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Chemical and Photochemical Reactions of Thioctic Acid and RelatedDisulfides

Description: The carbon cycle of photosynthesis is briefly reviewed in its entirety and the experiments involving it which led to the implication of disulfide rupture in photosynthesis are indicated. A review of the organic, physical and photochemistry of disulfides, with particular reference to the five-membered disulfide rings as they appear in thioctic acid, is given.
Date: June 10, 1954
Creator: Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Metabolism of Thioctic Acid in Algae

Description: Thioctic acid labeled with sulfur-35 has been prepared and i t s metabolism b y algae has been studied. It i s converted by the algae into a number of forms, all of which upon hydrolysis yield either the disulfide o r i t s sulfoxide. One of these constituted the major portion of the labeled material in the chloroplasts. Aerobic metabolism for some minutes i s required to produce this form. Preliminary studies of the chemical nature of this form suggest i t to be esterified on the carboxyl group with a moiety of very high lipid solubility.
Date: April 17, 1956
Creator: Grisebach, Hans; Fuller, R.C. & Calvin, M.
Partner: UNT Libraries Government Documents Department

Absorption Spectra of Aromatic Disulfides

Description: The effect of solvents and temperature on the optical absorption spectrum of a number of substituted aromatic disulfides is reported. The problems offered by the disulfide link and the exchange reactions between disulfides, and between disulfides and thiols, are receiving increasing attention. Recently the base-catalyzed exchange between various alkyl disulfides and the corresponding thiols was studied by means of a radioactive-tracer technique. Our initial purpose was to extend these investigations to a large number of compounds in a variety of experimental conditions using a spectrophotometric technique that, if applicable, would have been incomparably faster.
Date: October 31, 1956
Creator: Fava, Antonio & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Atom transfer and rearrangement reactions catalyzed by methyltrioxorhenium, MTO

Description: Methyltrioxorhenium (MTO) catalyzes the desulfurization of thiiranes by triphenylphosphine. Enormous enhancement in rate is observed when the catalyst is pretreated with hydrogen sulfide prior to the reaction. Using 2-mercaptomethylthiophenol as a ligand, the author synthesized several model complexes to study the mechanism of this reaction. With suitable model systems, they were able to show that the active catalyst is a Re(V) species. The reactions are highly stereospecific and very tolerant to functional groups. As part of the studies, he synthesized and crystallographically characterized the first examples of neutral terminal and bridging Re(V)sulfidocomplexes. Some of these complexes undergo fast oxygen atom transfer reactions with organic and inorganic oxidants. Studies on these model complexes led them to the discovery that MTO catalyzes the selective oxidation of thiols to disulfides. This report contains the Introduction; ``Chapter 6: Isomerization of Propargylic Alcohols to Enones and Enals Catalyzed by Methylrhenium Trioxide``; and Conclusions.
Date: May 10, 1999
Creator: Jacob, J.
Partner: UNT Libraries Government Documents Department


Description: The nonionic superbase P(MeNCH{sub 2}CH{sub 2}){sub 3}N (A) efficiently desulfurizes trisulfides to disulfides and monosulfides, disulfides to monosulfides, and propylene sulfide to propene. S=P(MeNCH{sub 2}CH{sub 2}){sub 3}N (B) was formed as the sulfur acceptor. P(NMe{sub 2}){sub 3} was a much poorer desulfurizing agent than A under the same reaction conditions. Thiocyanates and triphenylphosphine sulfide were also desulfurized with A, but N-(phenylthio)phthalimide formed [A-SP]{sup +} phthalimide in quantitative yield.
Date: August 31, 1998
Creator: Verkade, John G.
Partner: UNT Libraries Government Documents Department


Description: The reactions of dialkyl mono- and disulfides and functionalized alkylthio compounds with sodium in refluxing hydrocarbon solvent (tetradecane, mesitylene or toluene) resulted in sulfur-free products in very high yields. Greater than 95% sulfur removal was observed when dialkyl mono or polysulfides were treated with Na in liquid ammonia. Polycyclic aromatic sulfur heterocycles were only moderately desulfurized under these conditions while phenylthio derivatives gave thiophenol as the major product and dithiophenols as the minor products.
Date: February 28, 1998
Creator: Verkade, John G.
Partner: UNT Libraries Government Documents Department

