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Using the Abraham Solvation Parameter Model to Predict Solute Transfer into Various Mono- and Multi-Functional Organic Solvents (open access)

Using the Abraham Solvation Parameter Model to Predict Solute Transfer into Various Mono- and Multi-Functional Organic Solvents

The Abraham Solvation Parameter Model (ASPM) is a linear, free-energy relationship that can be used to predict various solute properties based on solute-solvent interactions. The ASPM has been used to predict log (K or Cs,organic/Cs,gas) values, as well as log (P or Cs,organic/Cs,water) values for solute transfer into the following organic solvents: 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-isopropoxyethanol and 2-butoxyethanol. The derived log (K or Cs,organic/Cs,gas) correlations describe the experimental data to within 0.14 log units (or less). The derived log (P or Cs,organic/Cs,water) correlations describe the experimental data to within 0.16 log units (or less). The ASPM has also been used to predict the enthalpies of solvation of organic solutes dissolved in the following solvents: acetic acid, dimethyl carbonate, diethyl carbonate, 1-butanol, 1-pentanol, 1-hexanol. The derived enthalpy of solvation correlations, using the L solute descriptor, describe the experimental data to within 2.50 log units (or less). The derived enthalpy of solvation correlations, using the V solute descriptor, describe the experimental data to within 3.10 log units (or less). Validation analyses have been performed on several of the correlations; and, as long as the solute descriptors fall within the given ranges as reported, the original correlations show good predictive ability for determining …
Date: May 2018
Creator: Hart, Erin F
System: The UNT Digital Library
Computational Investigation of DNA Repair Enzymes: Determination and Characterization of Cancer Biomarkers and Structural Features (open access)

Computational Investigation of DNA Repair Enzymes: Determination and Characterization of Cancer Biomarkers and Structural Features

Genomic integrity is important for living cells' correct functioning and propagation. Deoxyribonucleic acid as a molecule is a subject to chemical reactions with agents that can come from environment as well as from internal metabolism processes. These reactions can induce damage to DNA and thus compromise the genetic information, and result in disease and death of an organism. To mitigate the damage to DNA, cells have evolved to have multiple DNA repair pathways. Presented here is a computational study of DNA repair genes. The structure of the Homo sapiens direct DNA repair gene ALKBH1 is predicted utilizing homology modeling methods and using AlkB and DBL proteins as templates. Analysis of the obtained structure and molecular dynamics simulations give insights into potentially functionally important residues of the protein. In particular, zinc finger domains are predicted, and lysines that could perform catalytic activities are investigated. Subsequent mutagenesis experiments revealed the effect of the residues predicted to form zinc fingers on activity of ALKBH1. Structure and dynamics of AlkD, a Bascillus cereus base excision DNA repair protein is also studied. This protein has been shown to bind DNA with large alkyl adducts and perform excision catalysis without base flipping which is characteristic to …
Date: May 2018
Creator: Silvestrov, Pavel
System: The UNT Digital Library
Utilizing Rapid Mass Spectrometry Techniques to Profile Illicit Drugs from Start to Finish (open access)

Utilizing Rapid Mass Spectrometry Techniques to Profile Illicit Drugs from Start to Finish

The increasingly complex world of illicit chemistry has created a need for rapid, selective means of determining the threat posed by new drugs as they are encountered by law enforcement personnel. To streamline this process, the entirety of the problem, from the production of illicit drugs all the way to the final analysis have been investigated. A series of N-alkylated phenethylamine analogues were synthesized in a shotgun method and subjected to direct-infusion analysis. A range of products were detected without the need for time-consuming purification steps, which was extended to novel pharmacological and receptor-binding assays where mass spectrometry is used as a detector. This direct-infusion technique was also applied to studies of methamphetamine and fentanyl production to preemptively determine improvements to common reaction conditions and explore the origins of common impurities. The ability to utilize these rapid techniques directly from the fume hood has also been critically reviewed to highlight gaps in current research and opportunities for improvement. When combined, these studies seek to provide a means for rapid, simplified analysis of illicit drugs to improve the quality of data and dramatically increase throughput.
Date: August 2018
Creator: McBride, Ethan
System: The UNT Digital Library
High-Energy, Long-Lived Charge-Separated States via Molecular Engineering of Triplet State Donor-Acceptor Systems (open access)

