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Designing the Ideal Uranyl Ligand: a Sterically-Induced Speciation Change in Complexes with Thiophene-Bridged Bis(3-hydroxy-N-methylpyridin-2-one)

Description: Structural characterization of a mononuclear uranyl complex with a tetradentate, thiophene-linked bis(3-hydroxy-N-methylpyridin-2-one) ligand reveals the most planar coordination geometry yet observed with this ligand class. The introduction of ethylsulfanyl groups onto the thiophene linker disrupts this planar, conjugated ligand arrangement, resulting in the formation of dimeric (UO{sub 2}){sub 2}L{sub 2} species in which each ligand spans two uranyl centers. Relative energy calculations reveal that this tendency toward dimer formation is the result of steric interference between ethylsulfanyl substituents and linking amides.
Date: September 11, 2009
Creator: Szigethy, Geza & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Reaction chemistry of cerium

Description: It is truly ironic that a synthetic organic chemist likely has far greater knowledge of the reaction chemistry of cerium(IV) than an inorganic colleague. Cerium(IV) reagents have long since been employed as oxidants in effecting a wide variety of organic transformations. Conversely, prior to the late 1980s, the number of well characterized cerium(IV) complexes did not extend past a handful of known species. Though in many other areas, interest in the molecular chemistry of the 4f-elements has undergone an explosive growth over the last twenty years, the chemistry of cerium(IV) has for the most part been overlooked. This report describes reactions of cerium complexes and structure.
Date: January 1, 1997
Partner: UNT Libraries Government Documents Department

Temperature-dependence of the ultrafast intermolecular dynamics of Amides: Formamide, N-methylformamide, N,N-dimethylformamide, N- methylacetamide, and N-methylpropionamide from 290-370 K

Description: Femtosecond optical-heterodyne detected, Raman-induced Car effect spectroscopy was used to characterize the full spectrum of the intermolecular vibrational and diffusive dynamics for these five amides, which are among the most interesting organic solvents. 50-fs, transform-limited pulses were used to excite all the intermolecular motions in the 0 to 400 cm{sup -1} range. Clear differences were found in the response vs temperature. 2 figs.
Date: June 1, 1996
Creator: Castner, E.W.
Partner: UNT Libraries Government Documents Department

Functional Characterization of Plant Fatty Acid Amide Hydrolases

Description: Fatty acid amide hydrolase (FAAH) terminates the endocannabinoid signaling pathway that regulates numerous neurobehavioral processes in animals by hydrolyzing a class of lipid mediators, N-acylethanolamines (NAEs). Recent identification of an Arabidopsis FAAH homologue (AtFAAH) and several studies, especially those using AtFAAH overexpressing and knock-out lines suggest that a FAAH-mediated pathway exists in plants for the metabolism of endogenous NAEs. Here, I provide evidence to support this concept by identifying candidate FAAH cDNA sequences in diverse plant species. NAE amidohydrolase assays confirmed that several of the proteins encoded by these cDNAs indeed catalyzed the hydrolysis of NAEs in vitro. Kinetic parameters, inhibition properties, and substrate specificities of the plant FAAH enzymes were very similar to those of mammalian FAAH. Five amino acid residues determined to be important for catalysis by rat FAAH were absolutely conserved within the plant FAAH sequences. Site-directed mutation of each of the five putative catalytic residues in AtFAAH abolished its hydrolytic activity when expressed in Escherichia coli. Contrary to overexpression of native AtFAAH in Arabidopsis that results in enhanced seedling growth, and in seedlings that were insensitive to exogenous NAE, overexpression of the inactive AtFAAH mutants showed no growth enhancement and no NAE tolerance. However, both active and inactive AtFAAH overexpressors displayed hypersensitivity to ABA, suggesting a function of the enzyme independent of its catalytic activity toward NAE substrates. Yeast two-hybrid screening identified Arg/Ser-rich zinc knuckle-containing protein as a candidate protein that physically and domain-specifically interacts with AtFAAH and its T-DNA knock-out Arabidopsis was hypersensitive to ABA to a degree similar to AtFAAH overexpressors. Taken together, AtFAAH appears to have a bifurcating function, via NAE hydrolysis and protein-protein interaction, to control Arabidopsis growth and interaction with phytohormone signaling pathways. These studies help to functionally define the group of enzymes that metabolize NAEs in plants, and further will ...
Date: December 2010
Creator: Kim, Sang-Chul
Partner: UNT Libraries

