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The Chemistry of 1,2-Dithiolane (Trimethylene Disulfide) As aModel for the Primary Quantum Conversion Act in Photosynthesis

Description: Some chemical and photochemical observations of 1,2-dithiolane and its derivatives are reported with particular reference to the possible mode of function of the naturally occurring system, 6-thioctic acid. Experimental evidence is presented to demonstrate that the strain energy in this 5-membered ring is not less than 6.5 Kcals and probably larger. Reagents which both oxidize and reduce this ring are described together with the conditions required for its reformation from the corresponding dithiol. Evidence is adduced to indicate that the primary product of photolysis of this ring in acetic media is very likely a thiol and sulfenic acid or derivative thereof.
Date: March 1, 1954
Creator: Barltrop, J.A; Hayes, P.M. & Calvin, M.
Partner: UNT Libraries Government Documents Department

Ming Parameter Input: Emma Model Redox Half Reaction Equation Deltag G Corrections for pH

Description: The purpose of this calculation is to provide appropriate input parameters for use in MING V 1.0 (CSCI 300 18 V 1.0). This calculation corrects the Grogan and McKinley (1990) values for {Delta}G so that the data will function in the MING model. The Grogan and McKinley (1990) {Delta}G data are presented for a pH of 12 whereas the MING model requires that the {Delta}G be reported at standard conditions (i.e. pH of 0).
Date: July 23, 1998
Creator: Jolley, D.M.
Partner: UNT Libraries Government Documents Department

Phosphorus Turnover and Photosynthesis

Description: The participation of phosphorus in biological oxidation-reduction reactions of the type found in glycolysis ADP + PO{sub 4}H{sup -} + 3-phosphoglyceraldehyde + DPN{sup +} = 3-phosphoglycerate{sup -} + 2H{sup +} + DPNH + ATP has suggested theories in which similar reactions are proposed for photosynthesis. In these theories the reducing power of photosynthesis is utilized not only for reduction of carbon dioxide but also, by means of coupled oxidations, for the generation of high-energy phosphate bonds, or in the last reference directly for the generation of high-energy phosphate. Since in these theories acyl phosphate is formed from inorganic phosphate, they are amenable to proof without isolation of particular intermediates, by means of radioactive phosphorus. It would be expected that the rate of conversion of inorganic phosphate to organic phosphate would be greater in light than in the dark. They have investigated this possibility under a variety of conditions and are unable to substantiate the theories.
Date: November 1, 1947
Creator: Aronoff, Sam & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Electrochemistry in concentrated organic redox solutions. Unusual reaction mechanisms and transport phenomena

Description: This report discusses and gives several examples of voltammetric studies in concentrated organic solutions and show that quantitative measurements can be performed under conditions where redox species is present in molar quantities. A brief description of experimental methods and theory of ultramicroelectrode techniques is presented. Examples of transport phenomena, coupled homogeneous reactions, and magnetic field effects in highly concentrated organic redox solutions are given.
Date: April 1, 1997
Creator: Ragsdale, S. R.; Paulson, S. C.; White, H. S. & Feldberg, S. W.
Partner: UNT Libraries Government Documents Department

Novel Computational Simulation of Redox Reactions Within a Metal Electrospray Emitter

Description: To further both our fundamental understanding implications of the electrolytic nature of the electrospray and our understanding of the analytical ion source, in the context of electrospray mass spectrometry (ES-MS), a computational simulation of the oxidation of chemical species inside a metal emitter has been developed. The analysis code employs a boundary integral method for the solution of the Laplace equation for the electric potential and current, and incorporates standard activation and concentration polarization functions for the redox active species in the system to define the boundary conditions. The specific system modeled consisted of a 100 {mu}m i .d., inert metal capillary CHICN/H2O (90/10 V/V). ES emitter and a spray solution comprised of an analyte dissolved in Variable parameters included the concentration (i.e., 5, 10, 20, and 50 ~M) of the easily oxidized analyte ferrocene (Fe, dicyclopentadienyl iron) in the solution, and solution conductivities of 1.9, 3.8, and 7.6 x 107 Mho/cm. ES currents were on the order of 0.05 {mu}A and the flow rate was 5 @A_nin. Under these defined conditions, the two most prominent reactions at the emitter metakolution interface were assumed to be H20 oxidation (2H20 = 02 + 4H+ + 4e") and Fe oxidation (Fe = Fe' +e-). Using this model it was possible to predict the inter-facial potentials, as well as the current density for each of the reactions, as a function of axial position from the emitter spray tip back upstream, under the various operational conditions. Computational fluid dynamics (CFD) calculations showed that the imposed flow rate through the emitter was adequate to prevent significant back-diffusion of Fe+ into the emitter against the flow direction. The computational simulations predict the same behavior for the ES ion source as has been observed experimentally and is consistent with the controlled-current electrolytic cell analogy of Van Berkel ...
Date: January 13, 1999
Creator: Bullock, J. S., IV; Giles, G. E.; Gray, L. J. & Van Berkel, G. J.
Partner: UNT Libraries Government Documents Department

