents and undergo further spectroscopic, redox and electrochemical tests.