The Influence of Linker Geometry on Uranyl Complexation by Rigidly-Linked Bis(3-hydroxy-N-methyl-pyridin-2-one)

Description: A series of bis(3-hydroxy-N-methyl-pyridin-2-one) ligands was synthesized, and their respective uranyl complexes were characterized by single crystal X-ray diffraction analyses. These structures were inspected for high-energy conformations and evaluated using a series of metrics to measure co-planarity of chelating moieties with each other and the uranyl coordination plane, as well as to measure coordinative crowding about the uranyl dication. Both very short (ethyl, 3,4-thiophene and o-phenylene) and very long ({alpha},{alpha}{prime}-m-xylene and 1,8-fluorene) linkers provide optimal ligand geometries about the uranyl cation, resulting in planar, unstrained molecular arrangements. The planarity of the rigid linkers also suggests there is a degree of pre-organization for a planar coordination mode that is ideal for uranyl-selective ligand design. Comparison of intramolecular N{sub amide}-O{sub phenolate} distances and {sup 1}H NMR chemical shifts of amide protons supports earlier results that short linkers provide the optimal geometry for intramolecular hydrogen bonding.
Date: April 22, 2010
Creator: Szigethy, Geza & Raymond, Kenneth
Partner: UNT Libraries Government Documents Department

For Stimul-Responsive Polymers with Enhanced Efficiency in Reservoir Recovery Processes

Description: Acrylamide-based hydrophobically modified (HM) polybetaines containing N-butylphenylacrylamide (BPAM) and varying amounts of either sulfobetaine (3-(2-acrylamido-2-methylpropanedimethylammonio)-1-propanesulfonate, AMPDAPS) or carboxybetaine (4-(2-acrylamido-2-methylpropyldimethylammonio) butanoate, AMPDAB) comonomers were synthesized via micellar copolymerization. The terpolymers were characterized via {sup 13}C NMR and UV spectroscopies, classical and dynamic light scattering, and potentiometric titration. The response of aqueous polymer solutions to various external stimuli, including changes in solution pH, electrolyte concentration, and the addition of small molecule surfactants, was investigated using surface tension and rheological measurements. Low charge density terpolymers were found to show greater viscosity enhancement upon the addition of surfactant compared to the high charge density terpolymers. The addition of sodium dodecyl sulfate (SDS) produced the largest maximum in solution viscosity, while N-dodecyl-N,N,N-trimethylammonium bromide (DTAB), N-dodecyl-N,N-dimethylammonio-1-propanesulfonate (SB3-12), and Triton X-100 tended to show reduced viscosity enhancement. In most cases, the high charge density carboxybetaine terpolymer exhibited diminished solution viscosities upon surfactant addition. In our last report, we discussed solution thermodynamic theory that described changes in polymer coil conformation as a function of solution temperature and polymer molecular weight. These polymers contained no ionic charges. In this report, we expand polymer solution theory to account for the electrostatic interactions present in solutions of charged polymers. Polymers with ionic charges are referred to as polyions or polyelectrolytes.
Date: February 28, 2003
Creator: McCormick, Charles & Hester, Roger
Partner: UNT Libraries Government Documents Department

"Smart" Multifunctional Polymers for Enhanced Oil Recovery

Description: Herein we report the synthesis and solution characterization of a novel series of AB diblock copolymers with neutral, water-soluble A blocks comprised of N,N-dimethylacrylamide (DMA) and pH-responsive B blocks of N,N-dimethylvinylbenzylamine (DMVBA). To our knowledge, this represents the first example of an acrylamido-styrenic block copolymer prepared directly in homogeneous aqueous solution. The best blocking order (using polyDMA as a macro-CTA) was shown to yield well-defined block copolymers with minimal homopolymer impurity. Reversible aggregation of these block copolymers in aqueous media was studied by {sup 1}H NMR spectroscopy and dynamic light scattering. Finally, an example of core-crosslinked micelles was demonstrated by the addition of a difunctional crosslinking agent to a micellar solution of the parent block copolymer. Our ability to form micelles directly in water that are responsive to pH represents an important milestone in developing ''smart'' multifunctional polymers that have potential for oil mobilization in Enhanced Oil Recovery Processes.
Date: October 15, 2005
Creator: McCormick, Charles & Lowe, Andrew
Partner: UNT Libraries Government Documents Department

