Browsing by Author "Szulczewski, Gregory J."
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Item Applications of polyamidoamine dendrimers in polymer electrolyte membrane fuel cells(University of Alabama Libraries, 2009) Zhu, Huizhen; Thrasher, Joseph S.; University of Alabama TuscaloosaDendrimers are highly branched macromolecules with well-ordered three- dimensional architectures. Polyamidoamine (PAMAM), the most common class of dendrimers, have been widely studied due primarily to the following three features: 1) the interior amine and amide groups that can interact with ionic metal precursors through ligand exchange reactions; 2) the presence of an interior void space in the higher generation dendrimers; and 3) the exterior primary amine groups that permit further functionaliztion. These unique structural features have inspired many potential applications. This dissertation describes two applications of PAMAM dendrimers in polymer electrolyte membrane fuel cells (PEMFCs). First, in an effort to improve the utility of Pt in PEMFCs, PAMAM G4 was used as both a template and a stabilizer to synthesize dendrimer encapsulated Pt nanoparticles (Pt DENs) by photoreduction. These nanoparticles are highly monodisperse, exhibit high specific activity for the oxygen reduction reaction, and are inert to methanol oxidation, showing great potential for application in PEMFCs. Then, a simplified membrane electrode assembly (MEA) has been fabricated by the electrostatic self-assembly between Nafion® and Pt DENs and characterized. Two methods were proposed to increase Pt loading: layer-by-layer self-assembly and immobilization of Pt DENs and carbon powder on carbon fibers. Approximately 80 layers were proposed to reach the required loading using a dipping machine. Immobilization of Pt DENs and carbon powder simultaneously on carbon fibers can easily be achieved by electrochemical coupling, which is promising for replacing the conventional method of electrode fabrication. Secondly, in order to reduce the methanol crossover in direct methanol fuel cells (DMFCs), PAMAM G0 doped Nafion® membranes were prepared. Direct TEM imaging of the Naifon® embedded with nanoparticles demonstrates that PAMAM G0 can penetrate into the bulk of Nafion® through cluster channels to re-organize the distribution of sulfonate clusters by interacting with the sulfonic acid groups in different clusters. The presence of PAMAM G0 in the Nafion® membrane causes reduction of both methanol permeability and proton conductivity, but a very beneficial trade off can be reached when a doping concentration of 10⁻⁴ M PAMAM G0 is used. The fuel cell performance is much improved When Nafion® was treated with 10⁻⁴ M PAMAM G0.Item Borafluorenes and polyborafluorenes boron doped varients of fluorene(University of Alabama Libraries, 2017) Adams, Ian; Rupar, Paul A.; University of Alabama TuscaloosaA series of novel boron containing variants of fluorene were synthesized. Boron was incorporated synthetically via lithium halogen exchange and Grignard reaction pathways. Once incorporated, the borafluorene could be polymerized or undergo further functionalization via Yamamoto and Stille coupling reactions. This incorporation of boron into a conjugated system imparted Lewis acidic and electron deficient properties into a conjugated system. It is our hope that this will dope fluorene and create novel n-type semiconductors. A novel polymer of borafluorene, poly(9-borafluorene) (P9BF) was synthesized. HOMO and LUMO levels of P9BF were estimated by cyclic voltammetry. As predicted in prior DFT studies, P9BF has a reduced band gap and a lower lying LUMO compared with polyfluorene. To examine how the HOMO and LUMO levels of borafluorene systems could be tuned, copolymers of 9-borafluorene were synthesized. Four of the copolymers were a series of donor-acceptor (DA) type copolymers. A borafluorene-fluorene (P9BF-OF) copolymer and borafluorene-diketopyrrolopyrrole (P9BF-DPP), as an acceptor-acceptor (AA) copolymer were also synthesized. The series of DA copolymers showed higher energy HOMO and LUMO levels in correlation with the relative donating ability of the donor monomer. P9BF-OF has a reduced LUMO level in comparison with P9BF. P9BF-DPP has a very low band gap (1.8eV), with absorption well into the near-IR region. To examine ways to make borafluorene more air stable, a series of borafluorenes bearing bismethylmethoxyphenyl (BMMP) ligands were investigated. Interestingly, ii bismethylmethoxyphenyl-borafluorene (BMMP-BF) exhibits an exceptionally large Stokes shift of 16000 cm-1. To extend the conjugation and change the Stokes shift, thiophene containing derivatives BMMP-BF-T, BMMP-BF-2T, and BMMP-BF-3T were synthesized. These thiophene containing compounds exhibited anomalous two wavelength fluorescence. During our fluoride titration experiments, we noticed spectral impurities when using tetrabutylammonium fluoride (TBAF) as our fluoride source. Examining this more closely, we found that commercial samples of TBAF were found to absorb light at 295 and 370 nm and fluoresce as 435 nm. This was not expected for analytically pure TBAF, so we concluded that there must be an impurity present in commercial TBAF. The source of this impurity was found to be I3- which occurs from the oxidation of I-.Item Characterization of bismuth telluride two-dimensional nanosheets for thermoelectric applications(University of Alabama Libraries, 2015) Guo, Lingling; Wang, Hung-Ta; University of Alabama TuscaloosaSolid-state thermoelectric devices are compact, scalable, quiet, and environmentally friendly, which are widely used as thermal engines or refrigerators. Bismuth telluride (Bi2Te3) and other V-VI group chalcogenides are known as one of the best thermoelectric materials specifically for applications in a temperature environment from room temperature to 300 ℃. Recently, the unique topological surface states were discovered in Bi2Te3 family materials, and these novel surface states are arisen from a strong spin-orbit coupling in topological insulators. Topological surface states are protected against time-reversal perturbations (i.e., non-magnetic impurities or surface defects), making the electronic transport essentially dissipation-less. Such unique transport behavior with zero energy loss provides new opportunities