32 Matching Results

Search Results

Advanced search parameters have been applied.

The intermolecular vibrational dynamics of substituted benzene and cyclohexane liquids, studied by femtosecond OHD-RIKES

Description: By using the femtosecond optical-heterodyne detected, Raman-induced Kerr effect spectroscopy (OHD-RIKES), we have studied the intermolecular dynamics of toluene, benzyl alcohol, benzonitrile, cyclohexane, and methylcyclohexane in both the time and frequency domains.
Date: June 1, 1995
Creator: Castner, E.W. Jr. & Chang, Yong Joon
Partner: UNT Libraries Government Documents Department

A novel carbon fiber based porous carbon monolith

Description: A novel porous carbon material based on carbon fibers has been developed. The material, when activated, develops a significant micro- or mesopore volume dependent upon the carbon fiber type utilized (isotropic pitch or polyacrylonitrile). The materials will find applications in the field of fluid separations or as a catalyst support. Here, the manufacture and characterization of our porous carbon monoliths are described.
Date: July 1, 1995
Creator: Burchell, T.D.; Klett, J.W. & Weaver, C.E.
Partner: UNT Libraries Government Documents Department

Tandem metal-mediated synthesis

Description: This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Boronic acids RB(OH){sub 2} are currently of interest for applications involving molecular recognition such as amine and sugar sensors and selective transport of biomolecules. They have also been shown to be powerful enzyme inhibitors and alpha-aminoboronic acids (ABAs) are particularly selective inhibitors of serine proteases. Unfortunately, current multistep synthetic routes to the latter compounds do not allow for the incorporation of a wide variety of organic substituents R that may lead to new, more selective enzyme inhibitors. In this work the author describes several direct routes to ABAs based on metal-catalyzed addition of diboron compounds to imines and nitriles. Several other applications of diboron additions to heteroatom-containing unsaturated organics are also described.
Date: December 31, 1998
Creator: Baker, R.T.
Partner: UNT Libraries Government Documents Department

On the response of rubbers at high strain rates.

Description: In this report, we examine the propagation of tensile waves of finite deformation in rubbers through experiments and analysis. Attention is focused on the propagation of one-dimensional dispersive and shock waves in strips of latex and nitrile rubber. Tensile wave propagation experiments were conducted at high strain-rates by holding one end fixed and displacing the other end at a constant velocity. A high-speed video camera was used to monitor the motion and to determine the evolution of strain and particle velocity in the rubber strips. Analysis of the response through the theory of finite waves and quantitative matching between the experimental observations and analytical predictions was used to determine an appropriate instantaneous elastic response for the rubbers. This analysis also yields the tensile shock adiabat for rubber. Dispersive waves as well as shock waves are also observed in free-retraction experiments; these are used to quantify hysteretic effects in rubber.
Date: February 1, 2010
Creator: Niemczura, Johnathan Greenberg (University of Texas-Austin)
Partner: UNT Libraries Government Documents Department

Interactions of Jet Fuels with Nitrile O-Rings: Petroleum-Derived versus Synthetic Fuels

Description: A transition from petroleum-derived jet fuels to blends with Fischer-Tropsch (F-T) fuels, and ultimately fully synthetic hydro-isomerized F-T fuels has raised concern about the fate of plasticizers in nitrile-butadiene rubber o-rings that are contacted by the fuels as this transition occurs. The partitioning of plasticizers and fuel molecules between nitrile o-rings and petroleum-derived, synthetic, and additized-synthetic jet fuels has been measured. Thermal desorption of o-rings soaked in the various jet fuels followed by gas chromatographic analysis with a mass spectrometric detector showed many of the plasticizer and stabilizer compounds were removed from the o-rings regardless of the contact fuel. Fuel molecules were observed to migrate into the o-rings for the petroleum-derived fuel as did both the fuel and additive for a synthetic F-T jet fuel additized with benzyl alcohol, but less for the unadditized synthetic fuel. The specific compounds or classes of compounds involved in the partitioning were identified and a semiquantitative comparison of relative partitioning of the compounds of interest was made. The results provide another step forward in improving the confidence level of using additized, fuIly synthetic jet fuel in the place of petroleum-derived fueL
Date: January 1, 2008
Creator: Gormley, R.J.; Link, D.D.; Baltrus, J.P. & Zandhuis, P.H.
Partner: UNT Libraries Government Documents Department