Method for direct production of carbon disulfide and hydrogen from hydrocarbons and hydrogen sulfide feedstock

Description: A method for converting hydrocarbons and hydrogen sulfide to carbon disulfide and hydrogen is provided comprising contacting the hydrocarbons and hydrogen sulfide to a bi-functional catalyst residing in a controlled atmosphere for a time and at a temperature sufficient to produce carbon disulfide and hydrogen. Also provided is a catalyst for converting carbon sulfides and hydrogen sulfides to gasoline range hydrocarbons comprising a mixture containing a zeolite catalyst and a hydrogenating catalyst.
Date: December 1998
Creator: Miao, Frank Q. & Erekson, Erek James
Partner: UNT Libraries Government Documents Department

Solving Globally-Optimal Threading Problems in ''Polynomial-Time''

Description: Computational protein threading is a powerful technique for recognizing native-like folds of a protein sequence from a protein fold database. In this paper, we present an improved algorithm (over our previous work) for solving the globally-optimal threading problem, and illustrate how the computational complexity and the fold recognition accuracy of the algorithm change as the cutoff distance for pairwise interactions changes. For a given fold of m residues and M core secondary structures (or simply cores) and a protein sequence of n residues, the algorithm guarantees to find a sequence-fold alignment (threading) that is globally optimal, measured collectively by (1) the singleton match fitness, (2) pairwise interaction preference, and (3) alignment gap penalties, in O(mn + MnN{sup 1.5C-1}) time and O(mn + nN{sup C-1}) space. C, the topological complexity of a fold as we term, is a value which characterizes the overall structure of the considered pairwise interactions in the fold, which are typically determined by a specified cutoff distance between the beta carbon atoms of a pair of amino acids in the fold. C is typically a small positive integer. N represents the maximum number of possible alignments between an individual core of the fold and the protein sequence when its neighboring cores are already aligned, and its value is significantly less than n. When interacting amino acids are required to see each other, C is bounded from above by a small integer no matter how large the cutoff distance is. This indicates that the protein threading problem is polynomial-time solvable if the condition of seeing each other between interacting amino acids is sufficient for accurate fold recognition. A number of extensions have been made to our basic threading algorithm to allow finding a globally-optimal threading under various constraints, which include consistencies with (1) specified secondary structures (both cores ...
Date: April 12, 1999
Creator: Uberbacher, E.C.; Xu, D. & Xu, Y.
Partner: UNT Libraries Government Documents Department

A cell nanoinjector based on carbon nanotubes

Description: Technologies for introducing molecules into living cells are vital for probing the physical properties and biochemical interactions that govern the cell's behavior. Here we report the development of a nanoscale cell injection system-termed the nanoinjector-that uses carbon nanotubes to deliver cargo into cells. A single multi-walled carbon nanotube attached to an atomic force microscope tip was functionalized with cargo via a disulfide-based linker. Penetration of cell membranes with this 'nanoneedle', followed by reductive cleavage of the disulfide bonds within the cell's interior, resulted in the release of cargo inside the cells. The capability of the nanoinjector was demonstrated by injection of protein-coated quantum dots into live human cells. Single-particle tracking was employed to characterize the diffusion dynamics of injected quantum dots in the cytosol. This new technique causes no discernible membrane or cell damage, and can deliver a discrete number of molecules to the cell's interior without the requirement of a carrier solvent.
Date: January 30, 2007
Creator: Chen, Xing; Kis, Andras; Zettl, Alex & Bertozzi, Carolyn R.
Partner: UNT Libraries Government Documents Department