to enhance thermoelectric properties. Although the promise in thermoelectric properties of topological insulators have been shown in theoretical reports, there is a lack of experimental investigations for a better understanding of their basic properties. This research work focuses on the characterizations of fundamental properties of Bi2Te3 two-dimensional (2D) nanosheets. Samples were prepared via respective solvothermal synthesis and van der Waals epitaxy. The charged surface properties of Bi2Te3 2D nanosheets were investigated using kelvin probe force microscopy. The measured electrical potential difference between aminosilane self-assembled monolayer and Bi2Te3 nanosheet surfaces is found to be ∼650 mV, which is larger than that (∼400 mV) between the silicon oxide substrate and Bi2Te3 nanosheet surface. The elastic properties of Bi2Te3 2D nanosheets (i.e., Young’s modulus and prestress) were acquired by analyzing the thickness dependence of 2D nanosheet deformations creating by atomic force microscopy tips. The Young's modulus by fitting linear elastic behaviors of 26 samples is found only 11.7–25.7 GPa, significantly smaller than the bulk in-plane Young's modulus (50–55 GPa). Furthermore, the thermoelectric properties of Bi2Te3 2D nanosheets were characterized in the cryostat system at a temperature range of 20-400 K. The results reveal that electrical conductivity of 2D nanosheets decreases with increasing temperature and thickness, while the measured Seebeck coefficient does not show a strong thickness dependence and the value is smaller than bulk Bi2Te3. These fundamental properties would help improve the basic understanding of topological surface states towards practical applications.Item Computational studies of transition metal catalysts(University of Alabama Libraries, 2010) Craciun, Raluca; Dixon, David A.; University of Alabama TuscaloosaHigh level electronic structure calculations were used to evaluate reliable, self-consistent thermochemical data sets for the second and third row transition metal hexafluorides, as well as for metal phosphines (M=Ni, Pd, Pt). For the transition metal hexafluorides, the electron affinities, heats of formation, first (MF₆ → MF₅ + F) and average M-F bond dissociation energies, and fluoride affinities of MF₆ (MF₆ + F⁻ → MF₇⁻) and MF₅ (MF₅ + F⁻ → MF₆⁻) were calculated. For the transition metal phosphines, the first metal-phosphine binding energy in MPH₃, M(PH₃)₂, MPH₃Cl₂ and M(PH₃)₂Cl₂ was calculated. The electron affinities, which are a direct measure for the oxidizer strength, increase monotonically in the second and third row series, from WF₆ to AuF₆, and from MoF₆ to AgF₆. The hexafluorides of the last two elements of each series, Pt, Au in the third row and Pd and Ag in the second, form extremely powerful oxidizers. The inclusion of spin orbit corrections is necessary to obtain the correct qualitative order for the electron affinities. The calculated electron affinities increase with increasing atomic number, are in good agreement with the available experimental values and, for the third row are: WF₆ (3.15 eV), ReF₆ (4.58 eV), OsF₆ (5.92 eV), IrF₆ (5.99 eV), PtF₆ (7.09 eV), and AuF₆ (8.20 eV). The electron affinities of the second row hexafluorides are even larger than for the second row: MoF₆ (4.23 eV), TcF₆ (5.89 eV), RuF₆ (7.01 eV), RhF₆ (6.80 eV), PdF₆ (7.95 eV), AgF₆ (8.89 eV). A wide range of density functional theory exchange-correlation functionals were also evaluated and only three gave satisfactory results as compared to the higher level electronic structure calculations. The corresponding pentafluorides are extremely strong Lewis acids. The optimized geometries of the corresponding MF₇⁻ anions show classical structures with M-F bonds for W through Ir and for Mo, Tc and Rh; however, for PtF₇⁻, AuF₇⁻, RuF₇⁻, PdF₇⁻, and AgF₇⁻ nonclassical anions were found with a very weak external F-F bond between an MF₆⁻ fragment and a fluorine atom. These anions are text book examples for "superhalogens" and can serve as F atom sources under very mild conditions.Item The computational studies on the chemistry of titanium dioxide nanoparticles(University of Alabama Libraries, 2010) Wang, Tsang-Hsiu; Dixon, David A.; University of Alabama TuscaloosaThe chemistry of TiO_2 and SiO_2 nanoclusters is studied using computational methods. The potential energy surfaces (PESs), thermochemistry of the intermediates, and the reaction paths for the initial steps of the hydrolysis of TiCl_4 were calculated. Transition state theory and RRKM unimolecular rate theory are used to predict the rate constants. Clustering energies and heats of formation are calculated for neutral clusters, and the calculated heats of formation were used to study condensation reactions. The reaction energy is substantially endothermic if more than 2 HCl are eliminated. The calculations show that the reported values for ΔH_f^0(TiOCl_2) should be remeasured. Transition metal oxides such as TiO_2 can be used as photocatalysts to control chemical transformations for energy production. An important applications for TiO_2 is its use to photochemically split water to produce H_2 and O_2. The PES for splitting water on the ground and first excited state surfaces of (TiO_2)_n (n=1-4) nanoparticles have been studied up through the coupled cluster CCSD(T)/complete basis set level. Water is readily split to form hydroxyl groups without the need for a photon. Experimental measurements of the photoconversion of ketones (C(O)RR') on the rutile TiO_2 (110) surface show that one can eliminate R or R'. The bond dissociation energies of R=CH_3 and a wide range of R' for the gem-diols CRR'(OH)_2 were calculated at the density functional theory (DFT) and G3(MP2) levels. The calculated bond dissociation energies are in excellent agreement with the experimental values. The calculations show that most of the photodissociation processes are under thermodynamic control except for R'=CF_3. X-ray photoelectron spectroscopy (XPS) and DFT electronic structure calculations were used to study the average formal oxidation state of silicon in fumed silica (CAB-O-SIL®). The results show that the average surface oxidation state of the silicon in fumed silica is predominantly +1 and suggest a notably less hydrophilic character for CAB-O-SIL® than the oxides of silicon