A comparative study of the complexation of Np(V) with N,N-dimethyl-3-oxa-glutaramic acid and related ligands: thermodynamics, optical properties and structural aspects

Description: Complexation of Np(V) with N,N-dimethyl-3-oxa-glutaramic acid (DMOGA) was studied in comparison with its diamide analog, N,N,N{prime},N{prime}-tetramethyl-3-oxa-glutaramide (TMOGA), and dicarboxylate analog, oxydiacetic acid (ODA). Thermodynamic parameters, including the stability constant and the enthalpy of complexation, were determined by spectrophotometry and calorimetry. Single-crystal structure of NpO{sub 2}(H{sub 2}O)(DMOGA){center_dot}H{sub 2}O(c) was identified by X-ray diffractometry using synchrotron radiation. Like ODA and TMOGA, DMOGA forms a tridentate Np(V) complex, with three oxygen atoms coordinating to the linear NpO{sub 2}{sup +} moiety via the equatorial plane. The stability constants, enthalpy and entropy of complexation generally decrease in the order ODA > DMOGA > TMOGA, suggesting that the complexation is entropy driven and the substitution of a carboxylate group with an amide group reduces the strength of complexation with Np(V) due to the decrease in the entropy of complexation.
Date: March 29, 2010
Creator: Rao, Linfeng; Tian, Guoxin & Teat, Simon J.
Partner: UNT Libraries Government Documents Department

Efficient Route to Highly Water-Soluble Aromatic Cyclic Hydroxamic Acid Ligands

Description: 2-Hydroxyisoquinolin-1-one (1,2-HOIQO) is a new member of the important class of aromatic cyclic hydroxamic acid ligands which are widely used in metal sequestering applications and metal chelating therapy. The first general approach for the introduction of substituents at the aromatic ring of the chelating moiety is presented. As a useful derivative, the highly water-soluble sulfonic acid has been synthesized by an efficient route that allows general access to 1,2-HOQIO 3-carboxlic acid amides, which are the most relevant for applications.
Date: February 6, 2008
Creator: Seitz, Michael & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Acceleration of Amide Bond Rotation by Encapsulation in the Hydrophobic Interior of a Water-Soluble Supramolecular Assembly

Description: The hydrophobic interior cavity of a self-assembled supramolecular assembly exploits the hydrophobic effect for the encapsulation of tertiary amides. Variable temperature 1H NMR experiments reveal that the free energy barrier for rotation around the C-N amide bond is lowered by up to 3.6 kcal/mol upon encapsulation. The hydrophobic cavity of the assembly is able to stabilize the less polar transition state of the amide rotation process. Carbon-13 labeling studies showed that the {sup 13}C NMR carbonyl resonance increases with temperature for the encapsulated amides which suggests that the assembly is able to favor a twisted for of the amide.
Date: April 8, 2008
Creator: Pluth, Michael D.; Bergman, Robert G. & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Rh(I)-Catalyzed Arylation of Heterocycles via C-H Bond Activation: Expanded Scope Through Mechanistic Insight