Biosynthesis of the Cyclotide MCoTI-II using an Engineered Intein

Description: Cyclotides are an emerging family of naturally occurring circular mini-proteins ({approx}30-40 amino acids) characterized by six conserved Cys residues (forming 3 disulfide bridges) that create a topologically unique structure designated as a cyclic cysteine knot (CCK). The cysteine knot motif, which is embedded within the macrocylic backbone, is described as two disulfide bridges that form a ring that is penetrated by the third disulfide bridge. The cyclic backbone and CCK motif together confer cyclotides with a remarkable stability and resistance to proteolytic, chemical, and thermal degradation. Further, cyclotides are functionally diverse and display a wide range of functions including uterotonic activity, trypsin inhibition, cytotoxicity, neurotensin binding, anti-HIV, antimicrobial, and insecticidal activity. Together, these characteristics make cyclotides attractive candidates for both drug design and agricultural applications, both in their native forms and as molecular scaffolds for the incorporation of novel bioactivities. [1] The ability to manipulate production of cyclotides within biological systems is critical for mutagenesis studies, production of grafted products, and the mass production of cyclotides with novel activities. My adviser's hope is to achieve this capability by employing recombinant DNA expression techniques to generate large combinatorial libraries of cyclotides. The advantage in creating a biosynthetic library (containing {approx}10{sup 6}-10{sup 10} members/library vs. chemically based libraries with typical values ranging from {approx}10{sup 3}-10{sup 5} members/library) is that it can be lead to the in vivo application of biological screening and selection methodologies based on a specific clone's ability to affect certain cellular processes.
Date: August 15, 2006
Creator: Cantor, J & Camarero, J A
Partner: UNT Libraries Government Documents Department

Selective extraction of copper, mercury, silver and palladium ionsfrom water using hydrophobic ionic liquids.

Description: Extraction of dilute metal ions from water was performed near room temperature with a variety of ionic liquids. Distribution coefficients are reported for fourteen metal ions extracted with ionic liquids containing cations 1-octyl-4-methylpyridinium [4MOPYR]{sup +}, 1-methyl-1-octylpyrrolidinium [MOPYRRO]{sup +} or 1-methyl-1-octylpiperidinium [MOPIP]{sup +}, and anions tetrafluoroborate [BF{sub 4}]{sup +}, trifluoromethyl sulfonate [TfO]{sup +} or nonafluorobutyl sulfonate [NfO]{sup +}. Ionic liquids containing octylpyridinium cations are very good for extracting mercury ions. However, other metal ions were not significantly extracted by any of these ionic liquids. Extractions were also performed with four new task-specific ionic liquids. Such liquids containing a disulfide functional group are efficient and selective for mercury and copper, whereas those containing a nitrile functional group are efficient and selective for silver and palladium.
Date: June 25, 2007
Creator: Papaiconomou, Nicolas; Lee, Jong-Min; Salminen, Justin; VonStosch, Moritz & Prausnitz, John M.
Partner: UNT Libraries Government Documents Department


Description: The toxigenic strains of Clostridium botulinum produce seven serologically distinct types of neurotoxins labeled A - G (EC, while Clostridium tetani produces tetanus neurotoxin (EC Botulinum and tetanus neurotoxins (BoNTs and TeNT) are produced as single inactive chains of molecular mass of approximately 150 kDa. Most of these neurotoxins are released after being cleaved into two chains, a heavy chain (HI) of 100 kDa and a light chain (L) of 50 kDa held together by an interchain disulfide bond, by tissue proteinases. BoNT/E is released as a single chain but cleaved by host proteinases [1]. Clostvidium botulinum neurotoxins are extremely poisonous proteins with their LD{sub 50} for humans in the range of 0.1 - 1 ng kg{sup -1} [2]. Botulinum neurotoxins are responsible for neuroparalytic syndromes of botulism characterized by serious neurological disorders and flaccid paralysis. BoNTs block the release of acetylcholine at the neuromuscular junction causing flaccid paralysis while TeNT blocks the release of neurotransmitters like glycine and {gamma}-aminobutyric acid (GABA) in the inhibitory interneurons of the spinal cord resulting in spastic paralysis. In spite of different clinical symptoms, their aetiological agents intoxicate neuronal cells in the same way and these toxins have similar structural organization [3].
Date: November 19, 2001
Creator: Swaminathan, S. & Eswaramoorthy, S.
Partner: UNT Libraries Government Documents Department

Development of Novel, Simple, Multianalyte Sensors for Remote Environmental Analysis