Interactions of Jet Fuels with Nitrile O-Rings: Petroleum-Derived versus Synthetic Fuels

Description: A transition from petroleum~derived jet fuels to blends with Fischer-Tropsch (F~T) fuels, and ultimately fully synthetic hydro-isomerized F-T fuels has raised concern about the fate of plasticizers in nitrile-butadiene rubber a-rings that are contacted by the fuels as this transition occurs. The partitioning of plasticizers and fuel molecules between nitrile a-rings and petroleum-derived, synthetic, and additized-synthetic jet fuels has been measured. Thermal desorption of o-rings soaked in the various jet fuels followed by gas chromatographic analysis with a mass spectrometric detector showed many of the plasticizer and stabilizer compounds were removed from the o-rings regardless of the contact fuel. Fuel molecules were observed to migrate into the o-rings for the petroleum-derived fuel as did both the fuel and additive for a synthetic F-T jet fuel additized with benzyl alcohol, but less for the unadditized synthetic fuel. The specific compounds or classes of compounds involved in the partitioning were identified and a semiquantitative comparison of relative partitioning of the compounds of interest was made. The results provide another step forward in improving the confidence level of using additized, fully synthetic jet fuel in the place of petroleum-derived fuel.
Date: January 1, 2009
Creator: Gormley, R.J.; Link, D.D.; Baltrus, J.P. & Zandhuis, P.H.
Partner: UNT Libraries Government Documents Department

Direct numerical simulation of solidification microstructures affected by fluid flow

Description: The effects of fluid flow on the solidification morphology of pure materials and solute microsegregation patterns of binary alloys are studied using a computational methodology based on a front tracking/finite difference method. A general single field formulation is presented for the full coupling of phase change, fluid flow, heat and solute transport. This formulation accounts for interfacial rejection/absorption of latent heat and solute, interfacial anisotropies, discontinuities in material properties between the liquid and solid phases, shrinkage/expansion upon solidification and motion and deformation of the solid. Numerical results are presented for the two dimensional dendritic solidification of pure succinonitrile and the solidification of globulitic grains of a plutonium-gallium alloy. For both problems, comparisons are made between solidification without fluid flow and solidification within a shear flow.
Date: December 1, 1997
Creator: Juric, D.
Partner: UNT Libraries Government Documents Department

Low Cost Carbon Fiber From Renewable Resources

Description: The Department of Energy Partnership for a New Generation of Vehicles has shown that, by lowering overall weight, the use of carbon fiber composites could dramatically decrease domestic vehicle fuel consumption. For the automotive industry to benefit from carbon fiber technology, fiber production will need to be substantially increased and fiber price decreased to $7/kg. To achieve this cost objective, alternate precursors to pitch and polyacrylonitrile (PAN) are being investigated as possible carbon fiber feedstocks. Additionally, sufficient fiber to provide 10 to 100 kg for each of the 13 million cars and light trucks produced annually in the U.S. will require an increase of 5 to 50-fold in worldwide carbon fiber production. High-volume, renewable or recycled materials, including lignin, cellulosic fibers, routinely recycled petrochemical fibers, and blends of these components, appear attractive because the cost of these materials is inherently both low and insensitive to changes in petroleum price. Current studies have shown that a number of recycled and renewable polymers can be incorporated into melt-spun fibers attractive as carbon fiber feedstocks. Highly extrudable lignin blends have attractive yields and can be readily carbonized and graphitized. Examination of the physical structure and properties of carbonized and graphitized fibers indicates the feasibility of use in transportation composite applications.
Date: August 10, 2001
Creator: Compere, A.L.
Partner: UNT Libraries Government Documents Department