Description: A practical, functional group tolerant method for the Rh-catalyzed direct arylation of a variety of pharmaceutically important azoles with aryl bromides is described. Many of the successful azole and aryl bromide coupling partners are not compatible with methods for the direct arylation of heterocycles using Pd(0) or Cu(I) catalysts. The readily prepared, low molecular weight ligand, Z-1-tert-butyl-2,3,6,7-tetrahydrophosphepine, which coordinates to Rh in a bidentate P-olefin fashion to provide a highly active yet thermally stable arylation catalyst, is essential to the success of this method. By using the tetrafluoroborate salt of the corresponding phosphonium, the reactions can be assembled outside of a glove box without purification of reagents or solvent. The reactions are also conducted in THF or dioxane, which greatly simplifies product isolation relative to most other methods for direct arylation of azoles employing high-boiling amide solvents. The reactions are performed with heating in a microwave reactor to obtain excellent product yields in two hours.
Date: July 18, 2007
Creator: Lewis, Jared; Berman, Ashley; Bergman, Robert & Ellman, Jonathan
Partner: UNT Libraries Government Documents Department

Chemistry induced by the selective excitation of core electrons in biomolecules. Final project report, April 1, 1993--April 30, 1996

Description: The key feature of this research is the use of tunable monochromatic x-rays from synchrotron sources to investigate the effects of ionizing radiation on uracil and prolinamide. These sources provide the new capability of enhancing significantly the selective ionization or excitation of a specific atom in a molecule by tuning the photon energy to the core-ionization threshold for that atom or by tuning to a neutral core-hole resonance associated with that atom. As a result, chemical transformations caused directly by the core-electron ionization or excitation can be separated from those caused by secondary excitation steps. The chemistry associated with the secondary excitations also can be examined more precisely than has been done in the past because the energy of the emitted photoelectrons and Auger electrons can be controlled and varied, and direct ionization of the solvent or matrix also can be controlled, i.e. reduced or enhanced selectively by varying the x-ray energy and selecting matrix materials with small or large x-ray absorption cross sections. Experiments are performed by isolating target molecules in thin solid films.
Date: August 1, 1997
Creator: Hanson, D.M.
Partner: UNT Libraries Government Documents Department

New deposition processes for the growth of oxide and nitride thin films

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The goal of this effort is to study the use of homoleptic metal amido compounds as precursors for chemical vapor deposition (CVD). The amides offer potential for the deposition of a variety of important materials at low temperatures. The establishment of these precursor compounds will enhance the ability to exploit the properties of advanced materials in numerous coatings applications. Experiments were performed to study the reactivity of Sn[NMe{sub 2}]{sub 4} with oxygen. The data demonstrated that gas-phase insertion of oxygen into the Sn-N bond, leading to a reactive intermediate, plays an important role in tin oxide deposition. Several CVD processes for technologically important materials were developed using the amido precursor complexes. These included the plasma enhanced CVD of TiN and Zr{sub 3}N{sub 4}, and the thermal CVD of GaN and Al N. Quality films were obtained in each case, demonstrating the potential of the amido compounds as CVD precursors.
Date: November 1, 1998
Creator: Apen, E.A.; Atagi, L.M.; Barbero, R.S.; Espinoza, B.F.; Hubbard, K.M.; Salazar, K.V. et al.
Partner: UNT Libraries Government Documents Department

Computational Studies of C–H/C–C Manipulation Utilizing Transition Metal Complexes

Description: Density Functional Theory (DFT) is an effective tool for studying diverse metal systems. Presented herein are studies of a variety of metal systems, which can be applied to accomplish transformations that are currently difficult/impossible to achieve. The specific topics studied utilizing DFT include: 1) C–H bond activation via an Earth-abundant transition metal complex, 2) C–H bond deprotonation via an alkali metal superbase, 3) and amination/aziridination reactions utilizing a CuI reagent. Using DFT, the transformation to methanol (CH3OH) from methane (CH4) was examined. The transition metal systems studied for this transformation included a model FeII complex. This first-row transition metal is an economical, Earth-abundant metal. The ligand set for this transformation includes a carbonyl ligand in one set of complexes as well as a phosphite ligand in another. The 3d Fe metal shows the ability to convert alkyls/aryls to their oxidized counterpart in an energetically favorable manner. Also, “superbasic” alkali metal amides were investigated to perform C—H bond cleavage. Toluene was the substrate of interest with Cs chosen to be the metal of interest because of the highly electropositive nature of this alkali metal. These highly electrophilic Cs metal systems allow for very favorable C—H bond scission with a toluene substrate. Finally, the amination and aziridination of C–H and C=C bonds, respectively, by a CuI reagent was studied. The mechanism was investigated using DFT calculations. Presently, these mechanisms involving the use of coinage metals are debated. Our DFT simulations shed some insight into how these transformations occur and ultimately how they can be manipulated.
Date: May 2015
Creator: Pardue, Daniel B.
Partner: UNT Libraries

