Browsing by Author "Szulczewski, Gregory"

Now showing 1 - 6 of 6
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    Controlled Synthesis and Characterization of Magnetic Chalcospinels Nanocrystals
    (University of Alabama Libraries, 2020) Akbari Afkhami, Farhad; Gupta, Arunava; University of Alabama Tuscaloosa
    Binary and ternary metal chalcogenides have become well-known materials among chemists, physicists, material scientists, and other researchers of the field, and they have attracted significant attention because of their novel chemical, magnetic, electronic, mechanical and optical properties. Among the metal chalcogenides, chromium-based chalcospinels ACr2X4 (A = Cu, Co, Fe, Cd, and Hg; X = S, Se, and Te) have gained significant attention because they are a notable class of magnetic materials such as semiconductors, magnetic metals, and insulators. In this work, a general overview of binary and ternary metal chalcogenides and their nanocrystals has been provided. We have also provided an overview of the wet-chemical colloidal methods as an important approach to size and shape-controlled synthesize of nanocrystals. We have also discussed the importance of metal doping reactions as a pathway to create previously unavailable multielemental materials for high-performance applications. In this set of studies, colloidal nanocrystals of chromium-based chalcospinels of CuCr2S4 and CuCr2Se4 have been synthesized via hot-injection and heat-up methods and were characterized using experimental methodology comprised of different microstructural and structural tests. The magnetic properties of these nanocrystals have also been studied. The next studied system was Cr-doped pyrite CuSe2 nanocrystals, eventually leading to the observation of significant enhancement of ferromagnetic moment by Cr-doping in octahedral sites of the pyrite structure. We performed a unique reaction in which nanocrystals of CrxCu1-xSe2 (x = 0.1-0.5) formed in the pyrite phase, which is not stable in bulk form. The host p-CuSe2 nanocubes did also undergo a degradation influenced by the reaction temperature and the doping of Cr3+ ions in the pyrite crystal structure. The Cr-doped nanocrystals of the pyrite phase were formed during the heat-up procedure and by increasing the reaction temperature transformed to CuCr2Se4 spinel nanocrystals. To the best of our knowledge, no cationic substitution of chromium for copper has been reported on pyrite CuSe2 systems so far, likely due to the significant size difference between chromium and copper. Therefore, the results of this work are a powerful approach for the design and fabrication of new multielemental materials that may not be stable in the bulk form.
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    The Deprotonation and Dissociation of Amino Acids and Peptides by Negative Ion Mode Mass Spectrometry
    (University of Alabama Libraries, 2021) Cui, Can; Cassady, Carolyn J.; University of Alabama Tuscaloosa
    Investigation of negative ion mass spectrometry (MS) is important to proteomics due to its superior ability to analyze acidic peptides and provide complementary information to positive ion mode. This dissertation focuses on the deprotonation and dissociation of amino acids and peptides, which provides fundamental knowledge and assists in development of negative ion MS. Gas-phase acidities (GA) of acidic peptides were determined experimentally and compared to computational values. In electrospray ionization (ESI), either one major structure or multiple structures with very similar GAs were formed. Peptides with acidic residues at the C-terminus are more acidic than those at the N-terminus. Replacing glutamic acid residues (E) with aspartic acid (D) can increase the acidities when E is at the C-terminus but has no effect if E is at the N-terminus. Bond dissociation energies of deprotonated amino acids, dipeptides, and their amides were investigated by combining MS and computations. The loss of H2O occurs in collision-induced dissociation (CID) from all amides except glycine amide. Loss of the C-terminus is only seen in CID of deprotonated dipeptides. In addition, an intense y1 ion forms from dipeptides and their corresponding amides. In the comparison among radical-based dissociation techniques, negative ion in-source decay (nISD) has the best performance for peptides. nISD gives the highest sequence coverage and consistently generated singly charged c- and z-ions. Besides, nISD produced the least neutral loss products and is the fastest technique. The disadvantage of nISD is its inability to select precursor ions. For the investigation of nISD with oxidizing matrices on acidic peptides, 4-nitro-1-naphthylamine (4N1NA) was used as a MALDI matrix for the first time and was found to be the most useful matrix. The overall sequence coverage obtained with 4N1NA is higher than with three other matrices. The formation of c- and a-ions indicates that 4N1NA has both reducing and oxidizing characteristics.
