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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

I. Studies Towards the Synthesis of Manassantins A and B and Analogues II. Efforts Towards a FRET-Based Assay to Characterize Palmitoylation of Src Kinases III. Synthesis of Oxepanes via Organocatalytic Oxa-Michael Reactions

Kasper, Amanda Clare January 2010 (has links)
<p>This dissertation focuses on three main projects that include aspects of natural product synthesis, synthetic methodology, as well as the development of a small molecular probe for the study of protein palmitoylation. This first project introduces studies towards the synthesis of manassantins A and B which are potent inhibitors of hypoxia-inducible factor 1 (HIF-1). In addition, the preparation of manassantin A analogues is described along with preliminary structure-activity relationship (SAR) studies providing further insight into the structural requirements for HIF-1 inhibitory activity. The second project describes efforts towards the development of a fluorescence resonance energy transfer (FRET)-based assay system to characterize the palmitoylation of oncogenic Src family kinases. The initial work on this project involves the synthesis of a modified lipopeptide mimicking the critical N-terminus sequence of Src signaling proteins required for activation. Lastly, the third project focuses on the development of an asymmetric organocatalytic method to synthesize 2,7-cis- and 2,7-trans oxepanes as well as its application to the preparation of a simple cyclic ether. Ultimately, the goal of this work would be to extend this methodology to the preparation of complex, biologically active cyclic ethers.</p> / Dissertation
2

INVESTIGATION OF ADSORPTION, REACTION AND CONFINEMENT OF MOLECULES IN SINGLE WALL CARBON NANOTUBES

Byl, Oleg 17 March 2006 (has links)
Adsorption of simple molecules (CF4, Xe, CO2, NO and H2O) inside single wall carbon nanotubes has been investigated by means of infrared spectroscopy. It was demonstrated that confinement has a profound effect of the IR spectra of the internally adsorbed species. The spectral changes relate to the enhanced binding of the adsorbates to the nanotube interior walls and to the spatial limitations that prohibit formation of bulk-like structures. It was found that CF4 exhibits a 15 cm-1 redshift in its í3 symmetric stretching mode when adsorbed on the exterior surface of closed SWNTs. Adsorption on the nanotube is accompanied by adsorption in the interior in the case of opened SWNTs and the í3 mode is redshifted 35 cm-1. In addition it was shown that confined CF4 does not exhibit LO-TO splitting observed in the bulk phase. Physisorption of NO inside of carbon nanotubes results in cis-(NO)2 dimer formation for almost all adsorbed NO, indicating that confinement shifts the equilibrium according to Le Chatelier's Principle. In all cases Xe was used as a displacing agent to verify the internal adsorption. It was shown that Xe preferentially adsorbs inside nanotube displacing high coverage CF4 molecules. The externally bound adsorbates do not form a full monolayer and therefore Xe adsorbs non-competitively on empty external sites. Confinement of H2O in the nanotube interior leads to appearance of a sharp mode at 3507 cm-1 that is indicative of a weaker hydrogen bond relative to hydrogen bonding in bulk ice. Molecular simulations show that the confined water forms stacked ring structures with bulk-like intra-ring and weaker inter-ring hydrogen bonds. The spectroscopy studies of adsorption in nanotubes were accompanied by nitrogen volumetric adsorption studies of bulk nanotubes. It was demonstrated that n-nonane can be utilized as a nanotube interior blocking agent. The oxidation of SWNTs by ozone, followed by heating to remove oxidized carbon atoms as carbon oxides occurs preferentially on the outer surface of bulk samples of nanotubes. The high surface reactivity of O3 at the outer surface of a bulk nanotube sample causes this effect. It was found that CF4 exhibits a 15 cm-1 redshift in its í3 symmetric stretching mode when adsorbed on the exterior surface of closed SWNTs. Adsorption on the nanotube is accompanied by adsorption in the interior in the case of opened SWNTs and the í3 mode is redshifted 35 cm-1. In addition it was shown that confined CF4 does not exhibit LO-TO splitting observed in the bulk phase. Physisorption of NO inside of carbon nanotubes results in cis-(NO)2 dimer formation for almost all adsorbed NO, indicating that confinement shifts the equilibrium according to Le Chatelier's Principle. In all cases Xe was used as a displacing agent to verify the internal adsorption. It was shown that Xe preferentially adsorbs inside nanotube displacing high coverage CF4 molecules. The externally bound adsorbates do not form a full monolayer and therefore Xe adsorbs noncompetitively on empty external sites.
3

