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Novel metalloporphyrin catalysts for the oxidation of hydrocarbons

Description: Work was done for developing biomimetic oxidation catalysts. Two classes of metalloporphyrin catalysts were studied. The first class of catalysts studied were a novel series of highly substituted metalloporphyrins, the fluorinated iron dodecaphenylporphyrins. These homogeneous metalloporphyrin catalysts were screened for activity as catalysts in the oxidation of hydrocarbons by dioxygen. Results are discussed with respect to catalyst structural features. The second type of catalysts studied were heterogeneous catalysts consisting of metalloporphyrins applied to inorganic supports. Preliminary catalytic testing results with these materials are presented.
Date: November 1, 1996
Creator: Showalter, M.C.; Nenoff, T.M. & Shelnutt, J.A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Heterogeneous nucleation of calcium oxalate on native oxide surfaces

Description: The aqueous deposition of calcium oxalate onto colloidal oxides has been studied as a model system for understanding heterogeneous nucleation processes of importance in biomimetic synthesis of ceramic thin films. Calcium oxalate nucleation has been monitored by measuring induction times for nucleation using Constant Composition techniques and by measuring nucleation densities on extended oxide surfaces using an atomic force microscope. Results show that the dependence of calcium oxalate nucleation on solution supersaturation fits the functional form predicted by classical nucleation theories. Anionic surfaces appear to promote nucleation better than cationic surfaces, lowering the effective energy barrier to heterogeneous nucleation.
Date: April 1, 1994
Creator: Song, L.; Pattillo, M. J.; Graff, G. L.; Campbell, A. A. & Bunker, B. C.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Nonlinear optical properties of porphyrin and chlorophyll dimers studied by degenerated four wave mixing

Description: As one of the important elements in natural and artificial electron transfer and energy transfer processes, porphyrin and its derivatives have received much attention in photoelectronics and photoelectronic materials. As our first attempt to relate the {pi}-{pi} electronic couplings between porphyrin macrocycles to apparent third order nonlinear susceptibilities, we measured {chi}({sup 3}) for several porphyrin and chlorophyll a derivatives, including dimers with different configurations. Our preliminary results show that the dimers have enhanced {chi}({sup 3}) compared to those of the monomer. This enhancement is related to the relative orientations between the two macrocycles in the dimers. The parallel dimers with close face-to-face distances seem to have the highest enhancement in {chi}({sup 3}). Thus, we believe that {chi}({sup 3}) is strongly related to the {pi}-{pi} electronic coupling between the two conjugated ring systems.
Date: December 31, 1992
Creator: Chen, L. X. Q.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Solubility testing of actinides on breathing-zone and area air samples

Description: A solubility testing method for several common actinides has been developed with sufficient sensitivity to allow profiles to be determined from routine breathing zone and area air samples in the workplace. Air samples are covered with a clean filter to form a filter-sample-filter sandwich which is immersed in an extracellular lung serum simulant solution. The sample is moved to a fresh beaker of the lung fluid simulant each day for one week, and then weekly until the end of the 28 day test period. The soak solutions are wet ashed with nitric acid and hydrogen peroxide to destroy the organic components of the lung simulant solution prior to extraction of the nuclides of interest directly into an extractive scintillator for subsequent counting on a Photon-Electron Rejecting Alpha Liquid Scintillation (PERALS{reg_sign}) spectrometer. Solvent extraction methods utilizing the extractive scintillators have been developed for the isotopes of uranium, plutonium, and curium. The procedures normally produce an isotopic recovery greater than 95% and have been used to develop solubility profiles from air samples with 40 pCi or less of U{sub 3}O{sub 8}. Profiles developed for U{sub 3}O{sub 8} samples show good agreement with in vitro and in vivo tests performed by other investigators on samples from the same uranium mills.
Date: February 1, 1996
Creator: Metzger, R.L.; Jessop, B.H. & McDowell, B.L.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Artificially-structured photorefractive and biomimetic materials. Final report

Description: This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Organic materials have shown great promise for near term applications in electro-optic, photorefractive, and electroluminescent devices. Electro-optic materials are useful for fast optical switching, photorefractive materials are essential for optical computing and information storage; electroluminescence is the basis for light-emitting diodes (LEDs). Existing organic electro- optic and photorefractive materials require a breakthrough in techniques to control the microscopic molecular orientation while maintaining economical processing. Our unique approach addresses this problem by building ordered superlattices by molecular engineering. Existing organic LEDs suffer from device breakdown, probably catalyzed by interfacial defects. Our approach allows molecular level control of the electronic properties of the polymer interfaces by designing charge transport layers to isolate the active polymer layer. This project sought to create electro-optic and photorefractive materials by engineering rationally designed nonlinear molecular building blocks into multilayer thin films using self assembly techniques.
Date: September 1, 1996
Creator: McBranch, D.; Bishop, A.; Donohoe, R.; Heeger, A.; Li, D.; Maniloff, E. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Biomimetic thin film deposition