Study of intermediates from transition metal excited-state electron-transfer reactions. Final report, August 4, 1986--August 31, 1997

Description: The techniques of continuous photolysis and pulsed laser flash photolysis, continuous and pulse radiolysis, fast-scan cyclic voltammetry, and time-resolved fluorimetry have been used to examine intramolecular electron transfer within the solvent quenching cage, photodynamics of quenching of the excited states of transition-metal photosensitizers, the properties of excites states and one-electron reduced forms, ground- and excited-state interactions with solutes, and photoinduced oxidations of organic solutes in aqueous solution. The following specific areas were examined: (1) the parameters that govern the yields of redox products from excited-state electron-transfer quenching reactions; (2) the mediation of the properties of excited states and one-electron reduced forms by the ligands and the solution medium; (3) the effect of the interactions between the ground state of the complex and the solution components on the behavior of the excited state; (4) the yields of singlet oxygen from excited-state energy-transfer quenching by O{sub 2}; and (5) the oxidations of solutes by singlet oxygen, excited-state electron-transfer quenching, and free radicals. This report contains the abstracts of 50 publications describing the studies.
Date: December 31, 1997
Creator: Hoffman, M.Z.
Partner: UNT Libraries Government Documents Department

Reduction of Heavy Metals by Cytochrome c(3)

Description: We report on reduction and precipitation of Se(VI), Pb(II), CU(II), U(VI), Mo(VI), and Cr(VI) in water by cytochrome c{sub 3} isolated from Desulfomicrobium baczdatum [strain 9974]. The tetraheme protein cytochrome c{sub 3} was reduced by sodium dithionite. Redox reactions were monitored by UV-visible spectroscopy of cytochrome c{sub 3}. Analytical electron microscopy work showed that Se(VI), Pb(II), and CU(II) were reduced to the metallic state, U(W) and Mo(W) to U(IV) and Mo(IV), respectively, and Cr(VI) probably to Cr(III). U(IV) and Mo(W) precipitated as oxides and Cr(III) as an amorphous hydroxide. Cytochrome c{sub 3} was used repeatedly in the same solution without loosing its effectiveness. The results suggest usage of cytochrome c{sub 3} to develop innovative and environmentally benign methods to remove heavy metals from waste- and groundwater.
Date: January 18, 2000
Creator: ABDELOUAS,A.; GONG,W.L.; LUTZE,W.; NUTTALL,E.H.; SPRAGUE,F.; SHELNUTT,JOHN A. et al.
Partner: UNT Libraries Government Documents Department

Parameter Identification and On-line Estimation of a Reduced Kinetic Model

Description: In this work, we present the estimation techniques used to update the model parameters in a reduced kinetic model describing the oxidation-reduction re- actions in a hydrothermal oxidation reactor. The model is used in a nonlinear model-based controller that minimizes the total aqueous nitrogen in the reac- tor effluent. Model reduction is accomplished by com- bining similar reacting compounds into one of four component groups and considering the global reac- tion pathways for each of these groups. The reduced kinetic model developed for thk reaction system pro- vides a means to characterize the complex chemical reaction system without considering each chemicaJ species present and the reaction kinetics of every pos- sible reaction pathway. For the reaction system under study, model reduction is essential in order to reduce the computational requirement so that on-line imple- mentation of the nonlinear model-based controller is possible and also to reduce the amount of a priori information required for the model.
Date: February 1, 1999
Creator: Dellorco, P.C.; Flesner, R.L.; Le, L.A.; Littell, J.D. & Muske, K.R.
Partner: UNT Libraries Government Documents Department