Description: We will develop simple, inexpensive new chemical sensing materials which can be used as visual color test strips to sensitively and selectively report on the concentration and identity of environmental pollutants such as cations of Pb, U, Pu, Sr, Hg, Cs, Co as well as other species. We will develop inexpensive chemical test strips which can be immersed in water to determine these analytes in the field. We will also develop arrays of these chemical sensing materials which will be attached to fiber optic bundles to be used as rugged multichannel optrodes to simultaneously monitor numerous analytes remotely in hostile environments. These sensing materials are based on the intelligent polymerized crystalline colloidal array (PCCA) technology we recently developed. This sensing motif utilizes a mesoscopically periodic array of colloidal particles polymerized into an acrylamide hydrogel. This array Bragg diffracts light in the visible spectral region due to the periodic array of colloidal particles. This material also contains chelating agents for the analytes of interest. When an analyte binds, its charge is immobilized within the acrylamide hydrogel. The resulting Donnan potential causes an osmotic pressure which swells the array proportional to the concentration of analyte bound. The diffracted wavelength shifts and the color changes. The change in the wavelength diffracted reports on the identity and concentration of the target analyte. Our successful development of these simple, inexpensive highly sensitive chemical sensing optrodes, which are easily coupled to simple optical instrumentation, could revolutionize environmental monitoring. In addition, we will develop highly rugged versions, which can be attached to core penetrometers and which can be used to determine analytes in buried core samples. Research Progress and Implications This report summarizes work after 21 months of a three year project. We have developed a new method to crosslink our PCCA sensing materials with disulfide bridges. ...
Date: June 1, 2000
Creator: Asher, Sanford A.
Partner: UNT Libraries Government Documents Department

Comments on cathode contaminants and the LBNL test stand

Description: This report collects information on cathode contaminants we have gathered in the process of operating the LBNL DARHT cathode test stand. Information on contaminants is compiled from several sources. The attachment, ''Practical Aspects of Modern Dispenser Cathodes'', is from Heat Wave Corp. (TB-134) and was originally published in Microwave Journal, September 1979. Cathode contamination depends on both material choices and residual gases. Table 1 of TB-134 lists materials that can poison dispenser cathodes. These include reactive residual gases or vapors such as oxygen, water vapor, benzene, chlorine, fluorine, sulfur, silicon, and most metals other than molybdenum, rhenium, tungsten, and copper. The metals interact with the cathode surface through their vapor pressure. A paper by Nexsen and Turner, J. Appl. Phys. 68, 298-303 (1990) shows the threshold effects of some common residual gases or vapors on cathode performance. The book by Walter H. Kohl, Handbook of Materials and Techniques for Vacuum Devices, also contains useful information on cathodes and poisoning agents. A plot of the vapor pressures and poisoning effect of certain metals (from Kohl) is shown below. Note that the vapor pressure of zinc is 1.1 x 10{sup -8} Torr at 400 K = 127 C, and 2.7 x 10{sup -5} at 500 K = 227 C. By contrast iron reaches a vapor pressure 1 x 10{sup -8} between 800 and 900 C. Therefore it is important to eliminate any brass parts that could exceed a temperature of 100 C. Many structural components of the cathode assembly contain steel. At 500-600 C in an oxygen atmosphere chromium oxide may outgas from the steel. [Cho, et.al., J. Vac. Sci. Technol. A 19, p. 998 (2001)]. Steel may also contain silicon, and sulfur at low concentrations. Therefore use of steel should be limited or avoided at high temperature near the cathode. Materials ...
Date: November 13, 2006
Creator: Bieniosek, F.; Baca, D.; Greenway, W.; Leitner, M. & Kwan, J.W.
Partner: UNT Libraries Government Documents Department