with Si in the formal +3 and +4 oxidation states. Once the +3 oxidation state is formed, water on the silica surface facilitates the conversion of the Si^+3 to the Si^+4 oxidation state.Item Drug binding characterization of CYPs utilizing CW and pulsed EPR(University of Alabama Libraries, 2015) Cuce, Alex Andrew; Bowman, Michael K.; University of Alabama TuscaloosaElectron paramagnetic resonance (EPR) methods have been used to study drug and ligand interactions with a super family of monooxygenase enzymes known as Cytochrome P450 (CYP). We examined the active-site of four different isoforms of CYPs before and after the addition of drug using EPR. Two of the CYPs studied, CYP3A4 and CYP2C9, play a major role in drug metabolism and the other two, CYP51B1 and CYP125A1, are attractive as therapeutic targets for the pathogen Mycobacterium tuberculosis. EPR has shown to be a quick and highly resolved method, in comparison to current methods such as crystal structure analysis and UV/Vis optical difference spectroscopy, to study CYPs ferric heme active-site before and after drugs bind, which could be very valuable in drug design. Chapter 2 examines pulsed EPR methods for studying the active-site in CYPs. The explanation of practical aspects of experimentation along with data processing provides the EPR background for studying ferric heme-containing enzymes enabling a researcher to extract highly resolved active-site information. The experimental EPR methods described in Chapter 2 are the methods used in Chapter 3 and 4. Chapter 3 examines the resting state active-site of all four isoforms which is structurally described as a single water molecule bound to the distal position of the ferric heme. CW EPR spectroscopy of the isoforms all gave different g-values and MCD showed that water ligands bind at different strengths depending on the CYP isoform which sheds light on substrate specificity in each isoform. An attempt was made at predicting nIR MCD transitions with the EPR parameters but results were unclear. Chapter 4 studied CYP2C9 and CYP125A1 in complex with drugs that had the same binding mode but different optical difference spectra. We showed that the low-spin complex between a drug-metabolizing CYP2C9 variant in complex with a drug PPT retains the water ligand seen in the resting state. Hydrogens from the axial water ligand are observed by pulsed EPR spectroscopy for both drug-free and drug-bound species showing that the drug does not displace the water ligand seen in the resting state. An 15N-label incorporated into PPT is .444 nm from the heme iron indicating that PPT is in the active-site. CYP125A1 gave the same EPR signatures seen for CYP2C9 and PPT along with an X-ray crystal structure of CYP125A1 in complex with LP10 showing a water-bridged complex. The same binding mode was seen in both complexes but optical difference spectra of CYP2C9 and PPT resemble ‘classic’ type II behavior while those of CYP125A1 and LP10 have reverse type I behavior, again providing direct evidence that optical difference spectra are not reliable for characterization of drug binding mode.Item The effect of fluoride on the crystallinity and photoactivity of titania(University of Alabama Libraries, 2012) Brauer, Jonathan Isaac; Szulczewski, Gregory J.; University of Alabama TuscaloosaThis dissertation describes the synthesis and characterization of fluorinated N-doped TiO_2 nanoparticles under ambient conditions. Samples were synthesized by sol-gel methods that utilized the controlled hydrolysis of titanium(IV) tetra-isopropoxide in acidic solutions. Nitrogen doping was achieved by two different methods. In one scheme triethylamine (TEA) was added post-synthesis to the nanoparticle formation. In the other scheme, ammonium chloride (NH_4 Cl) was added during the acid catalyzed hydrolysis reaction. A freeze-drying process of the sol-gel was used to prevent aggregation during dehydration and was found to retain the high surface area of the powder. Post-synthesis the hydroxyl groups on the surface were exchanged with fluoride by stirring the powders in acidic solution of NaF. Using this synthetic approach the amount of nitrogen and fluoride could be independently controlled. The nanoparticles were characterized by numerous spectroscopic techniques including DRS, FTIR, Raman, and XPS. Vibrational spectroscopy shows that the particles contain significant amounts of organic impurities after doping with TEA. In contrast, particles synthesized with NH_4 Cl showed much less contamination. XPS analysis revealed that a single nitrogen species with a binding energy of 400.6 eV when using TEA as the N precursor. In contrast, when NH_4 Cl was used as the nitrogen precursor two nitrogen species were observed with binding energies at 402.6 and 401.2 eV. These latter peaks are assigned to interstitial nitrogen in the N^(1+) and N^0 oxidation states. The as-synthesized nanoparticles also show a significant differences in their optical properties. In general, the particles doped from TEA and NH_4 Cl were yellow and white, respectively, despite containing approximately the same amount of nitrogen (~5% with respect to Ti). The difference is attributed to a high fraction of oxygen-vacancies in the TEA doped nanoparticles. XRD and Raman measurements determined that the as-synthesized samples were amorphous, but could be converted to the anatase phase by two different methods. Thermal annealing was shown to convert the amorphous particles to the anatase polymorph. The presence of surface fluoride was found to significantly lower the temperature to observe the amorphous to anatase transition. In the second method, stirring the powders in acidic solutions of NaF at room temperature for 12-168 hours produced the anatase phase with an average crystallite size of 4 nm. It was found that the phase transition only occurs when the pH is below the point of zero charge of the particles. The photoactivity of the nitrogen and nitrogen / fluoride-doped particles was tested for their ability to degrade methylene blue (MB) with visible light (> 400 nm). In general the particles with a surface fluoride were more photoactive that those without. In addition, particles with nitrogen were more photoactive than pure TiO_2 . By analyzing the decomposition products with electrospray ionization mass