High-Energy, Long-Lived Charge-Separated States via Molecular Engineering of Triplet State Donor-Acceptor Systems

Molecular engineering of donor-acceptor dyads and multimodular systems to control the yield and lifetime of charge separation is one of the key goals of artificial photosynthesis for harvesting sustainably solar energy. The design of the donor-acceptor systems mimic a part of green plants and bacterial photosynthetic processes. The photochemical events in natural photosynthesis involve the capturing and funneling of solar energy by a group of well-organized chromophores referred to as an ‘antenna' system causing an electron transfer into the ‘reaction center,' where an electron transfer processes occur resulting a long-lived charge separated state. Over the last two to three decades, many efforts have been directed by the scientific community designing of multi-modular systems that are capable of capturing most of the useful sunlight and generating charge separated states of prolonged lifetimes with adequate amounts of energy. In this dissertation, we report on the design and synthesis of donor–acceptor conjugates with the goal of modulating the yield and lifetime of their charge separated states and hence, improving the conversion of light energy into chemical potential. In simple donor-acceptor systems, generally, the energy and electron transfer events originate from the singlet excited state of the donor or acceptor and can store the …
Date: August 2018
Creator: Obondi, Christopher O
System: The UNT Digital Library
Applications of Metallic Clusters and Nanoparticles via Soft Landing Ion Mobility, from Reduced to Ambient Pressures (open access)

Applications of Metallic Clusters and Nanoparticles via Soft Landing Ion Mobility, from Reduced to Ambient Pressures

Nanoparticles, simple yet groundbreaking objects have led to the discovery of invaluable information due to their physiological, chemical, and physical properties, have become a hot topic in various fields of study including but not limited to chemistry, biology, and physics. In the work presented here, demonstrations of various applications of chemical free nanoparticles are explored, from the determination of a non-invasive method for the study of the exposome via using soft-landing ion mobility (SLIM) deposited nanoparticles as a matrix-assisted laser desorption/ionization (MALDI-MS) matrix replacement, to the direct SLIM-exposure of nanoparticles onto living organisms. While there is plenty of published work in soft-landing at operating pressures of 1 Torr, the work presented here shows how this technology can be operated at the less common ambient pressure. The ease of construction of this instrument allows for various modifications to be performed for a wide array of applications, furthermore the flexibility in metallic sample, operating pressure, and deposition time only open doors to many other future applications. The work presented will also show that our ambient SLIM system is also able to be operated for toxicological studies, as the operation at ambient pressure opens the door to new applications where vacuum conditions are …
Date: August 2018
Creator: Aguilar Ayala, Roberto
System: The UNT Digital Library
Detection of Harmful Chemicals in the Air using Portable Membrane Inlet Mass Spectrometry (open access)

Detection of Harmful Chemicals in the Air using Portable Membrane Inlet Mass Spectrometry

Portable mass spectrometry has become an important analytical tool for chemical detection and identification outside of a lab setting. Many variations and applications have been developed to benefit various fields of science. Membrane inlet mass spectrometry is used to allow certain analytes to pass into the mass spectrometer without breaking vacuum or letting in large particulate matter. These two important analytical tools have been applied to the detection of harmful chemicals in the air. Earth-based separations and reverse gas stack modelling are useful mathematical tools that can be used to locate the source of a chemical release by back calculation. Earth-based separations studies the way different molecules will diffuse and separate through the air. Reverse gas stack modelling refers to the concentration differences of a chemical in relation to its distance from its source. These four analytical techniques can be combined to quickly and accurately locate various harmful chemical releases. The same system can be used for many applications and has been tested to detect harmful chemicals within and air-handling system. The monitoring of air-handling systems can greatly reduce the threat of harm to the building occupants by detecting hazardous chemicals and shutting off the air flow to minimize human …
Date: August 2018
Creator: Kretsch, Amanda Renee
System: The UNT Digital Library
Synthesis and Studies of AzaBODIPY Derived Donor-Acceptor Systems for Light Induced Charge Separation (open access)