Biosynthesis of the cyclotide Kalata B1 using protein splicing tools

Description: Cyclotides are a new emerging family of large cyclic polypeptides ({approx}30 residues long) that share a disulfide-stabilized core (3 disulfide bonds) with an unusual knotted structure (Fig. 1A) [1]. Cyclotides contrast with other circular polypeptides in that they have a highly defined three-dimensional structure, and despite their small size, can be considered as miniproteins. Their unique circular backbone topology and knotted arrangement of 3 disulfide bonds makes them exceptionally stable to thermal and enzymatic degradation. Furthermore, their well defined structures have been also associated with a range of biological activities, including uterotonic activity, inhibition of neurotension binding, hemolytic, anti-HIV, insecticidal as well as trypsin inhibitory activity. Altogether, these characteristics make cyclotides ideal candidates to be used as molecular scaffolds for the development of stable peptide drugs [2]. Access to biosynthetic cyclotides using recombinant DNA expression techniques would offer the exciting possibility of producing large combinatorial libraries of highly stable miniproteins using the tools of molecular biology. This would allow the generation of cell-based combinatorial libraries that could be screened inside living cells for their ability to regulate cellular processes. In the present work we describe for the first time the biosynthesis of the cyclotide Kalata B1 in E. coli. Our approach is based on the use of an intramolecular version of the native chemical ligation combined with the use of a modified protein splicing unit [3]. In order to accomplish the cyclization of Kalata B1, the different linear precursors tested in this work (Fig. 1B) were fused at the N-terminus with a Met residue, and at the C-terminus with an VMA engineered intein (available in the pTXB expression vectors family from New England Biolabs). The Met residue was efficiently removed in vivo in E. coli by an endogenous Met amino peptidase. This in vivo proteolytic event unmasked the required N-terminal ...
Date: July 13, 2005
Creator: Kimura, R.; Krishnan, K. & Camarero, J. A.
Partner: UNT Libraries Government Documents Department

Biosynthesis of the Cyclotide Kalata B1 using a Protein Splicing Unit

Description: Cyclotides are a newly emerging family of large backbone cyclic polypeptides ({approx}30 residues long) characterized by a disulfide-stabilized core (3 disulfide bonds) with an unusual knotted structure. In contrast to other cyclic polypeptides, cyclotides have a well-defined three-dimensional structure. Therefore, despite their small size, they can be considered miniproteins. The unique cyclic-backbone topology and knotted arrangement of 3 disulfide bonds endow cyclotides with exceptional stability and resistance to chemical, enzymatic and thermal degradation. Furthermore, their well-defined structures have been associated with a range of biological functions. Together, these characteristics suggest that cyclotides are ideal molecular scaffolds for the development of stable peptide drugs. Despite the fact that the chemical synthesis of circular peptides has been well explored and a number different approaches involving solid-phase or liquid-phase exist, recent developments in the fields of molecular biology and protein engineering have now made possible the biosynthesis of cyclic peptides. This progress has been made mainly in two areas, non-ribosomal peptide synthesis and Expressed Protein Ligation (EPL)/protein trans-splicing. Access to biosynthetic cyclotides using recombinant DNA expression techniques offers the exciting possibility of producing large combinatorial libraries of highly stable miniproteins. This would allow the generation of cell-based combinatorial libraries that could be screened either in vitro or in vivo for their ability to regulate cellular processes. In the present work, we describe the biosynthesis of the cyclotide Kalata B1 (KB1) in E. coli using an engineered intein. Our approach (Figure 1) is based on an intramolecular version of Native Chemical Ligation (NCL). NCL involves the chemoselective reaction between a N-terminal Cys residue of one peptide and an {alpha}-thioester group of a second peptide. Importantly, incorporation of these two groups into the same synthetic polypeptide leads to efficient circularization.
Date: August 13, 2005
Creator: Kimura, R H; Tran, A T & Camarero, J A
Partner: UNT Libraries Government Documents Department

Biological Applications and Transmission Electron Microscopy Investigations of Mesoporous Silica Nanoparticles

