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Reversible Guest Exchange Mechanisms in Supramolecular Host-Guest Assemblies

Description: Synthetic chemists have provided a wide array of supramolecular assemblies able to encapsulate guest molecules. The scope of this tutorial review focuses on supramolecular host molecules capable of reversibly encapsulating polyatomic guests. Much work has been done to determine the mechanism of guest encapsulation and guest release. This review covers common methods of monitoring and characterizing guest exchange such as NMR, UV-VIS, mass spectroscopy, electrochemistry, and calorimetry and also presents representative examples of guest exchange mechanisms. The guest exchange mechanisms of hemicarcerands, cucurbiturils, hydrogen-bonded assemblies, and metal-ligand assemblies are discussed. Special attention is given to systems which exhibit constrictive binding, a motif common in supramolecular guest exchange systems.
Date: September 1, 2006
Creator: Pluth, Michael D. & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Low-level copper concentration measurements in silicon wafers using trace-element accelerator mass spectrometry

Description: This article discusses low-level copper concentration measurements in silicon wafers using trace-element accelerator mass spectrometry.
Date: June 8, 1998
Creator: McDaniel, Floyd Del. (Floyd Delbert), 1942-; Datar, Sameer A.; Guo, Baonian N.; Renfrow, Steve N.; Anthony, J. M. & Zhao, Z. Y.
Partner: UNT College of Arts and Sciences

Determination of trace noble gases in air and natural gas

Description: From symposium on noble gases; Las Vegas, Nevada, USA (24 Sep 1973). A method was developed for the analysis of air and natural gas samples containing trace amounts of noble gases. The gas samples are preconcentrated by reaction with calcium at 900 to 1000 deg C and analyzed by mass spectrometry on an automated instrument. Methods of relating the concentrated sample to the original sample and the preparation of gas standards are given. The accuracy of the technique at the 25 ppM level was determined. The precision of the method and requirements for improving the technique are also discussed. (auth)
Date: September 1, 1973
Creator: Newton, J.C.; Stephens, F.B. & Stump, R.K.
Partner: UNT Libraries Government Documents Department

Raman spectroscopic and mass spectrometric investigations of the hydrogen isotopes and isotopically labelled methane

Description: Suitable analytical methods must be tested and developed for monitoring the individual process steps within the fuel cycle of a fusion reactor and for tritium accountability. The utility of laser-Raman spectroscopy accompanied by mass spectrometry with an Omegatron was investigated using the analysis of all hydrogen isotopes and isotopically labeled methanes as an example. The Omegatron is useful for analyzing all hydrogen isotopes mixed with the stable helium isotopes. The application of this mass spectrometer were demonstrated by analyzing mixtures of deuterated methanes. In addition, it was employed to study the radiochemical Witzbach exchange reaction between tritium and methanes. A laser-Raman spectrometer was designed for analysis of tritium-containing gases and was built from individual components. A tritium-compatible, metal-sealed Raman cuvette having windows with good optical properties and additional means for measuring the stray light was first used successfully in this work. The Raman spectra of the hydrogen isotopes were acquired in the pure rotation mode and in the rotation-vibration mode and were used for on. The deuterated methanes were measured by Raman spectroscopy, the wavenumbers determined were assigned to the corresponding vibrations, and the wavenumbers for the rotational fine-structure were summarized in tables. The fundamental Vibrations of the deuterated methanes produced Witzbach reactions were detected and assigned. The fundamental vibrations of the molecules were obtained with Raman spectroscopy for the first time in this work. The @-Raman spectrometer assembled is well suited for the analysis of tritium- containing gases and is practical in combination with mass spectrometry using an Omegatron, for studying gases used in fusion.
Date: February 24, 1997
Creator: Jewett, J.R., Fluor Daniel Hanford
Partner: UNT Libraries Government Documents Department

[Photon burst mass spectrometry technique.] Final report

Description: The basic tools have been developed and demonstrated for selective detection of Kr isotopes in the Photon Burst Mass Spectrometry technique. The effort is divided into: photon burst measurements on Mg{sup +} demonstrating high isotopic selectivity, charge exchange of Kr{sup +} with Cs and Rb to produce metastable Kr atoms, development of a diode laser system for photon burst detection of Kr{sup +}, and measurements of photon bursts detection of Kr.
Date: April 1, 1996
Creator: Fairbank, W.M. Jr
Partner: UNT Libraries Government Documents Department

The Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory

Description: CAMS operates an HVEC FN tandem accelerator for use in both basic research and technology development. The accelerator is operated under a distributed computer control system with sophisticated auto-scaling, beam flat-topping, archiving, and recall capabilities, which makes possible rapid and precise switching between experimental configurations daily. Using the spectrometer, the AMS group can routinely measure the isotopes {sup 3}H, {sup 9}Be, {sup 10}Be, {sup 14}C, {sup 26}Al, {sup 36}Cl, {sup 41}Ca, and {sup 129}I at abundances as low as 1 part in 10{sup 16}.
Date: October 1, 1996
Creator: Roberts, M.L.; Heikkinen, D.W.; Southon, J.R. & Proctor, I.D.
Partner: UNT Libraries Government Documents Department

Organometallic Vapor Phase Epitaxy of n-GaSb and n-GaInAsSb for Low Resistance Ohmic Contacts

Description: A comparison of n-GaSb and n-GaInAsSb epilayers for ohmic contacts in GaSb-based devices is studied. The epilayers were grown by organometallic vapor phase epitaxy and doped with Te. At similar electron concentrations, the atomic Te concentration, as determined by secondary ion mass spectroscopy, is more than 2 times higher in n-GaSb compared to n-GaInAsSb. In addition, the electron mobility is lower in n-GaSb than n-GaInAsSb at similar electron concentrations. The electron concentration saturates at about 1.3 x 10{sup 18} cm{sup -3} for n-GaSb, but linearly increases for n-GaInAsSb. Pd/Ge/Au/Pt/Au metallization was studied for ohmic contacts. A specific contact resistivity of 1 x 10{sup -5}{Omega}-cm{sup 2} for n-GaSb was measured. The specific contact resistivity can be greatly improved by contacting n-GaInAsSb, and a significantly lower specific contact resistivity of 2 x 10{sup -6} {Omega}-cm{sup 2} for n-GaInAsSb was measured.
Date: July 10, 2003
Creator: Wang, C.A.; Shiau, D.A.; Huang, R.K.; Harris, C.T. & Connors, M.K.
Partner: UNT Libraries Government Documents Department

Measurement of plutonium and other actinide elements at the center for accelerator mass spectrometry: a comparative assessments of competing techniques

Description: Low-level measurements of the long-lived actinide isotopes have a number of important applications throughout the DOE complex. These include radiobioassay programs, environmental assessments, characterization of radioactive wastes, evaluation of waste storage and treatment options, environmental remediation, basic research in chemistry and geochemistry, and other specialized non- proliferation and national security applications. As an example, it has been estimated that for the next few decades more than 1 million radiochemical analyses per year will be needed in support of US efforts to remediate the legacy of radioactive waste generated by weapons production and the nuclear power industry (Crain, 1996). Traditional radiometric counting methods do not have sufficient sensitivity to address many of these requirements. There is also a growing need to evaluate and monitor exposures to DOE workers involved in decommissioning, environmental management and/or remediation of contaminated sites and facilities. Quantitative measurements based on low-level detection techniques are of particular interest in the validation of radionuclide transport models and improving radiation dosimetry/risk estimates. Quantitative data and information are required to assess the potential health-effects of exposures occurring under special conditions (e.g., resuspension/inhalation of high-specific activity particles), of inhomogeneous radiation exposure and assessment of associated dose distributions to different parts of the body/tissue, of low dose exposure, and to validate and/or develop new and improved dosimetry models. Atom counting technology has now developed sufficiently to provide substantially better sensitivity than ionizing radiation detectors for selected long- lived radionuclides. Clearly the development of a robust, high-throughput, highly sensitive actinide measurement capability based on this new technology would have broad and sustainable impact on a range of DOE initiatives. One potential measurement technique for meeting these requirements is accelerator mass spectrometry (AMS). AMS is a widely accepted analytical technique for measurement of isotopes such as 14 C, 26 Al, 36 Cl (Vogel et al., ...
Date: February 1, 1999
Creator: Hamilton, T H & McAninch, J
Partner: UNT Libraries Government Documents Department

Impact of phenolic substrate and growth temperature on the arthrobacter chlorophenolicus proteome

