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Molecular Dynamics Simulations of Hexadecane/Silicalite Interfaces

Description: The interface between liquid hexadecane and the (010) surface of silicalite was studied by molecular dynamics. The structure of molecules in the interracial region is influenced by the presence of pore mouths on the silicalite surface. For this surface, whose pores are the entrances to straight channels, the concentration profile for partially absorbed molecules is peaked around 10 monomers inside the zeolite. No preference to enter or exit the zeolite based on absorption length is observed except for very small or very large absorption lengths. We also found no preferential conformation of the unabsorbed tails for partially absorbed molecules.
Date: January 20, 1999
Creator: Grest, G.S. & Webb, E.B.
Partner: UNT Libraries Government Documents Department

Design Molecular Recognition Materials for Chiral Sensors, Separtations and Catalytic Materials

Description: The goal is the development of materials that are highly sensitive and selective for chid chemicals and biochemical (such as insecticides, herbicides, proteins, and nerve agents) to be used as sensors, catalysts and separations membranes. Molecular modeling methods are being used to tailor chiral molecular recognition sites with high affinity and selectivity for specified agents. The work focuses on both silicate and non-silicate materials modified with chirally-pure fictional groups for the catalysis or separations of enantiomerically-pure molecules. Surfactant and quaternary amine templating is being used to synthesize porous frameworks, containing mesopores of 30 to 100 angstroms. Computer molecukw modeling methods are being used in the design of these materials, especially in the chid surface- modi~ing agents. Molecular modeling is also being used to predict the catalytic and separations selectivities of the modified mesoporous materials. The ability to design and synthesize tailored asymmetric molecular recognition sites for sensor coatings allows a broader range of chemicals to be sensed with the desired high sensitivity and selectivity. Initial experiments target the selective sensing of small molecule gases and non-toxic model neural compounds. Further efforts will address designing sensors that greatly extend the variety of resolvable chemical species and forming a predictive, model-based method for developing advanced sensors.
Date: November 1, 1998
Creator: Jia, S.; Nenoff, T.M.; Provencio, P.; Qiu, Y.; Shelnutt, J.A.; Thoma, S.G. et al.
Partner: UNT Libraries Government Documents Department

Toward a Molecular-Based Understanding of High-Temperature Solvation Phenomena in Aqueous Electrolyte Solutions

Description: The theoretical treatment of the solvation phenomenon of simple ions in aqueous solutions has been rather difficult, despite the apparent simplicity of the system. Long-range solvent-screened electrostatic interactions, coupled to the large variation (with state conditions) of the dielectric permittivity of water, give rise to a variety of rather complex solvation phenomena including dielectric saturation, electrostriction, and ion association. Notably, ion solvation in high-temperature/pressure aqueous solutions plays a leading role in hydrothermal chemistry, such as in the natural formation of ore deposits, the corrosion in boilers and reactors, and in high-temperature microbiology. Tremendous effort has been invested in the study of hydrothermal solutions to determine their thermodynamic, transport, and spectroscopic properties with the goal of elucidating the solute-solvent and solute-solute interactions over a wide range of state conditions. It is precisely at these conditions where our understanding and predictive capabilities are most precarious, in part, as a result of the coexistence of processes with two rather different length scales, i.e., short-ranged (solvation) and long-ranged (compressibility-driven) phenomena (Chialvo and Cummings 1994a). The latter feature makes hydrothermal systems extremely challenging to model, unless we are able to isolate the (compressibility-driven) propagation of the density perturbation from the (solvation-related) finite-density perturbation phenomena (Chialvo and Cummings 1995a).
Date: October 30, 1999
Creator: Chialvo, A. A.; Cummings, P. T.; Kusalik, P. G. & Simonson, J. M.
Partner: UNT Libraries Government Documents Department

