856 Matching Results

Search Results

Advanced search parameters have been applied.

A Positive Ion Source

Description: This paper describes the construction of a positive ion source of the electrodeless discharge type and may be divided into two main topis; (1) the radio frequency oscillator and power amplifier and associated power supply and (2) the ionization chamber.
Date: 1948
Creator: Hannah, Kenneth W.
Partner: UNT Libraries

Methods Development for Simultaneous Determination of Anions and Cations by Ion Chromatography

Description: The problem with which this research is concerned is the determination of inorganic anions and cations with single injection ion chromatography. Direct detection of the separated analyte ions occurs after the analyte ions have passed through ion-exchange resins where they are separated according to their affinity for the ion-exchange resin active sites. The techniques involve the use of essentially a non-suppressed ion chromatographic system followed by a suppressed ion chromatographic system. With this system it is possible to accomplish both qualitative and quantitative determinations.
Date: May 1987
Creator: Jones, Vonda K. (Vonda Kaye)
Partner: UNT Libraries

Enantioselective Catalysis of the Aza-Cope Rearrangement by a Chiral Supramolecular Assembly

Description: The chiral supramolecular catalyst Ga{sub 4}L{sub 6} [L = 1,5-bis(2,3-dihydroxybenzoylamino)naphthalene] is a molecular tetrahedron that catalyzes the 3-aza-Cope rearrangement of allyl enammonium cations. This catalysis is accomplished by preorganizing the substrate in a reactive conformation within the host. This work demonstrates that through the use of enantiopure assembly, its chiral cavity is capable of catalyzing the 3-aza-Cope rearrangement enantioselectively, with yields of 21-74% and enantiomeric excesses from 6 to 64% at 50 C. At lower temperatures, the enantioselectivity improved, reaching 78% ee at 5 C. This is the highest enantioselectivity to date induced by the chiral cavity of a supramolecular assembly.
Date: July 29, 2009
Creator: Brown, Casey J.; Bergman, Robert G. & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

The Effects of Common Electrolytes on Growth and Development of Selected Species of Aquatic Actinomycetes

Description: The role that aquatic actinomycetes play, in the production of tastes and odors in water supplies has been investigated since 1948. The ability of these organisms to produce by-products in lakes and streams, which renders the water unpalatable, is of considerable public health importance. It is desirable that the waterworks industry has as much information as possible concerning the factors that contribute to the growth of these organisms. Since it appears that the aquatic actinomycetes may be isolated from most fresh-water sources, the problem of diversified environments and nutritional requirements offers an excellent field of investigation. The fresh-waters of the world contain variable quantities of electrolytes that may determine in part the biological activity of these organisms. The unsolved questions in this instance are concerned with the electrolytes present and their quantitative effects on the growth and development of these forms.
Date: August 1959
Creator: Sissom, Stanley L.
Partner: UNT Libraries

The Determination of Total Non-U Cations in UF₄ by Penta-Ether Extraction

Description: "In consideration of the known high efficiency of penta-ether on the extraction of [Uranium] from aqueous solution without particularly affecting most other cations in the solution, it was felt that a TNU (total non-U cation) determination could be based upon the use of pents-ether to remove the U from non-U cations. After such separation, the non-U cations could then be determined in essentially the same manner as in the present TNU method (Method 50, CD-3801). The use of the penta-ether separation would have the advantage of reducing the amount of handling of the sample required in the present procedure and of reducing the time required to complete a TNU determination."
Date: 1946
Creator: Yellin, H. & Sinclair, E. E.
Partner: UNT Libraries Government Documents Department

Synthesis and physico-chemical properties of ionic liquidscontaining tetrakis(perfluorophenyl)borate, tetraphenylborate andtrifluorophenylborate anions.

