SUGAR ALCOHOLS: A NOVEL PLATFORM FOR FUNCTIONAL MOLECULAR GELS
Year of Dissertation:
2012
The rise in interest in molecular gels is evident from the ample variety of molecular gelators (MGrs) being developed for diverse applications, ranging from medicinal to electronic devices. MGrs, typically amphiphiles, exhibit high biocompatibility and biodegradability, accounting for their emergence as potential successors to polymeric gelators. However, most of these gelators have been discovered serendipitously. Therefore there is a strong impetus to probe: (i) the process of gelation; and (ii) structural requirements for a molecule to be a successful gelator. Such systematic investigation rationalizes the relationship between the gelator structure and properties of gels. In this research work, this challenge is addressed for a new class of gelators: sugar alcohol-fatty acid conjugates.
Synthesis, Characterization and Chemistry of Platinum and Iridium Nanoparticles in Solution and Nanoporous Silicas
Year of Dissertation:
2012
This project focuses on the synthesis of catalytically-active, transition-metal nanoparticles, their adsorption into porous Vycor glass (PVG), the removal of the poly(vinylpyrrolidone) (PVP) surfactant employed in their synthesis and their chemistry with Ru(II) diimine complexes. Platinum and iridium nanoparticles with a narrow size distribution were prepared by the alcohol reduction method with poly(vinylpyrrolidone) (PVP) as the size limiting surfactant. PVP/Pt nanoparticles adsorb into PVG and as much as 46 ± 4% of the PVP can be removed without further nanoparticle aggregation. XANES spectra show that removal of the PVP surfactant occurs without oxidation of the Pt nanoparticle. EXAFS of the adsorbed Pt nanoparticles after removal of the PVP yield a Pt-Pt bond length of 2.74 ± 0.01 Å which is slightly shorter than the Pt-Pt bond length measured in Pt foil, 2.78 Å. We have shown that the Pt nanoparticles, both the stripped and the unstripped of PVP in porous Vycor glass, does not influence their reactivity with either the [Ru(bpy)2dpp]2+ or the [Ru(bpy)2ppz]2+ complexes.
EUROPIUM REDUCTION AND LANTHANIDE COORDINATION IN POLYOXOMETALATES
Year of Dissertation:
2010
Polyoxometalates (POMs) are a unique class of metal-oxygen cluster anions in which the early transition metals are in their highest oxidation states. POMs have applications in quite diverse disciplines including catalysis, medicine and material sciences, many of which are based upon their reduction-oxidation (redox) properties. The variation of metal coordination environments and metal-oxygen framework architectures influences redox properties of POMs, and the extent of that influence depends on the nature of the incorporated metal ion. When combined with lanthanide (Ln) ions, Ln-POMs form new structures, exhibit catalytic properties, and offer unique functionality, such as the creation of luminescent and Lewis acid catalytic centers. Because of this, Ln-POM derivatives have attracted increasing attention in recent years.
New Materials for Supramolecular Nanoscale Devices
Year of Dissertation:
2013
The projects reported here seek to employ the very small - molecules, nanoparticles, films of materials far thinner than a human hair - to create diverse useful systems. We have focused our attention of a class of molecules which strongly absorb light and can be induced to interact with other materials to create devices which can harvest the energy in sunlight, change the way they respond to external stimulus based on the way they are being illuminated, and hopefully in the future make electronic devices more efficient, sustainable, smaller and broadly better.
RADICAL FORMATION AND FUNCTIONS IN MYCOBACTERIUM TUBERCULOSIS CATALASE-PEROXIDASE (KatG) AND IN CRYPTOCOCCUS NEOFORMANS MELANIN
Year of Dissertation:
2012
Advisor:
Richard Magliozzo
The dual-function heme enzyme catalase-peroxidase, KatG, is found in many microorganisms but in the human pathogen M. tuberculosis it is the only catalase (2H2O2 → O2 + 2H2O) and plays an important role in protecting this organism against oxidative stress. The structural and functional origins of its high catalase activity are therefore of special interest. KatG also exhibits a broad-spectrum peroxidase activity (ROOH + 2AH → 2ROH + 2A·) and in M. tuberculosis it is responsible for peroxidative activation of the pro-drug isoniazid used to treat tuberculosis infection.