Design and Evaluation of Ionic Liquids as Novel CO2 Absorbents

Description: Progress from the fourth quarter 2005 activity on the project ''Design and Evaluation of Ionic Liquids as Novel CO{sub 2} Absorbents'' is provided. Major activities in three areas are reported: compound synthesis, property measurement and molecular modeling. Last quarter we reported the first ever experimental measurement of SO{sub 2} solubility in an ionic liquid. We showed that SO{sub 2} was very soluble in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([hmim][Tf{sub 2}N]). This quarter, we have measured SO{sub 2} solubility in two more ionic liquids: 1-hexyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide ([hmpy][Tf{sub 2}N]) and 1-hexyl-3-methylimidazolium lactate ([hmim][lactate]). As with [hmim][Tf{sub 2}N], we find very high solubility of SO{sub 2} in these ionic liquids, but the lactate compounds shows the highest affinity for SO{sub 2} at low pressure. CO{sub 2} solubility was measured in three new compounds: [boronium][Tf{sub 2}N], 1-hexyl-3-methylimidazolium acesulfumate ([hmim][ace]), and 1-hexyl-3-methylimidazolium saccharinate ([hmim][sac]). We find relatively poor solubility of CO{sub 2} in the latter two compounds, and solubility comparable to [hmim][Tf{sub 2}N] in the boronium compound. We also synthesized four new ionic liquids this quarter and continued refinement of our molecular simulation technique for measuring gas solubility.
Date: January 12, 2006
Creator: Maginn, Edward J.
Partner: UNT Libraries Government Documents Department

Molecular and Genetic Analysis of Hormone-Regulated Differential Cell Elongation in Arabidopsis

Description: The authors have utilized the response of Arabidopsis seedlings to the plant hormone ethylene to identify new genes involved in the regulation of ethylene biosynthesis, perception, signal transduction and differential cell growth. In building a genetic framework for the action of these genes, they developed a molecular model that has facilitated the understanding of the molecular requirements of ethylene for cell elongation processes. The ethylene response pathway in Arabidopsis appears to be primarily linear and is defined by the genes: ETR1, ETR2, ERS1, ERS2, EIN4, CTR1, EIN2, EIN3, EIN5 EIN6, and EIN. Downstream branches identified by the HLS1, EIR1, and AUX1 genes involve interactions with other hormonal (auxin) signals in the process of differential cell elongation in the hypocotyl hook. Cloning and characterization of HLS1 and three HLS1-LIKE genes in the laboratory has been supported under this award. HLS1 is required for differential elongation of cells in the hypocotyl and may act in the establishment of hormone gradients. Also during the award period, they have identified and begun preliminary characterization of two genes that genetically act upstream of the ethylene receptors. ETO1 and RAN1 encode negative regulators of ethylene biosynthesis and signaling respectively. Progress on the analysis of these genes along with HOOKLESS1 is described.
Date: December 3, 2002
Creator: Ecker, Joseph R.
Partner: UNT Libraries Government Documents Department

Models of the solvent-accessible surface of biopolymers

Description: Many biopolymers such as proteins, DNA, and RNA have been studied because they have important biomedical roles and may be good targets for therapeutic action in treating diseases. This report describes how plastic models of the solvent-accessible surface of biopolymers were made. Computer files containing sets of triangles were calculated, then used on a stereolithography machine to make the models. Small (2 in.) models were made to test whether the computer calculations were done correctly. Also, files of the type (.stl) required by any ISO 9001 rapid prototyping machine were written onto a CD-ROM for distribution to American companies.
Date: September 1, 1996
Creator: Smith, R.E.
Partner: UNT Libraries Government Documents Department

Wave propagation in ordered, disordered, and nonlinear photonic band gap materials

