Alumni Dissertations

 

Alumni Dissertations

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  • Development of Mesoporous Silicas, Responsive Polymer Microgels, and Related Nanocomposites

    Author:
    Yingyu Li
    Year of Dissertation:
    2014
    Program:
    Chemistry
    Advisor:
    Michal Kruk
    Abstract:

    This dissertation covers research on polymer-templated nanoporous materials and functional soft materials, and it consists of four major parts. The first part is on introduction. The next part (Chapters 2-3) describes the research work on the synthesis of silicas with spherical mesopores. Chapter 2 is focused on the synthesis of large-pore FDU-12 silicas at room temperature by using surfactants with large hydrophilic blocks and relatively small hydrophobic blocks (such as Pluronic F108 (EO132PO50EO132)) as the template. Chapter 3 discusses an interesting mesopore structure, which is the hollow silica nanosphere (HSN). The single-micelle-templating strategy provides a general approach for the synthesis of HSNs at room temperature, and the judicious choice of the framework precursor and synthesis conditions allows for the synthesis of HSNs with pore void diameter tunable from ~ 10 nm to ~ 44 nm. In addition, the one-pot room-temperature synthetic approach can be employed to the construction of hybrid organic/inorganic hollow spheres. The third part involved the preparation of glucose-responsive polymer microgels (Chapter 4-6). In Chapter 4 and 5, two kinds of dye-composited microgel sensors have been developed, and they exhibited good stability, high selectivity, and good reproducibility for detection of glucose. In Chapter 6, a glucose responsive core-shell structured microgel was designed and developed for insulin release at proper physiologically needed glucose levels. The last part of this dissertation (Chapter 7, 8) was about the synthesis of inorganic particle/polymer hybrid materials. In Chapter 7, the stimuli-responsive polymer brushes were successfully grafted from the surface of hollow silica nanospheres via surface-initiated atom transfer radical polymerization with activators regenerated by electron transfer (SI-ARGET ATRP), and the polymer loading was well controlled. Besides, the core-shell-structured nanocomposites were successfully fabricated in Chapter 8. Magnetite nanoparticles were adopted as the core, and the multifunctional polymer layer was coated on their surface. They demonstrated significant adsorption capacity towards cobalt ions, and suitability for magnetic separation, making it an excellent absorbent for waste water treatment.

  • Two Types of Protein Salt Bridges Studied by Quantum Calculation

    Author:
    Sing Liao
    Year of Dissertation:
    2009
    Program:
    Chemistry
    Advisor:
    Michael Green
    Abstract:

    Abstract Two types of protein salt bridges in an aqueous environment, the arginine-acid salt bridge and the lysine-acid salt bridge, are studied here. The former is modeled by propionic acid and ethylguanidine, the latter by propionic acid and propyl amine. Both have been investigated by quantum calculations for the purpose of obtaining improved salt bridge potentials in an aqueous environment with constraints on the distances between the two functional groups, which are defined as the bridge lengths in this report, designed for applications to molecular dynamics simulations of ion channels. For the arginine-acid salt bridge, we perform optimization calculations on 13 molecular clusters corresponding to the salt bridge with 0 to 12 water molecules. For the lysine-acid salt bridge, we perform optimization calculations on 2 molecular clusters for the salt bridge with 0 or 1 water molecule. To each of the model systems, after obtaining its optimized geometry, we slowly vary the bridge lengths and bridge angles in three dimensions, and subsequently we perform COSMO, frequency and NBO calculations on the contracted and expanded model systems. COSMO calculations give the dielectric constant dependence, and the frequency provides the thermodynamic properties of the system while the NBO provides the electronic distributions and bonding information. We found: (1) there is a fill-in mechanism for water molecules to enter into the salt bridge systems; such a fill-in order may have periodicity in energy, as a function of number of water molecules. (2) we show that the salt bridge systems have both hydrophilic and hydrophobic properties; (3) we look into the proton ionization process from several new aspects in terms of comparison between potentials in two different salt bridge systems and the rates of Wiberg bond order change; (4) we have an in-depth look at effects that can cause large variations to system potentials, and we take note of effects that resulted from environments of limited amounts of local waters and that may have been missed by classical treatments; (5) we look into a new aspect in the applications of Wiberg bond order that are closely associated with the electron density in predicting the formation and disruption of bonding in the systems; (6) in regard to applications to simulations of ion channels, we discuss a possible method to formulate system potentials in specific environments.