Description: Synthesis and some physico-chemical properties are reported for six new hydrophobic ionic liquids containing tetrakis(perfluorophenyl)borate, tetraphenylborate or trfluorophenylborate anions and imidazolium or pyridinium cations.
Date: March 1, 2006
Creator: Papaiconomou, Nicolas; Salminen, Justin; Yakelis, Neal & Prausnitz, John M.
Partner: UNT Libraries Government Documents Department

Cation-cation interactions, magnetic communication and reactivity of the pentavalent uraniumion [U(NR)2]+

Description: The dimeric bis(imido) uranium complex [{l_brace}U(NtBu)2(I)(tBu2bpy){r_brace}2] (see picture; U green, N blue, I red) has cation-cation interactions between [U(NR)2]+ ions. This f1-f1 system also displays f orbital communication between uranium(V) centers at low temperatures, and can be oxidized to generate uranium(VI) bis(imido) complexes.
Date: January 1, 2009
Creator: Spencer, Liam P; Schelter, Eric J; Boncella, James M; Yang, Ping; Gsula, Robyn L; Scott, Brian L et al.
Partner: UNT Libraries Government Documents Department

Aza Cope Rearrangement of Propargyl Enammonium Cations Catalyzed By a Self-Assembled `Nanozyme

Description: The tetrahedral [Ga{sub 4}L{sub 6}]{sup 12-} assembly (L = N,N-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene) encapsulates a variety of cations, including propargyl enammonium cations capable of undergoing the aza Cope rearrangement. For propargyl enammonium substrates that are encapsulated in the [Ga{sub 4}L{sub 6}]{sup 12-} assembly, rate accelerations of up to 184 are observed when compared to the background reaction. After rearrangement, the product iminium ion is released into solution and hydrolyzed allowing for catalytic turnover. The activation parameters for the catalyzed and uncatalyzed reaction were determined, revealing that a lowered entropy of activation is responsible for the observed rate enhancements. The catalyzed reaction exhibits saturation kinetics; the rate data obey the Michaelis-Menten model of enzyme kinetics, and competitive inhibition using a non-reactive guest has been demonstrated.
Date: February 27, 2008
Creator: Hastings, Courntey J.; Fiedler, Dorothea; Bergman, Robert G. & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Connecting the molecular scale to the continuum scale for diffusion processes in smectite-rich porous media

Description: In this paper, we address the manner in which the continuum-scale diffusive properties of smectite-rich porous media arise from their molecular- and pore-scale features. Our starting point is a successful model of the continuum-scale apparent diffusion coefficient for water tracers and cations which decomposes it as a sum of pore-scale terms describing diffusion in macropore and interlayer 'compartments.' We then apply molecular dynamics (MD) simulations to determine molecular-scale diffusion coefficients D{sub interlayer} of water tracers and representative cations (Na{sup +}, Cs{sup +}, Sr{sup 2+}) in Na-smectite interlayers. We find that a remarkably simple expression relates D{sub interlayer} to the pore-scale parameter {delta}{sub nanopore} {<=} 1, a constrictivity factor that accounts for the lower mobility in interlayers as compared to macropores: {delta}{sub nanopore} = D{sub interlayer}/D{sub 0}, where D{sub 0} is the diffusion coefficient in bulk liquid water. Using this scaling expression, we can accurately predict the apparent diffusion coefficients of tracer H{sub 2}O, Na{sup +}, Sr{sup 2+} and Cs{sup +}+ in compacted Na-smectite-rich materials.
Date: December 1, 2009
Creator: Bourg, I.C. & Sposito, G.
Partner: UNT Libraries Government Documents Department


Description: The status and near-term goals of the LBL/LLL neutral-beam-development program are described. The emphasis in this paper is on the technology of systems based on the acceleration and neutralization of positive ions; this approach will be used in the near term, probably through 1985 at least. For more efficient injection, part of our plan is to develop a negative-ion approach suitable for 200- to 400-kV injectors on confinement experiments in the 1985-90 period. However, the negative-ion based program is still very much in the research phase, and it is difficult to project how it will phase into fusion reactor fueling experiments.
Date: November 1, 1977
Creator: Berkner, K.H.; Berkner, K.H.; Ehlers, K.W.; Pyle, R.V. & Hooper Jr., E.B.
Partner: UNT Libraries Government Documents Department

Geochemical Methods for the Identification of ASR Gel

Description: This paper presents a geochemical method for staining various products of the alkali-silica reaction. The method is based on both the composition of ASR gel and one of its properties (the ability to exchange cations with a fluid). The stained concrete can be observed in normal light and serves as both a rapid field screening method and a useful aid for detailed petrographic examinations.
Date: July 1, 1998
Creator: Guthrie, G.D. & Carey, J.W.
Partner: UNT Libraries Government Documents Department

The transfer of neutral molecules, ions and ionic species from water to ethylene glycol and to propylene carbonate; descriptors for pyridinium cations

Description: Article on the transfer of neutral molecules, ions and ionic species from water to ethylene glycol and to propylene carbonate and descriptors for pyridinium cations.
Date: June 29, 2010
Creator: Abraham, M. H. (Michael H.) & Acree, William E. (William Eugene)
Partner: UNT College of Arts and Sciences

"A Novel Synthesis of Zeolite W..."