Synthesis and Studies of AzaBODIPY Derived Donor-Acceptor Systems for Light Induced Charge Separation

The efficiency and mechanism of electron- and energy transfer events occurring in both in natural and synthetic donor-acceptor systems depend on their distance, relative orientation, and the nature of the surrounding media. Fundamental knowledge gained from model studies is key in building efficient energy harvesting and optoelectronic devices. Faster charge separation and slower charge recombination in donor-acceptor systems is often sought out. In our continued effort to build donor-acceptor systems using near-IR sensitizers, in the present study, we report ground and excited state charge transfer in newly synthesized, directly linked, tetrads featuring bisdonor (donor = phenothiazine and ferrocene), BF2-chelated azadipyrromethane (azaBODIPY) and C60 entities. The tetrads synthesized using multi-step synthetic procedure revealed strong charge transfer interactions in the ground state involving the donor and azaBODIPY entities. The near-IR emitting azaBODIPY acted as a photosensitizing electron acceptor along with fullerene while the phenothiazine and ferrocene entities acted as electron donors. The triads (bisdonor-azaBODIPY) and tetrads revealed ultrafast photoinduced charge separation leading to D•+-azaBODIPY•–-C60 and D•+-azaBODIPY-C60•– (D = phenothiazine or ferrocene) charge separated states from the femtosecond transient absorption spectral studies in both polar and nonpolar solvent media. The charge separated states populated the triplet excited state of azaBODIPY prior returning to …
Date: December 2018
Creator: Collini, Melissa A.
System: The UNT Digital Library
Computational Simulations of Cancer and Disease-Related Enzymatic Systems Using Molecular Dynamics and Combined Quantum Methods (open access)

Computational Simulations of Cancer and Disease-Related Enzymatic Systems Using Molecular Dynamics and Combined Quantum Methods

This work discusses applications of computational simulations to enzymatic systems with a particular focus on the effects of various small perturbations on cancer and disease-related systems. First, we cover the development of carbohydrate-based PET imaging ligands for Galectin-3, which is a protein overexpressed in pancreatic cancer tumors. We uncover several structural features for the ligands that can be used to improve their binding and efficacy. Second, we discuss the AlkB family of enzymes. AlkB is the E. coli DNA repair protein for alkylation damage, and has human homologues with slightly different functions and substrates. Each has a conserved active site with a catalytic iron and a coordinating His...His...Asp triad. We have applied molecular dynamics (MD) to investigate the effect of a novel single nucleotide polymorphism for AlkBH7, which is correlated with prostate cancer and has an unknown function. We show that the mutation leads to active site distortion, which has been confirmed by experiments. Thirdly, we investigate the unfolding of hen egg white lysozyme in 90% ethanol solution and low pH, to show the initial steps of unfolding from a native-like state to the disease-associated beta-sheet structure. We compare to mass spectrometry experiments and also show differing pathways based on …
Date: May 2018
Creator: Walker, Alice Rachel
System: The UNT Digital Library
Electrodeposition of Molybdenum-Based Coatings from Aqueous Alkaline Solutions for Enhanced Corrosion Resistance (open access)

Electrodeposition of Molybdenum-Based Coatings from Aqueous Alkaline Solutions for Enhanced Corrosion Resistance

Zn-Mo coatings are very promising environment friendly anticorrosive coatings as replacement materials for cadmium and chromium (VI) based conversion layers. Electrodeposition has become a favorable technique in fabricating coatings due to its low cost, ease of use, and overall experimental control of coating quality. Very little research so far has been done for the electrodeposition of Zn-Mo coatings under alkaline conditions. In this work, Zn and Zn-Mo coatings were electrochemically deposited on stainless steel from an aqueous alkaline citrate solution. An organic compound, vanillin, was added to the electrolyte as a leveling agent for improving interlayer adherence and corrosion resistance of Zn-Mo coatings. Ni-Mo alloys have been known to possess high tensile strength and excellent corrosion protection of steels, and MoTe2 layers have a potential for the application in anticorrosive coatings due to their hydrophobic properties. In this study, MoTe2-Ni-Mo coatings were deposited on stainless steel using both sputtering and electrodeposition methods. These coatings with high corrosion resistance and other desirable properties are in demand in the oil and gas industry since they can protect and thus extend the lifetime of the underlying materials when exposed to aggressive environments. The Zn-Mo and MoTe2-Ni-Mo coatings were evaluated for chemical composition and …
Date: May 2018
Creator: Zhou, Ting
System: The UNT Digital Library
Allowing Students to Have VOICES (Voluntary Options in Chemical Education Schedules) in General Chemistry I (open access)