  • Development of Highly Efficient Transition Metal-Catalyzed Addition Reactions

    Author:
    Yuanxi Liao
    Year of Dissertation:
    2011
    Program:
    Chemistry
    Advisor:
    Qiaosheng Hu
    Abstract:

    Development of new and efficient reactions as powerful tools for synthetic chemistry is one of the most important tasks in modern chemistry. Transition metal-catalyzed carbon-carbon bond-forming reactions including addition reactions are some of the most powerful transformations in organic synthesis. My research is on developing highly efficient transition metal-catalyzed addition reactions as powerful tools for organic synthesis. There are two parts of my Ph. D. dissertation research projects. In the first part, based on our understanding on transmetalation and reductive elimination of palladium catalysis, we minimized the decomposition of catalysts and developed a series of new, highly efficient Pt(II), Pd(II), Rh(I) and Cu(II)-catalyzed addition reactions of organoboron reagents with carbonyl-containing compounds. Since Pt complexes can undergo reductive elimination very reluctantly, we explored the platinacycle-catalyzed addition reaction of arylboronic acids with aldehydes with low catalyst loadings. However, the low catalyst loading catalysis with platinacycles as catalysts was achieved at the expense of the catalyst catalytic activity. In order to minimize the decomposition of catalyst as well as keep the catalytic activity, a new anhydrous condition of addition reactions was established and a novel non-transmetalation mechanism of the Pd-catalyzed addition reaction was proposed and demonstrated. Under the guidance of the new reaction mechanism, we pinpointed that some addition reactions which are thought to be hardly achievable before may be accomplished now. By using the anhydrous condition, we explored Cu-catalyzed addition reactions of arylboroxines with carbonyl-containing compounds and Rh-catalyzed addition reactions of arylboroxines with ketones. In the second part, to make the addition reactions we developed in the first part be more powerful, we explored new tandem/sequential reactions involved such addition reactions as one of bond-forming reactions. Specifically, we combined Pt(II)-catalyzed 1,2-addition reactions of arylboronic acids and aldehydes with the secondary alcohol oxidation process in a tandem fashion to synthesis aryl ketones from readily available aldehydes and arylboronic acids. We also developed the synthesis of â-arylated ketones via the aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reaction in a sequential and tandem fashion. Such sequential/tandem protocols offer us rapid entry to synthesize complex materials or biological active compounds from simple precursors.

  • Electronic spectroscopy and computational studies of GSCbl, H2OCbl, and MeCbl

    Author:
    Iya Likhtina
    Year of Dissertation:
    2011
    Program:
    Chemistry
    Advisor:
    RONALD BIRKE
    Abstract:

    In the present study we are interested in the electronic and geometric structure of GS-Cbl and the chemical nature of its Co(III)-S bond in comparison with aquo- and methyl- axial ligand bonds to Co(III) in cobalamins. We examine the structures with DFT calculations of truncated models of the entire molecule. Furthermore, we compare the electronic spectroscopy (UV-VIS and CD) of GS-Cbl(III) with H2O-Cbl(III) and CH3-Cbl(III) using both experimental spectra and TD-DFT calculated spectra. The AOMIX program was used to analyze molecular orbital, MO, compositions, partial density of states, DOS, between molecular fragments, and generalized Wiberg and Mayer bond orders, Charge Decomposition Analysis, CDA, and Energy Decomposition Analysis, EDA. Natural Bond Order (NBO) analysis as implement in G03 and G09 was made on gas phase and aqueous ground state structures.

