Browsing by Subject "Aromatic compounds"
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Item A study of certain aromatic cation-radicals in sulfuric acids(Texas Tech University, 1964-08) Small, Robert JNot availableItem Adsorption, reaction and interfacial electronic structures of aromatic molecules on single crystal surfaces(2005) Wei, Wei; White, John M.Electron transfer at organic/metal interfaces is fundamental to a large number of problems in surface science. Electronic interactions at such an interface are responsible for charge injection from an electrode to the molecular film. The efficiency or rate of charge injection is determined by the energetic alignment of molecular orbitals to the metal Fermi level and the electronic coupling strength (wavefunction mixing) between molecular orbitals and metal bands. Two experimental investigations were performed with two-photon photoemission spectroscopy (2PPE). First, the energetic alignments of naphthalene/Cu(111) were probed. Three transitions involving unoccupied orbitals were found and identified as having π* molecular orbital character—the first lying 0.4 eV above the vacuum level vii (π* b1u), the second 0.3 eV below the vacuum level (π* b3g), and the third 1.1 eV below the vacuum level (π* b2g). In the second experiment, the interfacial electronic structures of chemisorbed styrene on Cu(111) were successfully investigated. We observed unoccupied states 3.5 eV above the Fermi level and occupied states 2.0 eV below the Fermi level. Polarization results reveal that the occupied and unoccupied states arise from bonding and antibonding orbitals formed by hybridization of copper (surface state and d-band orbitals) and styrene (π1* and π2* orbitals). For the first time, two-photon photoemission spectroscopy was employed to explore a surface chemical reaction: epoxidation of styrene on Cu(111). With 100 L oxygen on a Cu(111) surface, the atomic oxygen occupies three-fold hollow HCP sites rather than FCC sites. Its 2p states hybridize strongly with the dz2 states of the Cu atoms in the second layer. After styrene is adsorbed on Cu metal sites of this oxygen-covered surface, it undergoes efficient epoxidation to styrene oxide. The 2PPE results show that the change in the electronic structures of the adsorbed reactant is consistent with the surface reaction: the oxygen-induced feature from the Cu-O bonding disappears and a new state appears. However, 1000 L oxygen-covered Cu(111) is catalytically inert for styrene epoxidation: as styrene is added, no new features appear in 2PPE, and there is no evidence for chemical reaction in thermal desorption. This study could open up a new area of solid state and surface catalytic chemistry.Item Aromatic donor-acceptor interactions : bridging abiotic and peptide folding(2008-05) Bradford, Valerie Jean, 1980-; Iverson, Brent L.Aromatic donor-acceptor interactions have been utilized by the Iverson group in the development of abiotic molecules, called aedamers, that achieve new folding motifs, intermolecular association in heteroduplexes, and new material properties. These molecules exploit the interaction between the electron-rich 1,5-dialkoxynapthalene (DAN) and electron-deficient 1,4,5,8-naphthalenetetracarboxylic diimide (NDI) units in a face-centered stacking geometry in aqueous solution. This dissertation describes the use of DAN-NDI interactions in the realm of peptides and proteins to expand the scope for applications of this interaction. This work specifically focuses on three areas of aromatic donor-acceptor interactions: achieving protein behavior with abiotic molecules, introducing the interaction into natural peptides, and utilizing the interaction in the intermolecular association of an abiotic molecule and a natural peptide. Chapter 2 refines the model of aggregation of an amphiphilic aedamer, which forms a hydrogel upon heating. The aedamer behaves similarly to proteins called amlyoids, which form fibrils and plaques in vivo which have been implicated in a variety of diseases, including Alzheimer's. Chapter 3 describes the synthesis of [alpha]-amino acids with DAN- and NDI-containing side chains. These amino acids can be used in a peptide model of [beta]-hairpin secondary structure. The model system can determine whether aromatic donor-acceptor interactions are useful in stabilizing peptide and protein structure. Chapter 4 describes the study of the Anchored Periplasmic Expression System (APEx) for use in screening random peptide libraries. A random peptide library is used to determine the sequence of a natural peptide, potentially containing electron-rich aromatic residues, which could bind an NDI oligomer with high affinity for use as a protein expression tag. Chapter 5 describes work toward the use of cyclic NDI bisintercalators for binding both the major and minor grooves of a specific sequence of DNA simultaneously, in addition to the use of cyclic NDI and DAN molecules for the further study of NDI-DAN interactions in abiotic intermolecular assembiles. Overall, this work has advanced the application of aromatic donor-acceptor interactions in peptides and should serve as a foundation for the future study of this interaction in protein folding and behavior in biological systems.Item Aromatic electron donor-acceptor interactions in novel supramolecular assemblies(2006) Reczek, Joseph James; Iverson, Brent L.Item Exploiting aromatic donor-acceptor recognition in the folding and binding of naphthyl oligomers(2004) Gabriel, Gregory John; Iverson, Brent L.Biomolecules, for example, DNA and enzymes, perform nearly all the chemical processes essential for life. Their functions are dependent though on their ability to fold and bind into precise three-dimensional conformations and assemblies. A variety of oligomers that adopt compact conformations in solution, termed foldamers, have been