Managing Tight Binding Receptors for New Separations Technologies

Description: An Imprinting System based on Hydrogen Bonding. In our first explorations we chose to use a tetradentate macrocyclic ligand, N,N',N'',N'''-tetra(2- carbamoylethyl)-1,4,8,11- tetraazacyclotetradecane (4cyclam), to provide strong metal ion binding, with four appended arms that terminate in amide functions to provide hydrogen bonding with corresponding groups in the polymer (Structure 1). Nickel(II) ion was chosen for these studies because of the kinetic inertness of the square planar complexes it forms with tetraazamacrocycles. Because covalent interactions tend to involve slow kinetics we use those that are non-covalent for the affinity between the MIP and the imprinting metal complex. The immediate issue is ''can non-covalent interactions be strong enough to produce the proposed new methodology''? The literature indicates that imprinting using, for example, hydrogen bonding supports only 10 to 15%, certainly less than 20%, re-binding capacity. An equally compelling issue is the relationship of the combined advantages of selective complex formation and selective binding of the complex to the polymer. Further, are these macroporous polymers durable enough to be used in a separations methodology? In considering these issues, binding and selectivity have been studied at both the complex formation and the polymer/imprint level.
Date: June 14, 2003
Creator: Busch, Daryle H. & Givens, Richard S.
Partner: UNT Libraries Government Documents Department


Description: The objective of the project is to develop biochemical pathways for the selective cleavage of C-N bonds in molecules found in petroleum. The initial phase of the project was focused on the isolation or development of an enzyme capable of cleaving the C-N bond in aromatic amides, specifically 2-aminobiphenyl. The objective of the second phase of the research will be to construct a biochemical pathway for the selective removal of nitrogen from carbazole by combining the carA genes from Sphingomonas sp. GTIN11 with the gene(s) encoding an appropriate deaminase. The objective of the final phase of the project will be to develop derivative C-N bond cleaving enzymes that have broader substrate ranges and to demonstrate the use of such strains to selectively remove nitrogen from petroleum. During the first year of the project (October, 2002-September, 2003) enrichment culture experiments resulted in the isolation of microbial cultures that utilize aromatic amides as sole nitrogen sources, several amidase genes were cloned and were included in directed evolution experiments to obtain derivatives that can cleave C-N bonds in aromatic amides, and the carA genes from Sphingomonas sp. GTIN11, and Pseudomonas resinovorans CA10 were cloned in vectors capable of replicating in Escherichia coli. During the second year of the project (October, 2003-September, 2004) enrichment culture experiments succeeded in isolating a mixed bacterial culture that can utilize 2-aminobiphenyl as a sole nitrogen source, directed evolution experiments were focused on the aniline dioxygenase enzyme that is capable of deaminating aniline, and expression vectors were constructed to enable the expression of genes encoding C-N bond cleaving enzymes in Rhodococcus hosts. The construction of a new metabolic pathway to selectively remove nitrogen from carbazole and other molecules typically found in petroleum should lead to the development of a process to improve oil refinery efficiency by reducing the poisoning, ...
Date: October 1, 2004
Creator: II, John J. Kilbane
Partner: UNT Libraries Government Documents Department

Supramolecular Chemistry of Selective Anion Recognition for Anions of Environmental Relevance

