Theses and Dissertations - Department of Chemistry & Biochemistry
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Browsing Theses and Dissertations - Department of Chemistry & Biochemistry by Author "Bao, Yuping"
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Item Azobenzene and 2,3-dichloro-5,6-dicyanobenzoquinone donor-acceptor complexation and analysis of the magnetic anisotropy of the nitroso substituent in aromatic systems(University of Alabama Libraries, 2015) Reach, Savannah; Blackstock, Silas C.; University of Alabama TuscaloosaThe first part of this thesis describes the evaluation of a new electron donor-acceptor (DA) bond between azobenzene (AB) with the electron deficient quinone 2,3-dichloro-4,5-dicyanobenzoquinone (DDQ), the former acting as an electron-donor and the latter as an electron acceptor. A novel feature of AB is that it may exist in one of two interconvertable isomer forms, cis-AB (contracted structure) and trans-AB (extended structure). Since both of these isomers have different shapes and electronic properties, my research is designed to test the binding of the cis/trans AB isomers to DDQ in solution. Another goal is to grow cocrystals of the AB isomers with DDQ for imaging these molecular aggregates in the cocrystal state by X-ray diffraction analysis. AB/DDQ association in solution is observed optically for the trans-isomer as newly formed red complexes. Concentration of the red solutions results in trans-AB/DDQ cocrystals whose X-ray diffraction structure has been determined. Attempts to cocrystallize cis-AB/DDQ complexes have been attempted, so far without success. The second part of this thesis involves experimental and computational studies of nitrosobenzenes to evaluate the dramatic anisotropic magnetic shielding effects of the nitroso group on the NMR chemical shifts of nearby nuclei. The large magnetic anisotropy gives a ∆∂ of 3.5 ppm for the syn and anti ortho 1H NMR signals and a ∆∂ of 34 ppm for the syn and anti ortho 13C NMR signals. Fifty-six proton chemical shifts in 14 nitrosobenzene structures have been calculated using B3LYP density functional theory with several different basis sets and correlated with experimental values. In addition, forty-four proton chemical shifts from a series of simple aromatic structures lacking the nitroso group (e.g. styrene, benzaldehyde, benzonitrile, and anilines) have been added to the correlation for comparison. The best linear fit of the calculated shifts to experimental values for 1H-NMR is obtained for B3LYP/6-31G*, with an rms deviation of 0.074 ppm for 1H NMR. For 13C NMR, the best linear fit is for B3LYP/DZVP2//TZVP, with an rms deviation of 3.140 ppm. By modeling NMR shifts of nitrosobenzene, we aim to better understand the basis of the large magnetic anisotropy observed for the nitroso group.Item Electron-deficient heterofluorene conjugated polymers and small molecules(University of Alabama Libraries, 2018) Cassidy, Stephen Joel; Rupar, Paul A.; University of Alabama TuscaloosaA series of heterofluorene polymers, containing electron-deficient heteroatoms, were designed for investigation. Indium was first chosen for heteroatom substitution, due to the known Lewis acidity of Group-13 elements, and supermesityl (2,4,6-tri-tert-butylphenyl) was used as a protective substituent to reduce unwanted hydrolysis of indafluorene by sterically protecting the vacant p-orbitals of the indium heteroatom. An indafluorene small molecule was synthesized as a model system; however, 1H NMR analysis showed the compound demonstrated poor stability when exposed to air, so an indafluorene polymer based on this design was not pursued. A novel borafluorene was investigated, featuring an OCO pincer-type ligand as the protective substituent, which stabilizes the boron heteroatom through weak B-O dative bonds. A borafluorene small molecule (BMMP-BF) was synthesized as a model system, and demonstrated robust stability under ambient conditions. Surprisingly, BMMP-BF also exhibited an extraordinarily large Stokes shift, and the cause behind this intriguing optical behavior was investigated. The borafluorene was then functionalized as a monomer and incorporated into two copolymer systems in order to examine the effects that extended conjugation and comonomer electron affinity would have on the optoelectronic properties. Optical characterization showed that both copolymers had a change in their optical behavior, relative to BMMP-BF, as demonstrated by smaller Stokes shifts, and CV analysis revealed that both copolymers possessed low lying LUMOs and narrow optical bandgaps. It is our hope that this research will lead to the development of novel n-type semiconductors. A novel carbazole-based polymer was explored, featuring a cationic ammonium functional group incorporated in the conjugated polymer backbone. A quaternized carbazolium small molecule was synthesized through an intramolecular