Browsing by Subject "Oxidation-reduction reaction"
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Item Amperometric DNA sensing using wired enzyme based electrodes(2003) Zhang, Yongchao; Heller, AdamA water soluble copolymer of acrylamide and 4-vinylpyridine complexed with [Os(bpy)2Cl]+/2+ (bpy = 2,2’-bipyridine), was synthesized. An electrodeposition method of making redox polymer films on electrodes was developed. This method was also shown to be effective in incorporating enzymes and amine-terminated DNA sequences in the redox polymer film. A 38-base DNA sequence was detected at 20 pM concentration in 15-35 μL droplets by an electrochemical enzyme-amplified sandwich-type assay on a mass-manufacturable screen printed carbon electrode with a diameter of 3.5 mm. A DNA-capturing oligonucleotide was attached to the pre-deposited redox polymer film using the electrodeposition method. The electrode was exposed to the droplet containing the tested DNA sample, and was then treated with a droplet containing horseradish peroxidase-labeled detection sequence. Formation of the capture-target-detection sandwich brought the horseradish peroxidase-label of the detection sequence in electrical contact with the redox polymer, making the sandwich an electrocatalyst for the reduction of hydrogen peroxide to water at + 0.2 V (Ag/AgCl). The radial diffusion of electrons through the redox polymer film on the microelectrode allowed the electrodeposition of a thicker film of the redox polymer, an increase in the loading of the capture sequence, and increased the collection efficiency of the electron vacancies originating in the electroreduced H2O2. With a 10-μm diameter carbon fiber microelectrode, as few as 3000 copies of the 38-basse DNA sequence were detected at 0.5 fM concentration in a 10 μL sample. A biofuel cell operating at a power density of 50 μW cm–2 at 0.5 V under physiological conditions (air saturated, pH 7.4, 0.14 M NaCl, 37.5°C, 15 mM glucose) was developed. The cell had a glucose electro-oxidizing anode and an O2 electro-reducing cathode. The anode and the cathode were 7 μm diameter, 2 cm long carbon fibers, on which the catalytic enzyme-redox polymer adducts were cross-linked. When the miniature cell operated at 0.5 V, the power output dropped to about 60% of its initial value after 2 days of continuous operation at 37.5°C.Item Cation radical induced oxidative chemistry of hydrazones and oximes(Texas Tech University, 1990-05) Hoque, A. K. M. MansurulElectron transfer reactions of cation radicals have drawn much interest (1). Shine and Sugiyama were the first to observe that alkyl radicals were formed by an initial electron transfer step in reactions of thianthrene cation radical with organomercurials (2). The possibility that thianthrene cation radical might efficiently trap the alkyl radicals led to attempts to generate alkyl radicals by the photolysis of azoalkanes in the presence of thianthrene cation radical at room temperature. It was found, however that the azoalkanes which were chosen reacted rapidly with thianthrene cation radical in the absence of light, leading to the reduction of the cation radical and formation of alkyl cation and radical products. This led to the study of the reactions of cation radicals with a number of azoalkanes (1). During the study of the reaction of thianthrene cation radical with azotoluene in acetonitrile, an interesting product, 1-benzyl-3-phenyl-5-methyl-1,2,4-triazole, was obtained as a major product along with alkyl cation and alkyl radical products (1, 3). It was found that the triazole was formed by a reaction in which the cation radical induced oxidative cycloaddition of benzaldehyde benzylhydrazone, a tautomer of azotoluene, to acetonitrile. This observation led to an interest in the study of reactions of cation radicals with arylhydrazones. The objective of studying the reactions of cation radicals with arylhydrazones was to explore the cation radical induced oxidative cycloaddition of hydrazones to nitrites to give trisubstituted 1,2,4-triazoles.Item Cation-radical induced oxidative chemistry of azoalkanes and arylhydrazones(Texas Tech University, 1986-05) Hoque, A. K. M. MansurulNot availableItem Evaluation of genome designs for oxidation resistance: guanine minimization and scavenger guanine(2003) Friedman, Keith Albert; Heller, AdamThe genome's environment contains strong oxidizers, some of which selectively attack guanine, the most readily oxidized nucleotide. The ranking of guanine oxidation rates is central G in GGG (GGG) ≥ 5' G in GG (GG) > isolated or 3' G. Vulnerability to selective oxidants puts mutation pressure on guanine. This is apparent in the differences between observed levels of GGG and levels predicted by probability from total G. GGG is below probability predictions in the genomes of D. melanogaster, C. elegans, A. thaliana, S. cerevisiae and S. pombe. GGG is statistically under-represented in H. sapiens exons, but over-represented in H. sapiens introns and intergenic domains. It is not under-represented in E. cuniculi. It is over-represented P. falciparum chromosomes 2 and 3, but this organism's total G levels are extremely low. GG generally is not underrepresented in these