Allowing Students to Have VOICES (Voluntary Options in Chemical Education Schedules) in General Chemistry I

The purpose of this investigation (a quasi-experimental design called a non-equivalent design group (NEDG)) was to determine if allowing students in a science majors general Chemistry I course the choice in establishing the due dates that their homework was due to the instructor would improve course averages. This study covered two semesters with a total of 288 students participating with n = 158 in the fall and n = 130 in the spring. The students self-selected the homework group, VOICES, that best fit his/her needs which included (1) the instructor's homework schedule, (2) a student-customized schedule or a schedule that followed the exam schedule, or (3) all homework due by the last class day prior to the final exam. Online homework was assigned and graded with individual assignment and homework average grades collected and analyzed. No statistically significant differences were found among the VOICES groups with respect to final course average. Other results of this study replicated findings in the literature; namely, that there is a higher correlation between mathematics skills and course success. Course averages of students who had completed Calculus I or higher were statistically significantly higher than students with less completed mathematics coursework in all VOICES groups. …
Date: December 2018
Creator: Ford, Robyn Lynn
System: The UNT Digital Library
Optoelectronically Active Metal-Inorganic Frameworks and Supramolecular Extended Solids (open access)

Optoelectronically Active Metal-Inorganic Frameworks and Supramolecular Extended Solids

Metal-organic frameworks (MOFs) have been intensely researched over the past 20 years. In this dissertation, metal-inorganic frameworks (MIFs), a new class of porous and nonporous materials using inorganic complexes as linkers, in lieu of traditional organic linkers in MOFs is reported. Besides novel MIF regimes, the previously described fluorous MOF "FMOF-1", is re-categorized herein as "F-MIF1". F-MIF-1 is comprised of [Ag4Tz6]2- (Tz = 3,5-bis-trifluoromethyl-1,2,4-triazolate) inorganic clusters connected by 3-coordinate Ag+ metal centers. Chapter 2 describes isosteric heat of adsorption studies of F-MIF1 for CO2 at near ambient temperatures, suggesting promise for carbon capture and storage. We then successfully exchanged some of these Ag(I) centers with Au(I) to form an isostructural Au/F-MIF1. Other, nonporous MIFs have been synthesized using Ag2Tz2 clusters with bridging diamine linkers 4,4'-bipyridine, pyrazine, and a Pt(II) complex containing two oppositely-situated non-coordinating pyridines. This strategy attained luminescent products better-positioned for photonic devices than porous materials due to greater exciton density. Chapter 3 overviews work using an entirely inorganic luminescent complex, [Pt2(P2O5)4]4- (a.k.a. "PtPOP") to form new carbon-free MIFs. PtPOP is highly luminescent in solution, but as a solid shows poor quantum yield (QY ~0.02) and poor stability under ambient conditions. By complexing PtPOP to various metals, we have …
Date: August 2018
Creator: Ivy, Joshua F.
System: The UNT Digital Library
Ultrafast Photoinduced Energy and Electron Transfer Studies in Closely Bound Molecular and Nanocarbon Donor-Acceptor Systems (open access)

Ultrafast Photoinduced Energy and Electron Transfer Studies in Closely Bound Molecular and Nanocarbon Donor-Acceptor Systems