spectrometry and UV-Vis spectroscopy, it was possible to elucidate a different decomposition pathway for the nitrogen-doped samples. When TEA was the dopant precursor, MB primarily decomposed by a ring-cleavage pathway using superoxide. In contrast, when NH_4 Cl was the dopant precursor, MB decomposed through demethylation pathway induced by hydroxyl radicals. The as-synthesized particles were found to be more photoactive those thermally annealed. The loss of photoactivity could be ascribed to two main factors: (1) loss of nitrogen and fluoride and (2) loss of surface area by sintering.Item Effects of transition metal cationization on peptide dissociation by mass spectrometry(University of Alabama Libraries, 2011) Watson, Heather Malone; Cassady, Carolyn J.; University of Alabama TuscaloosaPeptide sequencing is fundamental to understanding a protein's structure and function. The field of proteomics is dedicated to how these aspects relate to human health and disease. Unfortunately, the majority of peptides and proteins are not fully sequenced. In mass spectrometry, this is often due to spectral complications and incomplete fragmentation. There is a need to develop new sample preparation techniques or dissociation methods to increase sequence information. The dissociation of transition metal-cationized peptides by collision-induced dissociation (CID), electron-transfer dissociation (ETD), and electron-transfer collisionally activated dissociation (ETcaD) has been investigated in a quadrupole ion trap (QIT). The resulting mass spectra provide a wealth of information about the primary structures of the peptides. Using transition metal ions as cationizing reagents proves beneficial to peptide sequencing by CID and, in some cases, is better than the analysis of protonated species. For instance, spectra obtained from CID of singly and doubly charged Cu(II)-heptaalanine ions, [M + Cu - H]^+ and [M + Cu]^2, are complementary and together provide cleavage at every residue and no neutral losses. This contrasts with protonated heptaalanine, [M + H]^+, which results in fewer backbone cleavages by CID and does not allow sequencing of the first three residues. Multiply charged precursor ions are required in order to carry out ETD and ETcaD. This can be problematic for acidic or neutral peptides. This work demonstrates that addition of transition metals as a cationizing reagent allows peptides to be submitted to ETD and ETcaD that do not otherwise form multiply charged precursors. ETD spectra were less complex than those produced by CID. ETcaD increases backbone cleavages for all samples studied relative to ETD. In addition, complexes that result in very few cleavages by CID are cleaved at every residue when submitted to ETcaD. Evidence for macrocyclic metallated a- and b-ions is found in ETD and ETcaD spectra in the form of nonsequential product ions. The sequence (pEEEEGDD) of the peptide component of biologically derived low-molecular-weight chromium binding substance (LMWCr) is obtained as a result of extensive mass spectrometric studies. LMWCr is proposed to be involved in carbohydrate metabolism. The sequencing of the peptide component of LMWCr by MS represents a potentially significant milestone towards understanding the pharmacological role of chromium at a molecular level.Item Electrical characterization of large-area donor-acceptor molecular junctions(University of Alabama Libraries, 2016) Johnson, Marcus Shabazz; Metzger, R. M.; University of Alabama TuscaloosaThe electrical properties of five different donor – bridge – acceptor large-area monolayer molecular junctions show current rectification. Langmuir-Blodgett deposition onto thermally evaporated gold yielded four out of the five monolayers. The fifth system was as a monolayer formed by self-assembly onto template-stripped gold. Of the four Langmuir-Blodgett films studied, three had perylene bisimide as the common acceptor with the donors, pyrene, ferrocene, and tetramethyl-p-phenylenediamine. The fourth Langmuir-Blodgett film is an iron complex. The large extinction coefficient of the three perylene monolayer films make them visible on the water surface. They are also visible on all three substrates used for characterization. The self-assembled monolayer is a dimethoxybenzene donor bridged to a benzoquinone acceptor. X-ray photoelectron spectroscopy, atomic force microscopy, and ultra-violet – visible spectroscopy were the primary tools for surface characterization. The electrical characterization of the monolayer films showed a few things. Primarily the electrical work showed that large-area junctions give better results when a feedback current established contact. The perylene-based monolayers had similar current-voltage behavior, showing a Janus effect of the current enhancement. At low bias (V < ±1.5 V) more current passes at positive bias than at negative bias but switches to more current passing at negative bias than at positive bias at higher voltage (V > ±2.0 V). The largest bias that provided stable molecular junctions was 2.5 V. The rectification ratio increases with increasing donor strength. An additional feature is that the increasing donor strength leads to the formation of a charged state in the molecular junction. This charged state inhibits tunneling and all other mechanisms, resembling a coulomb blockade. The metal complex measured for electrical properties was only stable up to 1.0 V, but all of the molecular junctions have similar current-voltage behavior rectifying at positive bias.Item Electron transfer dissociation mass spectromerty studies of peptides(University of Alabama Libraries, 2014) Feng, Changgeng; Cassady, Carolyn J.; University of Alabama TuscaloosaElectron transfer dissociation (ETD) is an important tandem mass spectrometry technique in peptide and protein sequencing. In the past, ETD experiments have primarily involved basic peptides. A limitation of ETD is the requirement that analytes be at least doubly cationized by electrospray ionization (ESI). In this research, a method has been developed for enhancing protonation of acidic and neutral peptides. This has allowed doubly protonated ions, [M+2H]2+, to be produced from peptides without basic residues and has enabled their study by ETD. This dissertation includes the first extensive study of non-basic