Description: This project involves the design and synthesis of receptors for anions of environmental importance, including emphasis on high level and low activity waste. Polyammonium macrocycles as receptors and nitrate as target anion were the focus of the first phase of this project. A second phase involved the synthesis of lipophilic amide based receptors in order to increase the potential for obtaining workable receptors for both separations and sensing applications on site. In the renewal of this project, anions have been extended especially to include selective recognition and binding of sulfate. A three tier approach was employed: I. Design, synthesis, and physical and structural characterization of receptors; II. Examination of the technique known as ITIES, Interface Between Two Immiscible Electrolyte Solutions, as an analytical probe for anion analysis; and III. Separations studies using lipophilic amide receptors for anion binding done at the Oak Ridge National Laboratory by Bruce Moyer. The result of this program will impact a variety of needs of the Environmental Science Management Program in both sensing and separations areas.
Date: June 4, 2002
Creator: Bowman-James, Kristin; Wilson, George S. & Moyer, Bruce
Partner: UNT Libraries Government Documents Department

A regulatory role for N-acylethanolamine metabolism in Arabidopsis thaliana seeds and seedlings.

Description: N-Acylethanolamines (NAEs) are bioactive acylamides that are present in a wide range of organisms. Because NAE levels in seeds decline during imbibition similar to ABA, a physiological role was predicted for these metabolites in Arabidopsis thaliana seed germination and seedling development. There is also a corresponding increase of AtFAAH (fatty acid amide hydrolase), transcript levels and activity, which metabolizes NAE to ethanolamine and free fatty acids. Based on whole genome microarray studies it was determined that a number of up-regulated genes that were responsive to NAE were also ABA responsive. NAE induced gene expression in these ABA responsive genes without elevating endogenous levels of ABA. It was also determined that many of these NAE/ABA responsive genes were associated with an ABA induced secondary growth arrest, including ABI3. ABI3 is a transcription factor that regulates the transition from embryo to seedling growth, the analysis of transcript levels in NAE treated seedlings revealed a dose dependent, inverse relationship between ABI3 transcript levels and growth, high ABI3 transcript levels were associated with growth inhibition. Similar to ABA, NAE negatively regulated seedling growth within a narrow window of early seedling establishment. When seedlings are exposed to NAE or ABA within the window of sensitivity, the induction of genes normally associated with the ungerminated desiccation tolerant state resumed. The NAE tolerant FAAH overexpressor and the NAE sensitive FAAH knockout both had a NAE/ABA sensitive window similar to the wild type A. thaliana. The abi3-1 ABA insensitive mutant does not undergo growth arrest upon exposure to ABA, but NAE did induce growth arrest when treated within the sensitivity window. This evidence showed that although NAE functions within an ABA dependent pathway, it also functions in an ABA independent signaling pathway. The FAAH overexpressor is tolerant to NAE through its ability to quickly metabolize NAE from the ...
Date: May 2009
Creator: Teaster, Neal D.
Partner: UNT Libraries


Description: Ruthenium in uranyl nitrate solutions from the Purex Process was adsorbed by the solid residue that remains when the solutions are concentrated by evaporation after treatment with thiocarbanilide and thioacetarnide. Other chemicals were tested and the results are summarized. (auth)
Date: June 1, 1958
Creator: Prohaska, C.A.
Partner: UNT Libraries Government Documents Department

A new optical parametric amplifier based on lithium thioindate used for sum frequency generation vibrational spectroscopic studies of the Amide I mode of an interfacial model peptide

Description: We describe a new optical parametric amplifier (OPA) that employs lithium thioindate, LiInS{sub 2} (LIS), to create tunable infrared light between 1500 cm{sup -1} and 2000 cm{sup -1}. The OPA based on LIS described within provides intense infrared light with a good beam profile relative to similar OPAs built on silver gallium sulfide, AgGaS{sub 2} (AGS), or silver gallium selenide, AgGaSe{sub 2} (AGSe). We have used the new LIS OPA to perform surface-specific sum frequency generation (SFG) vibrational spectroscopy of the amide I vibrational mode of a model peptide at the hydrophobic deuterated polystyrene (d{sub 8}-PS)-phosphate buffered saline interface. This model polypeptide (which is known to be an ?-helix in the bulk solution under the high ionic strength conditions employed here) contains hydrophobic leucyl (L) residues and hydrophilic lysyl (K) residues, with sequence Ac-LKKLLKLLKKLLKL-NH{sub 2}. The amide I mode at the d{sub 8}-PS-buffer interface was found to be centered around 1655 cm{sup -1}. This can be interpreted as the peptide having maintained its {alpha}-helical structure when adsorbed on the hydrophobic surface, although other interpretations are discussed.
Date: May 3, 2008
Creator: York, Roger L.; Holinga, George J.; Guyer, Dean R.; McCrea, Keith R.; Ward, Robert S. & Somorjai, Gabor A.
Partner: UNT Libraries Government Documents Department