Description: The research presented and discussed within involves the development of novel biological applications of mesoporous silica nanoparticles (MSN) and an investigation of mesoporous material by transmission electron microscopy (TEM). Mesoporous silica nanoparticles organically functionalized shown to undergo endocytosis in cancer cells and drug release from the pores was controlled intracellularly and intercellularly. Transmission electron microscopy investigations demonstrated the variety of morphologies produced in this field of mesoporous silica nanomaterial synthesis. A series of room-temperature ionic liquid (RTIL) containing mesoporous silica nanoparticle (MSN) materials with various particle morphologies, including spheres, ellipsoids, rods, and tubes, were synthesized. By changing the RTIL template, the pore morphology was tuned from the MCM-41 type of hexagonal mesopores to rotational moire type of helical channels, and to wormhole-like porous structures. These materials were used as controlled release delivery nanodevices to deliver antibacterial ionic liquids against Escherichia coli K12. The involvement of a specific organosiloxane function group, covalently attached to the exterior of fluorescein doped mesoporous silica nanoparticles (FITC-MSN), on the degree and kinetics of endocytosis in cancer and plant cells was investigated. The kinetics of endocystosis of TEG coated FITC-MSN is significantly quicker than FITC-MSN as determined by flow cytometry experiments. The fluorescence confocal microscopy investigation showed the endocytosis of TEG coated-FITC MSN triethylene glycol grafted fluorescein doped MSN (TEG coated-FITC MSN) into both KeLa cells and Tobacco root protoplasts. Once the synthesis of a controlled-release delivery system based on MCM-41-type mesoporous silica nanorods capped by disulfide bonds with superparamagnetic iron oxide nanoparticles was completed. The material was characterized by general methods and the dosage and kinetics of the antioxidant dependent release was measured. Finally, the biological interaction of the material was determined along with TEM measurements. An electron investigation proved that the pore openings of the MSN were indeed blocked by the Fe{sub 3}O{sub 4} ...
Date: May 1, 2006
Creator: Trewyn, Brian G.
Partner: UNT Libraries Government Documents Department

PROSPECT: A Computer System for Globally-Optimal Threading

Description: This paper presents a new computer system, PROSPECT, for protein threading. PROSPECT employs an energy function that consists of three additive terms: (1) a singleton fitness term, (2) a distance-dependent pairwise-interaction preference term, and (3) alignment gap penalty; and currently uses FSSP as its threading template database. PROSPECT uses a divide-and-conquer algorithm to find an alignment between a query protein sequence and a protein fold template, which is guaranteed to be globally optimal for its energy function. The threading algorithm presented here significantly improves the computational efficiency of our previously-published algorithm, which makes PROSPECT a practical tool even for large protein threading problems. Mathematically, PROSPECT finds a globally-optimal threading between a query sequence of n residues and a fold template of m residues and M core secondary structures in O(nm + MnN{sup 1.5C{minus}1}) time and O(nm + nN{sup C{minus}1}) space, where C, the topological complexity of the template fold as we term, is a value which characterizes the overall structure of the considered pairwise interactions in the fold; and N represents the maximum number of possible alignments between an individual core of the fold and the query sequence when its neighboring cores are already aligned. PROSPECT allows a user to incorporate known biological constraints about the query sequence during the threading process. For given constraints, the system finds a globally-optimal threading which satisfies the constraints. Currently PROSPECT can deal with constraints which reflect geometrical relationships among residues of disulfide bonds, active sites, or determined by the NOE constraints of (low-resolution) NMR spectral data.
Date: August 6, 1999
Creator: Xu, D. & Xu, Y.
Partner: UNT Libraries Government Documents Department