peptides by ETD. The effects of a basic residue on ETD were investigated using a series of heptapeptides with one lysine, histidine, or arginine residue. The spectra contain primarily c"- and z'-ions, which result from cleavage of N-C_α bonds along the backbone. Almost all of product ions include the basic residue. Enhanced fragmentation occurs on the C-terminal side of the basic residue. Also, cn-1 formation is enhanced, where n is the number of residues in the peptide. Addition of Cr(III) nitrate to a solution of the neutral peptide heptaalanine yields abundant [M+2H]2+ formation by ESI. Eleven metal ions were tested and Cr(III) gave by far the most intense supercharging of peptides. In contrast, Cr(III) does not increase protonation of proteins. Experiments were performed to explore the supercharging mechanism. Addition of Cr(III) to the sample solution was used to produce [M+2H]2+ in the remainder of this research. Neutral peptides with alkyl side chains were studied by ETD and found to produce b- and c-ions. Two mechanisms are proposed for b-ion formation, which involves cleavage of backbone amide (O=C)-N bonds. The length of peptide chain affects ETD fragmentation, but the identity of the alkyl residue has minimal effect. Acidic peptides with one or two aspartic or glutamic acid residues produce b-, c- and zOe-ions. The mechanism of b-ion formation is probably the same as that for neutral peptides, while c- and zOe-ions result from a radical mechanism involving oxygen atoms on the acidic side chains. For highly acidic heptapeptides, c- and zOe-ions are the major products, which supports a radical mechanism.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 Enhanced Protonation of Peptides Using Trivalent Chromium in Mass Spectrometry(University of Alabama Libraries, 2022) Dieke, Nnenna; Cassady, Carolyn J.; University of Alabama TuscaloosaIonization of peptides is an important step in mass spectrometry (MS)-based bottom-up proteomics. Electrospray ionization (ESI) is a common method of converting peptide ions into the gas phase. ESI is known to produce multiply protonated ions, [M + nH]n+. The addition of trivalent chromium, Cr(III), to peptide solutions undergoing ESI was discovered to increase the protonation of peptides. This dissertation contains fundamental studies of peptide ionization using trivalent chromium, Cr(III), as an additive.Experimental studies were completed to deduce the mechanism of Cr(III) enhanced protonation in ESI. Cr(III) enhances the protonation of model peptides with an acidic residue at the C-terminus to a greater extent than when the acidic residue is further away. The protonation of model peptide amides containing no carboxyl groups at the C-terminus or sidechain are enhanced by the addition of Cr(III). This indicates that carboxyl and amide groups are involved in the mechanism. Enhanced protonation with Cr(III) was ineffective with phosphorylated peptides and contributed to a pH effect in proteins.A survey of twenty-seven biological peptides was completed to gauge the analytical utility of Cr(III) in MS-based proteomics. Not all peptides underwent enhanced protonation by ESI upon addition of Cr(III), but Cr(III) did enhance the protonation of eleven peptides by adding an additional proton or increasing the signal intensity. Compared to model peptides, the interactions between sidechains of biological peptides are of higher complexity and can prevent the binding and/or dissociation of Cr(III) from the peptide.Different methods of delivering Cr(III) into the ESI source region were attempted to incorporate Cr(III) in MS-based proteomic workflows. Post-column addition of Cr(III) is possible using a tee union to introduce the Cr(III) solution or by doping the nebulizing gas with Cr(III). This signifies that Cr(III) does not have to be added to peptide solutions but can be introduced with the nebulizing gas during desolvation or as a separate solution into the ESI source bypassing chromatography. Dissociation of protonated ions formed by Cr(III) were also studied. The electron transfer dissociation (ETD) products of precursor ions generated upon addition of Cr(III) did not differ from those of precursor ions generated using 1% acetic acid. Higher charge states (n) generate better sequence coverage than [M + 2H]2+. Certain residues (i.e., proline, basic, and acid residues) direct fragmentation and the type of product ions produced in ETD. This residue effect is more prevalent with [M + 2H]2+ and subsides with higher charge states. Matrix-assisted laser desorption ionization (MALDI) is another method of ionizing peptides. Singly protonated ions, [M +H]+, are generally formed in MALDI. Additional protons are not expected to be added with Cr(III), but rather an increase in the intensity of [M + H]+. Although some promising results were obtained, the effect of Cr(III) as an additive in MALDI analysis of peptides was inconclusive due to poor reproducibility, which is common in MALDI.Item Fundamental and applied studies of organic photovoltaic systems(University of Alabama Libraries, 2014) Hill, Caleb M.; Pan, Shanlin; University of Alabama TuscaloosaPresented here are applied and fundamental studies of model organic photovoltaic (OPV) systems. Graphene oxide (GO) nanosheets were investigated as a potential electron acceptor in bulk heterojunction organic solar cells which employed poly[3-hexylthiophene] (P3HT) as an electron donor. GO nanosheets were transferred into organic solution through a surfactant-assisted phase transfer method. Electron transfer from P3HT to GO in solutions and thin films was established through fluorescence spectroscopy. Bulk heterojunction solar cells containing P3HT, P3HT-GO, and P3HT-phenyl-C61-butyric acid methyl ester (PCBM, a prototypical elector acceptor employed in polymer solar cells) were constructed and evaluated. Single molecule fluorescence spectroscopy was employed to study charge transfer between conjugated polymers and TiO2 at the single molecule level. The fluorescence of individual chains of the conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) at TiO2 surfaces was shown to exhibit increased intermittent (on/off "blinking") behavior compared to molecules on glass substrates. Single molecule fluorescence excitation anisotropy measurements showed the