Photoredox reactions: Energy storage and halocarbon degradation

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objectives of this project were the following: (1) To characterize the structures and the structural dynamics of the singlet and triplet states of selected metal-metal bonded systems; (2) To characterize the post-excitation intramolecular electron transfer reactions of these complexes; (3) To investigate strongly adiabatic photo-oxidative addition reactions, including the addition of halocarbons to the electronically excited complexes and their hydrogen-evolving reactions; (4) To seek effective reductant systems that will function in catalytic cycles and regenerate the original, reduced dimer; and (5) To explore the chemistry of metals less expensive than iridium or platinum with regard to their potential for photochemical reactivity. The results include studies of W and Mo clusters with potential multielectron excited state redox reactivity, metal-metal bonded dimers sequestered in liquid crystal environments, d{sup 7} dimers with long-lived photocycles, and photochemically produced oxygen-fluorine systems.
Date: July 1, 1997
Creator: Woodruff, W.H.; Dyer, R.B. & Gray, H.B.
Partner: UNT Libraries Government Documents Department

Redox behavior of europium in the Preyssler heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-}

Description: In aqueous, mineral-acid electrolytes, the cyclic voltammetry of the europium- exchanged Preyssler heteropolyanion, [Eu{sup III}P{sub 5}W{sub 30}O{sub 110}]{sup 12-}, is unique among all the other trivalent-lanthanide-exchanged anions, [Ln{sup III}P{sub 5}W{sub 30}O{sub 110}]{sup 12-} for Ln {triple_bond} Ce-Lu. All [LnP{sub 5}W{sub 30}O{sub 110}]{sup 12-}, including Eu, form heteropoly blues upon reduction. In order to obtain insights about this issue, we conducted in situ Eu L{sub 3}-edge XANES (X-ray absorption near edge structure) spectroelectrochemical experiments on an aqueous solution of [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-} (5.5 mM) in a supporting electrolyte of 1 M H{sub 2}SO{sub 4} at two extreme potentials. The results demonstrate that the Eu{sup III} ion in the colorless Preyssler anion solution at open circuit potential (+0.21 V vs Ag/AgCl) is electroactive and is reduced to Eu{sup II} in the resulting dark blue solution from constant-potential bulk electrolysis at -0.55 V vs Ag/AgCl. This unusual redox behavior of [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-} may be of technological importance in the area of oxidation catalysis.
Date: August 1, 1997
Creator: Antonio, M.R. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

Probing the structure of metal-substituted molecular sieves by solid-state NMR

Description: Paramagnetic metal ions exert large influences on the NMR spectra of neighboring nuclei. The authors are using these effects to probe metal sites in zeolites and AlPO{sub 4} molecular sieves. In particular, they are studying [Co]-AlPO{sub 4}-5 because similar cobalt substituted AlPO{sub 4} sieves are reported in the literature. They have extended that work to probe the titanium zeolite TS-1 by comparing spectra of normal TS-1 to samples where the titanium has been reduced to the paramagnetic Ti{sup 3+}. This promises to be a useful technique for determining framework substitution in many zeolite systems.
Date: July 1998
Creator: Labouriau, A.; Crawford, S.N.; Ott, K. & Earl, W.L.
Partner: UNT Libraries Government Documents Department

Stability of plutonium(VI) in WIPP brine

Description: The redox stability of plutonium (VI) in WIPP brine was investigated by monitoring the oxidation state as a function of time using a combination of absorption spectrometry, radiochemical counting and filtration. Studies were performed with Pu-239 and Pu-238 in four WIPP brines at concentrations between 10{sup {minus}3} and 10{sup {minus}8} M for durations as long as two years. Two synthetic brines, Brine A and ERDA-6, and two underground collected brines, DH-36 and G-Seep, were used. The stability of Pu(VI) depended on the brine composition and the speciation of the plutonium in that brine. When carbonate was present, a Pu(VI)-carbonate complex was observed that was stable. In the absence of carbonate, Pu(VI) hydrolytic species predominated which had a wide range of stability in the brines investigated. The results reported will help define the speciation of plutonium in WIPP brine and hence its potential for migration.
Date: December 1, 1993
Creator: Reed, D.T. & Okajima, S.
Partner: UNT Libraries Government Documents Department