genomes. Beyond enzymatic elimination of the oxidizing agents and their precursors, and excision and repair of oxidative lesions, we propose that genomes are built to mitigate damage to essential domains. Resistance to oxidation could be enhanced by making genomes more “noble” by reducing the fractions of total G, GG and particularly GGG. Alternately, if the duplex conducts electron vacancies (holes) over ∼100 bp, oxidation could be shifted from essential domains to sacrificially oxidizable GGG and GG in nonessential domains. The distribution of GGG and GG in exons, introns and intergenic domains of eight model genomes suggests ennoblement in six, protection by sacrificial anodes in one, and no guanine-based protection in one (E. cuniculi). GGG triads are excluded or are statistically underrepresented in exons and short splicing-controlling introns of D. melanogaster, C. elegans, A. thaliana, S. cerevisiae, S. pombe and P. falciparum chromosomes 2 and 3. The introns of H. sapiens, which are about twenty times longer than those of the other organisms, are rich in sacrificially oxidizable GGG triads that are 50-100 bp from the exons. Their frequency correlates with the presence of protection-requiring GGG triads in the exons.Item Investigation of alkylindium-metal carbonyl reaction and synthesis of xenophilic compounds(Texas Tech University, 2002-12) Li, ZhengrongThe study of the salt elimination reactions of transition metal chlorides with tetracarbonylferrate, tetracarbonylcobaltate and pentacarbonylmanganesate to synthesize xenophilic complexes in which the Type A metal has neutral ligands was carried out. The reduction-oxidation reactions in which electrons were transferred from the pentacarbonyl-manganesate and tetracarbonylferrate anions to the transition metal cations hindered the formation of the metal-metal bond between transition metals. In the reactions of transition metal chlorides with tetracarbonylcobaltate anion no reaction occurred unless tetracarbonylcobaltate anion yielded anionic carbonyl cobalt clusters when the less polar solvents replaced THF (THF = tetrahydrofuran). The exception was that the Group 4 metal chlorides reacted with tetracarbonylcobaltate anion to yield the hydrotetracarbonylcobalt. The introduction of pyrroUdine reduced the oxidation potentials of Group 7, 8 metal cations so that the synthesis of xenophilic complexes was possible. In the reaction of an equal molar mixtvire of trimethyl and triethyl indium with octacarbonylcobalt that generates ketone, the statistical distribution of ketone products was obtained. The pathways for such reaction are proposed. The compound Mn2(CO)8(C4H9N)2 (C4H9N = pyrrolidine) has been synthesized by placing Mn2(CO)10 into hexanes containing pyrrolidine. A single crystal X-ray structure determination shows the pyrrolidine molecules attach to the manganese atoms in the equatorial position. The bond length between manganese atoms is 2.9415(7) A, longer than that in Mn2(CO)10 and in diaxial substibuted Mn2(CO)10. This is the first disubstituted Mn2(CO)10 by monodentate nitrogen ligand that has trans-equatorial geometry.Item Kinetic and redox studies of the copper(II)-mercaptide complexes(Texas Tech University, 1985-08) Baek, Haesun KangNot availableItem Kinetics and equilibrium studies of the reduction of copper(II) with a tetradentate bis(pyridyl)-dithioether ligand(Texas Tech University, 1986-12) Castillo, Maria C. G.The reduction of [Cu(pmas)]+2 by hydroxyethylferrocene [HEF] has been studied in the presence of azide, imidazolate and pyridine. Both reactants exhibit a first order dependence at 25.0°C, pH 6.0, I = O.IM (NaNO^) with second order rate constant of 1.3 x 10 M~ s~ . +2/+ The apparent Cu(pmas) self-exchange electron transfer rate constant calculated on the basis of relative Marcus theory (k,, = 4.7 x 10 M s ) agrees well with previous findings on ferrocyto--4 +2 chrome £, Fe(CN)g and Ru (NH^)^ py reactions with +2 [Cu(pmas)] . The copper complex reduction has been studied as a function of temperature, and the enthalpy and entropy of activation are 10.1 Kcal/mol and -6 e.u., respectively. The formation constants of the 1:1 and 2:1 complexes of Cu(pmas)+ 2 with azide were measured spectrophotometrically. The values (K^, = 3.3 x 10 M ) and 5 -1 +2( K ^ ^ = 3 . 5 x l O M ) were compared with Cu(tmpa) [tris(2- yridylmethyl)amine] copper(II) binding constants. The latter 2-1 only presented one value (K^ = 6.6 x 10 M ), up to 0.15 M N^ (25.0°C, pH 6.0, I = 0.2 M), which demonstrates that a thioether sulfur atom is displaced in the uptake of a second N^ nit by Cu(pmas)(N^) . The effect of thioether sulfur displacement by azide ion on the redox reaction rate may be understood entirely through the tendency of N^ to shift the position of the redox equilibrium towards reactant side. Cyclic voltammetry measurements showed that the eduction potentials of Cu(pmas) +2 in the presence of 5 and 150 mM N^ are 307 and 254 mV respectively, as compared with that of free complex, 398 mV. The rate constant is decreased when azide is present (k (25.0°C) = 3 x IO^M'-'-S"-'- pH 6.0, I = 0.2 M). This demonstrates the importance of bond breaking in the activated complex for reduction of five-coordinate