Modeling Organorhodium Catalysis

Bayden, Alexander S 16 March 2006 (has links)
The first project considered in this dissertation was the improvement of an existing global optimization algorithm that uses extended dimensionality to find global minima of Lennard-Jones clusters. The speed of this algorithm was increased by three orders of magnitude, primarily by improving the algorithm for compressing the system from 4D to 3D at constant energy. The second project was modeling the adsorption of H2 molecules on the Si(100) surface using density functional theory (DFT) with the PW91 functional. Consistent with the experiments, the calculations predicted an energetic preference for clustering of occupied sites in a dimer row. However, our calculations did not verify the unbuckling induced by H2 adsorption reported by Buehler and Boland. The third project was modeling molybdenum and rhodium-catalyzed [2 + 2 + 1] cycloisomerization reaction using DFT with the B3LYP functional. We found that in the rhodium-catalyzed [2 + 2 + 1] cycloisomerization reactions of allenes the oxidative addition step determined both the rate and the product of the reaction. For the molybdenum-catalyzed reaction the rate was controlled not by oxidative addition, but by the next step, the attachment of a carbon monoxide molecule from the media to the molybdenum atom. The fourth project was modeling the transfer of hydrogen from one side of the heterocyclic ring to another in rhodium(I) catalyzed allenic Pauson-Khand type reactions. Our calculations showed that this process occurs after the cyclization step. We have also discovered a novel mechanism for this process - hydride transfer; however, we believe that in most cases the reaction proceeds by beta-hydride elimination.
4

The Development of an Electron Transfer Initiated Cyclization Approach Toward the Total Synthesis of Mycalamide B. The Synthesis of the N7-C25 Fragment of Psymberin

Rech, Jason Christopher 20 March 2006 (has links)
The electron transfer initiated cyclization (ETIC) has been shown to be an efficient method for the generation of cyclic amido acetals. The tetrahydrofuranyloxy methyl ether was shown to be a stable nucleophilic hemiacetal surrogate allowing for the incorporation of a formaldehyde equivalent in the ETIC reaction. The ETIC reaction was employed in the stereoselective synthesis of amido trioxadecalin systems relevant to the synthesis of the mycalamides, onnamides and theopederins. The stereoselectivity resulting from these cyclizations was controlled by the substituents of the tetrahydropyran ring and the conformational bias of the developing trioxadecalin system. The epimerization of the N-acylaminal center of the amido trioxadecalin system was possible under mildly acidic conditions. An efficient and stereoselective synthetic route has been developed that intends to employ the ETIC reaction to selectively generate the N-acylaminal of mycalamide B. A linear approach to the generation of the right half of mycalamide B has been applied allowing for expedient access to the dimethyl tetrahydropyran core. The synthetic sequence employs an asymmetric Leighton allylation, selective boron mediated aldol, 1,3-syn-reduction, and selective epoxidation and syn-vinylation to establish the stereochemistry of the right hand fragment of mycalamide B. The stereoselective synthesis of the N7-C24 fragment of psymberin was developed. The synthesis is highlighted by the de novo generation of the C25-C17 pentasubstituted arene that allows for the expedient generation of multigram quantities of this intermediate. The stereochemistry of this fragment was established by an asymmetric Brown crotylation and Leighton allylation, selective Mukaiyama aldol addition, 1,3-syn-reduction, and a selective Lewis acid catalyzed TMSCN displacement of an acyl lactol.
5

Structures, charge distributions, and dynamical properties of weakly bound complexes of aromatic molecules in their ground and electronically excited states.

kang, cheolhwa 20 March 2006 (has links)
Complexes or clusters are non-covalently bound assemblies of two or more molecules that are held together by hydrogen bonding, van der Waals interactions, and other weak forces. The derived values of the rotational constants can be used to determine the structures of such species, in both their ground and electronically excited states. Some species exhibit different structures in the two states, owing to photon-induced changes in their electronic distributions. Evidence for the motion of one species relative to another along some intermolecular coordinate also is observed in some cases. We describe the application of these techniques to nitrogen and water complexes of p-difluorobenzene and Ar and water complexes of indole and azaindole, as models of hydrophobic and hydrophilic interactions. These studies have provided detailed information about how the electronic charge distributions of the species interact, how the structures of the individual species are modified when they interact, and how the properties of the complex are different from its component parts.
6