Description: Biological mineral deposition for the formation of bone, mollusk shell and other hard tissues provides materials scientists with illustrative materials processing strategies. This presentation will review the key features of biomineralization and how these features can be of technical importance. We have adapted existing knowledge of biomineralization to develop a unique method of depositing inorganic thin films and coating. Our approach to thin film deposition is to modify substrate surfaces to imitate the proteins found in nature that are responsible for controlling mineral deposition. These biomimetic surfaces control the nucleation and growth of the mineral from a supersaturated aqueous solution. This has many processing advantages including simple processing equipment, environmentally benign reagents, uniform coating of highly complex shapes, and enhanced adherence of coating. Many different types of metal oxide, hydroxide, sulfide and phosphate materials with useful mechanical, optical, electronic and biomedical properties can be deposited.
Date: September 1, 1995
Creator: Rieke, P.R.; Graff, G.E.; Campbell, A.A.; Bunker, B.C.; Baskaran, S.; Song, L. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Biomimetic TiO{sub 2} photocatalysis: A model system for pyotosynthesis

Description: Illumination of semiconductor colloids with light having energy greater than the band gap leads to the formation of electron/hold pairs. Similar to the natural photosynthetic systems, rapid recombination of photogenerated carriers is prevented by removal of one or both carriers from the semiconductor particle. Since the lifetime of charged pairs is very short, only very fast reactions with adsorbed species lead to efficient charge separation. Concurrently, surface adsorption also results in the blocking of the surface states that thermalize photogenerated charges and convert useful energy into heat. Thus, if the surface of the colloid is properly engineered the kinetics of the photochemical reactions and the redox properties of photogenerated charges in the modified colloids may be enhanced for stabilized charge separation, such as in natural photosynthesis. We have shown that adsorption of {alpha}-substituted mercapto-carboxylic acids on small particle TiO{sub 2} colloids results in the bidentate coordination of surface Ti atoms with carboxyl and mercapto groups. This complex is stabilized by the formation of a five membered ring which is the optimal configuration for octahedral coordination of Ti atoms. This surface modification of TiO{sub 2} results in the formation of a charge transfer complex that shifts the optical absorption threshold to the visible region of the spectrum (520 nm). These complexes provide more favorable absorbance properties for solar energy conversion. In this work we are applying electron paramagnetic resonance (EPR) to study the transient species formed by the reactions initiated by charge transfer or colloid photoabsorption.
Date: March 1, 1996
Creator: Thurnauer, M.C.; Rajh, T. & Tiede, D.M.
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Partner: UNT Libraries Government Documents Department

Light hydrocarbon gas conversion using porphyrin catalysts

Description: The objective of this project is to develop novel catalysts for the direct conversion of natural gas to a liquid fuel. The current work investigates the use of biomimetic metalloporphyrins as catalysts for the partial oxidation of light alkanes to alcohols.
Date: July 1, 1995
Creator: Showalter, M.C. & Shelnutt, J.A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Proceedings of the Nineteenth DOE Solar Photochemistry Research Conference

Description: This document is a compilation of reports presented at the Nineteenth DOE Solar Photochemistry Research Conference. Sessions included photophysical properties of transition metal complexes, cage effects on photochemistry, charge transfer, photo-induced charge separation in biomimetic molecules, photosynthesis, and electron transfer.
Date: July 1, 1995
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Biomimetic lithography and deposition kinetics of iron oxyhydroxide thin films

Description: Heterogeneous nucleation and crystal growth on functionalized organic substrates is a critical step in biological hard tissue formation. Self assembled monolayers can be derivatized with various organic functional groups to mimic the ``nucleation proteins`` for induction of mineral growth. Studies of nucleation and growth on SAMs can provide a better understanding of biomineralization and can also form the basis of a superior thin film deposition process. We demonstrate that micron-scale, electron and ion beam, lithographic techniques can be used to pattern SAMs with functional organic groups that either inhibit or promote mineral deposition. Patterned films of iron oxyhydroxide were deposited on the areas patterned with nucleation sites. Studies of the deposition kinetic of these films show that indeed the surface induces heterogeneous nucleation and that film formation does not occur via absorption of polymers or colloidal material formed homogeneously in solution. The nucleus interfacial free energy was calculated to be 24 mJ/m2 on a SAM surface composed entirely of sulfonate groups.
Date: December 1, 1993
Creator: Rieke, P. C.; Wood, L. L.; Marsh, B. M.; Fryxell, G. E.; Engelhard, M. H.; Baer, D. R. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