Description: Zeolite W has been synthesized using organometallic silicon and aluminum precursors in two hydrothermal systems: organocation containing and organocation-free. The reaction using the organocation yielded a fully crystalline, relatively uniform crystal size product, with no organic molecules occluded in the pores. In contrast, the product obtained from an identical reaction, except for the absence of the organocation, contained amorphous as well as crystalline material and the crystalline phase showed a large diversity of both crystal size and morphology. The use of organometallic precursors, either with or without an organocation, allows for the crystallization of the MER framework at much lower 0H/Si02 and (K+ Na - Al)/Si ratios than is typical of inorganic systems. The reaction products were characterized by XRD, SEM, EDS, and thermal analyses.
Date: May 7, 1999
Creator: Nenoff, Tina M. & Thoma, Steven G.
Partner: UNT Libraries Government Documents Department

The Influence of the Linker Geometry in Bis(3-hydroxy-N-methyl-pyridin-2-one) Ligands on Solution-Phase Uranyl Affinity

Description: Seven water-soluble, tetradentate bis(3-hydroxy-N-methyl-pyridin-2-one) (bis-Me-3,2-HOPO) ligands were synthesized that vary only in linker geometry and rigidity. Solution phase thermodynamic measurements were conducted between pH 1.6 and pH 9.0 to determine the effects of these variations on proton and uranyl cation affinity. Proton affinity decreases by introduction of the solubilizing triethylene glycol group as compared to un-substituted reference ligands. Uranyl affinity was found to follow no discernable trends with incremental geometric modification. The butyl-linked 4Li-Me-3,2-HOPO ligand exhibited the highest uranyl affinity, consistent with prior in vivo decorporation results. Of the rigidly-linked ligands, the o-phenylene linker imparted the best uranyl affinity to the bis-Me-3,2-HOPO ligand platform.
Date: August 12, 2010
Creator: Szigethy, Geza & Raymond, Kenneth
Partner: UNT Libraries Government Documents Department

Femtosecond isomerization dynamics in the ethylene cation measured in an EUV-pump NIR-probe configuration

Description: Dynamics in the excited ethylene cation C{sub 2}H{sub 4}{sup +} lead to isomerization to the ethylidene configuration (HC-CH{sub 3}){sup +}, which is predicted to be a transient configuration for electronic relaxation. With an intense femtosecond EUV (extreme ultraviolet) pump pulse to populate the excited state, and an NIR (near infrared) probe pulse to produce the fragments CH{sup +} and CH{sub 3}{sup +} (which provides a direct signature of ethylidene), we measure optimum fragment yields at a probe delay of 80 fs. Also, an H{sub 2}-stretch transient configuration, yielding H{sub 2}{sup +} upon probing, is found to succeed the ethylidene configuration. We find that a simple single- or double-decay model does not match the data, and we present a modified model (introduction of an isomerization delay of 50 {+-} 25 fs) that does provide agreement.
Date: March 17, 2009
Creator: van Tilborg, Jeroen; Allison, Tom; Wright, Travis; Hertlein, Marc; Falcone, Roger; Liu, Yanwei et al.
Partner: UNT Libraries Government Documents Department

Structural simulations of nanomaterials self-assembled from ionic macrocycles.

