Alumni Dissertations

 

Alumni Dissertations

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  • FACTORS AFFECTING THE REMOVAL OF AMMONIA FROM AIR ON CARBONACEOUS ADSORBENTS: INVESTIGATION OF REACTIVE ADSORPTION MECHANISM

    Author:
    Camille Petit
    Year of Dissertation:
    2011
    Program:
    Chemistry
    Advisor:
    Teresa Bandosz
    Abstract:

    Air pollution related to the release of industrial toxic gases, represents one of the main concerns of our modern world owing to its detrimental effect on the environment. To tackle this growing issue, efficient ways to reduce/control the release of pollutants are required. Adsorption of gases on porous materials appears as a potential solution. However, the physisorption of small molecules of gases such as ammonia is limited at ambient conditions. For their removal, adsorbents providing strong adsorption forces must be used/developed. In this study, new carbon-based materials are prepared and tested for ammonia adsorption at ambient conditions. Characterization of the adsorbents' texture and surface chemistry is performed before and after exposure to ammonia to identify the features responsible for high adsorption capacity and for controlling the mechanisms of retention. The characterization techniques include: nitrogen adsorption, thermal analysis, potentiometric titration, FT-IR spectroscopy, X-ray diffraction, Energy Dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Electron Microscopy. The results obtained indicate that ammonia removal is governed by the adsorbent's surface chemistry. On the contrary, porosity (and thus physisorption) plays a secondary role in this process, unless strong dispersive forces are provided by the adsorbent. The surface chemistry features responsible for the enhanced ammonia adsorption include the presence of oxygen- (carboxyl, hydroxyl, epoxy) and sulfur- (sulfonic) containing groups. Metallic species improve the breakthrough capacity as well as they lead to the formation of Lewis acid-base interactions, hydrogen-bonding or complexation. In addition to the latter three mechanisms, ammonia is retained on the adsorbent surface via Brønsted acid-base interactions or via specific reactions with the adsorbent's functionalities leading to the incorporation of ammonia into the adsorbent's matrix. Another mechanism involves dissolution of ammonia in water when moisture is present in the system. Even though this process increases the breakthrough capacity of a material, it provides rather weak retention forces since ammonia dissolved in water is easily desorbed from the adsorbent's surface.

  • PEPTIDE NANOTUBES AND THE EXPERIMENTAL DESIGN INTEGRATING NANOPARTICLES FOR USE IN NANOELECTRONICS

    Author:
    Precila Porrata
    Year of Dissertation:
    2009
    Program:
    Chemistry
    Advisor:
    Hiroshi Matsui
    Abstract:

    Scientists have just begun to explore the world of nanotechnology, as instruments become more sophisticated areas previously unable to be seen or probed can now be studied. Peptide nanotubes are often used in experiments since they are extremely versatile. They are nontoxic, self-assembled, they have available functional groups in order to bind to other compounds and the tubule structure allows for the exclusivity of inside or outside binding. The ability of the peptide tubes to bind to other compounds permits biomineralization and additionally creates an atmosphere of selective binding to desired locations. The importance in using peptide nanotubes for study becomes the ability to rely on consistency of the shape and size. Ph factors can regulate whether a tubule or sheet is formed in solution, while controlling the diameter has been achieved through the use of various membranes, such as polycarbonate and alumina oxide. One of the main goals in nanotechnology is the ability to create functional machines of decreased size, improved storage capacity and faster cooler electrical components, therefore, making peptide nanotubes with electrical properties is of extreme interest. This dissertation takes a look at the properties of peptides coated with FePt and Pt.

  • PEPTIDE NANOTUBES AND THE EXPERIMENTAL DESIGN INTEGRATING NANOPARTICLES FOR USE IN NANOELECTRONICS

    Author:
    Precila Porrata
    Year of Dissertation:
    2009
    Program:
    Chemistry
    Advisor:
    Hiroshi Matsui
    Abstract:

    Scientists have just begun to explore the world of nanotechnology, as instruments become more sophisticated areas previously unable to be seen or probed can now be studied. Peptide nanotubes are often used in experiments since they are extremely versatile. They are nontoxic, self-assembled, they have available functional groups in order to bind to other compounds and the tubule structure allows for the exclusivity of inside or outside binding. The ability of the peptide tubes to bind to other compounds permits biomineralization and additionally creates an atmosphere of selective binding to desired locations. The importance in using peptide nanotubes for study becomes the ability to rely on consistency of the shape and size. Ph factors can regulate whether a tubule or sheet is formed in solution, while controlling the diameter has been achieved through the use of various membranes, such as polycarbonate and alumina oxide. One of the main goals in nanotechnology is the ability to create functional machines of decreased size, improved storage capacity and faster cooler electrical components, therefore, making peptide nanotubes with electrical properties is of extreme interest. This dissertation takes a look at the properties of peptides coated with FePt and Pt.