SYNTHESIS AND CHARACTERIZATION OF CARBON NANOFILMS FOR CHEMICAL SENSING
Year of Dissertation:
2012
Advisor:
Alexander Zaitsev
Carbon nanofilms obtained by high temperature graphitization of diamond surface in inert atmospheres or vacuum are modified by treatment in plasma of different precursor gases. At temperatures above 1000 oC, a stable conductive film of thickness between 10 - 100 nm and specific resistivity 10-3-10-4 ohm.m, depending upon the heating conditions and the growth atmosphere, is formed on diamond surface. A gray, thin film of high surface resistivity is obtained in high vacuum, while at low vacuum (below 10-4 mbar), a thick black film of low surface resistivity forms. It is observed that the exposure to plasma reduces the surface conductance of carbon nanofilms as result of a partial removal of carbon and the plasma-stimulated amorphization. The rate of the reduction of conductance and hence the etching ability of plasma depends on the type of precursor gas. Hydrogen reveals the strongest etching ability, followed by oxygen and argon, whereas SF6 is ineffective. The carbon nanofilms show significant sensitivity of their electrical conductance to temperature and exposure to the vapors of common organic compounds. The oxygen plasma treated films exhibit selective response to acetone and water vapors. The fast response and recovery of the conductance are the features of the carbon nanofilms. The plasma-treated carbon nanofilm on graphitized diamond surface is discussed as a promising sensing material for development of all-carbon chemical sensors, which may be suitable for biological and medical applications.
Strategies Towards Modular Syntheses of Fluorocarbons
Year of Dissertation:
2012
Synthesis of TMS-protected fluoropropargyl benzothiazolyl sulfone, a bifunctional fluoro-Julia-Kocienski reagent, was achieved by metalation-electrophilic fluorination of benzothiazolyl propargyl sulfone. Reactions of the fluoro-Julia-Kocienski reagent with carbonyl compounds produced fluoroenynes in high yields and with high E-selectivity. Olefinations proceeded with LHMDS, or the milder base, DBU. A one-pot deprotection-copper-catalyzed azide alkyne cycloaddition (CuAAC) to the alkyne moiety in the Julia-Kocienski reagent provided a new class of triazole-derived fluorinated and unfluorinated Julia-Kocienski reagents. Competitive experiments showed higher reactivity of the fluorinated reagent in the CuAAC than the protio analog. Computational analysis of electron densities in fluoro and protio propargyl sulfones showed that fluorine lowers electron density at the terminal alkynyl carbon, which can contribute to its higher reactivity. These triazole-derived "second generation" Julia-Kocienski reagents reacted smoothly with aldehydes and ketones, and olefinations could be tuned towards E- or Z-stereoselectivity by change in reaction conditions. The CuAAC-Julia olefination sequence was also used for the synthesis of triazole-derived analogs of biologically relevant combretastatin A-4. Biological testing of these compounds against HeLa cancer cell lines showed that two analogs displayed modest activity.
Synthesis of Analogs of Sphingophospholipids, Glycolipids, and Plasmalogen
Year of Dissertation:
2009
This dissertation presents the asymmetric syntheses of naturally occurring sphingoid bases and novel sphingolipid analogs, including (a) an unnatural sphingomyelin with a Δ4-cis double bond in the long-chain base (cis-SM), (b) L-threo-β-glucosyl and galactosyl-ceramides, (c) a photoactivatable analog of β-galactosyl sphingosine (psychosine), and (d) caged sphingosine 1-phosphate and ceramide 1-phosphate analogs. Also included in this dissertation is a novel synthesis of an unnatural analog of the glycerophospholipid plasmalogen with a trans-O-vinyl ether linkage at the sn-1 position of the glycerol backbone.
SYNTHESIS AND STRUCTURAL MODIFICATION OF THE MDMA ANTAGONIST NANTENINE: A NATURALLY OCCURRING APORPHINE ALKALOID
Year of Dissertation:
2010
MDMA ("Ecstasy") is a synthetic phenethylamine stimulant which is known to affect the re-uptake of serotonin, dopamine and nor-epinephrine in the brain. Adverse effects of "Ecstasy" in humans include development of hyperthermia, hallucinations, organ failure and in extreme cases, death. There is evidence that the behavioral and physiological effects of MDMA are mediated by α1-adrenergic and 5-HT2A receptors. Nantenine is a naturally occurring aporphine alkaloid which has been shown to block and reverse behavioral and physiological effects of MDMA in mice via antagonism of the aforementioned receptors. However, the relative role of these receptors in mediating the MDMA antagonizing effects of nantenine in vivo is unknown.
Atomic and Molecular Low-n Rydberg States in Supercritical Fluids
Year of Dissertation:
2009
The structure of low-n Rydberg states doped into supercritical fluids represents an important probe to investigate solvation effects, especially near the solvent (or perturber) critical point. We have investigated the solvation of excited atomic and molecular dopants in various perturbing fluids (both atomic and molecular). This systematic study was performed from low perturber number densities to the density of the triple point liquid, at both non-critical temperatures and on an isotherm near the critical isotherm. Dopant low-n Rydberg states were investigated using vacuum ultraviolet photoabsorption spectroscopy. The absorption spectra of these states were then simulated using a semi-classical statistical line shape function. With accurate line shape simulations, the perturber induced energy shift of the primary transition was obtained using a standard moment analysis.