Description: Recent research at Sandia has discovered a new class of organic binary ionic solids with tunable optical, electronic, and photochemical properties. These nanomaterials, consisting of a novel class of organic binary ionic solids, are currently being developed at Sandia for applications in batteries, supercapacitors, and solar energy technologies. They are composed of self-assembled oligomeric arrays of very large anions and large cations, but their crucial internal arrangement is thus far unknown. This report describes (a) the development of a relevant model of nonconvex particles decorated with ions interacting through short-ranged Yukawa potentials, and (b) the results of initial Monte Carlo simulations of the self-assembly binary ionic solids.
Date: October 1, 2010
Creator: van Swol, Frank B. & Medforth, Craig John (University of New Mexico, Albuquerque, NM)
Partner: UNT Libraries Government Documents Department

Physicochemical properties and toxicities of hydrophobicpiperidinium and pyrrolidinium ionic liquids

Description: Some properties are reported for hydrophobic ionic liquids (IL) containing 1-methyl-1-propyl pyrrolidinium [MPPyrro]{sup +}, 1-methyl-1-butyl pyrrolidinium [MBPyrro]{sup +}, 1-methyl-1-propyl piperidinium [MPPip]{sup +}, 1-methyl-1-butyl piperidinium [MBPip]{sup +}, 1-methyl-1-octylpyrrolidinium [MOPyrro]{sup +} and 1-methyl-1-octylpiperidinium [MOPip]{sup +} cations. These liquids provide new alternatives to pyridinium and imidazolium ILs. High thermal stability of an ionic liquid increases safety in applications like rechargeable lithium-ion batteries and other electrochemical devices. Thermal properties, ionic conductivities, viscosities, and mutual solubilities with water are reported. In addition, toxicities of selected ionic liquids have been measured using a human cancer cell-line. The ILs studied here are sparingly soluble in water but hygroscopic. We show some structure-property relationships that may help to design green solvents for specific applications. While ionic liquids are claimed to be environmentally-benign solvents, as yet few data have been published to support these claims.
Date: June 25, 2007
Creator: Salminen, Justin; Papaiconomou, Nicolas; Kumar, R. Anand; Lee,Jong-Min; Kerr, John; Newman, John et al.
Partner: UNT Libraries Government Documents Department

Remediation of Cr(VI) by biogenic magnetic nanoparticles: An x-ray magnetic circular dichroism study

Description: Biologically synthesized magnetite (Fe{sub 3}O{sub 4}) nanoparticles are studied using x-ray absorption and x-ray magnetic circular dichroism following exposure to hexavalent Cr solution. By examining their magnetic state, Cr cations are shown to exist in trivalent form on octahedral sites within the magnetite spinel surface. The possibility of reducing toxic Cr(VI) into a stable, non-toxic form, such as a Cr{sup 3+}-spinel layer, makes biogenic magnetite nanoparticles an attractive candidate for Cr remediation.
Date: September 4, 2009
Creator: Telling, N. D.; Coker, V. S.; Cutting, R. S.; van der Laan, G.; Pearce, C. I.; Pattrick, R. A. D. et al.
Partner: UNT Libraries Government Documents Department

Aqueous Ln(III) Luminescence Agents Derived from a Tasty Precursor

Description: The synthesis, aqueous stability and photophysical properties are reported for a novel tetradentate ligand derived from maltol, a commonly used flavor enhancer. In aqueous solution, this chelate forms stable complexes with Ln(III) cations, and sensitized emission was observed from Eu(III), Yb(III), and Nd(III). A comparison with recently reported and structurally analogous ligands reveals a slightly higher basicity but lower complex stability with Eu(III) [pEu = 14.7 (1)]. A very poor metal centered quantum yield with Eu(III) was observed ({Phi}{sub tot} = 0.04%), which can be rationalized by the similar energy of the ligand triplet state and the Eu(III) {sup 5}D{sub 0} emissive level. Instead, sensitized emission from the Yb(III) and Nd(III) cations was observed, which emit in the Near Infra-Red (NIR).
Date: June 2, 2008
Creator: Jocher, C.J.; Moore, E.G.; Pierce, J.D. & Raymond, K.N.
Partner: UNT Libraries Government Documents Department

Brilliant Sm, Eu, Tb and Dy chiral lanthanide complexes withstrong circularly polarized luminescence

Description: The synthesis, characterization and luminescent behavior of trivalent Sm, Eu, Dy and Tb complexes of two enantiomeric, octadentate, chiral, 2-hydroxyisophthalamide ligands are reported. These complexes are highly luminescent in solution. Functionalization of the achiral parent ligand with a chiral 1-phenylethylamine substituent on the open face of the complex in close proximity to the metal center yields complexes with strong circularly polarized luminescence (CPL) activity. This appears to be the first example of a system utilizing the same ligand architecture to sensitize four different lanthanide cations and display CPL activity. The luminescence dissymmetry factor, g{sub lum}, recorded for the Eu(III) complex is one of the highest values reported, and this is the first time the CPL effect has been demonstrated for a Sm(III) complex with a chiral ligand. The combination of high luminescence intensity with CPL activity should enable new bioanalytical applications of macromolecules in chiral environments.
Date: July 10, 2006
Creator: Petoud, Stephane; Muller, Gilles; Moore, Evan G.; Xu, Jide; Sokolnicki, Jurek; Riehl, James P. et al.
Partner: UNT Libraries Government Documents Department