Description: Photonic band gap materials are artificial dielectric structures that give the promise of molding and controlling the flow of optical light the same way semiconductors mold and control the electric current flow. In this dissertation the author studied two areas of photonic band gap materials. The first area is focused on the properties of one-dimensional PBG materials doped with Kerr-type nonlinear material, while, the second area is focused on the mechanisms responsible for the gap formation as well as other properties of two-dimensional PBG materials. He first studied, in Chapter 2, the general adequacy of an approximate structure model in which the nonlinearity is assumed to be concentrated in equally-spaced very thin layers, or 6-functions, while the rest of the space is linear. This model had been used before, but its range of validity and the physical reasons for its limitations were not quite clear yet. He performed an extensive examination of many aspects of the model's nonlinear response and comparison against more realistic models with finite-width nonlinear layers, and found that the d-function model is quite adequate, capturing the essential features in the transmission characteristics. The author found one exception, coming from the deficiency of processing a rigid bottom band edge, i.e. the upper edge of the gaps is always independent of the refraction index contrast. This causes the model to miss-predict that there are no soliton solutions for a positive Kerr-coefficient, something known to be untrue.
Date: December 10, 1999
Creator: Lidorikis, Elefterios
Partner: UNT Libraries Government Documents Department

Opportunities and challenges of high-performance computing in chemistry

Description: The field of high-performance computing is developing at an extremely rapid pace. Massively parallel computers offering orders of magnitude increase in performance are under development by all the major computer vendors. Many sites now have production facilities that include massively parallel hardware. Molecular modeling methodologies (both quantum and classical) are also advancing at a brisk pace. The transition of molecular modeling software to a massively parallel computing environment offers many exciting opportunities, such as the accurate treatment of larger, more complex molecular systems in routine fashion, and a viable, cost-effective route to study physical, biological, and chemical `grand challenge` problems that are impractical on traditional vector supercomputers. This will have a broad effect on all areas of basic chemical science at academic research institutions and chemical, petroleum, and pharmaceutical industries in the United States, as well as chemical waste and environmental remediation processes. But, this transition also poses significant challenges: architectural issues (SIMD, MIMD, local memory, global memory, etc.) remain poorly understood and software development tools (compilers, debuggers, performance monitors, etc.) are not well developed. In addition, researchers that understand and wish to pursue the benefits offered by massively parallel computing are often hindered by lack of expertise, hardware, and/or information at their site. A conference and workshop organized to focus on these issues was held at the National Institute of Health, Bethesda, Maryland (February 1993). This report is the culmination of the organized workshop. The main conclusion: a drastic acceleration in the present rate of progress is required for the chemistry community to be positioned to exploit fully the emerging class of Teraflop computers, even allowing for the significant work to date by the community in developing software for parallel architectures.
Date: June 1, 1995
Creator: Guest, M.F.; Kendall, R.A. & Nichols, J.A.
Partner: UNT Libraries Government Documents Department

Ion Association in High-Temperature Aqueous HCl Solutions. A Molecular Simulation Study

Description: The profiles of the potential of mean force for the <i>Cl<sup>-</sup> - H<sub>3</sub>O<sup>+</sup></i> pair, as predicted by two <i>ab initio</i> models, are determined by constraint molecular dynamics simulation at a near-critical condition. The corresponding association constants are then determined and compared with that from conductance measurements to test the reliability of the current simulation models for <i>HCl</i>.
Date: October 30, 1999
Creator: Chialvo, A.A.; Cummings, P.T.; Mesmer, R.E. & Simonson, J.M.
Partner: UNT Libraries Government Documents Department

DUPLEX: A molecular mechanics program in torsion angle space for computing structures of DNA and RNA

Description: DUPLEX produces energy minimized structures of DNA and RNA of any base sequence for single and double strands. The smallest subunits are deoxydinucleoside monophosphates, and up to 12 residues, single or double stranded can be treated. In addition, it can incorporate NMR derived interproton distances an constraints in the minimizations. Both upper and lower bounds for these distances can be specified. The program has been designed to run on a UNICOS Cray supercomputer, but should run, albeit slowly, on a laboratory computer such as a VAX or a workstation.
Date: July 1, 1992
Creator: Hingerty, B. E.
Partner: UNT Libraries Government Documents Department