Cu(II) to four-coordinate (Cu(I) because the aqueous form has a weakly-held coordinated water molecule, but the azide form has a strongly-retained nitrogen-donor ligand. Also the dependence of the reaction rate on acetonitrile concentration will be described.Item Mechanistic flexibility in the reduction of copper(II) complexes of aliphatic polyamines by mercapto amino acids(Texas Tech University, 1985-05) Anderson, Clinton HNot availableItem Oxidation reduction properties of thioredoxin and related proteins(Texas Tech University, 2001-12) Setterdahl, Aaron TaitThioredoxins are redox-active proteins that contain two cysteines separated by two amino acids. These cysteines form an intreimolecular disulfide bond which when reduced, can activate or inactivate a number of other redox-sensitive proteins. This dissertation focuses on thiol-containing proteins that are involved in redoxsensitive dithiol/disulfide processes. Escherichia coli thioredoxin is a widely studied protein. However, much remains to be learned about the mechanism by which it reduces target proteins. An investigation of redox properties of the wild-type protein and site-specific mutants has been undertaken. Thioredoxin h from the green alga Chlamydomonas reinhardtii is a structurally similar protein to E. coli thioredoxin and its redox properties have also been investigated. The ligation of the heme group in cytochrome c involves a dithioydisulfide protein cascade. HelX and Ccl2 are involved in this cascade in Rhodobacter capsulatus, ultimately reducing the disulfide on apo-cytochrome c so that it can bind heme. DisuMde/dithiol systems are also involved in the oxygen sensing mechanism of Rb. capsulatus, where the DNA-binding protein CrtJ contains a redox-active disulfide. Other proteins investigated for their disulfide/dithiol activity include an engineered E. coli malate dehydrogenase, in which a redox-active disulfide was introduced, and APS reductase from Arabidopsis thaliana, which contains a redox-active regulatory disulfide.Item Oxidative chemistry on gold : unraveling molecular transformations at surfaces(2009-05) Gong, Jinlong, 1979-; Mullins, C. B.Gold has been considered catalytically inert due to its resistance to oxidation and corrosion. However, decades ago, it was discovered that gold nano-particles (<5nm) on metal oxides demonstrate superior chemical activity towards many reactions. These seminal findings spurred considerable interest in investigations of the mechanistic details of oxidative reactions on gold-based catalysts. However, the active site and structure of supported Au nanoclusters as well as the active oxygen species remains elusive. Achieving high selectivity toward partial oxidation products also remains a challenge. In this dissertation, an oxygen-covered Au(111) crystal under ultra vacuum conditions was used as a model system to gain insights into oxidative reactions in gold-based catalysis. I have been able to demonstrate that (i) surface-bound oxygen atoms are metastable at low temperature; (ii) the oxygen atoms participate in surface reactions as a Brønsted base or a nucleophilic base; and (iii) the acid-base reactions that have been observed on silver and copper may also occur on gold. Low temperature CO oxidation and the associated mechanistic aspects are investigated. CO reacts with hydroxyls formed from water-oxygen interactions to produce CO₂ on Au(111) populated with atomic oxygen at low temperatures. Directing an ¹⁶O beam toward C¹⁸O₂ pre-adsorbed Au(111), the formation of carbonate is significantly enhanced. This reaction is suggested to follow a hot-precursor-mediated mechanism. The identification of reaction pathways in oxidation of N-containing molecules such as ammonia and propylamine is presented. Abstraction of hydrogen from ammonia or propylamine by O atoms is the initial step in the surface decomposition of NHx (or RNHx-1) on Au(111). Atomic oxygen or hydroxyl-assisted dehydrogenation steps have lower barriers than the recombination steps under relevant conditions. 100% selectivity of N₂ or propionitrile can be obtained if the oxygen coverage is below the stoichiometric value. The surface oxidative chemistry of alcohols on Au(111) is also investigated. Except for methanol that is fully oxidized, alcohols initially undergo O-H bond cleavage (producing alcoxides) followed by selective β-C-H bond activation to form aldehydes or ketones. This finding reveals that the interaction of Au with the metal oxide support might not be essential to facilitate the reactions if active oxygen species are readily present, particularly at low temperatures.Item Oxidative degradation of polyethylene(Texas Tech University, 1971-05) Spore, Richard LawrenceNot availableItem Perturbations of the homo level of oxo-bridged chromium(III) dimers(Texas Tech University, 1992-12) Tekut, Thomas FrancisNot availableItem Studies on the mechanism of the conversion of emodin to chrysophanol catalyzed by partially purified emodin deoxygenase from Pyrenochaeta terrestris(Texas Tech University, 1989-12) Lin, Bor-kangNot availableItem The nature of N-5 reactivity in flavins and D-amino acid oxidase-inhibitor complexes(Texas Tech University, 1978-12) Choi, Jung-DoNot available