As part of the study, photosynthetic system constructs based on BF2-chelated dipyrromethene (BODIPY), BF2-chelated azadipyrromethene (AzaBODIPY), porphyrin, phthalocyanine, oxasmaragdyrin, polythiophene, fullerene (C60), single-walled carbon nanotube and graphene are investigated. Antenna systems of BODIPY dyads and oligomers having BODIPY as an excitation energy donor connected to different acceptors including BODIPY, azaBODIPY, oxasmaragdyrin and aluminum porphyrin are studied. Different synthetic methodologies are used to afford donor-acceptor systems either directly linked with no spacer or with short spacers of varying length and orientation. The effect of donor orientation, donor optical gap as well as nature of donor-acceptor coupling on the donor-acceptor spectral overlap and hence the rate of excitation energy transfer is investigated. In all these systems, an ultrafast energy transfer followed by electron transfer is observed. In particular, in a directly connected BODIPY-azaBODIPY dyad an unusually ultrafast energy transfer (~ 150−200 f) via Förster mechanism is observed. The observation of energy transfer via Förster instead of Dexter mechanism in such closely coupled donor-acceptor systems shows the balance between spatial and electronic coupling achieved in the donor-acceptor system. Moreover, in donor-acceptor systems involving semiconducting 1D and 2D materials, covalently functionalized single-walled carbon nanotubes via charge stabilizing (TPA)3ZnP and noncovalently hybridized exfoliated graphene via …
Date: August 2018
Creator: Gobeze, Habtom Berhane
System: The UNT Digital Library
Teaching First-Semester General Chemistry Using 3D Video Games following an Atoms First Approach to Chemistry (open access)

Teaching First-Semester General Chemistry Using 3D Video Games following an Atoms First Approach to Chemistry

The unified learning model (ULM) focuses on students' engagement, motivation, prior knowledge, and working memory. This study employs the use of video games to assess students' learning through a 3D chemistry gaming environment. In this human-subjects research, students carried out missions and applied reasoning to solve problems appropriate for general chemistry content. For learning to occur, students must be engaged and motivated as stated in the ULM. Learning cannot necessarily be accomplished by experience alone, and critical thinking is required to turn the experience into learning. The interpretation of educational theory applied to video games and this proposed study are discussed. A moderately positive correlation was found between exam score and study time (playing the game). Essentially the more time spent playing the game or an online activity the higher the exam scores. There was an alpha level less than 0.05 (p < 0.05) between the experimental group and non-traditional group (no game or online activity). Supporting that there was a statistically significant difference between groups, the null hypothesis was accepted between the game and online activity. Furthermore, as stated under the ULM, engagement is necessary for optimal learning.
Date: August 2018
Creator: Jenkins, Dave A
System: The UNT Digital Library
Silver(I) and Copper(I) Complexes from Homoleptic to Heteroleptic:  Synthesis, Structure and Characterization (open access)

Silver(I) and Copper(I) Complexes from Homoleptic to Heteroleptic: Synthesis, Structure and Characterization

A plethora of novel scientific phenomena and practical applications, such as solid-state molecular solar cells and other optoelectronic devices for energy harvesting and lighting technologies, have catalyzed us to synthesize novel compounds with tunable properties. Synthetic routes, single crystal structures, and spectral and materials properties are described. Reactions of Ag(I) and Cu(I) precursors with various types of ligands -- including the azolates, diimines, and diiphosphines -- lead to the corresponding complexes in high yield. Varying the metal ions, ligands, synthetic methods, solvents, and/or stoichiometric ratio can change the properties including the molecular geometry or packing structure, reactivity, photophysical and photochemical properties, semiconducting behavior, and/or porosity of the functional coordination polymers obtained. For solar cells purposes, the absorption energy can be extended from the ultraviolet (UV) region, through the entire visible (Vis) region, onto a significant portion of the near-infrared (NIR) portion of the solar spectrum with high absorption coefficients due to the infinite conjugation of Cu(I) with diimine ligands. Twenty-eight crystal structures were obtained by conventional crystal growth methods from organic solvents, whereas their bulk product syntheses also included "green chemistry" approaches that precluded the use of hazardous organic solvents. The resulting products are characterized by powder x-ray diffraction (PXRD), …
Date: December 2018
Creator: Almotawa, Ruaa Mohammed
System: The UNT Digital Library