[Resonance Raman spectroscopy of metalloporphyrins and photoreaction centers]. Final report

Description: Critical has been understanding the role of intrinsic cyanometalate overlayers in modulating interfacial photoinduced charge transfer processes occuring at the Cd chalconide/aqueous ferri-ferrocyanide interface. Structural and charge transfer studies of [CdFe(CN){sub 6}]{sup 2-/1-} overlayers were undertaken; a picture has evolved which directly links charge transfer mediated cation intercalation processes to surface overlayer crystal structure, and overlayer structure to critical charge transfer parameters.
Date: December 31, 1992
Creator: Bocarsly, A. B.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Learning foraging thresholds for lizards

Description: This work gives a proof of convergence for a randomized learning algorithm that describes how anoles (lizards found in the Carribean) learn a foraging threshold distance. This model assumes that an anole will pursue a prey if and only if it is within this threshold of the anole`s perch. This learning algorithm was proposed by the biologist Roughgarden and his colleagues. They experimentally confirmed that this algorithm quickly converges to the foraging threshold that is predicted by optimal foraging theory our analysis provides an analytic confirmation that the learning algorithm converses to this optimal foraging threshold with high probability.
Date: January 12, 1996
Creator: Goldberg, L.A.; Hart, W.E. & Wilson, D.B.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Biological and chemical technologies research. FY 1995 annual summary report

Description: The annual summary report presents the fiscal year (FY) 1995 research activities and accomplishments for the United States Department of Energy (DOE) Biological and Chemical Technologies Research (BCTR) Program. This BCTR program resides within the Office of Industrial Technologies (OIT) of the Office of Energy Efficiency and Renewable Energy (EE). The annual summary report for 1995 (ASR 95) contains the following: program description (including BCTR program mission statement, historical background, relevance, goals and objectives); program structure and organization, selected technical and programmatic highlights for 1995; detailed descriptions of individual projects; a listing of program output, including a bibliography of published work; patents; and awards arising from work supported by the BCTR.
Date: March 1, 1996
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

The multi-niche crowding genetic algorithm: Analysis and applications

Description: The ability of organisms to evolve and adapt to the environment has provided mother nature with a rich and diverse set of species. Only organisms well adapted to their environment can survive from one generation to the next, transferring on the traits, that made them successful, to their offspring. Competition for resources and the ever changing environment drives some species to extinction and at the same time others evolve to maintain the delicate balance in nature. In this disertation we present the multi-niche crowding genetic algorithm, a computational metaphor to the survival of species in ecological niches in the face of competition. The multi-niche crowding genetic algorithm maintains stable subpopulations of solutions in multiple niches in multimodal landscapes. The algorithm introduces the concept of crowding selection to promote mating among members with qirnilar traits while allowing many members of the population to participate in mating. The algorithm uses worst among most similar replacement policy to promote competition among members with similar traits while allowing competition among members of different niches as well. We present empirical and theoretical results for the success of the multiniche crowding genetic algorithm for multimodal function optimization. The properties of the algorithm using different parameters are examined. We test the performance of the algorithm on problems of DNA Mapping, Aquifer Management, and the File Design Problem. Applications that combine the use of heuristics and special operators to solve problems in the areas of combinatorial optimization, grouping, and multi-objective optimization. We conclude by presenting the advantages and disadvantages of the algorithm and describing avenues for future investigation to answer other questions raised by this study.
Date: September 1, 1995
Creator: Cedeno, W.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department

Twenty-five years of artificial photosynthesis research at Ernest Orlando Lawrence Berkeley National Laboratory

Description: This report summarizes the research done on artificial photosynthesis by the Calvin Group between 1970 and 1995 when the program was terminated. It contains a compilation of the personnel involved as well as a bibliography of publications supported by the project.
Date: February 1, 1996
Creator: Otvos, J.W. & Calvin, M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Energy transfer in real and artificial photosynthetic systems

Description: Fluorescence emission from the photosynthetic organisms Tribonema aequale, Anacystis nidulau, and Chlorelia vulgais and from some chlorophyll model systems have been recorded as a function of excitation wavelength and temperature. Considerable similarity was observed in the effects of excitation wavelength and temperature on the fluorescence from intact photosynthetic organisms and the model systems. The parallelism in behavior suggest that self-assembly processes may occur in both the in vivo and in vitro systems that give rise to chlorophyll species at low temperature that may differ significantly from those present at ambient temperatures.
Date: February 1, 1995
Creator: Hindman, J.C.; Hunt, J.E. & Katz, J.J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Vectorial electron transfer in spatially ordered arrays. Progress report, January 1991--January 1994

