ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
Displaying 1 - 6 of 6
Filtering by
- All Subjects: Chemistry
- Creators: Birkel, Christina
- Creators: Heyden, Matthias
Description
MAX phases are an intriguing class of materials with exotic combinations of properties, essentially turning them into metallic ceramics. Despite this unique feature, no commercialization has been accomplished yet. Looking at the state of the art within the MAX phase community, almost all published studies can be summarized using the term “traditional high temperature synthesis”. Contrasting the scientific interest that has been on the rise especially since the discovery of MXenes, the synthetic spectrum has been largely the same as it has been over the past decades.Herein, the newly-emerging sol-gel chemistry is being explored as an alternative non-conventional synthetic approach. Building on the successful sol-gel synthesis of Cr2GaC, this study focuses around the expansion of sol-gel chemistry for MAX phases. Starting with a thorough mechanistic investigation into the reaction pathway of sol-gel synthesized Cr2GaC, the chemical understanding of this system is drastically deepened. It is shown how the preliminary nano-structured metal-oxide species develop into bulk oxides, before the amorphous and disordered
graphite partakes in the reaction and reduces the metals into the MAX phase.
Furthermore, the technique is extended to the two Ge- based MAX phases V2GeC and Cr2GeC, a critical step needed to prove the viability and applicability of the newly developed technique. Additionally, by introducing Mn into the Cr-Ga-C system, a Mn-doping was achieved, and for the first time for (Cr1–xMnx)2GaC, a unit cell increase could be recorded. Based on magnetometry measurements, the currently widely accepted assumption of statistically distributed Mn in the M-layer is challenged.
The versatility of wet chemistry is explored using the model system Cr2GaC. Firstly, the MAX phase can be obtained in a microwire shape leveraging the branched biopolymer dextran, eliminating the need for any post-synthesis machining. Via halide intercalation, the electrical transport properties could be purposefully engineered.
Secondly, leveraging the unique and linear biopolymer chitosan, Cr2GaC was obtained as thick films and dense microspheres, drastically opening potential areas of application for MAX phases. Lastly, hollow microspheres with diameters of tens of μm were synthesized via carboxymethylated dextran. This shape once more opens the door to very specific applications requiring sophisticated structures.
ContributorsSiebert, Jan (Author) / Birkel, Christina (Thesis advisor) / Gould, Ian (Committee member) / Kouvetakis, John (Committee member) / Arizona State University (Publisher)
Created2022
Description
Due to the potential synergistic properties from combining inorganic and organic moieties, inorganic/organic hybrids materials have recently attracted great attention. These hybrids are critical components in coating and nanocomposite additive technologies and have potential for future application in catalysis, energy production or storage, environmental remediation, electronic, and sensing technologies. Most of these hybrids utilize low dimensional metal oxides as a key ingredient for the inorganic part. Generally, clay materials are used as inorganic components, however, the use of low dimensional transition metal oxides may provide additional properties not possible with clays. Despite their potential, few methods are known for the use of low dimensional transition metal oxides in the construction of inorganic/organic hybrid materials.Herein, new synthetic routes to produce hybrid materials from low dimensional early transition metal oxides are presented. Included in this thesis is a report on a destructive, chemical exfoliation method designed specifically to exploit the Brønsted acidity of hydrated early transition metal oxides. The method takes advantage of (1) the simple acid-base reaction principle applied to strong two-dimensional Brønsted solid acids and mildly basic, high-polarity organic solvents, (2) the electrostatic repulsion among exfoliated nanosheets, and (3) the high polarity of the organic solvent to stabilize the macroanionic metal oxide nanosheets in the solvent medium. This exfoliation route was applied to tungstite (WO3∙H2O) and vanadium phosphate hydrate (VOPO4∙H2O) to produce stable dispersions of metal oxide nanosheets. The nanosheets were then functionalized by adduct formation or silane surface modification. Both functionalization methods resulted in materials with unique properties, which demonstrates the versatility of the new exfoliation methods in preparing novel hybrid materials.
Further extension of the method to aqueous systems allowed discovery of a new synthetic method for electrically-conducting polyaniline-polyoxometalate hybrid materials. Namely, destructive dissolution of MoO2(HPO4)(H2O) in water produces protons and Strandberg-type phosphomolybdate clusters, and in the presence of aniline and an oxidizing agent, the clusters self-assemble with protonated anilines and selectively form polyaniline-phosphomolybdate hybrids on various types of surfaces through in situ oxidative chemical polymerization. New conductive nanocomposite materials were produced by selectively coating the surface of silica nanoparticles.