Structures and related properties of helical, disulfide-stabilized peptides

Description: The three dimensional structure of several peptides were determined by NMR spectroscopy and distance geometry calculations. Each peptide formed a predictable, rigid structure, consisting of an {alpha}-helix, a {open_quotes}scaffold{close_quotes} region which packed along one face of the helix, and two disulfide bridges which covalently connect the helix and scaffold regions. The peptide Apa-M5 was designed to constrain the M5 peptide from MLCK in a helical geometry using the apamin disulfide scaffold. This scaffold constrains the N- terminal end of the helix with two disulfide bridges and a reverse turn. Like the M5 peptide, Apa-M5 was found to bind calmodulin in a Ca{sup 2+}-dependent 1:1 stoichiometry. However, the dissociation constant of the (Apa-M5)-calmodulin complex, 107 nM, was 100-fold higher than the dissociation constant of the M5-calmodulin complex. This difference was due to a putative steric overlap between the Apa-M5 scaffold and calmodulin. The peptide Apa-Cro was designed to replace the large structural protein matrix of {lambda} Cro with the apamin disulfide scaffold. However, Apa-Cro did not bind the consensus DNA operator half-site of {lambda} Cro, probably due to a steric overlap between the Apa-Cro disulfide framework and the DNA. The amino acid sequence of the scaffold-disulfide bridge arrangement of the peptide Max was derived from the core sequence of scyllatoxin, which contains an {alpha}-helix constrained at the C-terminal end by two disulfide bridges and a two-stranded {beta}sheet scaffold. Max was shown to fold with >84% yield to form a predictable, stable structure that is similar to scyllatoxin. The folding and stability properties of Max make this scaffold and disulfide bridge arrangement an ideal candidate for the development of hybrid sequence peptides. The dynamics of a fraying C-terminal end of the helix of the peptide Apa-AlaN was determined by analysis of {sup 15}N NMR relaxation properties.
Date: November 1, 1993
Creator: Pagel, M. D.
Partner: UNT Libraries Government Documents Department

Improved Fischer-Tropsch Slurry Reactors

Description: The conversion of synthesis gas to hydrocarbons or alcohols involves highly exothermic reactions. Temperature control is a critical issue in these reactors for a number of reasons. Runaway reactions can be a serious safety issue, even raising the possibility of an explosion. Catalyst deactivation rates tend to increase with temperature, particularly of there are hot spots in the reactor. For alcohol synthesis, temperature control is essential because it has a large effect on the selectivity of the catalysts toward desired products. For example, for molybdenum disulfide catalysts unwanted side products such as methane, ethane, and propane are produced in much greater quantities if the temperature increases outside an ideal range. Slurry reactors are widely regarded as an efficient design for these reactions. In a slurry reactor a solid catalyst is suspended in an inert hydrocarbon liquid, synthesis gas is sparged into the bottom of the reactor, un-reacted synthesis gas and light boiling range products are removed as a gas stream, and heavy boiling range products are removed as a liquid stream. This configuration has several positive effects for synthesis gas reactions including: essentially isothermal operation, small catalyst particles to reduce heat and mass transfer effects, capability to remove heat rapidly through liquid vaporization, and improved flexibility on catalyst design through physical mixtures in addition to use of compositions that cannot be pelletized. Disadvantages include additional mass transfer resistance, potential for significant back-mixing on both the liquid and gas phases, and bubble coalescence. In 2001 a multiyear project was proposed to develop improved FT slurry reactors. The planned focus of the work was to improve the reactors by improving mass transfer while considering heat transfer issues. During the first year of the project the work was started and several concepts were developed to prepare for bench-scale testing. PowerEnerCat was unable to ...
Date: March 20, 2009
Creator: Lucero, Andrew
Partner: UNT Libraries Government Documents Department

Bioanalytical Applications of Real-Time ATP Imaging Via Bioluminescence

Description: The research discussed within involves the development of novel applications of real-time imaging of adenosine 5'-triphosphate (ATP). ATP was detected via bioluminescence and the firefly luciferase-catalyzed reaction of ATP and luciferin. The use of a microscope and an imaging detector allowed for spatially resolved quantitation of ATP release. Employing this method, applications in both biological and chemical systems were developed. First, the mechanism by which the compound 48/80 induces release of ATP from human umbilical vein endothelial cells (HUVECs) was investigated. Numerous enzyme activators and inhibitors were utilized to probe the second messenger systems involved in release. Compound 48/80 activated a G{sub q}-type protein to initiate ATP release from HUVECs. Ca{sup 2+} imaging along with ATP imaging revealed that activation of phospholipase C and induction of intracellular Ca{sup 2+} signaling were necessary for release of ATP. Furthermore, activation of protein kinase C inhibited the activity of phospholipase C and thus decreased the magnitude of ATP release. This novel release mechanism was compared to the existing theories of extracellular release of ATP. Bioluminescence imaging was also employed to examine the role of ATP in the field of neuroscience. The central nervous system (CNS) was dissected from the freshwater snail Lymnaea stagnalis. Electrophysiological experiments demonstrated that the neurons of the Lymnaea were not damaged by any of the components of the imaging solution. ATP was continuously released by the ganglia of the CNS for over eight hours and varied from ganglion to ganglion and within individual ganglia. Addition of the neurotransmitters K{sup +} and serotonin increased release of ATP in certain regions of the Lymnaea CNS. Finally, the ATP imaging technique was investigated for the study of drug release systems. MCM-41-type mesoporous nanospheres were loaded with ATP and end-capped with mercaptoethanol functionalized CdS monocrystals. Aggregates of nanospheres were bathed in imaging solution, ...
Date: December 12, 2003
Creator: Gruenhagen, Jason Alan
Partner: UNT Libraries Government Documents Department