cyclization mechanism, and served as a model system. The small molecule was characterized by NMR and XRD, and exchange of the counter ion was effectively demonstrated. We intended to synthesize a carbazole polymer and characterize the polymer in a non-ionic state, then quaternize the monomer sub-units during a post-polymerization phase to achieve a carbazolium polyelectrolyte. However, the non-ionic polymer had poor solubility in common organic solvents, which restricted access to the desired polyelectrolyte, and several efforts to form a soluble polymer were ultimately unsuccessful.Item Enhancing energy harvesting and conversion efficiencies of heterogeneous photocatalysts for solar water splitting using surface plasmon resonance and cathodic reduction methods(University of Alabama Libraries, 2015) Wang, Jue; Pan, Shanlin; University of Alabama TuscaloosaThis dissertation presents surface enhanced photocatalytic characteristics of heterogeneous catalysts (e.g., α-Fe2O3 and CdS) for solar water splitting. The enhancement can be obtained by either incorporating plasmonic metallic nanostructures, such as Au nanorods (NRs), or cathodic reduction of catalytic materials. This dissertation also presents various electrochemical methods for large-scale synthesis of plasmonic structures (e.g., vertically aligned NRs) for surface enhanced photoelectrochemistry. Four major aspects of the dissertation are described briefly. First, surface-enhanced light absorption and photoelectrochemical characteristics of α-Fe2O3 thin film modified with Au NRs in a top configuration are studied. The photoelectrochemical reaction of the plasmon active substrates for water oxidation is performed and compared at various α-Fe2O3 thicknesses. The photocurrent increase in the surface plasmon region is attributed to the enhanced visible light absorption of α-Fe2O3 in the presence of Au NRs. Second, a template-free technique is invented for a facile fabrication of vertically standing metal NRs and nanowires (NWs). The growth mechanism of NRs and NWs is explored through investigating their morphological changes as the electrodeposition proceeds. Because of their large specific surface area, one direction alignment, stability, and wide tunability over the diameter, length, and coverage, these NRs and NWs will have broad applications in surface enhanced photoelectrochemical reaction and optical spectroscopy. Third, cathodic reduction methods are introduced and they are capable of improving the photoelectrochemical performance of α-Fe2O3 photoanode. The morphology and photoelectrochemical responses of α-Fe2O3 thin-film photoanode are presented before and after the cathodic reduction. The photocurrent of ~20 nm α-Fe2O3 thin film is enhanced by about 7 times after the cathodic reduction. The enhancement is attributed to the conductivity improvement. Finally, vertical-aligned Ag nanoplates and NWs are presented at the outlet of this dissertation. These nanostructures are electrochemically deposited on Indium Tin Oxide (ITO) substrates with the assistance of sacrificial templates such as anodic aluminum oxide (AAO) templates. Ag nanostructures obtained using this method have minimum contamination because no surfactant is adopted for the synthesis; therefore they are suitable for surface modifications for applications in surface-enhanced Raman scattering, surface-enhanced photocatalyst, and metal-enhanced fluorescence.Item Investigations Involving Proton/Hydrogen Transfer in Peptides Using Mass Spectrometry(University of Alabama Libraries, 2020) Jing, Xinyao; Cassady, Carolyn J.; University of Alabama TuscaloosaMass spectrometry (MS) has been an important technique to ionize and sequence peptides, which makes MS indispensable in the field of proteomics. This dissertation contains studies of peptide ionization and dissociation using different methods. Various types of peptides were ionized with electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALDI) and dissociated by collision-induced dissociation (CID) or electron transfer dissociation (ETD). Mass spectra presented in this dissertation provide abundant information about peptide ionization and peptide sequencing. The addition of trivalent chromium, Cr(III), complexes to peptide solutions can increase the intensity of doubly protonated peptides, [M + 2H]2+, by ESI. [Cr(H2O)6](NO3)3·3H2O and [Cr(THF)3]Cl3 work as reagents that provide the most abundant [M + 2H]2+, the greatest [M + 2H]2+ to [M + H]+ ratio, and the cleanest mass spectra. The requirement of the aqueous solution indicates that water is involved in the mechanism, and the effect of the ESI design suggests that this Cr(III)-induced effect occurs during the ESI desolvation process. Cr(III) complexes and iron oxide nanoparticles can not be used as MALDI matrices to analyze acidic peptides. Cr(III) complexes produce intense background ions, and no peptide ions were observed