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A Carbon-13 and Lithium-6 NMR Study of Alkyllithium Compounds

Description: A variable temperature 13C and 6Li NMR study has been conducted for 6Li-enriched ethyl-, n-propyl-, isopropyl-, n-butyl-, isobutyl-, t-butyl--, isopentyl-, 2-ethylbutyl-, and n-hexyllithium in cyclopentane. Significant differences in the 13C NMR parameters are observed as a function of the alkyl group and temperature. These changes are compared to the 6Li spectra and explained in terms of the aggregates present. 13C-6Li coupling is readily observed in both the 13 6 C and Li spectra of compounds which contain branching at either the alpha or beta carbons of the alkyl group. This coupling has been used to identify the aggregates present in solution and to identify the fluxional behavior of these aggregates.
Date: December 1983
Creator: Jensen, Randy M.
Partner: UNT Libraries

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

Isotope tracers of organic carbon during artificial recharge

Description: This project developed an analytical technique for measuring the isotope abundance for 14C and 13C in total organic carbon (TOC) in order to test whether these measurements can trace TOC interaction with sedimentary material at the bottom of rivers and lakes, soils, and subsurface aquifer rocks.
Date: February 9, 1998
Creator: Davisson, M.L.
Partner: UNT Libraries Government Documents Department

Stable isotope labeling of oligosaccharide cell surface antigens

Description: The overall goal of this Laboratory Directed Research and Development (LDRD) project was to develop new methods for synthesis of {sup 13}C-labeled oligosaccharides that are required for nuclear magnetic resonance (NMR) studies of their solution conformation. Oligosaccharides are components of the cell`s outer surface and are involved in important processes such as cell-cell recognition and adhesion. Recently, Danishefsky and coworkers at Slone-Kettering Cancer Center developed a method for the solid-phase chemical synthesis of oligosaccharides. The specific goal of this LDRD project was to prepare uniform {sup 13}C-labeled aldohexose precursors required for the solid-phase synthesis of the Lewis blood-group antigenic determinants. We report the synthesis of {sup 13}C-labeled D-glucal, D-galactal and Fucosyl precursors. We have been collaborating with the Danishefsky group on the synthesis of the Lewis oligosaccharides and the NMR analysis of their solution conformation.
Date: December 31, 1998
Creator: Unkefer, C.J.; Silks, L.A. III & Martinez, R.A.
Partner: UNT Libraries Government Documents Department

Carbon-13 isotopic abundance and concentration of atmospheric methane for background air in the Southern and Northern Hemispheres from 1978 to 1989

Description: Atmospheric methane (CH{sub 4}) may become an increasingly important contributor to global warming in future years. Its atmospheric concentration has risen, doubling over the past several hundred years, and additional methane is thought to have a much greater effect on climate, on a per molecule basis, than additional C0{sub 2} at present day concentrations (Shine et al. 1990). The causes of the increase of atmospheric CH{sub 4} have been difficult to ascertain because of a lack of quantitative knowledge of the fluxes (i.e., net emissions) from the numerous anthropogenic and natural sources. The goal of CH{sub 4} isotopic studies is to provide a constraint (and so reduce the uncertainties) in estimating the relative fluxes from the various isotopically distinct sources, whose combined fluxes must result in the measured atmospheric isotopic composition, after the fractionating effect of the atmospheric removal process is considered. In addition, knowledge of the spatial and temporal changes in the isotopic composition of atmospheric CH{sub 4}, along with estimates of the fluxes from some of the major sources, makes it possible to calculate growth rates for sources whose temporal emissions trends would be difficult to measure directly.
Date: March 1995
Creator: Stevens, C. M.; Sepanski & Morris, L. J.
Partner: UNT Libraries Government Documents Department

Two dimensional NMR and NMR relaxation studies on coal structure. Final report, September 13, 1994--January 31, 1995

Description: This research program focused on developing new solids nuclear magnetic resonance (NMR) techniques for improved analysis of coal structure. Most work has been concentrated on the development of spectral editing NMR methods for solids.
Date: October 1, 1995
Creator: Zilm, K.W.
Partner: UNT Libraries Government Documents Department

Two dimensional NMR and NMR relaxation studies of coal structure. Progress report, July 1, 1992--September 30, 1992