Description: Objective was to find methods for rapid, controlled placement of light absorbers, relays, and multi-electron catalysts at defined sites with respect to a semiconductor or metal surface and thus to develop methods for preparing chemically modified photoactive surfaces as artificial photosynthetic units. Progress has been made in four areas: synthesis of new materials for directional electron transfer, preparation and characterization of anisotropic composites containing organic and inorganic components, elaboration of mechanisms of electrocatalysis, and development of new methods for surface modification of metals and semiconductors.
Date: January 1, 1994
Creator: Fox, M. A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

[Fundamental studies in oxidation-reduction in relation to water photolysis]. Final report, February 15, 1990--July 31, 1993

Description: Broad objectives are to improve the conceptual view of ways in which membranes and interfaces can be used to control chemical reactivity. Focus was on three elementary processes central to developing membrane-based integrated chemical systems for water photolysis or related photoconversion/photostorage processes. It was sought to identify the influence of interfaces on charge separation/recombination reactions, pathways for transmembrane charge separation across hydrocarbon bilayer membranes, and mechanisms of water oxidation catalyzed by transition metal coordination complexes. The supramolecular assemblies studied comprise primarily small unilamellar vesicles doped with amphiphilic viologens (N,N`dialkyl-4,4`-bipyridinium ions) which can function as transmembrane charge relays.
Date: July 1, 1994
Creator: Hurst, J. K.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Femtosecond transient grating studies of electron transfer in porphyrin and chlorophyll donor-acceptor molecules

Description: Transient grating studies of electron transfer in artificial photosynthetic systems are described. These systems include simple donor-acceptor molecules where the donor, a chlorophyll or porphyrin, is rigidly attached to an easily reduced species such as napthoquinone or benzoquinone. We have previously synthesized acceptor molecules which have well defined absorption bands upon reduction and are well removed from the excited and cationic states of porphyrins and chlorophylls. They also possess large molar extinction coefficients that dominate the spectra and have well defined polarization characteristics. These traits are ideal for polarization sensitive transient grating experiments which enable accurate determination of the angle of the transition dipole between the initial excitation and the acceptor probe, dynamic solvation effects on the charge separated species, and any time dependent rotation of the chromophores relative to each other. An example of the type of molecule utilized for these experiments is a free base porphyrin (HP) donor and a pyromellitic diimide (PI) acceptor directly bonded to the porphyrin ring.
Date: April 1, 1994
Creator: Wiederrecht, G. P.; Svec, W. A. & Wasielewski, M. R.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Photochemical energy conversion by membrane-bound photoredox systems. Progress report, July 1, 1989--March 1, 1992

Description: Most of our effort during the past grant period has been directed towards investigating electron transfer processes involving redox proteins at lipid bilayer/aqueous interfaces. This theme, as was noted in our previous three year renewal proposal, is consistent with our goal of developing biomimetic solar energy conversion systems which utilize the unique properties of biological electron transfer molecules. Thus, small redox proteins such as cytochrome c, plastocyanin and ferredoxin function is biological photosynthesis as mediators of electron flow between the photochemical systems localized in the membrane, and more complex soluble or membrane-bound redox proteins which are designed to carry out specific biological tasks such as transbilayer proton gradient formation, dinitrogen fixation, ATP synthesis, dihydrogen synthesis, generation of strong reductants, etc. In these studies, we have utilized two principal experimental techniques, laser flash photolysis and cyclic voltammetry, both of which permit direct measurements of electron transfer processes.
Date: March 1, 1992
Creator: Tollin, G.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Catalytic oxidation of hydrocarbons by dinuclear iron complexes. Progress report