Description: We compared the Arthrobacter chlorophenolicus proteome during growth on 4-chlorophenol, 4-nitrophenol or phenol at 5 C and 28 C; both for the wild type and a mutant strain with mass spectrometry based proteomics. A label free workflow employing spectral counting identified 3749 proteins across all growth conditions, representing over 70% of the predicted genome and 739 of these proteins form the core proteome. Statistically significant differences were found in the proteomes of cells grown under different conditions including differentiation of hundreds of unknown proteins. The 4-chlorophenol-degradation pathway was confirmed, but not that for phenol.
Date: February 15, 2009
Creator: Unell, Maria; Abraham, Paul E.; Shah, Manesh; Zhang, Bing; Ruckert, Christian; VerBerkmoes, Nathan C. et al.
Partner: UNT Libraries Government Documents Department

Accurate determination of impurity concentrations in plutonium metals by statistical evaluation of analytical data

Description: Analytical data from a plutonium-metal exchange program conducted by six ERDA laboratories are statistically evaluated. The objective is an accurate determination of five metal impurities (aluminum, chromium, iron, nickel, silicon) in each of three plutonium metals by using data from four analytical methods. The statistical evaluation yields the weighted mean and its standard deviation for each method, plutonium metal, and impurity, using a procedure that minimizes the effect of outliers by assigning zero weights to the most extreme values and variable weights to the remaining data. Where possible, weighted means from the various analytical methods are pooled. (auth)
Date: July 1975
Creator: Martell, C. J.; Tietjen, G. L. & Horita, M. M.
Partner: UNT Libraries Government Documents Department


Description: The Gaseous Ions: Structures, Energetics and Reactions Gordon Research Conference will focus on ions and their interactions with molecules, surfaces, electrons, and light. The conference will cover theory and experiments, and systems ranging from molecular to biological to clusters to materials. The meeting goal continues to be bringing together scientists interested in fundamentals, with those applying fundamental phenomena to a wide range of practical problems. Each of the ten conference sessions will focus on a topic within this spectrum, and there will also be poster sessions for contributed papers, with sufficient space and time to allow all participants to present their latest results. To encourage active participation by young investigators, about ten of the poster abstracts will be selected for 15 minute 'hot topic' talks during the conference sessions. Hot topic selection will be done about a month before the meeting. Funds should be available to offset the participation cost for young investigators.
Date: March 4, 2011
Creator: Anderson, Scott
Partner: UNT Libraries Government Documents Department

Making Amines Strong Bases: Thermodynamic Stabilization ofProtonated Guests in a Highly-Charged Supramolecular Host

Description: A highly-charged, cavity-containing supramolecular assembly formed by metal-ligand interactions acts as a host to dramatically shift the effective basicity of encapsulated protonated amine guests. The scope of encapsulated protonated amine and phosphine guests shows size selectivity consistent with a constrained binding environment. Protonation of the encapsulated guests is confirmed by {sup 31}P NMR studies, mass spectrometry studies, and the pH dependence of guest encapsulation. Rates of guest self-exchange were measured using the Selective Inversion Recovery method and were found to correlate with the size rather than the basicity of the guests. The activation parameters for guest self-exchange are consistent with the established mechanism for guest exchange. The binding constants of the protonated amines are then used to calculate the effective basicity of the encapsulated amines. Depending on the nature of the guest, shifts in the effective basicities of the encapsulated amines of up to 4.5 pK{sub a} units are observed, signifying a substantial stabilization of the protonated form of the guest molecule and effectively making phosphines and amines strong bases.
Date: April 16, 2007
Creator: Pluth, Michael D.; Bergman, Robert G. & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Single cell analysis: the new frontier in 'Omics'

Description: Cellular heterogeneity arising from stochastic expression of genes, proteins, and metabolites is a fundamental principle of cell biology, but single cell analysis has been beyond the capabilities of 'Omics' technologies. This is rapidly changing with the recent examples of single cell genomics, transcriptomics, proteomics, and metabolomics. The rate of change is expected to accelerate owing to emerging technologies that range from micro/nanofluidics to microfabricated interfaces for mass spectrometry to third- and fourth-generation automated DNA sequencers. As described in this review, single cell analysis is the new frontier in Omics, and single cell Omics has the potential to transform systems biology through new discoveries derived from cellular heterogeneity.
Date: January 14, 2010
Creator: Wang, Daojing & Bodovitz, Steven
Partner: UNT Libraries Government Documents Department

Recent improvements of a new thermal ionization cavity source for mass spectrometry