  • Polymerization in a small droplet on a superhydrophobic surface

    Author:
    Fang-Ju Lin
    Year of Dissertation:
    2013
    Program:
    Chemistry
    Advisor:
    Alan Lyons
    Abstract:

    Droplets of fluids have been used as small volume reactors in microfluidic applications, including polymerase chain reaction, as well as synthesis of small-molecules, polymers, and gel particles. More recently, reactions within individual droplets on superhydrophobic surfaces have been studied. However, the fundamentals of polymerization reactions in a droplet on a superhydrophobic surface have not been reported. To address this issue, firstly, a temperature- and atmosphere-controlled environmental chamber was designed to maintain a constant volume of the droplet on superhydrophobic surface by insuring an equilibrium solvent vapor pressure, eliminating extraneous evaporation or condensation of water. A new technique, micro-dilatometry, was developed to measure the change in volume of the droplet in real-time as a function of photopolymerization conditions. Experimental parameters include photoinitiator concentration, UV light intensity and surface type. In this way, polymerization rate could be calculated in isolated 10 uL droplets. Droplets on a superhydrophobic surface can be easily and completely lifted off the surface with a syringe because of the weak interactions between liquid and solid surface. Because of this unique aspect of superhydrophobic surfaces, small droplets could be easily analyzed in an external instrument such as NMR or GPC. The percent conversion of monomer to polymer, calculated by micro-dilatometry, was verified by NMR for the same droplet. The molecular weight of the formed polymer could also be measured by injecting the droplet into a GPC. These results demonstrated good correlation between micro-dilatometry and NMR for percent conversions ranging from 5 - 18%. Above 18% conversion, experiments demonstrated significant deviations between micro-dilatometry and NMR. Main reason of these discrepancies is proofed to be changes in the vapor pressure of water within the droplet as the concentration of solute molecules decreased significantly during polymerization. Using the micro-dilatometry technique, the kinetics of polymerization of acrylamide was studied. The polymerization rate within isolated 10 uL droplets was found to be significantly higher than in a well-stirred vial. In addition, the molecular weight of polymers formed in droplets was found to be larger than in the well-stirred system. A hypothesis is presented to explain the higher polymerization rate and molecular weight in small isolated droplets.

  • Synthesis of C-Glycoside Analogs of the Immunostimulatory Glycosphingolipid, alfa-Galactosylceramide

    Author:
    Zheng Liu
    Year of Dissertation:
    2011
    Program:
    Chemistry
    Advisor:
    Robert Bittman
    Abstract:

    This dissertation presents the asymmetric total synthesis of immunostimulatory &alpha-C-galactosylceramide (&alpha-C-GalCer) glycolipids and D-ribo-phytosphingosine. Also included in this dissertation is an improved two-step synthetic route to primary allylic alcohols from aldehydes and verification of configurations of three contiguous stereogenic centers in the phytosphingosine backbone of &alpha-1C-GalCer, the nonisosteric analog of &alpha-C-GalCer in which the glycosidic oxygen atom linking the sugar with phytosphingosine is deleted.. Chapter 1 presents an improved two-step synthetic route to primary allylic alcohols from aldehydes. A modification of the Horner-Wadsworth-Emmons (HWE) olefination reaction in H2O/2-propanol (1:1) and a convenient protocol to prepare AlH3 in tetrahydrofuran from LiAlH4 and n-butyl bromide are the key factors in the improvement. Chapter 2 presents an asymmetric synthesis of D-ribo-phytosphingosine. The synthesis was achieved by utilizing the ProPhenol-catalyzed alkynylation of an unsaturated aldehyde to afford an allylic propargylic alcohol followed by asymmetric epoxidation and opening of a propargylic epoxy alcohol with NaN3/NH4Cl. Deprotection and reduction of the resulting acyclic azide then gave D-ribo-phytosphingosine. The acyclic azide was also subjected to an intramolecular click reaction, generating a bicyclic triazole, whose diacetate derivative was found to have almost identical cis and trans vicinal coupling constants. The relative stereochemistry of the final product was assigned by NMR analysis of corresponding Mosher esters and amides, and confirmed by comparison of NMR spectra and specific rotations of its tetraacetate derivative with reported data. The stereochemical assignment based on comparing J values with reported data in bicyclic triazoles, generated by a copper-free intramolecular click reaction, was inconclusive. Alkynyl-azide, an efficient glycosyl acceptor in the synthesis of &alpha-galactosylceramide derivatives, was also readily prepared by this route. Chapter 3 presents (1) a modification of the first generation synthesis of &alpha-1C-galactosylceramide featuring the two-step HWE olefination and alane reduction protocol described in Chapter 1 and the ProPhenol-catalyzed asymmetric alkynylation reaction, and (2) a detailed verification of the configurations of three contiguous stereogenic centers in the phytosphingosine moiety. Given the possible intramolecular participation by the 2'-O-benzyl group of the galactosyl moiety in epoxide opening by the azide anion, an attempt was made to assign the relative stereochemistry of the azide-bearing carbon through the coupling constants (J4,5 and J5,6) in a bicyclic triazole, which was obtained via an intramolecular click reaction and acetylation of diol. The cis J4,5 and trans J5,6 displayed almost the same values, suggestive of possible retention in the opening of the epoxide; however, nOe analysis was inconclusive. Model compounds containing the same bicyclic triazole skeleton were prepared via the same reaction sequence, and their cis J4,5 and trans J5,6 coupling constants showed similar values as to those in the sugar counterpart. According to the systematical investigation of the model compounds described in Chapter 2, the epoxide-opening reaction did indeed proceed with inversion. These results exclude intramolecular participation by the 2'-O-benzyl group and emphasize the need for caution when coupling constants alone are used to judge the relative configuration in bicyclic triazoles and related systems. Chapter 4 presents stereocontrolled syntheses of &alpha-C-GalCer and its &alpha-C-acetylenic analog from 1-hexadecene and D-galactose. The key transformations include Sonogashira coupling, Sharpless asymmetric epoxidation, and Et2AlCl-catalyzed cyclization of an epoxytrichloroacetimidate to generate a protected dihydrooxazine synthon.

  • Synthesis, Fabrication and Characterization of Magnetic and Dielectric Nanoparticles and Nanocomposite Films

    Author:
    Xiaohua Liu
    Year of Dissertation:
    2014
    Program:
    Chemistry
    Advisor:
    Stephen O'Brien
    Abstract:

    Materials science is an interdisciplinary field investigating the structure-property relationship in solid-state materials scientifically and technologically. Nanoscience is concerned with the distinctive properties that matter exhibits when confined to physical dimensions on the order of 10-9 meters. At these length scales, behaviors of particles or elaborate structures are often governed by the rules of quantum mechanics in addition to the physical properties associated with the bulk material. The work reported here seeks to employ nanocystals, binary nanocomposites and thin films of materials, to build versatile, functional systems and devices. With a focus on dielectric, ferroelectric, and magnetoelectric performance, a series of materials has been synthesized and different types of nanocomposites have been built. Barium strontium titannate particles at various sizes was developed, aiming at high dielectric constant and low loss at high frequency range. Cobalt ferrite-polymer nanocomposite was fabricated with potential magnetoelectric coupling. Along with synthesis, advanced electron microscopies (TEM, SEM, STEM, EELS) at atomic resolution were employed to thoroughly investigate the crystallinity, morphology and composition. By means of spin-coating and printing techniques, single and multiple layered capacitors featuring improved dielectric performance (high k, low loss, high breakdown voltage, etc.) were developed through a) electrode deposition, b) dielectric layer deposition, and c) parylene evaporation. Such capacitors are further incorporated into electric power converters for LED lighting. Hopefully in the future we can make electronic devices more efficient, sustainable, smaller and cheaper. By advancing our knowledge of nanomaterials, especially those with potential of multifunction, energy efficiency and sustainability, we have strived to push the limits of synthesis, characterization, fabrication and property analysis of nanostructures towards new, reliable and low-cost multifunctional systems. Some of our efforts are described in the following chapters.