CHARGE TRANSFER COMPLEXES WITH HEXAFLUDROBENZENE ANDPENTAFLUOROBENZONITRILE AS ACCEPTOR COMPONENTS

Description: Charge transfer associations are a well-established phenomena and a rather extensively investigated one also. Since the acceptor component of such complexes normally does not exist as a liquid under standard conditions, they wish to report on two organic liquids which function as acceptor components with suitable complimentary molecules. As indicated in Figure 1 (the presence of an extended shoulder in the spectra of the mixture), pentafluorobenzonitrile (PFBN) complexes with N,N,N{prime},N{prime}-tetramethyl-p-phenylenediamine (TMPD), with N,N-dimethylaniline (DMA), and with phenothiazine in cyclohexane. In addition, crystalline complexes of TMPN-PFBN and DMA-PFBN are obtained when the pure materials are mixed. These two organic bases also form solid complexes with hexafluorobenzene (HFB) when the materials are mixed in the pure state in a ratio of 1:1. However, new absorption bands are not detected in the spectra (in cyclohexane solutions) of mixtures of TMPD or DMA with HFB. When HFB is used as a solvent for TMPD or DMA, the solutions are visibly yellow. However, with time a reaction occurs as evident by the formation of a black precipitate. The solid complex formed between TMPD-PFBN, which is orange, was analyzed by a combination extraction and spectroscopic method and by vapor phase chromatography and found to contain a ratio of the two components of 1:1 which agrees with an elemental analysis of this complex. Analysis of DMA-PFBN or DMA-HFB complexes were complicated by the presence of excesses of the liquid components on the crystalline complexes. When attempts are made to dry the crystals, the crystals dissociate as the excesses evaporate until the crystals and the two components totally disappear. The TMPD-HFB complex was not analyzed. The complex between phenothiazine and PFBN as not isolated as a crystalline material. The association constants for the TMPD-PFBN and MDA-PFBN complexes were determined according to the method of Hildebrand and Benesi. The ...
Date: October 31, 1967
Creator: Corker, Gerald A. & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Evaluation of polyacrylonitrile (PAN) as a binding polymer for absorbers used to treat liquid radioactive wastes

Description: The chemical and radiation stability of polyacrylonitrile (PAN) in the form of beads (B-PAN), similar to the beads of composite absorbers, and one selected composite absorber (ammonium molybdophosphate, the active component in PAN binder [AMP-PAN], a prospective candidate for the treatment of acidic wastes) were studied. Aqueous 1M HNO{sub 3} + 1M NaNO{sub 3}, 1M NaOH + 1M NaNO{sub 3}, and 1M NaOH were chosen as simulants of DOE acidic and alkaline wastes. In addition,radiation stability was determined indistilled water. The chemical stability of B-PAN and AMP-PAN beads was tested for a period up to one month of contact with the solution at ambient temperature. The radiation stability of the beads was checked in a radiation dose range 10{sup 3}--10{sup 6} Gy (10{sup 5}--10{sup 8} rads). In acidic solutions the stability of PAN binder was proved not to be limited by either chemical or radiation decomposition. PAN binder may thus be used for preparing composite absorbers for treatment of acid wastes from DOE facilities. The same conclusion is valid for alkaline solutions with pH up to 13. In highly alkaline solutions (concentration of NAOH higher than I M) and in the presence of NaNO{sub 3}, the stability of the tested polyacrylonitrile polymer was sufficient for applications not extending over 10 days. Cross-linking of the polymer caused by ionizing radiation was found to have a positive influence on chemical stability. This effect enables a longer period of applicability of PAN-based composite absorbers. Because of the high sorption rate achievable with PAN-based absorbers, the stability achieved is sufficient for most applications in the DOE complex. The chemical stability of binding polymer may also be further improved by testing another, more suitable type of polymer from the broad family of polyacrylonitrile polymers.
Date: November 1995
Creator: Sebesta, F.; John, J.; Motl, A. & Stamberg, K.
Partner: UNT Libraries Government Documents Department