with any iron oxide nanoparticles due to adsorption interactions. In both positive and negative ion modes, high-energy CID produces greater sequence coverage and less abundant product ions containing neutral losses compared with low-energy and medium-energy CID. The formation of immonium ions and the side-chain fragmentation can indicate the presence of specific amino acid residues. High-energy CID from [M ? H]? provides complementary sequence information to results from [M + H]+. In addition, the absence of selective cleavage adjacent to proline from [M ? H]? is beneficial because y-ions from [M + H]+ commonly dominate the mass spectra. Selective cleavage adjacent to acidic residues and C-terminal residue exclusion occur in both ion modes. In ETD of doubly protonated ions, [M + 2H]2+, carboxylic acid groups from either the C-terminus or the side chains of acidic residues do not have a significant effect on sequence coverage of c- and z-ions. With permethylation (conversion of -COOH to -COOCH3), the zn//+ to zn/+ ratios increase only for peptides with basic residues at the C-terminus. Therefore, hydrogen bonding between a carboxylic acid group and a basic residue may interfere with zn//+ formation. The generation of y-ions may involve a CID-like mechanism and could be affected by deprotonation of either -COOH and -SH through zwitterion formation.Item A magnetically triggered, targeted therapeutic drug delivery system from polymer micelles(University of Alabama Libraries, 2014) Glover, Amanda Louise; Nikles, David E.; University of Alabama TuscaloosaCurrent chemotherapeutic treatment options rely on delivering high doses of toxic chemicals to a patient in the hopes that some of the drug will kill the cancer. This method of treatment leads to side effects ranging from hair loss to healthy cell mutation. To combat the potential for these side effects a method of delivery for therapeutics has been developed from polymer micelles housing the drug that specifically targets and binds to cancer cells. Not only can the cancer cells be targeted directly, thus reducing the detrimental side effects, but temporal control of therapeutic delivery can be achieved by a magnetically triggered mechanism. In the semi-crystalline core of the micelles, magnetic nanoparticles are housed with the therapeutic drug. Once an alternating current (ac) magnetic field is applied to the micelles, the magnetic particles heat, allowing the cores to melt, which allows the drug to diffuse from the cores of the micelles.Item Medusa particles: a magnetically triggered drug delivery system consisting of peg-pcl diblock polymer brushes bound to the surface of single crystal magnetite nanoparticles(University of Alabama Libraries, 2016) McCormick, Benjamin Joseph; Nikles, David E.; University of Alabama TuscaloosaCurrent cancer chemotherapy treatment involves intravenous administration of highly toxic drugs relying on the strategy that some of the chemotherapy agent will reach the site of cancer and effectively kill those cells. This method leads to mutation and damage of healthy cells, which can manifest into side effects including fatigue, alopecia, and death. To combat these side effects and to target cancer cells preferentially, we aimed to develop a drug delivery system in which chemotherapy agents, such as doxorubicin, are entrapped within a semi-crystalline polymer shell covalently attached to the surface of magnetic nanoparticles. Not only could these “medusa particles” be directed to specific sites of cancerous tissue using targeting ligands attached to an external polymer corona, but their release of drug could also be temporally controlled by a magnetically triggered thermal induction mechanism. Once the particles reach the sites of cancer, an external radio frequency alternating current magnetic field would be applied to heat the nanoparticles causing the polymer shell to melt and allowing the drug to diffuse out of the core. This mechanism could have extensive biomedical applications due to the wide variety of targeting ligands and drugs one could utilize in the drug delivery system. In this thesis, we have demonstrated synthesis of magnetite nanoparticles verified by the x-ray photoelectron spectroscopy in the Fe 2p binding energy region, and were determined to be 11 nm in diameter as seen by transmission electron microscopy. Doxorubicin was successfully loaded into medusa particles at about 2-3% by total weight on average. Magnetically triggered release of doxorubicin from medusa particles was demonstrated and monitored using UV-Vis spectroscopy, electrochemical methods including linear sweep and differential pulse voltammetry, and cell studies involving CHO-K1 cells.Item Redox auxiliary mediated catalysis of organic thermal reactions. Stilbene isomerization and Aza-claisen rearrangement(University of Alabama Libraries, 2018) Nwankwoala, Chinenyeze I.; Blackstock, Silas