Description: This report covers the progress made on the title project for the project period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups that determine the reactivity of coals. Special attention is being paid to methods that are compatible with the very high magic angle sample spinning rates needed for operation at the high magnetic field strengths available today. Polarization inversion methods utilizing the difference in heat capacities of small groups of spins are particularly promising. Methods combining proton-proton spin diffusion with {sup 13}C CPMAS readout are being developed to determine the connectivity of functional groups in coals in a high sensitivity relay type of experiment. Additional work is aimed at delineating the role of methyl group rotation in the proton NMR relaxation behavior of coals.
Date: November 25, 1992
Creator: Zilm, K. W.
Partner: UNT Libraries Government Documents Department

CARBON-13 NMR STUDIES OF LIQUID CRYSTALS

Description: High resolution, proton decoupled {sup 13}C nmr are observed for a series of neat nematic liquid crystals, the p-alkoxyazoxybenzenes, and a smectic-A liquid crystal, diethylazoxydibenzoate in a magnetic field of 23 kG. The (uniaxial) order parameters S = <P{sub 2}(cos{theta})> are found to be about 0.4 and 0.9 for the nematic and smectic-A phase respectively at the clearing points. The order parameter increases with decreasing temperature in the nematic phase but is constant, or nearly so, with temperature in the smectic-A phase. In the nematic series studied, the ordering exhibits an even-odd alternation along the series and qualitative agreement with a recent theory due to Marcelja is found. In both phases, the spectra show that the molecule rotates rapidly about its long axis. Tentative conclusions about molecular conformational motion and {sup 14}N spin relaxation are presented for both nematic and smectic-A phases. In the smectic-A phase, the sample is rotated about an axis perpendicular to H{sub 0} and the resulting spectra are discussed. The theory of observed chemical shifts in liquid crystals is treated in an appendix. Equations are derived which relate the nmr spectra of liquid-crystals to the order parameters. A model for the smectic-C phase due to Luz and Meiboom and Doane is described and lineshapes are determined on the basis of this model for special cases. Experiments on smectic-C liquid crystals are currently underway for comparison with the theory. Also treated in an appendix is the dependence of the order parameters on the molecular potential which give rise to the various degrees of order in the different liquid crystalline phases. To a good approximation the functional dependence of the order parameters on the molecular potential is shown to be a simple one in the limit of small tilt angle in the smectic-C phase.
Date: June 1, 1975
Creator: Allison, Stuart
Partner: UNT Libraries Government Documents Department

A dynamic soil chamber system coupled with a tunable diode laser for online measurements of delta-13C, delta-18O, and efflux rate of soil respired CO2

Description: High frequency observations of the stable isotopic composition of CO(2) effluxes from soil have been sparse due in part to measurement challenges. We have developed an open-system method that utilizes a flow-through chamber coupled to a tunable diode laser (TDL) to quantify the rate of soil CO(2) efflux and its delta(13)C and delta(18)O values (delta(13)C(R) and delta(18)O(R), respectively). We tested the method first in the laboratory using an artificial soil test column and then in a semi-arid woodland. We found that the CO(2) efflux rates of 1.2 to 7.3 micromol m(-2) s(-1) measured by the chamber-TDL system were similar to measurements made using the chamber and an infrared gas analyzer (IRGA) (R(2) = 0.99) and compared well with efflux rates generated from the soil test column (R(2) = 0.94). Measured delta(13)C and delta(18)O values of CO(2) efflux using the chamber-TDL system at 2 min intervals were not significantly different from source air values across all efflux rates after accounting for diffusive enrichment. Field measurements during drought demonstrated a strong dependency of CO(2) efflux and isotopic composition on soil water content. Addition of water to the soil beneath the chamber resulted in average changes of +6.9 micromol m(-2) s(-1), -5.0 per thousand, and -55.0 per thousand for soil CO(2) efflux, delta(13)C(R) and delta(18)O(R), respectively. All three variables initiated responses within 2 min of water addition, with peak responses observed within 10 min for isotopes and 20 min for efflux. The observed delta(18)O(R) was more enriched than predicted from temperature-dependent H(2)O-CO(2) equilibration theory, similar to other recent observations of delta(18)O(R) from dry soils (Wingate L, Seibt U, Maseyk K, Ogee J, Almeida P, Yakir D, Pereira JS, Mencuccini M. Global Change Biol. 2008; 14: 2178). The soil chamber coupled with the TDL was found to be an effective method for capturing soil ...
Date: January 1, 2009
Creator: Powers, Heath H; Mcdowell, Nate; Hanson, David & Hunt, John
Partner: UNT Libraries Government Documents Department