THEORETICAL STUDY OF SOLVATION OF IONS BY ARGON ATOMS

Tsai, Ming-Kang Brad 20 March 2006 (has links)
Gas phase experiments have been used to study the molecular properties of finite systems in order to minimize the environmental perturbations. The measurements conducted in vacuum environment setup the standard reference value of experimental observables which builds up the foundation of non-vacuum scientific researches. The solvents, e.g. noble gas atoms, used in the gas phase experiments play an important role, i.e. cooling down the system temperature in order to approach the 0?K and provide better spectroscopic measurement quality. The binding position of the solvent atoms also impacts the interpretation of the experimental results. The aid from the theoretical studies was limited due to the computational expense. Three projects are shown in this thesis to show the theoretical challenges in studying different complex systems. The first project is a model potential development with the inclusion of electron correlation at quantum chemistry level to study the (H2O)Arn- clusters. The second project is using the ab inito calculations to explain the infrared spectroscopic measurement of Mg+(H2O)Arn clusters. The last project is a study of the complex electronic structure of Fe+(H2O)Arn clustes with using state-of-the-art ab intio methods
7

CHIRALITY TRANSFER IN 5-EXO CYCLIZATIONS OF AXIALLY CHIRAL O-IODOANILIDES

Lapierre, Andre Joseph Benjamin 20 March 2006 (has links)
Stereoselective 5-exo radical and Heck cyclizations of axially chiral o-iodoanilides to enantioenriched oxindoles and dihydroindolones are described. Mechanisms for the transfer of chirality from the atropisomeric anilides to the newly formed stereocenters in the cyclic products are proposed and supported with physical data. Additionally, the N-aryl bond rotation barriers for eight o-iodoanilides are reported. A series of axially chiral N-allyl-o-iodoanilides were cyclized under room temperature radical conditions to dihydroindolones with good to excellent chirality transfer (7497 %). Cyclization rate constant data is presented to rationalize the regioselective preference for N-allyl over N-acryloyl cyclization when an o-methyl group is present. X-ray crystallography was used to assign absolute configurations to a cyclization precursor/product pair. Radical 5-exo cyclizations of axially chiral o-iodoanilides bearing branched, bulky N-substituents are covered. The bulkiness of N-substituents permitted the resolution of a series of novel o-iodoanilides lacking a second ortho substituent. Radical cyclizations of these o-iodoanilides transferred this transient axial chirality into a new stereocenter in the oxindole products with high fidelity (7892 %). The first Heck cyclizations of axially chiral o-iodoanilides with chirality transfer (8489 %) are described. X-ray crystallographic data is presented for one anilide cyclization precursor with studies to elucidate the mechanism of chiral transfer.
8

Extension of ketene-mediated asymmetric methodology

Raelin, Jeremy M 20 March 2006 (has links)
Ketenes are molecules containing a carbonyl group connected to an alkylidene group by way of a double bond (a pi-bond). The electrophilic nature of ketenes at their center, sp-hybridized carbon atom is the origin of many of the chemical transformations availible to these molecules. Previously in the Nelson laboratory, ketenes had been successfully employed in the acyl halide-aldehyde cyclocondensation (AAC) reaction. Both Lewis acid- and Lewis base-catalyzed AAC processes provide access to optically active 3,4-disubstituted-syn-2-oxetanones. The work described herein employs ketene in the Lewis base-catalyzed AAC reaction in an attempt to improve and expand the general utility of this reaction technology. This improved AAC methodology was then applied in the total synthesis of the natural product motuporin. Ketene was subsequently employed in the development of a novel ketene-Claisen rearrangement.
9

HIGH RESOLUTION STUDY OF THE CONFORMATIONAL LANDSCAPE OF BIOMOLECULES IN THE GAS PHASE

Nguyen, Tri 30 March 2006 (has links)
Rotationally resolved electronic spectroscopy has been used to map the conformational landscape of isolated biomolecules in the gas phase. A multivariate analysis based on experimental measurements supplemented by ab initio calculations provides a detailed description of the low energy regions of the potential energy surface (PES) in both the ground and excited states. Our findings lead to interesting insights into the interactive forces shaping the contours of the PES and the dynamics of interconversion pathways. A novel perspective centered on the electron distribution is presented to address the issue of the correlation of shape and functionality.
10

Rotationally Resolved Electronic Spectra of 1-Methoxynaphthalene in the Gas Phase

Hong, Seung-hoon 20 March 2006 (has links)
Rotationally resolved fluorescence excitation spectra of the band of the S1]S0 transition of 1-methoxynaphthalene have been observed using a high resolution laser spectrometer operating in the ultraviolet. The trans-1-methoxynaphthalene band is an ab hybrid band with 38% a-type character and 62% b-type character. The band origin is at 31671.7 cm-1, and the rotational constants are A" = 1643.98, B" = 832.62 and, C" = 554.83 MHz in the ground state, and A' = 1626.6, B' = 818.5, and C'= 546.6 MHz in the excited state. Two other bands at +16 and ¡V70 cm-1 from the origin band of trans-1-methoxynaphthalene exhibit a band head shape. The possibility of a perpendicular conformer as being the source of these bands is discussed.

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