conformation of the polymer molecules did not differ appreciably between glass and TiO2 substrates. The similarities in molecular conformation suggest that the observed differences in blinking activity are due to charge transfer between MEH-PPV and TiO2, which provides additional pathways between states of high and low fluorescence quantum efficiency. The electrodeposition of individual Ag nanoparticles (NPs), which can be used to enhance light harvesting in organic photovoltaic systems, was studied in situ via dark field scattering (DFS) microscopy. The scattering at the surface of an indium tin oxide (ITO) working electrode was measured during a potential sweep. Utilizing Mie scattering theory and high resolution scanning electron microscopy (SEM), the scattering data were used to calculate current-potential curves depicting the electrodeposition of individual Ag NPs. The oxidation of individual presynthesized and electrodeposited Ag NPs was also investigated using fluorescence and DFS microscopies.Item Hemibiquinones: synthesis and computational validation of an asymmetric d—a biphenyl system(University of Alabama Libraries, 2016) Meany, Joseph E.; Woski, Stephen A.; University of Alabama TuscaloosaIn order to help determine the governing characteristics behind asymmetric current flow in molecules (molecular rectification), it is important to establish size limitations for the electron transfer processes which make rectification possible. Here I present the rational design and synthesis of a molecular template which has been tested for its rectification properties, alongside important derivatives. The molecule template in question, hemibiquinone (HBQ), is an asymmetric biphenyl derivative composed of a dimethoxybenzene ring covalently bonded to a benzoquinone (2,5-cyclohexadiene-1,4-dione) ring. It contains a 2-position group allowing the molecule to self-assemble. Early recognition that the molecule already possessed electroactive donor (dimethoxybenzene) and acceptor (benzoquinone) sections led the author to hypothesize that the torsion angle between the rings of biphenyl is orbital isolating enough to be the requisite tunneling barrier necessary for unimolecular rectification. Spectroscopic and electrochemical data are presented to validate predictions made by Density Functional Theory. A monolayer of the molecule sandwiched between gold is found to rectify with a forward/reverse current ratio approaching 200. This result demonstrates that larger, saturated carbon bridges are not necessary components in the design of a molecular diode. Any way of breaking conjugation in the system will suffice. Beyond establishing a lower limit for D-σ-A rectifiers, this work also lays the foundation to experimentally test how properties such as polarity, torsion angle, end group effects and HOMO-LUMO gap energy affect the rectification efficiency for a given structure. Future work will focus on the systematic change of functionality to the hemibiquinone motif, and relating the measured conduction and rectification ratio to one another.Item Iridium and Ruthenium Complexes of N-Heterocyclic Carbene- and Pyridinol-Derived Chelates as Catalysts for Aqueous Carbon Dioxide Hydrogenation and Formic Acid Dehydrogenation: The Role of the Alkali Metal(American Chemical Society, 2017) Siek, Sopheavy; Burks, Dalton B.; Gerlach, Deidra L.; Liang, Guangchao; Tesh, Jamie M.; Thompson, Courtney R.; Qu, Fengrui; Shankwitz, Jennifer E.; Vasquez, Robert M.; Chambers, Nicole; Szulczewski, Gregory J.; Grotjahn, Douglas B.; Webster, Charles Edwin; Papish, Elizabeth T.; University of Alabama Tuscaloosa; Mississippi State University; San Diego State UniversityHydrogenation reactions can be used to store energy in chemical bonds, and if these reactions are reversible, that energy can be released on demand. Some of the most effective transition metal catalysts for CO, hydrogenation have featured pyridin-2-ol-based ligands (e.g., 6,6 '-dihydroxybipyridine (6,6 '-dhbp)) for both their proton-responsive features and for metal-ligand bifunctional catalysis. We aimed to compare bidentate pyridin-2-ol based ligands with a new scaffold featuring an N-heterocyclic carbene (NHC) bound to pyridin-2-ol. Toward this aim, we have synthesized a series of [Cp*Ir(NHC-py(OR))Cl]OTf complexes where R = Bu-t (1), H (2), or Me (3). For comparison, we tested analogous bipyderived iridium complexes as catalysts, specifically [Cp*Ir(6,6 '-dxbp)Cl]OTf, where x = hydroxy (4(Ir)) or methoxy (5(Ir)); 4(Ir) was reported previously, but 5(Ir) is new. The analogous ruthenium complexes were also tested using [(eta(6)-cymene)Ru(6,6 '-dxbp)CljOTf, where x = hydroxy (4(Ru)) or methoxy (5(Ru)); 4(Ru) and 5(Ru) were both reported previously. All new complexes were fully characterized by spectroscopic and analytical methods and by single-crystal X-ray diffraction for 1, 2, 3, 5(Ir), and for two [Ag(NHC-py(OR))(2)]OTf complexes 6 (R = Bu-t) and 7 (R = Me). The aqueous catalytic studies of both CO2 hydrogenation and formic acid dehydrogenation were performed with catalysts 1-5. In general, NHC-py(OR) complexes 1-3 were modest precatalysts for both reactions. NHC complexes 1-3 all underwent transformations under basic CO2 hydrogenation conditions, and for 3, we trapped a product of its transformation, 3(sp), which we, characterized crystallographically. For CO2 hydrogenation with base and dxbp-based catalysts, we observed that x = hydroxy (4(Ir)) is 5-8 times more active than x = methoxy (5(Ir)). Notably, ruthenium complex 4(Ru) showed 95% of the activity of 4(Ir). For formic acid dehydrogenation, the trends were quite different with catalytic activity showing 4(Ir) >> 4(Ru) and 4(Ir) approximate to 5(Ir). Secondary coordination sphere effects are important under basic hydrogenation conditions where the OH groups of 6,6 '-dhbp are deprotonated and alkali metals can bind and help to activate CO2. Computational DFT studies have confirmed these trends and have been used to study the mechanisms of both CO2, hydrogenation and formic acid dehydrogenation.Item Magnetic, electrical and magnetotransport properties of Cr O_2 and V O_2-based thin films and heterostructures(University of Alabama Libraries, 2013) Zhang, Xueyu; Gupta, Arunava; University of Alabama TuscaloosaIn this dissertation, thin films of two promising