  • SELF-ORGANIZED PORPHYRIN NANOMATERIALS FOR SOLAR ENERGY HARVESTING

    Author:
    Ivana Radivojevic
    Year of Dissertation:
    2010
    Program:
    Chemistry
    Advisor:
    Charles Drain
    Abstract:

    New concepts in the design and function of organic dyes as sensitizers for solar energy harvesting are needed. Commercial viability constrains these designs: (a) cost effective synthesis, (b) long-term stability, and (c) an important goal is to reduce the environmental impact of the product at the end of its life cycle. Simple porphyrinoid dyes meet these constraints, but new modes of incorporation into devices are needed to increase the efficiency of charge separation that drives any photonic device designed to harvest light. In this thesis, we will show how complex material architectures on surfaces need not to be the result of complex molecular structures or strong intermolecular forces that form in solution and deposit intact onto surfaces. Varying environmental conditions we can dictate morphology of self-organized structures on surfaces. These studies provide further insights into the design principles, processing, and extent of electron and energy transfer in supramolecular porphyrin materials. We are also developing a new strategy to couple porphyrinoid dyes to oxide surfaces using hafnium and zirconium metalloporphyrins and metallophthalocyanines. The mode of dye attachment to oxide surfaces is a key parameter for the construction of efficient dye sensitized solar cells. Porphyrinoid dyes containing oxophylic group (IV) metal ions that protrude from on face of the macrocycle allow connections directly to oxide surfaces, wherein the metal ion serves as the conduit. Since the charge transport efficiency is mediated by appropriate matching of molecular HOMO-LUMO gaps to semiconductor band gaps, we will show characterized solution phase ground and excited redox potentials of these dyes, and also photophysical properties of dye excited state using transient absorbance spectroscopy.

  • SELF-ORGANIZED PORPHYRIN NANOMATERIALS FOR SOLAR ENERGY HARVESTING

    Author:
    Ivana Radivojevic
    Year of Dissertation:
    2010
    Program:
    Chemistry
    Advisor:
    Charles Drain
    Abstract:

    New concepts in the design and function of organic dyes as sensitizers for solar energy harvesting are needed. Commercial viability constrains these designs: (a) cost effective synthesis, (b) long-term stability, and (c) an important goal is to reduce the environmental impact of the product at the end of its life cycle. Simple porphyrinoid dyes meet these constraints, but new modes of incorporation into devices are needed to increase the efficiency of charge separation that drives any photonic device designed to harvest light. In this thesis, we will show how complex material architectures on surfaces need not to be the result of complex molecular structures or strong intermolecular forces that form in solution and deposit intact onto surfaces. Varying environmental conditions we can dictate morphology of self-organized structures on surfaces. These studies provide further insights into the design principles, processing, and extent of electron and energy transfer in supramolecular porphyrin materials. We are also developing a new strategy to couple porphyrinoid dyes to oxide surfaces using hafnium and zirconium metalloporphyrins and metallophthalocyanines. The mode of dye attachment to oxide surfaces is a key parameter for the construction of efficient dye sensitized solar cells. Porphyrinoid dyes containing oxophylic group (IV) metal ions that protrude from on face of the macrocycle allow connections directly to oxide surfaces, wherein the metal ion serves as the conduit. Since the charge transport efficiency is mediated by appropriate matching of molecular HOMO-LUMO gaps to semiconductor band gaps, we will show characterized solution phase ground and excited redox potentials of these dyes, and also photophysical properties of dye excited state using transient absorbance spectroscopy.

