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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

Synthesis, RNA Binding and Antibacterial Studies of 2-DOS Mimetics AND Development of Polymer Supported Nanoparticle Catalysts for Nitroarene and Azide Reduction

Udumula, Venkata Reddy 01 June 2015 (has links)
Project I 2-Deoxystreptamine (2-DOS), the most conserved central scaffold of aminoglycosides, is known to specifically recognize the 5'-GU-'3 sequence step through highly conserved hydrogen bonds and electrostatic interactions within and without the context of aminoglycosides (Figure 1a). We proposed that a novel monomeric unnatural amino acid building block using 2-DOS as a template would allow us to develop RNA binding molecules with higher affinity and selectivity than those currently available. Conjugating two or more of the monomeric building blocks by an amide bond would introduce extra hydrogen bonding donors and acceptors that are absent in natural aminoglycosides and increase specificity of binding to a target RNA through a network of hydrogen bonds. In addition, the amide conjugation between the monomeric building blocks places two GU-base recognizing amines at 5 Å… distance, which is equal to the distance of neighboring base stacks in dsRNAs We hypothesized that targeting dsRNAs containing multiple consecutive 5'-GU-'3 sequence steps would become possible by connecting two or more of the monomeric building blocks by amide bonds. According to the proposed hypothesis, we designed three dimeric 2-DOS compounds connected by an amide bond. These three targets include the dimeric 2-DOS substrate connected by an amide bond, the dimeric 2-DOS containing the sugar moiety from Neamine, and a dimeric 2-DOS connected by a urea linker. These compounds were then tested for sequence specific binding against 8 different RNA strands, and for antibacterial activity against E. coli, actinobacter baumannii and klebsiella. Project II A dual optimization approach was used for to enhance the catalytic activity and chemoselectivity for nitro reduction. In this approach the composition of the nanoparticles and electronics effects of the polymer were studied towards nitro reduction. Bimetallic Ruthenium-Cobalt nanoparticles showed exceptional catalytic activity and chemoselectivity compared to monometallic Ruthenium nanoparticles. The electronic effects of the polymer also had a significant effect on the catalytic activity of the bimetallic nanoparticles. The electron-deficient poly(4-trifluoromethylstyrene) supported bimetallic nanoparticles undergo nitro reduction in 20 minutes at room temperature, whereas electron-rich poly(4-methylstyrene) and poly(4-methoxystyrene) supported bimetallic nanoparticles to longer reaction times to go to completion. Electronics of the polymers also effects the change in mechanism of nitroreduction. Polystyrene bimetallic Ruthenium-Cobalt nanoparticles showed excellent yields and chemoselectivity towards nitro functional group in the presence of easily reducible functional groups like alkenes, alkynes, allyl ethers, propargyl ethers. Monometallic ruthenium nanoparticles also showed excellent reactivity and chemoselectivity towards azide reduction in the presence of easily reducible functional groups. Interestingly monometallic ruthenium nanoparticles showed regioselective reduction of primary azides in the presence of secondary and benzylic azides, also aromatic azides can be selectively reduced in the presence of secondary azides. These polystyrene supported nanoparticles are heterogeneous and are easily separated from the reaction mixture and reused multiple times without significant of catalytic activity.
2

ADVANCED CHARACTERIZATIONS FOR THE IDENTIFICATION OF CATALYST STRUCTURES AND REACTION INTERMEDIATES

Nicole J Libretto (8953583) 16 June 2020 (has links)
<p>In recent decades, alternatives to traditional coal and fossil fuels were utilized to reduce carbon emissions. Among these alternatives, natural gas is a cleaner fuel and is abundant globally. Shale gas, a form of natural gas that also contains light alkanes (C2-C4), is presently being employed to produce olefins, which can be upgraded to higher molecular weight hydrocarbons. This thesis describes efforts to develop new catalytic materials and characterizations for the conversion of shale gas to fuels.</p> <p>In the first half, silica supported Pt-Cr alloys containing varying compositions of Pt and Pt<sub>3</sub>Cr were used for propane dehydrogenation at 550°C. Although a change in selective performance was observed on catalysts with varying promoter compositions, the average nano-particle structures determined by <i>in situ</i>, synchrotron x-ray absorption spectroscopy (XAS) and x-ray diffraction (XRD) were identical. Further, this work presents a method for the characterization of the catalytic surface by these methods to understand its relationship with olefin selectivity. From this, we can gain an atomically precise control of new alloys compositions with tunable surface structures.</p> <p>Once formed by dehydrogenation, the intermediate olefins are converted to fuel-range hydrocarbons. In the second half, previously unknown single site, main group Zn<sup>2+</sup> and Ga<sup>3+</sup> catalysts are shown to be effective for oligomerization and the resulting products follow a Schutlz Flory distribution. Mechanistic studies suggest these catalysts form metal hydride and metal alkyl reaction intermediates and are active for olefin insertion and b-H elimination elementary steps, typical for the homogeneous, Cossee-Arlman oligomerization mechanism. Evidence of metal hydride and metal alkyl species were observed by XAS, Fourier transform infrared spectroscopy (FTIR), and H<sub>2</sub>/D<sub>2</sub> isotope exchange. Understanding the reaction intermediates and elementary steps is critical for identifying novel oligomerization catalysts with tunable product selectivity for targeted applications. </p> <p> Through controlled synthesis and atomic level <i>in situ </i>characterizations, new catalysts compositions can be developed with high control over the resulting performance. An atomically precise control of the catalyst structure and understanding how it evolves under reaction conditions can help shed light on the fundamental principles required for rational catalyst design. </p>

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