rutile oxide materials (CrO2 and VO2) are studied. Additionally, magnetic tunnel junctions (MTJs) with these two materials as ferromagnetic (CrO2) and barrier layer(VO2) are fabricated and their properties are investigated. The CrO2 thin films are successfully grown on TiO2 (001) substrates by atmospheric pressure chemical vapor deposition (APCVD). Their structural and magnetic properties have been examined. The Stoner-Wohlfarth model is used to extract the distribution of the effective anisotropy field in the CrO2 (001) films for providing a better understanding of the out-of-plane magnetic behavior. The unexpected in-plane magnetic behavior is explained by the possible existence of stripe or vortex domain structures in the films. Besides CrO2, VO2 thin films and CrO2/VO2 heterostructures have been grown on TiO2 substrates of different orientations - (100), (110) and (001) - and their electrical and magnetic properties are studied. Finally, MTJs with CrO2 as the ferromagnetic electrode, heteroepitaxial VO2 as the barrier layer, and Co as the counter electrode are fabricated, and their transport and magnetic properties are investigated. The bias, temperature and barrier thickness dependence of the tunneling magnetoresistance (TMR) of these CrO2/VO2-based MTJs are presented. The Simmons and Brinkman models are used to estimate the barrier height of the tunneling device. In addition, the magnetic behavior of the MTJs at different temperatures is studied.Item Mass spectrometry studies of peptides cationized by trivalent metal ions(University of Alabama Libraries, 2018) Commodore-Botoklo, Juliette Joan; Cassady, Carolyn J.; University of Alabama TuscaloosaThe field of proteomics is dedicated to understanding how a protein’s structure and function relates to human health and disease. Peptide sequencing by mass spectrometry is important to the proteomics movement. Unfortunately, sequencing of many peptides and proteins, such as those with residues containing acidic and neutral side chains, can be difficult. Acidic side chains undergo facile deprotonation that make analysis challenging and can hinder formation of positive mode ions. New methods of sample preparation and dissociation techniques are needed to increase sequence information. This dissertation includes an extensive study of the effects on electron transfer dissociation (ETD) mass spectrometry of biological and model acidic non-phosphorylated and phosphorylated peptides adducted to trivalent lanthanide metal cations. Mass spectra contained herein provide abundant information about the primary structure of peptides. The ETD process requires multiply positively charged ions that can be difficult to obtain with acidic peptides. This work demonstrates that addition of trivalent lanthanide metal cations allows highly acidic peptides to be analyzed by ETD by forming multiply positively charged precursor ions by electrospray ionization (ESI). Using trivalent lanthanide cations as ionizing agents yields extensive sequence information for highly acidic peptides including definitive identification of phosphorylation sites. Peptides forming [M + Met + H]4+ and [M + Met]3+ generate full sequence coverage in many cases, but [M + Pr – H]2+ generates less sequence coverage. (Met is the trivalent metal cation.) The spectra contain primarily a mix of non-metallated and metal adducted c- and z- ions. All metallated product ions incorporate at least two acidic sites or a highly acidic phosphoresidue, which strongly suggests that the trivalent metal cation coordinates with residues that contain highly acidic side chains. All trivalent lanthanide cations are suitable for sequencing highly acidic peptides except europium and radioactive promethium. ETD spectra contain high signal-to-noise ratios making identification of product ions straightforward. Sequence coverage generally improves with increasing peptide chain length. Trivalent chromium enhances protonation of neutral peptides, which is important to ETD analysis. ESI conditions, particularly drying and nebulizing gas pressures are critical to formation of [M + 2H]2+ by neutral peptides.Item Mass Spectrometry Studies on the Dissociation of Metal-Adducted Oligosaccharides, Glycopeptides, and Fatty Acids(University of Alabama Libraries, 2024) Akor, Chioma Jane-Frances; Cassady, Carolyn J.; Szulczewski, Gregory J.Analyzing oligosaccharides, glycopeptides, and fatty acids poses a significant analytical challenge due to their structural complexity and diversity. Structural alterations in these biomolecules have direct implications for health and diseases, necessitating the development of analytical methods capable of providing comprehensive structural information. Mass spectrometry (MS) stands out as a leading technique for this purpose, although its efficacy is hindered by poor ionization and dissociation of these biomolecules. Consequently, derivatization is commonly employed to enhance ionization and dissociation efficiency.This dissertation focuses on exploring the use of in-source decay (ISD) and high-energy collision-induced dissociation (HE-CID) performed on a matrix-assisted laser desorption ionization (MALDI)/tandem time-of-flight (TOF-TOF) mass spectrometer to obtain complete structural information on underivatized oligosaccharides, glycopeptides, and fatty acids. Extensive experimentation with various MALDI matrices and metal cations led to the identification of optimal conditions for ionization and dissociation.Dissociation of the metal-adducted underivatized biomolecules by HE-CID generated extensive fragmentation and structural information not attainable through dissociation of the protonated biomolecule, or collision-induced dissociation (CID) performed on quadrupole-based mass spectrometers. The glycosidic bond cleavage, cross-ring cleavage, and internal cleavage ions generated by HE-CID of metal-adducted oligosaccharides and glycopeptides provided valuable information on sequence, linkage type, and monosaccharide ring content. Also, HE-CID of the structural isomeric tetrasaccharides studied produced distinct mass spectra and product ions necessary to distinguish between the isomers. In addition, HE-CID of metal-adducted unsaturated fatty acids facilitated the determination of double bond positions, distinguished double bond positional