Description: Deuterium magnetic resonance measurements of four members of the homologous series p-alkoxybenzylidene-p-alkylaniline (no {center_dot} m), perdeuterated in their alkoxy chains, are reported. The compounds studied were 40 {center_dot} 7, 50 {center_dot} 7, 60 {center_dot} 7 and 70 {center_dot} 7. For 50 {center_dot} 7 various isotopic species specifically deuterated in the alkoxy chains, as well as in the benzylidine moiety, were prepared and their DMR studied. These measurements allowed a complete assignment of the resonances from the alkoxy chain. The spectrum of all four compounds was studied over their whole mesomorphic regions. In most phases well resolved spectra were obtained yielding the various quadrupole splittings and in many cases also the dipolar interactions within the methylene and methyl groups. Using double quantum spectroscopy dipolar splitting between different methylene deuterons could also be resolved. The methylene quadrupolar splittings and the dipolar interaction within the methylene groups decrease along the chain towards the methyl end in a characteristic stepwise manner. This behavior is attributed to chain reorientational freedom and is quantitatively interpreted in terms of two structural factors: (i) Fast dynamical equilibrium between the all-trans conformation of the alkoxy chains and chain conformations involving one or more kinks, and (ii) A molecular model in which the aliphatic chain axis is inclined with respect to the molecular long axis. The characteristic pattern of the splitting can then be reproduced by assuming a monotonically increasing kink probabilities along the chain towards its methyl end. This interpretation is used to estimate the kink probability distribution in the alkoxy chains in the various compounds and mesophases. No significant effect of the mesophase structure on the kink statistics was found.
Date: October 1, 1977
Creator: Hsi, Shan; Zimmermann, Herbert & Luz, Zeev
Partner: UNT Libraries Government Documents Department

Improved model for statistical alignment

Description: The statistical approach to molecular sequence evolution involves the stochastic modeling of the substitution, insertion and deletion processes. Substitution has been modeled in a reliable way for more than three decades by using finite Markov-processes. Insertion and deletion, however, seem to be more difficult to model, and thc recent approaches cannot acceptably deal with multiple insertions and deletions. A new method based on a generating function approach is introduced to describe the multiple insertion process. The presented algorithm computes the approximate joint probability of two sequences in 0(13) running time where 1 is the geometric mean of the sequence lengths.
Date: January 1, 2001
Creator: Miklos, I. & Toroczkai, Z. (Zoltan)
Partner: UNT Libraries Government Documents Department

Macroscopic rates, microscopic observations, and molecular models of the dissolution of carbonate phases.

Description: Bulk and surface energies are calculated for endmembers of the isostructural rhombohedral carbonate mineral family, including Ca, Cd, Co, Fe, Mg, Mn, Ni, and Zn compositions. The calculations for the bulk agree with the densities, bond distances, bond angles, and lattice enthalpies reported in the literature. The calculated energies also correlate with measured dissolution rates: the lattice energies show a log-linear relationship to the macroscopic dissolution rates at circumneutral pH. Moreover, the energies of ion pairs translated along surface steps are calculated and found to predict experimentally observed microscopic step retreat velocities. Finally, pit formation excess energies decrease with increasing pit size, which is consistent with the nonlinear dissolution kinetics hypothesized for the initial stages of pit formation.
Date: May 1, 2004
Creator: Duckworth, Owen W. (Harvard University, Cambridge, MA); Cygan, Randall Timothy & Martin, Scot T. (Harvard University, Cambridge, MA)
Partner: UNT Libraries Government Documents Department

Atomistic modeling of nanowires, small-scale fatigue damage in cast magnesium, and materials for MEMS.