Morphology of a blend of zinc neutralized sulfonated poly(phenylene oxide) or polystyrene and an amino silicone

Description: A polymer blend of an ionomer based on zinc neutralized sulfonated poly(phenylene oxide) or polystyrene with a silicone copolymer containing 6.45% propylamine groups in place of one of the methyl groups on a backbone silicon was prepared. Carbon-13 magic angle spinning spectra show coordination of the amine, by the zinc ions. Morphological characterization was made by NMR spectroscopy based on proton spin diffusion, by small angle x-ray scattering and by energy filtered transmission electron microscopy. All experiments show domains in the range of 1 to 1000 nm and domain size can be controlled by the extent of coordination of the amine groups by the zinc ions and by thermal history. The different lead to an apparent hierarchy of domain sizes. The NMR domains, 2 to 10 nm, where contrast is produced by differences in chain mobility. Small angle x-ray scattering indicates domains of 16 nm while electron in the range of 100 to 1000 nm. The variation of the domain size between experiments may reflect the different sources of contrast in each cam.
Date: December 31, 1996
Creator: Jones, A.A.; Inglefield, P.T.; Zhang, Changlai & Bergquist, P
Partner: UNT Libraries Government Documents Department

Inductively coupled plasma mass spectrometry for stable isotope metabolic tracer studies of living systems

Description: This dissertation focuses on the development of methods for stable isotope metabolic tracer studies in living systems using inductively coupled plasma single and dual quadrupole mass spectrometers. Sub-nanogram per gram levels of molybdenum (Mo) from human blood plasma are isolated by the use of anion exchange alumina microcolumns. Million-fold more concentrated spectral and matrix interferences such as sodium, chloride, sulfate, phosphate, etc. in the blood constituents are removed from the analyte. The recovery of Mo from the alumina column is 82 {+-} 5% (n = 5). Isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) is utilized for the quantitative ultra-trace concentration determination of Mo in bovine and human blood samples. The average Mo concentration in reference bovine serum determined by this method is 10.2 {+-} 0.4 ng/g, while the certified value is 11.5 {+-} 1.1 ng/g (95% confidence interval). The Mo concentration of one pool of human blood plasma from two healthy male donors is 0.5 {+-} 0.1 ng/g. The inductively coupled plasma twin quadrupole mass spectrometer (ICP-TQMS) is used to measure the carbon isotope ratio from non-volatile organic compounds and bio-organic molecules to assess the ability as an alternative analytical method to gas chromatography combustion isotope ratio mass spectrometry (GC-combustion-IRMS). Trytophan, myoglobin, and {beta}-cyclodextrin are chosen for the study, initial observation of spectral interference of {sup 13}C{sup +} with {sup 12}C{sup 1}H{sup +} comes from the incomplete dissociation of myoglobin and/or {beta}-cyclodextrin.
Date: May 10, 1999
Creator: Luong, E.
Partner: UNT Libraries Government Documents Department

Characterization of aging in organic materials on atomic-, meso- and macro-length scales by {sup 13}C NMR spectroscopy

Description: A fundamental understanding of aging in an organic material requires that one understand how aging affects the chemical structure of a material, and how these chemical changes are related to the material`s macroscopic properties. This level of understanding is usually achieved by examining the material on a variety of length scales ranging from atomic to meso-scale to macroscopic. The authors are developing and applying several {sup 13}C nuclear magnetic resonance (NMR) spectroscopy experiments to characterize the aging process of organic materials over a broad range of length scales. Examples of studies which range from atomic to macroscopic will be presented.
Date: October 1, 1997
Creator: Assink, R.A.; Jamison, G.M.; Alam, T.M. & Gillen, K.T.
Partner: UNT Libraries Government Documents Department

A study of the abundance and {sup 13}C/{sup 12}C ratio of atmospheric carbon dioxide and oceanic carbon in relation to the global carbon cycle. Final technical report, February 15, 1990--July 31, 1995