  • Metal Nanoparticles Immobilized on Basic Supports as Catalysts for Hydrogenation and Dehydrogenation Reactions of Relevance to Cleaner Fossil Fuels and Alternative Sources of Energy

    Author:
    Reena Rahi
    Year of Dissertation:
    2014
    Program:
    Chemistry
    Advisor:
    Roberto Sanchez-Delgado
    Abstract:

    We developed a series of catalysts, composed of metal nanoparticles immobilized on basic supports for the hydrogenation of heteroaromatics of relevance to cleaner fossil fuels and biodiesel, and for the dehydrogenation of heteroaromatics of relevance to hydrogen storage in organic liquids. Our catalyst design involves nanostructured catalysts composed of metal particles immobilized on basic supports capable of ionic mechanism that may avoid catalyst poisoning and enhance catalytic activity. We prepared a new catalyst composed of Pd nanoparticles immobilized on MgO by NaBH4 reduction of Na2PdCl4 in methanol in the presence of the support. TEM measurements revealed well-dispersed 1.7 nm Pd particles attached to MgO, also characterized by XPS, XRD and hydrogen pulse chemisorption measurements. The new catalyst is efficient for the hydrogenation of the heterocyclic ring of quinolines, as well as for the mild reduction of a variety of alkenes representative of fuel components, and the partial saturation of biodiesel. In the second part, we switched our attention to ruthenium nanoparticles, with the aim of achieving higher activity and broader reactivity, supported on functionalized carbon nanotubes, of higher surface area. Our second catalyst was prepared by first attaching pyridine groups to the surface of the nanotubes, and then depositing the metal particles by NaBH4 reduction of RuCl3.3H2O. TEM, XRD and XPS analysis indicate the presence of 1.7 nm Ru(0) particles attached mainly to the surface of the nanotubes. The Ru/py-CNTs results in an unprecedentedly high activity for the selective hydrogenation of N-heteroaromatic compounds, with respect to other reported systems. The activity of this catalyst was extended also to plain aromatic compounds under mild conditions and to the challenging S-heteroaromatics under more forcing conditions. Lastly, we evaluated the efficacy of the catalyst for the dehydrogenation of 1,2,3,4-tetrahydroquinoline, which was achieved with reasonable turnover frequencies under moderate conditions. The hydrogenation/dehydrogenation reactions thus establish a cyclic process of possible utility in hydrogen storage in organic liquids. We screened other substrate pairs that may be adequate for hydrogen storage, by computational study of the thermodynamics of dehydrogenation, which allowed us to identify other N-heterocycles that may prove useful in future studies.

  • New Ruthenium (II)-Chloroquine Complexes and Metal-Free Aminoquinolines: Synthesis, Antimalarial Activity and Mechanism of Biological Activity

    Author:
    Chandima Rajapakse
    Year of Dissertation:
    2010
    Program:
    Chemistry
    Advisor:
    Roberto Sanchez-Delgado
    Abstract:

    New Ruthenium (II)-Chloroquine Complexes and Metal-Free Aminoquinolines: Synthesis, Antimalarial Activity and Mechanism of Biological Action by Chandima S. K. Rajapakse Advisor - Professor Roberto A. Sanchez-Delgado Malaria is widespread in many tropical and subtropical regions and causes between one and three million deaths annually. The disease is caused by a protozoan parasite of the genus Plasmodium that is transmitted primarily by the female Anopheles mosquito. Chloroquine (CQ) is the most commonly used antimalarial drug, but resistant strains of P. falciparum have emerged and thus improved chemotherapies are required. Modifications of the molecular structure of chloroquine led to other effective quinoline based drugs but unfortunately, resistance to these drugs is now also common in many parts of the world. The success of cisplatin and other platinum anticancer drugs has stimulated a renaissance of inorganic medicinal chemistry and the search for complexes of other transition metals with better biological properties. Among them, ruthenium complexes are attracting increasing attention as potential chemotherapeutic agents against a variety of diseases. Complexation of CQ to Ru has been previously shown by our group to enhance the activity against resistant strains of the malaria parasite, as for instance the complex [RuCl2(CQ)]2. In the first phase of this thesis we adopted a molecular design based on Ru(II) forming coordinate bonds to CQ through one of the basic nitrogen atoms. A series of new organo-RuII-CQ complexes were synthesized and characterized by use of a combination of NMR and FTIR spectroscopy with DFT calculations. All the new complexes were active against CQ-resistant (Dd2, K1, and W2) and CQ sensitive (FcB1, PFB, F32 and 3D7) malaria parasites (Plasmodium falciparum); importantly, the potency of these complexes against resistant parasites is consistently higher than that of the standard drug chloroquine diphosphate (CQDP). In order to understand the origin of the improved antimalarial activity, we have measured water/n-octanol partition coefficients, pKa values, heme binding constants, and heme aggregation inhibition activity of the new (π-arene)-Ru-CQ complexes. Measurements of heme aggregation inhibition activity of the metal complexes atq water/n-octanol interfaces qualitatively predict their superior antiplasmodial action against resistant parasites, in relation to CQ. Some interesting tendencies emerge from our data, indicating that the antiplasmodial activity is related to a balance of effects associated with the lipophilicity, basicity, and structural details of the compounds studied. We concluded that the increase in the lipophilicity of CQ caused by coordination to the Ru-containing fragments is beneficial for overcoming resistance but the reduction in basicity due to the blocking of one active nitrogen atom by the metal limits the therapeutic potential of the complexes. Therefore, new compounds combining the desired basicity and lipophilicity are needed. Based on this new model, two new metal free 4-aminoquinoline derivatives were synthesized and characterized by 1D/2D NMR spectroscopy, elemental analysis and mass spectrometry. Both compounds are highly active in vitro against CQ-resistant strains of P. falciparum (K1, K14 and Dd2) as well as a CQ-sensitive strain (D6). Both compounds are more basic and more lipophilic than the standard drug CQ. Our mechanistic studies demonstrate the validity of our hypothesis: that the structural and physicochemical modifications of 4-aminoquinoline imposed by the presence of the lipophilic substituent as a side chain lead to an enhanced activity against malaria parasites, while retaining heme aggregation as the main target of action.

  • De Novo Designed Safranine Enzymes

    Author:
    Gheevarghese Raju
    Year of Dissertation:
    2012
    Program:
    Chemistry
    Advisor:
    Ronald Koder
    Abstract:

    ABSTRACT DE NOVO DESIGNED SAFRANINE ENZYMES by Gheevarghese Raju Advisor: Professor Ronald L. Koder De novo designed safranine enzymes are functionally parallel to NAD(P)H: flavinnitroreductases. The non-natural redox cofactor safranine has a very low reduction potential, -290 mV versus flavins -190 mV. A difference of 100 mV provides an additional 2.3 Kcal/mol energy to drive reduction reactions. Also safranine has an intrinsic unstable semiquinone oxidation state providing a doorstep for hydride transfer mechanism. Hence safranine enzymes will perform the electron transfer reaction, which is similar to the natural nitroreductases avoiding all oxygen activating free-radical side reactions. We designed a whole series of safranine binding helical bundles which catalyzes NAD(P)H dependent nitroaromatic reduction. Latest studied saf-X and safX-Loop proteins hold promise towards fully functional artificial enzymes. A novel synthesis pathway of generating different safranine derivatives was developed. These derivatives differ in their characteristic reduction potentials, fluorescent and visible spectra. This will allow the amendment of reduction reaction towards any particular nitroaromatic substrate. Our goal is to create artificial safranine enzymes, which can be used for cancer prodrug activation, treatment of atherosclerosis, explosive sensing, biofuels as well as green chemical catalysis.

  • DESIGN AND SYNTHESIS OF SQUARAMIDE -BASED MOLECULAR MACHINES

    Author:
    Vijayakumar Ramalingam
    Year of Dissertation:
    2009
    Program:
    Chemistry
    Advisor:
    Prof. Rajeev Muthyala
    Abstract:

    Artificial molecular machines are sought after in a wide variety of fields. They are useful in the construction of nanodevices (molecular valves, brakes, nanocars, rotors and ratchets), for ion transport and also for optical data storage. In an effort to develop new ion-transportand drug delivery strategies we became interested in designing molecular machines based on amide derivatives of squaric acid (squaramides). In this study, we first determined that secondary diaryl squaramides, which exist in the extended ZZ conformation, are excellent neutral receptors for biologically important anions such as chloride, carboxylate, and dihydrogen monophosphate. Next, we envisioned a molecular valve approach to regulate anion binding to squaramides via changes in the external environment (for example, a change in solvent polarity). We reasoned that in non-polar solvents, intramolecular hydrogen bonding between the carbonyl groups and the squaramide NHs would block anion binding (OFF state) while in a polar solvent disruption of intramolecular hydrogen bonding and reorientation of the carbonyl allows anion binding (ON state). Using ortho benzoyl substituted squaramides, we successfully applied the molecular valve approach to chloride binding. We subsequently studied the generality of the molecular valve approach with other ortho substituents such as secondary and tertiary amides, esters, and nitro groups. We found that the success of the molecular valve approach depends on whether, in a given solvent, intra-molecular hydrogen bonding is stronger or weaker relative to intermolecular hydrogen bonding with chloride ion. A significant effort was also spent on developing tertiary squaramide-based molecular machines for drug delivery. Initial studies revealed that simple (for example, N, N'-dimethyl derivatives) tertiary diaryl squaramide exhibited a preference for folded EE conformation regardless of solvent polarity. For our goal of transforming these squaramides to functional molecular machines, we decided to exploit the hydrophobic effect. In nonpolar solvents we anticipated that the tertiary squaramides would exhibit a preference for EE conformation while in aqueous medium we reasoned that the conformation would switch to ZZ driven by the hydrophobic effect. However we soon experienced major synthetic challenges. The literature procedures for the synthesis of these tertiary aryl squaramides routinely resulted in low yields with significant squaraine impurities. We therefore developed a novel copper-based method to synthesize symmetrical tertiary diaryl squaramides. Importantly, this method also enabled synthesis of unsymmetrical tertiary diaryl squaramides. Syntheses, conformational preferences, and our attempts at developing hydrophobically driven molecular machines will also be discussed in this dissertation.

  • DESIGN AND SYNTHESIS OF SQUARAMIDE -BASED MOLECULAR MACHINES

    Author:
    Vijayakumar Ramalingam
    Year of Dissertation:
    2009
    Program:
    Chemistry
    Advisor:
    Prof. Rajeev Muthyala
    Abstract:

    Artificial molecular machines are sought after in a wide variety of fields. They are useful in the construction of nanodevices (molecular valves, brakes, nanocars, rotors and ratchets), for ion transport and also for optical data storage. In an effort to develop new ion-transportand drug delivery strategies we became interested in designing molecular machines based on amide derivatives of squaric acid (squaramides). In this study, we first determined that secondary diaryl squaramides, which exist in the extended ZZ conformation, are excellent neutral receptors for biologically important anions such as chloride, carboxylate, and dihydrogen monophosphate. Next, we envisioned a molecular valve approach to regulate anion binding to squaramides via changes in the external environment (for example, a change in solvent polarity). We reasoned that in non-polar solvents, intramolecular hydrogen bonding between the carbonyl groups and the squaramide NHs would block anion binding (OFF state) while in a polar solvent disruption of intramolecular hydrogen bonding and reorientation of the carbonyl allows anion binding (ON state). Using ortho benzoyl substituted squaramides, we successfully applied the molecular valve approach to chloride binding. We subsequently studied the generality of the molecular valve approach with other ortho substituents such as secondary and tertiary amides, esters, and nitro groups. We found that the success of the molecular valve approach depends on whether, in a given solvent, intra-molecular hydrogen bonding is stronger or weaker relative to intermolecular hydrogen bonding with chloride ion. A significant effort was also spent on developing tertiary squaramide-based molecular machines for drug delivery. Initial studies revealed that simple (for example, N, N'-dimethyl derivatives) tertiary diaryl squaramide exhibited a preference for folded EE conformation regardless of solvent polarity. For our goal of transforming these squaramides to functional molecular machines, we decided to exploit the hydrophobic effect. In nonpolar solvents we anticipated that the tertiary squaramides would exhibit a preference for EE conformation while in aqueous medium we reasoned that the conformation would switch to ZZ driven by the hydrophobic effect. However we soon experienced major synthetic challenges. The literature procedures for the synthesis of these tertiary aryl squaramides routinely resulted in low yields with significant squaraine impurities. We therefore developed a novel copper-based method to synthesize symmetrical tertiary diaryl squaramides. Importantly, this method also enabled synthesis of unsymmetrical tertiary diaryl squaramides. Syntheses, conformational preferences, and our attempts at developing hydrophobically driven molecular machines will also be discussed in this dissertation.