895 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

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

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

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

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

STATUS OF THE LBL/LLL DEVELOPMENT PROGRAM

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

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

Layered Double Hydroxides as Anion- and Cation-Exchanging Materials

Description: Layered double hydroxides (LDH) have been principally known as anion-exchanging, clay-like materials for several decades, and continues to be the main driving force for current and future research. The chemical interactions of LDH, with transition metallocyanides, have been a popular topic of investigation for many years, partly due to the use of powder x-ray diffraction and infrared spectroscopy as the main characterization tools. Each transition metallocyanide has a characteristic infrared stretching frequency that can be easily observed, and their respective sizes can be observed while intercalated within the interlayer of the LDH. The ability of LDH to incorporate metal cations or any ions/molecules/complexes, that have a postive charge, have not been previously investigated, mainly due to the chemical and physical nature of LDH. The possibility of cationic incorporation with LDH would most likely occur by surface adsorption, lattice metal replacement, or by intercalation into the LDH interlayers. Although infrared spectroscopy finds it main use through the identification of the anions incorporated with LDH, it can also be used to study and identify the various active and inactive bending and stretching modes that the metal hydroxide layers have.
Date: May 2007
Creator: Richardson, Mickey Charles
Partner: UNT Libraries

In Situ Template Generation for Zincophosphate Synthesis Leading to C2H7N4O-ZnPO4 Containing Template-to-Template N--H...O Hydrogen Bonds

Description: The synthesis, structure and some properties of C{sub 2}H{sub 7}N{sub 4}O {center_dot} ZnPO{sub 4} (guanylurea zinc phosphate) are reported. The cationic template was prepared in situ by partial hydrolysis of the neutral 2-cyanoguanidine starting material. The resulting structure contains a new, unprotonated, zincophosphate layer topology as well as unusual N-H-O template-to-template hydrogen bonds which help to stabilize a ''double sandwich'' of templating cations between the inorganic sheets. Crystal data: C{sub 2}H{sub 7}N{sub 4}O {center_dot} ZnPO{sub 4}, M{sub r} = 229.44, monoclinic, P2{sub 1}/c, a = 13.6453 (9) {angstrom}, b = 5.0716 (3) {angstrom}, c = 10.6005 (7) {angstrom}, {beta} = 95.918 (2){sup 0}, V = 729.7 (1) {angstrom}{sup 3}, R(F) = 0.034, wR(F) = 0.034.
Date: December 20, 2000
Creator: HARRISON,WILLIAM T.A.; RODGERS,JENNIFER A.; PHILLIPS,MARK L.F. & NENOFF,TINA M.
Partner: UNT Libraries Government Documents Department

Molecular analysis of a thylakoid K+ channel

Description: The work undertaken during the prior granting period sought to use a novel probe to identify and clone plant ion (K) channels. It was also proposed that in vitro biochemical studies of cation transport across purified preparations of thylakoid membrane be employed to characterize a putative K channel in this membrane system. Over the last several years (including those of the previous grant period), an enormous data base of partially-sequenced mRNAs and numerous genomes (including those of plants) has evolved and provides a powerful alternative to this brute-force approach to identify and clone cDNAs ending physiologically important membrane proteins such as channels. The utility of searching genetic databases for relevant sequences, in addition to the difficulty of working with membrane proteins, led to changes in research focus during the prior granting period, and has resulted in the identification of a new class of plant ion channels, which will be the focus of research during the proposed new granting period.
Date: May 1, 2000
Partner: UNT Libraries Government Documents Department

Immiscibility in the Fe3O4-FeCr2O4 Spinel Binary

Description: A recent thermodynamic model of mixing in spinel binaries, based on changes in cation disordering (x) between tetrahedral and octahedral sites, is investigated for applicability to the Fe{sub 3}O{sub 4}-FeCr{sub 2}O{sub 4} system under conditions where incomplete mixing occurs. Poor agreement with measured consolute solution temperature and solvus is attributed to neglect of: (1) ordering of magnetic moments of cations in the tetrahedral sublattice antiparallel to the moments of those in the octahedral sublattice and (2) pair-wise electron hopping between octahedral site Fe{sup 3+} and Fe{sup 2+} ions. Disordering free energies ({Delta}G{sub D}), from which free energies of mixing are calculated, are modeled by {Delta}G{sub D} = {alpha}{chi} + {beta}{chi}{sup 2} - T(S{sub c} + {chi}{sigma}{sub el} + {gamma}{chi}{sigma}{sup mag}) where the previously-neglected effects are accommodated by: (1) adding a non-configurational entropy term to provide coupling between cation disordering and magnetic ordering and (2) revising the configurational entropy (S{sub c}) analysis. Applying the constraint {alpha} = -(2/3){beta} and regressing the existing database for Fe{sup 2+} ion disorder in Fe{sub 3}O{sub 4} gives: {beta} = -31,020 {+-} 1050 J mol{sup -1}, {sigma}{sub el}/R = -0.730 {+-} 0.081 and {gamma}, the coupling parameter between cation disordering and magnetic ordering, = -0.664 {+-} 0.075. The revised mixing model predicts a consolute solution temperature (T{sub cs}) = 600 C and a solvus at 500 C of n = 0.05 and 0.70 for the Fe(Fe{sub 1-n}Cr{sub n}){sub 2}O{sub 4} spinel binary.
Date: March 20, 2003
Creator: Ziemniak, S.E. & Castelli, R.A.
Partner: UNT Libraries Government Documents Department

Development of Novel, Simple Multianalyte Sensors for Remote Environmental Analysis

Description: Advancement of our polymerized crystalline colloidal array chemical sensing technology. They have dramatically advanced their polymerized crystalline colloidal array chemical sensing technology. They fabricated nonselective sensors for determining pH and ionic strength. They also developed selective sensors for glucose and organophosphorus mimics of nerve gas agents. They developed a trace sensor for cations in water which utilized a novel crosslinking sensing motif. In all of these cases they have been able to theoretically model their sensor response by extending hydrogel volume phase transition theory. They also developed transient sampling methods to allow their ion sensing methods to operate at high ionic strengths. They also developed a novel optrode to provide for simple sampling.
Date: February 18, 2003
Creator: Asher, Sanford A.
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

Pysico-chemical properties of hydrophobic ionic liquids containing1-octylpyridinium, 1-octyl-2-methylpyridinium or1-octyl-4-methylpyridinium cations

Description: This paper reports synthesis of some ionic liquids based on cations 1-octylpyridinium, 1-octyl-2-methylpyridinium or 1-octyl-4-methylpyridinium and anions dicyanamide [N(CN)2]-, bis(trifluoromethylsulfonyl)imide [Tf2N]-, bis(pentafluoroethylsulfonyl)imide [BETI]-, trifluoromethyl sulfonate [TfO]-, nonafluorobutyl sulfonate [NfO]-, tetrafluoroborate [BF4]-, trifluorophenylborate [BF3Ph]- or hexafluoroarsenate [AsF6]-. Melting points, decomposition temperatures, densities, mutual solubilities with water, and viscosities have been measured. Unlike similar ionic liquids containing imidazolium cations, pyridinium ionic liquids studied here are nearly immiscible in water. Viscosities are similar and water content is slightly lower than those for ionic liquids containing imidazolium cations.
Date: September 15, 2006
Creator: Papaiconomou, Nicolas; Salminen, Justin; Lee, Jong-Min & Prausnitz, John M.
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