Copoly(arylene ether)s containing pendant sulfonic acid groups as proton exchange membranes

Description: A copoly(arylene ether) (PAE) with high fluorine content and a copoly(arylene ether nitrile) (PAEN) with high nitrile content, each containing pendant phenyl sulfonic acids were synthesized. The PAE and P AEN were prepared from decafluorobiphenyl (DFBP) and difluorobenzonitrile (DFBN) respectively, by polycondensation with 2phenylhydroquinone (PHQ) by conventional aromatic nucleophilic substitution reactions. sulfonic acid groups were introduced by mild post-sulfonation exclusively on the para-position of the pendant phenyl ring in PHQ. The membrane properties of the resulting sulfonated copolymers sPAE and sPAEN were compared for fuel cell applications. The copolymers sPAE and sPAEN, each having a degree of sulfonation (OS) of 1.0 had high ion exchange capacities (IEC{sub v})(wet) (volume-based, wet state) of 1.77 and 2.55 meq./cm3, high proton conductivities of 135.4 and 140.1 mS/cm at 80 C, and acceptable volume-based water uptake of 44.5 -51.9 vol% at 80 C, respectively, compared to Nafion. The data points of these copolymer membranes are located in the upper left-hand corner in the trade-off plot of alternative hydrocarbon polyelectrolyte membranes (PEM) for the relationship between proton conductivity versus water uptake (weight based or volume based), i.e., high proton conductivity and low water uptake. Furthermore, the relative selectivity derived from proton conductivity and methanol permeability is higher than that of Nafion.
Date: January 1, 2009
Creator: Dae Sik, Kim; Yu Seung, Kim; Gilles, Robertson & Guiver, Michael D
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

Lithium intercalation in porous carbon anodes

Description: Carbon foams derived from the phase separation of polyacrylonitrile/solvent mixtures were investigated as lithium intercalation anodes for rechargeable lithium-ion batteries. The carbon foams have a bulk density of 0.35--0.5 g/cm{sup 3}, low surface area (< 50 m{sup 2}/g), and an average cell size of 5--10 {mu}m. Polyacrylonitrile-based carbon foams doped with phosphoric acid had capacity as high as 450 mAh/g. Carbon capacity increased with increasing phosphoric acid concentration in the doping solution. The doped porous carbon anodes exhibited good cyclability and excellent coulombic efficiency.
Date: November 23, 1994
Creator: Tran, T.D.; Pekala, R.W. & Mayer, S.T.
Partner: UNT Libraries Government Documents Department

Lithium intercalation in porous carbon electrodes

Description: Carbons derived from the phase separation of polyacrylonitrile/solvent mixtures were investigated as lithium intercalation anodes for rechargeable lithium-ion batteries. The carbon electrodes have a bulk density of 0.35-0.5 g/cm{sup 3}, relatively low surface areas (< 10 m{sup 2}/g), and micron-size cells. Pyrolysis temperature influences the reversible lithium intercalation and the irreversible capacity (associated with the formation of the passivating layer). Carbon electrodes pyrolyzed at 600{degrees}C have first-cycle capacity as high as 550 mAh/g as well as large irreversible capacity, 440 mAh/g. Electrodes prepared at 1050{degrees}C have reversible capacities around 270 mAh/g with relatively lower capacity losses (120 mAh/g). Doping the organic precursors with phosphoric acid, prior to pyrolysis at 1050{degrees}C, leads to carbon electrodes with reversible capacities as high as 450 mAh/g. The capacity of doped carbon increased with increasing phosphorus concentration in the samples. The doped carbon anodes exhibited good cycleability and excellent coulombic efficiency. The electrochemical performance is related to morphology, chemical composition, and local structural order.
Date: April 1, 1995
Creator: Tran, T.D.; Feikert, J. & Pekala, R.W.
Partner: UNT Libraries Government Documents Department

Pyrolysis and Combustion of Acetonitrile (CH{sub 3}CN)