  • Enhanced Raman Effect on MBE Grown Semiconductor Quantum Dots

    Author:
    Richard Livingstone
    Year of Dissertation:
    2010
    Program:
    Chemistry
    Advisor:
    John Lombardi
    Abstract:

    Using Surface Enhanced Raman Spectroscopy (SERS), I observed Raman enhancements (104-105) for pyridine, 4-tertbutylpyridine and other biological molecules adsorbed on a II-VI semiconductor CdSe/ZnBeSe sample of uncapped self-assembled quantum dots produced by molecular beam epitaxy. When a monolayer of Raman active molecule is adsorbed on these structures, excitation at 488 nm produces intense Raman spectra and a very large enhancement of the a1, b1 and b2 modes. This indicates the presence of charge-transfer as a contributor to the enhancement. Furthermore, the excitation wavelength is in the vicinity of several interband transitions located both in the quantum dots and the wetting layer, and it is likely that these resonances also contribute to the enhancement factor. The observed enhancement is among the largest yet seen on semiconductor quantum dot systems and is the first obseved on MBE grown quantum dots. The observed Raman spectrum shows several differences from the normal Raman spectrum, and is closer in some ways to the SERS observed on Ag nanoparticles. Among other things, the prominence of non-totally symmetric lines indicates the importance of charge-transfer contributions to the overall enhancement. In Ag nanoparticle SERS, both the charge-transfer and surface plasmon resonances have been shown to be responsible for the effect. However, in semiconductors, the excitation wavelengths are far from the region of surface plasmon resonance for CdSe and so the magnitude of enhancement must be attributed to other possible resonances. Bandgap dependence studies using 4-tertbutylpyridine on semiconductor quantum dots with varying bandgap energies, indicates that transitions to the bandgap are important contributors to the overall enhancement, and may possibly be regarded as a replacement for the surface plasmon resonance so important in metallic SERS. As in SERS, however, the observation of non-totally symmetric bands indicates additional contributions from charge-transfer resonances. It is most likely a combination of these two effects which is responsible for the rather large enhancements observed here.

  • Energy of the Quasi-free Electron in Repulsive Atomic and Molecular Fluids

    Author:
    Yevgeniy Lushtak
    Year of Dissertation:
    2013
    Program:
    Chemistry
    Advisor:
    Cherice Evans
    Abstract:

    The ability to predict accurately the energy V0<\sub>(ρ) of the quasi-free electron along the entire density V0<\sub>(ρ) range of a supercritical fluid has applications in determining the ideal thermodynamic conditions for chemical reactions involving charged species. The previously established field ionization method of extracting V0<\sub>(ρ) from the fluid density dependent shift Δ(ρ) in the ionization energy of a dopant molecule has led to the discovery of a novel effect on V0<\sub>(ρ) occurring near the critical isotherm of the fluid. Unfortunately this method has limitations in determining V0<\sub>(ρ) in fluids with low critical temperatures as well as fluids opaque to vacuum ultraviolet radiation. Thus, accurate determination of V0<\sub>(ρ) in repulsive fluids (i.e., those possessing a positive zero kinetic energy electron scattering length) using field ionization is difficult. The new method developed in this study, namely field enhanced photoemission, allows for the direct determination of the quasi-free electron energy from the density dependent shift in the work function of a metal electrode submerged in the fluid. This mitigates the problems posed by field ionization while producing results with iii similar precision. Field enhanced photoemission was verified by measuring V0<\sub>(ρ) of Ar, an attractive fluid (i.e., one with a negative zero kinetic energy electron scattering length) studied extensively in the past by field ionization, before applying the method to the study of V0<\sub>(ρ) in the repulsive fluids Ne, He and N2. The new results showed a distinct critical point effect on V0<\sub>(ρ), which was accurately modeled with the local Wigner-Seitz approach developed for attractive fluids. Thus, this work extends our theoretical model to repulsive fluids. Unlike the attractive fluids studied in the past, the quasi-free electron energy in the repulsive fluids presented here is strictly positive. A careful analysis of the terms contributing to V0<\sub>(ρ) within the local Wigner-Seitz model leads one to expect the quasi-free electron energy to be positive in repulsive fluids in general. A discussion of fluid density dependent behavior of the kinetic and potential energy terms contribut- ing to V0<\sub>(ρ) is presented along with an explanation of the evolution of the shape of the V0<\sub>(ρ) curves for the fluids studied.