ContributorsCiota, David (Author) / Seo, Dong-Kyun (Thesis advisor) / Trovitch, Ryan (Committee member) / Birkel, Christina (Committee member) / Arizona State University (Publisher)
Created2022
Description
Understanding solvent-mediated interactions in biomolecular systems at the molecular level is important for the development of predictive models for processes such as protein folding and ligand binding to a host biomolecule. Solvent-mediated interactions can be quantified as changes in the solvation free energy of solvated molecules. Theoretical models of solvent-mediated interactions thus need to include ensemble-averaged solute-solvent interactions. In this thesis, molecular dynamics simulations were coupled with the 3D-2PT method to decompose solvation free energies into spatially resolved local contributions. In the first project, this approach was applied to benzene derivatives to guide the development of efficient and predictive models of solvent-mediated interactions in the context of computational drug design. Specifically, the effects of carboxyl and nitro groups on solvation were studied due to their similar sterical requirements but distinct interactions with water. A system of solvation free energy arithmetics was developed and showed that non-additive contributions to the solvation free energy originate in electrostatic solute-solvent interactions, which are qualitatively reproduced by computationally efficient continuum models. In the second project, a simple model system was used to analyze hydrophilic water-mediated interactions (water-mediated hydrogen bonds), which have been previously suggested to play a key role in protein folding. Using the spatially resolved analysis of solvation free energies, the sites of bridging water molecules were identified as the primary origin of solvent-mediated forces and showed that changes in hydration shell structure can be neglected. In the third project, the analysis of solvation free energy contributions is applied to proteins in inhomogeneous electric fields to explore water-mediated contributions to protein dielectrophoresis. The results provide a potential explanation for negative dielectrophoretic forces on proteins, which have been observed experimentally but cannot be explained with previous theoretical models.
ContributorsLazaric, Aleksandar (Author) / Heyden, Matthias (Thesis advisor) / Ozkan, Banu S (Committee member) / Sulc, Petr (Committee member) / Arizona State University (Publisher)
Created2022
Description
Contrary to the traditional structure-function paradigm for proteins, intrinsically disorderedproteins (IDPs) and regions (IDRs) are highly disordered sequences that lack a fixed
crystal structure yet perform various biological activities such as cell signaling, regulation,
and recognition. The interactions of these disordered regions with water molecules are essential
in the conformational distribution. Hence, exploring their solvation thermodynamics
is crucial for understanding their functions, which are challenging to study experimentally.
In this thesis, classical Molecular Dynamics (MD), 3D-Two Phase Thermodynamics (3D-
2PT), and umbrella sampling have been employed to gain insights into the behaviors of
intrinsically disordered proteins (IDPs) and water.
In the first project, local and total solvation thermodynamics around the K-18 domain
of the intrinsically disordered protein Tau were compared, and simulated with four pairs
of modified and standard force fields. In empirical force fields, an imbalance between
intramolecular protein interactions and protein-water interactions often leads to collapsed
IDP structures in simulations. To counter this, various methods have been devised to refine
protein-water interaction models. This research applied both standard and adapted force
fields in simulations, scrutinizing the effects of each adjustment on solvation free energy.
In the second project, the MD-based 3D-2PT analysis was utilized to examine variations
in local entropy and number density of bulk water in response to an electric field, focusing
on the vicinity of reference water molecules.
In the third project, various peptide sequences were examined to quantify the free energy
involved when specific sequences, known as alpha-MoRFs (alpha-Molecular Recognition
Features), transition from intrinsically disordered states to structured secondary motifs
like the alpha-helix. The low folding free energy penalty of these sequences can be exploited
to design peptide-based or small-molecule drugs. Upon binding to alpha-MoRFs,
these drugs can stabilize the helix structure through a binding-induced folding mechanism.
Alpha-MoRFs were juxtaposed with entirely disordered sequences from known proteins,
with findings benchmarked against leading structure prediction models. Additionally, the
binding free energies of various alpha-MoRFs in their folded conformation were assessed
to discern if experimental binding free energies reflect the separate contributions of folding
and binding, as obtained from umbrella sampling simulations.
ContributorsMaiti, Sthitadhi (Author) / Heyden, Matthias (Thesis advisor) / Ozkan, S. Banu (Committee member) / Sulc, Petr (Committee member) / Arizona State University (Publisher)
Created2024
Description
Pure metal clusters serve as model systems by providing an avenue for the study of fundamental phenomena, specifically the interaction between light and matter. Bulk metal materials are known to display defining characteristics, namely thermal conductivity, electrical conductivity, and luster, which provide a quantifiable measure of their metallicity. These properties are all due to the electron delocalization throughout the metal. Nanoscale materials lack the ability to measure these properties, leading to the need for a manner of quantifying the metallic character at the nanoscale size regime.Excited state lifetimes vary for semiconducting and metallic systems, specifically metals relax to a ground state at a faster rate than semiconducting materials. Aluminum clusters have received decades of attention regarding their metallicity. Moreover, Al clusters have been debated to fit into the jellium model. The jellium model seeks to describe a cluster as a “superatom” where all electrons are delocalized around the positively charged metal center, like that of an atom. With three valence electrons, jellium shell closings can be met if the electrons involved in cluster bonding varies. This variance leads to a localization of electrons for instances in which all three electrons do not contribute to bonding. Localized electrons aren’t characteristic of the jellium model or metals more broadly. Tracking the excited state lifetimes of Al clusters produced through laser ablation seeks to uncover the onset of metallic character. Femtosecond pump-probe spectroscopy coupled with time-of-flight mass spectrometry has resolved the time dynamics for atomically precise Al clusters ranging in size from 1-43 atoms. At a size greater than 9 atoms, it’s identified that Al clusters show metallic character. This finding is supported by previous literature results and the fact that, above 9 atoms, Al cluster excited state lifetimes match that of the bulk scale Al excited state lifetime of ~300 fs.