Description: Acetonitrile (CH{sub 3}CN) is formed from the thermal decomposition of a variety of cyclic, noncyclic, and polymeric nitrogen-containing compounds such as pyrrole and polyacrylonitrile. The pyrolysis and combustion of acetonitrile have been studied over the past 30 years to gain a more detailed understanding of the complex mechanisms involved in the release of nitrogen-containing compounds such as hydrogen cyanide (HCN) in fires and nitrogen oxides (NOx) in coal combustion. This report reviews the literature on the formation of HCN and NOx from the pyrolysis and combustion of acetonitrile and discusses the possible products found in an acetonitrile fire.
Date: May 22, 2002
Creator: Britt, P. F.
Partner: UNT Libraries Government Documents Department

Vapor space characterization of waste Tank 241-TY-101: Results from samples collected on 4/6/95

Description: This report describes inorganic and organic analyses results from samples obtained from the headspace of the Hanford waste storage Tank 241-TY-101 (referred to as Tank TY-101). The results described here were obtained to support safety and toxicological evaluations. A summary of the results for inorganic and organic analytes is listed in Table 1. Detailed descriptions of the results appear in the text. Quantitative results were obtained for the inorganic compounds ammonia (NH{sub 3}), nitrogen dioxide (NO{sub 2}), nitric oxide (NO), and water vapor (H{sub 2}O). Sampling for hydrogen cyanide (HCN) and sulfur oxides (SO{sub x}) was not requested. In addition, quantitative results were obtained for the 39 TO-14 compounds plus an additional 14 analytes. Off these, 5 were observed above the 5-ppbv reporting cutoff. One tentatively identified compound (TIC) was observed above the reporting cutoff of (ca.) 10 ppbv and are reported with concentrations that are semiquantitative estimates based on internal-standard response factors. The six organic analyses identified are listed in Table 1 and account for approximately 100% of the total organic components in Tank TY-101. Two permanent gases, carbon dioxide (CO{sub 2}) and nitrous oxide (N{sub 2}O), were also detected. Tank TY-101 is on the Ferrocyanide Watch List.
Date: November 1, 1995
Creator: Klinger, G.S.; Clauss, T.W.; Ligotke, M.W.; Pool, K.H.; McVeety, B.D.; Olsen, K.B. et al.
Partner: UNT Libraries Government Documents Department

Cesium absorption from acidic solutions using ammonium molybdophosphate on a polyacrylonitrile support (AMP-PAN)

Description: Recent efforts at the Idaho Chemical Processing Plant (ICPP) have included evaluation of cesium removal technologies as applied to ICPP acidic radioactive waste streams. Ammonium molybdophosphate (AMP) immobilized on a polyacrylonitrile support (AMP-PAN) has been studied as an ion exchange agent for cesium removal from acidic waste solutions. Capacities, distribution coefficients, elutability, and kinetics of cesium-extraction have been evaluated. Exchange breakthrough curves using small columns have been determined from 1M HNO{sub 3} and simulated waste solutions. The theoretical capacity of AMP is 213 g Cs/kg AMP. The average experimental capacity in batch contacts with various acidic solutions was 150 g Cs/kg AMP. The measured cesium distribution coefficients from actual waste solutions were 3287 mL/g for dissolved zirconia calcines, and 2679 mL/g for sodium-bearing waste. The cesium in the dissolved alumina calcines was analyzed for; however, the concentration was below analytical detectable limits resulting in inconclusive results. The reaction kinetics are very rapid (2-10 minutes). Cesium absorption appears to be independent of acid concentration over the range tested (0.1 M to 5 M HNO{sub 3}).
Date: December 1, 1995
Creator: Miller, C.J.; Olson, A.L. & Johnson, C.K.
Partner: UNT Libraries Government Documents Department