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    Developing and Optimizing a Robust Spray-Capillary Ce-Ms Platform for Ultrasensitive Omics Analysis
    (University of Alabama Libraries, 2025) Abdelhamed, Ahmed Mohamed Amin; Wu, Si
    Single-cell multi-omics provides a vast amount of information, giving us an advantage in discovering mechanisms of gene regulation, protein expression dynamics, and epigenetic differences. This bolsters our understanding of cell heterogeneity in disease, which has implications for advancing diagnostics and treatments. Developing such methods may require the development of single-omics methods that could be paired. This thesis focuses on developing and optimizing an ultrasensitive, robust, and high-throughput spray-capillary CE-MS platform for multi-omics analysis of single cells.The spray-capillary CE-MS technology demonstrates high potential for emerging in single-cell and mass-limited sample analysis due to its enhanced detection limit and ultralow sample volume requirements. However, we had to address some challenges before proceeding with optimizing the system for mass-limited or single-cell analysis. These challenges included the rapid evaporation of such a small sample volume, in addition to the high fragility of the capillary’s tip. To mitigate these challenges, a humidity chamber was developed to maintain the small sample volume of a single cell, ensuring successful sample handling. Additionally, the tip structure of the capillary was modified to enhance the physical robustness of the tip and decrease the ESI voltage applied, which is expected to contribute to less oxidative interferences and a longer capillary life. The work also included optimizing the spray-capillary CE-MS system. First, we worked on improving reproducibility and robustness. Thus, a conditioning protocol was designed and further optimized for the top-down proteomics workflow. Second, to enhance separation and sensitivity, we optimized the CE separation voltage using the bottom-up proteomics workflow. These developments and optimizations were dedicated to enabling the analysis of mass-limited or single-cell samples by spray-capillary CE-MS. As a proof-of-principle experiment, HeLa protein digest single-cell samples were tested where peptides were detected from tiny fractions of single cells. Overall, this work has demonstrated that the optimized spray-capillary CE-MS platform implies a high potential for multi-omics analysis from single cells.
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    Investigation of structural changes in vanadium containing transition metal oxides
    (University of Alabama Libraries, 2020-12) Davenport, Matthew Austin; Allred, Jared M.; University of Alabama Tuscaloosa
    We have completed an experiment to obtain diffuse scattering data for use in a comprehensive study of the local-structure changes as a function of molybdenum composition and have made large strides in interpreting some of the major changes found in this study. For these experiments, single crystals of molybdenum substituted VO2 with the formula V1-xMoxO2 were synthesized, with molybdenum compositions up to x = 0.60, using a novel, two-step chemical vapor transport synthesis. Using these large single crystals for total scattering experiments, we report the discovery of the sudden collapse of three-dimensional order in the low-temperature phase of V1-xMoxO2 at x = 0.17 and the emergence of a novel frustrated two-dimensional order at x = 0.19, with only a slight change in electronic properties. Single crystal diffuse x-ray scattering reveals that this transition from the 3D M1 phase to a 2D variant of the M2 phase results in long-range structural correlations along symmetry-equivalent (11L) planes of the tetragonal rutile structure, yet extremely short-range correlations transverse to these planes. Additionally, we report a combined study using single crystal X-ray diffraction, powder X-ray diffraction, and representational analysis to examine both the local and crystallographically averaged atomic structures simultaneously near x = 0.50. Between about x = 0.50 and 0.60, the average structure of V1-xMoxO2 is the parent rutile phase, but the local symmetry is broken by atomic displacements that are best described by an orthorhombic cell in the spacegroup Fmmm. This model is locally identical to the two-dimensionally ordered 2D-M2 phase except the correlation length is much shorter in the 2D plane, and longer in the frustrated one, making it more isotropic.