Complexation of actinides with derivatives of oxydiaceticacid

Description: Complexation of Np(V), U(VI) and Nd(III) with dimethyl-3-oxa-glutaramic acid (DMOGA) and tetramethyl-3-oxa-glutaramide (TMOGA) was studied in comparison with the complexation with oxydiacetic acid (ODA). Stability constants and enthalpy of complexation were determined by potentiometry, spectrophotometry and calorimetry. Thermodynamic parameters, in conjunction with structural information of solid compounds, indicate that DMOGA and TMOGA form tridentate complexes with the ether-oxygen participating in bonding with actinide/lanthanide ions. The trends in the stability constants, enthalpy and entropy of complexation are discussed in terms of the difference in the hydration of the amide groups and carboxylate groups and the difference in the charge density of the metal ions.
Date: January 4, 2006
Creator: Rao, Linfeng & Tian, Guoxin
Partner: UNT Libraries Government Documents Department

Sum Frequency Generation Vibrational Spectroscopy Studies on ModelPeptide Adsorption at the Hydrophobic Solid-Water and HydrophilicSolid-Water Interfaces

Description: Sum frequency generation (SFG) vibrational spectroscopy has been used to study the interfacial structure of several polypeptides and amino acids adsorbed to hydrophobic and hydrophilic surfaces under a variety of experimental conditions. Peptide sequence, peptide chain length, peptide hydrophobicity, peptide side-chain type, surface hydrophobicity, and solution ionic strength all affect an adsorbed peptide's interfacial structure. Herein, it is demonstrated that with the choice of simple, model peptides and amino acids, surface specific SFG vibrational spectroscopy can be a powerful tool to elucidate the interfacial structure of these adsorbates. Herein, four experiments are described. In one, a series of isosequential amphiphilic peptides are synthesized and studied when adsorbed to both hydrophobic and hydrophilic surfaces. On hydrophobic surfaces of deuterated polystyrene, it was determined that the hydrophobic part of the peptide is ordered at the solid-liquid interface, while the hydrophilic part of the peptide appears to have a random orientation at this interface. On a hydrophilic surface of silica, it was determined that an ordered peptide was only observed if a peptide had stable secondary structure in solution. In another experiment, the interfacial structure of a model amphiphilic peptide was studied as a function of the ionic strength of the solution, a parameter that could change the peptide's secondary structure in solution. It was determined that on a hydrophobic surface, the peptide's interfacial structure was independent of its structure in solution. This was in contrast to the adsorbed structure on a hydrophilic surface, where the peptide's interfacial structure showed a strong dependence on its solution secondary structure. In a third experiment, the SFG spectra of lysine and proline amino acids on both hydrophobic and hydrophilic surfaces were obtained by using a different experimental geometry that increases the SFG signal. Upon comparison of these spectra to the SFG spectra of interfacial polylysine and ...
Date: December 19, 2007
Creator: York, Roger L.
Partner: UNT Libraries Government Documents Department

Molecular composites from liquid crystalline polymers and liquid crystalline thermosets

Description: We propose a new approach to molecular composites. This approach uses a mixture of a liquid crystalline polymer and a liquid crystalline thermoset to enhance the miscibility. Preliminary neutron scattering data is presented on a system of short and long rod aromatic amides. The data is interpreted using the interpenetrating phase model of Debye and Bueche. The analysis indicates that the scattering is consistent with this model and shows a characteristic length scale in the range of 70 to 80 A. The intensity of the scattering is lower than calculated for the strong segregation limit, suggesting that there is some intermixing of the components.
Date: July 1, 1993
Creator: Benicewicz, B. C.; Douglas, E. P. & Hjelm, R. P. Jr.
Partner: UNT Libraries Government Documents Department