isomers, and cis/trans isomers. While ISD proved less useful for fatty acids and glycopeptides, ISD complemented HE-CID in providing structural information for metal-adducted oligosaccharides.Remarkably, derivatization of oligosaccharides through permethylation was unnecessary for obtaining good ionization and structural information. Metal ions, particularly lithium (Li+), significantly enhanced the ionization and structural characterization of oligosaccharides, glycopeptides, and fatty acids. The choice of metal ions influenced the type and intensity of product ions, with lithium (Li+) consistently producing the most structural information. Furthermore, trihydroxyacetophenone (THAP) emerged as the optimal MALDI matrix for ionization and HE-CID, 2,5-dihydroxybenzoic acid (DHB) for ISD and HE-CID of long-chain oligosaccharides, and 4-dimethylaminobenzaldehyde (DMABA) for ISD of tetrasaccharides and pentasaccharides.Item Metal organic frameworks as sorbents for volatile organic compounds(University of Alabama Libraries, 2021) Shankwitz, Jennifer Elizabeth; Szulczewski, Gregory J.; University of Alabama TuscaloosaMetal organic frameworks (MOFs) are a class of highly porous materials with large surface areas, large pore volumes, and chemical tunability. These features make MOFs desirable as sorbents for applications such as gas storage, gas separation, and gas sensing. In this work, MOF thin films of UiO-66-R, where R = -H, -NH2, and-NO2, were fabricated onto Au-coated Si wafers and Au-coated quartz crystal microbalance surfaces using a vapor-assisted conversion method. The films were then characterized by scanning electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, reflection absorbance infrared spectroscopy, and Raman spectroscopy. The spectroscopy reveals that the films of UiO-66-H, UiO-66-NH2, and UiO-66-NO2 are polycrystalline and 1 – 3 µm thick. The diffraction patterns reveal that the UiO-66-NO2 film potentially has the most missing linker defects. The UiO-66-R films grown on quartz microbalance crystals were activated by heating under high vacuum and exposed to a known pressure of benzene, toluene, ethyl benzene, and the xylene isomers (BTEX). The Henry’s constant, which describes the adsorption capacity for each MOF, was calculated from the mass change during the adsorption isotherm at 30°C, 25°C, and 20°C. The enthalpy of adsorption and entropy change was determined by plotting the logarithm of Henry’s constants versus the reciprocal of temperature. The results reveal the Henry’s constant for BTEX increased in the following order: UiO-66-H < UiO-66-NH2 < UiO-66-NO2. The results suggest that the functional groups on the organic linker and missing linkers influence adsorption behavior. The Henry’s constant of the films UiO-66-H were an order of magnitude smaller than those obtained for UiO-66-NH2 and UiO-66-NO2 films, largely due to the large pore size and lack of any functional group. The results suggest that UiO-66-NO2 films contain more missing linker defects than UiO-66-NH2 films. As a result, the heat of adsorption and entropy change for BTEX molecules in UiO-66-NH2 films is more negative than UiO-66-NO2. In contrast, due to a large pore size caused by the missing linkers, the adsorption capacity of UiO-66-NO2 films is larger than UiO-66-NH2 films.Item Metal oxide thin films by chemical vapor deposition for photocatalytic water splitting(University of Alabama Libraries, 2016) Panikar, Archana Sathyaseelan; Gupta, Arunava; University of Alabama TuscaloosaPhotoelectrochemical cells (PEC) are devices which convert solar energy into consumable chemical energy by splitting water into oxygen and hydrogen. Photocatalytic activity at a semiconductor oxide surface forms the backbone of the PEC and thus the quest for high activity oxide materials and improving the cells efficiency is a widely explored field of research. Metal oxide semiconductors with band gaps in the visible spectrum are actively sought as photocatalytic electrode materials. The major advantages are that oxides are nontoxic, stable, and inexpensive. However, their overall efficiency is usually limited by short carrier diffusion length due to structural defects, limited light absorptivity and sluggish kinetics at the interface. To overcome these limitations crystalline semiconductor oxides synthesized by high temperature techniques are desired. A direct liquid injection chemical vapor deposition technique has been employed to synthesize films of Fe2O3 (hematite) and BiVO4 (bismuth vanadate) for use as photocatalysts. The high temperature synthesis technique is optimized to obtain good quality crystalline smooth films on fluorine doped tin oxide substrates and their photoelectrochemical characteristics have been studied. It is observed that the interlayer oxide material used for growth of the Fe2O3 and BiVO4 has a significant role in their photoactivity.The interlayer oxide serves as an efficient electron transport layer and also influences the grain characteristics of the film. For hematite it is observed that a n-type metal oxide interlayer (e.g. Nb2O5 or TiO2) helps improve the photoactivity as compared to a p-type oxide (NiO). BiVO4 has a poor electron diffusion length, and a WO3 interlayer improves the photocurrent in BiVO4 films by improving the charge collection efficiency. The low absorption coefficient of hematite requires a dense electrode for greater light absorption; however, the electrode thickness is limited by the poor hole diffusion length (~4 nm). Plasmonic metal nanostructures of gold (Au), silver (Ag), and copper (Cu), which are known to concentrate and scatter broad range wavelengths of incident light, are promising for enhancing the light absorption cross-section of a semiconducting material. Gold nanoparticles embedded in hematite films have been synthesized. About three times higher light absorption and photocurrent enhancement are obtained. A thickness-dependent study of photoactivity indicates a greater enhancement of gold-embedded hematite thin films compared to thicker films due to reduced charge transport distance and optimal local field enhancement effect. The embedded structure also has the advantage of consistent performance and protection of plasmonic nanostructures from electrochemical corrosion, resulting in long cycles of operation.