Preparation and discharge characteristics of solid redox polymerization electrodes employing disulfide polymers and copolymers

Description: Recent work in our laboratory on polymeric organodisulfides has shown these materials to perform well as positive electrodes in solid-state batteries. The polymeric materials have been named solid redox polymerization electrodes (SRPE's) due to the reversible polymerization/depolymerization reaction that occurs on charge/discharge of the electrode. The cell radiation for SRPE-based cells can be described for a simple case as, 2n M + (SRS){sub n} = n M{sub 2}SRS, where M is an alkali metal (Li, Na, K) and R is an organic group. In the broader sense SRPE's can have more than two S groups per monomer R unit, and are reversible to other monovalent and divalent metals. In the fully charged state SRPE's consist of polydisulfide polymers and are depolymerized on discharge by scission of sulfur-sulfur bonds, leading to the formation of dithiolate salts in the fully discharged cell. SRPE's are easy to synthesize, are air stable, and should be very inexpensive in bulk quantities. Depending on the redox potential of the polydisulfide and reaction condition, many disulfides can be copolymerized by oxidizing a mixture of dithiols, x HSRSH + y HSR'SH + (x+y)l{sub 2} = (SRS){sub x}(Sr'S){sub y} + 2(x+y) Hl, allowing modification of the physical and/or redox properties of the SRPE's. A series of simple aliphatic dithiols including (HSCH{sub 2}CH{sub 2}SH), (HSCH{sub 2}CH{sub 2}OCH{sub 2}CH{sub 2}SH), and (HSCH{sub 2}CH{sub 2}SCH{sub 2}CH{sub 2}SH) have been oxidized to polydisulfides and mixtures of the dithiols have been copolymerized. All of the resulting polymers and copolymers were evaluated in solid-state lithium cells, with some of the new materials demonstrating high levels of performance. The utilization of available capacity in the positive electrode was observed to be independent of electrode thickness for a number of SRPE's of loading levels up to 45% by weight. 8 refs., 5 figs. 2 tabs.
Date: January 1, 1991
Creator: Lerner, M.M. (Oregon State Univ., Corvallis, OR (United States). Dept. of Chemistry); Visco, S.J.; Doeff, M.M.; Dejonghe, L.C. (Lawrence Berkeley Lab., CA (United States)) & Ue, M. (Mitsubishi Petrochemical Co. Ltd., Tokyo (Japan))
Partner: UNT Libraries Government Documents Department

A Review of Tribological Coatings for Control Drive Mechanisms in Space Reactors

Description: Tribological coatings must provide lubrication for moving components of the control drive mechanism for a space reactor and prevent seizing due to friction or diffusion welding to provide highly reliable and precise control of reflector position over the mission lifetime. Several coatings were evaluated based on tribological performance at elevated temperatures and in ultrahigh vacuum environments. Candidates with proven performance in the anticipated environment are limited primarily to disulfide materials. Irradiation data for these coatings is nonexistent. Compatibility issues between coating materials and structural components may require the use of barrier layers between the solid lubricant and structural components to prevent deleterious interactions. It would be advisable to consider possible lubricant interactions prior to down-selection of structural materials. A battery of tests was proposed to provide the necessary data for eventual solid lubricant/coating selection.
Date: February 21, 2006
Creator: Larkin, CJ; Edington, JD & Close, BJ
Partner: UNT Libraries Government Documents Department