ContributorsJarman, Carter Korey (Author) / Sayres, Scott G (Thesis advisor) / Birkel, Christina (Committee member) / Chizmeshya, Andrew (Committee member) / Arizona State University (Publisher)
Created2024
Temperature and polarizability effects on electron transfer in biology and artificial photosynthesis
Description
This study aims to address the deficiencies of the Marcus model of electron transfer
(ET) and then provide modifications to the model. A confirmation of the inverted energy
gap law, which is the cleanest verification so far, is presented for donor-acceptor complexes.
In addition to the macroscopic properties of the solvent, the physical properties of the solvent
are incorporated in the model via the microscopic solvation model. For the molecules
studied in this dissertation, the rate constant first increases with cooling, in contrast to the
prediction of the Arrhenius law, and then decreases at lower temperatures. Additionally,
the polarizability of solute, which was not considered in the original Marcus theory, is included
by the Q-model of ET. Through accounting for the polarizability of the reactants, the
Q-model offers an important design principle for achieving high performance solar energy
conversion materials. By means of the analytical Q-model of ET, it is shown that including
molecular polarizability of C60 affects the reorganization energy and the activation barrier
of ET reaction.
The theory and Electrochemistry of Ferredoxin and Cytochrome c are also investigated.
By providing a new formulation for reaction reorganization energy, a long-standing disconnect
between the results of atomistic simulations and cyclic voltametery experiments is
resolved. The significant role of polarizability of enzymes in reducing the activation energy
of ET is discussed. The binding/unbinding of waters to the active site of Ferredoxin leads
to non-Gaussian statistics of energy gap and result in a smaller activation energy of ET.
Furthermore, the dielectric constant of water at the interface of neutral and charged
C60 is studied. The dielectric constant is found to be in the range of 10 to 22 which is
remarkably smaller compared to bulk water( 80). Moreover, the interfacial structural
crossover and hydration thermodynamic of charged C60 in water is studied. Increasing the
charge of the C60 molecule result in a dramatic structural transition in the hydration shell,
which lead to increase in the population of dangling O-H bonds at the interface.
(ET) and then provide modifications to the model. A confirmation of the inverted energy
gap law, which is the cleanest verification so far, is presented for donor-acceptor complexes.
In addition to the macroscopic properties of the solvent, the physical properties of the solvent
are incorporated in the model via the microscopic solvation model. For the molecules
studied in this dissertation, the rate constant first increases with cooling, in contrast to the
prediction of the Arrhenius law, and then decreases at lower temperatures. Additionally,
the polarizability of solute, which was not considered in the original Marcus theory, is included
by the Q-model of ET. Through accounting for the polarizability of the reactants, the
Q-model offers an important design principle for achieving high performance solar energy
conversion materials. By means of the analytical Q-model of ET, it is shown that including
molecular polarizability of C60 affects the reorganization energy and the activation barrier
of ET reaction.
The theory and Electrochemistry of Ferredoxin and Cytochrome c are also investigated.
By providing a new formulation for reaction reorganization energy, a long-standing disconnect
between the results of atomistic simulations and cyclic voltametery experiments is
resolved. The significant role of polarizability of enzymes in reducing the activation energy
of ET is discussed. The binding/unbinding of waters to the active site of Ferredoxin leads
to non-Gaussian statistics of energy gap and result in a smaller activation energy of ET.
Furthermore, the dielectric constant of water at the interface of neutral and charged
C60 is studied. The dielectric constant is found to be in the range of 10 to 22 which is
remarkably smaller compared to bulk water( 80). Moreover, the interfacial structural
crossover and hydration thermodynamic of charged C60 in water is studied. Increasing the
charge of the C60 molecule result in a dramatic structural transition in the hydration shell,
which lead to increase in the population of dangling O-H bonds at the interface.
ContributorsWaskasi, Morteza M (Author) / Matyushov, Dmitry (Thesis advisor) / Richert, Ranko (Committee member) / Heyden, Matthias (Committee member) / Beckstein, Oliver (Committee member) / Arizona State University (Publisher)
Created2019