General solutions for the oxidation kinetics of polymers

Description: The simplest general kinetic schemes applicable to the oxidation of polymers are presented, discussed and analyzed in terms of the underlying kinetic assumptions. For the classic basic autoxidation scheme (BAS), which involves three bimolecular termination steps and is applicable mainly to unstabilized polymers, typical assumptions used singly or in groups include (1) long kinetic chain length, (2) a specific ratio of the termination rate constants and (3) insensitivity to the oxygen concentration (e.g., domination by a single termination step). Steady-state solutions for the rate of oxidation are given in terms of one, two, three, or four parameters, corresponding respectively to three, two, one, or zero kinetic assumptions. The recently derived four-parameter solution predicts conditions yielding unusual dependencies of the oxidation rate on oxygen concentration and on initiation rate, as well as conditions leading to some unusual diffusion-limited oxidation profile shapes. For stabilized polymers, unimolecular termination schemes are typically more appropriate than bimolecular. Kinetics incorporating unimolecular termination reactions are shown to result in very simple oxidation expressions which have been experimentally verified for both radiation-initiated oxidation of an EPDM and thermoxidative degradation of nitrile and chloroprene elastomers.
Date: August 1, 1996
Creator: Gillen, K.T.; Clough, R.L. & Wise, J.
Partner: UNT Libraries Government Documents Department

Determination of spring modulus for several types of elastomeric materials (O-rings) and establishment of an open database for seals

Description: Seals that provide the containment system interface between the packaging body and closure must function in high and low temperature environments, under dynamic and static loading conditions, and with different types of contained media. It is one of the most critical elements in the container since the container fails to meet regulations if the seal does not function properly. A research and testing program for seal materials was initiated at Sandia in 1988 with the goal of characterizing the behavior of seal materials commonly used in packages conditions as specified in the regulations (NRC IOCFR Part 71) and American National Standards Institute (ANSI) 14.5. The performance of elastomeric seals in undeformed closures at both high and low temperatures has been investigated (Bronowski 1995). Work has begun with this program to determine the response of elastomeric seals to fast acting dynamic deformations`` in the closure. The response of elastomeric o-ring seals during closure movements due to long-term deformations has already been characterized. What has not been well characterized are short-term closure movements with durations of only a few milliseconds that result in the so called ``burp`` release. Methods for generating this type of response in a repeatable manner had not been developed and standard leak detection equipment does not have a fast enough response time to measure these transient events. One factor which affects the length of the burp is the ability of the o-ring to quickly close the gap to prevent a significant leak. The dynamic characteristics of the elastomeric o-ring material including the dynamic spring modulus and internal damping are directly related to its ability to quickly close the gap. A set of tests designed to determine the dynamic properties for various material types and durometers (hardness) of elastomers that were both lubricated and dry at ambient temperature were ...
Date: December 31, 1995
Creator: McMurtry, W.M. & Hohnstreiter, G.F.
Partner: UNT Libraries Government Documents Department

Review of organic nitrile incineration at the Toxic Substances Control Act Incinerator

Description: Lockheed Martin Energy Systems, Inc. (LMES) operates the East Tennessee Technology Park (ETTP), formerly called the Oak Ridge K-25 Site, where uranium was enriched under contract with the US Department of Energy (DOE). Currently, ETTP missions include environmental management, waste management (WM), and the development of new technologies. As part of its WM mission, ETTP operates the TSCA (Toxic Substances Control Act) Incinerator (TSCAI) for treatment of hazardous waste and polychlorinated biphenyls (PCBs) contaminated with low-level radioactivity. Beginning in the autumn of 1995, employees from diverse ETTP buildings and departments reported experiencing headaches, fatigue, depression, muscle aches, sleeplessness, and muscle tremors. These symptoms were judged by a physician in the ETTP Health Services Department to be consistent with chronic exposures to hydrogen cyanide (HCN). The National Institute for Occupational Safety and Health (NIOSH) was called in to perform a health hazard evaluation to ascertain whether the employees` illnesses were in fact caused by occupational exposure to HCN. The NIOSH evaluation found no patterns for employees` reported symptoms with respect to work location or department. NIOSH also conducted a comprehensive air sampling study, which did not detect airborne cyanides at the ETTP. Employees, however, expressed concerns that the burning of nitrile-bearing wastes at the TSCAI might have produced HCN as a combustion product. Therefore, LMES and DOE established a multidisciplinary team (TSCAI Technical Review Team) to make a more detailed review of the possibility that combustion of nitrile-bearing wastes at the TSCAI might have either released nitriles or created HCN as a product of incomplete combustion (PIC).
Date: October 1, 1997
Partner: UNT Libraries Government Documents Department