Description: Our efforts during the past eight months were directed towards characterizing synthetic complexes that model the electronic and reactivity properties of the active site of methane monooxygenase (MMO), a metalloenzyme found in methanotrophic bacteria responsible for the biological oxidation of methane to methanol. We have investigated the structural/electronic and reactivity properties of a series of dinuclear model complexes that can function as oxygen atom transfer catalysts. In particular, our studies focused on [Fe{sup 2+}{sub 2}(H{sub 2}Hbab){sub 2}(N-MeIm){sub 2}], its DMF solvated form, [Fe{sup 2+}{sub 2}(H{sub 2}Hbab){sub 2}(DMF){sub 2}(MeIm)], and the mixed valent species [Fe{sup 2+}Fe{sup 3+}(H{sub 2}Hbab){sub 2}(DMF){sub 4}]{sup +}, (H{sub 4}Hbab = 1,2-bis(2-hydroxybenzamido) benzene). We have also examined [Fe{sup 3+}{sub 2}(H{sub 2}Hbab){sub 2}(DMF){sub 4}]{sup 2+}, [Fe{sup 3+}{sub 2}(H{sub 2}Hbab){sub 2}(OMe){sub 2}], and {mu}-oxo-[Fe{sup 3+}{sub 2}(H{sub 2}Hbab){sub 2}(DMF){sub 2]}, which are unable to act as oxygen atom transfer catalysts.
Date: December 31, 1992
Creator: Caradonna, J. P.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Digital electronic bone growth stimulator

Description: The present invention relates to the electrical treatment of biological tissue. In particular, the present invention discloses a device that produces discrete electrical pulse trains for treating osteoporosis and accelerating bone growth. According to its major aspects and broadly stated, the present invention consists of an electrical circuit configuration capable of generating Bassett-type waveforms shown with alternative signals provide for the treatment of either fractured bones or osteoporosis. The signal generator comprises a quartz clock, an oscillator circuit, a binary divider chain, and a plurality of simple, digital logic gates. Signals are delivered efficiently, with little or no distortion, and uniformly distributed throughout the area of injury. Perferably, power is furnished by widely available and inexpensive radio batteries, needing replacement only once in several days. The present invention can be affixed to a medical cast without a great increase in either weight or bulk. Also, the disclosed stimulator can be used to treat osteoporosis or to strengthen a healing bone after the cast has been removed by attaching the device to the patient`s skin or clothing.
Date: January 1, 1993
Creator: Kronberg, J.W.
Item Type: Refine your search to only Text
Partner: UNT Libraries Government Documents Department

Strategies for mimicking the primary events of bacterial photosynthesis: Structure, function, and mechanism

Description: Some of the possible implications of the photochemistry of photosynthesis for artificial systems are presented. A major aspect of this paper involves the special conditions required to prevent the undesirable charge recombination via the excited triplet state of the primary donor. If a multi-jump model is operative in the primary events of photosynthesis, then artificial model systems are relatively easy to synthesize. Such systems prevent back reactions via a series of downhill chemical reactions. Each downhill step in energy results in an increase in charge separation distance. The annihilation reactions, even to the less energetic triplet state, involve intermediate states uphill in energy and consequently are greatly diminished. However, if superexchange is a correct explanation of photosynthesis, then model systems have not been developed that properly mimic the natural process. In particular, the triplet back reaction can occur due to the lack of any thermal activation barrier. In nature this downhill back reaction appears to be prevented by carefully balancing the energetics using four molecules in the electron transport system. If this is the case, artificial photosynthesis would also require fine tuning of the coupling and energetics with three or four molecules making duplication more difficult to achieve. 10 refs.
Date: January 1, 1990
Creator: Norris, J.R. (Argonne National Lab., IL (USA) Chicago Univ., IL (USA). Dept. of Chemistry) & Raghavan, M. (Chicago Univ., IL (USA). Dept. of Chemistry)
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Partner: UNT Libraries Government Documents Department

Supramolecular structures modeling photosynthetic reaction center function

Description: Work in our laboratory has focused on the influence of solvent motion on the rates and energetics of photochemical charge separation in glassy solids. The efficiencies of many nonadiabatic electron transfer reactions involving photochemical electron donors with relatively low excited state energies, such as porphyrins and chlorophylls, are poor in the solid state. Recent work has shown that placing a porphyrin-acceptor system in a glassy solid at low temperature significantly raises the energy of ks ion-pair state. This destabilization can be as much as 0.8 eV relative to the ion pair state energy in a polar liquid. This contrasts sharply with photosynthetic reaction centers, which maintain medium-independent electron transfer rates with relatively small free energies of charge separation. Using this information we have set out to design photochemical systems that produce long-lived radical ion pairs in glassy solids with high quantum efficiency. These systems maintain their efficiency when placed in other glassy matrices, such as polymers. An important consequence of this effort is the design of molecules that minimize the electronic interaction between the oxidized donor and reduced acceptor. This minimization can be attained by careful design of the spacer groups linking the donor and acceptor and by using more than a single electron transfer step to increase the distance between the separated charges as is done in natural photosynthesis.
Date: August 20, 1992
Creator: Wasielewski, Michael R.; Gaines, George L., III; Gosztola, David; Niemczyk, Mark P. & Svec, Walter A.
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Partner: UNT Libraries Government Documents Department