Description: Last year, we presented a prototype ion source design for mass spectrometry, which uses a tungsten crucible with a deep cavity for sample loading and enhanced surface ionization; the crucible is heated by high energy electron bombardment. This ion source was named as a thermal ionization cavity (TIC). In this present work, an TIC source has been designed with a vacuum interlock system and translational stage. It is now easier to operate and handle while maximizing sample throughput.
Date: June 1, 1996
Creator: Duan, Y.; Olivares, J. A.; Danen, R. E. & Cleland, T. J.
Partner: UNT Libraries Government Documents Department

Recent trends in inorganic mass spectrometry

Description: The field of inorganic mass spectrometry has seen substantial change in the author`s professional lifetime (over 30 years). Techniques in their infancy 30 years ago have matured; some have almost disappeared. New and previously unthought of techniques have come into being; some of these, such as ICP-MS, are reasonably mature now, while others have some distance to go before they can be so considered. Most of these new areas provide fertile fields for researchers, both in the development of new analytical techniques and by allowing fundamental studies to be undertaken that were previously difficult, impossible, or completely unforeseen. As full coverage of the field is manifestly impossible within the framework of this paper, only those areas with which the author has personal contact will be discussed. Most of the work originated in his own laboratory, but that of other laboratories is covered where it seemed appropriate.
Date: October 1, 1996
Creator: Smith, D.H.; Barshick, C.M.; Duckworth, D.C. & Riciputi, L.R.
Partner: UNT Libraries Government Documents Department

High-fidelity in isotope ratio measurements for resonance ionization mass spectrometry

Description: Calculations are performed to gauge the effect of the convolution of atomic spectral characteristics with laser sources upon isotope ratio measurements by Resonance Ionization Mass Spectrometry (RIMS). Comparison with experimental data is included. 7 refs., 3 figs.
Date: January 1, 1988
Creator: Miller, C.M.; Fearey, B.L.; Palmer, B.A. & Nogar, N.S.
Partner: UNT Libraries Government Documents Department

Secondary, non-resonant cw laser ionization efficiency enhancement for resonance ionization mass spectrometry

Description: Secondary, non-resonant laser ionization is used to significantly enhance the ionization efficiency of lutetium in CW Resonance Ionization Mass Spectrometry (RIMS). Spectral line-narrowing of hyperfine components is observed and understood in terms of a Raman mechanism. 7 refs., 3 figs.
Date: January 1, 1988
Creator: Fearey, B.L.; Miller, C.M.; Keller, R.A. & Parent, D.C.
Partner: UNT Libraries Government Documents Department

Trends in resonance ionization spectroscopy

Description: The author reviews the history of resonance ionization spectroscopy and then comments on the delineations of RIS with reference to many related laser processes. The substance of the paper deals with the trends in RIS and especially how the needs for sensitive analytical methods have overshadowed the orginal plan to study excited species. 9 refs., 1 fig.
Date: January 1, 1986
Creator: Hurst, G.S.
Partner: UNT Libraries Government Documents Department

Isotopically selective, Doppler-free, saturation spectroscopy of lutetium isotopes via resonance ionization mass spectrometry

Description: A new technique utilizing RIMS to obtain very high resolution atomic spectra with isotopic selectivity has been demonstrated. This technique allows the precise determination of HF splitting constants, limited only by the transition's natural linewidth. In addition, it is also feasible with this technique to accurately determine atomic isotope shifts. The exact determination of HF component line positions provides data for isotopically selective ionization which, in turn, will increase RIMS' dynamic range. Future work includes the incorporation of a /open quotes/vibrating/close quotes/ mirror and the study of rarer isotopes, i.e., /sup 174/Lu, /sup 173/Lu, /sup 172/Lu, /sup 171/Lu, and possibly, /sup 170/Lu. 13 refs., 3 figs.
Date: January 1, 1988
Creator: Fearey, B.L.; Parent, D.C.; Keller, R.A. & Miller, C.M.
Partner: UNT Libraries Government Documents Department

High ionization efficiency techniques for CW RIMS

Description: The demand to measure high dynamic range isotope ratios on small samples with RIMS continues to increase. This paper discusses high ionization efficiency methods which can be applied to CW RIMS to potentially achieve several tens of percent ionization efficiencies for certain elements. The primary technique under development to achieve this is an external laser cavity which can generate very high circulating laser powers.
Date: January 1, 1990
Creator: Fearey, B.L.; Johnson, S.G. & Miller, C.M.
Partner: UNT Libraries Government Documents Department