Development of a toolbox of organic synthetic reactions that can be induced on individual molecules by STM

Description: OAK B262 Final Report DOE Grant No.: DE-FG03-01ER15263 ''Development of a toolbox of organic synthetic reactions that can be induced on individual molecules by STM'' Abstract Bommisetty V. Rao, Ki-Young Kwon, Robert Perry, Luke Nysen, Gregory Pavin, Qibin Zhang, Casey Dugger and Ludwig Bartels University of California at Riverside, Pierce Hall, Riverside, CA92521, email: Ludwig.Bartels@ucr.edu The key scientific objective of this project is the development of a set of reliable techniques for the addressal of specific bonds of individual molecules in order to assemble functional molecules on a metal surface at single-atom precision. Success in this direction will open up a conceptually novel route to single molecule chemistry, which can provide its products at any desired surface location without involving any lithographic steps at all. In the course of this project a number of halo-substituted aryls and alkyls where investigated with special concern to two properties: clean deposition of the reactants from the gas phase on metallic surfaces and STM-based addressability of individual substituents of them. In order to prevent contamination of the sample by deposition of solvent residue, a special depositions source was developed that uses a skimmed molecular beam. Exemplary substances studied were 1,3-iodobromobenzene (IBB), 3 bromopropionitrile (BPN) and 4,4'-dibromobiphenyl (DBB). In STM-induced reactions, IBB shows concerted activation of both halogens, which does not allow the individual addressal of one bond at a time. The concept of individual addressabilities of bonds in bi-substituted molecule was confirmed by use of BPN. This reactant is, however, strongly bound to the substrate and, hence, not very suitable for the assembly of larger aggregates, even if the nitrile group could be activated. We found individual activation of one of the bromines of DBB. This molecule lies flat on the surface and it is a promising candidate for the assembly of larger molecular ...
Date: September 25, 2003
Creator: Bartels, Ludwig
Partner: UNT Libraries Government Documents Department

Sulfur K-Edge XAS and DFT Calculations on NitrileHydratase: Geometric and Electronic Structure of the Non-heme Iron Active Site

Description: The geometric and electronic structure of the active site of the non-heme iron enzyme nitrile hydratase (NHase) is studied using sulfur K-edge XAS and DFT calculations. Using thiolate (RS{sup -})-, sulfenate (RSO{sup -})-, and sulfinate (RSO{sub 2}{sup -})-ligated model complexes to provide benchmark spectral parameters, the results show that the S K-edge XAS is sensitive to the oxidation state of S-containing ligands and that the spectrum of the RSO- species changes upon protonation as the S-O bond is elongated (by {approx}0.1 {angstrom}). These signature features are used to identify the three cysteine residues coordinated to the low-spin Fe{sup III} in the active site of NHase as CysS{sup -}, CysSOH, and CysSO{sub 2}{sup -} both in the NO-bound inactive form and in the photolyzed active form. These results are correlated to geometry-optimized DFT calculations. The pre-edge region of the X-ray absorption spectrum is sensitive to the Z{sub eff} of the Fe and reveals that the Fe in [FeNO]{sup 6} NHase species has a Z{sub eff} very similar to that of its photolyzed Fe{sup III} counterpart. DFT calculations reveal that this results from the strong {pi} back-bonding into the {pi}* antibonding orbital of NO, which shifts significant charge from the formally t{sub 2}{sup 6} low-spin metal to the coordinated NO.
Date: September 28, 2006
Creator: Dey, Abhishek; Chow, Marina; /Stanford U., Chem. Dept.; Taniguchi, Kayoko; /Wako, RIKEN; Lugo-Mas, Priscilla et al.
Partner: UNT Libraries Government Documents Department