Description: Lightweight and miniaturized weapon systems are driving the use of new materials in design such as microscale materials and ultra low-density metallic materials. Reliable design of future weapon components and systems demands a thorough understanding of the deformation modes in these materials that comprise the components and a robust methodology to predict their performance during service or storage. Traditional continuum models of material deformation and failure are not easily extended to these new materials unless microstructural characteristics are included in the formulation. For example, in LIGA Ni and Al-Si thin films, the physical size is on the order of microns, a scale approaching key microstructural features. For a new potential structural material, cast Mg offers a high stiffness-to-weight ratio, but the microstructural heterogeneity at various scales requires a structure-property continuum model. Processes occurring at the nanoscale and microscale develop certain structures that drive material behavior. The objective of the work presented in this report was to understand material characteristics in relation to mechanical properties at the nanoscale and microscale in these promising new material systems. Research was conducted primarily at the University of Colorado at Boulder to employ tightly coupled experimentation and simulation to study damage at various material size scales under monotonic and cyclic loading conditions. Experimental characterization of nano/micro damage will be accomplished by novel techniques such as in-situ environmental scanning electron microscopy (ESEM), 1 MeV transmission electron microscopy (TEM), and atomic force microscopy (AFM). New simulations to support experimental efforts will include modified embedded atom method (MEAM) atomistic simulations at the nanoscale and single crystal micromechanical finite element simulations. This report summarizes the major research and development accomplishments for the LDRD project titled 'Atomistic Modeling of Nanowires, Small-scale Fatigue Damage in Cast Magnesium, and Materials for MEMS'. This project supported a strategic partnership between Sandia National Laboratories ...
Date: October 1, 2006
Creator: Dunn, Martin L. (University of Colorado, Boulder, CO); Talmage, Mellisa J. (University of Colorado, Boulder, CO); McDowell, David L., 1956- (,-Georgia Institute of Technology, Atlanta, GA); West, Neil (University of Colorado, Boulder, CO); Gullett, Philip Michael (Mississippi State University , MS); Miller, David C. (University of Colorado, Boulder, CO) et al.
Partner: UNT Libraries Government Documents Department

Design and Evaluation of Ionic Liquids as Novel CO2 Absorbents

Description: Progress from the third quarter 2006 activity on the project ''Design and Evaluation of Ionic Liquids as Novel CO{sub 2} Absorbents'' is provided. Major activities in two areas are reported: property measurement and molecular modeling. We have measured CO{sub 2} solubility in an ammonium lactate ionic liquid. Previous work has shown that the lactate anion enables chemical complexation to occur. We hypothesized that the lactate anion would not be as effective in complexing when paired with an ammonium cation as compared to when it is paired with an imidazolium cation. The results confirm this. We also measured CO{sub 2} solubility in a functionalized ionic liquid containing an amine group. These so-called task specific ionic liquids (TSILs) are expected to have dramatically higher CO{sub 2} solubility than physical absorbents. We report isotherms as well as entropies and enthalpies of absorption for CO{sub 2} in one TSIL. CO{sub 2} solubilities are higher in this compound than in any previous IL we have observed. Finally, we also developed a new simulation method that will enable us to compute full isotherms of gases in ionic liquids. So far, we have tested the method against model systems and found it to be highly effective.
Date: September 30, 2006
Creator: Maginn, Edward J.
Partner: UNT Libraries Government Documents Department

Molecular Simulation of Reacting Systems

Description: The final report for a Laboratory Directed Research and Development project entitled, Molecular Simulation of Reacting Systems is presented. It describes efforts to incorporate chemical reaction events into the LAMMPS massively parallel molecular dynamics code. This was accomplished using a scheme in which several classes of reactions are allowed to occur in a probabilistic fashion at specified times during the MD simulation. Three classes of reaction were implemented: addition, chain transfer and scission. A fully parallel implementation was achieved using a checkerboarding scheme, which avoids conflicts due to reactions occurring on neighboring processors. The observed chemical evolution is independent of the number of processors used. The code was applied to two test applications: irreversible linear polymerization and thermal degradation chemistry.
Date: March 1, 2002
Partner: UNT Libraries Government Documents Department