Calculations of fluid-mineral equilibria in the Aspo Hard Rock Laboratory

Description: The purpose of this report is to evaluate the utility of the EQ3/6 geochemical codes in describing mineral-fluid equilibria in the low temperature (<25{degrees}C) systems at the Aespoe Hard Rock Laboratory (HRL). Data on fluid chemistry and on fracture-filling mineralogy with depth were obtained from Smellie and Laaksoharju. Average temperatures in the HRL boreholes are generally less than 20{degrees}C. EQ3/6 was used to evaluate the extent to which equilibrium is achieved between minerals and fluids in these systems. Smellie and Laaksoharju used the PHREEQE geochemical modeling code to calculate saturation indices for fracture-lining minerals in boreholes KAS02, KAS03, KAS04 and KAS06 in order to ``support the presence or absence of the major fracture minerals``. They noted that only calcite and gypsum may be expected to attain equilibrium under the low temperature conditions Aespoe. However, they used closeness to equilibrium as an indicator of ``stable conditions, long bedrock residence/reaction times and slow to stagnant flow in the system.`` EQ3 was used to calculate mineral saturation indices for comparison, and EQ6 was used to try to predict the mineral assemblages coexisting with fluids.
Date: May 1, 1995
Creator: Bruton, C.J.
Partner: UNT Libraries Government Documents Department

Carbon microstructures for electrochemical studies

Description: Thin layers of photoresist were spin coated onto silicon wafers, and then carbonized to form smooth carbon films by heating in nitrogen for 1 hour at temperatures between 600 to 1100 C. Well-defined carbon microstructures on Si wafers that are being considered for electrodes in a microbattery concept were obtained by additional processing steps involving patterning and lithography of the photoresist prior to carbonization. The status of the fabrication of carbon microelectrodes obtained by pyrolysis of photoresist, characterization of the carbons by surface-sensitive techniques and electrochemical analysis by cyclic voltammetry of the I{sup -}/I{sub 3}{sup -} redox reaction is described.
Date: June 22, 2001
Creator: Kostecki, Robert; Song, Xiang Yun & Kinoshita, Kim
Partner: UNT Libraries Government Documents Department

Coupled modeling of groundwater flow solute transport, chemical reactions and microbial processes in the 'SP' island

Description: The Redox Zone Experiment was carried out at the Aespoe HRL in order to study the redox behavior and the hydrochemistry of an isolated vertical fracture zone disturbed by the excavation of an access tunnel. Overall results and interpretation of the Redox Zone Project were reported by /Banwart et al, 1995/. Later, /Banwart et al, 1999/ presented a summary of the hydrochemistry of the Redox Zone Experiment. Coupled groundwater flow and reactive transport models of this experiment were carried out by /Molinero, 2000/ who proposed a revised conceptual model for the hydrogeology of the Redox Zone Experiment which could explain simultaneously measured drawdown and salinity data. The numerical model was found useful to understand the natural system. Several conclusions were drawn about the redox conditions of recharge waters, cation exchange capacity of the fracture zone and the role of mineral phases such as pyrite, calcite, hematite and goethite. This model could reproduce the measured trends of dissolved species, except for bicarbonate and sulfate which are affected by microbially-mediated processes. In order to explore the role of microbial processes, a coupled numerical model has been constructed which accounts for water flow, reactive transport and microbial processes. The results of this model is presented in this report. This model accounts for groundwater flow and reactive transport in a manner similar to that of /Molinero, 2000/ and extends the preliminary microbial model of /Zhang, 2001/ by accounting for microbially-driven organic matter fermentation and organic matter oxidation. This updated microbial model considers simultaneously the fermentation of particulate organic matter by yeast and the oxidation of dissolved organic matter, a product of fermentation. Dissolved organic matter is produced by yeast and serves also as a substrate for iron-reducing bacteria. Model results reproduce the observed increase in bicarbonate and sulfate concentration, thus adding additional evidence for ...
Date: December 1, 2003
Creator: Samper, Javier; Molinero, Jorg; Changbing, Yang & Zhang, Guoxiang
Partner: UNT Libraries Government Documents Department

TRITIUM INCORPORATION STUDIES IN PHOTO-SYNTHETIC BACTERIA

Description: Although the detailed pathway of carbon, by which carbohydrates are formed from carbon dioxide during photosynthesis, has been established, comparatively little is known about the participation and transport of hydrogen in the complex series of reactions now known to be involved in photosynthesis. The transport of hydrogen may occur concurrently with the redox reactions of photosynthetic electron transport leading to the formation of ATP, as well as in the reduction of carbon dioxide. The participation of the chlorophylls, the carotenoids, the quinones, and other lipoid components in photosynthetic hydrogen transport has been the subject of considerable speculation. In an attempt to elucidate the pathway of hydrogen transport, we are studying the tritium labeling pattern in the lipid extracts of Rhodospirillum rubrum after the bacteria have been illuminated in growth medium containing tritiated water.
Date: July 1, 1967
Creator: Dehner, Thomas R.; Chan, W.-S.; Caple, Marianne B. & Calvin, M.
Partner: UNT Libraries Government Documents Department