synthesized to elucidate strategies to control folding and binding akin to biomolecules. The Iverson group has been developing a class of foldamers, called aedamers, which employ the aromatic-aromatic complexation between electronrich 1,8-dialkoxy-naphthalene (Dan) and electron-deficient 1,4,5,8-naphthalenevii tetracarboxylic diimide (Ndi) “building blocks”. It is expected that further work with these naphthyl oligomers will help establish aromatic interactions as a reliable tool for the construction of water-stable assemblies with tunable and predictable properties not found in nature. Overall, this dissertation describes the group’s first attempts to test the structural “designability” of naphthyl oligomers of previously unexplored sequences. Bottomline is that these studies have utilized the Dan:Ndi interaction to dictate intra- and inter- molecular associations to afford distinct folding topologies and achieve selective binding, respectively. Chapter 2 reports the observation that a previously studied amphiphilic aedamer happens to be an effective refolding inhibitor of RNase thus introducing the prospect of aedamer-protein interactions, a long-standing aim for these molecules. Chapter 3 presents the “shuffling” of the aedamer sequence (DanNdi)n to afford naphthyl oligomers, of the form Dann+1Ndin, that adopt turn structures. The results here demonstrate the ability of foldamers to access various secondary structures through changes to their primary sequence analogous to proteins. Chapter 4 details the first hetero-duplex system to operate via aromatic interactions in aqueous solutions. Dann and Ndin complementary strands exhibit high binding affinities and chain discrimination. The ability of the Dan:Ndi association to direct binding is expected to be extensively used by the laboratory to create discrete assemblies. As a whole, these projects probe the folding and binding of naphthyl oligomers in a variety of situations to demonstrate the wide reach of directed aromatic interactions to create various architectures. With this level of control established, surface patterning for microarrays, functional artificial proteins, biomolecule-aedamer ensembles, and other application-driven pursuits using naphthyl oligomers are possible in the near future.Item Phase transfer catalytic reactions of aromatic diazonium salts(Texas Tech University, 1981-08) Yang, Il-wooNot availableItem Photobenzidine rearrangement: photodecomposition of N.N'-dimethylhydrazoaromatics and 1,4-dialkyl-1,4-diphenyl-2-tetrazenes(Texas Tech University, 1973-12) Cheng, Jiin-DueyAcid-catalyzed and thermal rearrangements of hydrazoaromatics have been well documented; however, little is known about light-2 induced benzidine rearrangements^ Weiss reported that azobenzene and aniline were formed in the photolysis of an alcoholic solution of hydrazobenzene with a mercury lamp. Later, traces of rearrangement product, ortho- and para-semidines, were detected in the reaction fixture by paper chromatography. Recently, Shine and co-workers found that N,N'-dimethyl- -aminodiphenylamine can be isolated as the major product of irradiation of,N'-dimethylhydrazobenzene in cyclohexane. Part of the present work is to explore the scope and the mechanism of photobenzidine rearrangements of some N,N'-d1methyldrazoaromatics. The acid-catalyzed reactions of some of these substrates are also carried out for comparison.Item The P-semidine rearrangement and photochemistry of hydrazoaromatic compounds(Texas Tech University, 1970-05) Baldwin, Charles MiltonNot availableItem The reaction of aromatic cation radicals with fluoride ion(Texas Tech University, 1981-05) Stephenson, Michael ThomasNot availableItem The reductive coupling of aromatic nitro compounds with complex metal hydrides(Texas Tech University, 1961-08) Mallory, Harvey ENot availableItem Thermoreversible gelation of aromatic hydrocarbons(2002-12) Goldmann, Edward Louis; Willson, C. G. (C. Grant), 1939-; Barlow, Joel W.Fumed silica of nominal size 20 microns is used to fill many different polymer and prepolymer mixtures creating filled composite materials. Of interest in this work is silica combined with low-viscosity non-polar hydrocarbon liquids (aryl-vinyl monomers). Unless they are continuously mixed, unmodified binary mixtures that have flowable viscosity (<75 wt% solids) phase separate over time scales of several days to pure liquid and a close-packed cake of silica. It is desired that this phase separation not occur for at least several months with minimal required physical or chemical modification. This work investigates the thermodynamic and rheological (mainly elastic) properties of binary solutions of ethylbenzene, styrene, toluene, xylene, and tertbutyl styrene each with low concentrations of various molecular weight syndiotactic polystyrenes (SPS). These systems exhibit a distinct thermally reversible phase transformation when cooled, going from a low-viscosity polymer solution to a translucent waxy solid of varying physical properties. Various methods have been used to characterize both the polymers used in generating this behavior, as well as the resultant gels. Analyses include differential scanning calorimetry, nuclear magnetic resonance spectroscopy, gel permeation chromatography, and dynamic viscoelastic rheometry. For a given binary system gel formation temperatures and physical properties were found to be primarily a function of polymer loading and molecular weight. The molecular weight of polymer studied was between 4,300 and 42,000 Mn; concentrations used typically at or below 5 wt% polymer; observed modulii varied greatly and somewhat erratically but were in the 2 kPa to 20 kPa range. Nearly all mechanical property measurements were done in the elastic regime (0.1-0.2% strain; yield point 2-4%). Elastic networks were observed at extraordinarily low concentrations.