Evolution of random catalytic networks

Description: In this paper the authors investigate the evolution of populations of sequences on a random catalytic network. Sequences are mapped into structures, between which are catalytic interactions that determine their instantaneous fitness. The catalytic network is constructed as a random directed graph. They prove that at certain parameter values, the probability of some relevant subgraphs of this graph, for example cycles without outgoing edges, is maximized. Populations evolving under point mutations realize a comparatively small induced subgraph of the complete catalytic network. They present results which show that populations reliably discover and persist on directed cycles in the catalytic graph, though these may be lost because of stochastic effects, and study the effect of population size on this behavior.
Date: June 1, 1997
Creator: Fraser, S.M. & Reidys, C.M.
Partner: UNT Libraries Government Documents Department

Use of coupled passivants and consolidants on calcite mineral surfaces

Description: Deterioration of monuments, buildings, and works of art constructed of carbonate-based stone potentially can be arrested by applying a combination of chemical passivants and consolidants that prevent hydrolytic attack and mechanical weakening. The authors used molecular modeling and laboratory synthesis to develop an improved passivating agent for the calcite mineral surface based on binding strength and molecular packing density. The effectiveness of the passivating agent with and without a linked outer layer of consolidant against chemical weathering was determined through leaching tests conducted with a pH-stat apparatus at pH 5 and 25 C. For the range of molecules considered, modeling results indicate that the strongest-binding passivant is the trimethoxy dianionic form of silylalkylaminocarboxylate (SAAC). The same form of silylalkylphosphonate (SAP) is the second strongest binder and the trisilanol neutral form of aminoethylaminopropylsilane (AEAPS) is ranked third. Short-term leaching tests on calcite powders coated with the trisilanol derivative of SAAC, the triethoxy neutral form of SAP, and the trimethoxy neutral form of AEAPS show that the passivant alone does not significantly slow the dissolution rate. However, all passivants when linked to the sol consolidant result in decreased rates. Combined AEAPS plus consolidant results in a coating that performs better than the commercial product Conservare{reg_sign} OH and at least as well as Conservare{reg_sign} H. The modeling results indicate that there may be a threshold binding energy for the passivant above which the dissolution rate of calcite is actually enhanced. More strongly-binding passivants may aid in the dissolution mechanism or dissociate in aqueous solution exposing the calcite surface to water.
Date: February 1, 1997
Creator: Nagy, K.L.; Cygan, R.T.; Brinker, C.J.; Ashley, C.S. & Scotto, C.S.
Partner: UNT Libraries Government Documents Department

Modeling and characterization of molecular structures in self assembled and Langmuir-Blodgett films for controlled fabrication

Description: Self Assembled (SA) thin films and Langmuir-Blodgett (LB) thin films are emerging technologies for the development of chemical and bio-chemical sensors, electrooptic films, second harmonic generators (frequency doublers), templates for biomimetic growth etc. One of the goals of this project was to extend Sandia`s characterization techniques and molecular modeling capabilities for these complex two-dimensional geometries with the objective of improving the control of the fabrication of these structures for specific applications. Achieving this requires understanding both the structure throughout the thickness of the films and the in-plane lattice of the amphiphilic molecules. To meet these objectives they used atomic force microscopy (AFM), X-ray reflectivity, and molecular modeling. While developing these capabilities, three different materials systems were fabricated and characterized: (1) Self Assembled Monolayers (SAMs) of octadecyltrichlorosilane (OTS) and LB films of arachidic acid on silicon wafers; (2) SAMs on PZT substrates; and (3) electrochemical deposition of CdS on LB film templates.
Date: October 1997
Creator: Cesarano, J., III
Partner: UNT Libraries Government Documents Department