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    Phenolic Acid Complexes with Cycloamylose Supramolecular Hosts: Their Structures and Analytical Applications
    (University of Alabama Libraries, 2023) Yao, Xiyuan; Bonizzoni, Marco
    Phenolic acids are common phytochemicals in plants that can be beneficial to human health. Clarifying their identity and relative amounts in plant-based food products can help understand their nutritional values and advance their role in the food industry. However, working with phenolic acids is difficult because they are often present as mixtures in plants, they have very similar structures, and they display poor water solubility. Complexation with cyclodextrins (CDs) could significantly improve their processability and bioavailability. In this work, we studied the formation of these complexes and their application to analytical determination of phenolic acids in detail.Cyclodextrins are widely used as encapsulation and delivery carriers of organic drug molecules and food ingredients to improve the guest molecule's water solubility, stability, taste, and oral absorption. To study the formation of complexes between cyclodextrins and the phenolic acids of interest, we first used mass spectrometry to determine the general composition of these complexes. We then used isothermal titration calorimetry (ITC) to measure the thermodynamic parameters and affinity trends, so we could pinpoint the chemical driving forces behind these interactions. Lastly, we attempted to study the complex structure through nuclear magnetic resonance (NMR) experiments. We discuss here how the structure and position of various functional groups on the phenolic acid influence their complex behavior. Finally, we used our newfound insights to build a pattern-based recognition system for phenolic acids. In fact, due to their very similar structures, phenolic acids are difficult to discriminate with traditional analytical methods. We decided to use optical spectroscopy and construct a series of sensing complexes that could bind to phenolic acids in a promiscuous way. We selected HP-β-CD as the host thanks to its excellent water solubility, and paired it selected commercially available dye molecules to form a variety of [CD•dye] sensing complexes which, when exposed to analytes, undergo unique and distinctive changes in their spectroscopic signal. We used principal component analysis (PCA) to summarize the information contained in these spectroscopic measurements and were able to discriminate among structurally very similar phenolic acids, down to a 0.02 mM concentration.
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    Spectroelectrochemistry studies of perovskite electrode materials
    (University of Alabama Libraries, 2021) Yadav, Jeetika; Pan, Shanlin; University of Alabama Tuscaloosa
    Perovskite materials have interesting optoelectronic properties such as tunable bandgap, high photoluminescence, broad spectral range, and emission tunability in the entire visible region. These materials have been extensively used as an absorber layer in the solar cells however their applications in terms of electrochemiluminescence (ECL) in the lighting industry has not been explored. This dissertation presents a study of the electrochemiluminescence, stability, size-dependent, and luminescent properties of these materials. Chapter 1 of this dissertation provides extensive background and a broad review of current research progress made in the field of perovskite materials and their applications. Chapter 2 illustrates the operation principles of several selected electrochemistry and characterization techniques extensively applied in this doctoral research. The doctoral research work starts with the synthesis and photophysical studies of perovskite films in Chapter 3 to show their fluorescence emission and stability. Confocal fluorescence microscopy is used to study the red and green fluorescence from the perovskite films and the origin and relationship between both colors are described. The synthesized perovskite films are used as a device for light-emitting electrochemical cells (LECs) applications. Since the optoelectronics properties of perovskite materials are greatly dependent on their size and structure, a perovskite size and density gradient are developed on a conductive substrate upon a single potential application as shown in Chapter 4. Dark field scattering (DFS), fluorescence imaging, X-ray crystallography (XRD), and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) imaging mass spectrometry techniques demonstrate that the large-sized and low-density perovskite crystals are more stable than the smaller sized high-density perovskite crystals. Finally, spectroelectrochemistry and photophysics, stability of perovskite quantum dots are described in Chapter 5. The generated ECL of perovskite quantum dots studied by was stabilized by incorporated the perovskite quantum dots in polystyrene (PS) polymer matrix increasing the efficiency of ECL generation 2.5 folds. Challenges of this doctoral work and future perspectives are described in Chapter 6.