C.; University of Alabama TuscaloosaThis work focuses on the development of new general methods of reducing the activation barriers of organic thermal reactions using a diarylamino redox auxiliary (RA) group. Electron removal from the RA weakens bonds and/or changes the conformation of the appended structure to activate its chemical transformation. The electron transfer activation is catalytic, hence the name redox auxiliary catalysis (RAC). This work involves the development of RAC for two thermal organic reactions which normally require high temperatures: stilbene isomerization and the aza-Claisen rearrangement. The outcome is to enable these reactions at room temperature. Stilbenes may exist as cis and trans isomers, and photochemical switching between these forms allows for stilbenes use in molecular machines, light-controlled storage devices, and molecular switches including light responsive biological systems. The thermal cis to trans isomerization of stilbenes requires a large activation barrier of ∼46 kcal/mol, which corresponds to a half-life of ∼1012 years at 303 K. As a result, the thermal isomerization of cis-stilbene is negligible at room temperature. This barrier to isomerization can be dramatically reduced using RAC, thus yielding a photo electrochromic stilbene which is switched in one direction with photons and in the other direction with electron loss. The oxidized RA unit (RA.+) preferentially stabilize twist transition state, thereby reducing the isomerization barrier. Electron transfer between RA.+-trans-stilbene and RA-cis-stilbene completes a catalytic cycle. To date, we have synthesized eight different RA-stilbenes containing electron donating and withdrawing substituents. The RAC cis to trans stilbene isomerization rate enhancement is found to be ≥ 105. RA catalysis has also been investigated as a way to promote [3,3]-sigmatropic rearrangement of 1,5-hexadienes (Cope rearrangement) at room temperature. The parent Cope substrate has an activation barrier of ∼33.5 kcal/mol and requires temperatures above 200 ºC. Our RA-appended diene undergoes a facile [3,3]-sigmatropic rearrangement at room temperature upon a one electron oxidation of the RA to give predominantly an aza-Claisen product instead of the anticipated Cope product.Item Weak intermolecular interactions as binding probes and analytical tools(University of Alabama Libraries, 2018) White, Nicholas James; Bonizzoni, Marco; University of Alabama TuscaloosaOver the past several decades, polyelectrolytes have received a great deal of attention in supramolecular chemistry. Poly(amidoamine), or PAMAM, dendrimers are hyperbranched polyelectrolytes that can bind to small charged molecules through non-covalent interactions. These supramolecular structures are often involved in cooperative binding events to guest molecules in which they display enhanced affinity. This dissertation describes a series of studies aimed at gaining a deeper understanding of the fundamental intermolecular interactions involved in these binding events, and their relative importance. In order to accomplish this, this work introduces a series of small-molecule PAMAM analogues and focuses on using NMR spectroscopy to study their non-covalent interactions with carboxylates in deuterated methanol. In Chapter 2, the design and synthesis of these model molecules are discussed. Chapter 3 and Chapter 4 detail the NMR spectral changes that accompany proton transfer in deuterated methanol by the PAMAM analogues and carboxylates, respectively. Chapter 5 is focused on the observable non-covalent interactions between the protonated PAMAM analogues and carboxylates. The “intact” analogue formed the strongest binding interactions and induced the greatest change in carboxylate proton chemical shifts. The primary ammonium in the protonated PAMAM analogues was found to be the main driver of these interactions. These studies have provided a more complete understanding of the fundamental intermolecular interactions involved. Chapter 6 details a separate project based on a different family of fluorene-based conjugated polymers with analytical applications to the sensing of polycyclic aromatic hydrocarbons (PAHs). Through extensive benchtop titration studies, the fluorescence of these polymers was found to respond differentially to the presence of these hydrocarbons in organic solution. The decrease in fluorescence intensity was found to originate from a combination of static and dynamic quenching. An analytical array was constructed based on these polymers which was able to generate differential responses for each PAH analyte. Linear discriminant analysis (LDA) was successfully used to discriminate 16 PAHs (the infamous “EPA sixteen”) in solution. These studies provided insight into the interactions between these conjugated polymers and PAHs, and the polymer design features which lead to observable interactions with PAHs.