Description: Knowledge can be gained about the fluxes and storage of carbon in natural systems and their relation to climate by detecting temporal and spatial patterns in atmospheric CO{sub 2}. When patterns in its {sup 13}C/{sup 12}C isotopic ratio are included in the analysis, there is also a basis for distinguishing organic and inorganic processes. The authors systematically measured the concentration and {sup 13}C/{sup 12}C ratio of atmospheric CO{sub 2} to produce time series data essential to reveal these temporal and spatial patterns. To pursue the significance of these patterns further, the result also involved measurements of inorganic carbon in sea water and of CO{sub 2} in air near growing land plants. The study was coordinated with a study of the same title concurrently funded by the National Science Foundation (NSF). The study called for continued atmospheric measurements at an array of ten stations from the Arctic Basin to the South Pole. Air was collected in flasks brought back to the laboratory for analysis, except at Mauna Loa. Observatory, Hawaii, where continuous measurements were also carried out.
Date: December 31, 1995
Creator: Keeling, C.D.
Partner: UNT Libraries Government Documents Department

Helium-induced reactions in astrophysics

Description: Helium-induced reactions play a crucial role in stellar nucleosynthesis. Carbon and oxygen are produced mainly during the helium-burning phase by the chain of reactions {sup 8}Be({alpha}, {gamma} + e{sup +}e{sup {minus}}){sup 12}C({alpha}, {gamma}){sup 16}O. The first step, often called triple-{alpha} capture, was proposed by Hoyle to bypass the mass stability gap at {sup 8}Be. The second step gives rise to the largest uncertainty in most of the calculated stellar abundances. Later {alpha}-captures on {sup 13}C are believed to be a major source of s-process neutrons. The status of each of these important reactions is reviewed here.
Date: November 1, 1997
Creator: Hale, G.M.
Partner: UNT Libraries Government Documents Department

Raman characterization of the BEDT-TTF(ClO{sub 4}){sub 2} salt

Description: The major Raman scattering peaks of BEDT-TTF(ClO{sub 4}){sub 2} have been assigned by comparison to the isotopically labeled {sup 13}C(4)-BEDT-TTF(ClO{sub 4}){sub 2} and {sup 13}C(6)-BEDT-TTF(ClO{sub 4}){sub 2} salts. The {upsilon}{sub 2}, {upsilon}{sub 3}, and {upsilon}{sub 6} A{sub g} modes are associated with the C{double_bond}C vibrations and the Raman shifts are found to decrease with increasing oxidation state of the ET molecules. The {upsilon}{sub 9} and {upsilon}{sub 10} A{sub g} modes are associated with the sulfur (C{single_bond}S) related vibrations and the Raman shifts are observed to increase with increasing oxidation state of the ET molecules.
Date: December 31, 1995
Creator: Wang, H.H.; Kini, A.M. & Williams, J.M.
Partner: UNT Libraries Government Documents Department

Two interesting features in the infrared and raman spectra of the 12K organic superconductor {chi}-(ET){sub 2}Cu[N(CN){sub 2}]Br

Description: Two of the larger features in the infrared conductivity spectra of {chi}-(ET){sub 2}Cu[N(CN){sub 2}]Br are analyzed and one is reassigned with the aid of infrared and Raman spectra of isotopically substituted compounds.
Date: December 31, 1995
Creator: Eldridge, J.E.; Xie, Y.; Wang, H.H.; Williams, J.M.; Kini, A.M. & Schlueter, J.A.
Partner: UNT Libraries Government Documents Department

Self-regenerating column chromatography

Description: The present invention provides a process for treating both cations and anions by using a self-regenerating, multi-ionic exchange resin column system which requires no separate regeneration steps. The process involves alternation ion-exchange chromatography for cations and anions in a multi-ionic exchange column packed with a mixture of cation and anion exchange resins. The multi-ionic mixed-charge resin column works as a multifunction column, capable of independently processing either cationic or anionic exchange, or simultaneously processing both cationic and anionic exchanges. The major advantage offered by the alternating multifunction ion exchange process is the self-regeneration of the resins. Applications are to separation of nitrogen and sulfur isotopes.
Date: December 31, 1994
Creator: Park, Woo K.
Partner: UNT Libraries Government Documents Department