CO2 Sequestration and Recycle by Photosynthesis

Description: Hydrocarbon oxygenate synthesis from photocatalytic reactions of CO{sub 2} and H{sub 2}O over various catalysts is a very attractive process. However, the formation rate of the hydrocarbons and oxygenates is significantly lower than conventional catalysis. One possible reason for the low rate of product formation is the presence of oxidation sites which reoxidize the products back to CO{sub 2} and H{sub 2}O. For further improvement of catalytic activity for the reduction process, it is essential to understand the oxidation reaction process. We have studied photocatalytic oxidation of methylene blue and found the oxidation rate is significantly higher than the reduction rate.
Date: February 12, 2006
Creator: Chuang, Steven S.C.
Partner: UNT Libraries Government Documents Department

Formation and Reactivity of Biogenic Iron Microminerals

Description: Radionuclide and heavy metal contaminants at DOE sites pose immediate and long-term environmental problems. Under the NABIR program, bacteria are being considered for their role in the cycling of these contaminants because they influence many redox reactions in the subsurface. Dissimilatory metal reducing bacteria (DMRB) are particularly important to controlling the biogeochemistry of subsurface environments through enzymatic reduction of iron and manganese minerals. During reduction of FeIII, biogenic FeII phases form at the cell-mineral interface which may profoundly influence metal reduction.
Date: August 10, 2002
Creator: Beveridge, Terrance J. & Ferris, F. Grant
Partner: UNT Libraries Government Documents Department

Reactivity of biogenic manganese oxide for metal sequestration and photochemistry: Computational solid state physics study

Description: Many microbes, including both bacteria and fungi, produce manganese (Mn) oxides by oxidizing soluble Mn(II) to form insoluble Mn(IV) oxide minerals, a kinetically much faster process than abiotic oxidation. These biogenic Mn oxides drive the Mn cycle, coupling it with diverse biogeochemical cycles and determining the bioavailability of environmental contaminants, mainly through strong adsorption and redox reactions. This mini review introduces recent findings based on quantum mechanical density functional theory that reveal the detailed mechanisms of toxic metal adsorption at Mn oxide surfaces and the remarkable role of Mn vacancies in the photochemistry of these minerals.
Date: February 1, 2010
Creator: Kwon, K.D. & Sposito, G.
Partner: UNT Libraries Government Documents Department

Parameter identification and on-line estimation for reduced kinetic model

Description: The base hydrolysis process for the destruction of energetic or explosive materials results is a high pH hydrolysate solution with reaction products that include a series of carboxylic acid salts, glycolates, amines, and nitrates. The hydrolysate solutions obtained from this process contain from two to ten wt% of organic carbon and nitrogen compounds that must be further treated before disposal. Hydrothermal oxidation at elevated temperatures (450 C) and pressure (14,000 psi) was selected as the treatment process for the hydrolysate solutions obtained from hydrolysis of the high explosive PBX 9404 at the Department of Energy Pantex facility in Amarillo, Texas. In this work, the authors describe the use of receding horizon identification and estimation techniques to determine the model parameters for a reduced kinetic model describing the oxidation-reduction reactions in a hydrothermal oxidation reactor. This model is used in a model predictive controller that minimizes the total aqueous nitrogen in the hydrothermal oxidation reactor effluent.
Date: August 7, 1998
Creator: Littel, J.D.; Muske, K.R.; Del`Orco, P.C.; Le, L.A. & Flesner, R.L.
Partner: UNT Libraries Government Documents Department

Place-exchange mechanism of Pt (111) oxidation/reduction as observed by synchrotron X-ray scattering

Description: Structural changes in the Pt(111) single crystal surface associated with incipient electrochemical oxidation/reduction were studied by {ital in}{ital situ} synchrotron x-ray reflectivity. It was shown that lifting of Pt atoms of the surface layer occurs, substantiating the long-standing hypothesis of a place-exchange mechanism for solution/metal interface oxidation. It was also shown that, for a charge transfer of {approx_lt}1.7 e{sup -}/Pt atom, the initially flat surface structure could be recovered by electrochemical reduction. In constrast, the surface was irreversibly roughened for amounts of charge transfer exceeding {approx}1.7 e{sup -}/Pt, but the roughening involved only the atoms in the top layer of the original flat surface. A detailed mechanism is proposed for the place-exchange mechanism and the subsequent roughening of the electrode surface.
Date: July 1, 1996
Creator: You, H.; Nagy, Z.; Zurawski, D.J. & Chiarello, R.P.
Partner: UNT Libraries Government Documents Department