  • DESIGN, SYNTHESIS, AND ANTI-TUMOR ACTIVITIES OF BENZOPOLYSULFANE COMPOUNDS THAT MIMICS A TUNICATE-DERIVED NATURAL PRODUCT

    Author:
    Adaikapillai Mahendran
    Year of Dissertation:
    2011
    Program:
    Chemistry
    Advisor:
    ALEXANDER GREER
    Abstract:

    Benzopolysulfanes are untapped potential therapeutic compounds, which possess an impressive array of biological activities. By developing an entirely new class of compounds (polysulfanes) drug resistance can be evaded due to the lack of exposure of organisms to these compounds. However, polysulfanes are challenging compounds to prepare, and usually have very poor water-solubility. New synthetic methods and studies on solubility and cell-directed delivery are needed to explore the range of possibilities of this novel class of compounds. This thesis outlines (1) synthesis and biological activities of benzopolysulfane conjugates namely, PEGylated benzopoylsulfanes; and (2) mechanistic aspects on mode of introduction of sulfur atom to the catechol core; Benzopolysulfanes, 4-CH3(OCH2CH2)3NHC(O)-C6H4-1,2-Sx (x = 3-7, and 9) were synthesized with a PEG group attached through an amide bond and examined for water solubility, antitumor activity, and propensity to equilibrate and desulfurate. LCMS and HPLC data show the PEG pentasulfane ring structure predominates, and the tri-, tetra-, hexa-, hepta-, and nonasulfanes were present at very low concentrations. The presence of the PEG group improved water solubility by 50-fold compared to the unsubstituted benzopolysulfanes, C6H4Sx (x = 3, 5, and 7), based on intrinsic solubility measurements. Polysulfur linkages in the PEG compounds decomposed in the presence of ethanethiol and hydroxide ion. The PEG pentathiepin desulfurated rapidly and an S3 transfer reaction was observed in the presence of norbornene, no S2 transfer reaction was observed with 2,3-dimethylbutadiene. The antitumor activities of the PEG-substituted benzopolysulfane mixtures were analyzed against four human tumor cell lines PC3 (prostate), DU145 (prostate), MDA-MB-231 (breast), and Jurkat (T-cell leukemia). The PEG conjugated polysulfanes had IC50 values 1.2-5.8 times lower than the parent "unsubstituted" benzopolysulfanes. Complete cell killing was observed for the PEG polysulfanes with 4 µM for PC3 and DU145 cells, and with 12 µM for MDA-MB-231 cells. The results suggest that solubilization of the polysulfur linkage is a key parameter to the success of these compounds as drug leads. A mechanism is proposed for the formation of cyclic 5,6,7,8,9-pentathiabenzoc ycloheptene-1,2-diol, 4, from the reaction of o-benzoquinone with reduced elemental sulfur, H2Sx. 1,6-Conjugate addition to the quinone is favored over 1,4-conjugate addition. Hydrogen bonding to the quinone oxygen enhances the nucleophilicity of H2Sx by facilitating the removal of the S-H proton. We propose that initially formed 3-polysulfidobenzene-diol intermediates, 5, are oxidized to their corresponding quinones, 13, and closure of the polysulfur ring subsequently takes place at the C3-C4 bond leading to 4. A possible mechanism for the formation of pentasulfur linkage in 4 is discussed, which the key moiety is found in a number of natural products.