Application of integral equation theory to polyolefin liquids and blends

Description: The ability to model the packing of polymers in melts and blends is important in many polymer applications. One significant application is the development of new polymer blends. It would be exceedingly helpful to the materials chemist if molecular modeling could be employed to predict the thermodynamics and phase behavior of hypothetical polymer alloys before embarking on a time consuming and expensive synthesis program. The well known Flory-Huggins theory has been remarkably successful in describing many aspects of polymer mixing from a qualitative point of view. This theory is known, however, to suffer from several deficiencies which can be traceable to the fact that: (1) it is a lattice model requiring both monomer components to have the same volume; and (2) a mean field or random mixing approximation is made which effectively ignores chain connectivity. Because of these limitations the Flory-Huggins theory does not include packing effects and cannot be used to make quantitative molecular engineering calculations. Recently Curro and Schweizer developed a new approach for treating polymer liquids and mixtures which the authors call PRISM theory. This is an extension to polymers of the Reference Interaction Site Model (RISM Theory) developed by Chandler and Andersen to describe the statistical mechanics of small molecule liquids. The PRISM theory is a continuous space description of a polymer liquid, which includes chain connectivity and nonrandom mixing effects in a computationally tractable manner. The primary output from PRISM calculations is the average structure or packing of the amorphous liquid given by the radial distribution function denoted as g(r). This radial distribution function is employed to deduce thermodynamic or structural properties of interest. Here, the authors describe the theoretical approach and demonstrate its application to polyethylene, isotactic polypropylene, syndiotactic polypropylene, and polyisobutylene liquids and blends.
Date: November 1, 1997
Creator: Curro, J.G. & Weinhold, J.D.
Partner: UNT Libraries Government Documents Department

Molecular Mechanism of Biological Proton Transport

Description: Proton transport across lipid membranes is a fundamental aspect of biological energy transduction (metabolism). This function is mediated by a Grotthuss mechanism involving proton hopping along hydrogen-bonded networks embedded in membrane-spanning proteins. Using molecular simulations, the authors have explored the structural, dynamic, and thermodynamic properties giving rise to long-range proton translocation in hydrogen-bonded networks involving water molecules, or water wires, which are emerging as ubiquitous H{sup +}-transport devices in biological systems.
Date: September 1, 1998
Creator: Pomes, R.
Partner: UNT Libraries Government Documents Department

Various aspects of the chemistry of new pyridine phosphonates that are of specific interest to separations chemistry issues at Los Alamos National Laboratory. Final report, November 1992--September 1994

Description: The authors have used newly derived synthetic approaches to form several pyridine N-oxide phosphonates; they have fully characterized these new species; they have studied their coordination chemistry toward several lanthanide and actinide ions; and they have initiated solvent extraction studies of two ligands. The results for most of this work are described in three manuscripts that have been submitted or soon will be submitted for publication. In addition to that work the authors have also embarked on a major effort to survey the utility of computer assisted molecular modeling for the design of new chelating ligands for actinide ions. Finally, during this period the authors began to prepare large samples of selected ligands that will be used in future collaborative studies of extraction properties. It is expected that several of the new ligands will have superior extraction properties compared to existing chelate systems.
Date: August 1, 1998
Creator: Paine, R.T.
Partner: UNT Libraries Government Documents Department

The structure of tellurite glass: A combined NMR, neutron diffraction, and x-ray diffraction study

Description: Models are presented of sodium tellurite glasses in the composition range (Na{sub 2}0){sub x}-(TeO{sub 2}){sub 1{minus}x}. 0.1 &lt; x &lt; 0.3. The models combine self-consistently data from three different and complementary sources: sodium-23 nuclear magnetic resonance (NMR), neutron diffraction, and x-ray diffraction. The models were generated using the Reverse Monte Carlo algorithm, modified to include NMR data in addition to diffraction data. The presence in the models of all five tellurite polyhedra consistent with the Te{sup +4} oxidation state were found to be necessary to achieve agreement with the data. The distribution of polyhedra among these types varied from a predominance of highly bridged species at low sodium content, to polyhedra with one or zero bridging oxygen at high sodium content. The models indicate that the sodium cations themselves form sodium oxide clusters particularly at the x = 0.2 composition.
Date: April 4, 2000
Creator: McLaughlin, J. C.; Tagg, S. L.; Zwanzier, J. W.; Shastri, S. D. & Haeffner, D. R.
Partner: UNT Libraries Government Documents Department