Improved Synthesis of [Si6Cl14]2-Salts as Precursors for Si6H12and other Novel Silanes

Description: The reaction of excess HSiCl{sub 3} with the aforementioned triamines led to the formation of [Si{sub 6}Cl{sub 14}]{sup 2-} containing salts in all instances. The isolated complex salts were characterized using FT-IR and elemental analysis. IR spectra of these compounds showed characteristic Si-H stretching modes around 2100cm{sup -1} due to the hexacoordinate silane cation and Si-Cl active modes near 528cm{sup -1} as a result of the cyclic dianion. Reaction yields and elemental analysis (CHN) of the salts are summarized in a table. The reaction of peralkylated triamines with HSiCl{sub 3} in dry CH{sub 2}Cl{sub 2} gives ionic compounds based upon the tetradecachlorocyclohexasilane dianion. Several substituted triamines(R{sub 2}NC{sub 2}H{sub 4}NR{prime}C{sub 2}H{sub 4}NR{sub 2}where R = R{prime} = Et, {sup n}Pr; R = Et, R{prime}= {sup n}Bu, {sup n}Hexyl, Benzyl) were examined for this reaction and N,N,N{prime},N{prime}-tetraethyl-N{sup {double_prime}}-benzyl-diethylenetriamine produced the best yields of [Si{sub 6}Cl{sub 14}]{sup 2-} salt at 23% based on the amine reagent. This improvement in yield could be attributed to the decreased nucleophilicity of the central amine through increased steric hindrance of the alkyl substituents. The overall consequence of this substituent variation study has revealed new reagents for the synthesis of [Si{sub 6}Cl{sub 14}]{sup 2-} salts and further demonstrated the ability of triamines to efficiently dismutate, complex, and condense chlorosilanes. The increased production of these salts has also opened a route for the study of Si{sub 6}X{sub 12} and its Lewis acid/base adducts.
Date: August 18, 2009
Creator: Anderson, Kenneth; Dai, Xuliang; Nelson, Kendric; Schulz, Doug & Boudjouk, Philip
Partner: UNT Libraries Government Documents Department

Near Degenerate Rearrangement Between the Radical Cations of Formaldehyde and Hydroxymethylene

Description: Motivated by the recent experiments of Berkowitz, a systematic theoretical study of the ion isomerization H{sub 2}CO{sup +} {yields} HCOH{sup +} has been carried out. Structures and vibrational frequencies for H{sub 2}CO{sup +}, the transition state, and the cis and trans isomers of HCOH{sup +} have been determined at the double zeta basis set self-consistent-field (SCF) level of theory. Equilibrium geometries were also predicted from SCF theory using a double zeta plus polarization (DZ+P) basis set. Final energetics were pinned down using DZ+P configuration interaction, involving a total of 16,290 configurations. The most reliable theoretical results suggest that trans-HCOH{sup +} lies 5.5 kcal above H{sub 2}CO{sup +}. Zero-point vibrational energy corrections do not change this H{sub 2}CO{sup +}-HCOH{sup +} separation. Similarly cis-HCOH{sup +} is predicted to lie 4.1 kcal above the trans isomer, and the barrier to rotation between the two HCOH{sup +} isomers is -18 kcal. The barrier to H{sub 2}CO{sup +} {yields} HCOH{sup +} rearrangement is predicted to be 49.0 kcal, or 44.4 kcal after correction for zero-point vibrational energies is made. The relationship between this cationic 1,2-hydrogen shift and the corresponding neutral rearrangement is discussed in terms of qualitative molecular orbital theory.
Date: June 1, 1980
Creator: Osamura, Y.; Goddard, J.D.; Schaefer III, H.F. & Kim, K.S.
Partner: UNT Libraries Government Documents Department